research design and manufacture 3d printer using delta mechanism

In today''''s world, applications of rapid forming, meeting practical needs are the foundation for the development of rapid prototyping machines 3D printing – 3D printer.. For the purpose o

RESEARCH OVERVIEW

Introduction to rapid prototyping

Rapid prototyping is a method of quickly creating product models from 3D data by building them layer by layer under computer control Rapid Prototyping is also known variously as Layered Manuafacturing, Additive Manuafacturing or 3D Printing

Rapid prototyping technology can also be understood as a type of technology that can directly create a three-dimensional object in a very short time, usually through only 1 element With the help of CAD software, create physical models as databases for rapid prototyping machines The model object is created using an appropriate material depending on the method of the rapid prototyping machine 3D printing is one of the methods of rapid prototyping that creates a 3D object by stacking layers of material on top of each other until the object is completely shaped Each layer is a thin and horizontal slice of matter

The material added (additive) and bonded together to form the sample is not material cutting like traditional machining methods where the sample is created in a layered pattern, the latter layer is created on top of the previous layer

Allows prototyping of objects of complex shapes that cannot be machined with conventional cutting machining methods

Create shapes directly from CAD data

Allows prototyping of objects with complex shapes

The birth and development of rapid prototyping

The prototyping process is divided into three stages The latter two periods have only been born in the last 20 years or so Similar to computerized prototyping, the physical properties of samples were only developed in the third period

The first period was born several centuries ago During this period, typical samples are not highly complex, and fabricating an average sample takes about 4 weeks The prototyping method depends on workmanship and performs the work in an extremely heavy lifting way To this day this method of manual styling is still quite popular, in art universities with a Posing major, this method is still used

1 2 2 Second era: Prototyping software or virtual prototyping

The second period of styling developed very early, around the mid -70s In this period there was prototyping or virtual prototyping software The application of CAD / CAE / CAM has become very popular Prototyping software will sketch on the computer new ideas and ideas These samples are like a physical model: Tested, analyzed as well as stressed and calibrated accordingly if they are not satisfactory For example, analysis of fluid surface stress and tension can be accurately predicted because it is possible to accurately determine the properties and properties of materials

Moreover, the patterns during this period became much more complex than in the early period (about more than two times) Therefore, the time required for prototyping tends to increase to about 16 weeks, the physical properties of the sample still depend on the basic prototyping methods first However, the use of precision machining machines has better improved the physical properties of the sample

1 2 3 The Third Period: Rapid Prototyping

The physical properties of each part of the product during rapid prototyping are also known Hollow prototyping is suitable for production on lifting tables or layer manufacturing technology This technology represents the process of prototyping development in the third period The invention of rapid prototyping equipment was an important invention These inventions met the requirements of the business world during this period: Reduce production time, increase sample complexity, reduce costs At this time consumers demanded products both in terms of quality and design, so the complexity of the part also increased, three times the complexity that the parts were made in the 70s But thanks to rapid prototyping technology, the average time to form a part is only 3 weeks compared to 16 weeks in the second period In 1988, more than 20 rapid prototyping technologies were studied We see that the need to create the initial product model is a necessity in the production process,

Along with the advancement in the field of rapid prototyping in the third era, there is great help of the virtual prototyping process However, there is still controversy about the limitations of rapid prototyping technology such as: Material limitations (either because of high cost or different uses for each material to create parts).

Application of rapid prototyping

This is the most important application of rapid prototyping, in the process of developing new products, it shows the physical phenomena of designs that cannot be observed on computer models, including design aspects, helping designers evaluate the best product before putting it into mass design

1 3 2 Check the working function of the product

Based on the 3D model, it is difficult to ensure that the product when produced can meet the requirements of working operation, assembly Especially with gears, gearboxes, cams, eccentric shafts or couplings, joysticks Rapid prototyping will help engineers and designers deal with those problems Rapid prototyping technology can now "3D print" assembled parts, even in many different colors

Rapid prototyping is very strongly applied in the manufacture of parts to make silicone molds, composites, vacuum forming

The traditional mold making process is very complicated, time -consuming and expensive, increasing the time from design to production, the application of this rapid prototyping technology in this field will create a main driving force for the development of molding technology, highly economical for this industry

Fig 1.2: Creating mold with 3D printer.[12]

In the field of medicine, rapid prototyping technology is used to make medical models, bone replacement implants, and surgical aids

Artificial bones: There are accidents that cause a part of the bone on the body to break and cannot be recovered The requirement is to reconstruct the corresponding bone for high-precision implantation To do that, reverse engineering is used Rapid prototyping technology is also widely used in dentistry

Fig 1.3: The joints were created from a 3D printer to replace osteoarthritis patients.[13]

THEORETICAL BASIS

Rapid prototyping methods

2 1 1 SLA methodology (Stereo lithography apparatus)

As a technique that uses a laser to harden liquid materials to create serial layers until the finished product, the thickness of each layer can reach 0.06mm at most, so it is very accurate This technique can be visualized as follows: Placing a platform in a container of liquid material, the laser beam moves (by design) onto the top of the liquid material in the shape of a cross -section of the product, causing this layer of material to harden The pedestal containing the already hardened layer of material is lowered to create a new layer, the other layers are carried out continuing until the finished product

Fig 2.1: Prototyping method principle SLA.[14]

Rigid and fully automated system

High dimensional accuracy Typical size tolerance is about 0.0125mm

High resolution to suit intricate details

With the support of QuickCastTM software enables rapid and accurate prototyping of metal die casting processes

Must go through the post-processing stage

High operating and maintenance costs

2 1 2 SGC (Solid) method Ground Curing)

Also the method of layer-by-layer hardening Unlike SLA, this does not use a point laser source, but uses a beam of ultraviolet light to shine on the entire surface, which has been shielded through a mask The bright open material will solidify into one layer The mask is a negative film of the cut cross section

Fig 2.2: SGC Prototyping Method Principle.[15]

Parallel processing system: Prototyping and fine processing occur in parallel, thus saving time by 25-50%, reducing internal stress and product warping

Can manufacture multiple products at the same time

The price is a bit high, the working equipment is a bit noisy

Must go through the post-processing stage

High operating and maintenance costs

The wax must be removed from the product when it is finished making

2 1 3 LOM method (Laminated Object Manufacturing)

Use sheet materials coated with adhesive (mainly paper but can also use plastic sheets, metal sheets, etc.) The laser source creates each layer of the cross-section by cutting the sheet of material along the boundary of the object cross-section The sectional layers are glued one after another thanks to the heating roller system

Fig 2.3: LOM Prototyping Method Principle [16]

Diverse, inexpensive materials In principle, it is possible to use various types of materials: Paper, plastics, metals, composites and ceramics

High accuracy achieves better than 0.25 mm By cutting the material instead of solidifying it, the system can preserve the material's original properties

No need for support structures

High speed, faster than other layering methods because the laser does not cut the entire area, but only scans according to the outer perimeter Therefore, thick and thin materials have equal cutting speeds

There is no phase change during the fabrication of the part, so the shrinkage of the material is avoided

Non-toxic and polluting the environment

No residual material was recovered The warping of the part is often the main problem of the LOM method

Remove the product from the difficult supportin g structure

Surface gloss is not high

2 1 4 SLS Method (Selective Laser Sintering)

It is a laser sintering method After the roller spreads out on the work table a layer of powder with a predetermined thickness, the laser source scans the coating on the surface to be layered In that region, the material particles will stick together to form a layer Each vertical move of the equipment system will form the next layer The 3D Printing method works on the principle of "inkjet printing" A special glue ink is sprayed onto a layer of plastic powder that has been flattened and solidified So we created a layer and layer by layer gradually created the object

Fig 2.4: Prototyping method principle SLS.[17]

The high amount of material put into the process (Hight Through -put) makes the

Fabricate multiple parts at the same time

Details in the pitted state

The first layer may require a restrest to reduce heat effects (such as curlin g) Heterogeneous detail density

Changing materials requires thorough cleaning of the machine

2 1 5 FDM 3D Printing Method (Fused Deposition Manufacturing)

Using flowable wire materials, such as 3D printed ABS, PLA , the wire through the heating head will plasticize and be spread on the substrate according to the cross-sectional profile of the sample, in layers with a thickness equal to the cutting layer thickness The flexible plastic will bond in layers until the pattern is complete

Fig2.5: The principle of FDM prototyping method.[18]

Diverse, inexpensive materials In principle, it is possible to use various types of materials: Plastics, metals, composites and ceramics

High accuracy achieves better than 0.25 mm By layering the material on top of each other and then solidifying, the system can preserve the material's original properties

Save a lot of materials compared to traditional processing methods, because this is a non-chip processing method

No need for support structures

High speed, faster than other layering methods because the laser does not cut the entire area, but only scans according to the outer perimeter Therefore, thick and thin materials have equal cutting speeds

There is no phase change during the fabrication of the part, so the shrinkage of the material is avoided

Non-toxic and polluting the environment

The warping of the part is often the main problem of the LOM method

Surface gloss is not high

There are veins between the layers

May need support mechanisms (support)

Temperature fluctuations throughout the production process can lead to poor cohesion between layers, so the strength in the Z-direction is poor, and the machining speed is limited

The above introduces some typical methods in rapid prototyping technology using different forms of materials (liquid, powder, sheet, wire) with different properties The general thing is that they are all processed through each layer one by one Tomography, layering, and tomography are all not simple and have a great impact

Classification of fast machining methods based on printed materials

Because there are many aspects of production, there are many types of rapid prototyping systems on the market, to broadly classify rapid prototyping systems based on the basis of production materials In this type of classification, all rapid prototyping systems can be easily classified into three categories: :

Rapid prototyping systems are based on a liquid platform starting with material in a liquid state The prototyping process is a vulcanization process, where the material converts from a liquid state to a solid state The following are some rapid prototyping methods based on liquids:

3D Systems SLA stereoscopic prototyping equipment

Sony SCS Block Prototyping Equipment

The ultraviolet printing device creates Misuibishi's SOUP cubic object

Teijin Seiki's Block Imaging Equipment

Meiko Rapid Prototyping Equipment for Jewelry Industry

Denken's SLP Rapid Prototyping Equipment

Mitsui's COLAMM Rapid Prototyping Equipment

Fockele and Schwarze's LMS rapid prototyping equipment

With the exception of powdered materials, rapid prototyping systems with block base materials involve all forms of ceramic block materials of all forms: wire, roll, laminated and pellet The following are some rapid prototyping methods that symbolize this method:

Helisys LOM Thin-Layer Forming Equipment

Stratasys FDM Multilayer Spraying Equipment

Hot stamping equipment using KiRa's SAHP coupling agent

3D System Thermojet Multi-Nozzle Prototyping Equipment

IBM RPS Rapid Prototyping System

Sanders Prototype MM-6B prototyping equipment

Sparx AB's Hot Plot Rapid Prototyping Equipment

Scale Model Unlimited's CAMM Laser Prototyping Equipment.

In limited capacity, the powder state form is still considered the block state form However, it was created on the intention of being a type of device that does not depend on the base block state material rapid prototyping equipment system The following are some rapid prototyping methods that symbolize this method : DTM's SLS Laser Sintering Equipment

Soligen's DSPC Direct Thin Shell Molding Equipment

Fraunhofer's MJS multi-stage rigification device

Inkjet equipment, also known as BPM Technology's BPM

MIT's 3DP holographic printing device

Z-Corp Z-Printer rapid prototyping equipment

To do that, people use laser scanning technology to recapture the shape of the object, then use CAD / CAM software to design and process to recreate the shape of the product and finally use color to make the object look similar to the sample

FDM 3D Printing Method Analysis (Fused Deposition Manufacturing) 18 1 Reasons to choose FDM

FDM machines have advantages including using a variety of materials, easy to change materials, simple structure, low cost compared to machines using Stereolithography and Sinterin Lazer method, easy to repair, capable of producing thin parts and large size, No laser sources, lots of materials, and no toxic materials

To produce rapid prototyping without spending a lot of money on prototyping, FDM rapid prototyping may provide the best choice Compared to the Stereolithography and Lazer Sintering methods, the FDM method is clearly feasible to build a low-cost rapid prototyping machine that is still sufficient for rapid prototyping

Instead of lasers and materials, FDM builds by stretching molten plastic and solidifying layer by layer to create a dense part structure The material builds in the structure of a slender solid fiber, which is directed from a roll to the moving head controlled by a stepper motor When this fiber reaches the probe, it is melted by temperature, which is then ejected through the nozzle onto the part plane

When molten material is ejected, it is leveled by nozzles in the same way that a welder or painter uses the tip of a pipe to spread the material The width of the spread can vary between 0.193mm and 0.965mm and is determined by the size of the nozzle The nozzle cannot be changed during prototyping, so model analysis must be selected in advance

When the molten material is leveled evenly, it cools quickly by about 1/10(s) and solidifies When a coated layer is complete, the support plane moves downwards to a conventional thin layer of 0.178mm to 0.356mm and the process is repeated

As well as streolithography and laser sintering, the FDM system reads STL files according to the standard input of all rapid prototyping methods The STL file consists of a closed triangular mesh generated from the plane of the CAD model The software in the FDM system cuts the STL file into a series of cross sections, which are mapped by the material nozzle

To create accurate parting, it controls the critical temperature of the chamber and the part forming process The temperature of the chamber must be kept lower than the melting point of the material, so only a small amount of heat is enough to melt the ejected hair and form a part that does not sink or deform The part must be kept cold enough for the molten material to solidify and bond together

Protrusions or isolated parts of FDM parts require intermediate assistance during construction FDM machines use a second nozzle next to the basic nozzle to spray the required auxiliary material (Stratasys) offers 2 types of auxiliary materials Wax type material for machines with low price and water soluble material type with machine are more expensive Auxiliary wax can be damaged from the part but it is difficult to remove from internal grooves or small details Water-soluble auxiliary material can be dissolved in an agitated tank Other auxiliaries are removed, FDM details do not need post-processing

Stratasys' FDM system with a precision grade is in the ±0.005 inc (± 0.127 mm) range The surface roughness of FDM parts is not as good as those made by the Stereolithography method but higher than those manufactured by Sintering Lazer But on the contrary, the details using the projection method have a smooth texture The FDM detail appears ribbed because both the transverse layers and the displacement line appear repetitive

Over the years, Stratasys has developed a number of plastic powder materials for FDM systems One type for producing high -quality parts is ABS Other materials include wax for molds around parts, polycarbonate for durable parts, and polyphenyl sulfones for heat-resistant applications FDM parts, made from molten and solidified materials, exhibit closed physical properties compared to parts made from similar materials but by different methods

Because FDM systems create parts by narrowly stretching material particles, wide, blocky or thick-walled parts take a long time to complete Small or thin - walled details can be created fairly quickly The time required to fabricate the part depends on the solidification rate of the FDM system (determined by the size of the nozzle), the height of the part (the number of layers), the horizontal dimension of the part (the time required to solidify each layer), the quantity and complexity of the required additives (additives for each layer form a separate step)

FDM parts are stiffer and more durable than those manufactured by stereolithography but they have poor surface quality and are not sharp ASB, polycarbonate, polyphenyl sulfone materials are thermal, mechanical, and moisture resistant, so FDM parts can be used for a wide limit of specialized samples, depending on the application FDM details are not pitted and do not need to absorb me a second time Unlike stereolithography or laser sintering, FDM machines can be used in office environments and FDM materials do not require much special handling Many FDM systems are cheaper than stereolithography and laser sintering For companies that want to produce durable and accurate models for the company FDM can be a good choice

When laying out a detailed creation sequence using the method of concentrated melting, calculations

Detail size: It is possible for the part to be created from a simple workpiece thanks to machine supplies Large parts can be created from multiple workpieces then attached them together but it takes a lot of time and reduces accuracy

Auxiliary removal: There is plenty of room in the detail where the auxiliary and layer thickness increases the speed but is recommended for a part

Delta parallel robot structure applied in the topic

2 4 1 General introduction of Delta parallel robots

Stemming from the needs and flexibility in production, robot mechanisms are increasingly developing very diverse and rich In recent decades, parallel structure robots were studied by Gough and Whitehall in 1962 and attention to the application of parallel structure robots was started by Stewart in 1965 He was the creator of an airplane training chamber based on a parallel mechanism Currently, parallel structures are widely used in many fields

The typical type of parallel robot consists of a dynamic machine table connected to a fixed rack, driven in many parallel branches, also known as the number of pins Usually the number of pins is equal to the number of degrees of freedom, controlled by the drive source located on a fixed stand or directly on the foot It is for this reason that parallel robots are sometimes called pedestal robots The actuators control the external load, so the parallel actuator usually has a large load capacity

Due to the superiority of parallel robots, it is attracting more and more research scientists, and is also applied more and more widely in many fields:

Physics: Microscope holders, precision measuring equipment holders

Mechanical Engineering: Precision mechanical processing machines, machine tools

Post and Telecommunications Industry: Antenna racks, geostationary satellites Automotive industry: Car tire load testing system, car driving booth

Military industry: Tandem robots are used as stable platforms to be placed on ships, water structures and submarines To keep the antennas balanced, target tracking cameras, radars, laser measuring devices, stabilizers for artillery and missiles, cockpits for aircraft,

Like conventional robots, Delta parallel robots are robots with a closed -loop structure in which stitches (rods) are connected by dynamic joints

A conventional handrail mechanism motor diagram is a series of dynamic stages, from output (which is the stage that directly performs technological manipulation) to a fixed price In parallel robots, the last stage is connected to a fixed rack by several kinetic circuits, i.e connected in parallel with each other and also working in parallel with each other These differences in dynamic diagrams also create many distinct features in kinematics and dynamics

The choice of parallel robots to build 3D printers brings many advantages over conventional 3-axis robots, such as faster travel speed than conventional printers, z-axis is not limited by the low speed of threaded rods It uses a highly linear motion system (thanks to the mobility of the sliding ball bearings), and minimizes the mass of movement This means we can tackle a large volume with multiple printheads, and do it quickly With a parallel structure, the error depends only on the axial error of the individual leg mechanism assemblies, and the errors are not accumulated like serial robots

2 4 3 Some advantages and disadvantages of parallel robots

High load capacity: The structural components are smaller, so the mass of the components is also smaller

High rigidity due to their geometric structure:

• All simultaneous impact forces are shared for all pins

• The special kinematic structure of the linking joints allows all applied forces to be converted into tensile/compressive forces of the pins

Can perform complex operations and operate with high precision

Can design in different sizes

Simplify machine mechanisms and reduce the number of elements due to the pre-designed pins and couplings into standard assemblies

Provides high mobility during work due to its compact mass and size

The actuators can be positioned on the panel

The range of parallel mechanism robots is very wide from assembling extremely small parts to movements that perform complex functions, requiring high precision such as: milling, drilling, turning, welding, assembling

Parallel robots work without platforms and can move anywhere in the production environment They can work even when on a boat and hang from the ceiling, walls

The cost of parallel robots applied in mechanical processing is less than CNC machines with equivalent features

However, parallel robots also have certain disadvantages when compared to chain robots such as::

The workspace is small and difficult to design

The solving of complex kinetic and dynamical problems

There are many decays (singularities) in the workspace.

STUCTURAL DESIGN 3D-PRINTING MACHINE AND

Analyze some of the essentials of a Delta 3D printer

- The print head moves flexibly in 3-dimensional space

- The print table is perpendicular to the print head, with a small error within the allowable range (0.2-0.3mm)

- Make sure the printing plastic does not melt before going down the print head, ensuring that the plastic extrusion down the print head does not clog

- The machine arm mechanism must be rigid and not shaken during printing, causing errors that make false print position commands

- The stepper motor must be cooled due to reversing flow and continuous running

- Make sure the print head works within the allowed range, not exceeding the working space causing disruption to the manipulator structure (control code).

Make a design plan from the requirements given

In order for the print head to move in 3-dimensional space, we need to use a mechanism with at least 3 degrees of freedom, to avoid complicated programming, we should limit the number of degrees of freedom for the machine, but still meet the working requirements, we should choose 3 degrees of freedom for each machine arm

Using 3 parallel structure arms with 12 pairs of bridge joints to control the print head, each arm consists of 4 spherical joints linked to the print head and vertical sliding ball bearings to form a parallel parallel mechanism that binds each other, creating rigidity for the system, With 4 spherical joints linked together in a

Fig 3.1: Translational Structure Delta Parallel Robot Configuration [19]

To create perpendicularity between the print head and the print bed, the heating head attached to the print head needs to be CNC precision machining to reduce errors to a minimum

During prototyping, the print head moves continuously to produce the product, then the vibration process is inevitable, so it is necessary to design optimally to reduce the vibration influence during the creation work such as:

- Use good sliding ball bearings to avoid straw, reduce friction by lubricating with lubricant

- Use stepper motor and control by micro step mode to reduce sudden tooth step changes, reduce vibration

The bridge joints must be tightened with the machine arm, so that the working process does not shift, causing the wrong configuration size of the machine when preset programming

In the process of prototyping, the motor must be reversed continuously for a long time, damaging the motor, so it is necessary to install a radiator fan to cool down the motor for a long time

To ensure that the print head works within a certain range, we need to mount the travel sensor in a suitable position, avoiding that during the prototyping process, the print head runs past the working area to break the machine structure, this is a very important problem, if not well controlled, it will damage the machine mechanisms.

Analysis of truss frame design selection

• Using aluminum profiles to design the frame

• Profiled aluminum rods are coupled together by bolts -nuts

Disadvantages: High cost, hole processing for coupling is quite complicated, requires high precision, large machine volume

• Use mica and iron to design the chassis

• The mica plates are interconnected by bolts-nuts

Advantages: Easy to process (laser cutting machine cuts mica at will), lower cost than using aluminum profiles for processing, active in the design process, easy to assemble because the assembly hole of the mica plates is cut by precision laser machine, the machine volume is smaller than option 1 Disadvantages: Mica has brittleness, so when hit strongly, it is easy to break

❖ Selection of truss frame design option:

Option 1 is suitable for the purpose of designing a 3D printer with a sturdy structure with high precision to meet the purpose of rapid prototyping.

Analysis of powertrain selection

❖ Use a square slide rail transmission as a guide slider based on the translational movement between the slider and slider

Has high speed and accuracy

Smooth straight movement, little friction

Sliding rails can absorb forces from many directions

The force acting on the shaft and small drive

Transmission power up to 200Kw

Accuracy is reduced if the applied force is large, due to the elasticity of the bel t Error between tooth belt contact and gear

Can drive between axes far apart

Work quietly, without noise thanks to the flexibility of the belt, so it can drive at high speeds

Thanks to the elastic properties of the belt, vibrations generated by changing loads acting on the mechanism are avoided

Thanks to the slippage of the belt, it is recommended to prevent overloads occurring on the engine

The load acting on the shaft and drive is large, due to the need for initial belt tension (creating legal pressure on the belt to create frictional force)

The gear ratio changes due to slippage between the belt and the wheel

- When the printer is working, the hand must move flexibly continuously to respond quickly to the printing process, and the load of the hand is relatively large, so it is very reasonable to use a square slide rail transmission

- The use of a belt transmission meets the requirements of the machine, but the use of a tooth belt offers the advantage of not slipping due to the inertia and traction of the motor better than using a smooth belt So the use of tooth belt transmitters to make Delta 3D printers is appropriate.

Analysis of the selection of printing materials

3D printers in the world are mainly based on FDM (Fused Deposition Modeling) 3D printing technology – a method of coating materials layer by layer to shape products For FDM 3D printers, printing materials are mainly plastic fibers such as PLA, ABS, Nylon, Flexible, PVA, Wood with many different colorful colors, to meet all the creative and artistic needs of users 3D printer users in Vietnam today often compare two types of 3D printing materials, ABS and PLA, but according to actual records, PLA with a plastic fiber size of 1.75mm is the most popular and chosen material for the prototyping process in businesses

ABS (Acrylonitrile Butadiene Styrene) plastic fibers are synthetic materials derived from petroleum ABS is a very durable and well-bearing material, flexible and perfectly resistant to high temperatures 3D printers can use ABS plastic to function normally The printer will melt plastic through print nozzles at temperatures around 210-250°C Therefore, ABS is used a lot in a wide range of applications of the industry today Examples: Manufacture of sewer pipes, waste pipes, automotive components, electronic assembly, protection of headgear (ABS has good impact absorption), kitchen utensils

PLA (Polylactic Acid) plastic fiber is a biodegradable thermoplastic derived from renewable sources, such as cornmeal, sugarcane, cassava root or even potato starch This creates the most environmentally friendly solution in the field of 3D printing, compared to all other online petrochemical plastic products such as ABS or PVA PLA has become a very popular choice in the 3D printing community, because of its low toxicity and environmental friendliness compared to all petroleum-based plastic products Since the PLA source is renewable, it is readily available and will likely surpass ABS PLA is available in most colors and can be matte or solid PLA can glow in the dark This creates the most environmentally friendly solution in the field of 3D printing, compared to all other petrochemical plastic products on the network such as ABS or PVA

❖ Comparison of ABS plastic fiber (Acrylonitrile Butadiene Styrene) and PLA plastic fiber (Polylactic Acid)

ABS is more heat resistant than PLA The same printed product if taken to the sun, after drying for about 30 minutes, the PLA printed product is bent, while the ABS remains the same

After cooling, ABS shrinks more than PLA, this property makes ABS plastic printing products easily cracked after printing The larger the product, the more it will be affected by this shrinkage So if printing large -sized products, PLA will be a better choice, the product will be less cracked when printed

3D printed products when printed will have ridges There are 2 common ways to deal with this problem: Grinding with sandpaper and using polishing chemicals With sandpaper grinding, it can be applied to both PLA and ABS plastics However, this method is not very perfect because it is difficult to grind all the ridges, and the product after grinding often leaves scratches, which must be repainted

With chemical treatment, currently only ABS plastic can be treated with Acetone (using nail sanitizer) The PLA has yet to find chemicals that are safe to handle Thus, depending on the nature of the printed product, we can choose plastic accordingly

❖ Some problems when choosing plastic printing

The uneven diameter of large and small plastic fibers will affect the plastic extruder If the diameter of the 3D printed plastic fiber is suddenly too small, the gears in the plastic extruder cannot create enough pressure to pull the plastic fiber down the 3D print head As a result, plastic fibers are interrupted and 3D printed products are seriously defective When using FDM 3D printers, the 3D printer control software calculates the necessary parameters based on the filament diamete, nozzle size and flow rate (mm/s) Specifically, the 3D printer will control the amount of plastic extruded from the 3D print head by turning the extruder wheel and pushing 1 piece of plastic (length unchanged) to the hot end (the printed plastic heating part) If the diameter of the 3D printed plastic fiber is not standard, the printed plastic fiber is always under pressure from the extruder wheel If the plastic fiber is not evenly rounded, especially some sections with a cross -section that is not round but oval, it leads to either the extruder pulling more plastic or less than the amount of material calculated by the software This is an important criterion that we need to pay attention to One thing few people care about is the size of the plastic roll core: Some types of plastic originate in China because to reduce the cost to the minimum, they have cut the size of the plastic roll core This is really a bad thing In doing so, we discovered how difficult it was to spin plastic fibers into 3D printers The reason is that the plastic fiber is rolled too tightly (with a core of

One final note is the packaging and storage of 3D printed plastic rolls You need to know that 3D printed plastics, especially PLA, have hygroscopic properties Once moistened, the 3D printing process will appear air bubbles in the nozzle hole of the 3D print head and directly affect the quality of the 3D product Thus, when choosing printing plastic, we should use printing resins widely used by the 3D printing community and good branded plastics so that the product after printing reaches the best quality and limits errors in the printing process causing great damage.

Material nozzle

In the design process, the selection of the print head is the most important because it determines the product directly after printing

It is responsible for heating plastic fibers and then extruding them into additives on the model Therefore, 3D printing heads also have names such as material nozzles, 3D printed plastic extruders or 3D printed plastic nozzles

Fig 3.2: 3D printing material nozzle construction.[20]

- The main structure of the nozzle consists of 4 parts:

Printing material melting part: Here the temperature is maintained at the level of melting the printed material The heating head is mounted here to maintain heat and there is an additional temperature sensor to measure the temperature

Heat dissipation part: There is a function of thermal isolation between the melting part and the environment The material is aluminum and Teflon plastic pipe (PTFE)

Conductor part: The material is brought to the firing section through a pipe, pipe diameter from 1.75mm, 3mm,…

Nozzle part: Use to spray printing materials in liquid form after being melted, nozzle size from 0.2mm, 0.35mm, 0.4mm, 0.5mm

The printed material is fed into the fused section through the material conduction section At the firing part, the material is liquefied, pressure is created because the material is introduced continuously, so the molten material is pushed out to create a printed object through the nozzle The heat at the firing part will affect the jig, melting the printing material too soon, causing jamming, so it is necessary to dissipate heat quickly through the heat sink

3 6 2 The effect of temperature on the operation of the print head

A good nozzle is to overcome the jamming of printing material, and the amount of printed material flowing out must be even The main cause is the effect of heat

Fig 3.3: Comparison of temperature distribution between nozzles [21]

If there is no good heat dissipation, the temperature at the upper part and the firing part is almost the same As shown above, if the temperature of the firing part is from 213 -

230 degrees, the upper part of the print head is about 196 -200 degrees High temperatures expand to heat the print head jigs, the printing material melts before it reaches the firing part, causing material jamming or high friction between the printing material

Fig 3.4 : Jamming of material at the site of contact of two heat zones.[22]

At the transition zone between the firing part and the heat sink, there will be an enlargement of the printed material because here the temperature will be close to the

Fig 3.5: Add material at the heat transfer site.[24]

Fig 3.6: Add material at the heat transfer site.[25]

Popular types of 3D printer nozzles today: Buda Nozzle 3D Print Head, J Head 3D Print Head To ensure accuracy and stability when operating for 3D printers, it is recommended to purchase commercially available nozzles

J Head Nozzle kit, this type of nozzle is for assembly machines and is easy to use It proved to be very suitable for Reprop series printers, different materials when printing with this nozzle do not have difficulties, that is, it is diverse with printing materials, not necessarily using 1 type of material

The Buda nozzle injector, this head is also used for Reprap, but compared to the J

Head nozzle, the Buda nozzle in the upgraded version 2.0 gives noticeably high performance and print quality This version has a radiator on the extruder body Buda nozzle is compatible with 2 types of materials: ABS &; PLA Printed plastic fiber 1.75mm or 3mm diameter It is wired to be connected to RAMBO

With the cost of manufacturing 1 set of nozzles is quite high compared to the market price, choosing to buy a ready-made nozzle is suitable for making a 3D printer at a lower cost, and because it is sold on the market, it is also better improved by the manufacturer and also easier to replace

Choose the J Head Nozzle nozzle set to build the printer because it has a simple construction that is easy to use, extrudes a variety of plastics, is easy to improve, and is affordable to build a low-cost rapid prototyping machine.

CALCULATION, DESIGN

Consider the parallel robot structure to find out the number of degrees of

Calculating the number of degrees of freedom:

The whole structure has 6 degrees of excess freedom s: All belong to 6 spherical joints, each spherical joint has 1 degree of excess freedom which is the degree of freedom of the sphere rotating around the axis of the spherical joint

Number of degrees of freedom W=6*n-(5*p5+3*p3)-s+r

Conclusion: Delta parallel robot translational structure has 3 degrees of freedom.

Actuator selection

4.2.1 Design of the Stepper Motor

The linear velocity v of the stepper motor is calculated using Equation (1) [32]

(1) 𝑣 = 𝑟ꙍ; ꙍ = 2𝜋𝑁 where r is the radius of curvature of circular path = 6.25 mm; ω is the angular speed 60 of the motor; N is the constant speed of the motor = 600 rpm By computation, v = 392.69 mm/s

The force due to the electric motor is calculated using Equation

Therefore 6.72 kg can be pulled over a distance of 392.69 mm in one second using NEMA 17

With the movement option for the robot selected as above, we only need three motors to create translational motion thanks to the ball bearings sliding on the z - axis

In order to move the print head flexibly with coordinates changing according to the computer's program, the continuous change of direction of the motor will subject the engine to a large direct impact jet, causing the engine life to decrease while also reducing the responsiveness and increasing the delay time of the machine To overcome the above situation, we need to select motors with appropriate technical requirements to meet those requirements, here the group uses stepper motors as the main transmission mechanism for the following reasons:

- Precise position control is possible thanks to precise step -by-step rotation angle control

- The price is much cheaper than DC motors, servos (because the actuator here is the arm and the print head has a relatively small load, the use of DC, servo motors here is not necessary)

- Very good torque maintenance (no braking, variable speed)

- High torque at low speeds

- No adjustment of control parameters

- Shaft output shaft diameter: 5 mm

The width of the belt is calculated using Equation (3) [32]

𝜎𝑡 (3) where w is the width of the belt; σ is the ultimate strength of polyurethane= 20.77 MPa; F is the force of the electric motor; f is the factor of safety = 2; t is the belt thickness = 1.3 mm

By computation, w = 5.48 mm The standard width = 6 mm

The allowable tensile load on this belt is 134.4 N, and since the force exerted by the motor is 67.2 N, which is far less than the allowable tensile load, the selected belt would not fail under the design conditions

❖ Choosing a GT2 pulley for machine design:

- Shaft diameter: 5mm, or 6.35mm, or 8mm (mounted on motor shaft)

- Used for GT2 tooth belt with 6mm belt width

Fig 4.3: GT2 pulley motor gears.[28]

Fig 4.6: Arm using 2 bridge joints

Fig 4.7: Mobile platform (working head of the machine)

4 4 Kinematic calculations for mechanical hands

4 4 1 Prismatic delta robot configuration analysis

The coordinate origin B (XB, YB, ZB) is mounted on the chassis, the variable to control the movement for the machine is Li ( i = 1, 2, 3), we hav e the control variable matrix L={L1, L2, L3}T, and the actuator coordinate P is BPp={x, y, z}T

Coordinates of 3 translational joints relative to the root B:

From (1), (2), (3), (4) Vector coordinates 3 parallel arms:

2𝑅 𝐵 The machine orbital is the intersection of 3 spheres, we have a system of 3 equations : (I) {

A-point vector coordinates on translational joints : 𝐵 𝐴 𝑖 = 𝐵 𝐵 𝑖 + 𝐿 𝐵 𝑖 ; 𝑖 = 1,2,3

2(𝑐 − 𝑎) Replace x, y to (II): Az 2 +Bz +C=0

In the general case, two problems of kinematics are solved: forward and inverse These tasks were first solved for the delta robot The delta kinematics of the robot was originally described in Another more modern study of kinematics is the work Then similar mathematical models were obtained for the delta 3D printer The mechanism (robot or 3D printer) consists of fixed and small moving platforms, connected by three pairs of passive arms (Fig 4.12)

Fig 4.12: Mathematical model of 3D printer

Each pair of levers forms a parallelogram, the tops of which are connected by spherical joints One of the arms of each lever moves along the rods from a separate engine The other arm of the lever is pivotally connected to the movable platform Structurally, the parallelogram moves in such a way that one side is always parallel to the plane of the base Therefore, the movable platform will also always be parallel to the base In a delta robot, three motors are located at the top and each of them rotates on e of three levers In a delta 3D printer, the motors are located at the bottom and linearly move the arms along the rods through the belt drives In the direct problem, the coordinates of the position of the three rods determine the Cartesian co-ordinates of the extruder in the fixed platform system This task is more difficult, than inverse kinematics The solution to this problem is necessary for modeling trajectories and calculating the working area of a 3D printer We described such a problem in Inverse kinematics consists in determining the z coordinate of the three rods at a known position of the extruder This article uses inverse kinematics for modeling Consider the solution to the inverse kinematics problem It is required to find the distances h1, h2, h3 of points A1, A2, A3 of the attachment of the levers on the rods Cartesian coordinates Xc, Yc, Zc of the center of the circle C of the movable platform are given The geometrical dimensions of the platforms (radii r, R) and the length of the rods l are known The distances of the attachment points of the levers on the rods are determined by the dependencies:

{ h 1 = √𝑙 2 − (𝑋 𝐴1 − 𝑋 𝐵1 ) 2 + (𝑌 𝐴1 − 𝑌 𝐵1 ) 2 + 𝑍 𝑐 h 2 = √𝑙 2 − (𝑋 𝐴2 − 𝑋 𝐵2 ) 2 + (𝑌 𝐴2 − 𝑌 𝐵2 ) 2 + 𝑍 𝑐 h 3 = √𝑙 2 − (𝑋 𝐴3 − 𝑋 𝐵3 ) 2 + (𝑌 𝐴3 − 𝑌 𝐵3 ) 2 + 𝑍 𝑐 where l is the length of the rods; XA1, XA2, XA3, YA1, YA2, YA3 are Cartesian coordinates of the attachment points of the levers on the rods at points A1, A2, A3; XB1, XB2, XB3, YB1, YB2, YB3 are Cartesian coordinates of the levers attachment points at points B1, B2, B3 on the movable platform It is possible to determine the Cartesian coordinates of points A1, A2, A3, B1, B2, B3, based on the assumption that the movable platform does not have the ability to rotate Then the Cartesian coordinates of points A1, A2, A3 of the attachment of the levers on the rods are found from the following geometric relations:

𝑋 𝐴3 = −𝑅𝑐𝑜𝑠(𝜋/6); 𝑌 𝐴3 = −𝑅𝑠𝑖𝑛(𝜋/6) where r is the radius of the moving platform; R is the radius of the fixed platform

The Cartesian coordinates of the points B1, B2, B3 of the attachment of the levers on the movable platform are found from the following geometric relationships:

Fig 4.13: Simulation model of 3D printer

STL files are files that describe the surface of a 3D object The surface of the 3D object is logically subdivided into triangles The STL format is supported by many software, and is widely used in rapid prototyping systems and other CAD systems STL files come in two forms: ASCII and binary codes

An STL file consists of a data list of triangles Each triangle is formatted by a triangular perpendicular line with a length of one and three vertices (angles) Vertices containing coordinate information

Fig 4.12: The triangle in the STL file contains 3-vertex information and a directional vector The rule is that each triangular vertex is both the vertex of another triangle, so there is no vertex of one trian gle above the side of the other

The picture on the left violates the rule

The picture on the right is correct

Fig 4.14: The quality of the part depends on the smoothness of the STL file

The syntax for an ASCII STL file is as follows::

In bold indicate a keyword, these must appear The part in the {} sign contains information of a triangle, the + sign indicates that this part is repeated in an STL file Italics are parameters, which are real numbers "Facet normal" has parameters n which are vertices of vectors perpendicular to triangles, vertex contains parameters v which are vertex coordinates of triangles, vertex vertices are vertices of triangles arranged right-to-left

ASCII STL file ends with endsolid name, which is required

These binary formats use IEEE integers and floating-point numeric representation The syntax for a binary STL file is as follows:

Symbol "{ } +" means that the contents of the double pane can be repeated one or more times

Layering a 3D object from a *.stl format file is the addition of the intersections of the triangles with the cutting plane The triangles intersect the plane by a flat segment, in total these line segments become a contour Then to get the full surface, it is necessary to go through the step of scanned surface

Fig 4.15: Cut tail layer tail sample *.stl

Thus, the tomography software must identify triangles and planes parallel to the z-axis There are 5 cases between a triangle and a plane that are triangles and planes that do not intersect, intersecting each other at a point at the top of the triangle, intersecting each other at two points or triangles

Fig 4.16: Instances of shear occur between the triangle and the plan

Since the STL file contains information about triangular vertices, we are interested in the coordinates of triangular vertices On the triangular representation drawing located on the plane:

- Case 1: Identify 3 triangular vertices located on that plane

- Case 2: The two triangular vertices are located on the intersection plane of the triangle and the main plane is the line connecting those two vertices

- Case 3: There is one vertex located on the plane, one vertex located higher and one vertex located lower, in this case the intersection of the plane is the line connecting the vertex of the triangle with the intersection of the line connecting the other two vertices and the plane

- Case 4: There is one vertex below and two vertices located on the plane, at this time the intersection of the triangle and the plane is the line segment connecting the two intersections of the two sides with the plane

- Case 5: The intersection of the triangle with the plane is only one vertex

The program flowchart for finding the intersection of a 3D STL object with the plane is represented as shown below:

Fig 4.17: Tomography flowchart file *.stl

Intersection coordinate equation of a line segment passing through the plane:

Kinematic calculations for mechanical hands

4 4 1 Prismatic delta robot configuration analysis

The coordinate origin B (XB, YB, ZB) is mounted on the chassis, the variable to control the movement for the machine is Li ( i = 1, 2, 3), we hav e the control variable matrix L={L1, L2, L3}T, and the actuator coordinate P is BPp={x, y, z}T

Coordinates of 3 translational joints relative to the root B:

From (1), (2), (3), (4) Vector coordinates 3 parallel arms:

2𝑅 𝐵 The machine orbital is the intersection of 3 spheres, we have a system of 3 equations : (I) {

A-point vector coordinates on translational joints : 𝐵 𝐴 𝑖 = 𝐵 𝐵 𝑖 + 𝐿 𝐵 𝑖 ; 𝑖 = 1,2,3

2(𝑐 − 𝑎) Replace x, y to (II): Az 2 +Bz +C=0

In the general case, two problems of kinematics are solved: forward and inverse These tasks were first solved for the delta robot The delta kinematics of the robot was originally described in Another more modern study of kinematics is the work Then similar mathematical models were obtained for the delta 3D printer The mechanism (robot or 3D printer) consists of fixed and small moving platforms, connected by three pairs of passive arms (Fig 4.12)

Fig 4.12: Mathematical model of 3D printer

Each pair of levers forms a parallelogram, the tops of which are connected by spherical joints One of the arms of each lever moves along the rods from a separate engine The other arm of the lever is pivotally connected to the movable platform Structurally, the parallelogram moves in such a way that one side is always parallel to the plane of the base Therefore, the movable platform will also always be parallel to the base In a delta robot, three motors are located at the top and each of them rotates on e of three levers In a delta 3D printer, the motors are located at the bottom and linearly move the arms along the rods through the belt drives In the direct problem, the coordinates of the position of the three rods determine the Cartesian co-ordinates of the extruder in the fixed platform system This task is more difficult, than inverse kinematics The solution to this problem is necessary for modeling trajectories and calculating the working area of a 3D printer We described such a problem in Inverse kinematics consists in determining the z coordinate of the three rods at a known position of the extruder This article uses inverse kinematics for modeling Consider the solution to the inverse kinematics problem It is required to find the distances h1, h2, h3 of points A1, A2, A3 of the attachment of the levers on the rods Cartesian coordinates Xc, Yc, Zc of the center of the circle C of the movable platform are given The geometrical dimensions of the platforms (radii r, R) and the length of the rods l are known The distances of the attachment points of the levers on the rods are determined by the dependencies:

{ h 1 = √𝑙 2 − (𝑋 𝐴1 − 𝑋 𝐵1 ) 2 + (𝑌 𝐴1 − 𝑌 𝐵1 ) 2 + 𝑍 𝑐 h 2 = √𝑙 2 − (𝑋 𝐴2 − 𝑋 𝐵2 ) 2 + (𝑌 𝐴2 − 𝑌 𝐵2 ) 2 + 𝑍 𝑐 h 3 = √𝑙 2 − (𝑋 𝐴3 − 𝑋 𝐵3 ) 2 + (𝑌 𝐴3 − 𝑌 𝐵3 ) 2 + 𝑍 𝑐 where l is the length of the rods; XA1, XA2, XA3, YA1, YA2, YA3 are Cartesian coordinates of the attachment points of the levers on the rods at points A1, A2, A3; XB1, XB2, XB3, YB1, YB2, YB3 are Cartesian coordinates of the levers attachment points at points B1, B2, B3 on the movable platform It is possible to determine the Cartesian coordinates of points A1, A2, A3, B1, B2, B3, based on the assumption that the movable platform does not have the ability to rotate Then the Cartesian coordinates of points A1, A2, A3 of the attachment of the levers on the rods are found from the following geometric relations:

𝑋 𝐴3 = −𝑅𝑐𝑜𝑠(𝜋/6); 𝑌 𝐴3 = −𝑅𝑠𝑖𝑛(𝜋/6) where r is the radius of the moving platform; R is the radius of the fixed platform

The Cartesian coordinates of the points B1, B2, B3 of the attachment of the levers on the movable platform are found from the following geometric relationships:

Fig 4.13: Simulation model of 3D printer

Model tomography algorithm 3D (*.stl)