On material separation and cutting force prediction in micro milling through involving the effect of dead metal zone

Shearing and ploughing forces are the main cutting force components in cutting process. Traditional cutting force model, which considers ploughing force as an item independent of the uncut chip thickness, cannot be used in micro milling process. Thus, it is desired to further understand the contribution of the uncut chip thickness to the shearing and ploughing forces in micro milling. This article presents a new method to describe the material separation phenomenon together with the influence of the uncut chip thickness on micro milling force. By combining the plastic formation theory with the slip-line field theory, a material separation model is first developed to theoretically calculate the shape of the dead metal zone, which is a common physical phenomenon appearing in micro milling. As a result, the positions of three separation points, which are related to the cutting edge radius and the cutting parameters, are realized being calculated in an analytical way for the first time. Based on the developed separation model, the minimum uncut chip thickness (MUCT), which is the critical bound determining whether the material flows to the rake face or the clearance face, is theoretically derived and calculated. Finally, a cutting force model that can separately consider the shearing and ploughing effects is established. Both numerical simulations and experimental cutting tests validate that the proposed material separation model and the cutting force model are reasonable for micro milling process.