Papers by Author: Eung Ryul Baek

Abstract: Generally, metal injection molding (MIM) method utilizes SS 17-4 PH as material for application of orthodontic bracket. One of the process of MIM is thermal debinding, which binder is eliminated by thermal energy. In this study, thermal debinding process is conducted with variation of temperature, i.e. 480, 510, and 540°C, holding time, i.e. 0.5, 1 and 2 hours, heating rate, i.e. 0.5, 1, 1.5, and 2°C/min.The effect of temperature shows that the increased temperature will result in the mass reduction percentage due to formation of oxide on the sample, which will be proven through TGA testing. The highest mass reduction was 6.4137 wt% which was obtained at 480°C. For the variation of holding time, the longer the holding time will result in increased mass reduction and the highest mas reduction was 6.255 wt% which was obtained during 2 hours of holding time. For the heating rate, the slower the heating rate will result in increased mass reduction and decreased the presence of crack formation. The best variable was obtained at heating rate of 0.5°C/min, which resulted mass reduction of 6.2488 wt% and less crack formation.

Abstract: Malocclusion is one of the common problems encountered in the teeth and mouth of Indonesian people. This country is also confronted with problems that the bracket have to been imported from abroad. The purpose of this study is to produce national orthodontic bracket by metal injection molding (MIM) process in Indonesia, particularly by using vacuum sintering for 17-4 PH stainless steel because it is a material commonly used for orthodontic bracket. Sintering conducted at four different temperatures, at 1320 °C, 1340 °C, 1360 °C, and 1380 °C. The results showed that there are inclusions in sintering products. The relative density increases with increasing temperature sintering because the area of porosity are reduced. In addition, the results of sintering at 1360 °C has optimal hardness, which is amounted to 395 HV and higher than commercial bracket.

Abstract: Excessive iron in aluminum melt produces needle-shaped beta-AlFeSi intermetallic compounds during solidification. The presence of beta-AlFeSi intermetallic compounds can be harmful in the extrusion process because of the high pressure. As a common process, those compounds change from the needle-shaped to the globular-shaped alpha-AlFeMnSi intermetallic compounds through the addition of manganese to the aluminum melt. Those phases settle down during the solidification process, and then such is cut. Note, however, that the efficiency of iron elimination is very low. Our previous study reported that EMS can help the alpha-AlFeMnSi intermetallic compounds form easier and faster and settle down at the bottom of the aluminum melt through the centrifugal force of EMS. To investigate the effect on the efficiency of iron elimination in aluminum melt scrap, EMS current, holding temperature, and time of melt as well as the ratio of manganese to iron were controlled. As a result of this study, lower holding temperature and longer holding time of aluminum melt make iron elimination in aluminum melt more efficient with induced EMS. The best efficiency of iron elimination in aluminum melt was 65.2%with EMS induced at 923k for 4 minutes.

Abstract: The characteristics of Al-coating materials on low carbon steel sheets during high temperature oxidation process were investigated. The phases’ evolution and growth were systematically evaluated by SEM/EDS and XRD. The hardness distribution from the surface to the steel substrate was measured to check the brittleness of iron aluminides coating layers. The oxidation properties of coating materials were investigated using weight gain method. Intermetallic compound recognized as FeAl3 was initially formed on the interface between steel substrate and coating materials. After exposing the specimens at elevated temperature, FeAl3 layer was gradually transformed into Fe2Al5, FeAl2, and FeAl+Fe3Al. Oxidation rate increased fastly after α-Al in the coating completely transformed at 650 °C. The brittle FeAl3 and Fe2Al5 have the lower resistance to oxidation because the easier cracking during intermetallic reaction.

Abstract: Micro powder metal injection molding has received attention as a manufacturing technology for microparts. Small powder size is very useful in achieving detailed structures. STS nanopowders with an average diameter of 100 nm and STS micropowders with an average diameter of 5 micron were utilized to produce feedstock. The mixing behavior of the feedstock was indicated that the nanoparticle feedstock produce highest mixing torque at various powder_loading than the micropowder feedstock. Ares rheometer was utilized to examine visco-elatic flow behavior. The nanoparticles feedstocks showed that elastic properties are dominant in flow behavior and high viscosity. Whereas the micropowders feedstocks, viscous properties are dominant in flow behavior and less viscosity.