Development of hybrid laser arc welding process for automotive structural applications.

Abstract

In today’s world, two-wheelers (Motorcycles and Scooters) have become an indispensable part of people’s lives. Customers are demanding high quality product with superior performance of the vehicle. Frame is one of the safety critical part of a two-wheeler which highly contributes to the functional and aesthetic quality of the vehicle. Predominantly, gas metal arc welding (GMAW) process is being used for the manufacturing of frame. Limited depth of penetration and low welding speed of GMAW process significantly hinders the quality and productivity. Moreover, high heat input of this process consequently results in larger distortion. High fusion zone and HAZ area leads to degradation of material properties. Better structural integrity and consistent frame dimensions are required to meet the functional and finish quality requirements of a vehicle. Hence, advanced laser welding processes were investigated as an alternative method to GMAW process in the facets of productivity, heat input, weld bead geometry, aesthetic quality, gap bridgeability and distortion. Typically two- wheeler frame is made of low carbon steel. Thus low carbon steel of S275 grade was used for the evaluation. The outcomes were compared with existing GMAW process to quantify the benefits of laser welding. High power density of autogenous laser welding (ALW) process provided deeper penetration with significant improvement in productivity. When compared with GMAW process, productivity was improved by a factor of 8 times in 2 mm and 4 mm thick plates whereas 3 times improved productivity was achieved in 8 mm thick plates with complete penetration. However, lack of reinforcement and restricted part fit-up tolerance were found to be the critical limitations of ALW process. On the other hand, addition of filler metal using a GMAW arc in hybrid laser arc welding process (HLAW) ensured a better weld geometry and improved gap bridgeability of the process. Moreover, it was provided deeper penetration and significant improvement in productivity which is comparable to ALW process and far higher than GMAW process. Both HLAW and ALW processes produced ~75% and ~85% less distortion than GMAW process respectively. Moreover, HLAW process improved the productivity with considerably less increase in hardness than ALW process. For instance, in 2 mm thick material, productivity was improved by 8 times than GMAW process with 55% and 17% increase in average fusion zone hardness in ALW and HLAW processes respectively. Moreover, substantial reduction in fusion zone and HAZ width was obtained in both HLAW and ALW processes. In mechanical strength standpoint, all three welding processes produced weld region stronger than base material. Therefore, fracture was occurred in the base material during tensile test. Overall, HLAW process combines the advantages of both individual processes and eliminates the limitations of them. Hence, hybrid laser arc welding process can be considered as the future of welding in the automobile sector.