TWI Industrial Member Report Summary 865/2007
By S G Shi and S Westgate
The increasing demand for improved fuel efficiency and reduced emissions has prompted the automotive industry to seek methods of reducing vehicle body weight by using materials with good strength to weight ratio, such as ultra-high strength (UHS) steels and aluminium alloys. The application of thin-sheet UHS steels enables material savings and/or improved crashworthiness to be achieved without significant modifications to the manufacturing process. Consequently, these steels have been the fastest growing weight reducing materials to be used in vehicle structures in the last decade, despite competition from aluminium alloys and composite materials. Laser welding of UHS steels, either for tailor-welded blanks (TWBs) or, more recently, for continuous or stitched body-in-white (BIW) applications, will form part of this strategy of reducing vehicle weight.
There is little available information on the laser weldability and weld performance of UHS steels. The work in this project was concerned with the development of welding procedures for joining thin-sheet UHS steels, using fibre-delivered solid state lasers and establishing the performance and formability of the welds produced.
- Examine the effect of similar and dissimilar material/thickness combinations on the weldability of UHS steels.
- Establish the static performance and formability of laser welds in UHS steels.
- Examine the effect of laser process parameters on the weld and HAZ hardening/ softening.