Working Group A | Metallurgical joint

Investigation and enhancement on bonding by cold bulk metal forming processes

The aim of this research project is to investigate the bonding surfaces and the conversion of the inner and outer boundary layer in interdisciplinary cooperation with the methods of surface analysis to deepen the understanding of the bonding mechanism.

Abstract:

Cold bulk metal processes provide high dimensional accuracy and good material utilization. The manufactured components are featuring a high surface quality, a low machining allowance, while requiring only low energy consumption for the forming. Because of the cold hardening at low forming temperatures and high strains, cold bulk metal formed components are favorable for high mechanical loads.

Abstract:

The high tribological loads occurring during cold bulk metal forming can be used to bond two workpieces, enabling the possibility to combine the advantages of cold bulk metal forming with a functional material compound. The potential of this material compound comes along with the opportunity to combine high strength material with lightweight material for weight reduction. Further, expensive corrosion resistant materials can be used to cover surfaces of cheaper, corrosion-prone materials. This technique can also be used to include magnetic properties in a component locally.

In the second priority programme’s phase, the design for potential applications of the cold forge welding technology and further opportunities to increase the bond strength are subject to the institutes’ research work. Methods will be established to strengthen or promote bonding of steels to materials in combinations, which are traditionally seen as non-bondable during cold bulk metal forming. Beside the effect of heavy work hardening of the boundary layers by mechanical processes the effect will be analyzed of tempering the billets and varying the geometrical surface structure on the bond strength. Especially the effect of the billets temperature will be investigated intensely to promote bonding and to generate compressive stress due to shrinkage. Further emphasis is put on a subsequent forming processing of the joined components. Due to an unequal distribution of the surface exposure and contact stress, the resulting bond strength varies in a broad range along the weld interface. Thus, in a second forming step further mechanical stress and surface exposure is induced at primarily not welded regions of the component. The suitability and development of heat treatment strategies are pursued with the aim to increase the bond strength and not to influence the mechanical properties of the base material negatively. The research of the second phase leads to the design criterias’ provision for cold extrusion welding processes with specific regard to the material flow and bond formation.