Study on formation of exit edge defects in the milling process by using the combined theory of the energy conservation and orthogonal cutting mechanism

¹ In the milling process, due to machining materials and process parameters, the material at the edge of the part may break due to shear forces instead of cutting properly, resulting in the irregular pit (defect) at the exit edge. This seriously affects the surface quality of the workpiece. It is vital to understand the forming mechanism of the exit edge defect (EED) before one tries to eliminate or reduce the size of the EED and furthermore to improve the machining accuracy. Therefore, focusing on the milling process at exit edge of a workpiece, this paper presents a novel theoretical model to study the forming principle of the EED and predict the corresponding size. First, the forming process of the EED is separated into two stages. The beginnings of them are symbolized by the initial- and the fracture-negative shear planes. Then, the initial-negative shear plane which is defined by the initial negative shear angle is found. Furthermore, the location of the fracture-negative shear plane is defined using the fracture negative shear angle to study the EED. For the next step, the concentration force of Flamant-Boussinesq problem combined with the yield strength of the material is introduced to obtain the initial negative shear angle. Additionally, using the energy conservation theory, the negative fracture shear angle is calculated. Based on these, the mechanism of the EED is illustrated. Besides, the size (including length and depth) of the EED is predicted based on the geometric relationship between the initial and the fracture negative shear angle. Finally, the correctness of the theoretical model is verified by simulation and experiments. This study provides a promising step to reducing/eliminating the hazards of edge defects.