New Processes

Another central topic of work at the BIAS is the planning and qualification of new processes capable of significantly enlarging the process envelopes of laser beam welding now considered to be given. Laser GMA hybrid welding, a combination of a laser beam and a gas metal arc (GMA) in a common process zone, is one of these processes.

Figure 1: Laser GMA hybrid welding head in industrial pipe production

It enables the combination of the advantages of conventional GMA welding (such as a good gap bridging ability and a high energetic efficiency) with those of laser beam welding (as e.g. a high welding depth and high attainable welding speeds) whilst minimizing their respective disadvantages. Not only due to these advantages a CO2-Laser GMA welding process for continuously and longitudinally welding stainless steel linepipes was developed, qualified and implemented in an industrial environment together with important components of the system (e.g. an appropriate welding head, Figure 1) within the framework of the European research project JOTSUP.

Figure 2: Longitudinal pipe seam Ø 273 x 8 mm, supermartensitic stainless steel

Within this project, 100% defect-free weld seams (Figure 1) (according to the company's quality standards) have been achieved. Moreover, welding speed was increased from less than 0.3 m/min for arc welding to more than 1.2 m/min and thus reach the limitsations of the forming unit. For Aluminium and ist alloys, Laser GMA hybrid welding is excellently applicable, too. In the realization oft modern lightweight design concepts in waggon building, the use of laser technology for welding the longitudinal seams of extruded aluminium profiles has significant advantages compared to MIG welding applied up to now. In the framework of studies on this topic a 4 kW Nd:YAG laser was, ba the help of a specially designed hybrid welding head, combined with a 250 A MIG torch. As common in MIG welding of aluminium, a pulsed arc was applied. It could be demonstrated that Nd:YAG-Laser MIG hybrid welding was fit to safely fulfill the industrial demands concerning production tolerances and gap bridging ability. Thus, the process does not require increased efforts considering seamp reparation and clamping. This is an essential prerequisite for the application in longitudinal welding in waggon builiding. Figure 3 shows a model component of the ICN, which was welded with a seam length of 2 m without any special clamping.

Figure 3: Longitudinally welded roof component of the ICN (AlMgSi0,7; SZW AlSi12; PL = 4 kW, PMIG = 3,65 kW)

Here, hybrid welding also enables a welding speed several times increased at significantly reduced seam volume. The result is a total heat input reduced up to 85%, thus contributing in special to a significant reduction of distortion.