Chi Ping Lai

Effects of Stress Relieving on Limit Dome Height of Titanium Tailor-Welded Blanks at Elevated Temperatures

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.

Warm-Forming of Light-Weight Alloys under Multi-Stage Forming Process

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.

Warm forming simulation of titanium tailor‐welded blanks with experimental verification

The simulation of the forming process of Ti‐TWBs at elevated temperatures using finite element analysis to determine the optimum forming conditions of Ti‐TWBs is presented in this paper. For verification of the simulation results, titanium alloy (Ti‐6Al‐4V) was selected for the first instance to prepare the specimen of Ti‐TWBs. The thickness combinations of 0.7mm/1.0mm and in widths of 20mm, 90mm and 110mm were used. A specific tooling system with temperature control device was developed to the forming of Ti‐TWBs at 550°C. A cylindrical punch of 50mm diameter was designed and manufactured. Different forming parameters (i.e. traveling distance of the punch and the stroke as well as the time of each forming process) and material characteristics under various temperatures were measured. In addition, the true stress and strain values by tensile test as well as the major and minor strain distributions of forming Ti‐TWBs at elevated temperatures by Swift Forming test were carried out and applied as input into t...

Thermal forming of light-weight alloys under a multi-stage forming process

Abstract This article presents an experimental investigation aimed 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) of thickness 1 mm with different widths (i.e. 20, 90, and 110 mm) are selected as forming specimens. In order to carry out the multi-stage forming process, a special fixture with a heating system for the pre-straining process is designed and manufactured. The limit dome heights of both titanium alloys and aluminium alloys are measured and recorded. The experimental results reveal that both of the light-weight alloys yielded enhanced ductility at higher working temperatures, because of a decrease in the yield strength. The formability of selected materials is found to be sensitive to the forming temperatures and multi-stage forming processes.

Grids Reformation for Effective Strain Measurement of Forming Titanium Tailor-Welded Blanks at Elevated Temperatures

Titanium and its alloy are widely used in the automobile and aircraft industries because of a variety of advantages: good corrosion resistance, light in weight and high strength [1]. However, use of the titanium and its alloy has been highly selective due to its high cost. Titanium tailor-welded blanks (Ti-TWBs) are expected to be one of the candidate materials to address this issue. In fact, forming both titanium alloy and titanium tailor-welded blanks (Ti-TWBs) at room temperature is very difficult due to their specific characteristics: potential embitterment, low workability, and high springback effect [2]. To overcome these shortcomings, Ti-TWBs have been recommended to form at elevated temperatures not less than 150°C [2, 3]. However, the investigation on the effective strain measurement for forming Ti-TWBs at elevated temperatures is still quite limited.

Finite-Element Modeling of Thermal Forming of Ti-TWBs with Experimental Verification

The titanium tailor-welded blanks (Ti-TWBs) are being developed in different industries such as automobile and aerospace, combining the advantages of both tailor-welded blanks technology and titanium alloys. In recent decades, computer simulation of sheet metal forming processes has been employed increasingly over conventional production test and adjustment methodology to achieve the optimum and cost-effective operation procedures. Recently, certain amounts of theoretical analysis for the sheet metal forming process have been developed. However, these analyses could not be applied directly to the material under multi-stage forming process. Thus, some researchers have developed a damage-based model to predict the instability and failure of sheet metals, particularly for the above Ti-TWBs, with consideration of material damage under discontinuous or proportional loading strain paths. So far this model has been used and proved to be successful to predict formability of selected sheets of steel and aluminium alloy. However, the application of the damage-coupled model has yet to be extended to the Ti-TWBs under thermal multi-stage forming operation.The main objective of this paper is to investigate numerically the formability of Ti-TWBs under multi-stage forming process with experimental verification. Titanium alloy sheets (Ti-6Al-4V) in thickness of 0.7mm and 1.0mm were selected and laser-welded the specimen of Ti-TWBs. The model based on the damage mechanics is introduced to predict the thermal formability of Ti-TWBs with change of strain paths. In this study, the anisotropic damage model incorporate with the finite element codes and user-define material subroutine were developed to predict the formability of Ti-TWBs with change of strain paths. The mechanical properties and damage parameters of Ti-TWBs for the simulation were measured experimentally. The simulation of Ti-TWB under multi-stage forming process were then conducted and validated experimentally at similar forming conditions. The predicted results have been found to agree well with those obtained from the experiments. This analysis can be applied readily to design and manufacture TWB components or structures so as to satisfy the need of such market demands.

Microstructual Analysis of Stress Relieving on the Thermal Deformation Behaviors of Titanium Tailor-Welded Blanks

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.

Experimental Evaluation of Material Rollability in Profile Rolling

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.