Eung Ryul Baek

Effect of Particle Size in Feedstock Properties in Micro Powder Injection Molding

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.

Iron Removal in Aluminum Melts Containing Scrap by Electromagnetic Stirring

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.

Sintering of Stainless Steel Nanopowders for Micro-Component Part Applications

Micro Metal Injection Molding utilizing 316 steel nanopowder with 100 nm in mean size was investigated to fabricate micro part. The nanopowder was used since its advantages to produce better surface roughness and detail structure in the micro part fabrication. During nanopowder preparation, thin oxide must be formed intentionally to avoid powder burnt before its exposed to the air during mixing with the wax binder system. Unfortunately, this oxide still exist after sintering and decrease the mechanical properties (ductility and densification) by the formation of secondary phase which detected as chrome oxide. In this paper, deep elaboration for oxide characteristics and the ways to reduce it by vary the sintering parameters and in Hydrogen atmosphere were described briefly. Here, we infer by reducing the heating rate, increasing the sintering temperature and utilizing the Hydrogen atmosphere can be effectively optimize the utilizing of nanopowder for micro part fabrication.

Effect of Copper Addition on Mechanical Properties of Nodular Indefinite Chilled Iron (NICI)

Nodular infinite chilled iron (NICI) material with high content of nickel (~4.00%) was usually used as work roll in hot strip rolling mill. Microstructure of NICI was consists with nodular graphite and cementite with matrix phase consist of pearlite, martensite and ausferrite that depend on the alloying content. The introduction of copper was successfully increasing the hardenability of NICI by only using low nickel content (~2.50 %) with small addition of copper (0.52%). The development of NICI was done by hot shakeout of CO2 sand mold of as-cast iron and then isothermal heating in muffle furnace in temperature 300 oC in 6 hours to achieve ausferritic transformation. By achieving the martensite and ausferrite phase in as-cast condition, the sample will not need austenitizing and quenching process and the sample that will be free of quenching crack and thermal stress that usually occurred austenitizing and quenching process. It was confirmed by optical microscope and scanning electron microscope (SEM) observations that with the small addition of copper (0.52%), the amount of pearlite was very small (~1.00%), but with further addition of copper (2.02%), the amount of martensite was significantly increase the hardness until 51.56 HRC but the tensile strength was significantly dropped into 442 Mpa from previously 571 Mpa without copper addition. From hardness and tensile strength data it can be seen that the optimum content of copper is 1.45 % that have good combination of hardness (47.75 HRC) and moderate tensile strength (508 Mpa).

Interfacial Characteristics of Iron Aluminides Intermetallic Layers on Al-Coated Steel Sheet

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.

Vacuum Sintering Process in Metal Injection Molding for 17-4 PH Stainless Steel as Material for Orthodontic Bracket

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.

Thermal Debinding Process of SS 17-4 PH in Metal Injection Molding Process with Variation of Heating Rates, Temperatures, and Holding Times

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.