Product Code: ICA13_2103

Laser Welding of Fully Austenitic Twinning Induced Plasticity (Twip) Steels
Authors:
Velten Behm, Volkswagen AG; Wolfsburg Germany
Stefan Huinink, Sitech Sitztechnik Gmbh; Wolfsburg Germany
Manuel Otto, Salzgitter Mannesmann Forschung GmbH; Salzgitter Germany
Matthias Hofemann, Salzgitter Mannesmann Forschung GmbH; Salzgitter Germany
Andre Springer, Laser Zentrum Hannover E.V.; Hannover Germany
Stefan Kaierle, Laser Zentrum Hannover E.V.; Hannover Germany
Presented at ICALEO 2013

One of the key disciplines in today’s automotive engineering is the ever-increasing need to design lighter cars in combination with an increased crash performance. With this end in view, the use of conventional steel grades often leads to a compromise between weight and security. In other words, designing with conventional steel grades has almost reached its limit.
Fortunately, a recently introduced class of so called austenitic “twinning induced plasticity” (TWIP) steels offers promising mechanical properties, namely a high tensile strength as well as a high ductility. These steels provide the opportunity of shaping complex sheet metal geometries, having an advanced crash performance and a low weight at the same time.
Nevertheless recent studies have revealed limited weldability of TWIP steels regarding quality requirements. That is especially true for spot and inert gas welding techniques: the material’s characteristics can lead to hot cracking in the joints and distortion of the workpiece.
As there exist only a few data on laser welding of TWIP steels, it is the task of the present study to examine their laser weldability.
The welding equipment is set up of a 16kW disc laser, a linear 3-axis CNC machine and a basic processing head with a focal length of 560 mm. The resulting beam characteristics correspond closely to laser remote systems which are widely used in automotive production lines.
Main aspects of this work were to identify the welding tolerances and to determine the joint strength of different TWIP grades within a range of 0.9 mm to 1.5 mm thick sheets. The results show that laser welded joints are free of hot cracks and lead to less distortion of the material, compared to GMA welding. They also show that changing process parameters can significantly increase the joint’s quality, especially with regard to spatter formation.