TWI Industrial Member Report Summary 739/2002
D Downs and S Mulligan
Car manufacturers need to strike a balance between customer demands with regard to luxury and performance on the one hand and the ever-tightening (CO 2) emission and safety legislation on the other. This has led to the use of thinner but stronger gauges of steel to reduce vehicle body weight, and thereby increase fuel economy. Other, more recent developments include the use of laser welded tailored blanks, lightweight materials (aluminium and magnesium alloys) and hydroformed tubes.
The application of hydroformed tubes combines lower mass with increased stiffness and integrity when compared to the more traditional components made of resistance spot welded stampings. However, for the welding of body panels to the thin-walled hydroformed tubes, the absence of flanges and the lack of access to the inside of the tube means conventional resistance spot welding cannot be applied as this requires the weld area to be clamped between two spot electrodes. Therefore, different thin sheet welding techniques, referred to as 'single-sided' because access is required to only one side of the joint, need to be employed.
In this project, two welding techniques were investigated for welding of thin galvanised steel sheet to hydroformed tube. The techniques were Nd:YAG laser welding and pulsed alternating current metal active gas welding (AC MAG), as these should both be suitable for single-sided welding of thin sheet. Furthermore, the performance of two different types of Nd:YAG laser sources was compared, namely a lamp and a diode pumped source. The latter produces a beam with a higher beam quality than its lamp pumped counterpart and can therefore be guided using a smaller diameter optical fibre to give a smaller focused spot size.
- Determine the suitability of Nd:YAG laser and pulsed AC MAG welding for welding of thin, galvanised steel sheet to hydroformed tube.
- Compare the performance of diode and lamp pumped Nd:YAG laser sources in terms of travel speed, weld quality and process tolerance for welding of thin, galvanised steel sheet.