Comparative Study of Rapid and Hard Tooling for Injection Molding Application Using Metal Epoxy Composite (MEC)

materials

Article Hybrid Mold: Comparative Study of Rapid and Hard Tooling for Injection Molding Application Using Metal Epoxy Composite (MEC)

Radhwan Hussin 1,2,3,*, Saﬁan Sharif 1,*, Marcin Nabiałek 4,*, Shayfull Zamree Abd Rahim 2,3,*, Mohd Tanwyn Mohd Khushairi 5, Mohd Azlan Suhaimi 1 , Mohd Mustafa Al Bakri Abdullah 2,6, Mohd Hazwan Mohd Hanid 2,3, Jerzy J. Wysłocki 4 and Katarzyna Błoch 4

1 School of Mechanical Engineering, Faculty of Mechanical Engineering, Universiti Teknology Malaysia, Johor Bahru 81310, Malaysia; [email protected] 2 Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, Perlis 01000, Malaysia; [email protected] (M.M.A.B.A.); [email protected] (M.H.M.H.) 3 Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Perlis 01000, Malaysia 4 Department of Physics, Cz˛estochowaUniversity of Technology, 42-200 Cz˛estochowa,Poland; [email protected] (J.J.W.); [email protected] (K.B.) 5 IMU Centre for Life-Long Learning (ICL), International Medical University, Kuala Lumpur 57000, Malaysia; [email protected] 6 Faculty of Chemical Engineering Technology, Universiti Malaysia Perlis, Perlis 01000, Malaysia * Correspondence: [email protected] (R.H.); saﬁ[email protected] (S.S.); [email protected] (M.N.); [email protected] (S.Z.A.R.)

Citation: Hussin, R.; Sharif, S.; Abstract: The mold-making industry is currently facing several challenges, including new competi- Nabiałek, M.; Zamree Abd Rahim, S.; tors in the market as well as the increasing demand for a low volume of precision moldings. The Khushairi, M.T.M.; Suhaimi, M.A.; purpose of this research is to appraise a new formulation of Metal Epoxy Composite (MEC) materials Abdullah, M.M.A.B.; Hanid, M.H.M.; as a mold insert. The fabrication of mold inserts using MEC provided commercial opportunities Wysłocki, J.J.; Błoch, K. Hybrid Mold: and an alternative rapid tooling method for injection molding application. It is hypothesized that Comparative Study of Rapid and the addition of filler particles such as brass and copper powders would be able to further increase Hard Tooling for Injection Molding mold performance such as compression strength and thermal properties, which are essential in the Application Using Metal Epoxy Composite (MEC). Materials 2021, 14, production of plastic parts for the new product development. This study involved four phases, 665. https://doi.org/10.3390/ which are epoxy matrix design, material properties characterization, mold design, and finally the ma14030665 fabrication of the mold insert. Epoxy resins filled with brass (EB) and copper (EC) powders were mixed separately into 10 wt% until 30 wt% of the mass composition ratio. Control factors such as Academic Editor: Andrea Sorrentino degassing time, curing temperature, and mixing time to increase physical and mechanical properties Received: 18 December 2020 were optimized using the Response Surface Method (RSM). The study provided optimum parameters Accepted: 25 January 2021 for mixing epoxy resin with fillers, where the degassing time was found to be the critical factor with Published: 1 February 2021 35.91%, followed by curing temperature with 3.53% and mixing time with 2.08%. The mold inserts were fabricated for EB and EC at 30 wt% based on the optimization outcome from RSM and statistical Publisher’s Note: MDPI stays neutral ANOVA results. It was also revealed that the EC mold insert offers better cycle time compared to EB with regard to jurisdictional claims in mold insert material. published maps and institutional affil- iations. Keywords: hybrid mold; rapid tooling (RT); metal epoxy composite (MEC); material properties; injection molding process

Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. 1. Introduction This article is an open access article distributed under the terms and Currently, plastic parts for various applications are produced mainly through the conditions of the Creative Commons injection molding process under heat and pressure conditions to form the product into the Attribution (CC BY) license (https:// desired shape and size [1,2]. In general, molds for plastic injection molding are usually creativecommons.org/licenses/by/ made of tool steel through the machining process using a CNC (Computer Numerical Con- 4.0/). trol) precision machine [3–5]. Toolmakers need to invest in expensive equipment, such as

Materials 2021, 14, 665. https://doi.org/10.3390/ma14030665 https://www.mdpi.com/journal/materials Materials 2021, 14, x FOR PEER REVIEW 2 of 15

Materials 2021, 14, 665 2 of 15 made of tool steel through the machining process using a CNC (Computer Numerical Control) precision machine [3–5]. Toolmakers need to invest in expensive equipment, suchCNC as machine CNC machine tools, an tools, Electro-Discharge an Electro-Disc Machineharge Machine (EDM), drilling (EDM), machine drilling andmachine metrology and metrologyequipment, equipment, which have which high have flexibility high flexibility for small-to-medium for small-to-medium batch production batch production and mold andcomponent mold component fabrication fabrication [6]. The dimensional [6]. The dimensional accuracy of accuracy the tooling of andthe tooling fabrication and process fabri- cationdepends process on the depends strict requirements on the strict requiremen of the finalts product of the final which product requires which high requires precision high for precisioncomplex for geometry complex and geometry fine surface and fine finishing surface [ 7finishing]. In addition, [7]. In theaddition, market the also market demands also demandsproducts products of a higher of a quality, higher cheaperquality, costs,cheape shorterr costs, productshorter product development development cycles, and cycles, that andfulfill that the fulfill environmental the environmental requirements requirements for sustainability for sustainability [3,8]. Therefore, [3,8]. Therefore, innovations innova- in tionsappliance in appliance methods methods and materials and materials need to need be adopted to be adopted to meet to the meet product the product manufacturing manu- facturingcycle requirements cycle requirements [9–11]. [9–11]. InIn the the last last two two decades, decades, in order toto meetmeet the the new new trends trends within within the the plastics plastics industry, industry, the theconcept concept of aof hybrid a hybrid mold mold (Figure (Figure1) has 1) beenhas been developed developed for injection for injection molding molding applications. applications.A hybrid A hybrid mold ismold a novel is a novel method method in the in fabrication the fabrication of injection of injection molds molds which which combines com- binesthe conventional the conventional machining machining for mold-based for mold-bas anded Rapidand Rapid Tooling Tooling (RT) (RT) techniques techniques for mold for moldinserts inserts (core (core and cavity and cavity inserts) inserts) [10,12, 13[10,12,13].]. The advantages The advantages of this typeof this of moldtype areof mold efficiency are efficiencyin minimizing in minimizing waste and waste energy and consumption; energy consumption; agility to agility customize to customize and ease and of flexibility ease of flexibilityto change to and change incorporate and incorporate design concepts design co [14ncepts–16]. [14–16]. The advantages The advantages of this type of this of type mold ofare mold efficiency are efficiency in minimizing in minimizing waste and waste energy and consumption;energy consumption; agility to agility customize to customize and ease andof flexibilityease of flexibility to change to and change incorporate and incorp designorate concepts design [2 concepts,3,8]. Manufacturers [2,3,8]. Manufacturers have sought havethe non-conventionalsought the non-conventional process for process tooling fo fabricationr tooling fabrication which includes which RTincludes and exploredRT and exploredalternative alternative materials materials with faster with delivery, faster increased delivery, quality,increased reduced quality, product reduced development product developmenttime, and compatible time, and with compatible global trends with global [10]. trends [10].

FigureFigure 1. 1. ConceptConcept of of a ahybrid hybrid mold. mold. A common route for fabricating molding blocks and mold inserts is through the A common route for fabricating molding blocks and mold inserts is through the vac- vacuum casting process of the Metal Epoxy Composite (MEC) [17,18], whereby epoxy- uum casting process of the Metal Epoxy Composite (MEC) [17,18], whereby epoxy-based based material was mixed with the metal fillers (aluminum, brass, and copper) and then material was mixed with the metal fillers (aluminum, brass, and copper) and then poured poured into the well-prepared pouring container. Nevertheless, the non-uniform mixing of into the well-prepared pouring container. Nevertheless, the non-uniform mixing of the raw the raw materials, the curing agent, and the presence of trapped gases may cause problems materials, the curing agent, and the presence of trapped gases may cause problems in the in the fabricated molding blocks and mold inserts [19,20]. To establish the best composition fabricated molding blocks and mold inserts [19,20]. To establish the best composition and and mixing ratio based on percentage weight (wt%), the appropriate composition of mixing ratio based on percentage weight (wt%), the appropriate composition of metal fillers metal fillers needs to be determined [15,21–23]. Pontes and Queirós [12] evaluated the needsperformance to be determined of aluminum-filled [15,21–23]. epoxyPontes moldand Queirós inserts built[12] evaluated by using athe hybrid performance mold, and of aluminum-filledtested the mold epoxy insert mold for more inserts than built 600 by shots. using The a hybrid material mold, used and was tested not the just mold aluminum- insert forfilled more epoxy, than but600 ashots. modified The material mixture used of aluminum-filled was not just aluminum-filled epoxy with a nickel-phosphorusepoxy, but a mod- ifiedlayer mixture on its of cavity. aluminum-filled Tomori et al. epoxy [24] with investigated a nickel-phosphorus the ceramic-filled layer on epoxy its cavity. tool Tomori as mold etinserts al. [24] forinvestigated plastic injection the ceramic-filled molding. Duringepoxy tool the as first mold 150 inserts shots, for the plastic tool performedinjection mold- well ing.without During catastrophic the first 150 failure, shots,with the tool the performed injection pressure well without and temperature catastrophic being, failure, respectively, with the injection20 MPa pressure (200 bar) and and temperature 220 ◦C. However, being, therespectively, results showed 20 MPa a significant(200 bar) and effect 220 in°C. terms How- of ever,the increasethe results in surfaceshowed roughness,a significant flexural effect in strength terms of and the thermal increase conductivity in surface roughness, as a mold insert fabricated using RT methods instead of employing conventional methods. On the

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other hand, S. Rahmati and P. Dickens [25] pointed out that resin temperature (Tg), thermal conductivity of filler and fabrication process are important factors in considering how the molded component is affected by the molding process using mold inserts fabricated using the RT technique. There are still some difficulties in the manufacturing of plastic parts using hybrid molds which are related to the thermal properties, mechanical data and behavior of the materials which are either inaccessible or misunderstood [10]. One of the main issues encountered during the development of RT for the molding process is its low thermal conductivity, which results in slow heat transfer from the molten plastic to the coolant through the mold inserts. Rapid heating and cooling during the injection molding process can further degrade the mold inserts and consequently affect the quality of the part and dimensional accuracy [16,26]. Selection of the best composition of filler and well preparation process of mold insert will lead to enhanced mechanical properties that are capable of a higher production volume, such as hardness, strength, and cost-effective molds [15,16,27]. However, the metal fillers will perform better in the epoxy matrix with uniform dispersion as well as suspension in the mixture, and they do not sink to the bottom [15]. This is an important factor that needs to be considered in order to produce effective MEC mold inserts. In addition, there are several other factors based on the manufacturer’s guidelines and also reported by previous studies [15,23,28] such as curing temperature, curing time, composition of metal fillers based on its weight ratio, degassing time, mixing time, etc. [29], which will affect the physical, thermal and mechanical properties of the mold inserts produced. To understand the effect of these parameters, the interactions between all of these parameters to the responses should be examined. Response Surface Methodology (RSM) is useful in correlating the factors and responses as it is less time consuming and is able to detect the true optimum factor [30,31]. This allows a number of factors to be simultaneously evaluated and eliminates the need for a large number of independent tests that are otherwise necessary for a standard one-factor or trial and error approach [29,32].

2. Methodology The methodology of this research can be divided into four phases, as presented in Figure2. The first phase starts with the investigation on the filler particles which emphasizes the literature review of previous studies on the use of filler particles as metal epoxy composite material. Based on previous studies, ALWA High Temperature resin M2200 manufactured by ALWA resin systems and porous slabs, Grunau, Germany for tooling applications and irregular-shaped brass and copper filler particles were selected for the purpose of improving the ability of mold inserts with regard to its durability and high thermal conductivity. In the second phase, the new MEC formulation was evaluated by producing specimens for various tests and characterization. The specimens were fabricated using filler particle materials of different metals mixed with epoxy resin. The physical characteristics of the newly formed MEC with different filler percentage compositions were evaluated mechanically and thermally for their suitability to be used as mold inserts in injection molding application. By using RSM, the optimum mixing parameters affecting the hardness of the MEC were determined. Experimental design to correlate mixing parameters with mechanical properties of MEC blend was based on two-level factorial designs generated using the optimization software (Design Expert 7, Stat-Ease Inc., Minneapolis, MN, USA). In the third phase, the mold inserts were designed using Computer-Aided Design (CAD) software (Solidworks 2014, Dassault Systems, S. A., Suresnes, France) with incorporating the cooling channels, gating systems, and considering the molded parts as tensile test specimens. Then, the design was simulated using Moldflow simulation software (Autodesk Moldflow Insight 2012, Moldflow, Melbourne, Australia) to obtain the recommended setting of processing parameters for the actual injection molding process. Next, the mold inserts were fabricated using a new MEC formulation and the performance of the mold inserts were evaluated experimentally using an injection molding Materials 2021, 14, x FOR PEER REVIEW 4 of 15 Materials 2021, 14, 665 4 of 15

performance of the mold inserts were evaluated experimentally using an injection mold- ingmachine machine (Nissei (Nissei NEX1000, NEX1000, Nissei Nissei Plastic Plastic Industrial Industrial Co., Co., LTD., LTD., Minamijo, Minamijo, Japan). Japan). Finally, Fi- nally,in the in last the phase, last phase, the moldthe mold inserts inserts were were assembled assembled as aas sub-assembly a sub-assembly and and fitted fitted into into a astandard standard mold mold base base as as a a hybrid hybrid mold. mold. The The mold mold was was tested tested and and rectified rectified before before producing produc- ingspecimens specimens for for testing testing purposes. purposes. Tensile Tensile strength strength tests tests were were performed performed on theon the specimen speci- menproduced produced from from the injectionthe injection molding molding process. process. The The molded molded part’s part’s test test was was conducted conducted to determine the effect of fillers on the molded parts. to determine the effect of fillers on the molded parts.

Figure 2. FlowFlow chart. chart.

2.1.2.1. Filler Filler Particle Particle Selection Selection SelectionSelection of of an an appropriate appropriate filler filler particle particle is is very very important important in in ensuring ensuring good good perfor- perfor- mancemance of of an an MEC mold insert. Many Many studies studies have have been been conducted on on various types of thermalthermal and and mechanical mechanical tests tests to to examine examine the the most most influential influential parameters parameters in in the the injection moldingmolding process, process, i.e., i.e., the the cooling cooling time time [15,16,23,27,33]. [15,16,23,27,33]. In In this this research, research, the selection of brassbrass and coppercopper fillersfillers are are based based on on the the properties properties of theseof these materials materials which which offer offer good good ther- thermalmal conductivity conductivity [23, 33[23,33]] while while maintaining maintaining or increasing or increasing the compressive the compressive strength strength [16,27] [16,27]compared compared to other to typesother types of fillers of fillers that havethat have been been used used in previous in previous studies studies [15 ,[15,34].34]. In Inorder order to to overcome overcome these these problems, problems, many many attempts attempts have havebeen been mademade toto loadload epoxy with irregular-shapedirregular-shaped brass brass or or copper copper fillers fillers to to evaluate evaluate their their effectiveness effectiveness in in improving the propertiesproperties of of the the epoxy. epoxy. Table Table 11 presentspresents thethe fillerfiller propertiesproperties suppliedsupplied byby ChengduChengdu HuaruiHuarui IndustrialIndustrial Co., Co., Ltd, Ltd, Ch Chendu,endu, China, China, that that were were used in this study.

TableTable 1. Filler properties.

Filler Filler Shape Average Shape Particle Size Average (mm) Particle Metal SizeContents (mm) (%) Metal Contents (%) Brass BrassIrregular Irregular 20–60 µm 20–60 µm 95 95 Copper Irregular 20–60 µm 99 Copper Irregular 20–60 µm 99

2.2. Sample Preparation 2.2. Sample Preparation Epoxy resin ALWA HT resin M2200 manufactured by ALWA resin systems and porous Epoxy resin ALWA HT resin M2200 manufactured by ALWA resin systems and po- slabs, Gronau, Germany [35], were selected for the tooling matrix, mixed with metal fillers rous slabs, Gronau, Germany [35], were selected for the tooling matrix, mixed with metal of brass (EB) and copper (EC). ALWA HT Resin is characterized by its good electronic fillers of brass (EB) and copper (EC). ALWA HT Resin is characterized by its good electronic insulation with outstanding properties such as high glass transition temperature, high insulation with outstanding properties such as high glass transition temperature, high dis- distortion temperature, low thermal expansion and good chemical resistance to acids, tortion temperature, low thermal expansion and good chemical resistance to acids, alkalis alkalis and organic solvents. Table2 tabulates the various compositions of the metal fillers and organic solvents. Table 2 tabulates the various compositions of the metal fillers (EB and (EB and EC), epoxy resin and hardener. Before mixing the epoxy resin with metal fillers, a EC), epoxy resin and hardener. Before mixing the epoxy resin with metal fillers, a silicon silicon rubber mold was prepared with different geometries to produce the test samples for rubber mold was prepared with different geometries to produce the test samples for various various testing parameters, such as hardness, compression strength, and thermal properties testing parameters, such as hardness, compression strength, and thermal properties accord- according to American Society for Testing and Materials (ASTM) standards [36–38], as ingshown to American in Figure Society3. The mixturefor Testing of epoxy and Mate resinrials with (ASTM) hardener standards material [36–38], has the as following shown in Figurespecifications 3. The mixture as provided of epoxy by resin the with manufacturer hardener material with a mixinghas the following ratio of 100:50 specifications (Epoxy: asHardener) provided and by 45the min manufacturer to 1 h pot lifewith in a liquid mixing form. ratio of 100:50 (Epoxy: Hardener) and 45 min to 1 h pot life in liquid form.

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TableTableTable 2. 2. Composition Composition of of of Metal Metal Metal Epoxy EpoxyEpoxy Composite CompositeComposite (MEC) (MEC)(MEC) for forfor 1 1 1set setset specimen specimenspecimen (thermal, (thermal,(thermal, compression compression andandand hardness). hardness). hardness).

MixingMixingMixing Composition Composition Composition (grams) (grams) (grams) No.No. TotalTotalTotal (100%) (100%) (100%) MetalMetalMetal Fillers Fillers Fillers Epoxy Epoxy Epoxy Resin Resin Resin Hardener Hardener Hardener 1.1. 10%10%10% 7 7g g 7 g60% 60% 60% 42 42 g g 42 g 30% 30% 30% 21 21 g 21g g 70 70 70 g g g 2.2. (EB(EB(EB or or orEC) EC) EC) 20% 20% 20% 14 14 g g 14 53.3% g53.3% 53.3% 37.3 37.3 g 37.3 g g 26.7% 26.7% 26.7% 18.7 18.7 18.7 g g g 70 70 70 g g g 3.3. 30% 30% 30% 21 21 g g 21 46.7% g46.7% 46.7% 32.7 32.7 g 32.7 g g 23.3% 23.3% 23.3% 16.3 16.3 16.3 g g g 70 70 70 g g g

(a()a ) (b(b) )

Figure 3.FigureFigureSpecimen 3. 3. Specimen Specimen preparation: preparation: preparation: (a) silicone ( a()a )silicone rubber silicone mold;rubber rubber ( bmold; )mold; MEC ( b( testb) )MEC MEC samples. test test samples. samples.

AfterAfterAfter mixing mixingmixing the the resin, resin, resin, hardener, hardener, hardener, and and and filler filler filler according according according to to the tothe theprescribed prescribed prescribed composition, composition, composi- thetion,the mixture mixture the mixture is is stirred stirred is stirred manually manually manually until until the untilthe resulting resulting the resulting mixture mixture mixture is is well well isblended blended well blended (within (within (within 5 5to to 10 10 min).5min). to 10 Next, Next, min). the theNext, mixture mixture the mixture was was de-gassed de-gassed was de-gassed in in th the evacuum vacuum in the vacuumcasting casting machine castingmachine machine(CM2000, (CM2000, (CM2000, Cybron Cybron TechnologyCybronTechnology Technology (M) (M) Sdn. Sdn. (M) Bhd, Bhd, Sdn. Peneng, Peneng, Bhd, Peneng,Malaysia) Malaysia) Malaysia) and and then then and poured poured then pouredinto into the the intosilicone silicone the siliconerubber rubber mold.rubbermold. The The mold. mixture mixture The mixturein in the the silicone silicone in the mold silicone mold was was mold then then was pre-cured pre-cured then pre-cured at at room room temperature at temperature room temperature for for 24 24 h. h. ◦ Later,forLater, 24 it h.it was was Later, cured cured it wasat at 180 180 cured °C °C for for at 8 180 8h h in in Can an for oven oven 8 h (Memmert in(Memmert an oven UM200, (MemmertUM200, Memmert Memmert UM200, GmbH GmbH Memmert + +Co. Co. KG,GmbHKG, Schwabach, Schwabach, + Co. KG, Germany) Germany)Schwabach, following following Germany) the the followingmanu manufacturer’sfacturer’s the manufacturer’s recommendation. recommendation. recommendation. It It was was found found thatItthat was after after found the the sample thatsample after is is produced, theproduced, sample sediment sediment is produced, o occursccurs sediment where where the the occurs mixed mixed where filler filler theparticles particles mixed fall fall filler to to theparticlesthe bottom, bottom, fall as toas shown theshown bottom, in in Figure Figure as shown 4. 4. It It can in can Figure be be seen seen4. It that canthat sedimentation besedimentation seen that sedimentation occurs occurs where where occurs brass brass fillerwherefiller showed showed brass filler more more showed sedimentation sedimentation more sedimentation compared compared tocompared to copper copper filler. tofiller. copper Therefore, Therefore, filler. Therefore, parameter parameter param- opti- opti- mizationetermization optimization using using RSM RSM using is is required required RSM is to required to obtain obtain tooptimal optimal obtain sampling sampling optimal samplingwhich which can can which improve improve can the improvethe mate- mate- rialtherial properties. material properties. properties.

(a()a ) (b(b) )

FigureFigureFigure 4. 4. 4. FillerFiller Filler sedimentation sedimentation sedimentation occurring occurring occurring at at sample sample brass brass and and copper: copper: (a ())a brass)brass brass ﬁller;filler; filler; ((bb ()b) copper)copper copper ﬁller. filler.filler. 2.3. Material Properties Testing 2.3.2.3. Material MaterialThe primary Properties Properties concern Testing Testing in selecting the MEC material is to match the material properties thatThe haveThe primary primary to be tested concern concern according in in selecting selecting to the the the ASTM MEC MEC ma standardsmaterialterial is is to (Table to match match3) sothe the that material material the material proper- proper- tiesrequirementties that that have have asto to abe be mold tested tested insert according according is met. to Theseto the the AS propertiesASTMTM standards standards include (Table (Table physical, 3) 3) so so that mechanical, that the the material material and requirementthermalrequirement with as as a a combination amold mold insert insert ofis is met. RTmet. techniques. These These properties properties The tests include include were physical, physical, selected mechanical, basedmechanical, on previ- and and thermalousthermal studies with with that a acombination combination focused on of theof RT RT mechanical techniques techniques and. .The The thermal tests tests were were properties selected selected of based based the MECon on previous previous and its studiesapplicationstudies that that infocused focused the injection on on the the moldingmechanical mechanical process and and thermal [thermal15,39,40 properties ].properties of of the the MEC MEC and and its its appli- appli- cationcation in in the the injection injection molding molding process process [15,39,40]. [15,39,40].

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Table 3. Mechanical and thermal properties test of epoxy with metal ﬁllers.

Test Standards Equipment Used in this Study Vickers Hardness (Matsuzawa VMT-X Series, Hardness ASTM D2240-97 [38] Matsuzawa Co., Ltd, Akita, Japan) Universal Testing Machine (Instron 5900 Series Compressive Strength ASTM D695-96 [37] 50kN, Instron Corporation, Norwood, MA, USA) Thermal Properties Analyzer (Decagon KD2 Pro, Thermal conductivity ASTM C1113 [36] Decagon Devices Inc., Pullman, WA, USA)

2.4. Response Surface Method RSM is a statistical method to plan experiments, study the effect of process variables, obtain empirical input/output relationships, and determine optimal conditions [29,32]. RSM is one of the methods used for optimization which was introduced by Box and Wilson in 1951 [41]. It helps the researcher or experimenter to reach the goal of optimum response such as examining the hardness of samples in this research. Box–Behnken design (BBD) and central composite design (CCD) are RSM-based techniques to model the response in relation to the process parameters (control factors) for the manufacturing of quality composite specimens [30]. In this research, the selected factors and levels are tabulated in Table4 which were developed using the optimization software.

Table 4. Factors and levels of variable parameters.

Factor Process Parameter Unit Low Level (−) High Level (+) A Maximum Curing Temperature ◦C 120 180 B Mixing Time Min 5 15 C Degassing time Min 10 40

Box–Behnken Design (BBD) was selected for RSM according to the number of variable parameters and levels, as shown in Table4. It contains an embedded factorial design with 5 center points which allow for estimation of curvature. Therefore, 17 runs of experiments were generated.

2.5. Develop MEC Mold Insert 2.5.1. Mold Insert Design The 3D model for the thick flat part was designed using Computer-Aided Design (CAD) based on the international standard for multi-purpose plastic injection test samples, ISO 3167: 2002 (E) [42]. The design phase of the mold emphasizes various important characteristics, such as the design of part shape, mold type, mold dimensions, material for mold inserts (core and cavity inserts), and the base of the mold which must be selected properly [6,13]. Figure5 shows the mold insert design with two cavities that are used for this study. The result of fill + Pack analysis obtained from Moldflow simulation software was used to evaluate the packing pressure in the mold cavities and the recommended maximum packing pressure obtained to fill is 70 MPa according to the changes in the mass of the molded parts. Based on this value, the compression test of the MEC material should be higher than the required packaging pressure to avoid failure occurring on the MEC mold insert during the molding process. Materials 2021, 14, x FOR PEER REVIEW 7 of 15

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(a) (b)

Figure 5. Mold inserts designed for the thick flat part: (a) part design; (b) core insert design. (a) (b) 2.5.2. Fabrication of Mold Inserts for a Hybrid Mold FigureFigure 5. Mold 5. Moldinserts inserts designed designed for the for thick the thickflat part: flat ( part:a) part (a) design; part design; (b) core (b) insert core insert design. design. The design of the hybrid mold and the cross-section of the assembly drawing are 2.5.2. Fabrication of Mold Inserts for a Hybrid Mold illustrated2.5.2. in Fabrication Figure 6. The of Mold two-plate Inserts mold for afor Hybrid the thick Mold flat part as specimen was fabri- catedThe using design sets of of inserts the hybrid with moldstraight and cooling the cross-section channels. Two of thecombinations assembly drawingof materials are The design of the hybrid mold and the cross-section of the assembly drawing are usedillustrated were inP20 Figure as a6 .mold The two-platebase and moldMEC for as themold thick inserts flat part (core as specimenand cavity was inserts). fabricated The illustrated in Figure 6. The two-plate mold for the thick flat part as specimen was fabri- fabricationusing sets ofsteps inserts for the with MEC straight mold cooling inserts channels.include the Two degassing combinations of the epoxy of materials resin mixed used cated using sets of inserts with straight cooling channels. Two combinations of materials withwere metal P20 as fillers a mold in base a vacuum and MEC chamber as mold to inserts remove (core air and bubbles, cavity the inserts). pre-curing The fabrication at room used were P20 as a mold base and MEC as mold inserts (core and cavity inserts). The temperature,steps for the MECand the mold post-curing inserts include in the the oven degassing based on of the the control epoxy resin factors mixed of curing with metal tem- fabrication steps for the MEC mold inserts include the degassing of the epoxy resin mixed peraturefillers in aand vacuum duration chamber of curing to remove time [12,13 air bubbles,,27,43–45]. the After pre-curing the post-curing at room temperature, process, the with metal fillers in a vacuum chamber to remove air bubbles, the pre-curing at room finishingand the post-curing work using in machining the oven basedoperations on the for control fitting factors the mold of curing standard temperature components and temperature, and the post-curing in the oven based on the control factors of curing tem- (ejectorduration pins, of curing sprue timebushing, [12,13 etc.),27, 43were–45 ].perf Afterormed the post-curingto obtain the process, required the dimensions finishing work and perature and duration of curing time [12,13,27,43–45]. After the post-curing process, the tousing allow machining adjustments operations for fitting for the fitting mold the insert mold into standard the mold components base. The (ejector hybrid pins, mold sprue was finishing work using machining operations for fitting the mold standard components usedbushing, with etc.) seven were K-Type performed thermocouples to obtain the to record required the dimensions temperature and profile to allow of adjustmentsthe ambient (ejector pins, sprue bushing, etc.) were performed to obtain the required dimensions and temperaturefor fitting the (T5), mold the insert temperatur into thee of mold the base.coolants The at hybrid the inlet mold (T1 wasand usedT3), and with the seven outlet K- to allow adjustments for fitting the mold insert into the mold base. The hybrid mold was (T2Type and thermocouples T4) of the core to and record cavity, the temperatureand the temperature profile of of the the ambient core (T6) temperature and the cavity (T5), (T7) the used with seven K-Type thermocouples to record the temperature profile of the ambient duringtemperature experimental of the coolants work. The at the thermocouples inlet (T1 and are T3), connected and the outlet to the (T2 Data and Acquisition T4) of the coreSys- temperature (T5), the temperature of the coolants at the inlet (T1 and T3), and the outlet temand (DAQ) cavity, and(TcDAQ-9188, the temperature National of theInstruments core (T6) andCorporation, the cavity Austin, (T7) during TX, USA), experimental and the (T2 and T4) of the core and cavity, and the temperature of the core (T6) and the cavity (T7) recordedwork. The data thermocouples are saved on are the connected computer to and the Datathen Acquisitionconverted for System further (DAQ) analysis (TcDAQ- into during experimental work. The thermocouples are connected to the Data Acquisition Sys- graphical9188, National form. Instruments Corporation, Austin, TX, USA), and the recorded data are saved on thetem computer (DAQ) and (TcDAQ-9188, then converted National for further Instruments analysis Corporation, into graphical Austin, form. TX, USA), and the recorded data are saved on the computer and then converted for further analysis into graphical form.

(a) (b)

Figure 6. HybridHybrid mold mold design design was was instrumented instrumented with with seven seven sensors: sensors: (a) (hybrida) hybrid mold mold design; design; (b) schematic (b) schematic diagram diagram con- nectionconnection of the of thethermocouples. thermocouples. (a) (b)

Figure 6. Hybrid mold design was instrumented with seven sensors: (a) hybrid mold design; (b) schematic diagram con- 3. Results Results and and Discussion Discussion nection of the thermocouples. 3.1. Thermal Thermal Conductivity Conductivity Results Results The3. Results results indicateindicate and Discussion thatthat the the thermal thermal conductivity conductivity of of the the copper copper filler filler is higheris higher than than the thebrass brass filler3.1. filler Thermal of irregular of irregular Conductivity shape, shape, as Results shown as shown in Figure in Figure7. The 7. The value value of thermal of thermal conductivity conductivity for unfilled epoxy was in the range 0.6–0.9 W/m·K, while commercially available aluminum The results indicate that the thermal conductivity of the copper filler is higher than filler epoxy composite is within 1.2 to 1.43 W/m·K. The rapid increase in thermal con- the brass filler of irregular shape, as shown in Figure 7. The value of thermal conductivity ductivity can be attributed to the onset of interactions between irregular-shaped fillers

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for unfilled epoxy was in the range 0.6–0.9 W/m∙K, while commercially available alumi- Materials 2021, 14, 665 for unfilled epoxy was in the range 0.6–0.9 W/m∙K, while commercially available alumi-8 of 15 num filler epoxy composite is within 1.2 to 1.43 W/m∙K. The rapid increase in thermal num filler epoxy composite is within 1.2 to 1.43 W/m∙K. The rapid increase in thermal conductivity can be attributed to the onset of interactions between irregular-shaped fillers conductivity can be attributed to the onset of interactions between irregular-shaped fillers when exceeding 10% by weight composition [33] compared to spherical-shaped fillers when exceeding 10% by weight composition [33] compared to spherical-shaped fillers whenused by exceeding previous 10%researchers by weight [3,16,27,28,46]. composition A rapid [33] compared increase in to thermal spherical-shaped conductivity fillers was used by previous researchers [3,16,27,28,46]. A rapid increase in thermal conductivity was notused observed by previous at low researchers compositions [3,16, 27below,28,46 10]. Awt%, rapid due increase to the indiffusion thermal effect conductivity in the bulk was notnot observed observed at at low low compositions compositions below below 10 10 wt%, wt%, due due to to the the diffusion diffusion effect effect in in the bulk matrix almost without interaction. The most important finding is that irregular-shaped matrixmatrix almost almost without without interaction. interaction. The The most most important important finding finding is is that irregular-shaped fillers can rapidly increase the thermal conductivity. Copper filler is a thermal conductiv- fillersfillers can can rapidly increase the thermalthermal conductivity.conductivity. Copper Copper filler filler is is a a thermal thermal conductivity conductivity enhancing element and this rapid increase in thermal conductivity is obviously due to ityenhancing enhancing element element and and this this rapid rapid increase increase in thermalin thermal conductivity conductivity is obviously is obviously due due to the to the initial interaction of irregular particle filler shapes. This finding is similar to a previous theinitial initial interaction interaction of of irregular irregular particle particle filler filler shapes. shapes. This This finding finding is is similarsimilar toto a previous study in which the thermal conductivity of the composites increased with the addition of studystudy in in which which the the thermal thermal conductivity conductivity of of the the composites composites increased increased with with the the addition addition of of the filler to the epoxy mixture [24]. thethe filler filler to to the the epoxy epoxy mixture mixture [24]. [24].

4.5 4.5 3.85 4 3.85 4 3.5 3.5 3.33 3 3.33 3 K) ∙ 2.5 2.12 K) ∙ 2.5 2.12 2

(W/m 2 1.26 1.77 (W/m 1.5 1.26 1.5 0.86 1.77 1 0.86 1.14 Brass

Thermal Conductivity 1 1.14 Brass Thermal Conductivity 0.5 0.5 Copper 0 Copper 0 0% 10% 20% 30% 0% 10% 20% 30% Filler Composition (wt%) Filler Composition (wt%)

Figure 7. Effects of fillers on thermal conductivity. FigureFigure 7. 7. EffectsEffects of of fillers fillers on on thermal thermal conductivity. conductivity. 3.2. Compression Results 3.2.3.2. Compression Compression Results Results In the injection molding process, the compression test strength of the MEC mold in- InIn the the injection injection molding molding process, process, the the compression compression test test strength strength of the of theMEC MEC mold mold inserts is an important material property to withstand the clamping strength and packing sertsinserts is isan an important important material material property property to to withstand withstand the the clamping clamping strength strength and and packing packing pressure in the mold cavity and is useful for extending the life of the epoxy mold [47]. As pressurepressure in in the the mold mold cavity cavity and and is isuseful useful for for extending extending the the life life of the of theepoxy epoxy mold mold [47]. [ 47As]. Aspresented presented in Figure in Figure 8, brass8, brass and andcopper copper fillers fillers at 20 atwt% 20 composition wt% composition indicate indicate the highest the presented in Figure 8, brass and copper fillers at 20 wt% composition indicate the highest averagehighest averagevalue of value compressive of compressive strength strength of 104 of 104and and 90 90MPa, MPa, respectively. respectively. Both Both fillersfillers average value of compressive strength of 104 and 90 MPa, respectively. Both fillers demonstrated a downward trend of its compre compressivessive strength after 20 wt% composition. demonstrated a downward trend of its compressive strength after 20 wt% composition. However, thethe graphgraph dropped dropped gradually gradually when when adding adding filler filler composition composition more more than than 25–30% 25– However, the graph dropped gradually when adding filler composition more than 25– wt.30% Previous wt. Previous studies studies [15,23 [15,23,27,48],27,48] on compression on compression strength strength results results indicated indicated a non-linear a non- 30% wt. Previous studies [15,23,27,48] on compression strength results indicated a non- lineartrend betweentrend between the filler the weight filler weight percentage percentage and the and compression the compression strength. strength. Adding Adding more linear trend between the filler weight percentage and the compression strength. Adding morefillers fillers to the to epoxy the epoxy matrix matrix beyond beyond 20 wt% 20 decreases wt% decreases the compressive the compressive strength strength because thebe- more fillers to the epoxy matrix beyond 20 wt% decreases the compressive strength be- causeepoxy the matrix epoxy starts matrix becoming starts becoming more viscous, more the viscous, porosity the is porosity increased is andincreased the fillers and arethe cause the epoxy matrix starts becoming more viscous, the porosity is increased and the fillersagglomerated, are agglomerated, consequently consequent reducingly thereducing stiffness the [15 stiffness]. [15]. fillers are agglomerated, consequently reducing the stiffness [15].

110 110 104 105 104 105 98 100 97 98 100 97 95 90 95 90 90 87 90 87 (MPa) 81 (MPa) 85 80 85 80 81 80 80 Brass

Compressive Strength 75 Brass

Compressive Strength 75 70 Copper 70 Copper 0% 10% 20% 30% 0% 10% 20% 30% Filler Composition (wt%) Filler Composition (wt%) Figure 8. Effects of ﬁllers on compressive strength.

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Materials 2021, 14, 665 9 of 15 Figure 8. Effects of fillers on compressive strength.

3.3.3.3. Hardness Hardness Results Results TheThe hardness hardness of ofthe the epoxy epoxy matrix matrix composite composite is another is another important important parameter parameter affecting affecting thethe durability durability and and life life of ofthe the mold. mold. Figure Figure 9 shows9 shows the the results results of of hardness hardness variations variations with with differentdifferent filler filler ratios. ratios. Brass Brass fillers fillers showed showed better better hardness hardness compared compared with with copper copper fillers. fillers. TheThe curve curve of ofhardness hardness reflects reflects an an upward upward tren trend,d, having having a apositive positive slope. slope. This This result result is is similarsimilar to tothose those of ofSenthilkumar Senthilkumar et al. et al.[28] [28 and] and Srivastava Srivastava and and Verma Verma [23], [23 where], where hardness hardness graduallygradually increased increased with with the the increase increase in infiller filler material. material.

25 24.41 24.5 24.21 23.83 24 23.56 23.5 23.68 23 22.52 Hardness (Hv) 22.35 Brass 22.5 22 Copper 0% 10% 20% 30% Filler Composition (wt%) FigureFigure 9. Effects 9. Effects of fillers of ﬁllers on onthe the hardness. hardness.

3.4.3.4. Optimization Optimization Results Results TheThe result result of ofthe the hardness hardness test test from from the the Box–Behnken Box–Behnken Design Design (BBD) (BBD) was was generated generated using Design-Expert software to determine the inﬂuence of the mixing time, degassing using Design-Expert software to determine the influence of the mixing time, degassing time, and maximum curing temperature. The experimental results of the hardness were time, and maximum curing temperature. The experimental results of the hardness were obtained from the 17 runs’ specimens. The values of hardness of the specimens were obtained from the 17 runs’ specimens. The values of hardness of the specimens were meas- measured using Vickers Hardness and are tabulated in Table5. ured using Vickers Hardness and are tabulated in Table 5. Table 5. Experimental results of hardness strength. Table 5. Experimental results of hardness strength ◦ Run A) Curing TempA) Curing ( C) Temp B) Mixing Time, (min) C) Degassing Time (min) HardnessHardness (Hv) Run B) Mixing Time, (min) C) Degassing Time (min) 1 120(°C) 5 25(Hv) 24.23 21 180120 5 5 25 25 24.23 26.23 32 120180 15 5 25 25 26.23 25.54 43 180120 15 15 25 25 25.54 24.90 5 120 10 10 23.00 4 180 15 25 24.90 6 180 10 10 23.50 75 120120 10 10 40 10 23.00 26.37 86 180180 10 10 40 10 23.50 26.50 97 150120 5 10 10 40 26.37 22.72 108 150180 15 10 10 40 26.50 22.47 119 150150 5 5 40 10 22.72 26.70 1210 150 150 15 15 40 10 22.47 26.27 1311 150 150 10 5 25 40 26.70 24.13 1412 150 150 10 15 25 40 26.27 24.32 15 150 10 25 24.37 13 150 10 25 24.13 16 150 10 25 24.43 14 150 10 25 24.32 17 150 10 25 24.28 15 150 10 25 24.37 16 150 10 25 24.43 173.4.1. Analysis150 of Results 10 25 24.28 ANOVA is a statistical analysis tool used to test the differences between two or more 3.4.1.means Analysis across of the Results different groups and to investigate the relationship between independent and dependent variables [30,32,41]. In this study, ANOVA is one of the initial methods in determining the factors that affect the hardness value of the specimens. In deciding the

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signiﬁcance of the process parameters, p-value must be used along with the F statistic and F test to correctly interpret the results, of which the value of P must be smaller than the value of alpha (α = 0.05) [49]. The value of F can be determined based on the number of degrees of freedom and the total number of degrees of freedom of the factors with α = 0.05 [49]. Table6 presents the results of the ANOVA obtained.

Table 6. Analysis of Variances (ANOVA) of Ra.

Source Sum of Squares df Mean Square F Value p-Value Prob > F Model 29.37 6 4.89 100.61 <0.0001 signiﬁcant A-Curing 0.50 1 0.50 10.18 0.0097 Temperature B-Mixing time 0.06 1 0.06 1.26 0.2880 C-Degassing 25.03 1 25.03 514.52 <0.0001 time AB 1.74 1 1.74 35.82 0.0001 AA 1.55 1 1.55 31.96 0.0002 BB 0.39 1 0.39 8.04 0.0177 Residual 0.49 10 0.05 Lack of Fit 0.44 6 0.07 5.65 0.0578 not signiﬁcant Pure Error 0.05 4 0.01 Cor Total 29.85 16

From the results of the analysis obtained, this model is significant due to the larger F-value compared to the p-value which is 0.0001. This model also shows non-significant lack of fit, which is good. On the other hand, from the F-value and Prob > F in the ANOVA result obtained as shown in Table6, the most significant factor affecting the hardness is degassing time, which is 35.91%, followed by curing temperature which is 3.53% and mixing time which is 2.08%. Based on the ANOVA results, high values of R2 and adjusted-R2 indicate a good explanation of the variability from the selected model (Table7). It indicates that this model can predict the hardness result with 98.37% accuracy as shown in Figure 10.

Table 7. Adequacy of the model.

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0.2205 0.9837 0.9739

28 27 26 25 24

23 Experiment Hardness, Hv 22 Prediction 21 20 1234567891011121314151617 DOE runs FigureFigure 10. 10.Experiment Experiment versus versus prediction prediction results. results.

3.4.2. Confirmation Experiment. Table 8 shows the optimal parameters that can maximize the hardness and the optimization result of RSM obtained by using Design Expert 7 software. Optimal hardness is achieved and proven by conducting validation experiments on the specimens produced according to the optimal parameters proposed.

Table 8. Optimal parameters for hardness strength.

Parameters Units Optimal Values (A) Curing Temperature °C 174.78 (B) Mixing time Min 6.66 (C) Degassing time Min 38.92 Response Hardness (Predicted) Hv 27.09 Hardness (Experimental) Hv 27.53

4. Mold Inserts Trials The fabrication of MEC mold inserts is based on the results of mechanical and thermal tests conducted by selecting the appropriate composition. The composition is set at 30 wt% due to the high thermal conductivity value offered (Figure 7) and the value of compression strength (Figure 8) is above the packing pressure required in the mold cavities which is more than 70 MPa (based on simulation studies using Moldflow simulation software). Based on the compression results, at 30 wt%, EB and EC mold inserts can withstand maximum pressures of 98 and 81 MPa, respectively. Several samples of mold inserts fabricated using MEC material are produced and tested using an injection molding machine. Acrylonitrile Butadiene Styrene (ABS) material was used as a plastic resin in these trials.

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3.4.2. Conﬁrmation Experiment. Table8 shows the optimal parameters that can maximize the hardness and the optimization result of RSM obtained by using Design Expert 7 software. Optimal hardness is achieved and proven by conducting validation experiments on the specimens produced according to the optimal parameters proposed.

Table 8. Optimal parameters for hardness strength.

Parameters Units Optimal Values (A) Curing Temperature ◦C 174.78 (B) Mixing time Min 6.66 (C) Degassing time Min 38.92 Response Hardness (Predicted) Hv 27.09 Hardness (Experimental) Hv 27.53

4. Mold Inserts Trials The fabrication of MEC mold inserts is based on the results of mechanical and thermal tests conducted by selecting the appropriate composition. The composition is set at 30 wt% due to the high thermal conductivity value offered (Figure7) and the value of compression strength (Figure8) is above the packing pressure required in the mold cavities which is more than 70 MPa (based on simulation studies using Moldﬂow simulation software). Based on the compression results, at 30 wt%, EB and EC mold inserts can withstand maximum pressures of 98 and 81 MPa, respectively. Several samples of mold inserts fabricated using MEC material are produced and tested using an injection molding machine. Acrylonitrile Butadiene Styrene (ABS) material was used as a plastic resin in these trials.

4.1. Simulation Results of Cooling Time for MEC Mold Inserts Using Simulation Software In this research, transient thermal analysis using simulation software (Ansys Fluent 180, ANSYS, Inc., Canonsburg, PA, USA) was used to evaluate the temperature distribution and cycle time during the molding cycle in the mold inserts. The setting of simulation parameters is divided into two steps; the heating phase to reach the melting temperature of 245 ◦C and a cooling phase to reach the ejection temperature of 110 ◦C before parts were ejected out from the mold. The convection coefﬁcient for the cooling channel is 5098 W/m2 ◦C. Figure 11 and Table9 show the results of temperature distribution and cycle time for EA, EB, and P20 mold inserts from Ansys Fluent simulation software. It can be seen that the EC mold insert offers a better cycle time than the EB mold insert. Table9 shows that the difference in cycle time compared to the P20 mold insert is increasing two times and 2.33 times for EC and EB, respectively. Although the cycle time results obtained from MEC mold inserts are higher than P20 mold inserts, the use of this type of ﬁller with irregular shape for low volume production has achieved less cycle time when compared to results from previous researchers [12,16,50] who used MEC mold inserts.

Table 9. Result of cooling time.

Mold Material Cooling Time, tc (s) Comparison of MEC with P20 Material EB 19.48 EC > 2.33 time increasing of P20 EC 16.8 EC > 2 time increasing of P20 P20 8.35 - Materials 2021, 14, x FOR PEER REVIEW 12 of 15

EA, EB, and P20 mold inserts from Ansys Fluent simulation software. It can be seen that the EC mold insert offers a better cycle time than the EB mold insert. Table 9 shows that the difference in cycle time compared to the P20 mold insert is increasing two times and 2.33 times for EC and EB, respectively. Although the cycle time results obtained from MEC Materials 2021, 14, x FOR PEER REVIEWmold inserts are higher than P20 mold inserts, the use of this type of filler with irregular12 of 15 shape for low volume production has achieved less cycle time when compared to results from previous researchers [12,16,50] who used MEC mold inserts.

EA, EB, and P20 mold inserts from Ansys Fluent simulation software. It can be seen that the EC mold insert offers a better cycle time than the EB mold insert. Table 9 shows that the difference in cycle time compared to the P20 mold insert is increasing two times and 2.33 times for EC and EB, respectively. Although the cycle time results obtained from MEC Materials 2021, 14, 665 mold inserts are higher than P20 mold inserts, the use of this type of filler with irregular12 of 15 shape for low volume production has achieved less cycle time when compared to results from previous researchers [12,16,50] who used MEC mold inserts.

(a) (b) (c) Figure 11. Result of transient thermal analysis: (a) EB mold insert; (b) EC mold insert; (c) P20 mold insert.

Table 9. Result of cooling time.

Mold Material Cooling Time, (s) Comparison of MEC with P20 Material

EB 19.48 EC > 2.33 time increasing of P20 (a) EC (b 16.8) EC > 2 time(c) increasing of P20 P20 8.35 - Figure 11. Result of transient thermal analysis: (a) EB mold insert; (b) EC mold insert;insert; ((c)) P20P20 moldmold insert.insert.

Table4.2.4.2. Experimental Experimental9. Result of cooling Results Results time. of of Cooling Cooling Time Time for for MEC MEC Mold Mold Inserts Inserts Using Using Machine Machine Injection InjectionMolding Molding Mold Material Cooling Time, (s) Comparison of MEC with P20 Material TheThe molded molded parts parts for for the the tensile tensile strength strength are are produced produced by by different different MEC MEC mold mold insert insert EB 19.48 EC > 2.33 time increasing of P20 materialsmaterials including including the the P20 P20 mold mold insert, insert, and and the the injection injection process process is is used used with with a a cooling cooling systemsystemEC (Figure (Figure 12 12).). The part part 16.8 was was molded molded using using Acrylonitrile Acrylonitrile EC > 2 time Butadiene increasing Butadiene Styrene of Styrene P20 (ABS) (ABS) ma- material.terial. P20From From the the actual actual trials, trials,8.35 the the total total cycle cycle time time of of the the injection injection molding - molding process process using using EB EBand and EC EC mold mold inserts inserts are are31 and 31 and24 s, 24 respecti s, respectively.vely. The dimensions The dimensions and mass and of mass the molded of the 4.2.moldedparts Experimental are parts consistent are Results consistent as ofwell Cooling as as well the Time as conditio the for condition MECn of Mold the of MECInserts the MEC mold Using mold without Machine without any Injection anydefects defects after Moldingafterproducing producing 100 100shots. shots. The molded parts for the tensile strength are produced by different MEC mold insert materials including the P20 mold insert, and the injection process is used with a cooling system (Figure 12). The part was molded using Acrylonitrile Butadiene Styrene (ABS) material. From the actual trials, the total cycle time of the injection molding process using EB and EC mold inserts are 31 and 24 s, respectively. The dimensions and mass of the molded parts are consistent as well as the condition of the MEC mold without any defects after producing 100 shots.

(a) (b) (c)

FigureFigure 12. 12.(a ()a MEC) MEC mold mold inserts; inserts; ((bb)) moldmold inserts installed installed to to mold mold based based for for injection injection molding molding process; process; (c) ejected (c) ejected parts. parts.

5.5. Conclusions Conclusions Mold inserts of injection mold for the injection molding process can be fabricated using alternative materials other than steel by using rapid tooling techniques for low volume

production. MEC mold inserts can be used successfully to mold the plastic parts up to (a) 100 shorts using ABS material(b) without any defects on the mold(c) inserts. By fabricating a hybrid mold in this research (MEC materials as mold inserts), most aspects related to the Figure 12. (a) MEC mold inserts; (b) mold inserts installed to mold based for injection molding process; (c) ejected parts. tool design, material performance, and influence on molded part properties are identified 5.and Conclusions understood. The investigation on epoxy resin with the addition of metal fillers (brass and copper) was able to establish a new material as mold inserts for the injection molding process. The addition of brass (EB) and copper (EC) in epoxy resin is able to improve the material performance in terms of mechanical and thermal properties. Theoretically, the findings from this current research are:

1. The selection of the ﬁller composition at 20–30 wt% as a mold insert is based on the maximum value of the compression strength test obtained. 2. The thermal conductivity and hardness of MEC increased with a positive slope when the composition of the ﬁller on the epoxy matrix increased. Materials 2021, 14, 665 13 of 15

3. Brass fillers demonstrated a good effect for hardness and compression properties, while copper filler offered better thermal conductivity of the MEC produced. 4. The optimum parameters during the preparation of MEC material showed that the degassing time to remove bubbles from the mixture is the most important control factor (35.91%), which reduces voids and improves the structure of the epoxy matrix, followed by curing temperature (3.53%) and finally mixing time (2.08%). The future work will continue with the multi-optimization of the compression and thermal conductivity properties by considering the combination of wt% composition for both brass and copper fillers.

Author Contributions: Conceptualization, R.H., S.S., S.Z.A.R., M.M.A.B.A., and M.T.M.K.; data curation, R.H., M.N., and M.H.M.H.; formal analysis, R.H., and M.H.M.H., and M.A.S.; investigation, R.H., and M.N.; methodology, R.H., M.T.M.K., and S.Z.A.R.; project administration, S.S., R.H., and M.T.M.K.; software, J.J.W., K.B., and M.N.; validation, S.S., S.Z.A.R., R.H., M.N., and M.H.M.H.; writing of review and editing, S.S., M.A.S., J.J.W., K.B., M.M.A.B.A. and S.Z.A.R. All authors have read and agreed to the published version of the manuscript. Funding: The authors wish to thank the Ministry of Higher Education Malaysia and Research Management Centre of UTM and UniMAP for the collaboration and financial support of this study through the UTM RUG Grants 06G38, 07G23 and FRGS/1/2020/TK0/UNIMAP/03/19. For the publishing fees, authors paid the APCs using their own funds. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Conflicts of Interest: The authors declare no conflict of interest.

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