Part special issue on computer-aided welding engineering

This part special issue on computer-aided welding engineering contains selected work presented at the recent 2nd International Symposium on ‘Computer-aided welding engineering’ (CAWE 2012), which was held on 24–26 August 2012 at Shandong University in China, under the sponsorship of the National Natural Science Foundation of China, Shandong University and the China Welding Society.

Two hundred and twelve researchers, including four keynote lecturers and 18 invited speakers, gathered at this international conference and presented their papers in oral or poster format. The object of the symposium is to provide a forum for researchers and engineers to exchange information and discuss on the state-of-the-art in computer-aided welding engineering and relevant fields. Attention was focused on the following fields: welding process modelling and simulation; sensing and control of welding processes; visualising the evolution of microstructure and properties in weld joints; prediction of residual stress and distortion; advanced materials joining processes including friction stir welding (FSW), laser beam and laser-arc hybrid welding, and development of welding engineering software packages. I appreciate the efforts and contributions of all the people involved.

After the conference, the organising committee of the CAWE 2012 recommended a short list of papers presented at this conference for publication in Science and Technology of Welding and Joining (STWJ), a leading journal in the international welding and joining community. Following peer review, five original research papers were selected for publication in this issue.

The paper by Xu et al.1 presents a new developed global optimisation method for the finite element simulation of welding induced residual stress in multipass butt-welded 2·25Cr–1·6W steel pipes with considering bainite transformation. The pattern search algorithm was applied to determine the kinetics parameters in J-M-A-K equation which was further modified into an explicit form during a continuous cooling process to improve calculation efficiency. With considering the phase transformation effects, the agreement extent between the calculated and the measured welding residual stresses is improved.

Mehta et al.2 proposed a low cost methodology to measure the torque and traverse force by monitoring the corresponding electrical power and current usage of the driving spindle motor (for tool rotation) and feed motor (for tool feed) during FSW process. A three-dimensional heat conduction model based on finite element method is also developed and used to compute temperature field, torque and traverse force. The computed results are validated against corresponding measured values in FSW of AA 7075-T6 and AA 2524-T351, and both are found to be in fair agreement. Such a method provides an economical and robust route for indirect measurement of real-time torque and traverse force in FSW.

To examine the effect of the various tungsten electrode tips on the distribution of the arc pressure and the quality of welding seams, Sun et al.3 measured the arc pressure in narrow-gap GTA welding under the controlling magnetic field condition. They found that the tungsten electrode with a terrace tip (2×0·8 mm) results in larger arc pressure at both the bottom centre and the side walls and the resultant largest weld width and side-wall fusion, so that the problem of side-wall incomplete fusion in narrow-gap GTA welding of titanium is well solved.

Laser beam welding of aluminium–lithium (Al–Li) alloys has significant application potential in aerospace industry. Cui et al.4 characterised and evaluated the microtextures at the selected zones from base metal (BM), heat affected zone (HAZ) and weld metal (WM) of the welded joint in 5A90 Al–Li alloys welded by Nd∶YAG laser welding. A change of microtexture in the WM and HAZ of the welded joint was observed in terms of the component and intensity of the texture. It is found that the typical, strong rolling microtexture of the BM is completely eliminated and replaced by weak and random microtexture in the WM of the welded joint by Nd∶YAG laser welding.

The paper by Wang et al.5 shows the evolution of the residual stress in dissimilar steel overlays during surfacing and post-weld heat treatment. Both as welded residual stresses and heat-treated residual stresses are measured with blind hole and X-ray method, and the residual stresses are analysed with experimental data. Finite element simulation demonstrates that the residual stress decreases after long soaking because of stress relaxation behaviour at high temperature, while, in the cooling stage of post-weld heat treatment, residual stresses will increase because the elastic modulus of the weld metal recovers gradually with decreasing temperature.

In summary, these papers represent the recent progress in computer-aided welding engineering and relevant fields. I would like to thank the contributors and the reviewers who gave critical comments and suggestions on the submissions. I am grateful to Professor T. DebRoy, the editor of STWJ, and Emma Leighton, managing editor at Maney Publishing, for the time and effort they have given in order to ensure the successful publication of this special issue.