P 961 - Stress and production-oriented bonding of fibre-reinforced composites in multi-material design

P 1011 - Use of modified spray arc processes to optimise welding-related stresses on components made of high-strength fine-grain structural steels Due to current lightweight construction efforts and demands for energy and resource efficiency, high-strength fine-grain structural steels with yield strengths ≥ 690 MPa are increasingly being used in modern steel structures. These are primarily processed with yield strengths of up to 960 MPa and joined using MAG welding processes. Modern inverter technology has recently enabled numerous company developments (e.g. "DeepARC", "forceArc"), which have led to modified spray arc welding (mod. SLB) with similar properties. In addition to the well-known economic advantages of these mod. SLB, the reduced possible seam opening angles and the lower heat input are expected to have a positive effect on welding-related stresses. Initial residual stress analyses in previous weldability tests with mod. SLB have already shown lower residual tensile stresses in the weld seam in free-shrinking laboratory samples compared to conventionally welded samples. However, the operationally stable design of high-strength welded constructions and the utilisation of high yield strengths require sufficient quantification of welding-related stresses in mod. SLB under defined, component-relevant shrinkage restraint. This concerns both the forces and stresses in the local weld seam area and the overall stress as well as the influence of heat conduction, component geometry, degree of clamping and seam opening angle. There was hardly any knowledge of this in the industry, especially among SMEs, and the aim of this research project was therefore to develop this knowledge. The comparative investigations with conventional arc and mod. SLB with adapted seam configuration were carried out with the aid of special testing equipment that can be used to model real component stiffnesses. With both process variants, weld seams could be realised with the selected parameters while fulfilling the requirements for the mechanical-technological properties. During the analyses, a significant reduction in internal stresses due to reduced heat input was observed when using a seam configuration with a lowered seam opening angle. In particular, the narrower seam gaps proved to be effective in reducing multi-axial stress states due to bending moments in the welds close to the component. The knowledge gained and recommendations made were presented to the relevant standardisation committees in order to facilitate simpler design and safe processing of high-strength fine-grain structural steels in the medium term, especially for SMEs. Standardisation can reduce qualification and approval costs, which are currently often necessary when using high-strength steels. Furthermore, the results will enable companies to utilise the technical and economic advantages of mod. SLB processes and to achieve significant savings in filler metal, welding and set-up time as well as optimised results with regard to the load-bearing capacity of components, taking into account the inherent stresses, and to increase productivity. Publication: 2017 Authors: T. Kannengießer, D. Schröpfer