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Mapping Particle Size Distributions into Predictions of Properties for Powder Metal Compacts
German Randall M. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Discrete element analysis is used to map various log-normal particle size distributions into measures of the in-sphere pore size distribution. Combinations evaluated range from monosized spheres to include bimodal mixtures and various log-normal distributions. The latter proves most useful in providing a mapping of one distribution into the other (knowing the particle size distribution we want to predict the pore size distribution). Such metrics show predictions where the presence of large pores is anticipated that need to be avoided to ensure high sintered properties.
Rapid Heating Concepts in Sintering
German, Randall M. The Korean Powder Metallurgy Institute 2013 한국분말재료학회지 (KPMI) Vol.20 No.2
Powder metallurgy applied rapid heating to sintering starting year 1900. Since 1970 the study has intensified. Now rapid sintering concepts embrace a spectrum of options ranging from dunk cycles to microwave, induction, exothermic, electric field, and spark approaches. Most of the efforts are targeting reduced microstructure coarsening during sintering, although reduced material decomposition is another common goal. The efforts are impressive for simple shapes and success metrics such a small grain size after densification. Several barriers need to be removed prior to application in powder metallurgy commercial sintering. Rapid heating research needs to focus on significant property gains, accurate product dimensions, and lower costs. So far each property gain obtained with rapid heating is matched by traditional sintering and composition changes. Several examples are cited to show the goals for the next round of innovations.
Design Regression for Identification of Optimal Components for Metal Powder Injection Molding
German Randall M. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Production components fabricated by metal powder injection molding are analyzed for features to identify the design window for this powder technology. This reverse approach lets the designer see where PIM has a high probability to succeed. The findings show that the most suitable components tend to be less than 25 mm in size and less than 10 g in mass, are slender, and have high complexity.
Various Master Sintering Curve Concepts and its Applications
Park Seong-Jin,Blaine Deborah C.,German Randall M. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The master sintering curve (MSC) is derived from densification data over a range of heating rates and temperatures. To improve the accuracy, several modifications were proposed: multi-phase MSC for solid state sintering with phase changes, MSC for liquid phase sintering, and MSC with consideration of grain growth. The developed MSC models were applied to several material systems such as molybdenum, stainless steels, and tungsten heavy alloys (WHA), in order to evaluate the effect of compaction pressure, phase change, grain growth, and composition on densification, to classify regions having different sintering mechanism, and to help engineer design, optimize, and monitor sintering cycles.
Unified Molding and Simulation for Nano-structured Tungsten Carbide
Park Seong-Jin,Johnson John L.,German Randall M. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Nano-structured tungsten carbide compacts with cobalt matrices (WC-Co) offer new opportunities for achieving superior hardness and toughness combinations. A unified modeling and simulation tool has been developed to produce maps of sintering pathways from nanocrystalline WC powder to sintered nano-structured WC-Co compacts. This tool includes (1) die compaction, (2) grain growth, (3) densification, (4) sensitivity analysis, and (5) optimization. All material parameters were obtained by curve fitting based on results with two WC-Co powders. Critical processing parameters are determined based on sensitivity analysis and are optimized to minimize grain size with high density.
Sintering and Microstructure Characteristics of 42CrMo4 Steel Processed by Spark Plasma Sintering
Ridvan Yamanoglu,William Bradbury,Eugene A. Olevsky,Randall M. German 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5
Rapidly solidified micron sized 42CrMo4 steel powder with a size range of 150-250 μm produced by plasma rotating electrode process was consolidated using a recently developed spark plasma sintering (SPS) process. The relationship between sintering parameters (temperature and soaking time) and microstructural properties was investigated. The effect of slow and high heating regimes on the consolidation of sintered compacts has been also investigated. Maximum relative density (99.2%) was obtained at 1000 °C, under 50 MPa pressure, with 8 min holding time and 200 °C/min heating rate. The microstructure of sintered steel was influenced by carburization occuring inside the graphite SPS process die. The diffusion of carbon produced martensite structure near the surface region and hardened the surface. This effect was investigated in detail using optical microscopy and hardness measurement. Scanning electrone microscopy was also used to examine the fracture surface of sintered compacts. High heating rate promoted the relative density at low temperature compared to high temperature.
Effects of process parameters in plastic, metal, and ceramic injection molding processes
이시우,안석영,황철진,박성진,Sundar V. Atre,김주권,Randall M. German 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.3
Plastic injection molding has been widely used in the past and is a dominant forming approach today. As the customer demands require materials with better engineering properties that were not feasible with polymers, powder injection molding with metal and ceramic powders has received considerable attention in recent decades. To better understand the differences in the plastic injection molding, metal injection molding, and ceramic injection molding, the effects of the core process parameters on the process performances has been studied using the state-of-the-art computer-aided engineering (CAE) design tool, PIMSolver The design of experiments has been conducted using the Taguchi method to obtain the relative contributions of various process parameters onto the successful operations.
Investigation on Sintering Mechanism of Nanoscale Tungsten Powder Based on Atomistic Simulation
Amitava Moitra,Sungho Kim,Seong-Gon Kim,Seong Jin Park,Randall M. German,Mark F. Horstemeyer 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Atomistic simulations focusing on sintering of crystalline tungsten powders at the submicroscopic level are performed to shed light on the processing on the nanoscale powders. The neck growth and shrinkage were calculated during these sintering simulations, so it is possible to extend these results to the global physical property evolution via sintering. The densification and grain growth during sintering were calculated with variations in temperature, pressure, particle configuration, additives, and crystalline misalignment between particles. These findings lay a foundation for a virtual approach to setting the processing cycles and materials design applicable to nanoscale powders.
Effects of process parameters in plastic, metal, and ceramic injection molding processes
Lee, Shi-W.,Ahn, Seok-Young,Whang, Chul-Jin,Park, Seong-Jin,Atre, Sundar V.,Kim, Jook-Won,German, Randall M. 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.3
Plastic injection molding has been widely used in the past and is a dominant forming approach today. As the customer demands require materials with better engineering properties that were not feasible with polymers, powder injection molding with metal and ceramic powders has received considerable attention in recent decades. To better understand the differences in the plastic injection molding, metal injection molding, and ceramic injection molding, the effects of the core process parameters on the process performances has been studied using the state-of-the-art computer-aided engineering (CAE) design tool, PIMSolver$^{(R)}$ The design of experiments has been conducted using the Taguchi method to obtain the relative contributions of various process parameters onto the successful operations.