MAG welding in carmakers

The steady rise in oil and fuel prices since the oil crisis of the 1970s, and the demand for weight and CO ₂ emission reductions expressed at the Kyoto conference, have given a strong impetus to the process of reducing the weight of motor vehicles. To reduce vehicle mass, metallurgists have been engaged since the early 1980s in the development of new ultra-high-strength (THR) steels, to meet both this lightweighting objective and improved passenger safety in the event of an accident. Carmakers have access to steels with strengths ranging from 180 to 2,000 MPa, most of which are coated on both sides with a zinc layer around 0.01 mm thick to ensure good corrosion resistance. A car body is made up of around 250 parts, usually cold-formed, but some are hot-formed at around 900°C. These parts are made from an increasing volume of THR steels. Frame parts with thicknesses of between 1.5 and 4 mm withstand the highest stresses and strains. They are arc-welded using the MAG (Metal Active Gas) process. The vast majority of welds are lap welds, with a few T-joints and almost no butt welds.

Today, all welding operations are automated, with the welding torch transported by a robot. The filler metal is very often a solid wire with a diameter of 1 mm. On the other hand, the nature of the active gas is quite variable: depending on the manufacturer, we find gases whose composition varies from 5 to 100% CO ₂ , the remainder being argon. MAG welding, invented in the 1940s, is a simple and rapid assembly process. Since then, welding generators have evolved considerably, making this welding process the most widely used in the world.

The aim of this article is to present the state of the art of MAG welding in the automotive industry, as well as the welding behavior of very high strength (VHS) steels.