Analysis of defect mechanisms in polishing of tool steels

The polishing process in the mold and die making industries is nowadays still predominantly done manually. As a consequence of this the quality of the mold strongly depends on the worker’s skill, experience and also on his form on the day, patience and concentration. Furthermore, polishing is in most cases the last manufacturing step of the process chain and occurring surface defects are critical and often a “knock-out-criterion”. Until now there exists no systematical acquisition or explanation for the appearance of this polishing defects. This paper shows the results of experiments describing the polishing process and defect mechanisms in order to generate process strategies for manufacturing “defect-free” high-gloss polished tool steel surfaces. Ten different steel grades were analyzed in order to see how the final surface quality is influenced by e.g. the polishing system, the degree of purity or the microstructure. The surface quality is represented by roughness values and SEM-images. It could be concluded that the degree of purity and the homogeneity of the steel material are crucial to the final surface quality. The lower the amount of inclusions, the better the surface quality. Furthermore, a classification of the occurred defects during the polishing process is shown in this paper.