Effect of indirect cryogenic cooling on the machining accuracy and tool vibration in the turning of polysulfone

Cutting deformation and cracks are common problems during the machining of precise polymer parts. This paper aims to explore the effect of different conditions on the contour profile of machined surfaces and tool vibration. Turning experiments of polysulfone (PSU) were performed under three conditions: dry, conventional flood cooling, and indirect cryogenic cooling. Then the formation mechanism of machined surfaces contour profile under different cutting conditions was clarified by the Eyring equation from the perspective of molecular chains relaxation time. Furthermore, extension models of crazing and cracks were proposed through the microscopic morphology of machined surfaces and the discriminant formula of crazing generation to explain the differences in tool vibration. The results indicated that the indirect cryogenic cooling condition with the internally cooled cutting tool could significantly improve the machinability of polysulfone, and have an excellent performance on the contour profile of machined surfaces with and the inhibition of crazing. Compared with dry and conventional flood cooling, indirect cryogenic cooling could reduce the mean of the Contour profile (Ra) by 40.3% and 30.1% and the machining accuracy error by 41% and 83%. The indirect cryogenic cooling method proposed in this work provides a reference for the cryogenic machining for polymers.

Finite Element Investigation of Cutting Performance of Cr/W-DLC/DLC Composite Coated Cutting Tool

Coupled with a thermo-mechanical metal cutting process, rapid tool wear, higher surface roughness and mass heat are caused by the rapid plastic deformation of the workpiece and by the friction along the tool-chip interface. This phenomenon is more predominant in the machining of difficult-to-cut materials. DLC film has been applied as coating material in the machining of difficult-to-cut materials, and shows a good cutting performance. In this study, Cr/W-DLC/DLC coated tools were compared with other three coated tools (i.e., TiC-, TiAlN-, Al 2 O 3 -) to investigate the cutting performance in the machining of Al-Si alloy (AC9B). In addition, the influence of Cr/W-DLC/DLC coated tools on the cutting performance under different cutting speeds was studied. Cutting force, cutting temperature, heat transfer coefficient of the rake face of the tool, cutting deformation rate, plastic deformation of machined surface, the interface temperature and stress were investigated numerically based on Finite Element Method (FEM). Actual cutting experiments were carried out to the verification of the FEM models by means of the cutting force and cutting temperature measurement. The investigation results showed that Cr/W-DLC/DLC coated tools has the lowest cutting force and cutting temperature, good cutting deformation characteristics and lower coating-substrate interface temperature and stress, however appears the maximum value of heat partition coefficient into the cutting tool. With the increasing of cutting speeds, cutting force and cutting temperature showed an increase trend, while the plastic deformation depth of machined surface and heat partition into cutting tool all showed a decrease trend. This investigation can provide the theory basis or technical guidance for the cutting practice of Cr/W-DLC/DLC coated tools.

A Study on Work Hardening in the Laser-Assisted Machining of Si3N4 Ceramics under Different Material Removal Modes

In order to understand the work hardening phenomenon and mechanism of laser-assisted machining (LAM) of Si3N4 ceramics, the work hardening degree of LAM Si3N4 under different material removal modes was studied. Two sets of single-factor experiments were performed in which the laser power and the cutting depth were changed respectively. The results show that work hardening is the result of the combination of heat and cutting deformation during cutting. The work hardening degree decreases with the increase of material softening degree. When the material is removed plastically, the work hardening degree is 110–115%.

Characters of Deformation and Surface Quality and Cutter Wearing at High-Speed Cutting

In this paper, the impact of cutting speed and feed amount on cutting deformation and surface quality and cutter wear have been studied by the test of high manganese steel cutting with metal ceramic tool at high speed. The results show that it is feasible by cutting high manganese steel with cermet tool at high-speed cutting (HSC). Chip changes into succession segment from band in macrostate. Sawteeth can be seen on the top surface of chip while high temperature feature in burning color and cold welding form appear on the bottom of the chip. The model of surface roughness built can be used to predict surface quality at HSC, and provided cutting optimized parameters scheme. Further research indicates that high-speed cutting has its special deformation mechanism and plastic chips exhibit hot brittleness which provides a favorable condition for solving the chip breaking problem in the cutting of high manganese steel.