Mechanism of burr accumulation and fracture pit formation in ultraprecision microgroove fly cutting of crystalline nickel phosphorus

In precision glass molding (PGM) of glass materials with a high melting point, heat treatment of nickel phosphorus (Ni-P) should be made in advance to eliminate mold deformation during the high temperature molding. During the process, crystallization occurs on the plating and crystalline Ni-P with a particular micro-machinability is generated. Burrs of large sizes with a fibrous structure are observed on the microgroove ridge during the study of the fly cutting microgrooving. The Poisson burr accumulation in each material removal period is considered as the reason for the burr formation and a model of the burr accumulation in fly cutting is established based on the concept of maximum effective cutting thickness. According to the model, a high feed rate leads to the restriction of burr formation while fracture pits tend to be generated on the microgroove ridge. The fracture pits caused by the brittle removal of the material could be eliminated through the feed rate adjustment of fly cutting. The optimal processing parameter is proposed in consideration of the burr formation restriction and the elimination of fracture pits. The efficiency of microgroove mold machining is significantly improved. A high-quality microgroove mold is fabricated and the serviceability of the mold is tested through a PGM experiment.