Performance of coated tungsten carbide tools on milling printed circuit board

This study investigates the performance of the ZrN tools coated by the pulsed-DC reactive magnetron sputtering on milling memory modules of PCB (printed circuit board). A speed-adjustable rotation system was designed to find out the optimal process parameters through grey relational analysis and Taguchi method, such as the sputtering distance, flow rate of nitrogen and rotational speed of tool. From the sputtering experiment, the two parameters having greatest effects are the ratio of argon to nitrogen as well as the rotational speed of tool. Within the range of the experimental equipments, the optimal ratio of argon to nitrogen flow rate is 10:4 (sccm), and the optimal rotational speed of tool is around 8 rpm. The average micro-hardness of the surface of the ZrN-coated tools are increased from 15 GPa to 21 GPa compared with uncoated tools by nano-indentator measurement. From the cutting experiments, the cutting tool life of an uncoated tungsten carbide tool is around 38 m, and that of a ZrN-coated tool is around 115 m. And the statistical process capability index (Cpk) of the coated tool also rises from 0.788 to 1.858. It is observed that a ZrN-coated tool not only can extend its used life, but also can improve the cutting quality.