On the correlation of hammer-peened surfaces and process, material and geometry parameters

Abstract

Hammer-peening can replace extensive hand-polishing during the processing of freeform surfaces, but it is rarely applied in practice due to the interplay of numerous parameters, including the process and tool parameters as well as the geometry and the material of the workpiece. In the present study we systematically investigate the effect of tool radii, tool angles, pressure, path and impact distance and the path definition (with respect to the direction of previous surface milling) on the resulting surface roughness and strain hardening of a cast iron, a low- and a high-alloyed steel using a pneumatic tool setup and complementary Finite Element (FE) simulations. Our experimental results show that an impact and path distance of 0.18 mm, a pressure of 7.3 bar and a tool radius of 8 mm reduce the surface roughness of a face-milled surface with an average roughness of Ra = 0.8 μm to an average roughness of Ra = 0.5 μm for all materials under consideration. The FE simulations indicate that, for a ball-milled surface, the surface roughness Ra decreases (and the arithmetical mean height Sa increases) the most for a tool angle of 45° and for a hammer-peening path perpendicular to the previous ball-milling path. These results contribute to the development of a mathematical model that allows to identify suitable parameter combinations prior to hammer-peening processing for a given workpiece surface.