Effect of milling modes on surface integrity of KDP crystal processed by micro ball-end milling

Micro-milling has been widely considered as the most promising method to repair the micro-defects on the surface of KH₂PO₄ (KDP) crystal. However, achieving an ultra-smooth repaired surface by ball-end milling remains a longstanding challenge for KDP crystal due to its soft-brittle properties. In micro ball-end milling of KDP crystal, selection of milling mode is the prerequisite to determine the integrated combination of other cutting parameters (e.g. spindle speed, feed rate and the depth of cut). In this paper, with the aim to investigate the influences of the milling mode on the surface integrity of KDP brittle crystal, the micro-groove experiments were carried out comprehensively. All the milling modes were considered (pull-milling, push-milling, up-milling and down-milling) and corresponding cutting parameters selections were also examined. The results demonstrated that the pull-milling and down-milling are both conducive to ductile mode machining, while the push-milling and up-milling cause adverse impacts on the machined surface integrity. In addition, the optimal combination of cutting parameters were also recommended to guide the mitigation of micro-defects on the surface of KDP crystal by micro ball-end milling process.