Prediction And Measurement Of Cutting Temperature For Coated Tools

Coated cutting tools play an important role in manufacturing industries. It is reported that more than 80% cutting tools currently used are coated cutting tools. The coatings of the cutting tool have great influence on cutting heat generation and heat conduction in the tool during machining. The coatings of coated cutting tools affect accuracy of the machined surface and strongly influence tool wear, tool life and frictional behavior in cutting process. The methods to determine temperature in cutting process include analytical method, experimental measurement, numerical analysis, hybrid technique and heat source method. Because the partial different equations of heat conduction are hard to resolve, the method mainly used to obtain the coated tools temperature is numerical analysis method and experimental measurement at present. Past studies have investigated temperatures of coated cutting tools, however, the influence of coating material and coating thickness on temperature distribution in coated tools has not been gotten agreement by now. It has not been built a temperature measurement system to monitor coated tools cutting temperature in real time during machining.An aim of this research is to find the appropriate proprieties of coating material and coating thickness in heat conduction respect and build a measuring system for cutting coated tools temperature.To discover how to choose thermal properties of coated cutting tools when calculating cutting temperature, the temperature distributions were obtained with temperature-dependent properties and temperature-independent properties of coated tools using numerical method. The results indicated that temperature-dependent properties should be considered when calculating cutting temperature. To simplify calculation, selecting the thermal conductivities at average temperature to substitute for temperature-dependent properties can reduce calculating error. The method to determine the heat flux into coated tools was proposed based on heat transfer principle. The heat brought away by chip was taken as being transferred to the coated tool firstly, then, carried away by chip from the coated tool with a particular transfer coefficient. The results of the calculated examples indicated that the heat flux and the tool-chip contact temperature can be developed and the optimal cutting parameters can be obtained using this new method.The present investigation has been conducted in order to develop a new sensor to measure temperatures, especially for cutting presses with coated cutting tools. For this purpose, a novel thermocouple sensor using a tool coating and its substrate has been first fabricated. In order to calibrate the novel sensor accurately, a special instrument was been designed. The working principle of the developed sensor was analyzed. The experimental results showed that this novel technology for measuring cutting temperature is valid in manufacturing processes with coated cutting tools.In order to find the principle of the influence which coating impact on cutting temperature, several mathematical models of heat conduction in monolayer coated tools has been proposed. The temperature distribution formulations in monolayer coated tools were obtained using analytical method. The influence of different parameters including thermophysical properties of tool coating and tool substrate and thickness of the coating layer on temperature distribution in monolayer coated tools were discussed and illustrated. The experiments were conducted using three different cutting tools with coating layers: TiAlN, TiCN/Al₂O₃, TiCN/Al₂O₃/TiN coated flat-faced inserts of cemented carbide substrate. The work materials used in this study were AISI 1045 carbon steel. The tool-chip contract temperature ware measured. Using the above studied method about thermal properties of coated tools and heat flux into coated tools, the temperature distribution formulations in monolayer coated tools which were deduced analytically previous in this section were validated. Results indicated that low thermal diffusivity coefficient and high thickness of the coating make low transient temperature, and low thermal conductivity coefficient, and high thickness make low steady state temperature in the coated cutting tool, and the calculated temperatures are identical with the measured ones.A novel approach to prediction of cutting temperatures within coated tools is presented lastly in this paper. The diffusion layer which results thermal resistance between coating and its substrate is considered. A diffusion layer model was firstly developed. Equations for effective thermal conductivity of diffusion layer were then derived. The influences of diffusion layer on cutting temperatures of coated tools were analyzed using finite element method. Results indicated that the simulated temperature with the new model is more accurate than that of the conventional one compared with measured temperature.In this study the influence of the coatings on coated tools were analyzed. Several models of heat condition in coated tools have been constructed. It is discovered the principle of the coating material and coating thickness affects heat conduction in coated cutting tools. The conclusions of this research developed in this work provide a methodology for design and choice of coated tools in manufacturing industries. A novel sensor using tool-coating and its substrate as thermocouple was firstly fabricated. The coating-substrate thermocouple provides a method to measure cutting temperature of coated tools in real time during machining. The cutting temperatures of coated tools with temperature-dependent and constant thermal properties were investigated. This work provides a methodology of how to choose the thermal parameter of coatings when calculating cutting coated tool temperature. The diffusion layer theory about coated tools was firstly developed. The model considering diffusion layer of coated tools in more reasonable than the conventional one.This dissertation is supported by National Great Project of Scientific and Technical Supporting Programs of China During the 11th Five-year Plan (NO. 2008BAF32B01) and National Basic Research Program of China (No.2009CB724401).