Surface integrity of turned laser-welded hybrid shafts

Abstract

For applications like components of vehicle drives, e.g. drive shaft or motor shaft, the increasing amount of CO₂ emission becomes a major challenge. Weight reduction of vehicle parts is one possibility to reduce CO₂ emission. Therefore functionally adapted components must be designed in order to become smaller and lighter. Consequently monolithic material is not sufficient anymore, so there is a demand for tailored hybrid parts consisting of more than one material. Those tailored hybrid parts have to pass through a processing chain. There is the option of joining different materials in the hybrid part to meet the requirements. The discussed combination is a SAE1020-SAE5120 compound. Laser beam welding is an appropriate joining process due to its reduced heat influence, the resulting narrow welds and a low post-processing effort. Thus semi-finished products for the manufacturing of tailored hybrid shafts with graded properties can be produced efficiently. Further in the process chain there is the need for machining to reach an adequate level of accuracy of shape and dimension. Moreover the residual stress modification by the machining process has a deep impact on the lifespan of hybrid components. Therefore in this paper the machinability of the SAE1020-SAE5120 compound compared with a SAE1020-SAE1020 compound will be examined. The effect of cutting edge micro geometry on the surface and subsurface properties is analysed. Relationships between process forces, residual stresses and surface roughness are investigated. Metallographic cross sections and hardness measurements will show the connection between welded materials. The transition zone—the weld between the monomaterials—is the centre of attention for the investigations.