Car bodies first to be friction stir welded

The technique is debuting on the 2004 Mazda RX-8.

Previously, resistance welding was the most feasible joining process for assembling aluminum body panels. This technique passes a large current through the aluminum using large, specialized machines. With the new spot-joining method developed by Mazda, a welding gun holds the parts from both sides with a welding tool. The tool spins as pressure is applied. This generates frictional heat that softens the aluminum. The resulting plastic flow of the metal joins the parts.

The only energy consumed with friction stir welding is the electricity needed to rotate and apply force to the welding tool. The process eliminates the need for the large current and coolant/compressed air that conventional resistance welding requires. Energy consumption drops nearly 99% for aluminum and 80% for steel. Equipment costs also drop by 40% as there's no longer a need for large-scale sources of electricity and specialized joining equipment. The process also produces no weld spatter, which makes for a cleaner and safer assembly line.

Use of aluminum for automobiles is one important approach to make vehicles lighter, which leads to enhanced fuel efficiency and improvements in safety and dynamic performance. Experts expect aluminum to be used in other areas. Previously, it was difficult to join parts with welding methods such as resistance, arc and laser, as aluminum is a much better conductor of electricity and heat than steel. In addition, other methods presented cost issues. For example, rivet cost is an issue with riveted joints while mechanical clinching requires large equipment.

Mazda's friction-stir-welding operation reduces energy consumption by 99% compared to resistance welding.

The rear doors and bonnet of the Mazda RX-8 are friction-stir-welded aluminum.