Effect of Machine Hammer Peening and Ball Burnishing on the Surface Properties of Deposited Layers by Directed Energy Deposition

Surface of parts produced by Laser Metal Deposition (LMD) often requires post-processing, particularly for tooling applications. This study investigates ball burnishing (BB) and machine hammer peening (MHP) for improving the surface of LMD parts made from 316L-Si stainless steel and Ferro55 tool steel. Single tracks (1D) and single-layer square areas (2D) were deposited to evaluate local and areal surface responses. BB was performed at different pressures, whereas MHP was applied at different impact energies. For the 2D areas, three relative tool-path overlaps were investigated. Surface roughness, hardness, and geometric deformation were evaluated after post-processing. The results show that the two processes generate different material-dependent surface responses within the investigated parameter windows. In 316L-Si, BB produces a clear pressure-dependent response, resulting in pronounced roughness reduction and near-surface hardening. MHP also improves the areal surface quality of 316L-Si, particularly when high overlap is applied. In Ferro55, the overall roughness reduction is more limited because of the higher hardness and lower plastic deformability of the material. Nevertheless, repeated impact loading under MHP promotes measurable areal smoothing at high overlap. Because BB and MHP differ in tool geometry, loading mode, and energy transfer, the results are interpreted as process-window-specific material responses rather than as a direct ranking of the two methods. The relationship between 1D and 2D measurements shows that single-track experiments are useful for identifying local deformation trends but cannot directly predict the final areal surface quality, especially for MHP.