Investigation Of Transient Cutting Temperature Of Workpiece And Cutting Tool In High Speed Intermittent Machining Process

High-speed machining (HSM) is one kind of mechanical manufacturing technologies, which is characterized with high efficiency, high accuracy and low cost. It has been widely applied in the aerospace, automotive, mold making industries. Continuous cutting and intermittent cutting are obviously different in cutting heat source, heat transfer, heat partitioning and thermal loading pattern. Investigation of cutting tool and workpiece temperature variation with cutting speed in the intermittent cutting processes could be helpful to control cutting speed to reduce thermal shock, which has both theoretical value and actual application value.In this thesis, the combination methods of metal cutting principle, heat transfer theory, finite element simulation and experimental research are used to investigate the temperature variation of cutting tool and workpiece with cutting speed in high speed interrupted cutting, and choosing AISI 1045, H13, Aermet 100 and Ti6A14V as workpiece materials. The effect of ratio of cutting time to non-cutting time on temperature variation of cutting tool and workpiece is also researched. The main contents are as follows.Firstly, based on the thermocouple sensor, two measurement systems are developed to obtain temperature of cutting tool and workpiece during intermittent cutting. The workpiece endures periodical thermal load, and the temperature gradient inside the workpiece is high. The measurement of workpiece temperature requires fast response, high frequency acquisition and multichannel measurement at different depths inside the workpiece. A multichannel thermocouple measurement system is developed in this paper, and it works well to obtain workpiece temperature variation during intermittent cutting. A wireless thermocouple temperature measurement system is proposed to obtain milling tool temperature through integrating the thermocouple and wireless transmission technology.Secondly, a finite element intermittent cutting model is proposed based on the Johnson-Cook constitutive equation to investigate the temperature distribution variation of cutting tool and workpiece with cutting speed. It is found from the simulation results that the temperatures of cutting tool and workpiece grow with the increasing cutting speed to a maximum value and then fall down. More generated heat is carried away by cutting chip, and heat flowing into workpiece and cutting tool decrease after a critical cutting speed. The heat source in a milling period varies due to varying cutting depth. A regression equation about heat flux and tool-chip contact length with cutting depth is established to provide foundation for the theoretical model of cutting tool and workpiece temperatureThirdly, an analytical prediction model of tool temperature is proposed in interrupted cutting, and Green function method and separation of variables method are used to obtain the transient cutting temperature of tool intert. It is revealed that cutting temperature of tool insert increases first and then decreases as the cutting speed grows. Increasing cutting speed results in three factors such as increasing heat generation, reducing heat transfer time and enhancing heat convection between tool and air. As the cutting speed grows, the cutting temperature variation of tool insert is a combination result of the above three factors. The tool temperature grows when the heat generation increasing factor dominates, and the milling tool temperature grows as the cutting speed increases in low cutting speeds. The tool temperature drops when the other two factors dominate, and the milling tool temperature decreases as the cutting speed increases in high cutting speeds. Through the comparison of cutting tool temperature at different ratios of cutting time to noncutting time, it is found that decreasing ratio makes the tool temperature falls and changes softly, and thus reduces the thermal shock.Lastly, an analytical model of transient cutting temperature of workpiece is presented by moving heat source method, to investigate the effect of cutting speed on transient cutting temperature in intermittent cutting. It is found that, more cutting heat is generated per unit time and heat transfer time into workpiece decreases as the cutting speed grows, and thus heat partition ratio into workpiece decreases. The cutting temperature variation of workpiece is affected by both heat source moving speed and heat flux into workpiece. The increasing extent of heat generation is higher than the decreasing extent of heat partitioning into workpiece in low cutting speed, and the workpiece temperature increases as the cutting speed grows. The increasing extent of heat generation is lower than the decreasing extent of heat partitioning into workpiece in high cutting speed, and the workpiece temperature decreases as the cutting speed grows. It is found that relative high temperature region decreases and temperature gradient and thermal shock increase as the cutting speed grows. Results of slot milling of 1045 steel, Aermet100, Ti6A14V and H13 at different cutting speeds agree well with analytical prediction model of workpiece transient cutting temperature.This research is supported by National Natural Science Foundation of China (51425503) and National Basic Research Program of China (2009CB724401) for financial supports.