Investigation Of Tool Crater Wear And Plastic Deformation In Metal Cutting

Metal cutting, as the most basic manufacturing processes, are widely used in varieties of modern manufacturing enterprises. During the cutting process, severe friction, high temperature and pressure occurring in tool-chip interface cause crater wear on tool rake face. This leads to the change of cutting condition, decrease of the tool intensity, and finally tool failure. Therefore the investigation of crater wear mechanism and model is quite necessary. In addition, workpiece suffers severe plastic deformation in primary shear zone in machining. Research on the plastic deformation is significant for basic understanding of cutting process, and provides some insight for exploring material constitutive law at high temperature and high strain rate.This research focuses on crater wear modeling, evaluation of plastic deformation in primary shear zone and influences of chip morphology on tool-chip contact length when uncoated cemented carbide tool cutting low carbon steel. The dissertation includes the following aspects:(1) Based on crater wear experiments, an empirical crater wear model for conventional speed machining is established to describe the relationship between wear rate and process variables. Finite element simulation for machining process is used to obtain temperature distribution on tool-chip interface, which is the important parameter in wear model. Regression analysis can determine the coefficients in wear model. The proposed crater wear model gives good prediction to crater wear profile in similar cutting conditions, and also shows the contribution percentage of different wear mechanism along crater profile.(2) With high speed machining experiments, crater wear model for high cutting speed is established. It can accurately predict crater wear profile with cutting time before tool fail. According to the temperature distribution on tool-chip interface observed by using ballistic set-up, a temperature model corresponding to crater profile is proposed to determine temperature parameter in wear model. Regression analysis can determine the coefficients in wear model. (3) In order to analyze plastic deformation in primary shear zone, deformed flow lines on cutting material are obtained from high speed orthogonal cutting experiments performed by ballistic set-up. A general streamline model is innovatively used to present plastic flow of cutting material in high speed machining. Accordingly velocity, strain rate and strain distribution of cutting material in primary shear zone are calculated based on the streamline model. Furthermore, this streamline model is also applied to determine the plastic deformation in conventional speed machining. The differences of plastic deformation between conventional and high speed machining are analyzed.(4) High tool-chip contact length with low feed is found in the investigation of crater wear in high speed machining. Therefore, a series of experiments with large range of feed are carried out in ballistic set-up to record chip morphology and tool-chip contact length. The influences of chip morphology on tool-chip contact length are quantitatively analyzed.