Vienna (TU). - „Cylindrical stainless steel parts showing significant deformations are being manufactured by the millions and built into cars. The intricate shapes are consequences of the extremely limited space in the engine compartment,” explains Professor Dieter Schuöcker of the Institute for Forming and High Power Laser Technology of the Vienna University of Technology. The process of hydroforming is being widely applied in the automobile industry. Now the researchers succeeded in optimising it by applying a special heat treatment based on a laser beam.“ For hydroforming a stainless steel blank is being put inside an exterior tool. Then water is being pumped into the tube under very high (up to 2.000 bar) pressure and causes a dilatation of the workpiece, which has to adapt to the shape of the afore mentioned exterior tool, “ explains project collaborator Alexander Kratky.

One complication with the manufacture of such parts is consituted by tubes with so-called  domes or cylindrical protuberances, that serve as connectors of different parts of the exhaust system. More often than not it is impossible to shape those protuberances in just one step of hydroforming. Kratky: “Steel hardens with every forming step endured. This can eventually even lead to collapse of the part. We call that “strain hardening”. The objective is the exact shaping of the workpiece while avoiding tears at the edges.”

A laser beam heating the workpieces between hydroforming steps exactly in the zones that have to undergo the greatest deformations replaces laborious interstage annealing in an oven. This heat treatment permits the forming of parts with perfect edges without tears. Even more the hydroforming process will be significantly less costly due to the application of the laser treatment. The research project, carried out in cooperation with the company “ELB-Form” situated in the Montafon has been funded by the “FFG” (Österreichische Forschungsförderungsgesellschaft mbH).