Papers by Author: Heng Shye Yunn

Abstract: In this paper, an attempt has been made to mill constituent of WC and Co powder towards achieving volumetric percentage of WC (91%) and Co (9%). The ball milling technique was conducted under dry and wet condition using various milling parameters, rotation speed, time and ethanol as milling medium. Electron dispersive spectrometer (EDS) detected the elemental distribution, whilst SEM and particle size analysis was done to study the effect of changes in particle morphology and reduction of particle size. As a conclusion, powder milled by parameter of wet milling by ethanol, speed of rotation at 250 rpm and 90 minutes of milling time exhibits best results in term of volumetric percentage of 91%WC and 9%Co and particle size reduction.

Abstract: Optimization of injection parameters in Micro Metal Injection Molding (μMIM) was described in this study. Stainless steel powder was mixed with Polyethelena Glycol (PEG), Polymethyl Methacrilate (PMMA) and Cellulose Acetate Butyrate (CAB) to produce feedstock. Design of Experiments (DOE) of Taguchi L-27 (313) orthogonal array technique has been used to investigate the significance and optimal injection molding parameters. The signal-to-noise ratio and analysis of variance (ANOVA) are applied to study the optimum levels and effects of process parameters. Simultaneous optimization to obtain the highest green density and excellent surface appearance was discussed. The result concluded that the mold temperature (D) is the most statistically significant process parameter and its contribution to the best appearance and density is the highest.

Abstract: Micro powder injection molding (µPIM) is a preferred technology for the production of micro parts or micro structured parts which derived from the well known thermoplastic injection molding technique. It is suitable for a large-scale production of ceramic and metallic parts without final machining. In the hardmetal industry, submicron and ultrafine hardmetals are the most demanding and also the fastest growing grades in production and application. Four stages involve in µPIM are mixing, injection, debinding and sintering. The volumetric ratio of solid powder to the total volume of powder and binder, which is usually called powder loading, largely determines the success or failure of subsequent processes. Critical solid loading of the powder can be estimated by torque variation, density, melt flow, density and viscosity versus composition. In this paper, critical solid loading of WC-10%Co is determined using torque variation method and its rheological behavior is studied. During the process, the wet surface of the powder particle WC-10%Co will cohesive together and resulted to the torque. Progressive powder is added-in after torque decrease and critical solid loading is identified when torque becomes unstable. Hence, critical solid loading WC-10%Co with WC (APS < 1 µm) is 46% and 42, 43 and 44 vol% of powder loading are selected to mix with wax-based binder system. The viscosity of feedstock show the pseudoplastic behavior and flow index (n) are 0.444, 0.491 and 0.492 for powder loading 42%, 43% and 44% respectively.

Abstract: Micro powder injection molding (µPIM) is the combination of micro injection molding and powder injection molding (PIM) technology. The increasing demands on market of microparts further intensify the development of this technology. µPIM process enables the use of a wide range of materials and broadens the applications of micro components. This process is well suitable for large volume production of micro-components at low costs. Requirement of powder and binder is more stringent since product fabricate in micron scale, therefore criterion of the powder and binder has been reviewed in this paper. In addition, the process parameter and development in the computer aid plays an important due to the narrow process window requires even tighter as the quality of the micro-component is sensitive to the parameter. This paper outlines recent development in µPIM. Challenges and further explore for µPIM is concluded in the last part of this paper.