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The distance between tie bars of the machine is 254mm.Therefore, the maximum width of the mould plate shouldnot exceed this distance. Furthermore, 4mm space had beenreserved between the two tie bars and the mould for mouldsetting-up and handling purposes. This gives the final max-imum width of the mould as 250mm. The standard mouldbase with 250mm×250mmis employed. Themould base isfitted to themachine usingMatex clamp at the upper right andlower left corner of the mould base or mould platen. Dimen-sions of other related mould plates are shown in Table 1.The mould had been designed with clamping pressurehaving clamping force higher than the internal cavity force(reaction force) to avoid flashing from happening.Based on the dimensions provided by standard mould set,thewidth and the height of the core plate are 200 and 250mm,respectively.These dimensions enabled design of two cavitieson core plate to be placed horizontally as there is enoughspace while the cavity plate is left empty and it is only fixedwith sprue bushing for the purpose of feedingmolten plastics.Therefore, it is only one standard parting line was designed atTable 1Mould plates dimensions.Components Size (mm)−width×height×thicknessTop clamping plate 250×250×25Cavity plate 200×250×40Core plate 200×250×40Side plate/support plate 37×250×70Ejector-retainer plate 120×250×15Ejector plate 120×250×20Bottom clamping plate 250×250×25 the surface of the product. The product and the runner werereleased in a plane through the parting line during mouldopening.Standard or side gatewas designed for thismould.The gateis located between the runner and the product. The bottomland of the gate was designed to have 20◦ slanting and hasonly 0.5mm thickness for easy de-gating purpose. The gatewas also designed to have 4mm width and 0.5mm thicknessfor the entrance of molten plastic.In the mould design, the parabolic cross section type ofrunnerwas selected as it has the advantage of simplermachin-ing in one mould half only, which is the core plate in thiscase. However, this type of runner has disadvantages such asmore heat loss and scrap comparedwith circular cross sectiontype. This might cause the molten plastic to solidify faster.
This problem was reduced by designing in such a way thatthe runner is short and has larger diameter, which is 6mm indiameter.It is important that the runner designed distributesmaterialor molten plastic into cavities at the same time under thesame pressure and with the same temperature. Due to this,the cavity layout had been designed in symmetrical form.Another design aspect that is taken into consideration wasair vent design. The mating surface between the core plateand the cavity plate has very fine finishing in order to preventflashing fromtaking place.However, this can cause air to trapin the cavity when the mould is closed and cause short shotor incomplete part. Sufficient air vent was designed to ensurethat air trap can be released to avoid incomplete part fromoccurring.The cooling system was drilled along the length of thecavities and was located horizontally to the mould to alloweven cooling. These cooling channels were drilled on bothcavity and core plates. The cooling channels provided suffi-cient cooling of themould in the case of turbulent flow. Fig. 2shows cavity layout with air vents and cooling channels oncore plate.In this mould design, the ejection system only consists ofthe ejector retainer plate, sprue puller and also the ejectorFig. 2. Cavity layout with air vents and cooling channels.plate. The sprue puller located at the center of core plate notonly functions as the puller to hold the product in positionwhen the mould is opened but it also acts as ejector to pushthe product out of the mould during ejection stage. No addi-tional ejector is used or located at product cavities becausethe product produced is very thin, i.e. 1mm. Additional ejec-tor in the product cavity area might create hole and damageto the product during ejection.Finally, enough tolerance of dimensions is given consid-eration to compensate for shrinkage of materials.Fig. 3 shows 3D solid modeling as well as the wireframemodeling of the mould developed using Unigraphics.3. Results and discussion3.1. Results of product production and modificationFrom the mould designed and fabricated, the warpagetesting specimens produced have some defects during trialrun. The defects are short shot, flashing and warpage. Theshort shot is subsequently eliminated bymilling of additionalair vents at corners of the cavities to allow air trapped to escape. Meanwhile, flashing was reduced by reducing thepacking pressure of the machine. Warpage can be controlledby controlling various parameters such as the injection time,injection temperature and melting temperature.After these modifications, the mould produced high qual-ity warpage testing specimen with low cost and requiredlittle finishing by de-gating. Fig. 4 shows modifications ofthe mould, which is machining of extra air vents that caneliminate short shot.3.2. Detail analysis of mould and productAfter themould and productswere developed, the analysisofmould and the product was carried out. In the plastic injec-tion moulding process, molten ABS at 210 ◦C is injected intothe mould through the sprue bushing on the cavity plate anddirected into the product cavity.