Papers by Author: Hooman Abolhasani

Abstract: The influence of a binder system to the rheological behavior of a Metal Injection Molding (MIM) feedstock is presented in the paper. The binder systems used are: a) PEG & PMMA b) Palm stearin & LLDPE and, c) Tapioca starch & LLDPE. The viscosity and shear rate of the feedstocks were measured at various range of temperature and shear rate across the L/D = 10 capillary rheometer. The flow behavior index, n and activation energy, E of each feedstock were measured to show its significance as MIM feedstock. Generally, the result indicates all feedstock exhibits a shear thinning behavior and the binders are suitable as MIM binder. Additionally, the present paper has discovered that the binder system does not have much influence to the activation energy. In order to show the relevance of the rheological behavior to the actual injection molding performance, green parts has been injection molded and the result shows an agreement with the rheological behavior result.

Abstract: In this study, a combination of starch, glycerol, linear low density polyethylene (LLDPE) and other additives was utilized as the binder composition. The effect of different parameters such as thickness, temperature and time on debinding process of green parts was investigated. Discs of different thicknesses consisting of 2, 2.7 and 3 mm were submitted to the water bath in order to obtain curves of time versus remaining mass of binder. Moreover, the injected tensile bar test specimens was utilized to observe specially the effect of temperature on rate of binder extraction from the green parts. The experiments were conducted at three sets of temperatures including 70, 80 and 90°C. The rate of binder removing considerably increased by decreasing the thickness of the discs. On the other hand, proportion of removed binder in injected tensile bar specimens increased in higher temperatures. The debinding process was successfully performed on injected tensile bars and the components did not suffer from any cracks and swellings. Moreover, the results show that more than 80% of the binder system can be extracted in 6 hours, which is in the acceptable time range. The investigation confirms that from the viewpoint of debinding, starch has a good potential as a binder component in MIM process.

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: A new starch-based binder as a natural polymer has been developed for metal injection molding (MIM). In this study tapioca starch which is cheap and readily available in Malaysia has been used as a binder which composed of starch, glycerol, linear low density polyethylene (LLDPE), citric acid and stearic acid. This developed binder system was mixed with 316 L stainless steel powder to prepare the feedstock at three different of powder loadings of 56, 57 and 58% vol. The rheological behavior of the binder and feedstock were evaluated at different temperatures using a capillary rheometer. The rheological behavior of binder shows less than 10 Pa s and the flow behavior index of the feedstocks were determined to less than 1, which indicates the flow characteristic is pseudo-plastic which is suitable for MIM process. Finally, among these three feedstocks, the feedstock of 57% vol. powder loading was selected and its viscosity values within expected shear rate range are less than 1000 Pa s.