The technique will deploy welded steel to aluminium joinings on a seatback for the Cadillac CT6 luxury vehicle, and thereafter on the CT6’s hood reinforcement. The CT6 structure comprises 11 different materials and uses multiple joining processes.

GM has said that the new technique solves the problem of joining two disparate metals through spot welding, which is often problematic as the melting points of aluminium and steel are widely disparate. Furthermore, aluminium’s propensity to oxidise has also led to welding failures. The method removes the need to rivet steel to aluminium, reducing the number of parts needed.

Cost savings on rivets alone are estimated at US$5 to US$100 per vehicle. Weight savings are estimated at 0.3 to 0.5 kilograms.

The steel-to-aluminium spot-welding system makes use of a welding tip design patented by GM. However, the tip fits with conventional tooling so there is no need for specialised welding equipment. GM is expected to make the process available to other automakers.

This new welding process is the next in step in the manufacturing evolution that saw aluminium-to-aluminium welding capability introduced in 2008 that has now gained widespread application in today’s factories.

Automakers are looking to cut weight in vehicles in part to boost fuel economy and to meet increasing federal fuel economy mandates.