Spot-welding aluminum components

Georg Fischer successfully exploiting innovative resistance spot-welding process

Automobile industry supplier Georg Fischer Automotive is exploiting an alternative version of the resistance spot-welding process. Unlike conventional spot-welding, DeltaSpot overcomes the obstacles that have so far always prevented high-productivity joining of aluminum. Experts from Georg Fischer worked with their welding-system partner Fronius to develop a solution for the door-frame of the new Porsche Panamera. According to Wolfgang Hintsteiner, the engineer in charge of this project at Georg Fischer, the production installation has proven to be both reliable and cost-effective.

The characteristic feature of DeltaSpot is its spooling process tapes. These prevent direct contact between the electrode and the workpiece, mediating this contact indirectly instead. This helps to drastically reduce wear-and-tear on the electrode, and makes it possible to regulate and thus optimise the thermal input into the join.

Aluminum is used as the lightweight construction material for both the approx. 3 mm thick frames of the vehicle doors and for the 2 mm thick stiffening plates welded to these frames. The firm’s experts took a novel approach towards solving this task. They had previously reviewed a number of joining processes in terms of their production-engineering suitability and economic viability – conventional resistance spot welding, friction-stir welding, clinching, punch riveting and an adhesive bonding process. “Then we looked at DeltaSpot, which the development engineers from Fronius described as being particularly good at joining aluminum”, recalls Wolfgang Hintsteiner. DeltaSpot emerged from the selection process as the most suitable joining process. The coated die-cast and sheet aluminum parts joined using DeltaSpot pass all the quality tests.

Unlike in conventional resistance spot welding, the spot-welded joins between the door and frame of each vehicle door are executed with almost no spattering, meaning that there is no impairment of the main seal at this sensitive point. Thermally induced workpiece distortion is tightly limited and can be corrected if necessary. DeltaSpot also fulfils the high dimensional accuracy required on the outside flange. By contrast, clinching and punch riveting would not have met this requirement and would also have caused intolerable surface damage due to the shape-distorting action of mechanical forces. Adhesive-bonded joins cannot be subjected to loading before they have hardened, and the adhesive contaminating the surface would interfere with subsequent and parallel joining-processes.

Wolfgang Hintsteiner sums up: “The process tape lets us produce uniform, exactly replicable spot-welds. We weld one of the doors in an approximately 100-second cycle, after which we don’t need to do any finishing-work on the surface. For applications like ours, with weldable castings, a defined surface, an anti-corrosive coating and adequate accessibility, DeltaSpot is the system of choice.”