Femtosecond laser trimming of CVD-diamond coated punch for fine embossing

Femtosecond laser machining was employed to trim the surface roughness of diamond coating and to sharpen the edge corner of diamond coated punch toward fine piercing and embossing processes in metal forming. CVD-diamond coated WC (Co) punches with the head diameter of 2 mm were prepared for this laser-trimming process. The initial coated diamond film was 9 µm thick; the curvature of coated punch shoulder was 12 µm. The rotating jig was utilized to attain the homogeneous trimming of punch side surface as well as punch head. SEM (Scanning Electron Microscopy) and Raman spectroscopy were employed to describe the microstructure evolution with trimming as well as the effect of trimming on the nanostructure of diamonds. Fine embossing process into 0.1 mm thick AISI304 sheets with narrow clearance, was utilized to describe their plastic flow around the punch shoulder as well as the geometric distortion by elastic recovery. In addition, EBSD (Electron Back-Scattering Diffraction) was also employed to analyze the difference in plastic flow of AISI304 sheets during micro-embossing between the untrimmed and trimmed punches. The applied load to stroke relation, the plastic strain distribution and the phase mapping as well as the shear droop were compared between two diamond-coated punches to investigate the effect of laser-trimming on the quality of embossed product.