Development of a Low-Cost Silicone Mold Tool for Injection … · 2021. 1. 9. · Keywords: injection molding, rapid prototyping, rapid tooling, design of experiments 1 INTRODUCTION

Paper presented at the 7th Annual Composites and Advanced Materials Expo (CAMX 2020), Florida, United States.

Development of a Low-Cost Silicone Mold Toolfor Injection Molding Plastic Parts

Irfan Tahir, John Rapinac, Abdulaziz Abutunis, Venkatagireesh Menta

Department of Mechanical and Industrial Engineering, University of Minnesota Duluth, Duluth MN 55812

Abstract: The design and development of injection molding (IM) tools is a very expensive and time-

consuming process which makes it difficult to incorporate traditional IM into the prototyping stage of

a product. Currently, the most widely researched method used for rapid prototyping of IM tools is 3D

printing with engineered plastics. This project investigates an alternative to 3D printed IM tools by

investigating a cost-effective mold tool made of silicone. Design of Experiment (DOE) is used to measure

the main and interaction effects of design parameters (e.g., durometer hardness, geometry, and design

complexity) on the performance of the silicone mold. It was found that a durometer of Shore A Hardness

40 is the most optimal value for a silicone mold tool. Using 3D printed inserts and a short runner improved

the mold performance. Comparison of mechanical properties of the silicone mold test coupons with those

produced using a metallic mold tool revealed that there was a 7.3% decrease in Ultimate Tensile Strength,

better than those previously reported for some 3D printed mold tools. Results show that the silicone mold

tool is a promising alternative to 3D printed mold tools for low-volume injection molding.

Keywords: injection molding, rapid prototyping, rapid tooling, design of experiments

1 INTRODUCTION

Injection molding (IM) is a widely used polymer pro-cessing technique for fabricating plastic parts of differentshapes and profiles. The main working principle of theprocess involves injecting molten plastic material into amold tool where it cools and hardens to take the shapeof the mold. Due to the ability to mass-produce at highspeeds, high accuracy for complicated shapes, and lowermass-production costs, the IM process has become oneof the most popular processing methods in the polymerindustry [1].

In addition to this, plastic parts produced via injec-tion molding offer excellent repeatability [2]. Some ofthe products manufactured using injection molding arebottles, toys, automotive parts, storage containers, andmedical device components. One of the major limitationsof the IM process is the high initial start-up cost duringthe design and development stage of a product. Any de-sign improvements or modifications of the part at laterstages is quite difficult. Overall, the design of the moldtool is time-consuming and expensive during product de-velopment. Thus, injection molding is typically avoidedin making prototypes [3].

Rapid prototyping (RP) is a well-known process thathas come to light with the advancements in three-dimensional (3D) printing and lower cost associated with

Computer Numerical Control (CNC) machining. The ad-ditively manufactured molds that are created using RPare built with shorter lead time and at a fraction of thecost when compared to traditional tooling. However,mold tools created using RP have challenges and partdesign limitations that must be addressed. The materialthat is chosen to replace the traditional metallic toolingmust be able to withstand the appropriate pressures andtemperatures needed to inject the thermoplastic material.Likewise, the mold must be rigid and maintain its shapeunder the clamping pressure of the injection molding ma-chine, so the final product comes out as intended. More-over, the thermal conductivity of the rapidly prototypedmold tool is less than that of the metallic mold as RPmold tools are made of polymer. The lower cooling rate(lower thermal conductivity) of thermoplastics can alterthe microstructure and change the mechanical propertiesof the injected part. Another issue with RP is the limi-tation of injection materials for alternative methods suchas 3D Printing, in contrast to IM where there is a verylarge range of plastic and biodegradable materials easilyavailable.

As 3D printing is the current standard for rapid pro-totyping of mold tools, it is worth highlighting some ofthe work that has been done in this area. Bartlett in-vestigated the effects on the mechanical properties of PPplastic parts produced using a desktop 3D printed moldtool with Digital ABS material [4]. The results showed

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that the Ultimate Tensile Strength (UTS) decreased by11%, Young’s modulus of the parts increased by 9.4%,and strain at break, or ductility of the parts, decreasedsignificantly by 87% when compared to parts made us-ing a metallic mold. Annealing the samples before tensiletesting helped increase ductility but it was not as good assteel mold parts. Simpson et al. also used Digital ABSwith PolyJet 3D printing and investigated the effects ofdifferent 3D printing materials and the injection materialon the mold tool [5]. The authors reported that the strainat break of Digital ABS was consistent with that of thesteel mold, but stiffness was reduced by 28.5%.

Another technique for rapid prototyping injectionmold tools is to use 3D printed inserts, also known assteel/plastic hybrid molds. Dawson et al. investigatedcomposite molds made out of atactic polystyrene andcompared the properties of the plastic sample with a tra-ditional steel mold [6]. Results showed that parts pro-duced using a composite mold had 17% lower UTS, similarYoung’s modulus, 19% higher flexural strength, and 20%lower ultimate elongation than parts produced using asteel mold. Mischkot et al. used the design of experimentsto study a disk-shaped insert built using PolyJet 3D print-ing technology [7]. The material that was injected intothe mold was Low-Density Polyethylene (LDPE). The au-thors reported that a cooling time of 50 seconds was nec-essary to enable the injection of the parts without anymajor deformations or discoloration. The inserts lastedbetween 25 and 116 production runs with a cycle time of300 seconds. The authors concluded that a 3D printedinsert is a viable option for medium-sized molds (80 x 60x 20 mm3).

Starting with the most basic question of whether ornot it is possible to inject plastic material into a siliconemold tool, this project investigates the development of amold tool made out of silicone for simple and cost-effectiveprototyping of injection molded parts. These mold toolshave the potential of enabling researchers and materialsscientists to add variability to their designs. The manu-facturing cost of a silicone mold tool can be as much as 10times cheaper than the manufacturing of a metallic moldtool. The low cost associated with silicone also attractscustomers who are not experts in designing a mold toolas the process is relatively fast and simple and uses com-mercially available materials. An additional advantage ofsilicone is the wide operating range for high-temperatureinjection materials. For biopolymers such as lignin, al-ginate, PLA, and other “sticky” materials, silicone moldtools can prove to be beneficial as materials tend not tostick to it and there is no need for a mold release agent.This is especially useful for medical device componentsused in vivo studies.

(a) 3D printed mold toolcast

(b) Pouring the liquid sili-cone into the cast

(c) Waiting for liquid tolevel

(d) Shape of the mold aftercuring for 24 hours

Figure 1: Making the silicone mold tool

2 EXPERIMENTATION

2.1 Materials

The silicone materials used in this project were sourcedfrom the Smooth-On company from their location inPennsylvania, United States. In total, Mold StarTM sili-cone of Shore A Durometer Hardness 30 and Mold MaxTM

silicone of Shore A Durometer Hardness of 40 and 60 re-spectively were used. Polypropylene (PP) in pellet formwas obtained with a donation from the University of Min-nesota Duluth’s Materials Science Laboratory. The cast-ing mold to manufacture the silicon mold was 3D printedusing Hatchbox PLA filament with a diameter of 1.75mm.

2.2 Silicone Mold Tool Process

An outer cast (Figure 1 (a)) for the silicone mold tool was3D printed with a Creality Ender 3 using PLA and aninfill of 20%. The liquid silicone components were pouredinto a measuring cup then mixed and vacuum degassedfor 180 seconds. The mixture was then poured in the 3Dprinted cast cavity at a single point and left to cure for24 hours. The same process was followed for each siliconemold tool. Figures 1 (b)-(d) illustrate these steps.

2.3 Injection Molding

A Morgan Press G-125T injection molding machine wasused for producing ASTM D638 Type IV standard tensiletest coupons. Injection molding parameters for each run

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were changed according to the DOE studies. A metallicouter frame was used to encompass the silicone mold asshown in Figure 2.

Figure 2: Schematic showing the pieces of the silicone moldtool. The pieces in gray were made out of metal.

2.4 Mechanical Testing

Tensile tests were carried out as per the ASTM D638 stan-dard using the Applied Testing Systems (ATS) UniversalTesting Machine. All the tests were performed at a crosshead speed of 5 mm/min using a 500 lbs. load cell. Jawgrippers without extensometers were used for holding thetensile samples.

2.5 Design of Experiments

The purpose of performing the DOE was two-fold: (a)to determine the proper silicone durometer and (b) todetermine the right operating parameters for a successfulinjection run.

2.5.1 DOE #1 Durometer vs. Mold Height vs.Corner Radius

The first DOE was conducted to determine the rightdurometer hardness of the silicone mold tool. Eight vari-ables kept the constant in the first DOE (Table 1).

Table 1: Constant parameters for DOE #1

Parameter ValueNozzle Temperature (F) 440Barrel Temperature (F) 420Plate Temperature (F) 250Hold Time (min) 4Injection Pressure (psi) 1500Injection Time (sec) 5Clamping Pressure (psi) 8000Material PP

A full factorial DOE study with 23 = 8 injection runswas conducted with three factors and two levels each (Ta-ble 2). The factors were durometer hardness, mold height,and outside corner radius (Figure 3). The reason for se-lecting the height of the mold tool as a factor was to in-

vestigate whether having more material between the moldcavity and the bottom of the mold will have any effect onthe rigidity of the mold. The outside corner radius wasinvestigated to see if increasing the radius of the curve,where the melted plastic flows from the runner to thetensile specimen, will help the plastic flow with ease.

A quantitative response, fill percentage, was used tomeasure the performance of each injection run. The fillpercentage was calculated by taking a photo of the in-jected part and calculating its surface area using the soft-ware ImageJ. By measuring a real distance on the sam-ple, a relationship was established in ImageJ of knowndistance vs. the same distance in pixels. Depending onthe type of injection (under-fill or over-fill), this surfacearea was compared to the original 100% fill percentage.In addition to this, other responses such as mold deterio-ration, warpage, sink marks, flash, and discoloration werealso taken into account.

Figure 3: 40 durometer mold with a mold height of 16 mmand outside corner radius of 10 mm. The arrows show thelocation of the outside corner radius.

Table 2: Factors and levels for DOE #1

Factors DurometerMold

Height (mm)Corner

Radius (mm)Levels 30 16 5

40 26 10

2.5.2 DOE #2 Injection Pressure vs. Time vs.Clamping Pressure

The second DOE was conducted to determine the right in-jection molding parameters for a successful injection run.Eight variables kept the constant in this DOE (Table 3).

A full factorial DOE study with 23 = 8 injection runswas conducted with three factors and two levels each (Ta-ble 4). The first chosen DOE factor was injection pres-sure. In the our previous work [8], injection pressurewas found to have the greatest effect on the fill percent-age. In this previous study [8], the same injection mold-ing machine was used to inject high-density polyethylene(HDPE) material into a metallic mold. The second cho-sen DOE factor was injection time. If injection time is

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Table 3: Constant parameters for DOE #2

Parameter ValueNozzle Temperature (F) 440Barrel Temperature (F) 420Plate Temperature (F) 250Hold Time (min) 4Mold Height (mm) 16Outside Corner Radius (mm) 10Durometer 40Material PP

too short or too long, there will be an injection failurecaused by the short shot or flash, respectively. The thirdfactor was clamping pressure. It was hypothesized thatbesides the long injection time, the failure due flash wascaused by the imperfect/weak contact between the twomold surfaces. If there are any gaps, the melted plasticwill leak from the runner as it is injected.

Table 4: Factors and levels for DOE #2

FactorsInjection

Pressure (psi)InjectionTime (s)

ClampingPressure (psi)

Levels 1500 5 80003000 10 10000

2.6 Other Mold Designs: Center Injection and 3DPrinted Inserts

To add rigidity to the area around the runner, a 3Dprinted material was inserted into the mold (Figure 4).The materials used for 3D printed inserts were PLA andNylon. Additionally, a short runner geometry with a cen-ter injection was also carried out (Figure 5).

Figure 4: Mold tool design with 3D printed inserts

3 RESULTS AND DISCUSSION

3.1 Design of Experiments

3.1.1 Analysis of Response for DOE #1

After running the experiments and calculating the surfacearea of each test sample, the fill percentage was obtainedusing ImageJ and input into Minitab. The Pareto chartof the first DOE study is shown in Figure 6. The dottedline represents the standardized effect value. Any effectwith bars reaching beyond the standardized effect line is

Figure 5: Mold tool design with a simpler geometry

considered a significant effect. In this Pareto chart, itcan be seen that the durometer significantly affects theresponse (the fill percentage). The outside corner radiusand mold height did not have as large of an effect and inthe case of mold height, the effect is almost negligible asseen in the Pareto chart.

An ideal sample will have a fill percentage of 100%.The main effects plots shown in Figure 7 can aid in de-termining which specific levels will result in a 100% fillpercentage. Each slope has a maximum and minimumvalue represented by blue dots. The vertical axis of themain effects plot shows us the mean fill percentage of theDOE study. To determine which level should be used infuture DOE study, the factor level which is closest to a100% mean fill percentage should be used. In this case,those factors and levels are durometer 40, mold height 16mm, and outside corner radius of 10 mm.

Figure 6: Pareto chart for DOE #1

Figure 7: Main effects plot for DOE #1

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3.1.2 Mold Deterioration and Sample Quality

In addition to exhibiting a high fill percentage and conse-quently failure by flash, the 30 durometer mold tool alsoshowed deterioration at the four corners (Figure 8) morethan the 40 durometer mold tool (Figure 9) after 8 runs.This can be attributed to the fact that the mold toolshad an outer metal frame which limited the silicone moldtool’s deformation. In contrast to this, the durometer 40mold tool showed a slight deterioration in the corner, butit was much less than the mold tool made using durome-ter 30. This shows that the durometer 30 silicone is moreprone to deformations which in part led to a failure byflash.

Figure 8: Mold deterioration for durometer 30

Figure 9: Mold deterioration for durometer 40

The samples which were over-filled did not show anyshrinkage, warpage or dimensional instability (Figure 10).This can be explained by the fact that after the materialhas finished injecting, it is not subjected to high pressurein the gate location. So, even if the mold tool is deformedwhile injecting, it returns to its original flat shape oncethe injection is finished. For samples that were under-filled, there was a slight shrinkage that was observed inthe necking area of the sample (Figure 11). This can beattributed to the material not completely filling the cavityof the mold tool.

3.1.3 Effect of Increasing Durometer Hardness

Durometer was found to have the most significant effecton the mold tool response. The main effects plot (Figure7) showed that to reach an ideal fill percentage of 100%,the durometer should increase. Hence, along with 30 and

Figure 10: Sample of run #1

Figure 11: Sample of run #7

40, durometer hardness 60 was used to conduct furtherexperiments. The reason for not using durometer 50 wasbecause that durometer number is not commercially avail-able from the manufacturers of the silicone material.

The minimum possible injection molding pressure of1500 psi an injection time of 5 seconds was used to avoidbrittle failure of the mold. However, on the first injectionrun, a brittle fracture propagated through the runner ofthe mold (Figure 12 and 13). The experiment was re-peated two more times. For all three of these experiments,a brittle failure to the mold caused the melted plastic toseep through the mold as soon as it was injected. Thus,it was concluded that a durometer of 60 is too high for asilicone mold and it was eliminated from any further DOEstudies. From the results of DOE #1, it was concludedthat a durometer 40 silicone is more suitable to use in theexperiments than a durometer 30 silicone as the latter ismore prone to deformation and deterioration. In addi-tion, a mold height of 16 mm was chosen as it uses lesssilicone material and an outside corner radius of 10 mmwas chosen as samples obtained from that type of moldwere the closest to the ideal case.

Figure 12: Durometer 60 mold tool, where the circle showsthe location of the crack.

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Figure 13: Bottom of the Durometer 60 mold tool showingthe leaked PP material

3.1.4 Analysis of Response for DOE #2

During DOE #2, For an injection pressure of 3000 psi, allthe samples failed by flash. When the injection pressurewas half of that, there were short shots (or under-fill) butthe fill percentage was much closer to 100%. This madeit clear that an injection pressure of 3000 psi was too highfor the silicone mold tool. Additionally, an injection timeof 10 seconds when combined with an injection pressureof 1500 psi and clamping pressure of 10000 psi gave theclosest fill percentage (108%) to an ideal sample.

The Pareto chart in Figure 14 shows that two of theemployed factors, injection pressure and injection time,significantly influence the fill percentage. A third signif-icant effect came from the interaction between injectionpressure and clamping pressure. The main effects plotsin Figure 15 also show how injection pressure and injec-tion time had the greatest effect on the fill percentage.Changing the clamping pressure from 8000 psi to 10000psi did not result in a large change in the fill percentage.This was contrary to past experiments on metal mold inwhich increasing the clamping pressure reduced the flash.This meant that the upper limit that was selected for theclamping pressure was not high enough.

Figure 14: Pareto chart for DOE #2

The bottom left quadrant of Figure 16 shows the in-teraction of injection pressure with clamping pressure inrelation to fill percentage. It can be observed that an in-jection pressure of 3000 psi with a clamping pressure of8000 psi resulted in a higher fill percentage than with a

Figure 15: Main effects plot for DOE #2

clamping pressure of 10000 psi. When the injection pres-sure was 1500 psi, the opposite was observed. Also, thehigher clamping pressure (10000 psi) with the injectionpressure of 1500 psi resulted in a fill percentage closer to100%, as seen in the y-axis of Figure 16. As injectionpressure was increased and clamping pressure was low-ered, the molten plastic flowed outside the cavity with ahigher rate and resulted in higher failure by flash. Thiscan be observed from the steeper slope of 8000 psi clamp-ing pressure compared to the 10000 psi. Even when therewas an under-fill, the melted plastic “leaked” from therunner when applied pressures were not appropriate. Thiscan be seen in Figure 17 in which as the melted plasticflowed through the mold cavity, it simultaneously flashedfrom the runner.

Figure 16: Interaction effects plot for DOE #2

Figure 17: Sample of run #2 from DOE #2 showing leakageof material from runner

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3.1.5 Effect of Increasing Clamping Pressure

Based on the interaction plot results (Figure 18) of DOE# 2, additional experiments were conducted to measurethe response of the mold tool to the variation in theclamping pressure.

Results showed that increasing the clamping pressure to14000 psi with an increased injection time did result in thereduction of flash as seen in Figure 16. However, it alsoled to dimensional instabilities in the shape of the sample.The runner area of the mold tool expanded due to the highclamping pressure. As the problem of leakage from therunner was not solved, a change in mold geometry wasimplemented.

Figure 18: Sample of run #1 obtained by increasing clamp-ing pressure

3.2 Effects of 3D Printed Inserts and Short RunnerLength

3.2.1 3D Printed Inserts

The PLA insert was melted into the PP plastic as it has amelting point (150°C) lower than the nozzle temperature(220°C) as shown in Figure 19. The Nylon insert was ableto sustain the high nozzle temperature without melting asNylon’s melting point is 240°C. Results showed that theinsert was able to control failure by the flash from therunner and this kind of mold tool gave the best samplesin terms of quality so far (Figure 20). The brown coloringof the sample was due to oxidation. This occurred whenthe sample was taken out of the mold earlier than thespecified hold time. Mischkot et al. injected LDPE intoa disk-shaped steel mold and found 50 seconds to be asufficient hold time to avoid any loss in the original color[7]. However, in this mold tool, whenever the hold timewas below 240 seconds, a slight brown coloration of thesamples was observed.

3.2.2 Short Runner

A new approach was implemented in parallel with the3D printed inserts. In the revised mold geometry, therunner was eliminated while the neck length of the tensilespecimen was kept the same (see Figure 5). For the firstinjection run, a small amount of flash was observed at the

Figure 19: Sample of run with PLA insert

Figure 20: Sample of run with Nylon insert

center. The leakage of the molten plastic from the centerwas attributed to the imperfect contact between the topmetallic plate and the bottom silicon mold. When thematerial was injected into the center of the mold with highpressure, the silicone mold tried to expand. However, theouter metallic frame prevented it from doing so, whichresulted in a slight curve in the mold. This curve, inturn, created gaps between the silicone mold and the topmetallic plate and hence led to the leakage of the meltedplastic. Taking these factors into account, an injectionrun was carried out with a borderless straight metallicplate so that the mold is free to expand and does notcurve.

Using an injection pressure of 1500 psi, injection timeof 5 sec, and clamping pressure of 10000 psi, an idealsample with no flash was obtained as shown in Figure 21.This injection run was repeated 3 more times, and eachtime an ideal sample was obtained. The samples werethen post-processed and cut into half so that they can betested using a tensile testing machine.

Figure 21: Sample obtained with center injection withoutouter frame without any failure by flash

3.3 Mechanical Properties

Firstly, to check if the tensile tests were done correctly,the UTS values of the PP samples obtained from themetal mold were compared with those present in onlinedatabases. In total, three sources were used as references.The comparisons showed that there was a 2.4%, 3.7%,

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and 8.0% error in UTS respectively for each of the threesources [9-11]. Overall, the tensile tests of metal moldsamples showed a better consistency than the siliconemold samples. This can be quantitatively assessed bycalculating the standard deviation of UTS of each sam-ple set, where the metal mold and silicone mold samplesshowed a standard deviation of 0.527 and 0.912 respec-tively (Table 5).

Table 5: Comparison of mechanical properties with standarddeviations

Property (MPa) Metal Mold Silicone MoldUTS 32.197 ± 0.527 29.854 ± 0.912Young’s Modulus 360.255 ± 14.41 142.511 ± 31.75Yield Strength 18.194 ± 0.242 11.935 ± 1.158

Comparing the average UTS, it was observed that therewas a 7.3% decrease for the silicone mold tool samples .This decrease in UTS is less than the ones reported inthe literature, where the decrease in UTS was as high as11% for 3D printed mold [4] and 21% for composite mold[12]. On average, there was a 60.4% decrease in Young’smodulus and a 34.4% decrease in the yield strength whengoing from metal to silicone mold tool.

For PP tensile samples produced using a Fused Deposi-tion Modeling (FDM) 3D printed mold tool made out ofABS Digital, Bartlett reported a 9.4% increase in Young’smodulus compared to parts produced using a steel mold[4]. Leon-Cabezas et al. reported a 45.98% decreasein Young’s modulus for tensile specimens produced us-ing a Polyjet 3D printed mold tool when compared toparts produced using a metal mold tool [13]. In anotherstudy of polystyrene composite molds, Young’s modulusremained unchanged [12]. The difference in silicone moldtool and 3D printed material’s thermal conductivity canbe attributed to such a difference.

Figure 22: Stress vs. Strain plots for metal mold samples

Figure 23: Stress vs. Strain plots for silicone mold samples

4 CONCLUSIONS

It has been shown that it is possible to develop a moldtool made out of a flexible material like silicone to in-ject Polypropylene. Results show that not only siliconecan withstand the high temperatures and pressures, butalso able to resist mold deterioration at certain durome-ter hardness. It was found that the plastic parts producedfrom silicone mold did not show many types of commonfailures found in injection molded samples like sink marks,warpage, or blisters.

There are limitations to using a silicone mold tool forinjection molded parts. Mainly, these are related to thegeometry of the mold cavity. It was found that even withthe right type of durometer, the length of the runner ofthe mold tool can have a significant effect on whether ornot the part will fail due to flash. Another type of failuredue to a short shot was also observed when the injectiontime was too low. The most ideal defect free sample wasobtained using a combination of a short runner, low in-jection pressure, short time, high clamping pressure, andthe absence of any outer frame.

The use of silicone mold tools is promising especiallyfor material scientists and manufacturers experimentingwith plastic parts in the early stages of their research. Inits solid form, silicone is an excellent choice when dealingwith materials that tend to stick to other surfaces. Ex-amples of these include medical-grade biomaterials suchas PLA, PGLA, lignin, alginate, and bio-based PET. An-other advantage of using a silicone mold tool to producesimple medical device components is that the mold sur-face does not require any type of release agent to besprayed prior to injection. This eliminates the risk of anypossible contamination in the medical components. Com-pared to most types of 3D printed molds, the silicone moldis also able to withstand higher temperatures. It has thepotential to inject resins with high melting temperaturessuch as PEEK, PPA, and PEI. Also, commercially avail-able materials for the silicone mold tool are 3 times less

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expensive than those used in 3D printed molds. The de-crease in UTS was also relatively better for silicone moldtool parts when compared to 3D printed mold tool parts.

For future work, it is recommended that a DOE studyis conducted with 3D printed inserts as that proved tobe a viable solution to failure through flash without com-promising the mold geometry. Flexural, Izod impact, andhardness tests of the injected plastic should be conducted.Repetitions of all the tensile tests should be carried outto verify the results with larger sample size. DSC testsshould be conducted to measure the crystallinity of theinjected parts.

Using the silicone mold tool, researchers can continueusing injection molding for their prototypes instead of re-verting to other techniques such as casting, 3D printing,or compression molding. For design projects where the fi-nal part will be made using injection molding, the siliconemold tool provides consistency during the design process.In conclusion, this project can be expanded further byconducting tests and experimenting with more complexgeometries so that the gap between preliminary researchand production of a part can be filled.

References

[1] M. P. Groover, ”Shaping Processes for Plastics,”in Fundamentals of Modern Manufacturing: MaterialsProcesses, and Systems, 5th ed., New York: John WileySons, 2012, pp. 316-326.[2] J. C. Viana, N. M. Alves, and J. F. Mano, ”Mor-phology and Mechanical Properties of Injection MoldedPoly (Ethylene Terephthalate),” Polymer EngineeringScience, vol. 44, no. 12, pp. 2174-2184, 2004.[3] T. Rogers, ”Everything You Need To KnowAbout Injection Molding,” in Creative MechanismsBlog, ed. Creative Mechanisms, 2015. Available:http://www.creativemechanisms.com/blog/everything-you-need-to-know-about-injection-molding[4] L. P. Bartlett, ”A Preliminary Study of Using PlasticMolds in Injection Molding,” The Ohio State University,2017.[5] P. Simpson, A. D. Zakula, J. Nelson, J. K. Dworshak,E. M. Johnson, and C. A. Ulven, ”Injection Molding withan Additive Manufactured Tool,” Polymer EngineeringScience, vol. 59, no. 9, pp. 1911-1918, 2019.[6] E. Dawson and J. Muzzy, ”The Effect of RapidPrototype Tooling on Final Product Properties,” SPEANTEC Technical Paper, no. 45, pp. 456-460, 1999.[7] M. Mischkot et al., ” Injection Moulding PilotProduction: Performance Assessment of Tooling ProcessChains Based on Tool Inserts Made from Brass and a 3DPrinted Photopolymer,” in Annual Technical Conference2017 of the Society of Plastic Engineers, pp. 1898-1902,2017.[8] Mahmood S, Tahir I, Menta V. Thermo-Mechanical

Characterization of HDPE-Tobacco Lignin Blends. TheComposites and Advanced Materials Expo; California2019.[9] Polypropylene (PP). MakeItFrom.com, 8 Sept. 2018.Available: https://www.makeitfrom.com/material-properties/Polypropylene-PP-Copolymer[10] Polypropylene (PP). Mechanical Properties, PolymerDatabase, Available: https://polymerdatabase.com[11] “Typical Properties of Polypropylene.” Tap Plastics,Available: https://www.tapplastics.com/[12] M. Damle, ” Effect of Fiber Orientation on theMechanical Properties of an Injection Molded Part anda Stereolithography Insert Molded Part,” in AnnualTechnical Conference (ANTEC 1998) of the Society ofPlastic Engineers, Atlanta, USA, pp. 584 - 588, 1998.[13] M. Leon-Cabezas, A. Martınez-Garcıa, and F.Varela-Gandıa, ”Innovative Advances in Additive Man-ufactured Moulds for Short Plastic Injection Series,”Procedia Manufacturing, vol. 13, pp. 732-737, 2017.

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Development of a Low-Cost Silicone Mold Tool for Injection … · 2021. 1. 9. · Keywords: injection molding, rapid prototyping, rapid tooling, design of experiments 1 INTRODUCTION