Micro-milling of fused silica based on instantaneous chip thickness

The micro-milling process of brittle materials involves macro-scale tool and nano-scale cracks. This multi-scale coupling problem makes it difficult to accurately predict the milling morphology using conventional methods. In this paper, a novel method is proposed to predict the milled surface quality of brittle materials by the combined method of analytical model and finite element method (FEM) simulation. In the proposed method, the chip thickness model for inclined ball end mills was established. Thus, the multi-scale coupling milling process of fused silica was discretized into several nano-scale local cutting processes to accurately calculate the crack. The chip thickness, as the dominant factor to influence cracks of brittle materials, not only can be used to solve the multi-scale coupling problem, but can predict the crack distribution on the milling groves. In this paper, an instantaneous chip thickness model for inclined ball end mills was established. Then, the chip thickness and cutting force under different tool inclination angles were analyzed. Next, the chip thickness of serial characteristic positions were used as the cutting depth, and the nano-scale local simulations was carried out at several characteristic positions on the cross section of the milled grooves. At last, the milling experiments were carried out under different inclination angles and feed rates to verify the effectiveness of the proposed method. Besides, the collapse phenomenon on the upper surface and side surface was observed and discussed.