On finishing of pressing die surfaces using machine hammer peening

Artikel i vetenskaplig tidskrift, 2011

Machine hammer peening (MHP) is a new method for finishing of surfaces. With this method, the workpiece surface is hammered with a spherical carbide tool. The main objective of the study was to evaluate whether the MHP method could become a plausible substitute for manual polishing in pressing die manufacturing where nodular cast iron is a common workpiece material. To do this, sample nodular cast iron surfaces were hammered and evaluated. Changes to the surfaces were evaluated using surface roughness measurements, hardness measurements and optical images. First of all, the workpiece surface was smoothened. Secondly, the surface hardness was increased significantly. Thirdly, the nodules on the workpiece surface were affected. They appeared to be smaller and not as visible. This effect would likely create a die surface less prone to galling since the cavities would not be filled with sheet metal to the same extent in a forming operation. In addition, with MHP, the amount of polishing needed to manufacture a die surface can be reduced because of the smoothening effect.