Inhibition behavior of milling hole outlet defects inhibition on quartz fiber polyimide composite through LN2 inner cooling

The helical milling hole process of quartz fiber reinforced polyimide composites (QFRP) aimed to remove high-strength fiber and low-strength resin through thermodynamic interaction. But the defects, especially delamination at hole outlet, were difficult inhabited because of heterogeneous and anisotropic of composite. A mechanics model of milling hole force of QFRP was established by considering the shearing force of single fiber and temperature. A liquid nitrogen (LN2) inner-cooling machining equipment was employed for cryogenic milling hole testes. Compared with the conventional dry milling hole, the processed composite surface morphologies, cutting temperature, and milling force were investigated at hole outlet in detail. The study results show the predict values of the established model are compared and verified through the experimental measurement. And the cryogenic coolant processes can improve the composite mechanics properties, milling forces, and cutting heat. The composite can be completely chip breaking in cryogenic cooling, and the burr and delamination are effectively inhabited at hole outlet. Meanwhile, the rapid decline of cutting force and lower interlamination bonding force problems can be solved by the cryogenic cooling cutting. And the fiber avoidance can be improved through the increased tangential force, and the fiber can be efficiency chip breaking under the bigger tangential force. In addition, LN2 cooling can inhabit the cutting high temperature and increase the bonding force, the delamination defect of composite can be adequately improved in cryogenic.