Development of surface residual stress and surface state of 42CrMo4 in multistage grinding

In this study, cylindrical grinding of a 42CrMo4 (AISI 4140) steel with varied grinding sequence stages is analyzed regarding the effect of the different loads during multistage grinding up to the resulting final residual stress state and material structure. The grinding process was adjusted in a way to enhance the mechanical load with varying intensity and generate a pronounced compressive residual stress state in the final grinding step. Furthermore, consecutive multistage grinding processes were carried out and investigated. Using a mobile XRD system with a cos α method mounted on a robotic positioning arm, repetitive measurements of the ground surfaces were performed in the machine tool without sample removal, giving information about the surface residual stress development for each step of the process sequence. The information about the surface integrity development and possible effects of the grinding process during each step is relevant for the contact conditions and modification mechanisms which lead to the final surface integrity. It is shown that the final material state, normally accessible in post-process investigations, can also be achieved reliably by sequencing the process into several steps of a regular grinding process and depends strongly on the contact parameters in a non-linear way. It could be shown, that even the spark out step can lead to significant changes in the surface residual stress state.