Papers by Author: Tai Chiu Lee

Abstract: This paper aims at presenting an experimental investigation to compare the rolling behaviors of selected materials under profile rolling process. Copper alloy (C37700), aluminum alloy (AA6063) and stainless steel (AISI304) in 6 mm diameter were selected as rolling specimens. The process parameters, i.e. spindle speed, forward speed, and fractorgraphic analysis were carried out to determine the deformation behaviours of selected materials. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality precision components efficiently.

Abstract: In this paper, the effect of strain rate has been considered in the simulation of forming process with a simple form combined into the material law. Quite a few researchers have proposed various hardening laws and strain rate functions to describe the material tensile curve. In this study, the strain rate model Cowper-Symonds is used with anisotropic elasto-plastic material law in the simulation process. The strain path evolution of certain elements, when the strain rate is considered and not, is compared. Two sheet materials, Cold-reduced Carbon Steel (SPCC) JIS G3141 and Aluminum alloy 6112 are used in this study. Two yield criteria, Hill 48 and Hill 90, are applied respectively to improve the accuracy of simulation result. They show different performance when strain rate effect is considered. Strain path of the elements in the fracture risk area of SPCC (JIS G3141) varies much when the strain rate material law is used. There is only little difference of the strain distribution of Al 6112 when the strain rate effect is included and excluded in the material law. The simulation results of material SPCC under two conditions indicate that the strain rate should be considered if the material is the rate-sensitive material, which provides more accurate simulation results.

Abstract: Cathodic Arc Physical Vapor deposition (CAPVD) uses a high current, low and negative voltage arc to vaporize a cathodic electrode (cathodic arc) and deposit the vaporized material on a substrate. The vaporized material is ionized in a vacuum chamber and the substrates are usually biased so as to accelerate the ions to the substrate surface. CAPVD provides a very dense film with excellent adhesion to the substrates. Therefore, this technique is mainly used to deposit on cutting tools such as end mills, drills, inserts, plastics and metal molds and high wear resistance tribology components. However, this coating technique will produce unwanted micro particles (droplets) [1] which usually are the target materials that cannot be reacted in coating process. These particles will affect the coating roughness and the surface morphology. To optimize this condition, Taguchi method is introduced to obtain the best experimental parameter settings. In this study, Atomic Force Microscope (AFM) is used to analyze the roughness of the coating for the following factors: bias voltage, arc current, nitrogen pressure and coating thickness.

Abstract: This study descripts processing of biphasic calcium-phosphate (BCP) and poly-L-lactide (PLLA) biocomposite implant material. The composite was obtained by mixing completely dissolved PLLA with granules of high crystalline BCP and was compacted by hot pressing using cylindrical dies at 450 K temperature and 98.1 MPa pressure, for 30 and 60 minutes. Wide-angle Xray structural (WAXS) analyses of BCP, PLLA and BCP/PLLA composite blocks were made followed by calorimetric (DSC) tests in the 320-520 K temperature range. Compression tests revealed that Young’s modulus and compressive strength of the composite increased with extended hot pressing time and were found to be within the bounds of the cortical bone values.