Papers by Author: Luen Chow Chan

Abstract: In this paper, a visualisation system will be discussed that can be used to capture the deformation profile of the sheet blank during sheet metal forming processes, such as deep drawing and shape forming. The visualisation system utilizes a 2D laser displacement sensor for deformation profile acquisition. The sensor is embedded in the die and the laser propagates through the die to detect the profile change of the specimen concealed in the die during operation. The captured profile data will be collected, manipulated and transferred to a monitor for display via a controller. This visualisation of the deformation profile will provide engineers and researchers with an intuitive means of analysing and diagnosing the deformation process during sheet metal forming.

Abstract: This paper presents a numerical simulation and experimental study on profile-rolling process for micro-teeth components. The target component was made of AISI 304 stainless steel with 6.0 mm outer diameter, and its number of teeth was 25. Three raw material rods with different diameters 5.6 mm, 6.0 mm, and 6.4 mm were investigated in the finite-element simulation. The spindle speed of the rolls was 60 rpm, and the material forward speed was 1.8 mm/s, which were reasonably compatible with the practical profile-rolling conditions. The simulation results showed that the different numbers of teeth were produced by employing different diameters of raw materials. Only the rod with the 6.0 mm diameter could be rolled into the near desired shape. Experimental verification was also undertaken. The numerical simulation was found to be in good agreement with the measured profile of the actual rolled component. The microstructure of the material after rolling was improved also as the hardness of the teeth was 40% higher than that of the core.

Abstract: This paper aims to investigate the microstructual analysis of titanium tailor-welded blanks (Ti-TWBs) undergoing the stress relieving (SR) during a thermal deformation. A modified HILLE machine, with a specific heating device that can adjust the working temperature, was employed in this study. Qualified Ti-TWBs specimens were prepared in different widths and lengths. In order to compare the performance of both SR and non-SR Ti-TWBs, the formability analyses at room temperature and around 550degC were then carried out accordingly. The limit dome heights (LDH) of these specimens were measured and it was found that the ductility of the SR Ti-TWBs was improved due to the removal of the hardening effect as well the working stress during the cold working. Moreover, the fracture surface of the Ti-TWBs also revealed that the microstructure was fine and equaxial after the heat treatment. It can be concluded that the microstructual evolution is useful to enhance the strength of Ti-TWBs.

Abstract: The microstrctural evolution pre and post heat treatment is critical to achieve a successful product for metal forming process. This paper aims to investigate the microstructual effect of the magnesium alloy tubes undergone various heat treatment conditions to achieve material homogenization. The heat treatment conditions under various periods of time (1, 2, 6, 12 and 30 hours) at 400 °C were employed to investigate the microstructural effect on hydroforming magnesium tubes. The greatly reduced impurity embedded in grain boundaries and more uniform grain sizes do indicate the improvement of material strength and ductility. To validate the conclusion, corresponding tensile tests at the different temperatures (20 °C and 200 °C) were carried out. The increased engineering strain in two directions (hoop and longitudinal) implies that the microstructural evolution is unquestionably useful to enhance the ductility of the magnesium tubes. Subsequently, the tubes after optimal heat treatment condition at 400 °C for 6 hours were used to further carry out the thermal hydroforming process for validation. The defect-free hydroformed tubes were produced under the same working condition, which is unable to be achieved for tubes without the heat-treatment process.

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: To evaluate the hydroformablility of tubular components in the tube hydroforming (THF) process, the conventional method is to measure the deformed square or circle grids printed on the surface of the tubular parts. However, the reliability of those measured data is affected greatly by the grid size and its measurement method on the curved surface. It is well-known that material hardness varies under different plastic deformation conditions, especially before and after the forming process. And it is more convenient to obtain the Vickers’ hardness values and distribution around the burst area of deformed components. This paper mainly presents an effective and reliable approach to evaluate the hydroformability of tubular components using micro-hardness measurement. At first, the Vickers’ hardness values and distribution around the burst area of the deformed components were obtained. The plastic strain, together with its distribution in such an area could then be derived by the measured micro-hardness through the developed equations. As a result, it was found to be more suitable to evaluate the hydroformability of tubes using this approach instead of the traditional grids measurement.

Abstract: This paper aims at presenting an experimental investigation to obtain the optimum formability of light-weight alloys under the multi-stage forming process. Titanium alloy sheets (Ti-6Al-4V) and aluminium alloy sheets (AA5052) are selected as forming specimens. The special fixture with heating device is applied in order to carry out the prestraining process. The swift forming test at warm-forming condition is performed for measuring the limit dome heights after the multi-stage formign process. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality light-weight components efficiently.

Abstract: Strong interest in producing ultra-light-weight, high corrosion-resistant, heat-proof and tougher advanced products has prompted potential development of titanium tailor-welded blanks (Ti-TWBs) to construct the critical parts of structures and panels in automotive applications and some other advanced industries. However, the capability to predict the forming behavior of the stamped TWBs without failure lags far behind the manufacturing technology. It is proven that the ductility for most of the titanium alloy sheets can be significantly improved at elevated temperatures. Nevertheless, such study of stress-strain behavior on the weldment of Ti-TWBs has not been fully investigated. This paper aims to analyze the forming behavior of the Ti-TWBs at different elevated temperatures using a finite element analysis. The distinctive mechanical properties of the base metals and weldment for the forming simulations will be acquired experimentally. Finally, it is found that, due to the increase of ductility, the forming behavior of Ti-TWBs will not be considerably improved unless the forming temperature is kept between 500oC and 600oC.

Abstract: This paper aims to study the effect of stress relieving on Limit Dome Height (LDH) of Ti-TWBs at elevated temperatures. This is achieved by developing a newly constructed heating system. The elevated temperature of the system can be varied and monitored by a separately control panel. All Ti-TWBs were prepared and used to examine the LDHs under elevated temperatures. Selected specimens were heat-treated at 600°C within an hour before being formed by HILLE machine. Meanwhile, the temperature of tool heating system was also adjusted from room temperature to 550°C. Specified tests were carried out to examine the stress relieving effects of Ti-TWBs on the LDHs with the temperature control panel. In addition, investigations were carried out to ascertain whether the elevated temperatures of the critical tooling components, i.e. the die and the blank holder, could result in any significant effects on LDHs of Ti-TWBs. The findings show that LDHs of Ti-TWBs can be improved by stress relieving. The stress relieving condition can be obtained by nearly isothermal forming of specimens at a range of 550°C to 600°C.

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.