Shot Peening

Shot peening is a cold working process where shot media is accelerated and focused by nozzle onto the machined workpiece. The Shot media is the tool of the peening process technology and is generally deployed in the form of hard grains. The surface treatment by means of shot media is based on the impact that each individual grain generates on the workpiece surface upon collision.

The impact of the grains, which mainly consist out of materials like steel, ceramics and glass, causes primarily an increase of the near-surface compressive residual stresses and changes in the topography and roughness of the workpiece. The changes in the stress state of the material are based on local inhomogeneous elastic-plastic deformations. If the impact-induced

The challenge of these materials is that damage can emerge before the occurrence of higher plastic deformation. For this reason, it was initially assumed that the hardening of brittle materials by deformation induced compressive stresses is not possible. However, recent publications reveal that shot peening can be performed by using favourable peening conditions in order to induce micro-plastic deformation and to increase near-surface strength of brittle materials. For example, compressive residual stresses up to 2500 MPa and with a depth of 130 µm can be introduced in a surface of a tool steel. Furthermore a load carrying capacity, which indicates the hardness of a component, up to 3 times higher than the initial state is achievable. Beside the challenges regarding to the mechanical characteristics of tool materials, there are also process related

The resulting rough and brittle surface is also called the white layer. The challenge for the peening process is to remove the white layer and to improve the quality of EDM machined surfaces. Several investigations prove that the removal of the white layer and the heat-affected zone is possible by using SiC grains and certain other parameters. In addition, peening reduces the roughness caused by EDM and compensates the reduction of fatigue strength by introducing compressive stresses. As a conclusion, peening was found out to have definitely the potential to be applied under specific peening conditions in tool manufacturing to achieve improvements of tool surfaces in terms of strength and fatigue