MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING Ho Chi Minh City, March 2024GRADUATION PROJECT MACHINE MANUF
OVERVIEW
G ENERAL INTRODUCTION OF INVESTMENT CASTING , 3D PRINTING TECHNOLOGY , AND
The investment casting process, also known as the lost wax process, is a foundry method for producing high-precision metal castings [1], [2] One of the main advantages of this process is its ability to produce castings with a smooth surface finish, complex shapes, thin walls, and delicate features that would be difficult or impossible to machine [3], [4] It is particularly well suited for casting complex shapes and features that would be difficult or impossible to produce using other casting methods [5] Investment casting is advanced manufacturing when compared with other casting methods such as sand casting, squeeze casting, die casting, semi-solid die casting, and plaster mold casting because there are no metallurgical limitations with this technique [6] Many products are made by investment casting like turbine blades, electrical equipment, electronic hardware and radar, statues and art castings, prosthetics, golf club heads, agricultural equipment, electronic parts, machine tool components, hand tools, fuel systems, making jewelry, aircraft engines, turbocharger, computer hardware, automobile components, dentistry and are produced with smooth surface roughness without the metallurgical limitations [7] It is not only used in industry but also medicine such as dental tools and hip joint implants [7], [8], [9]
To produce wax patterns for the investment casting process, conventional mold manufactured via the machining process is being used Furthermore, mold is fabrication using traditional methods such as machining limitations including restrictions on minimum wall thickness, the need to eliminate sharp corners, and undercuts which require increased angles of inclination and result in increased fabrication costs [10] On the other hand, using conventional tooling for wax model production may lead to extra time and cost, resulting in a reduction of overall throughput and reducing the benefit of using such an approach, particularly for batch production [11] With the disadvantage above, the developing of new designs with low volume production or prototypes is not effective in cost and time [5]
These disadvantages of investment casting could be overcome by using AM technology [8], [9], [12] This process also known as 3D printing or rapid prototyping is a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies This toolless manufacturing approach can give the industry new design flexibility, reduce energy use, and shorten time to market [13] This method can save a lot of time and cost because it avoids using dies, patterns, and tools, which are time and money-consuming for preparation [14] So, rapid investment casting refers to the use of AM technologies in investment casting, the application of 3D printing models can replace wax models with fast time and low cost, especially in small quantities and with complex shapes [15] According to Jiayi Wang et al The lead time and production costs can
2 be reduced by 89% and 60%, respectively by using AM in investment casting [12] However, for a medium number of casting parts and products is difficult to use 3D printing models, traditional methods and large production preparation time are still limited [5], [10], [16]
Chander Prakash et al say that the use of AM in investment casting reduces not only cost and time but also energy consumption and CO2 emission [15] The application of 3D printing technology to producing mold is also applied in this case such as the plastic injection molding industry There is some research to evaluate using 3D printing to make injection mold [17], [18], [19], [20] Rossella Surace et al design optimal cooling channels for 3D printing molds in plastic injection molding to reduce the cycle time The result showed that the rectangular channel is the most effective [17] John Ryan C Dizon et al make injection molds with different 3D printing ways and materials in polymers to compare their dimensional accuracy As a result, SLA and polyjet showed the best finish while that of FFF printed mold using PEEK material appeared delamination after printing [18] Faryar Etesami et al used a device that they manufactured to help resin producers identify the most important properties that influence mold performance The findings demonstrate that these materials react differently to load, temperature, and time John Ryan C Dizon et al [19] experiment of the polylactic acid is injected into 3D printing molds created via SLA and FDM, and the quality of the injected parts is evaluated by dimensional precision and mechanical damage mechanisms Furthermore, it is feasible to avoid the use of wax injection molds when producing prototypes or units of casting, but doing so requires adding new materials to the manufacturing system with particular characteristics such as silicone rubber mold Using AM to design molds has several advantages, including faster and cheaper production less material is to more versatile designs, and the ability to create complex shapes and intricate surface details [20].
O BJECTIVE
The work of this study consists of:
Design and manufacture wax injection mold by using 3D printing and CNC methods
Compare and evaluate the surface roughness of 3D printing molds to aluminum mold: This objective will be achieved by measuring the surface roughness of both types of molds using the surface roughness tester machine
Compare and evaluate the cooling time of 3D printing molds to aluminum mold: This objective will be achieved by measuring the time it takes for molten metal to cool in both types of molds
This study also researches the effect of pouring temperature, and preheat temperature on the shrinkage porosity of SKD 61tool steel and finds the optimized process parameters for the
3 casting process This objective will be achieved by using numerical simulation and statistical methods
The results of this study can enhance the knowledge of using 3D printing for manufacturing mold in investment casting, it promises to improve productivity and reduce the time and cost for investment casting when the number of parts is low.
R ESEARCH LIMITATIONS
- Scope of the report: university materials laboratory, company support
- Research subjects: papers, research, and documents on 3D printing and investment casting
R ESEARCH METHODS
THEORETICAL BACKGROUND
I NVESTMENT CASTING
The investment casting process is the ancient method to produce cast parts In the period of Pharaohs, the Egyptians used this method to produce jewelry made of gold, bronze, and copper Investment casting can make the product with a high-accuracy complex shape and smooth finish surface with dimension accuracy This technique can be used to create a product that is hard to machining by machine tool It is hard to find its origin, but in Iran, Syria, Palestine, and Thailand, the components produced by investment casting are found [3]
This technique is applied for many centuries for producing many things such as jewelry, idols, and casting parts The jewelry is found in many places in the world such as Central/South America, Europe, Greece, etc Eddy et al (1974) described multiple applications and benefits of the investment casting technique for the modern era It is used for generating everything from power cables to hip replacement implants, turbocharger wheels to golf club heads, general engineering to aerospace engineering, and defense outlets By value, steel investment casting contributes to a third of the overall output Aluminum and its alloys have a wide range of applications among the non-ferrous alloys Metallurgical requirements do not apply to investment castings This method has a great advantage because of its excellent surface finish It is possible to cast letters, splines, bosses, holes, and even certain threads This technique can create very thin pieces and intricate details This approach does not need complex or expensive tools For example turbine blades in aircraft engines, and so on The conventional machining method could not meet the high requirements of the war so investment casting has been chosen as an alternative method It recommended the way to produce many complex shape components, undercut parts, etc Investment casting can create many kinds of products so it is the reason why it is developing [21]
According to S Pattnaik et al, the process of investment casting includes seven main steps:
The first step in the investment casting process is to create a wax pattern of the desired part This can be done using a variety of methods, such as injection molding, 3D printing, or hand carving The pattern must be accurate and have a smooth surface finish, as this will be reflected in the finished casting If injection molding is used, a master die of the part is first created The master die is then used to create a cavity mold, which is used to produce the wax patterns If 3D printing is used, the wax pattern is printed directly from a CAD file If hand carving is used, the wax pattern is carved from a solid block of wax
The pattern wax requires several characteristics: First, a material to form a shape with the best dimensional precision, it should have the lowest possible thermal expansion Secondly, minimize the formation of surface cavitation and distortion of thick portions, its melting point should not be significantly greater than the surrounding temperature Third, it must be able to withstand breaking Fourth, produce a final cast item with a smooth surface, it must have a smooth and wettable surface When melted, it ought to have a low viscosity to fill the die's thinnest regions After forming, it ought to be effortlessly extracted from the die Fifth, ensure that there is no ash left inside the ceramic shell, it should contain very little ash Finally, it ought to be safe for the environment [21]
Melted metal is poured into a thin-walled ceramic shell that has been constructed to create an investment casting According to the nature of the casting alloy, a high level of trust in the shell itself is essential since the cost of a failed shell during casting can be unacceptably large, leading to both material loss and plant delay To effectively cast the necessary component in investment casting, the ceramic shell needs to meet specific specifications The conditions required are: First the green strength of the ceramic shell should be adequate to resist the removal of wax without breaking Secondly, enough fired strength to support the weight of the metal in the cast Third, High resistance to heat shock (to avoid cracking while pouring metal) Fourth, high chemical resistance (to stop the metal from growing mold) Finally, sufficient thermal conductivity (to maintain enough heat transfer through the mold wall and so allow the metal to cool) While these specifications remain true for the most part, in certain unique situations, such as casting super alloys, etc., the ceramic shell needs to satisfy additional requirements [21]
Following the coating comes the last phase of creating the ceramic shell needed for casting the necessary component Wax needs to be removed from the ceramic structure's interior after the shell has been created Usually, the wax is removed, cleaned to get rid of any contaminants from the process, and then used again to create fresh designs
Heating the ceramic shell and letting the molten wax flow out of the mold is typically how the wax is removed from the inside of the ceramic shell The mold needs to be heated up quickly The moderately expanding ceramic shell will be cracked by the rapidly expanding wax if the mold is heated slowly
Conventionally, dewaxing has been done by autoclave dewaxing, flash fire dewaxing, etc Dewaxing is often done in industrial autoclaves, where ceramic molds with wax patterns
6 are inserted, in the majority of investment casting companies After that, the ceramic molds are melted at a high temperature and pressure in a damp, warm environment [21]
Various methods have been in practice to introduce molten metal into the shells using gravity, pressure, vacuum, and centrifugal methods When the molten metal in the shell has solidified and cooled down sufficiently, the casting may be removed from the shell However, the microstructure of the cast component must be within the acceptable form, as it is likely to be affected because of the pouring and cooling processes [21]
After the metal solidifies, the refractory is knocked, shaken out, or chipped out A pneumatic vibration machine or physical labor can be used to chip out a layer of ceramic refractory To obtain the last component, the casting tree's riser and gate are divided It is important to complete this process carefully to lower post-machining costs Refractory should have high collapsibility and be quickly knocked out after solidification, but imperfections and a lack of refractory qualities make it difficult to remove the shell Nevertheless, it is discovered that adding alkali salts to earth metal makes shell removal easier
The casting may be further processed, such as machining, heat treating, or finishing This will depend on the specific requirements of the application
Figure 2 1: Schematic illustration of conventional investment casting process [7]
The performance comparisons of different casting processes are illustrated in Table 2 1 It is worthwhile to notice that as far as the dimensional accuracy is concerned, the lost wax
7 investment casting process remains the most accurate process in which the typical percentage linear dimensional tolerance is 0.05 (5 parts/1000) This ultimately resolves the issue of dimensional accuracy, a property for which lost wax investment are unsurpassed
Table 2 1: Comparison of accuracy and efficiency of different casting processes [21]
Lost foam process Freeze cast process
Linear dimensional tolerance (mm/254 mm)
Despite the wide range of applications in many industries, the standard investment casting process practiced in modern foundries has its drawbacks High tooling costs and lengthy lead times are associated with the fabrication of metal molds required for producing the sacrificial wax patterns used in investment casting High tooling costs involved in conventional investment casting result in cost justification problems when small numbers of castings are required [7]
High tooling costs and lengthy lead times are associated with the fabrication of metal molds required for producing the sacrificial wax patterns used in investment casting The high tooling costs involved in conventional investment casting result in cost justification problems when small numbers of castings are required
To produce wax patterns for the investment casting process, conventional mold manufactured via the machining process is being used Furthermore, mold is fabrication using traditional methods such as machining limitations including restrictions on minimum wall
8 thickness, the need to eliminate sharp corners, and undercuts which require increased angles of inclination and result in increased fabrication costs [10] On the other hand, using conventional tooling for wax model production may lead to extra time and cost, resulting in a reduction of overall throughput and reducing the benefit of using such an approach, particularly for batch production [11] With the disadvantage above, the developing of new designs with low volume production or prototypes is not effective in cost and time [5]
Another limitation is that the microporosity in high-performance castings can reduce mechanical properties and consequently degrade both component life and durability Therefore, casting engineers must be able to both predict and reduce casting microporosity Porosity formed in castings leads to a decrease in the mechanical properties One of the most effective ways to minimize porosity defects is to design a feeding system using porosity prediction modeling In such a way, the casting analysis can determine the location and magnitude of porosity such that the feeding system can be redesigned This process is repeated until porosity is minimized and not likely to appear in the critical areas of the castings [22] Microporosity still occurs in superalloy castings even though they are vacuum refined and vacuum melted The porosity can be detrimental to the mechanical properties of high- temperature superalloys because it reduces the fatigue and stress rupture properties Many advances in melt processing and casting design procedures have been made to reduce this defect; nevertheless, it is still an important concern in the production of superalloy castings Many modern foundries have resorted to experimental and numerical research to minimize, and if possible, eliminate this defect, predicting the formation or avoidance of porosity in castings as a timely research topic [23] Susan et al investigated how casting porosity affected the mechanical performance of investment casting Studies are conducted on 17-4PH stainless steel and the impact of heat treatment on the alloy's susceptibility to casting flaws The yield strength and ultimate tensile strength are decreased by porosity, which is created during the solidification and shrinkage of the alloy This reduction is usually proportionate to the decrease in the load-bearing cross-section They look into how casting porosity affects ductility For the high-strength H925 condition, they discovered that 10% porosity decreased the ductility of 17-4PH stainless steel by over 80% The alloy's ductility is further decreased by tensile testing at -10C (263 K), both with and without pores [24] Both the shrinkage during solidification and entrapped gas in the product cause the porosity The shrinkage porosity is divided into micro or macro shrinkage This defect is quite sensitive to casting geometry, running process parameters, and gating-system design Volumetric shrinkage upon solidification causes the porosity The volumetric shrinkage creates the shrinkage porosity if casting parameters are not properly controlled which tends to be distributed in the last areas to solidify [25] The mechanical properties and strength will be weakened if exist defects, such as shrinkage defects and gas porosity As the CAE analysis can offer conclusions for
MATERIALS AND METHODS
M ATERIALS
Wax injection material in investment casting can be liquid or paste-like (semi-solid) At low temperatures, they are able to form patterns using paste injection Although it necessitates significantly greater pressures, it is preferred because it reduces shrinking and strengthens the wax pattern The injection must be also supplied by the whole die cavity filling at the same time For huge patterns, for example, when the pressure cannot be as high, the liquid injection into the dies can be used
Overall, investment casting waxes are intricate blends of several substances, such as water, solid organic fillers, natural or synthetic resin, and wax or synthetic The complicated thermomechanical and thermal behavior of investment casting waxes, however, makes it challenging to characterize the material properties because of the additions used in them
In this study, a wax mixture of 118174 Freeman Flakes Wax—Super Pink from (Freeman Manufacturing & Supply Company, Avon, OH, USA) is used The thermal conductivity is presented in Table 3 1
Table 3 1:Thermal conductivity of wax [35]
The material properties of the 3D printing molds must also be considered: thermal conductivity, melting and softening temperatures, mechanical strength (yield and ultimate stress limits), stiffness in the elastic range (Young’s modulus), hardness, and impact sensitivity (IZOD) In the past, the thermal and mechanical properties of AM materials significantly limited the quality and endurance life of the AM molds but recently, new material with improved performance developed for this application
The SLA 3D printing injection mold made of Rigid 10K resin (Formlabs Ltd., Somerville,
MA, USA) is used The Rigid 10K resin is selected for analysis because it is characterized by the highest thermal conductivity of all the photopolymer resins offered by Formlabs The thermal conductivity of Rigid 10k is presented in
Table 3 2: Thermal conductivity of rigid 10k [35]
The selection of aluminum for aluminum mold is based on its excellent thermal conductivity and popularity as an investment casting mold material Aluminum is chosen to make the injection molds used in the industrial process of investment casting This is because creating a large number of casting patterns is required to create the casting molds Heat dissipation is therefore a crucial factor to consider when choosing a material for a wax injection mold [4] Compared to steel materials, aluminum mold exhibits benefits in weight, heat transmission, and low production cost
In this study, 6061 aluminum material is used to manufacture aluminum mold 6061 is popular in wax molding so it has excellent thermal conductivity, excellent corrosion, low price, etc [13] [35] It can create a large number of casting patterns Table 3 3 presents the chemical composition of 6061 aluminum
Table 3 3: Chemical composition of Al 6061 [36]
Element Mg Fe Si Cu Mn V Ti Al
Table 3 4: Thermal conductivity of Al6061 [37]
In this study, SKD 61 tool steel is chosen as a casting material for the investment casting process This material is widely used in industry to produce dies and tools, with extremely high hardness, high toughness, and high strength The chemical composition of SKD 61 is presented in Table 3 5
Table 3 5: Chemical composition of SKD 61 [38]
Element C Si Mn P S Cu Ni Cr V Mo Fe
M ETHODS
To determine the surface roughness of aluminum mold and 3D printing M, the Mitutoyo SJ-
210 (Mitutoyo, Ka is aki, Kanagawa, Japan) surface roughness measurer is used for indicating the surface roughness of each particle with different positions As a probe moves on the flat of these molds, the surface roughness readings of these molds are recorded on the work line Three indexes can be obtained by the results of Mitutoyo SJ- 210 surface roughness measurement including Ra, Rz, and Ry Roughness parameters Ra is chosen to measure Units are measured by micrometer (àm)
Figure 3 1 illustrates the Mitutoyo SJ-210 surface roughness machine To compare the surface roughness, the measuring tool uses two kinds of mold with six different positions to inspect the surface roughness
Figure 3 1: The Mitutoyo SJ-210 surface roughness tester
The Niyama criterion is presently the most widely used criterion function in metal casting It is used to predict feeding-related shrinkage porosity caused by shallow temperature gradients All casting simulation software packages calculate the Niyama criterion as a standard output; foundries worldwide use this criterion to predict the presence of shrinkage
23 in castings Foundry-simulation users view Niyama contour plots predicted by a casting simulation and expect that shrinkage porosity will form in regions that contain Niyama values below some threshold value [39]
Cooling time is an important factor of injection wax Identification of cooling time can help to improve the gating system design Thus, simulation results can help to reduce the possibility of failure in directional solidification Inspire casting (Altair, Troy, Michigan, United States) simulation software is applied to study the cooling time
The simulation step is illustrated in Figure 3 2 There are five steps to get the results from 3D CAD to the results
Firstly, the 3D cad is imported into Inspire cast software and the cast part and runner system are defined Then, the gates are selected to generate one After that, select the mold icon to define the mold material and initial temperature Next, select module low pressure as a type of simulation Finally, click run analyze to select the element size and start the simulation process
There are two kinds of simulation applied in this study The aim of the first simulation is for the cooling time of two kinds of mold and the second one for microporosity and Niyama Figure 3 7 and Table 3 7 show the technical parameters that remain unchanged in two kinds of numerical simulation
Figure 3 2: Steps to get the results of the simulation Table 3 6: Technical parameters for cooling time simulation of two molds
Shell thickness 0.01 m Mold material Silica-Sand Filling time 5 s Gate diameter 0.03 m Element size 0.003 m
Table 3 7: Technical parameters for cooling time simulation of two molds
Taguchi method is one of the most power design of experiments to understand process characteristics and to investigate how experimental parameters affect results based on statistical backgrounds [40] It uses the orthogonal array model to explore the fundamental control factors through a small number of experiments by dispensing the elements in a balanced manner and converting the experimental results into signal-to-noise ratio (S/N) to investigate the optimal conditions For optimization problems, there are three types of S/N ratio basically: “Larger the Better”, “Nominal the Better”, and “Smaller the Better” [41]
For the microporosity, the SB type is used to calculate For the Niyama, LB types use to calculate Three levels are selected for the factor The range of values of each factor is set at three levels, namely 1, 2, and 3, as presented in Table 3 8 A combination of all different levels of factors as presented in is carried out The responses measured are microporosity and Niyama Different assembly methods are illustrated in Figure 3 3
𝑦 𝑢 : the value of the u th measurement
Temperature mold 24 ℃ Step time from 5s to 100s 5 s Initial temperature 52 ℃ Element size 0.001 m
25 n: Number of experiments in the orthogonal array
The design of experiments is established by Minitab 21 (Minitab, State College, Pennsylvania, United States) software The sort of experiment is presented in Table 3 9
Table 3 8: Levels of process parameters
Different assembly methods are illustrated in Figure 3 3 There are 40 casting parts in each kind of assembly method and its volume is the same
ANOVA statist s are performed to determine the percentages of each factors contribution to the output Minitab 21 Software is used for the whole statistical analysis and creation of the plots.
P REPARATIONS
The product is designed by Creo Parametric 8 software The model is designed with a symmetrical shape with embossed letters on both sides This product can be used as a decoration or gift Figure 3 4 illustrates the shape of the product
Figure 3 4: Design of the model
The first step in the CNC machining process is also using Creo Parametric 8.0 to create a CAD model The CNC machine's toolpaths are then generated using the Mastercam software Your 3D model will then be translated into G-code by the Mastercam (CNC Software,
Tolland, Connecticut, United States), which is a language that the CNC machine can comprehend The CNC machine needs to be set up next Installing the right cutting tools and placing the workpiece in the vise are the steps involved in this process To build the mold, the CNC machine will finally remove material from the workpiece according to the toolpaths that are generated in the Mastercam program
Figure 3 5: Aluminum molds after preparing
In this study, the SLA 3D printing mold is chosen because it is a well-known method that can print parts with low resolution, low surface roughness, and good dimensional accuracy, made of polymers with high mechanical properties This technology makes these features particularly suitable for tiny parts manufacturing with complicated 3D geometry and shape details with good surface roughness
In this project, the SLA technology is applied to make a 3D printing M insert The process is used by using a Form3 machine (Form3, Formlabs, Somerville, MA, USA ), which assembled bottom-up exposure (inverted) stereolithography In this particular version of the process, the polymerized layer is separated from the resin tank by a peeling mechanism when the current layer has been fully treated The peeling step can be crucial to the part's geometrical accuracy if it is not handled properly The build volume of this 3D printer is 145 ì 145 ì 185 mm 3 , and its light source is a class 1 violet laser with a spot diameter of 85 àm and a power of 250 mW, extending at a wavelength of 405 nm The XY plane (layer) positioning resolution of 50 àm may be accomplished with the 3D printer, and the layer thickness resolution along the z-axis can be set to 200, 100, 50, or 25 àm
The process of making 3D printing mold includes: first, the molds are designed by Creo Parametric 8.0 (PTC, Boston, Massachusetts, United States) Next, the STL file is chosen to export the part After that, the part geometry (STL file) is preprocessed utilizing the slicer program Formlabs Preform, and by appropriately selecting the algorithm parameters, supports and laser pathways are generated on layers
To achieve high resolution and precision, the layer thickness is established at 50 àm The Formlabs Form Wash is used to wash the 3D-printed samples To get rid of the liquid resin on the part surfaces, the 3D-printed samples are immersed in high-purity 99.9% isopropyl alcohol for 20 minutes in a Formlabs Form Wash machine After removing all of the supports using a cutter, the samples experienced heat treatment and UV exposure in a Formlabs Form Cure machine Following 3D printing, it took approximately 60 minutes at
60 for washing and UV curing, and 90 minutes at 125 for heat treatment The manufacturing and assembly steps of the AM mold insert are illustrated in Figure 3 7, and Figure 3 9
In this study, 3D printing molds required about 168 milliliters of material and processing times of about 12 h 2 min There are 1488 layers and the layer height is 0.05 mm After the 3D printing, washing in isopropyl alcohol and UV curing took about 2.5 hours The fabrication and assembly steps of the 3D printing mold insert are illustrated in Figure 3 1
Figure 3 7: Process preparing 3D printing molds [19]
Table 3 10: Post-processing parameters for 3D printing molds
Post-Processing Temperature ℃ Time min
Washing isopropyl alcohol Room Temperature 20
Figure 3 9: 3D printing molds after preparing and assembly process
3.3.4 Wax pattern injection molding process
That is one of the most crucial processes, similar to the plastic injection molding process First of all, the wax is heated at 53℃ After that, it is forced into the mold by the vertical injection machine After it is cool, the pattern will be eliminated from the molds Table 3 11 shows the parameters of this process
Table 3 11: Technical parameters of the wax injection process
Cooling temperature ℃ 24 Injection pressure MPa 30 Holding pressure MPa 65
Figure 3 10: The wax pattern after preparing
Firstly, the wax patterns are coated in ceramic four times, roughly, using the following steps: they are dipped in a ceramic slurry made of 16.86 wt% colloidal silica 830, 83.3 wt% zircon flour, 0.1 wt% de-foaming, and 0.06 wt% degassing After that, they are covered in ceramic particles (zircon 22 s and zircon 35 s) Then, they are dried at 25 ℃ and 70% humidity Finally, to obtain the mold cavities, the wax patterns are extracted from the outer shell and heated to 900 ℃ in a chamber furnace Ultimately, the cavities are filled with molten materials
RESULTS AND DISCUSSION
E VALUATE THE SURFACE ROUGHNESS OF THE CAVITY IN 3D PRINTING MOLDS ,
molds, and casted parts in investment casting
This study measures and evaluates the surface roughness of 3D printing mold and aluminum mold Moreover, the surface roughness of wax patterns and casting parts from two molds are also examined The effect of mold surface roughness on the wax patterns and casting parts is discussed Both aluminum molds and 3D printing molds have the same evaluation position Figure 4 1, Figure 4 3, and Figure 4 5 illustrates the positions that will be measured of molds, wax patterns, and casting parts, respectively
Figure 4 1 and Figure 4 3 at positions 1,2,3,4,5,7,8,9,10,11,12, the probe of the machine will be moved horizontally, while at positions 6 and 12, it will be moved vertically
In Figure 4 5, the probe of the machine will be moved horizontally at all positions, as shown
In each of the positions, the measurement process is conducted 3 times and then take the average Figure 4 7 illustrates the average of surface roughness in each process of both molds
The investigated surface roughness of the aluminum mold and 3D printing molds are illustrated in Figure 4 2 and Table 4 1 Thiss process allows a comparison of the surface roughness of two kinds of molds From the graph and table, the surface roughness of aluminum mold is better than 3D printing molds at all positions and smaller than many times The surface roughness of aluminum mold ranges from 0.05 àm to 0.45 àm, while that of 3D printing mold fluctuates from 0.7 àm to 2.8 àm The biggest surface roughness of aluminum mold at 10 and the smallest at 4, about 3D printing mold at 1 and 6 for the biggest position and 11 for the smallest position The surface roughness of a 3D printing mold fluctuates more than an aluminum mold even though the 3D mold uses the same layer height for the entire surface and the aluminum mold uses several cutting conditions It could be because the roughness of SLA 3D printing molds is also affected by other factors such as blade gap, hatch space, and position on the platform [42]
After the wax injection process, the measured surface roughness step is conducted to investigate the surface roughness of the wax pattern, the results surface roughness of the wax pattern are presented in Table 4 2 and Figure 4 4 From the findings, the surface roughness wax pattern of aluminum mold corresponding to mold is not always higher at all positions The biggest surface roughness is at 11 followed by position 5 and the smallest is at 9 At 4,5,6,11, the surface roughness of the aluminum mold is even higher than the 3D printing mold The surface roughness of 3D printing mold fluctuates from 0.6 àm to 1.9 àm, while aluminum mold fluctuates between 0.61 àm and 1.54 àm For the 3D printing mold, the
33 biggest and smallest surface roughness are at 12 and 4, respectively Compared to the molds, the increase in surface roughness of the wax pattern from the aluminum mold is greater at all positions On the other hand, in the 3D printing mold, the surface roughness of the wax pattern is smaller than the mold at 1, 2, 3, 4, 7, 8, 9, 10 Although the surface roughness of the mold affects the wax patterns, the high tension of molten wax, stopped it from filling the micro slots in the printed surface during the wax injection process [43]
After the casting process, the results of the measured surface roughness of the casted part are investigated and presented Table 4 3 and Figure 4 6 The surface roughness of the casted part from 3D printing molds and aluminum molds ranged from 2.3 àm to 3.6 àm and from 2.3 àm to 4.3 àm, respectively As can be seen, the surface roughness of two kinds of mold is equal or nearly equal at 1, 3, and 9 The highest surface roughness of the two mold types is located at the same place at 8 It may be a defect in the casting process that affects the measurement results The surface roughness of casted parts from the two mold types is equal at most of the positions Although there are big differences in surface roughness between the two kinds of mold But the surface roughness of the casted part from 2 molds is not or small difference
Figure 4 7 illustrates the average surface roughness in each process of both molds As can be seen, the average surface roughness of 3D printing molds is higher than aluminum mold at 1.7 àm vs 0.25 àm However, the wax pattern from the 3D printing mold and aluminum mold is nearly the same at 1 for the aluminum mold and 1.2 àm for the 3D printing mold
These above results implied that the 3D printing mold can produce wax patterns for investment casting without affecting the surface roughness of the casting part
Figure 4 1: The positions of molds will be measured The names (a1), and (2) in the figure belong to aluminum molds and 3D printing molds, respectively
Table 4 1 The surface roughness between 3D printing molds and aluminum molds
1 st 2 nd 3 rd Average Standard deviation
1 st 2 nd 3 rd Average Standard deviation
Figure 4 2: The surface roughness between 3D printing molds and aluminum molds
Figure 4 3: The positions of wax patterns will be measured The names (a1), and (2) in the figure belong to aluminum mold and 3D printing molds, respectively
Su rf ace ro u gh n es s (à m )
PositionsAluminum molds 3D printing molds
Table 4 2: The surface roughness of wax patterns
1 st 2 nd 3 rd Average Standard deviation
1 st 2 nd 3 rd Average Standard deviation
Figure 4 4: The surface roughness of wax patterns
Figure 4 5: The positions of casted parts will be measured The names (a1), and (2) in the figure belong to aluminum mold and 3D printing molds, respectively
Su rf ace ro u gh n es s (àm)
PositionsAluminum molds 3D printing molds
Table 4 3: The surface roughness of casting parts
1 st 2 nd 3 rd Average Standard deviation
1 st 2 nd 3 rd Average Standard deviation
Figure 4 6: The surface roughness of casting parts
Su rf ace ro u gh n es s (àm)
PositionsAluminum molds 3D printing molds
Table 4 4: Average value for surface roughness in each process
Mold Wax pattern Casted part
Figure 4 7: The average surface roughness in each process of both molds.
C OMPARE COOLING TIME BETWEEN 3D PRINTING MOLDS AND ALUMINUM MOLDS
To evaluate the cooling time between the 3D printing mold and the aluminum mold, a simulation process is conducted The results of the simulation process are illustrated in Figure
4 8 and Table 4 5 This process will predict the temperature of two molds within 100 s from the wax injection stage to the open stage After a period of 100s, the temperature of the aluminum molds are reduced to 26.04 ℃ and the 3D printing mold went down to 34.41 ℃ Furthermore, the temperature of the 3D printing mold at 100 s is nearly equal to aluminum mold at 45 s At 100 s, the temperature of the 3D printing mold is higher than aluminum mold by about 8.37 ℃, indicating that the cooling time of the 3D printing mold is slower than aluminum mold by about 55 s The reason for the results is that the thermal conductivity of aluminum mold is higher than 3D printing mold [21]
Mold Wax pattern Casting part
The experiment is carried out at Juki (Tan Thuan, District 7, Ho Chi Minh City) The parameters of the test are presented in Table 3 11 In this experiment, the injection time of the test is changed from 5 s to 30 s, each time this figure is increased to 5 units the remaining specification is leveled off and the other parameters remained during the test The purpose of the test is to comparison of the cooling effectiveness and ability to use 3D printing mold in reality From the test, the ability cooling of the mold made of aluminum mold is good from 5 s to 30 s Regarding the 3D printing mold, from the 20s to 30s, the ability to remove from the mold is the same with aluminum mold but it is harder when the time is reduced below 20s because the temperature did not decrease to the injected temperature As a result, the cooling time of the 3D printing mold in reality slower than aluminum mold by 15 s
With the results above, the cooling time of 3D printing molds is slower than aluminum mold by about 15s but this result is acceptable when it comes to a small or medium-sized production Furthermore, the 3D printing molds are successful in producing the wax pattern
Table 4 5: The cooling time of aluminum mold and 3D printing molds
Figure 4 8: Compare the cooling time of both molds
E FFECT OF PROCESS PARAMETERS ON SHRINKAGE POROSITY
The effect of preheat temperature, pouring temperature, and type taken on the microporosity of SKD 61 tool steel in investment casting has been discussed in this section
The experiments are conducted by combining all the factors and levels The results of the simulation are presented in Table 4 6 Figure 4 9, Figure 4 10 show the lowest and highest values of microporosity and Niyama
As can be seen in Figure 4 11, the value of microporosity fluctuated between 1.21 % and 2.44 % There are two values between 1 and 1.5 %, three values for 1.5 – 2 %, and 3 values for 2 – 2.5 %
In terms of Niyama, the value varies from 16.09 to 26.42 There are eight values between 15 and 20, and one value for 25 – 30
Figure 4 9: The lowest and highest value of microporosity
Figure 4 10: The lowest and highest values of Niyama
Table 4 7: S/N ratio for microporosity and Niyama
The values of the microporosity and Niyama are collected from numerical simulation and presented in Table 4 6 In this thesis, the “smaller the better” type is selected to get the S/N ratio for the microporosity responses, and the “larger the better” type is chosen for the Niyama These values of the S/N ratio for microporosity and Niyama are used to optimize the input parameters with their levels, as presented in Table 4 7 with Delta being distinct between the minimum value and the maximum The results of microporosity indicate that the input factor pouring temperature has the most significant influence on microporosity (with Delta value of 2.789), followed by assembly method (with Delta value of 1.875) and preheat temperature (with Delta value of 0.61) In terms of Niyama, the results indicated that pouring temperature is also the most significant parameter on Niyama (with a Delta value of 2.1), followed by preheat temperature (with a Delta value of 1.27) and assembly method (with Delta value of 0.93) The best setting for a parameter is the one that makes the least amount of microporosity The best input values to minimize the microporosity are: preheat temperature = 1100℃; level 3, pouring temperature = 1560℃; level 1, assembly method II; level 2 and the best setting for a parameter is the one that makes the largest Niyama value The best input values to maximize the Niyama value are: preheat temperature = 1100℃; level
3, pouring temperature = 1760℃; level 3, assembly method = II; level 2
Table 4 8: Average effect response table of S/N ratio for microporosity
Table 4 9: Average effect response table of S/N ratio for MRR Niyama
Figure 4 13: Effect of process parameters on microporosity
Figure 4 14: Effect of process parameters on Niyama
ANOVA technique is applied to determine which process parameters considerably affect microporosity ANOVA tables for microporosity are calculated by Minitab software and presented in Table 2 Moreover, the degree of freedom (DF), mean square (MS), and F values (F) in the table show the P-values (P) associated with each factor level and interaction
The greatest contribution is the assembly method for 32.9%, followed by the pouring temperature for 17.7% and the preheat temperature for 1%
In the case of the Niyama, the obtained results indicated that among the input parameters, the pouring temperature had the major effect on the Niyama at 48.83% followed by the preheat temperature at 21.99 % and assembly method at 11.92%
The results above indicated that the pouring temperature has the largest impact on the microporosity and Niyama
Source DF Seq SS Adj SS Adj MS F P Contribution
Source DF Seq SS Adj SS Adj MS F P Contribution
CONCLUSION
L ESSONS LEARNED
In this study, the application of 3D printing for making mold and optimizing process parameters to minimize defects are discussed
1 The application of 3D printing for making investment casting is successful
2 The average surface roughness of 3D printing molds is higher than aluminum mold at 1.7 àm vs 0.25 àm
3 Average surface roughness of the wax patterns and castings obtained through the two types of molds are 1 àm and 2.9 àm, respectively
3 The temperature of both molds after 100s are 26.04 ℃ and 34.4 ℃ for the aluminum mold and 3D printing mold, respectively and the temperature of the 3D printing molds after 100s is nearly equal to the aluminum mold after 55s
The findings of this study are very practical, provide the potential application of 3D printing in IC, and improve the productivity of IC.
F UTURE WORKS
There are some factors of 3D printing molds should be pursued in further research:
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