Honda Motor Co. Ltd. reported some details of a new technology it developed for continuous welding of dissimilar metals — steel and aluminum — and how it has been applied for producing the subframe of a mass-production vehicle.

The subframe is a critical structural element of a vehicle body frame. The automaker indicated it adopted this new method for the first time in the North American version of its new 2013 Accord, which is available this month. The new process will be expanded sequentially to other models.

Honda explained that as it aimed to reduce vehicle weight in its effort to increase fuel economy, it focused on friction stir welding (FSW) and developed a new approach for the continuous welding of steel and aluminum.

FSW is a solid-state joining method used mainly for applications where the original metal characteristics must be maintained to the greatest possible extent. It works by mechanically intermixing the two pieces of metal at the junction, transforming them into a softened state that allows the metal to be fused using mechanical pressure. It is frequently used for joining aluminum, often for large pieces that may be difficult to heat treat after welding to recover temper characteristics.

Honda noted that FSW technology generates a new, stable metallic bond between steel and aluminum by moving a rotating tool on the top of the aluminum, which is lapped over the steel with high pressure. As a result, Honda said, the welding strength becomes equal to or greater than conventional metal inert gas (MIG) welding — the most common method for welding common materials, steel-to-steel or aluminum-to-aluminum.

This new technology contributes to improvements in fuel economy by reducing body weight by 25%, compared to a conventional steel subframe. Also, Honda noted that electricity consumption during welding is reduced by approximately 50%. And, the new process allows a change in the structure of the subframe and the mounting point of suspension, which increased the rigidity of the mounting point by 20% and contributes to the vehicle’s dynamic performance.

Furthermore, Honda established a new method to apply this technology to mass-production vehicles. Conventionally, FSW required use of large equipment, but Honda developed a FSW continuous welding system applied to a versatile industrial robot. This system can be used for aluminum-to-aluminum welding, too, and thus the welding system with the same specifications can be used to produce a full-aluminum subframe.

Honda further noted that it has developed a non-destructive inspection system* using a highly sensitive infrared camera and laser beam, which allows in-line inspection of the bonding location for every unit.