Rapid manufacturing  the technologies and applications of rapid prototyping and rapid tooling

Historical Perspectives

This section is based on [Beaman, 1997]

The roots of RP can be traced to two technical areas [Beaman, 1997]: topography and photo sculpture

In 1890, Blanther introduced a layered method for creating molds for topographical relief maps, utilizing wax plates cut along contour lines This approach was enhanced by researchers such as Perera, Zang, and Gaskin over the following decades Matsubara later developed a layer manufacturing process for casting molds, employing refractory particles coated with photopolymer resin that is selectively cured with light Additionally, DiMatteo proposed a method for producing 3D objects from contoured metallic sheets using milling techniques Nakagawa further explored lamination techniques for the fabrication of various tools, including blanking, press forming, and injection molding tools.

ASOFACTOR& or co 'TOUR BELIEF WAPS

Figure 1.1 A method for making moulds for topographical relief maps [Blanther,

Photosculpture, a technique proposed by Bogart in the 19th century, allows for the creation of 3D object replicas by using 24 cameras arranged in a circular setup to capture simultaneous photographs Each image's silhouette is then utilized to carve one-twenty-fourth of the object's cylindrical portion Subsequent developers, including Baese and Monteah, sought to enhance this method by streamlining the manual carving process Morioka further advanced the technique in the 1930s by introducing structured lighting to generate photographic contour lines, which could be used to cut and assemble objects from sheets In 1956, Munz patented a layer manufacturing system that fabricates scanned object cross-sections by selectively exposing a transparent photo emulsion, creating layers through a piston mechanism that adds photo emulsion and fixing agent.

Figure 1.2 The layer manufacturing system proposed by Munz [1956]

Development work in the area of RP continued in the 1960s and 1970s and a number of patents have been filed on different methods and systems [Beaman, 1997] These include:

• A method for fabricating objects from powdered materials by heating particles locally and fusing them together employing a laser, electron beam, or plasma beam [Ciraud, 1972]

• A process for producing plastic patterns by selective 3D polymerisation of a photosensitive polymer at the intersection of two laser beams [Swainson, 1977]

• A photopolymer RP system for building objects in layers [Kodama, 1981] A mask is used to control the exposure of the UV source when producing a cross- section of the model

• A system that directs a UV laser beam to a polymer layer by means of a mirror system on an x-y plotter [Herbert, 1982]

Further to this list there are numerous patents covering existing commercial RP processes The most prominent patents as listed by Beaman [Beaman, 1997] are shown in Figure 1.3

The significant rise in commercially available Rapid Prototyping (RP) systems during the 1990s can be attributed to advancements in 3D CAD modeling, Computer-Aided Manufacturing, and Computer Numerical Control, initially driven by the competitive automotive and aerospace industries Sales of RP systems experienced annual growth rates of 40-50% in the early to mid-1990s, although this rapid expansion has slowed in recent years Despite this, the sector remains vibrant, evidenced by the filing of 208 new patents in the past two years and a 22% sales growth in 1999, with an estimated 3.4 million parts produced globally using RP technologies Moreover, the application of RP has extended to various other economic sectors, indicating strong and optimistic prospects for the future of the RP industry.

Name Housholder Murutani Masters Andre et al Hull Pomerantz et al Feygin Deckard Fudim Arcella et al Crump Helinski Marcus Sachs et al Levent et al Penn

The evolution of three-dimensional (3D) manufacturing technologies is marked by significant patents from various countries In December 1979, the U.S introduced the optical mould method, followed by Japan's computer automated manufacturing process in May 1984 Notable advancements in France included an apparatus for creating three-dimensional objects via stereolithography in July 1984 By June 1986, Israel developed a method for forming integral objects from laminations, while the U.S continued to innovate with selective sintering and photo solidification techniques throughout the late 1980s The period also saw the emergence of three-dimensional printing and thermal spray methods, with the U.S leading in patent filings Overall, these developments highlight the rapid growth and diversification of 3D printing technologies from the late 1970s to the early 1990s.

5.5% 7.7% • Con umcr Products o Busincs Machines o Medici.1 Acadcmic

Figure 1.4 The use ofRP systems in different sectors [Wohlers, 2000]

Rapid Prototyping - An Integral Part of Time Compression Engineering

Geometrical Modelling Techniques

The advent of computer-controlled fabrication systems, particularly Numerical Controlled machine tools, over 40 years ago necessitated the electronic representation of product data The initial generation of computer-aided design (CAD) tools emerged as 2D drafting systems, replicating traditional drafting processes in a digital format These 2D geometrical models are composed of graphical primitives, including lines, arcs, text, symbols, and various notations essential for representing engineering drawings electronically.

The first generation of CAD systems offered limited modeling capabilities, primarily supporting only basic design applications that fell short of addressing real industrial design challenges However, the foundational concepts from these early systems paved the way for the next generation of CAD systems, which introduced 3D modeling capabilities The growing complexity of products and the demand for integration and automation in design and manufacturing significantly propelled the advancement of these 3D CAD systems.

To be widely accepted in engineering applications, geometrical models must provide three-dimensional, unique, and complete representations of products These models enable the use of consistent data across various engineering tasks, including documentation, engineering analysis, rapid prototyping, and manufacturing The three fundamental techniques for creating 3D designs are wireframe, surface, and solid modelling.

Chapter 1 Introduction 9 1.2.1.1 Wire/rame Modelling

Wireframe models, akin to 2D geometrical representations, consist of graphical primitives defined in three-dimensional space, showcasing 3D design objects through edges and vertices While creating valid 3D models using wireframe techniques can be a complex and time-consuming process due to the extensive input data and command sequences required, these models are efficient in terms of storage, requiring minimal computer memory and allowing for quick retrieval, editing, or updating Primarily, wireframe models facilitate the generation of engineering documentation and can also provide input data for finite element analysis Through the application of geometrical transformations to the graphical primitives, various projections of the 3D object can be generated.

3D designs represented by wireframe models often lack unique interpretation, making complex object models difficult to understand To mitigate confusion, edges can be hidden, dashed, or blanked Consequently, many companies primarily use 3D wireframe systems in a two-dimensional mode due to these interpretative challenges Additionally, wireframe models do not include surface and volume data, rendering them unsuitable for rapid prototyping (RP) Overall, wireframe modeling techniques are viewed as natural extensions of traditional drafting methods.

Figure 1.6 Wire frame and solid models of a watch

Wireframe models serve as the foundational elements for creating surface models, with most surface modeling software relying on wireframe primitives to generate surfaces Users define surface boundaries by inputting vertices and edges, which are then utilized to fit surfaces to these edges Various mathematical techniques can represent surfaces, including Coons, Bezier, Non-Uniform Rational B-splines (NURBS), as well as quadratic, cylindrical, and spherical surfaces.

Surface models offer more comprehensive and clearer representations compared to wireframe models, as they contain richer geometrical databases that provide detailed information about the surfaces connecting model edges This extensive data is essential for generating cutter paths for NC machining, making surface models the foundation for most CAM systems.

Surface models primarily represent the geometry of objects without capturing their topology, limiting them to a collection of surfaces associated with a single object Consequently, shared edges between surfaces are not recorded, resulting in gaps that prevent surface models from defining closed volumes To effectively utilize surface models for rapid prototyping, these gaps need to be eliminated, a process that can often be challenging or even unfeasible.

Solid modeling offers a straightforward approach to defining models, requiring minimal input data and utilizing simpler command sequences compared to other modeling techniques Most solid modeling software supports Constructive Solid Geometry (CSG), enabling users to create complex objects from predefined 3D primitives These primitives include basic shapes like planes, cylinders, cones, and spheres, as well as more intricate solid objects formed by sweeping 2D wireframe sections To define a solid model, these primitives are combined through boolean operations such as union, intersection, and difference.

Solid models provide a complete and unambiguous representation of objects [Zeid,

The effectiveness and clarity of solid modeling techniques stem from the comprehensive information held in their databases Once a component is created, the solid modeller transforms the input into a data structure that preserves both the geometry and topology of the object.

In contrast to both wire frame and surface models that store only geometrical data, solid modelling databases are complete and the models are very easy to verify

Solid modeling data can be stored using various representation schemes, with the most popular being Constructive Solid Geometry (CSG) and Boundary Representation (B-Rep) CSG organizes objects in a tree structure, where solid primitives are the leaves and boolean operations form the interior nodes In contrast, B-Rep relies on the topological concept that each 3D object is defined by a collection of faces, edges, and vertices, ensuring the model's topological consistency Most solid modeling software supports multiple representation schemes, designating one as the primary scheme while deriving others from it.

Figure 1.7 A construction tree for a solid model

Solid modeling plays a crucial role in bridging the gap between design and manufacturing, as highlighted by Zeid in 1991 The significant advancements in computing power and its cost-effectiveness over the past decade have facilitated its widespread adoption Today, solid modeling is recognized as the most dependable method for generating 3D models for rapid prototyping (RP) applications.

Figure 1.8 Boundary representation of a solid model

RPDataFormats

3D modeling software utilizes various representation techniques and data formats to store geometrical data, but the incompatibility of these formats complicates data exchange with downstream CAM applications To address this issue, there are two primary solutions: a direct method, which involves creating interfaces between systems—often impractical—and an indirect method that uses neutral database structures for information exchange These neutral data structures are vendor-independent and contain essential definitions needed to support a specific set of applications.

In rapid prototyping (RP), an indirect approach is utilized, with various neutral formats suggested, including STL (STereoLithography), SLC, CLI (Common Layer Interface), and RPI (Rapid Prototyping Interface).

The STL format is the most widely used standard for interfacing CAD and RP systems, established as the de facto standard since its introduction Although other formats like LEAF and LMI have been proposed to overcome the limitations of STL, their adoption remains limited in comparison.

STL files are created by tessellating precise CAD models, where the surfaces of 3D models are represented by triangular facets Each triangle is uniquely defined by its three vertices and outward normal vector Adhering to specific requirements during the generation of STL files is crucial for ensuring accuracy and quality.

I Data about triangle vertices must be stored in the file in an ordered fashion to identify interior or exterior surfaces A clockwise vertex ordering defines an interior surface, and an anti-clockwise ordering the exterior surface The right- hand rule (Figure 1.9) is applied

2 A triangle must share exactly two common vertices with each adjacent triangle (Figure 1.10) This is known as the vertex-to-vertex rule

Figure 1.10 Vertex-to-vertex rule

Virtually every 3D modelling package provides an interface for exporting the internal CAD representation into the STL format

STL files can be stored in either ASCII or binary formats, with binary files being preferred due to their smaller size The STL file format is structured with a header, followed by the number of triangles and a list of those triangles [Jacobs, 1996].

To store a triangle in a binary format, 50 bytes are needed Therefore, the total size of the binary file can be calculated by multiplying the number of triangles by 50 and adding 84 bytes for the header and triangle counter.

The utilization of various standard formats for product data exchange, including IGES (Initial Graphical Exchange Specification), HPGL (Hewlett-Packard Graphics Language), and STEP (Standard for Exchange of Product Model Data), is essential for ensuring seamless communication and interoperability in design and manufacturing processes.

Since the introduction of VRML (Virtual Reality Modelling Language) in 1993, it has been considered as an alternative to STL for data representation in rapid prototyping (RP) applications However, due to persistent issues, these alternative formats have not gained widespread acceptance Ongoing efforts to develop new formats aim to meet the increasing demands for more precise data representation in RP applications.

RP Information Workflow

All RP systems have a common information workflow (Figure 1.11) The main stages in preparing and pre-processing data for automated fabrication of 3D objects are as follows:

To create geometric data, a 3D CAD package or a 2D scanning device can be utilized It is essential that the generated data is represented in a model that forms a closed 3D volume, ensuring there are no holes, zero-thickness surfaces, or more than two surfaces converging along common edges.

1997] Formally, the model is valid if the system can determine uniquely for each point in the 3D space whether it lies inside, on, or outside the object surfaces

To export a valid 3D model from a CAD package, it is typically saved in a neutral format, most commonly STL Many CAD software options also provide the ability to adjust the model's resolution, allowing users to control the size of the generated file effectively.

Data validation and repair are crucial steps in ensuring the accuracy of exported data, which serves as an approximation of the precise internal 3D model This approximation process simplifies model surfaces into basic geometric shapes, primarily triangles However, STL models generated through this method often suffer from geometric errors, including holes and overlapping regions along surface boundaries.

Before further processing, it is essential to validate the generated files, as noted by Wozny (1997) Some rapid prototyping (RP) packages provide both automatic and manual model repair options These software tools assess STL models to identify any missing triangles, and if errors are found, they fill the gaps by adding new triangles.

Figure 1.11 RP information workflow oftware I

Part orientation and scaling are crucial in RP systems, as they construct parts along the Z axis of STL models By strategically reorienting parts in relation to the model coordinate systems, it is possible to enhance accuracy, improve surface finish, and reduce build time.

RP systems enable the simultaneous nesting of multiple parts within the system chamber, facilitating efficient production Additionally, these parts can be scaled to address potential anomalies caused by downstream processes, including deformation, shrinkage, warpage, and curling.

Liquid-based rapid prototyping processes necessitate the use of support structures to effectively construct overhanging sections of parts These support structures are typically generated automatically through specialized software tools By carefully choosing the build direction of the part, the need for support structures can be significantly reduced.

Setting up process parameters is crucial for defining the build style and desired attributes of the system These parameters can be tailored to meet specific part requirements and are influenced by the rapid prototyping (RP) material utilized Adjusting these settings ensures optimal performance and quality in the final output.

The generation of 2D slice data involves slicing an STL file to create successive cross-sectional layers of a model Each layer utilizes polylines to accurately represent the exterior and interior boundaries of the rapid prototyping (RP) models To address potential process errors, these polyline boundaries can be adjusted by a specific offset value Slice data can be produced either off-line for the entire model or on-line, generating one cross-section at a time during the part building process.

The process data generated following the stages outlined above is stored in a build file This file contains all the information needed to guide material additive processes to build 3D objects.

Summary

RP technologies play a crucial role in TCE by streamlining the product design and development process This chapter reviews the chronological advancements in RP, highlighting the importance of 3D modeling as a gateway to these technologies It discusses the benefits and drawbacks of various geometrical representation techniques and describes the existing formats for interfacing CAD and RP systems Additionally, it outlines the key stages involved in generating the data required to construct 3D objects layer by layer.

Beaman JJ (1997) Historical Perspective, Chapter 3 in JTECIWTEC Panel Report on Rapid Prototyping in Europe and Japan, WTEC Hyper-Librarian (http://itri.loyola.edu/rp/toc.htrn)

Brite EuRam (1994) Common layer interface (CLI), Version 1.31 Brite EuRam Project BE2578, RPT - Development and Integration of Rapid prototyping Techniques for Automotive Industry

DiMatteo PL (1976) Method of generating and constructing three-dimensional bodies, U.S Patent 3,932,923

Dolenc A and Malela I (1992) Leaf: a data exchange format for LMT processes, Proc 3th International Conference on Rapid Proto typing, Dayton, USA, pp 4-

Herbert AJ (1982) Solid object generation J Appl Photo Eng., Vol 8,4, pp 185-

Jacobs PF (1996) Stereo lithography and Other RP&M Techniques, ASME Press, New York

Kai CC, Jacob GGK and Mei T (1997) Interface between CAD and Rapid Prototyping systems Part 2: LMI - An Improved Interface, Int J Adv Manuf Technol., Vol 13, pp 571-576

Kodama H (1981) Automatic method for fabricating a three-dimensional plastic model with photo-hardening polymer Rev Sci Instrum, pp 1770-1773

Kunieda M and Nakagawa T (1984) Development oflaminated drawing dies by laser cutting Bull of JSPE, pp 353-354

Matsubara K (1974) Japanese Kokai Patent Application, Sho 51[1976]-10813 Monteah FH (1924) U.S Patent 1,516,199

Nakagawa T et al (1979) Blanking tool by stacked bainite steel plates Press Technique, pp 93-1Ol

Nakagawa T, Kunieda M and Liu S (1985) Laser cut sheet laminated forming dies by diffusion bonding, Proc 25th International MTDR Conference, pp 505-510

Owen J (1993) STEP An Introduction, Information Geometers

Reed K, Harrvd D and Comoy W (1990) Initial Graphics Exchanges Specification (lGES) version 5.0, CAD-CAM Data Exchange Technical Centre

Rock SJ and Wozny MJ (1991) A flexible file format for solid freeform fabrication,

Proceedings of Solid Freeform Fabrication Symposium, Texas, USA, pp 155-

Swainson WK (1977) Method, medium and apparatus for producing three- dimensional figure product, U.S Patent 4,041,476

VRML Repository (2000) Web3D Consortium, http://www.web3d.orglvrmVvrml.htm

Wohlers T (2000) Wohlers Report 2000: Executive Summary, Time-Compression Technologies, Vol 8, 4, pp 29-31

Wozny MJ (1997) CAD and Interfaces, Chapter 8 in JTECIWTEC Panel Report on Rapid Prototyping in Europe and Japau, WTEC Hyper-Librarian (http://itri.1oyola edu/rp/toc.htm)

Zeid I (1991) CAD/CAM Theory and Practice, McGraw-Hili, Singapore

This chapter categorizes various physical Rapid Prototyping (RP) processes and provides a detailed overview of each method Moving forward, the term RP will specifically denote physical Rapid Prototyping.

Classification of Rapid Prototyping Processes

RP processes can be categorized into two main types: those that add material and those that remove it According to Kruth (1991), material accretion methods are classified based on the initial state of the prototype material—liquid, powder, or solid sheets Liquid-based processes involve solidifying a resin through laser contact, electro-setting fluids, or melting and solidifying the material Powder-based methods aggregate particles using lasers or binding agents, while solid sheet processes depend on bonding techniques, either via lasers or adhesives Figure 2.1 illustrates Kruth's classification, which has been updated to include new methods, and the subsequent discussion will align with this framework.

D T Pham et al., Rapid Manufacturing © Springer-Verlag London Limited 2001

• + I Lirid t 1 I Solidification of;-l Liquid Polymer I Solidification of an Electroset Fluid (ES) H

Point by Point (SL, LTP, BIS) ~ Layer by Layer (Objet, SGC) Holographic Surface (HIS) t Solidification of a Molten Material Point by Point (BPM, MJM, FDM, 3DW, 1M) Layer by Layer (SDM)

Rapid prototyping methods can be classified into various categories based on their material removal and bonding techniques Key processes include the discrete fusing of particles, such as Selective Laser Sintering (SLS), Laser Engineered Net Shaping (LENS), and Granular Particle Deposition (GPD) Additionally, methods like Laminated Object Manufacturing (LOM) and PolyJet (PJT) focus on bonding sheets using adhesives Other techniques, including 3D Printing (3DP) and Stereolithography (SFP), emphasize joining particles and sheets with light-based technologies This classification is adapted from Kruth's work in 1991.

Processes Involving a Liquid

Solidification of a Liquid Polymer

This article discusses six processes that utilize electromagnetic radiation for resin solidification Among these, three methods focus on constructing parts layer by layer using points, while the remaining three techniques solidify entire layers or surfaces simultaneously.

Stereolithography (SL) is one of the most popular rapid prototyping processes, utilizing a photosensitive liquid resin that solidifies into a polymer when exposed to ultraviolet (UV) light This process occurs primarily at the surface due to the absorption and scattering of the UV beam, resulting in the formation of voxels—three-dimensional pixels Each voxel is defined by its horizontal line-width and vertical cure depth, as illustrated in Figure 2.2.

Figure 2.2 Single cured line of photo polymer [Jacobs, 1992]

A selective laser (SL) machine features a build platform submerged in a vat of resin, utilizing a UV Helium-Cadmium or Argon ion laser to create the first layer of a part based on a 3D solid CAD model The laser scans the layer's contour and fills the interior, after which the platform is lowered to coat the part thoroughly It is then raised to ensure the solidified part is level with the resin surface, and a blade wipes the resin to maintain a precise layer thickness above the part Subsequently, the part is lowered slightly below the surface to allow the liquid to settle, ensuring a flat surface and preventing bubble formation before the next layer is scanned.

All new SL machines utilize an advanced resin application method that surpasses the traditional deep-dip process This innovative technique addresses issues caused by high resin viscosity, which can result in inaccurate part dimensions due to inconsistent resin application by the recoating blade By spreading resin across the part as the blade moves through the vat, the new method ensures precise resin amounts are applied, enhancing accuracy and achieving a smoother surface finish Additionally, it significantly reduces non-productive recoating time and eliminates trapped volumes of resin, which can compromise part accuracy and potentially lead to delamination.

Chapter 2 Rapid Pro to typ ing Processes 23 or collision of the blade and part because of a build up of unwanted polymerised resin at the surface of the trapped volume ewly polym ri ed r In Unwanted pol ymcrisation xce s re in at surface of trapped volume

Desired resin level z y Figure 2.4 Trapped Volume in Stereo lithography

After the part is finished, it is taken out of the vat and the excess resin is drained, a process that can take several hours due to the resin's viscosity Subsequently, the 'green' part is placed in a UV oven for post-curing, which guarantees that no liquid or partially cured resin is left behind.

Ongoing research focuses on improving materials and addressing issues related to accuracy, warping, and shrinkage in parts For detailed insights into SL systems and their technical specifications, refer to Chapter 3.

This process resembles Stereolithography (SL) but utilizes thermosetting resin and an infrared laser to form voxels The use of heat can influence voxel size, potentially leading to distortion and shrinkage in the final part Nevertheless, these issues are reportedly manageable and not significantly worse than those encountered in SL Ongoing research continues to refine this system.

This innovative process employs two laser beams positioned at right angles, each emitting light at distinct frequencies to polymerize resin within a transparent vat The initial laser beam excites the liquid resin into a reversible metastable state, while the second beam induces polymerization of the excited resin.

Resin subjected to both beam i polymeri cd to form the part

Re in in the path of la er I is excited to a metastable tate

Figure 2.5 Beam Interference Solidification (Adapted from Kruth [Kruth, 1991])

To date, no commercial applications of this process exist because there are still technical difficulties to be solved:

• Shadows are cast from previously solidified sections

• There is a problem with light absorption because the intensity of the lasers drops with depth

• It is hard to intersect the laser beams due to diffraction variations in the resin caused by temperature gradients or solid sections [Kruth, 1991]

Chapter 2 Rapid Prototyping Processes 25 2.2.1.4 Objet Quadra Process

The Objet Quadra process utilizes 1536 nozzles to create parts by applying layers of photo-sensitive resin, which are cured with two UV lights The system's light intensity and exposure are precisely controlled to eliminate the need for post-curing With a printing resolution of 600 dpi and a layer thickness of 20 µm, the Objet system currently offers one photopolymer for model building, while additional materials are in development To enhance the support for overhanging areas and undercuts, a second material is applied, which can be easily separated from the model without leaving any marks or blemishes.

2000] For more information about the Objet system and its technical specifications, see Chapter 4

This system employs photopolymerizing resins and UV light to cure layers of resin directly from a CAD model A mask is positioned above the resin surface, allowing a powerful UV lamp to illuminate the entire layer, ensuring complete curing without the need for post-curing After curing, excess resin is removed, and any gaps are filled with wax, which is then cooled on a chill plate and milled flat before removing the wax chips This process is repeated with a new layer of resin.

The mask, made of glass, is created during the waxing, cooling, and milling of the current layer Each new layer's negative image is generated electrostatically on the glass and developed with toner, akin to the laser printing process.

Wax effectively fills gaps in cured resin, eliminating the need for additional supports in the interface software It supports overhangs and anchors protrusions, reducing distortion from warping and curling by keeping the part stable in the vat, thus negating the need for vibration-proof machines This system allows for the suspension of builds to prioritize urgent parts and solidifies entire layers at once, significantly decreasing part creation time, particularly for multi-part builds Additionally, nesting parts optimizes build volume, ensuring complete curing of all resin in a layer without the need for post-curing, resulting in more durable parts compared to those produced by other methods Operators also benefit from not handling partially cured, toxic resin, and wax removal can be automated in a specialized machine.

Figure 2.6 Solid Ground Curing (SGC)

The system has several disadvantages, including being noisy, large, and heavy, requiring constant supervision It also leads to significant wax waste that cannot be recycled and is susceptible to breakdowns The mask production process involves raster scanning, which can introduce inaccuracies due to steps in the x-y plane Additionally, the solid resin models created through SGC are unsuitable for investment casting, as the resin's thermal expansion coefficient is much higher than that of the ceramic molds, resulting in cracks during the burnout process.

For more information about SGC systems and their technical specifications, see Chapter 3

Chapter 2 Rapid Prototyping Processes 27 2.2.1.6 Holographic Interference Solidification (HIS)

A holographic image is projected into resin, leading to the solidification of the entire surface While data is sourced from the CAD model, it is not processed in traditional slices The build space measures 300x300x300 mm, and currently, there are no commercial systems available for this technology.

Solidification of an Electroset Fluid: Electrosetting (ES)

Electrodes are applied onto a conductive substrate, typically aluminum After printing all layers, they are stacked and submerged in an electro-setting fluid, which is then energized This process causes the fluid between the electrodes to solidify, forming the desired part Once the composite is extracted and drained, any excess aluminum can be trimmed away.

This technology offers several advantages, including the ability to control part density, compressibility, hardness, and adhesion by adjusting the voltage and current applied to aluminum Components can be created using materials such as silicone rubber, polyester, polyurethane, or epoxy Additionally, the necessary hardware for this system can be purchased at a low cost from off-the-shelf sources Currently, the software for the system is still under development.

Solidification of Molten Material

The melting and solidification of part material involve six distinct processes The first five methods deposit material at individual points, while the sixth process allows for the manufacturing of entire layers simultaneously.

A stream of molten material is expelled from a nozzle, forming droplets that impact the substrate and instantly cold weld to create the part When the substrate has a rough texture, it enhances thermal contact, thereby minimizing stresses within the formed part.

The stream in droplet generation can either be a drop-on-demand system or a continuous jet, with the latter being ejected through a nozzle excited by a piezoelectric transducer operating at approximately 60 Hz To prevent damage to the transducer, it is positioned away from the nozzle While a capillary stream typically breaks into droplets naturally, disturbances at the nozzle create a consistent stream of small, evenly spaced droplets By employing a low-frequency carrier wave modulated by a higher-frequency disturbance, customized streams can be achieved, allowing users to specify larger droplet separations than possible with a single frequency Additionally, regular streams can be generated that feature clusters of small droplets followed by larger, more widely spaced droplets, providing more time for the nozzle to reposition or for droplets to solidify as needed.

1 Movable Sub nate Figure 2.7 Ballistic Particle Manufacture

The characteristics of the final part are influenced by the temperature, velocity, and electrostatic charge of the droplets The droplets acquire charge when ejected, which aids in precise material placement; however, the maximum charge limits the droplet's deflection, necessitating a movable substrate or jet for a larger build area Temperature plays a crucial role in the solidification speed of the molten material—if droplets are too cold, they solidify before welding, while excessive heat can distort the part's shape Additionally, the velocity of the droplets affects both deformation and placement accuracy; slow-moving droplets result in poor accuracy, whereas fast droplets can become deformed upon impact.

Chapter 2 Rapid Prototyping Processes 29 2.2.3.2 Multi Jet Modelling (MJM)

The MJM machine utilizes a 3D printing technique akin to inkjet printing, employing a print head with 352 jets arranged in a linear array to construct models layer by layer with a specialized thermo-polymer material Each layer measures 40 microns in thickness, while the print head moves back and forth along the X-axis, repositioning the platform on the Y-axis for wider parts Once a layer is finished, the platform shifts along the Z-axis to initiate the next layer After the entire model is built, support structures are removed to complete the final product.

For more information about the MJM system and its technical specifications, see Chapter 4

Figure 2.8* Multi Jet Modelling Head

An FDM (Fused Deposition Modeling) machine features a movable head that extrudes a thread of molten material onto a substrate, with the build material heated to just above its melting point to ensure it solidifies quickly and adheres to previous layers Key factors influencing the printing process include maintaining a consistent nozzle speed and material extrusion rate, incorporating support structures for overhangs, and adjusting the head speed, which ultimately impacts the layer thickness.

Modern Fused Deposition Modeling (FDM) systems feature dual nozzles—one for the primary material and another for the economical support material, which can be easily removed without damaging the prototype's surface Additionally, horizontal supports can be utilized to reduce material consumption and construction time For further details on FDM systems, refer to Chapter 3.

Figure 2.9 The Fused Deposition Modelling process

Chapter 2 Rapid Proto typing Processes 31 2.2.3.4 Three-Dimensional Welding (3DW)

This innovative system employs an arc-welding robot to deposit material onto a platform, creating simple shapes that can be assembled into intricate structures Unlike traditional rapid prototyping methods, this approach does not rely on sliced CAD files for prototype construction.

Several challenges persist in the manufacturing process, particularly due to the lack of feedback mechanisms Heat accumulation can lead to the melting of prototypes, and the uneven layering results in a rough surface, which may cause the torch to make contact with the part during production.

In 1992, it remained unclear whether complex structures could be constructed using robotic systems A method must be developed to directly generate robot programming from CAD files, ensuring that both the orientation of each section and the assembly order are effectively determined.

A novel welding system under investigation employs a layered deposition of weld material, utilizing thermocouples for feedback control to monitor temperature and manage an on-line water cooling system To reduce oxidation of the workpiece, a grit blasting nozzle is implemented, while a suction pump and vacuum nozzle efficiently eliminate excess water vapors and grit.

The experimental layer-by-layer process involves spraying molten metal onto a substrate to create near net shapes, followed by the removal of excess material through NC operations Support material is applied either before or after the prototype material, depending on the presence of undercut features, to reinforce subsequent layers In cases of complex layers, support may be necessary on both sides of the prototype Each layer undergoes shot-peening to eliminate residual stresses, while a robotized pallet system transfers the prototype between stations with an accuracy of ±5 J UI1 Droplets, measuring 1-3 mm in diameter, are deposited at a rate of 1-5 droplets per second.

Stainless steel components reinforced with copper have been developed, which can be removed through immersion in nitric acid These prototypes exhibit a structure comparable to cast or welded parts while maintaining the precision of CNC milled components.

Various materials can be utilized, and components can be integrated into the structure Currently, there is no temperature control system for the substrate in place, and factors such as the temperature, size, and trajectory of the droplets remain unregulated.

Figure 2.10 Shape Deposition Manufacturing The construction of the first 3 layers ofa part is shown (from [Merz et aI., 1994])

1 Layer 1: part material is added

2 Layer 1: part material is milled

3 Layer 1: support material is added

4 Layer 1: support material is milled

Processes Involving Discrete Particles

Fusing of Particles by Laser

Selective Laser Sintering (SLS) and Laser Engineering Net Shaping (LENSTM) are key additive manufacturing processes The Gas Phase Deposition (GPD) technique involves the formation of discrete grains through the interaction of a reactive gas with a laser, which also serves to solidify the grains in relation to the final part.

Selective Laser Sintering (SLS) employs a fine powder that is heated with a CO2 laser, allowing the particles to overcome surface tension and bond together To reduce thermal distortion and enhance fusion with the previous layer, the entire powder bed is preheated to just below the material's melting point before the sintering process begins.

In the laser sintering process, the laser is precisely modulated to affect only the powder grains directly in contact with the beam This creates a sintered layer on the powder bed, which is subsequently lowered to allow a counter-rotating roller to evenly spread a new layer of powder over the build area The sintered material forms the desired part, while the unsintered powder remains to support the structure, allowing for easy removal and recycling after the build is complete.

More detailed information about SLS systems and their technical specifications can be found in Chapter 3 canning Sy tern

2.3.1.2 Laser Engineering Net Shaping (LENSTM)

The LENS process utilizes a nozzle to deposit powder onto the part bed while a laser simultaneously fuses the material The nozzle can be positioned either to the side of the bed or coaxially with the laser beam If positioned to the side, it is crucial to maintain a consistent orientation to avoid shadowing areas that need to be built Conversely, when the powder feeder is coaxial with the laser, any misalignment can lead to inaccuracies in the part's geometry and layer thickness.

The heating of the powder stream by the laser enhances fusion with the previous layer, but it also causes thermal distortion in the part To avoid such distortions, it is crucial to cool the part when it overheats, or alternatively, implement a temperature control system The minimum wall thickness is influenced by factors such as feed rate, particle stream width, spot size, and the laser's speed and power For comprehensive details on LENS systems, refer to Chapter 3.

Z Alas Poslllorung of f ocusing Lens

Figure 2.12* LENSTM process (Courtesy ofOptomec Design Co)

A laser decomposes the molecules of a reactive gas to produce a solid that adheres to a substrate, forming the desired part Currently, three distinct methods for constructing this part are under investigation.

The article discusses three advanced methods for part fabrication using laser technology The first method, Selective Area Laser Deposition (SALD), utilizes the solid components of decomposed gas to create parts from materials like carbon, silicon, carbides, and silicon nitrides The second method, Selective Area Laser Deposition Vapour Infiltration (SALDVI), involves applying a thin layer of powder, with decomposed solids filling the gaps between the grains Lastly, Selective Laser Reactive Sintering (SLRS) employs a laser to trigger a reaction between gas and powder layers, resulting in solid parts made of silicon carbide or silicon nitride.

Joining of Particles with a Binder

In the powder-based additive manufacturing process, layers of powder are applied to a substrate and selectively bonded using a binder that is sprayed through a nozzle To minimize powder disturbance during binding, it is crucial to first moisten the powder with water droplets After the build is finished, excess powder that supported the model is removed, revealing the fabricated part This method reduces distortion, as it does not involve any state change.

Sub trate move in negative Z direction

Chapter 2 Rapid Pro to typing Processes 37

Parts produced through this process eliminate the need for supports to stabilize overhanging features; however, they must incorporate a hole for the removal of excess powder (Sachs et al., 1993) This technology has notable drawbacks, including the potential fragility and porosity of the final parts, as well as challenges in extracting excess powder from cavities Additionally, the raster-scanning method utilized by the printhead results in a stair-stepping effect in both the X-V plane and the vertical build direction (Jacobs, 1996).

More detailed information about 3DP systems can be found in Chapter 4

This technology is being developed for prototyping specialised medical equipment in metal It is designed to produce high precision parts within a small build envelope of

The process begins with printing a negative of each layer onto a ceramic substrate using a ceramic pigmented organic ink, which is then cured with UV light This layering continues for approximately 30 layers, after which the positive space is filled with another ink containing metal particles, followed by curing and milling Once the prototype is fully constructed, it is heated in a nitrogen atmosphere to eliminate binders from both inks and sinter the metal particles Finally, the ceramic negative is removed in an ultrasonic bath, revealing the final piece, which is then infiltrated with liquid metal to create the metal prototype.

The sintering process results in up to 20% shrinkage in all directions, which must be considered during part design Ongoing research focuses on optimizing the binder removal process and automating the addition of the positive material, along with the subsequent milling operation.

A prototype system is currently utilized for creating pre-assembled microstructures for medical applications While no commercial systems are available yet, the technology can produce extruded parts with a consistent cross-section Theoretically, it is possible to achieve completely arbitrary geometries.

Processes Involving Solid Sheets

Laminated Object Manufacture (LOM)

The build material is applied from a roll and bonded to previous layers using a hot roller that activates a heat-sensitive adhesive Each layer's contour is precisely cut with a laser, ensuring it penetrates only to the intended depth Unwanted material is trimmed into rectangles for easier removal later but remains in place during the build to provide support The material sheet is wider than the build area, allowing the edges to stay intact after cutting the part's cross-section Once a layer is completed and the build platform is lowered, the excess material can be wound onto a second roller, enabling the process to continue seamlessly.

Figure 2.15 Laminated Object Manufacturing upply

The system utilizes a 25 or 50 Watt CO2 laser for precise material cutting To ensure effective waste removal, smaller hatches are essential on both upward and downward-facing surfaces, preventing waste material from adhering to the part Additionally, it may be necessary to pause the build process to extract paper from difficult-to-reach areas.

Chapter 2 Rapid Prototyping Processes 39 completed, they should be sealed with a urethane lacquer, silicone fluid or epoxy resin spray to prevent later distortion of the paper prototype through water absorption The height is measured and the cross-sections are calculated in real time to correct for any errors in the build direction [Jacobs, 1996]

LOM (Laminated Object Manufacturing) offers several advantages, including a diverse selection of cost-effective materials such as paper, plastic, and fiber-reinforced glass ceramic This method allows for the production of larger parts compared to other rapid prototyping techniques, making it particularly appealing to model makers due to the wood-like finish of the final products Additionally, LOM is significantly faster—approximately 5 to 10 times quicker than alternative processes—since it only requires tracing the outlines of the components.

One significant drawback of this technology is the challenge of removing finished parts from the build platform, which negatively impacts their surface finish Additionally, creating hollow components is difficult due to complications in core removal, alongside issues with undercuts and re-entrant features Other disadvantages include high scrap rates, the necessity for constant machine supervision, the requirement for manual finishing of parts, and compromised shear strength due to the layering of adhesive and foil Furthermore, the laser cutting process poses a fire hazard, necessitating the installation of inert gas extinguishers, while the removal of molten material (dross) formed during cutting is also essential.

For more information about the LOM process and its applications, see Chapter 3.

Paper Lamination Technology (PLT)

The PL T process closely resembles the LOM process, with key differences in material and cutting methods While LOM utilizes a CO2 laser, PL T employs a computerized knife for contour cutting In PL T, the part's cross-section is printed on paper and bonded to the work-in-progress using a hot roller A computer-driven knife then cuts the part's outline and cross-hatches the waste material This cycle continues until completion, allowing excess material to be peeled away, after which the model can be sealed with epoxy resin For more in-depth information on PL T systems, refer to Chapter 3.

Solid Foil Polymerisation (SFP)

In SFP (Solid Freeform Fabrication), parts are constructed using semi-polymerized foils that solidify and bond under UV light, becoming insoluble upon exposure After illuminating the cross-section, a new layer of foil can be applied Supportive foil areas, which do not form part of the final product, remain soluble for easy removal during the build process Once the part is complete, these non-bonded sections can be dissolved, resulting in the finished component Currently, there are no commercial systems available for this technology.

Summary

This chapter has described the technologies currently available for rapidly building physical prototypes The chapter has provided a classification of existing RP technologies followed by an outline of each method

Anon (1993) State of the Art Review-93-01, MTIAC, 10 West 35 Street, Chicago,

Anon (1995) Manufacturing Parts Drop By Drop, Compressed Air, March, Vol

Au S and Wright PK (1993) A Comparative Study of Rapid Prototyping Technology, Proceedings ASME Winter Conference, New Orleans, November, Vol 66, pp 73-82

Corbel S, Allanic AL, Schaeffer P and Andre JC (1994) Computer-Aided Manufacture of Three-Dimensional Objects by Laser Space-Resolved Photopolymerization, Journal ofintelligent and Robotic Systems, Vol 9, pp 310-

Crump SS (1991) Fast, Precise, Safe Prototypes with FDM, ASME Annual Winter Conference, Atlanta, December, Vol 50, pp 53-60

Cubital Ltd (1996) Advantages of the Solider System, Cubital Ltd., 13 Hasadna St., PO Box 2375, Industrial Zone North, Raanana, 43650 Israel

Dickens PM, Pridham MS, Cobb RC and Gibson I (1992) Rapid Prototyping Using 3-D Welding, Proceedings ofthe 3 rd Symposium on Solid Freeform Fabrication, Austin, Texas, September, pp 280-290

Dickens PM (1995) Research Developments in Rapid Prototyping, Proceedings IMechE, Journal of Engineering Manufacture, Part B, Vol 209, pp 261-266

Helisys Inc (1997) 2030H System, Helisys Inc., 24015 Gamier Street, Torrance,

Helisys Web page (2000) Helisys, Inc., 24015 Gamier Street, Torrance, California 90505-5319, USA, http://helisys.comi

Jacobs PF (1992) Fundamentals of Stereo lithography, First European Conference on Rapid Prototyping, Nottingham, July, pp 1-17

Jacobs PF (1996) Stereo lithography and Other RP&M Techniques, ASME Press, New York

Klocke F, Celiker T and Song Y-A (1995) Rapid Metal Tooling, Rapid Prototyping Journal, Vol 1,3, pp 32-42

Kruth JP (1991) Material Incress Manufacturing by Rapid Prototyping Technologies, CIRP Annals, Vol 40, 2, pp 603-614

Laboratory for Freeform Fabrication (1996) Web pages of University of Texas at Austin, Texas, USA

Merz R, Prinz FB, Ramaswami K, Terk M and Weiss LF (1994) Shape Deposition Manufacturing, Proceedings of the sth Symposium on Solid Freeform Fabrication, Aug 8-lO, Austin, Texas, pp 1-8

Objet Web page (2000) Objet Geometries Ltd Rehovot, Israel, http://clients.tia.co.il/objet/inner/products.html

Optomec Web page (2000) Optomec Design Company, 270l-D Pan American Freeway - Albuquerque, New Mexico - 87107, USA, http://www.optomec.comi

Orme M, Willis K and Courter J (1994) The Development of Rapid Prototyping of Metallic Components via Ultra Uniform Droplet Deposition, Proceedings of the sth

International Conference on Rapid Prototyping, Dayton, Ohio, June 12-15, pp 27-37

Rayleigh (1878) On the Instability of Jets, Proceedings of the London Mathematical Society, Vol 10, Part 4, pp 4-13

Renap K and Kruth JP (1995) Recoating Issues in Stereolithography, Rapid Prototyping Journal, Vol 1,3, pp 4-16

Sachs E, Cima M, Williams P, Brancazio D and Cornie J (1992) Three Dimensional Printing: Rapid Tooling and Prototyping Directly from a CAD Model, Transactions of ASME: Journal of Engineering for Industry, November, Vol 114, pp 481-

Sachs E, Cornie J, Brancazio D, Bredt J, Curodeau A, Fan T, Khanuja S, Lauder A, Lee J and Michaels S (1993) Three Dimensional Printing: the Physics and Implications of Additive Manufacturing, CIRP Annals, Vol 42, 1, pp 257-260

Stratasys Inc (1991) Fused Deposition Modelling for Fast, Safe Plastic Models,

12th Annual Conference on Computer Graphics, Chicago, April, pp 326-332

Stratasys Inc (1996) FDM-1650, Stratasys Inc., 14950 Martin Drive, Eden Prairie, Minneapolis 55344-2020, USA

In their 1995 paper presented at the IEEE Micro Electro Mechanical Systems Conference in Amsterdam, Taylor et al introduced "Spatial Forming," a novel three-dimensional printing process This innovative technique, discussed in detail on pages 203-208, highlights advancements in micro-electromechanical systems and their applications in various fields.

Waterman NA & Dickens P (1994) Rapid Product Development in the USA, Europe and Japan, World Class Design To Manufacture, Vol 1,3, pp 27-36

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3D Systems Press Release (1998) ThermoJet, 3D Systems, Worldwide Corporation

HQ, 26081 Avenue Hall, Valencia, California, USA

Technological Capabilities of Rapid Prototyping Systems

This chapter provides a comprehensive technical overview of commercially available rapid prototyping (RP) systems, focusing on key processes such as stereolithography, solid ground curing, fused deposition modeling, selective laser sintering, laminated object manufacturing, and laser engineering net shaping It evaluates the technical characteristics, strengths, and weaknesses of these systems, while also highlighting various successful applications across different industries.

Stereolithography Apparatus (3D Systems)

The Stereolithography Apparatus (SLNM) by 3D Systems, established in 1986, was the first commercially available layer-additive technology for creating physical objects directly from CAD data Their inaugural SLA machine was developed in 1987, and today, 3D Systems offers four different SLA models The SLA 250, the smallest model, utilizes a helium-cadmium laser with a wavelength of 325 nm, while the other models employ solid-state Nd:YV04 lasers emitting at 354.7 nm Among these, the SLA 3500 is currently the most popular choice for rapid prototyping and tooling Specifications for all 3D Systems SLA products are detailed in accompanying figures.

A Service Level Agreement (SLA) produces robust or semi-solid stereolithography (SL) components using acrylic or epoxy resins, employing various build styles, with the three most prevalent being ACESTM, STAR WEA VpM, and QuickCast™ [3D Systems, 1996] Typically, fully hollow parts are avoided due to their fragility in the green state, which makes them prone to deformation during handling.

Using ACESTM technology, the interior of parts is nearly fully cured by laser application, achieved through a hatch-spacing equal to half the line-width This method ensures uniform UV exposure across all solidified resin, resulting in flat downward-facing surfaces It is suitable only for epoxy resins with minimal shrinkage during polymerization to prevent warping This approach is the most precise among the three build styles for low-distortion resins and is preferred for creating high-precision components, despite having the longest drawing time.

Chapter 3 Characteristics and Capabilities of RP Systems 45

Laser type, Solid state frequency frequency

Wavelength, Heed,325 Nd:YV04, tripled tripled

Power nm,6mW 354.7 nm, Nd:YV04, Nd:YV04,

Drawing speed 635 mmls 2.54 mls up to 5.0 mls 2.54-9.52 mls

Operating system MS-DOS Windows NT Windows NT Windows NT

* Geometry, build style, material and parameter dependent

Figure 3.2 Technical specifications of SLA systems [3D Systems, 2000] z x y

Figure 3.3 ACESTM build style: Repeated, even laser exposure produces a flat base

STARWEAVETM enhances the stability of solid parts by incorporating a series of interior grids, offset by half the hatch spacing on alternating layers This design feature minimizes overall distortion by ensuring the grid ends do not connect to the part's border and keeping grid lines from touching, while positioning them as closely as possible to boost the part's green strength This build style is particularly effective with acrylic resins, which tend to shrink during polymerization, and is sometimes preferred over ACESTM for epoxy resins due to reduced draw time.

+- -t - -+- -1 r-r - j i 'Offset distance IS half the hatch spacing

The STARWEAVETM build style consists of a single layer featuring a cross-hatched grid that is separated from the part border Additionally, alternate layers of STARWEAVETM are strategically offset by half the hatch-spacing, enhancing structural integrity and design flexibility.

Part Border Vertex of one section is the centroid of the above previous section - - First Section

Figure 3.5 QuickCast™ build style: Parts are hatched with offset triangles

QuickCast™ is ideal for creating prototypes intended for investment casting, as it generates nearly hollow parts The process begins with outlining the layer before filling the interior, using either squares (QuickCast™ version 1.1) or equilateral triangles (QuickCast™ version 1.0) These shapes are strategically offset after a designated vertical build distance to enhance resin drainage In the case of triangles, their vertices are positioned above the centroids of the previous section's triangles, while squares are offset by half the hatch spacing This design choice allows for improved drainage due to the smaller meniscus of resin associated with squares, which have larger interior angles compared to triangles.

In the manufacturing process, horizontal sections forming the outer surface of parts, known as skinfill areas, are fully solidified to prevent 'pinholes' during support removal and to minimize sagging on upward-facing surfaces These skinfills enhance surface support, allowing for larger hatch spacing and resulting in a lower solid percentage of the prototype To facilitate the escape of excess resin, proper venting and drainage must be integrated into these areas QuickCast™ parts, due to their extensive surface area and hygroscopic nature, should be utilized promptly or stored in controlled humidity environments to avoid distortion from moisture absorption.

A range of several resins has been developed by Ciba-Geigy in collaboration with 3D Systems especially for the SL process The material properties of these resins are summarised in Figure 3.6

Several companies have developed rapid prototyping (RP) systems utilizing polymer curing with ultraviolet lasers Notable manufacturers of stereolithography (SL) systems include SONY, Computer Modelling and Engineering Technology Inc (founded by Mitsubishi Corp., NTT Data Corporation, and Asahi Denka Kogyo K.K in 1990), Teijin Seiki Ltd., Meiko Co Ltd., and AAROFLEX, Inc.

Stereolithography (SLA) offers several advantages, including a surface finish that rivals that of numerical control (NC) milling With over 1,000 machines in operation globally, SLA is a proven technology known for its speed and accuracy The systems achieve an impressive accuracy of ± 100 micrometers and can produce layers as thin as 25 micrometers, making them a reliable choice for high-quality 3D printing.

To utilize the resin vat fully and shorten production time, several parts may be built at once

The drawbacks of this material include its high cost, toxicity, and unpleasant odor, requiring protection from light to prevent premature polymerization Additionally, the limited selection of resins can lead to brittle and translucent parts that necessitate supports, potentially compromising surface finish upon removal Furthermore, replacing the resin in the vat is a time-consuming and expensive process.

Density @ 25° C Tensile strength Tensile modulus Elongation at break Flexural strength Flexural modulus Impact strength, 10 Hardness Glass deflection temp Heat deflection temp

The measurement methods for materials include ASTM D 638, which reports tensile strength values ranging from 59-60 MPa for method 51701 and 55-57 MPa for method 51901 Additionally, the tensile strength for method 51701 varies between 3737-2172 MPa, with a maximum of 4158 MPa, while method 51901 shows values up to 2275 MPa The elongation percentage for method 51701 is between 7-19%, and for method 51901, it is 9% Flexural strength measured by ASTM D 790 indicates values of 107-75 MPa for method 51701 and 2920-2110 MPa for method 51901, with a maximum of 3006 MPa and 2450 MPa, respectively Impact resistance, assessed by ASTM D 256, ranges from 27-30 J/m Shore D hardness, according to DIN 53505, is 85 for method 51701 and 80 for method 51901 Dynamic mechanical analysis (DMA) shows E" peak values after UV post-curing, with ASTM D 648 indicating a temperature of 55°C at 0.455 MPa and 49°C at 1.822 MPa The testing conditions include a 60-minute UV post-cure, a 90-minute UV post-cure followed by 2 hours at 120°C thermal post-cure, a 90-minute UV post-cure only, and a 90-minute UV post-cure with an additional 2 hours at 80°C thermal post-cure.

Resin Types 5195 52102 52203 54303 1.16 1.15 1.14 1.181 46.5 45 62 51-56 2090 3020 2703 2358- 2668 11-22 1.6 8.3 2.9-4.9 49.3 74 94 109- In 1628 3061 2951 3089- 3165 54 27 37 21 83 85 86 87 92°C 53°C 88° C 47° C 99°C 63° C 74°C 42°C 52° C 5 1.5-6 hours UV postcure; higher values are obtained with longer UV postcure times Figure 3.6 Properties of SL resins [3D Systems, 2000]

Solid Ground Curing Systems (Cubital Ltd)

Cubital Ltd., established in 1987 as an internal R&D unit of Scitex Corporation Ltd., developed the SGC systems, with the first installation occurring in 1991 The company offers two SGC-based systems: the Solider 4600, an entry-level RP machine, and the Solider 5600, designed for high-capacity users Figure 3.7 illustrates the Solider 4600 system, while Figure 3.8 provides a summary of the technical specifications for both models.

SGC systems offer the significant advantage of solidifying an entire layer simultaneously, which greatly reduces part creation time This method ensures complete curing of all resin within a layer, resulting in more durable parts compared to those produced with other processes, eliminating the need for post-curing Additionally, the use of wax to fill gaps in the resin and support the part means that no additional supports are required.

Figure 3.7 Cubital's Solider 4600 system (Courtesy of Cubital Ltd)

The SGC system has several disadvantages, including its noise and large size, which require constant supervision Additionally, it results in significant wax waste, as the used wax cannot be recycled after removal in hot water or citric acid Furthermore, SGC systems are susceptible to breakdowns, and the solid resin models they produce are not suitable for further processing.

Chapter 3 discusses the characteristics and capabilities of RP systems, highlighting the challenges associated with investment casting Notably, the resin's coefficient of thermal expansion significantly exceeds that of the ceramic system, leading to the potential cracking of ceramic molds during the burnout of the sacrificial part.

Min Feature Size O.4mm O.4mm

Net Production Rate 164 cm 3 /hour 426 cm 3 /hour

Layer Build Speed 120 s/layer 70 s/layer

Control system Unix based workstation Unix based workstation

Figure 3.8 Specifications of sac systems [Cubital, 2000]

The resolution (minimum feature size) of this system is 400 J.Un in the X-Y plane and 100 J.Un in the Z direction The least expensive sac machine costs around

$275,000 and weighs about 5000 kg The largest build chamber available is 500 x

A layer measuring 350 x 500 mm can typically be constructed in 70 to 120 seconds, depending on the machine utilized This process includes a 3-second exposure to a 2000W UV lamp, with the remaining time allocated for clearing the resin, as well as adding, chilling, and milling the wax.

Fused Deposition Modelling Systems (Stratasys, Inc.)

The Fused Deposition Modeling (FDM) process, developed by S Crump in 1988, led to the founding of Stratasys in 1989, which has since produced over 1,000 systems The company's inaugural product, the 3D MODELER, was launched in 1992, and Stratasys continues to offer a diverse range of FDM rapid prototyping systems.

The FDM systems, including the FDM 2000, FDM 3000, FDM 8000, and FDM Quantum, are equipped with dual nozzles—one designated for the primary part material and the other for the more economical support material This support material is designed to easily detach from the prototype, ensuring that the surface quality remains intact.

Horizontal supports can be implemented to reduce material usage and construction time, as highlighted by Crump in 1991 The FDM 2000 system, depicted in Figure 3.10, is a widely used option for creating functional prototypes or casting masters, with dimensions up to 254x254x254 mm Priced at approximately $87,000, this system offers an accuracy of ±127 µm, as reported by Stratasys in 2000.

0.254mm (up to 127 mm)and ±

Weight 160kg 160kg 392 kg 1134 kg

Power 220-240 V AC, 208-240 V AC, 220-240 V AC, 208-240 V AC, Require- 50/60 Hz, 10A 50/60 Hz, 10A 50/60 Hz, lOA 50/60 Hz, 50A ments single phase single phase single phase single phase

Materials ABS (White) ABS (White) ABS ABS

Layer Width 0.254 to 2.54 0.254 to 2.54 0.254 to 2.54 0.38 to 0.51 mm mm mm mm

Layer 0.05 to 0.762 0.05 to 0.762 0.05 to 0.762 0.18 to 0.25

Thickness mm mm mm mm

Figures 3.9 Technical characteristics ofFDM systems [Stratasys, 2000]

Figure 3.10 FDM 2000 system (Courtesy ofStratasys, Inc.)

In January 1998, Stratasys launched the FDM Quantum system featuring MagnaDrive technology, which utilizes an X-Y electromagnetic motion-control system alongside dual-axis linear motors This innovative design enables precise and repeatable two-axis motion control in a single plane without the need for a traditional gantry system, eliminating common moving parts like cables, belts, and pulleys As a result, the mechanics are simplified, enhancing reliability The MagnaDrive technology also facilitates high-precision coordinated movements, including contouring and circular interpolation.

Figure 3.11 FDM Quantum extrusion heads employing MagnaDrive technology

Figure 3.12 FDM Quantum system (Courtesy ofStratasys, Inc.)

Chapter 3 Characteristics and Capabilities ofRP Systems 55

In August 1999, Stratasys launched the FDM 3000 system, featuring an innovative support removal method utilizing a water-soluble ABS modeling material known as WaterWorks This process involves immersing the completed model in a water-based solution that effectively dissolves the support material, resulting in a clean model with smooth surfaces The FDM 3000 system is priced competitively within the market.

Fused Deposition Modeling (FDM) systems utilize various thermoplastic materials, including standard ABS, high-impact ABS, investment casting wax, and elastomers These materials are commercially available and supplied on spools, which are essential for the spool-based filament system used in the FDM process.

FDM systems serve as cost-effective and environmentally friendly desktop prototyping solutions in design offices, utilizing affordable, non-toxic, and odorless materials The availability of various materials enhances their versatility, while the stability of parts produced through this method is notable, as they are not hygroscopic.

One drawback of material extrusion is the inferior surface finish of the parts compared to those produced by stereolithography (SL), primarily due to the lower resolution dictated by filament thickness Additionally, it remains unproven whether material extrusion can be halted quickly enough to create small holes in vertical sections.

Selective Laser Sintering Systems (DTM Corp and EOS GmbH)

The SLS process, originally developed and patented by the University of Texas at Austin, was commercialized by the formation of DTM Corporation in Austin, Texas DTM holds 79 patents globally that encompass various elements of the SLS process, systems, and materials The company launched its first commercially available SLS system in 1992, with the latest model being the Sinterstation.

The Sinterstation 2500 Plus features a build chamber with dimensions of 381 mm in width, 330 mm in depth, and 457 mm in height A detailed summary of its specifications is illustrated in Figure 3.14 The approximate cost of the Sinterstation 2500 Plus is around [insert price].

A diverse array of materials can be utilized in the sintering process, including nylon, nylon composites, polystyrene, and polycarbonate, which are cost-effective, non-toxic, and safe options that can be sintered using low-power lasers (10 - 20 W) Additionally, metal powders and sand, when coated with an appropriate binder, can be sintered for the direct production of metal tooling inserts and sand cores For more detailed insights into the rapid tooling applications of the SLS process, refer to Chapter 7.

Figure 3.13 Sinterstation 2500 Plus (Courtesy DTM Corp.)

Currently, two nylon-based materials, DuraForm Polyamide and DuraForm Glass-filled, are commercially available for the SLS process These nylon materials are primarily utilized for producing prototypes and functional parts, such as hinges and clips, due to their ability to be finished to a smooth appearance The production of nylon parts is cost-effective for small quantities, typically ranging from 1 to 5 pieces Key properties of these nylon materials are illustrated in Figure 3.15, with an example part made from DuraForm PA displayed in Figure 3.16.

SLS materials are essential for creating casting patterns, with TrueForm and CastForm being the primary materials used TrueForm, an acrylic-based powder, is processed at lower temperatures than nylon, resulting in reduced shrinkage of only 0.6%.

In 1997, TrueForm was introduced for producing parts with good accuracy and moderate strength, featuring a density that ranges from 70 to 90% based on build parameters, and the capability to achieve a mirror-like finish In 1999, DTM launched CastForm, a polystyrene-based powder that provides substantial benefits over TrueForm, particularly for creating patterns used in investment casting.

Chapter 3 explores the characteristics and capabilities of RP systems, highlighting the advantages of CastForm, which boasts low ash content and compatibility with standard foundry practices The processing of CastForm results in porous, low-density patterns that are infiltrated with low-ash foundry wax, achieving a composition of 45% polystyrene and 55% wax Key material properties of TrueForm and CastForm are summarized in Figure 3.17.

Laser 50- or 100-Watt CO2 (Beam Diameter = 0.420 mm) Beam Delivery System M3ST Galvanometers, 3 axis

Scan Speed = 5,000mmisec Positional Accuracy = 50mm

DTM Sinterstation System Software Materialize NV, Magics RP® Software Computer System Pentium-based controller

System Dimensions Process Station = 2l33 w x 1346ux 1981 H mm

Computer Cabinet = 609 W x 609D X 1828 H mm Chiller = 533 W x 838D X 914 H mm

Peripherals Breakout Station 1 Air Handler 1 Sifter, Vacuum

Cleaner Power Requirements 240 V AC, 12.5 KV A, 50/60 Hz, 3-phase

Minimum Pressure = 1 7 bars Continuous Flow Rate = 19 lpm Atmospheric Requirements Temperature Range = 15° to 27° C

Figure 3.14 Sinterstation 2500"Ius system specifications

SLS materials are more cost-effective than SL resins, non-toxic, and safe, allowing for sintering with low-powered lasers However, nylon parts necessitate an extended cooling period in the machine, with nylon composite components taking 6-8 hours to cool before removal Additionally, the materials used are sensitive to varying heating and laser parameters, requiring specific settings for each type, which can be challenging and time-consuming to configure.

Unit ASTM Test DuraForm DuraForm

General Properties Method Polyamide Glass-Filled

Diffraction Particle Size Range, 90% 11m Laser 25-92 10-96

Tensile Strength at Yield MPa D628 44 38.1

Figure 3.15 Properties of DuraForm materials

Figure 3.16 Boeing air vehicle component (Courtesy ofDTM Corp)

One limitation of the SLS process is the necessity for sieving recycled powders to eliminate any globules that could disrupt the even application of subsequent powder layers Additionally, the sintering of materials must occur in an inert Nitrogen atmosphere.

Units Test Method TrueForm CastForm

Average Particle Size /-lm Laser 33 62

Particle Size Range, /-lm Laser 15-60 25-106

Powder Density, Tap g/cm3 ASTM D4164 0.3-0.4 0.46

As Processed (Ra) /-lm DTM 5.5 13

After Polishing (Ra) J.lm DTM 0.7 3

Figure 3.17 Material properties of TrueForm and CastForm

EOS GmbH Electro Optical Systems manufactures laser sintering systems, including the EOSINT P machines introduced in 1994 These machines are specifically designed for creating physical prototypes using thermoplastic powders like polystyrene and nylon The primary applications of EOSINT P include producing investment casting patterns and functional test parts A summary of the specifications for the EOSINT P350 can be found in Figure 3.18.

Laser scan speed up to 5 m/s

Building speed 10-25 mm heightlh (material dependent) Layer thickness (typ) 0.1-0.2 mm

Compressed air supply minimum 5.000 hPa; 6 m 3 /h

Cooling water supply 1.500 hPa - 4.000 hPa; 5 I/min

Interface to CAD Standard: STL, CLI

Optional: VDA-FS, IGES, CATIA

Figure 3.18 Specification of EOSINT P350 (Courtesy ofEOS GmbH)

Laminated Object Manufacturing Systems (Helisys, Inc.)

The LOM process, developed by Helisys Inc., marked a significant advancement in manufacturing when the company shipped its first commercial LOM system in 1991 Today, Helisys offers two models of the LOM system: the LOM-1015 Plus and the LOM-2030H, which utilize 25 W and 50 W CO2 lasers, respectively, for material cutting.

A summary of their specifications is given in Figure 3.20

Currently, there is no adjustment to the width of the CO2 laser beam, resulting in minor dimensional errors in the parts produced To effectively remove waste material bonded to the components, smaller hatches must be implemented on both up- and down-facing surfaces The process of detaching a LOM object from excess material may require halting the build to access hard-to-reach areas After completion, parts should be sealed with urethane, silicon, or epoxy spray to prevent distortion from water absorption Additionally, height measurements and real-time cross-section calculations are conducted to correct any build direction errors.

System controller Pentium-based Pentium-based

System software Windows NT OS Windows NT OS

Material size, mm 356 mm roll width, 356 711 mm roll width, 711 mm mm roll diameter roll diameter Dimensions, cm l22.6 L x 74.3 w x 130.8 H 206 L x 141 W x 140 Hand 59 L x 83w X l40H

Power requirements 220 V AC, 15 A, 50/60 Hz, 220 V AC, 30 A, 50/60 Hz, single phase single phase

Atmospheric Temperature = 20 0 to 27 0 C Temperature = 20 0 to 27 0 C Requirements Humidity = number of measured dimenSIons: along X: 29 afong Y: 30 along Z: 9 along X+Y+c 68 mean error along X: 0,28 along Y:-O,07 along Z: 0,37 along X+Y+Z: 0,14 variance: along X: 0,08 along Y: O,Og along c 0,15 along X+Y+Z: 0,13

Dislribution of errors of dImensions: _ •• along X along Y along Z along X+Y+Z

Figure 5.10 TrueFonn housing: Distribution of errors along different directions

Chapter 5 Applications of Rapid Prototyping Technology 95

Error as a percentage of dimension ('!o) number of measured dimensions: along X: 29 along Y: 30 along Z: 9 along X+Y+Z: 68 mean error: along X: 1.31 along Y: ().13 along Z: 4.11 along X+Y"'Z: 1.04 vanance: along X: 8_35 along Y: 4.65 along Z: 8.77 along X+Y"'Z: 8.66

Dislributionoferrorsofdimensions: _ " _ alongX 0 alongY - 6 alongZ~alongX+Y+Z

Figure 5.11 TrueFonn housing: Distribution of percentage errors along different directions

Figure 5.12 TrueFonn housing: Cumulative IT distribution

TrueForm exhibits properties similar to injection-moulded plastic, making it susceptible to sinking or sagging, particularly in thicker sections To mitigate sagging, part orientation should be carefully selected whenever possible; however, this may not always be feasible In such instances, shelling the model—transforming a solid structure into a hollow one—can effectively minimize distortion Although TrueForm generally offers good accuracy, the specific part orientation in this case, which primarily measured dimensions in the Z direction, contributed to a less favorable accuracy outcome due to inherent error sources in that orientation.

Figure 5.13 Cross section of a hollow TrueForm part

Figure 5.14 Sagging due to non-constant wall thickness Figure 5.15 Improvement of the accuracy on a hollow part

Using a larger SLS machine like the Sinterstation 2S00 would enable horizontal part orientation in the build area, improving accuracy to approximately ±0.12 mm, as specified for TrueForm material by the manufacturer Despite some dimensions potentially falling outside the general tolerance of ±0.12 mm, the aluminum castings remained satisfactory, as deviations could be corrected through subsequent machine finishing TrueForm patterns prove to be cost-effective for producing a limited quantity of complex designs, typically up to 50 parts, where the expense of creating molds for wax patterns is not feasible.

RP technologies are utilized in the medical field to create models that deliver both visual and tactile information These RP models find applications in various areas of medicine, enhancing understanding and interaction with anatomical structures.

Operation planning benefits significantly from real-size RP models of patients' pathologic regions, enabling surgeons to better understand physical issues and gain deeper insights into the surgical procedures Additionally, these RP models facilitate effective communication between surgeons and patients regarding the proposed operations.

Medical Models

RP technologies are utilized in the medical field to create models that deliver both visual and tactile information These RP models have various applications in medicine, enhancing practices in areas such as surgical planning and education.

Operation planning is significantly enhanced by utilizing real-size RP models of patients' pathological regions, allowing surgeons to better comprehend physical issues and gain deeper insights into the necessary procedures These RP models also facilitate effective communication between surgeons and patients regarding the proposed surgical interventions.

Surgery rehearsals utilizing RP models provide surgeons and their teams with the chance to practice intricate procedures with the same techniques and tools they will use in real operations These rehearsals have the potential to enhance surgical protocols and significantly lower risks associated with complex surgeries.

Training with RP models of unique medical deformities enhances the education of student surgeons and radiologists, providing valuable hands-on experience These models are also beneficial for conducting student examinations, ensuring a comprehensive understanding of complex cases.

Prosthesis design has been revolutionized by the use of RP models, which serve as master patterns for creating implants These implants, crafted from bio-compatible plastic materials, offer enhanced accuracy and cost-effectiveness compared to traditional manufacturing methods.

The building of RP models of anatomical structures involves the following steps:

Medical equipment such as CT scans, MRI scans, and 3D ultrasounds are essential for data acquisition, capturing a series of images of specific anatomical structures For instance, a CT scanner, illustrated in Figure S.16, demonstrates this imaging process effectively.

Figure 5.16 A CT scanner and a captured image (Courtesy of Materialise)

Interactive software tools, such as MIMICS developed by Materialise, facilitate the generation of STL files from scanned data by allowing users to control and correct image segmentation The software defines the segmentation volume based on pixels with a grey value above a set threshold, and it also supports segmentation between two threshold values This approach is particularly useful for segmenting soft tissues in CT images and for differentiating multiple structures in MR images.

Building RP models from generated STL files can utilize various RP technologies, each offering specialized materials for medical applications Notably, Fine Nylon Medical Grade is tailored for SLS processes and can withstand autoclave sterilization, while Stereocol resin, used in SLA processes, provides unique benefits despite being less accurate than epoxy resin This resin allows for color customization through additional UV laser treatments, enhancing the visual representation of certain model areas, especially since SLA models are inherently translucent.

Chapter 5 Applications of Rapid Proto typing Technology 99 can be viewed within the parts Figure 5.18 shows a medical model built using Stereocol v T,

Figure 5.17* User interface in the MIMICS software (Courtesy of Materialise)

Figure 5.18* A medical model built using the Stereocol resin (Courtesy of

Two case studies highlight the application of RP models in the medical field The first case, conducted by Anatomics™ in Queensland, Australia, involved the creation of two SLA medical models for a patient with a secondary carcinoma affecting the right superior orbital margin and the adjacent frontal bone The initial model served multiple purposes: it aided in planning the resection of the cancerous bone, acted as a reference during surgery, and facilitated patient consent Notably, the SLA model can be manipulated using standard surgical tools for bone resection A plastic template was produced based on the surgeon's specified resection line, allowing for a precise fit when placed over the model to verify alignment with the intended surgical plan.

Figure 5.19* The SLA model with the resection template (Courtesy of the British

A custom acrylic implant was created using the unaffected left superior orbital margin as a reference for design Both the resection template and the custom implant underwent gas sterilization prior to the operation The template was applied to the lesion to outline the resection line, after which the bone was excised Ultimately, the implant was successfully inserted into the resulting deficit.

The operation was a complete success The surgeon was fully satisfied with the quality and the cost of utilising RP models

Figure 5.20* The SLA model together with the template and the implant (Courtesy of the British Journal of Neurosurgery)

A case study by Materialise (2000) highlights the use of rapid prototyping (RP) technology in creating an obturator prosthesis for an oncologic patient Utilizing CT scan data, an RP tool was developed for direct molding of a biocompatible silicone implant The resulting prosthesis demonstrated superior fit compared to traditional methods, offering enhanced accuracy and significantly minimizing damage to sensitive surrounding tissues during surgery.

Rapid prototyping (RP) technologies are increasingly being utilized in the fields of art and design, allowing artists to create intricate models that enhance their creative processes While the initial expense of RP models restricted their size, the advent of Concept Modellers has made these techniques more affordable for various artistic projects With the precision of art models and the quality of RP materials now available, Concept Modellers provide sufficient technological capabilities to meet the demands of most art applications.

A: A hole resulted from the irradiation of a tumor in the mouth cavity This hole has to be filled by an implant to allow the patient to breathe and eat normally

B: The soft tissue surrounding the cavity was modelled by CT scanning This model was used to design a tool for direct moulding of the implant

C: A silicon implant was moulded from the tool

D: Without surgery, the deformable silicon prosthesis was implanted Magnets were used to fix the prosthesis to a hard dental implant

Figure 5.21 * Fabrication of obturator prosthesis using RP techniques Case study presented by Dr L.L Visch from Daniel den Hoed Kliniek Rotterdam

Figure 5.22* Cross-sections of the 3D model of a water splash

(Courtesy of the CALM project)

Figure 5.23 SLS model representing a water splash

The CALM (Creating Art with Layer Manufacture) project, supported by the Higher Education Funding Council for England, showcases three examples of RP techniques in art This initiative aims to enhance the integration of IT within the UK higher education art and design community.

M Harris's artwork features a splash design within a plexiglass vitrine, showcasing its innovative use of materials The final installation will include an RP model, carefully fitted into a plexi-box that matches the width of the splash, enhancing the visual impact of the piece.

K Brown's cybersculpture exemplifies an innovative artefact that defies conventional construction methods Initially intended for rapid prototyping and bronze casting, the artist was inspired by the SLS model's unique Dura form material and intricate lace-like Moire surface patterns This realization led to a profound appreciation for the artwork's inherent beauty, where the synergy of concept, process, material, color, and layered form creates an unprecedented experience in artistic expression.

Figure 5.24* 3D shaded image and a cross-section of the cybersculpture (Courtesy of the CALM project)

Figure 5.25 SLS model of a cybersculpture

Engineering Analysis Models 1 06

Computer Aided Engineering (CAE) analysis plays a crucial role in Time Compression technologies, utilizing various software tools primarily based on Finite Element Analysis (FEA) to accelerate product development through early design optimization However, creating precise FEA models for complex engineering objects can be time-consuming and labor-intensive By integrating Rapid Prototyping (RP) techniques, testing on physical models can commence earlier, enhancing the CAE data This article outlines four key applications of RP models in engineering analysis.

SLA models were utilized to optimize the cross-flow jacket of a V6 high-performance racing engine, incorporating 60 sensors to monitor local flow temperature and pressure The visualization of coolant flow patterns was achieved by injecting tiny air bubbles, with high-speed video capturing the flow dynamics This analysis revealed stagnation zones and poorly cooled areas, leading to the redesign of critical sections The production of modified SLA models allowed for rapid design iterations, with each cycle taking just one week, ensuring that the accuracy and surface quality were sufficient to replicate complex flow behaviors effectively.

Figure 5.27 Assembly of the cross-flow water jacket of a V6 high-performance racing engine [Jacobs, 1996]

Thermo Elastic Tension Analysis (THESA) enables the structural analysis of real parts using Rapid Prototyping (RP) models on test rigs, effectively correlating temperature changes in test components to applied loads By employing thermal imaging, the impact of specific loads on temperature patterns is assessed For instance, SLS models made from glass-filled nylon were utilized to enhance the design of a sports car's highly loaded wheel rim Initial experiments with various RP materials identified the optimal choice for THESA analysis, revealing that the temperature patterns of the glass-filled nylon model closely resembled those of cast metal parts This case study illustrates that the findings from SLS models using the THESA method can be effectively related to the behavior of series cast metal components.

Figure 5.28* Thermographic plots of aluminium rim (left) and SLS glass-filled nylon rim (right) [Gartzen et ai., 1998]

Photoelastic stress analysis is an effective method for evaluating stresses and strains in physical components under specific conditions, utilizing the temporary birefringence of transparent materials when subjected to load SLA models, particularly those made with the ACES build style, demonstrate the necessary birefringence, which can be visualized using polarized white and monochromatic light The insights gained from photoelastic analysis of SLA models can be applied to functional metal parts through fundamental similarity laws, enabling quick and cost-effective predictions of stress distributions in actual components.

In photoelastic stress analysis, rapid manufacturing techniques enable the "freezing" of stresses and strains by initially heating the loaded model above the resin's glass transition temperature, followed by a gradual cooling process back to room temperature.

Figure 5.29* The frozen stress distribution for a model of an aeroengine turbine rotor [3D Systems, 1994]

The aerospace and automotive industries continue to depend on experimental wind tunnel tests to validate new designs, despite advancements in CAE tools Rapid Prototyping (RP) techniques are effective for creating wind tunnel models that experience minimal loads Technologies such as SLA, SLS, FDM, and SGC yield models with the necessary strength, accuracy, and surface finish for testing non-structurally loaded components Additionally, SLS models made from RapidSteel or metal models created from RP patterns are suitable for applications with light loading.

Summary

This chapter offers a comprehensive overview of the application areas for Rapid Prototyping (RP) technologies, along with specialized software tools and the various building styles and materials utilized It includes case studies to help users explore potential RP applications tailored to their specific needs As RP technology continues to evolve, the listed application areas are not exhaustive, with numerous research and development centers globally actively pursuing new RP applications alongside advancements in technology and materials.

3D Systems Newsletter (1994) The Edge, Summer, 3D Systems, 26081 Avenue Hall, Valencia, California, USA

Anatomies Case Studies (2000), Anatomies Rty Ltd, Queensland, Australia, http://glacier.qmi.asn.au: 801 anatomics/

Beaman JJ, Barlow JW, Bourell DL, Crawford RH, Marcus HL and McAlea KP

(1997) Solid Freeform Fabrication: A New Direction in Manufacturing, Kluwer Academic Publishers, Dordrecht, The Netherlands

CALM Project Final Report (1998) University of Central Lancashire, Preston, http://www.uclan.ac.uklclt/cahn!overview.htm

DTM White paper (2000) Functional prototyping with DuraForm and SLS, DTM Corporation, Austin, Texas, USA, 2000

D'Urso PS, Atkinson RL, Lanigan MW, Earwaker WJ, Bruce II, Holmes A, Barker

TM, Effeney DJ and Thompson RG (1998) Stereo lithographic biomodelling in craniofacial surgery, The British Journal of Plastic Surgery, Vol 51, 7, pp 522-

D'Urso PS, Atkinson RL, Weidmann MJ, Redmond MJ, Hall BI, Earwaker WJ, Thompson RG and Effeney DJ (1999a) Biomodelling of skull base tumours The Journal of Clinical Neuroscience, Vol 6,1, pp 31-35

D'Urso PS, Barker TM, Earwaker WJ, Bruce II, Atkinson RL, Lanigan MW, Arvier

JF and Effeney DJ (1999b) Stereolithographic biomodelling in cranio-maxillofacial surgery: a prospective trial The Journal of Cranio-maxillofacial Surgery, Vol

D'Urso PS and Redmond MJ (2000), Method for the Resection of Cranal Tumours and Skill Reconstruction British Journal of Neurosurgery Vol 4, 6, pp 555-559, http://www.tandf.co.uk, see also [Anatomies, 2000]

Gatrzen J, Lingens H, Gebhardt A and Schwarz C (1998) Optimisation using THE SA, Prototyping Technology International '98, UK & International Press, Surrey, UK, pp 36-38

Ippolito R, Iuliano L and Gatto A (1995) Benchmarking of Rapid Prototyping Techniques in Terms of Dimensional Accuracy and Surface Finish, CIRP Annals, Vol 44,1, pp 157-160

Jacobs PF (1996) Stereolithography and other RP&M technologies, Society of Manufacturing Engineers - American Society of Mechanical Engineer

Materialise Product Information (2000) Mimics software, Materialise, Leuven, Belgium, http://www.materialise.be/

McAlea K, Lackminarayan U and Maruk P (1996) Selective Laser Sintering of Metal Molds: The Rapid ToolTM Process, Moldin'96, ECM Inc., Plymouth, MI

In their 1995 study, Lightman AJ, Vanassche B, D'Urso P, and Yamada S explored the applications of rapid prototyping in surgical planning, highlighting a comprehensive survey of global activities in this innovative field Presented at the 6th International Conference on Rapid Prototyping in Dayton, Ohio, the research emphasizes the significance of rapid prototyping techniques in enhancing surgical procedures and outcomes The findings, detailed on pages 16-21 of the conference proceedings, underscore the transformative potential of these technologies in modern medicine.

Pham DT, Dimov SS and Lacan F (1999) Selective Laser Sintering: Applications and Technological Capabilities, Proc IMechE, Part B: Journal of Engineering Manufacture, Vol 213, pp 435-449

Poulsen M, Lindsay C, Sullivan T and D'Urso PS (1999) Stereolithographic modelling as an aid to orbital brachytherapy The International Journal of Radiation Oncology, Biology and Physics, Vol 44, 3, pp 731-735

Raymond NC and Thomas VJ (1998) A Comparison of Rapid Prototyping Techniques Used for Wind Tunnel Model Fabrication, Rapid Prototyping Journal, MCB University Press, Vol 4, 4, pp 185-196

Van de Crommert S, Seitz S, Esser KK and McAlea K (1997) Sand, Die and Investment Cast Parts via the SLS Selective Laser Sintering process, DTM GmbH, Hilden, Germany

Chapter 6 Indirect Methods for Rapid Tool

Rapid Prototyping (RP) is evolving, leading to enhancements in material properties, accuracy, cost, and lead-time, which enable its use in tool production Traditional tool-making techniques have been adapted, and innovative methods for direct tool creation through RP have emerged This chapter focuses on indirect Rapid Tooling (RT) methods that are currently available or will soon be available for production runs of several hundred parts, utilizing materials similar to those of the final production components The RT methods discussed are termed "indirect" because they rely on RP patterns created through specific RP techniques to serve as models for mold and die fabrication.

Role ofIndirect Methods in Tool Production

Recent advancements in RP technologies have significantly minimized delays associated with the iterative processes required for high-quality product development These innovative technologies enable the swift production of three-dimensional solid objects directly from CAD-generated designs, reducing prototype completion time from several weeks to just a few days or even hours.

Rapid Prototyping (RP) techniques are constrained by a limited selection of materials for prototype creation While visualization and dimensional verification can be achieved, functional testing is frequently unfeasible because the mechanical and thermal properties of the prototypes differ significantly from those of the final production parts.

The RP industry is now focusing on tooling to leverage advancements in 3D CAD modeling and RP technology Enhanced accuracy in RP techniques has led to the development of various processes for creating tooling from RP masters Among the most commonly used indirect rapid tooling methods are the creation of silicone room temperature-vulcanizing (RTV) molds for plastic components and the use of RP masters as sacrificial models.

Investment casting of metal parts, as discussed by D T Pham et al in their 2001 work, is a rapid manufacturing process ideal for producing small batches of 1 to 20 components Commonly referred to as "soft tooling" techniques, these methods offer efficient solutions for limited production runs.

Despite the expanded range of materials available through soft tooling, options remain limited and cannot meet all requirements Consequently, alternative indirect methods for tool fabrication have emerged, enabling the creation of prototypes with the same materials and manufacturing processes as the final production components.

This chapter explores indirect methods that serve as a cost-effective alternative to traditional mold-making techniques These methods significantly reduce lead times and facilitate tool validation before incurring substantial expenses The primary objective of these rapid tooling (RT) methods is to bridge the gap between rapid prototyping (RP) and hard tooling, allowing for the production of tools suitable for short prototype runs.

The diverse array of indirect RT solutions complicates the selection of the most suitable method for specific projects It is essential for companies to be aware of all available processes and to understand their respective strengths and weaknesses, as well as the comparative advantages of the materials used.

Metal Deposition Tools

The process utilizes a rapid prototyping (RP) model with a smooth surface finish, incorporating a draft angle and accounting for the shrinkage of the molding material The pattern is set into plasticine along its parting line within a chase, with sprue, gates, and ejector pins added After applying a release agent to the exposed half of the mold, a thin shell of low-temperature molten metal, measuring 2-3 millimeters thick, is deposited It's important to note that high temperatures can soften and distort RP models, limiting the metal deposition techniques that can be used The most commonly employed methods for replicating RP patterns are highlighted.

Spray metal deposition is a widely used technique for metal application, primarily categorized into Gas Metal Spraying and Arc Metal Spraying Gas Metal Spraying utilizes a low melting point alloy that is atomized and propelled onto a substrate through a nozzle, while Arc Metal Spraying, also known as the Tafa process, employs an electric arc to melt metal wires, atomizing the molten material with compressed gas This method is efficient, allowing for the production of up to 2000 precise parts using the same material Additionally, spray metal tools are cost-effective, quick to produce, and capable of handling abrasive materials.

Chapter 6 Indirect Methods for Rapid Tool Production 113

Nickel electroforming involves spraying a model with electrically conductive paint and immersing it in an acid bath containing nickel powder By applying a voltage to the bath, nickel is attracted to the conductive surface through electrolysis This technique is versatile and suitable for various applications, including the production of injection mold cavities, embossing plates, fine printing plates, seamless belts, and laser pumping cavities.

Nickel Vapour Deposition (NVD) is a process that involves the deposition of pure nickel from gaseous vapour onto a heated pattern, typically at temperatures ranging from 110 to 190°C During this process, nickel carbonyl gas (Ni(CO)4) is introduced, resulting in a precise replica of the pattern's surface NVD allows for deposition rates between 0.005 and 0.8 mm/h, enabling the rapid production of shell moulds, regardless of their size or complexity.

After creating a metallic shell through various methods, water cooling lines are incorporated, and the shell is filled with epoxy resin or ceramic to enhance its strength These materials are chosen for their thermal expansion coefficients, which closely match those of the nickel or zinc used in the shells To improve thermal conductivity, aluminum powder is typically added to the epoxy resin or ceramic Once the backfilling material cures, it is machined flat, and the second half of the tool is constructed using the same procedure.

Metal spraying has limitations, particularly when dealing with parts that have projections obstructing the spray configuration or deep recesses that are difficult to reach Consequently, this technique is best suited for models with large, gently curved surfaces While metal spraying can create cost-effective tooling shells that offer good reproduction and dimensional accuracy, these shells often exhibit low mechanical strength and high porosity To enhance the thermal conductivity of the molds, a layer of metal with superior thermal properties and a higher melting point can be applied over the shell.

Ma,ler model Backfilling of Ihe mould ¢ ICh=m Sprue I ¢ ¢

Embedding oflhe model along ils pani ng Ii ne I nvcr,ion of Ihe firsl half of Ihe mould ¢

The spraying process for the first half of the mold is completed, followed by the spraying and backfilling of the second half This technique is illustrated in Figure 6.1, showcasing the spray metal deposition mold.

Nickel exhibits superior mechanical and thermal properties compared to alloys typically used in metal spraying; however, its electroforming deposition rate is relatively slow, approximately 10 µm/h, and the thickness of the deposition is influenced by the surface geometry Challenging areas such as deep corners, sharp edges, and narrow openings are particularly difficult to plate, often leading to premature wear of the nickel shell In contrast, NVD does not face these electroforming challenges but necessitates models that can endure temperatures up to 110°C.

Metal deposition is a well-established and efficient tooling technique that enables the production of thousands of parts This method is widely utilized across various applications, including sheet metal forming, injection molding, blow molding, and compression molding.

RTVTools

RTV tools, also referred to as silicone rubber molds, offer a cost-effective and efficient solution for creating prototype or pre-production tools The process of fabricating RTV molds typically involves several key steps, as outlined by Jacobs in 1996.

1 Producing a pattern Any RP method can be employed

2 Adding venting and gating to the pattern

3 Setting-up the pattern in a mould box with a parting line provided III a plasticine

4 Pouring silicone rubber to form one half ofthe mould

5 Inverting the first half of the mould and removing the plasticine

6 Pouring silicone rubber to produce the second half of the mould

There are two types of silicone used in this process: tin- and platinum-based silicones Tin-based silicone is generally less expensive and more durable

RTV tools are ideal for molding components using wax, polyurethane, and certain epoxy materials This technique is particularly effective for projects that require form, fit, or functional testing with a material that closely resembles the properties of the final production material.

Vacuum Casting, a method of RTV moulding, is essential for creating precise silicone tools that can produce parts with intricate details and thin walls This technique necessitates an initial investment in a specialized vacuum chamber, which consists of two sections: the upper section for mixing the resin and the lower section for casting the resin into the mould An example of a vacuum chamber made by MCP Systems is illustrated in Figure 6.2.

Figure 6.2 MCP vacuum casting chamber (Courtesy of MCP)

The MCP vacuum casting process includes nine steps as shown in Figure 6.3 [3D Systems, 1995]:

1 The first step is to produce a pattern using any of the available RP processes (SLA, SLS, FDM, etc.)

2 The pattern is fitted with a casting gate and set up on the parting line, and then suspended in a mould casting frame

3 Once the two-part silicone-rubber is de-aerated and then mixed, it is poured into the mould casting frame around the pattern

4 The mould is cured inside a heating chamber

Figure 2.8 Multi Jet Modelling Head, p.29

Figure 2.12 LENS™ process (Courtesy of Optomec Design Co), p.35

Figure 3.25 LENSTM process (Courtesy of Optomec Design Co), p.65

Figure 3.28 Parts produced employing LENS and stereolithography (Courtesy of

Figure 4.3 Example of model built using the ThermoJet printer, p.73

Figure 4.10 Examples of parts built using the 3DP process

Figure 4.7 A ring produced employing PatternMaster (Courtesy of Sanders

Figure 4.17 Example of models produced using the

Objet Quadra (Courtesy of Objet Geometry), p.84

Figure 5.17 User interface in the MIMICS software (Courtesy of Materialise), p.99

Figure 5.18 A medical model built using the Stereocol resin (Courtesy of

Figure 5.19 The SLA model with the resection template (Courtesy of the British

Figure 5.20 The SLA model together with the template and the implant (Courtesy of the British Journal of Neurosurgery), p.lOl

A: A hole resulted from the irradiation of a tumor in the mouth cavity This hole has to be filled by an implant to allow the patient to breathe and eat normally

B: The soft tissue surrounding the cavity was modelled by CT scanning This model was used to design a tool for direct moulding of the implant

C: A silicon implant was moulded from the tool

D: Without surgery, the deformable silicon prosthesis was implanted Magnets were used to fix the prosthesis to a hard dental implant

Figure 5.21 Fabrication of obturator prosthesis using RP techniques Case study presented by Dr L.L Visch from Daniel den Hoed Kliniek Rotterdam

Figure 5.22 Cross-sections of the 3D model of a water splash

(Courtesy of the CALM project), p.103

Figure 5.24 3D shaded image and a cross-section of the cybersculpture

(Courtesy of the CALM project), p.104

Figure 5.28 Thermographic plots of aluminium rim (left) and SLS glass-filled nylon rim (right) [Gartzen et aI., 1998], p.107

Figure 5.29 The frozen stress distribution for a model of an aeroengine turbine rotor [3D Systems, 1994], p.108

Figure 6.9 MCP Metal Part Casting System, p.127

Figure 7.4 Optical micrograph of a RapidSteel part surface

(a - Sintered Part, b - Partially copper infiltrated, c- Fully copper infiltrated), p.142

Figure 7.7 Optical micrograph of a RapidSteel2.0 part surface

(a - Sintered part, b - Fully bronze infiltrated part), p.l45

Figure 7.14 SandForm™ core (Courtesy of DTM), p.l5l

3 Building the mould using 3D printing process

4 Removal of the unbound powder 5 Casting the mould

Figure 7.19 Direct Shell Production Casting (Courtesy of Soligen), p.156

Figure 7.20 Examples of ceramic moulds and castings fabricated using DSPC

Figure 8.6 Micrograph and waviness colour coded map of the square feature surface of the EOSINT M insert after 16000 injections (magnification 1000x), p.169

Figure 8.8 Colour coded depth map and micrograph (magnification 1000x) of the gate of the non-coated EOSintM insert after 16000 injections, p.l71

Figure 8.10 Surface (magnification 250x) and waviness of the square feature for the

Molybdenum-coated RapidSteel 2.0 and EOSINT M inserts after 8000 injections, p.l72 a b

Figure 9.7 Over-curing effects on accuracy (a - thicker bottom layer, b - deformed hole boundary), p.l92

Figure 8.11 Surface (magnification 250x) and waviness of the square feature for the

Stellite-coated RapidSteel 2.0 and EOSINT M inserts after 8000 injections, p.173

Figure 9.16 Stair-steps around the periphery (a - facing upwards; b - facing downwards), p.198

Chapter 6 Indirect Methods for Rapid Tool Production I 17

Figure 6.3 MCP vacuum casting process (Courtesy ofMCP)

5 The pattern is removed from the silicone mould by cutting along the parting line

6 The urethane resin is measured, dye is added for coloured components and casting funnels placed Then, the mould is closed and sealed

Computer-controlled equipment efficiently mixes and pours resin into a vacuum chamber, ensuring the mold is completely filled without any air pockets or voids.

8 After casting the resin the mould is moved to the heating chamber for 2 to 4 hours to cure the urethane part

Once the casting has hardened, it is carefully extracted from the silicone mold, and any excess material such as the gate and risers is trimmed away to create an accurate replica of the original pattern If desired, the finished component can also undergo painting or plating for enhanced aesthetics.

Vacuum castings produce highly accurate replicas of patterns, ensuring dimensional precision without imperfections, while faithfully capturing all profiles and textures The market offers a range of specially formulated resins for vacuum casting, providing diverse characteristics such as hardness, toughness, flexibility, and temperature resistance.

Epoxy Tools

Epoxy tools are used to manufacture prototype parts or limited runs of production parts Epoxy tools are used for [3D Systems, 1995]:

• Moulds for prototype injection plastics;

The mould fabrication process starts by creating a basic frame along the parting line of the RP model After completing the mould, sprue gates and runners can be integrated To facilitate release, the model's surface is treated with a release agent before pouring epoxy over it Typically, aluminium powder is mixed into the epoxy resin, and copper cooling lines can be incorporated for effective temperature management.

Chapter 6 Indirect Methods/or Rapid Tool Production 119

Inversion of the first half of the mould and backfilling

Embedding of the model along its parting line and backfilling with epoxy resin

To enhance the thermal conductivity of the epoxy mould, the curing process is initiated After the epoxy cures, the assembly is inverted, allowing for the removal of the parting line block, which leaves the pattern embedded in the cast tool A new frame is then created, and epoxy is poured to form the opposite side of the tool Once the second side cures, the two halves of the tool are separated, and the pattern is extracted.

The Soft-Surface® rapid tool method involves machining an oversized cavity in an aluminum plate, creating an offset that facilitates the introduction of casting material This process allows for the model to be suspended in its desired position and orientation before the material is poured into the cavity.

In 1996, it was noted that while this method requires some machining, which may extend the mold building time, it offers the significant advantage of enhanced thermal conductivity compared to all-epoxy molds.

Epoxy curing is an exothermic reaction, making it challenging to cast epoxy directly around a rapid prototyping (RP) model without causing damage To address this, a silicone RTV mold is created from the RP pattern, which is then used to produce a silicone RTV model for aluminum-filled epoxy tooling This process can lead to a loss of accuracy through multiple reproduction steps Alternatively, constructing an RP mold as a master allows for a single silicone RTV reproduction step, enhancing precision Notably, epoxy tooling is a cost-effective technique that requires no special skills or equipment.

It is also one of the quickest Several hundred parts can be moulded in almost any common casting plastic material

Epoxy tools have the following limitations [3D Systems, 1995]:

• Tolerance dependent on master patterns;

• Aluminum-filled epoxy has low tensile strength

The life of injection plastic aluminium-epoxy tools for different thermoplastic materials is given in Figure 6.6 [3D Systems, 1995]

Figure 6.6 Approximate aluminium-epoxy tool life [3D Systems, 1995]

Ceramic Tools

Ceramic materials, rather than epoxy, can be utilized to create tool cavities by casting around a master, making them suitable for plastics processing, metal forming, and metal casting It is crucial to control the water content in ceramic tool production to prevent excessive shrinkage during the setting process Recently, there has been a growing interest in non-shrinking ceramics, particularly Calcium Silicate-based Castable (CBC) ceramics, which were originally designed for applications unsuitable for metal spraying.

The production process for the two halves of a CBC ceramic tool involves unique steps compared to the epoxy mould method CBC ceramics cure at a low temperature of approximately 50°C, allowing them to be poured directly over the RP master without causing damage To prevent air bubbles, the mould halves must be vacuum cast, and utilizing a vibration table can help compact the material effectively After about one hour, the RP pattern is removed, and the ceramic tool undergoes a 24-hour curing process in an oven Once fully cured, the back surfaces of the mould halves are machined flat, and guides are drilled for the ejector pins.

Ceramics, while effective for tool manufacturing, are porous materials that can hinder the molding of highly adhesive polymers To mitigate this issue, surface treatments such as dry film lubricants, release agents, silicone, or PTFE can be applied Due to their brittleness, ceramic tools require careful handling To improve fracture toughness and tensile strength, finely chopped fibers and aluminum fillers are often incorporated, enhancing thermal conductivity With these enhancements, ceramic tools can produce hundreds of parts, achieving injection molding cycle times as low as 30 seconds.

The primary benefit of this process is its cost-effectiveness due to the inexpensive ceramics utilized, along with the rapid mould construction time Recent beta tests of CBC ceramics indicate a curing duration of only a few hours, allowing for the creation of an injection tool within a single day following the acquisition of the RP model.

Cast Metal Tools

Metal moulds are generally time-consuming and expensive to machine, but by combining RP techniques with casting techniques, some zinc or aluminium alloy moulds can be rapidly made

Investment casting has evolved significantly with the integration of rapid prototyping (RP) technologies Initially, RP was utilized for creating sacrificial models in investment casting, and today, nearly all RP machines can produce models for this purpose These models can be generated directly without altering the building process, as seen in LOM, or by adapting the building style through methods like Quickcast™ Additionally, special materials such as SLS and FDM can be employed, and another innovative approach involves 3-D printing the ceramic shell required for investment casting.

Die-casting involves creating a ceramic mold specifically designed to cast a metal alloy mold This ceramic mold functions similarly to a traditional die cast mold, but it is limited to producing a single metal mold.

Spin-casting is a manufacturing process that involves injecting material through a central sprue into a rapidly rotating mould, typically made of heat vulcanised silicone Due to the high temperatures generated during the mould fabrication, a multi-step approach is required for producing metal parts Initially, an RTV rubber mould is created from a rapid prototyping (RP) master, from which a tin-based metal alloy part is cast This part serves as a model for creating a durable heat-vulcanised silicone mould, capable of producing spin-cast zinc alloy components These components exhibit physical strength properties comparable to die-cast aluminium and Zamak zinc parts, making spin-casting a viable option for high-quality metal fabrication.

The primary goal of utilizing an RP model in metal casting is to create a mould that closely resembles the final product, requiring only minimal finishing work This approach significantly reduces both time and machining costs in comparison to conventional mould-making techniques.

Unlike earlier tooling methods, these metal tools offer strong durability and excellent thermal conductivity, enabling effective clamping forces and injection pressures during the molding cycle Consequently, the injection molding conditions closely resemble standard production conditions; however, the lifespan of the mold typically does not exceed a thousand parts.

Molten mewl or liquid plastic cl1tml sprue

Investment Casting

The investment casting process, originating from ancient Egyptian techniques known as "lost wax," is utilized for creating intricate and precise components This method involves the use of wax patterns that define the desired shape, which are subsequently melted away Additionally, patterns can be made from various materials such as foam, paper, and polycarbonate, all of which can be easily melted or vaporized The investment casting process consists of several key steps that ensure the accuracy and complexity of the final product.

2 The patterns are assembled as a group on a "tree" where they are gated to a central sprue

3 The tree of patterns is dipped in a slurry of ceramic compounds to form a coating Then, refractory grain is sifted onto the coated patterns to form the shell

4 Step 3 is repeated several times to obtain the desired shell thickness (5-10 mm) and strength

5 After the tree has set and dried, the patterns are melted away or burned out of the shell, resulting in a cavity

6 Molten metal is poured into the shell to form the parts

7 The ceramic shell is broken away to release the castings

8 Finally, the castings are removed from the sprue and the gate stubs are ground off

Shell investment casting is a widely recognized process, while solid flask investment casting utilizes solid flask molds instead of shells This method fills molds using a vacuum differential pressure technique An automated solid flask investment casting system, developed by MCP, illustrates this process The production of castings with this system follows specific processing steps outlined by MCP in 2000.

Chapter 6 Indirect Methodsfor Rapid Tool Production 127

Figure 6.9* MCP Metal Part Casting System

1 A master is built using any of the available RP processes

2 A silicone mould is produced from the master under vacuum III the MCP Vacuum Casting System (see Section 6.3)

3 Multiple patterns are cast from the silicone mould in the same system under vacuum

4 The patterns are gated to a central sprue to create a pattern cluster The cluster is then placed in a flask

5 Ceramic embedding material is poured around the pattern cluster under a vacuum in a special vacuum chamber to avoid creating bubbles

6 After the ceramic mould has set and dried, the flask is placed in a furnace to melt out the patterns

The flask is then positioned in the casting chamber of the MCP Metal Part Casting system, where the melting chamber operates under a melting pressure that is independent of the casting chamber This design enables the mould to be filled with metal using vacuum differential pressure.

8 The ceramic mould is broken away from the castings using a water jet Then, the sprue and gate stubs are removed from the castings

The MCP Metal Part Casting system is manufactured in three unit sizes: MPA 150,

MP A 300 and MP A 1000 The technical specifications of these three models are given in Figure 6.10

Unit Type Casting Volume of Flask Size

Figure 6.10 Technical specifications of the MCP Metal Part Casting systems

Fusible Metallic Core

Fusible metallic core technology offers an innovative approach to creating intricate, hollow, one-piece plastic components that are challenging to manufacture using traditional methods This technique is a variation of investment casting, distinguished by the use of low melting point alloys instead of wax for sacrificial patterns Additionally, rapid prototyping techniques can be utilized to create part and core models, facilitating the fabrication of casting dies needed for core production.

I Bli ild RP model of Ihe core L \I~ nl.'" lI n.,} ('Ilr.: dl~' 5 CaS! a 10 \I' n£ Iling poin! al loy inlO core die ¢ ¢

ClII\." U I H:P "tH\" 2 U,c R P 'mdel '" a ,m;'lcrfor cn:al ing con: die 6 Place all o y core illto Ille injcclion nnuld ¢ ¢

Ih.'lvu 3 Build RP nvdel oflhe pan \I t' u l~oo pf ~~~ 7 Mcrnl core cmbedded illlO Ihc pla'lic pan ¢ ¢ Figure 6.11 Fusible metallic core technology [3D Systems, 1995]

-I U,c R P pan model", a n1a"CrlO produce Ihe injcclion ,muld, 8 Core Ill.' Ilcd OUI IO re\ crr l Ihe Iini,hed pan

Fusible cores are designed to match the internal passage shape of the part and are typically suspended within the mold cavity During the molding process, these cores are encapsulated by the material, which is later melted away using induction heating or by immersing the molded parts in hot water or oil This innovative technology streamlines production by allowing for complex internal geometries.

1995] The cores can have a melting point of up to 220°C depending on the alloys used

Figure 6.12 Inlet manifold (Courtesy ofMCP)

The innovative process allows for the production of complex parts with consistent thin walls, eliminating the need for splitting components or incorporating welding lines and bolt flanges This advanced technology is predominantly utilized in manufacturing parts for under-the-bonnet applications, such as fluid reservoirs, fuel and water pumps, and engine inlet manifolds A notable example of this technique is the creation of a one-piece inlet manifold, demonstrating the efficiency and capability of fusible core technology.

Sand Casting

The sand casting process is widely used for manufacturing larger metal components that do not demand high surface quality Rapid Prototyping (RP) techniques can be utilized to create master patterns for making sand molds This is achieved by placing RP patterns in a sand box, which is subsequently filled and compacted with sand to create the mold cavity.

Utilizing RP techniques simplifies the creation of patterns that account for casting shrinkage and provides extra machining stock for post-casting processes Additionally, these techniques lead to shorter lead times and enhanced pattern accuracy.

The 3D Keltool™ process is based on a metal sintering process which 3M introduced in 1976 This process converts RP master patterns into production tool inserts with very good definition and surface finish

The production of inserts employing the 3D Keltool™ process involves the following steps [Jacobs, 1996]:

1 Fabricating master patterns of the core and cavity;

2 Producing RTV silicone rubber moulds from the patterns;

To create "green" parts that replicate the masters, silicone rubber moulds are filled with a metal mixture consisting of powdered steel, tungsten carbide, and a polymer binder, featuring particle sizes of approximately 5 micrometers.

4 Firing the "green" parts in a furnace to remove the plastic binder and sintering the metal particles together;

5 Infiltrating the sintered parts (70% dense inserts) with copper in a second furnace cycle to fill the 30% void space;

6 Finishing the core and cavity

3D Keltool inserts, made from either Stellite or A-6 composite tool steel, exhibit remarkable durability, enduring over 1,000,000 molding cycles The DirectTool™ process enables the production of these high-performance inserts, as illustrated in Figure 6.13.

Figure 6.13 3D Keltool inserts (Courtesy of American Precision Products)

Indirect tooling methods serve primarily as prototyping or pre-production processes rather than for full-scale production As a result, tools created through these methods differ from production tools, featuring larger draft angles, simpler geometries, and lower mechanical and thermal specifications These variations impact production cycle times, part mechanical properties, and tool longevity However, the purpose of these methods is not to replace production tooling but to produce a limited number of parts, eliminating the need for long-term durability Consequently, these tools can operate with reduced efficiency compared to production tools, allowing for longer cycle times per part to offset their lower thermal conductivity.

Bettany S and Cobb RC (1995) presented a rapid ceramic tooling system designed for prototype plastic injection at the First National Conference on Rapid Prototyping and Tooling Research, held on November 6-7, 1995, in Buckinghamshire, UK The findings were published in the conference proceedings edited by G Bennett, spanning pages 201-210.

Childs THC and Juster NP (1994) Linear Accuracies From Layer Manufacturing, CIRP Annals, Vol 43-1, pp 163-167

Comeau D and Dobson S (1996) A soft surface tooling method for rapid prototyping, Society of Plastic Engineers - RETEC, Pioneer Valley, March 1996: updated November 1996

Davy D (1996) Century-old chemistry is reborn in moldmaking, Modern Plastics Magazine

Dickens PM, Stangroom R, Greul M, Holmer B, Hon K K B, Hovtun R, Neumann

R, Noeken Sand Wimpenny D (1995) Conversion of RP models to investment castings, Rapid Prototyping Journal, Vol 1,4, pp 4-11

Dickens PM (1996) Rapid Tooling: A review of the alternatives, Rapid News, Vol

Erickson R (1996) CASTTOOL prototyping for injection molding, where is it going, Proceedings ofthe 1996 Wescon Conference, Anaheim, CA, USA, pp 317-324

Jacobs PF (1996a) Recent Advances in Rapid Tooling from Stereolithography, White Paper, 3D Systems, Valencia, California, USA

Jacobs PF (1996b) Stereolithography and other RP&M technologies, Society of Manufacturing Engineers - American Society of Mechanical Engineer

Kamphuis K and VanHiel B (1996) Rapid tooling for injection molding using cast resin, Project Progress Report, Rapid Prototyping and Manufacturing Institute, Georgia Institute of Technology, Atlanta, Georgia

Maley K (1994) Using Stereolithography to Produce Production Injection Molds, Annual Technical Conference, Conference Proceedings, San Fransisco, CA, USA, Vol 53, 3, pp 3568-3570

MCP Web Page (2000), HEK GmbH, Kaninchenborn 24-28, D-23560 Lubeck, Germany, http://www.mcp-group.de

Mosemiller L and Schaer L (1997) Combining RP and Spin-Casting, Prototyping Technology International '97, UK & International Press, Surrey, UK, pp 242-246

Mueller T (1995) Stereolithography-Based Prototyping: Case Histories of Application in Product Development, IEEE Technical Application and Conference Workshops, Portland Oregon, October 10, pp 305-309

Plavcan JE (1995) Rapid tooling for compression molding of a thermoset, Annual Technical Conference, Conference Proceedings, Boston, MA, USA, Part 3, pp 4324-4326

Schaer L (1995) Spin-Casting fully functional metal and plastic parts from stereo lithography models, Proceedings of the 6 th International Conference on Rapid Prototyping, Dayton, Ohio, USA, Ch 27, pp 217-235

Tritech company literature (1997) Tritech Precision Products Ltd., Wrexham, UK

Whitward L (1996) Getting to metal quicker with RP patterns, Design Engineering, London, January, pp 39-42

3D Systems Application Guide (1995) 3D Systems, Valencia, California, USA 3D Systems White Paper (1996) Recent advances in Rapid Tooling from Stereolithogtaphy, 3D Systems, Valencia, California, USA

Chapter 7 Direct Methods for Rapid Tool

Indirect methods for tool production require at least one intermediate replication process, which can lead to accuracy loss and longer build times To address these drawbacks, some rapid prototyping manufacturers have introduced innovative rapid tooling methods that enable the direct creation of injection molding and die-casting inserts from 3D CAD models This chapter explores the commercially available direct rapid tooling solutions.

7.1 Classification of Direct Rapid Tooling Methods

Direct RT methods offer a viable alternative to conventional mould-making techniques by producing durable inserts that can withstand anywhere from dozens to tens of thousands of cycles The lifespan of these inserts varies significantly based on the material used and the specific RT method applied As a result, direct RT processes have a broad range of applications, including prototype, pre-production, and production tooling These processes can be categorized into two main groups based on their intended applications.

The initial category encompasses cost-effective techniques with quicker turnaround times, suitable for validating tools prior to incurring significant expenses These direct RT methods, which meet these criteria, are referred to as "firm tooling" methods.

Bridge tooling serves as a crucial link between soft and hard tooling, enabling the production of tools designed for short prototype runs of around fifty to one hundred parts This approach utilizes the same materials and manufacturing processes as those used for final production, ensuring consistency and quality in the prototypes.

The second group includes RT methods that allow inserts for pre-production and production tools to be built RP apparatus manufacturers market these methods as

"hard tooling" solutions Currently available solutions for "hard tooling" are based

D T Pham et al (2001) discuss the rapid manufacturing of sintered metal powder inserts, specifically focusing on materials such as steel, iron, and copper, which are subsequently infiltrated with copper or bronze This process utilizes technologies like Keltool™ from 3D Systems, DTM RapidTool™ process, EOSINT Metal from EOS, and Three-Dimensional Printing of metal parts from Soligen.

Figure 7.1 shows the classification of direct RT methods according to their application

Direct Methods for Rapid Tool Production

DTM RapidToofM Process DTM SandFormTooling I

L part, 1-3 days [Fritz, 1998] LOM Tooling in Ceramic

LOM Tooling in Polymer (Data not available) I

3DpTM Direct Metal Tooling 3DpTM Ceramic Shells I

Figure 7.1 Classification of direct RT methods

Chapter 7 Direct Methods for Rapid Tool Production 137

7.2 Direct ACESTM Injection Moulds (AIMTM)

Stereolithography is utilized to create epoxy inserts for injection molding tools used in thermoplastic part production Current curable epoxy resins, like Cibatool®SL5530HT, can withstand temperatures up to 200°C, while thermoplastics are injected at temperatures reaching 300°C (572°F) Therefore, specific guidelines must be followed in the manufacturing process of these injection molds, as detailed in the procedure outlined by Decelles and Barritt (1996).

The injection mould is designed using a 3D CAD package, incorporating features such as runners, fan gates, and ejector pin clearance holes, with a recommended shell thickness of 1.27mm (0.05") Constructed from Accurate Clear Epoxy Solid (ACES) on a stereolithography machine, the mould undergoes support removal and polishing along the draw direction for easier part release Notably, the thermal conductivity of stereolithography resins is approximately 300 times lower than that of traditional tool steels, which influences heat management during the injection moulding process To enhance cooling efficiency and minimize cycle times, copper water cooling lines are integrated, and the mould's back is filled with a composite of 30% aluminium granulate and 70% epoxy resin Additionally, air is blown onto the mould faces post-injection to facilitate cooling.

The primary drawback of Direct AIMTM (ACESTM Injection Moulds) is its reliance on the shape and size of the molded part, as well as the operator's skill in managing cooling cycles This process is more complex than indirect methods due to the need for finishing internal mold shapes Additionally, achieving proper part ejection necessitates draft angles of ½ to 1 degree and the application of a release agent during each injection cycle.

A Direct AIMTM mould typically lacks the durability of an aluminium filled epoxy mould While the backing operation can affect cooling time, it does not enhance the mould's lifespan, which is compromised by erosion from the injected material.

Summary

Indirect tooling methods are designed for prototyping or pre-production processes rather than for full-scale production As a result, tools created using these methods differ from production tools, featuring larger draft angles, simpler shapes, and lower mechanical and thermal specifications These variations influence production cycle times, part mechanical properties, and tool lifespan However, the primary goal of these methods is to produce a limited number of parts, meaning the tools do not need to be as durable or efficient as production tools Consequently, a longer cycle time per part is acceptable to offset the impact of reduced thermal conductivity.

Bettany S and Cobb RC (1995) presented a groundbreaking ceramic tooling system designed for rapid prototype plastic injection at the First National Conference on Rapid Prototyping and Tooling Research, held on November 6-7, 1995, in Buckinghamshire, UK The work, edited by G Bennett and published by MEP Pub Ltd., spans pages 201-210 and highlights advancements in efficient tooling methods for prototype development.