Modeling Of Temperature Distribution At Cutting Area In Cryogenic Machining

Cryogenic machining can greatly reduce the local high temperature at cutting area,increase the tool life,and improve the cutting performance of material,providing an effective solution for the high-quality and efficient manufacturing of difficult-to-machine metals such as titanium alloys.Cutting temperature is an important parameter in processing,which is also a characteristic factor for cryogenic machining.It is closely related to the wear of tool,the cutting force,and machined surface and sub-surface integrity.The dissipation of heat in cryogenic machining is mainly caused by the injecting and boiling of cryogenic coolant such as liquid nitrogen(LN).The injection of LN has been studied by current researches,but the effects of convective heat transfer at other boundaries and the boiling of LN has been still ignored.In this paper,the influences of LN injecting on the boundary condition and cutting parameters are considered,and an analytical model for the prediction of temperature distribution at cutting area for cryogenic machining is proposed.It can also be a valuable reference for the residual thermal stress,the worn mechanism of tool,the integrity of machined surface,and the optimization of cutting parameters.A predictive model of cutting parameters in cryogenic machining was established to compute the heat intensity of heat sources,where a correction term of average cutting temperature on cryogenic condition was introduced.In order to improve the efficiency and accuracy of calculation,genetic algorithm was used to obtain the cutting parameters in the cryogenic machining of titanium alloy.In addition,the convective coefficient of LN was measured by the injection experiment of LN.The boiling curve of LN was estimated by the inverse heat conduction problem,and the value range of the surface convective heat transfer coefficient was also determined,which was prepared for the subsequent calculation of heat intensity of heat losses.The main cutting heat sources and losses were determined according to the application method of LN after analyzing the mechanism of heat generation,transformation and dissipation during cryogenic machining.Based on the moving heat source and the image heat source method,temperature change at cutting area affected by one heat source or loss was calculated respectively.The convective heat transfer at other boundaries was considered,and the uniform distribution of heat intensity at the chip-tool interface was modified to ensure that the temperature at any point on both sides of the interface is the same.The predictive accuracy of the proposed model was verified by experiments of cryogenic turning of titanium alloy.The temperature field on the surface of cutting area was measured by a thermal imager,and the trend of measurement is similar as predicted.The temperature at the tool was measured with embedded thermocouples.Compared with predicted cutting temperature at the corresponding positions,it was shown that the proposed analytical model can accurately predict the temperature distribution at cutting area for cryogenic machining.The average predictive error is lower than 3.3%,and the maximum error is 6.7%.