Improvement of die life with surface texture control and solid lubricant

The methodology of controlling the surface texture of dies by means of Hybrid-shot peening was examined for the improvement of the die life cycle applied to high strength steel sheets. Hybrid-shot is double-shot peening, where the irst treatment is performed using large particles, and the second one is performed with iner shot particles. The specimens of tool steels for dies treated by Hybrid-shot showed a high resistance against galling which was evaluated by the galling generation load of the draw bead test by using an oil lubricant, compared with the single shot specimens. his result suggested that the surface texture influenced the galling property. For a quantitative analysis of surface texture of die mafterial, Fast Fourier Transformation (FFT) was used. Findings revealed that the ratio of the spectrum amplitude between high and low frequencies calculated by FFT corresponded to the galling generation load of draw bead tests. On the other hand, the conventional index of surface roughness, Rz, had no relationship to the galling generation load. Furthermore, the effect of solid lubricant, that is, the powder produced by scallop shell, on the galling property was studied. The addition of ine scallop shell powder in the oil lubricant increased the galling generation load.