• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2342-2354
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• 2002

The present study has numerically predicted both the flow -induced and thermally-induced residual stresses and birefringence in injection o. injection/compression molded center -gated disks. Analysis system for entire molding process was developed based on an ap propriate physical modeling including a nonlinear viscoelastic fluid model, stress-optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling a nd typical numerical analysis results of residual stresses and birefringence in the injection molded center-gated disk. Thermal residual stress was found to be extensional near the center, compressive near the surface and tend to become toward tensional at the surface. A double-hump profile was obtained across the thickness in birefringence distribution: nonzero birefringence is found to be thermally induced, the outer peak is due to the shear flow and subsequent stress relaxation during the filling stage a nd the inner peak is due to the additional shear flow and stress relaxation during the packing stage. Predicted birefringence including both the flow -induced and thermally-induced one becomes quite similar to the experimental one.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.29-34
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• 2002

This paper presents formation of ejector-pin hollowness in injection molding. Injection molding process is widely used in production of plastic part for good dimensional accuracy and high productivity. However, the injection molding leaves ejector-pin hollowness on pal, which causes bad part surface and quality. Dimensions and profiles of ejector-pin hollowness are measured for formation or ejector-pin hollowness. The formation of ejector-pin hollowness is traced with dimensions and profiles of ejector-pin hollowness. The compression force and moment cause ejector-pin to form hollowness on part surface.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.823-828
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• 1994

Dispersion condition of Si3N4 powder in molten wax was established by comparing relative viscosity of mixture with 20 vol% solids loading, while the evaluation of compression-molded sample was demonstrated as an effective method for developing a binder system for injection molding. The best dispersion of Si3N4 powder in molten wax was achieved when Si3N4 powder was treated with 5% stearic acid, and the critical powder volume fraction was determined to be about 0.51 from density measurement of compression-molded samples. Samples containing polar secondary binder showed markedly improved green strength, higher thermal expansion and increased wicking rate in the early stage.

• Transactions of Materials Processing
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• v.19 no.5
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• pp.296-304
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• 2010

It is still needed to study the effect of process conditions on the final properties of injection-molded parts for producing precision optical products. Especially, the optical anisotropy, i.e., birefringence, is a significant factor to affect the function of many optical components. In the present study we have focused on the effect of holding and compression processes on the birefringence remaining in the transparent disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of holding pressure, which came from the flow in packing stage. However, more uniform birefringence distribution than injection-only cases could be found in injection/compression cases. Depends on the process condition even the flow reversal could be found from the distribution of extinction angle. Finally, graphical representation of optical indicatrix was added for better understanding the final structure of injection-only and injection/compression cases.

• Transactions of Materials Processing
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• v.25 no.6
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• pp.402-408
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• 2016

A manufacturing technology of carbon fiber composites with thermoplastic polymer pellets and continuous woven fiber was investigated using a compression molding process. To secure the impregnation of resin into the porosity of fabric the composite specimens were prepared with general injection-molding grade polypropylene pellets and low viscosity polycarbonate pellets. Tensile tests of polypropylene and polycarbonate composites were performed. Polycarbonate composites showed higher fracture strength than that of polypropylene composites because of the difference of matrix properties. However, the increase rate of strength was lower than that of polypropylene composites due to the difference of coherence between matrix and reinforcement. To investigate the effect of carbon fiber volume fraction on the fracture strength variation polypropylene composites with different volume fraction were compression molded and tensile tests were performed together. It was shown that the fracture strength of the polypropylene composites increased by 3.2, 5.4 and 6.9 times with the increase of carbon fabric volume fraction of 0.256, 0.367, and 0.480, respectively.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.3
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• pp.360-368
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• 2003

Statement of Problem: The residual monomer of denture base materials causes hypersensitivity on oral mucosa and intereferes with the mechanical properties of the cured resin. The amount of residual monomer is influenced by materials, curing cycle, processing method, and etc. Purpose: The aim of this study was to investigate the residual methyl methacrylate(MMA) content of injection molded denture base polymer, and to compare this with the self-cured resin and the conventional compression molded heat-cured resin. Materials and Methods: Disc shaped test specimens (50mm in diameter and 3mm thick) were prepared in a conventional flasking technique with gypsum molding. One autopolymerized denture base resins (Vertex Sc. Dentimex. Netherlands) and two heat-cured denture base resins (Vertex RS. Dentimex. Netherlands, Ivocap. Ivoclar Vivadent, USA) were used. The three types of specimens were processed according to the manufacturer's instruction. After polymerization, all specimens were stored in the dark at room temperature for 7 days. There were 10 specimens in each of the test groups. 3-mm twist drills were used to obtain the resin samples and 650mg of the drilled sample were collected for each estimation. Gas chromatography (Agillent 6890 Plus Gas Chromatograph, Agillent Co, USA) was used to determine the residual MMA content of 10 test specimens of each three types of polymer. Results: The residual monomer content of injection molded denture base resins was $1.057{\pm}0.141%$. The residual monomer content of injection molded denture base resins was higher than that of compression molded heat cured resin ($0.867{\pm}0.169%$). However, there was no statistical significant difference between two groups (p>0.01). The level of residual monomer in self cured resin($3.675{\pm}0.791$) was higher than those of injection molded and compression molded heat cured resins (p<0.01). Conclusion: With respect to ISO specification pass / fail test (2.2% mass fraction) of residual monomer, injection molding technique($1.057{\pm}0.141%$) is a clinically useful and safe technique in terms of residual monomer.

• Journal of the korean Society of Automotive Engineers
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• v.18 no.5
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• pp.96-120
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• 1996

현재 자동차용 복합재료를 생산하는데 유리한 제조방법으로는 압축성형 (Compression Molding), 액상성형(Liquid Molding), 인발성형(Pultrusion), 필라멘트 와인딩성형(Filament Winding)등이 있다. 압축성형은 현재 자동차 외장부품 성형에 널리 알려져 있는 SMC(Sheet Molding Compound)성형, 최근에 많은 연구가 되고 있는 LMPC(Low Pressure Molding Compound)성형, GMT(Glass Mat Reinforced Thermoplastics)성형 등이 있다. 액상성형은 RTM(Resin Transfer Molding)과 VARI (Vacuum Assisted Injection Molding), SRIM(Structure Reaction Injection Molding) 등이 있으며, 자동차 산업뿐만 아니라 일반 산업에서도 최근 많은 각광을 받고 있다. 그러므로 본 소고에서는 자동차용 복합재료의 제조에 널리 사용되는 성형공정에 대하여 간단히 살펴보고, 자동차 부품에 있어서의 복합재료 응용 현장과 최근 환경문제가 대두되면서 관심의 초점이 되고 있는 자동차용 복합재료 재활용 기술에 대하여 고찰하고자 한다.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.4
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• pp.478-486
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• 2005

Statement of problem : Fracture and dimensional change of an acrylic resin denture are a rather common occurrence. Purpose : The purpose of this study was to compare differences in dimensional changes and flexural strength of separate maxillary complete dentures after immediate deflasking by injection molding and conventional compression processing. Material and method: To evaluate dimensional stability, the maxillary dentures were fabricated by using different materials and methods. Lucitone 199(Dentsply Trubyte. york, pennsylvania, USA) and Vertex(Dentimex, zeist, Netherlands) were used as materials. Compression and injection packing methods were used as processing methods. The impression surface of the dentures was measured by 3D Scann-ing System(PERCEPTRON USA) and overlapped original impression surface of the master cast. To evaluate flexural strength, resin specimens were made according to the different materials, powder/liquid ratio and processing methods. Flexural strength of the complete resin specimens (64mm$\times$10mm$\times$3.3mm) were measured by INSTRON 4467. (INSTRON, England) The data was analyzed by ANOVA, t-test and Tukey test. (p<.05 level of significance) Result: The results were as follows 1. There was no significant differences between master model and denture base for each group in overall dimensional changes. 2. Palatal area was more stable than flange or alveolar area in dimensional stability. but. there was no significant differences among each area. 3. Materials and power/liquid ratio had an effect on flexural strength. (P<.05) Especially materials was most effective. (P<.05) 4. Lucitone 199(powder/liquid ratio followed by manufacturer's direction) showed higher flexural strength than Vertex. Conclusion : Dimensional stability or flexural strength are affected by materials rather than packing techniques.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.289-301
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• 1998

The present study attempted to numerically simulate the process in detail by developing an appropriate physical modeling and the corresponding numerical analysis for precision injection and injection/compression molding process of center-gated disk. In part I, a physical modeling and associated numerical analysis of injection molding with a compressible viscoelastic fluid model are presented. In the distribution of birefringence, the packing procedure results in the inner peaks in addition to the outer peaks near the mold surface, and values of the inner peaks increase with the packing time. Also, values of the density in the core region increase with the packing time. From the numerical results, we also found that birefringence becomes smaller as the melt temperature gets higher and that it is insignificantly affected by the flow rate and the mold temperature. As far as the density distribution is concerned, mold temperature affected the distribution of density especially near the wall. But it was not significantly affected by flow rate and melt temperature. Numerical results of birefringence coincided with experimental data qualitatively but didn't quantitatively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1361-1366
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• 2010

This research aims to develop polymer composites which can be used for PEMFC separators by injection molding process. Considering the moldability and stiffness, we used PPS(Poly(phenylene sulfide)) and PP(Polypropylene) as base resin. In order to improve electrical conductivity and physical properties, we chose glass fiber, carbon fiber, carbon black, and both expanded graphite and synthetic graphite. The 3 type composites are prepared for injection molding of PEMFC separators. and CAE(Computer Aided Engineering) analysis was conducted to optimize injection processing parameters(injection pressure, heat time, mold temperature etc.). We did successfully fabricate the separators by injection molding, and measure the electrical conductivity of the samples by using four point probe device. Conclusively, PP/SG/CB composite showed better both electrical conductivity and moldability than the others.