• 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.

• Journal of Powder Materials
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• v.10 no.1
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• pp.6-14
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• 2003

The purpose of the present study is to investigate the method decreasing debinding time as well as lowering operation condition than pure supercritical $CO_2$ debinding by using cosolvent or binary mixture of propane + $CO_2$. First method is to add cosolvent, such as n-hexane, DCM, methanol, 1-butanol, in supercritical $CO_2$. In case of adding cosolvent, we were found the addition of non-polar cosolvent (n-hexane) improves dramatically the binder removal rate (more than 2 times) compared with pure supercritical $CO_2$ debinding, second method is to use mixture of supercritical propane + $CO_2$, as solvent. In case of using mixture of supercritical propane + $CO_2$, the rate of debinding speeded up with increasing of pressure and concentration of propane at 348.15 K. It was found that addition of cosolvent (e.g., n-hexane, DCM) and binary mixture propane + $CO_2$ for supercritical solvent remarkably improved binder removal rate for the paraffin wax-based binder system, in comparison with using pure supercritical $CO_2$.

• Journal of Powder Materials
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• v.19 no.2
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• pp.117-121
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• 2012

Tool steels serve a large range of applications including hot and cold workings of metals and injection mouldings of plastics or light alloys. The high speed steels (HSS) are specifically used as cutting tools and wear parts because it has high strength, wear resistance and hardness along with appreciable toughness and fatigue resistance. From the view of HSS microstructure, it can be described as metallic matrix composites formed by a ferrous with a dispersion of hard and wear resistant carbides. The experimental specimens were manufactured using the PIM with T42 powders (50~80 vol.%) and polymer (20~50 vol.%). The green parts were debinded in n-hexane solution at $60^{\circ}C$ for 8 hours and thermal debinded at an $N_2-H_2$ mixed gas atmosphere for 8 hours. Specimens were sintered in high vacuum ($10^{-5}$ Torr) and various temperatures.

• Journal of Powder Materials
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• v.18 no.3
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• pp.262-268
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• 2011

In order to investigate the microstructure and mechanical properties of WC-10 wt% Co insert tool alloy fabricated by PIM (Powder Injection Molding) process, the feedstock of WC-10 wt% and wax used as a kind of binder were mixed together by two blade mixer. After injection molding, the debinding process was carried out by two-steps. First, solvent extraction, in which the binder was eliminated by putting the specimen into normal hexane for 24 hrs at $60^{\circ}C$, and subsequently thermal debinding which was conducted at $260^{\circ}C$ and $480^{\circ}C$ for 6 hrs in the mixed gas of $H_2/N_2$, respectively. Meantime, in order to compensate the decarburization due to hydrogen, 1.2~1.8% of carbon was added to ensure the integrity of the phase. Finally, the specimens were sintered in vacuum under different temperatures, and the relative density of 99.8% and hardness of 2100 Hv can be achieved when sintered at $1380^{\circ}C$, even the TRS is lower than the conventional sintering process.

• Korean Journal of Materials Research
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• v.14 no.11
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• pp.795-801
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• 2004

The injection molded Fe sintered bodies were fabricated using two kinds of Fe powders haying 50 nm and $3\sim5{\mu}m$ in diameter. In the using of Fe powder having 50 nm in diameter, the comparatively dense bodies ($94\sim97\%$) were obtained even at low sintering temperature ($600\sim700^{\circ}C$), while in the sintered bodies ($1000^{\circ}C$) using $3\sim5{\mu}m$ Fe powder, their relative densities showed low values about $93\%$, although they were strongly depend on the sintering temperature and volume ratio of Fe powder and binder. In the sintered bodies using of 50 nm Fe powders, the volume shrinkage and grain size increased as the sintering temperature increased, but the values of hardness decreased. In the sample sintered at $650^{\circ}C$, the values of relative density, volume shrinkage and grain size were $96\%,\;37\%\;and\;0.97{\mu}n$, respectively and the minimum value of wear depth was obtained due to combination of fine grain and comparatively high density.

• Journal of Powder Materials
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• v.17 no.4
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• pp.312-318
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• 2010

High speed steels (HSS) were used as cutting tools and wear parts, because of high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. Conventional manufacturing process for production of components with HSS was used by casting. The powder metallurgy techniques were currently developed due to second phase segregation of conventional process. The powder injection molding method (PIM) was received attention owing to shape without additional processes. The experimental specimens were manufactured with T42 HSS powders (59 vol%) and polymer (41 vol%). The metal powders were prealloyed water-atomised T42 HSS. The green parts were solvent debinded in normal n-Hexane at $60^{\circ}C$ for 24 hours and thermal debinded at $N_2-H_2$ mixed gas atmosphere for 14 hours. Specimens were sintered in $N_2$, $H_2$ gas atmosphere and vacuum condition between 1200 and $1320^{\circ}C$. In result, polymer degradation temperatures about optimum conditions were found at $250^{\circ}C$ and $480^{\circ}C$. After sintering at $N_2$ gas atmosphere, maximum hardness of 310Hv was observed at $1280^{\circ}C$. Fine and well dispersed carbide were observed at this condition. But relative density was under 90%. When sintering at $H_2$ gas atmosphere, relative density was observed to 94.5% at $1200^{\circ}C$. However, the low hardness was obtained due to decarbonization by hydrogen. In case of sintering at the vacuum of $10^{-5}$ torr at temperature of $1240^{\circ}C$, full density and 550Hv hardness were obtained without precipitation of MC and $M_6C$ in grain boundary.

• Design & Manufacturing
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• v.13 no.2
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• pp.17-21
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• 2019

In this study, selective laser sintered 3D printing mold core and metal core were used to investigate the difference of the thickness shrinkage from the gate of the injection molded part at a constant interval. SLS 3D printing mold core was made of nylon-based PA2200 powder and the metal core was manufactured by conventional machining method. As the PA2200 powder material has low strength, thermal conductivity and high specific heat characteristics compared with metal, molding conditions were set with the consideration of molten temperature and injection pressure. Crystalline resin(PP) and amorphous resin(PS) with low melting temperature and viscosity were selected for the injection molding experiment. Cooling time for processing condition was selected by checking the temperature change of the cores with a cavity temperature sensor. The cooling time of the 3D printing core was required a longer time than that of the metal core. The thickness shrinkage of the molded part compared to the core depth was measured from the gate by a constant interval. It was shown that the thickness shrinkage of the 3D printing core was 2.02 ~ 4.34% larger than that of metal core. In additions, in the case of metal core, thickness shrinkage was increased with distance from the gate, on the contrary, in the case of polymer core showed reversed aspect.

• Clean Technology
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• v.18 no.2
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• pp.155-161
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• 2012

The purpose of this study is to remove paraffin wax binder effectively from powder injection molded part using supercritical fluids in powder injection molding process. For a thin powder injection molded part about 1-2 mm thickness, paraffin wax binder can be removed rapidly without any defect by traditional supercritical extraction process which has fixed high temperature and pressure condition. But, for a thick powder injection molded part, there are limitations in removing paraffin wax binder by the fixed high process condition because crack occurs at the beginning step. Therefore, here we studied variable condition debinding process that starts with mild process condition at the beginning step and then increase the process conditions simultaneously at each step. To find out the initial process condition that has the highest extraction yield without any defect for each sample thickness, we investigated various supercritical debinding conditions using 1-4 mm thickness ceramic injection molded sample. By using the variable condition debinding process that starts with the initial process condition at the first step and then increasing process conditions simultaneously at each step (temperature from 333.15 to 343.15 K, pressure from 12 to 27 MPa, and $CO_2$ flow rate from 1.5 to 10 L/min), over 95% of paraffin wax binder was removed from the 4 mm thick (10 mm diameter) ceramic injection molded disk samples within 5 hours.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.523-524
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.99-100
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• 2012