Laser-multi-pass-welding of aluminium and steel with sheet thickness above 50mm

Thick-walled components made of steel or aluminum alloys are widely used for industrial applications. Welded steel components with sheet thicknesses of 50 mm and above are used for example in big mobile cranes, housings of turbines for power plants and for the base plate of servo-hydraulic presses for automotive body parts etc. Thick-walled welded aluminum components can be found in applications of the chemicals industry and for transportation of liquid natural gases such as LNG tanker. For both material types conventional arc welding technologies are state of the art, often manually performed. Caused by size of the welding torch and the limited penetration depth of multi-pass welding, grove angles of 45° or more are essential. This leads to a high volume weld metal and a high heat input into the base material as well as to a high consumption of filler material. Weld distortion and therefore straightening of the components are cost drivers, too. The paper will be present the latest developments at the Fraunhofer IWS for laser-multi-pass-welding (laser-MPNG) using brilliant solid state laser with laser power of approximately 3 kW for welding aluminum as well as high power diode laser with up to 10 kW for welding of steel. Brilliant laser sources (fiber, disk) with a beam parameter product of 0.4 mm mrad and laser power up to 3 kW are used for multi-pass-narrow-gap welding of aluminum for welding depth of 50 mm and above. Very low groove angles of less than 4° are used, which leads to seam width of max. 4 mm@50 mm welding depth. Using high power diode laser with laser power of up to 10kW the groove angle can be reduced to 12° by using an edge preparation by plasma cutting as known from conventional arc welding technologies. Summarized potential industrial application will be presented. A comparison of laser-multi-pass-narrow-gap welding with the state of the art conventional welding technologies will be given with respect to welding speed, energy input per unit length as well as filler material consumption.