Analysis of Nonlinear Characteristics of Milling Force in Processing Splicing Joint Area of Automobile Mold

The structure and the cavity surface hardened steel mold of automobile cover is very complex. In the stamping process, the local structure bears higher extrusion stress than the type surface, which often causes local wear and even cracking. The process of multi-hardness splicing joint is applied to ensure the service life of the die according to the features of each part of the mold. The impact load caused by the repeatedly cutting in which always leads to the unevenness of cutting force in the whole process. The machining quality of the mold surface is reduced. Aiming at the ball-end milling process in mold splicing area, first, the impact behavior of tool workpiece cutting contact is analyzed. A prediction model for ball-end milling force in the splicing area is established by establishing the transient chip thickness model which considering the impact factors. Second, the experiment of cutting force measurement for Cr12MoV mold steel ball-end milling which is based on single hardness and multi-hardness are carried out to verify the model. Cross-correlation analysis based on data of milling force signal and machined surface roughness is carried out for getting the relevance of them in different processing states. Finally, the ApEn is used to analyze the nonlinear characteristics of the milling force signal at the multi-hardness splicing state. This explores the influence of the milling force on the machining quality. The experimental and analytical results show that the milling force signal exhibits more obvious chaotic characteristics in the multi-hardness stitching area than that in the single hardness region. This provides a basis for improving workpiece surface quality and improving cutting efficiency.