Product Code: PIC2008_306

Laser Welding of Ultra High Strength Steels for Automotive Applications
Steve Shi, TWI Ltd; Cambridge Great Britain
Steve Westgate, TWI Ltd; Cambridge Great Britain
Presented at PICALO 2008

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. 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, for continuous or stitched body-in-white (BIW) applications, forms part of this strategy of reducing vehicle weight. The work in this paper was concerned with the development of welding procedures for joining thin-sheet UHS steels, using fibre-delivered solid state lasers and establishing the strength and formability of the welds produced. Autogenous laser welding trials were conducted with three different fibre-delivered solid state lasers to achieve fully penetrating butt and lap welds in dual phase (DP), martensitic, transformation induced plasticity (TRIP), Usibor and boron steels of 0.8-1.5mm thickness and 600-1550N/mm2 tensile strength with similar and dissimilar material combinations. The hardening and softening behaviours in the fusion zone and the heat affected zone were determined. Influences of laser process parameters on welding speed, weld profile and joint performance were discussed.

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