Temperature Prediction And Experimental Research In Titanium Alloy Milling

Titanium alloy(Ti-6Al-4V)is widely used in the aviation and aerospace,automobile and biomedical fields because of its outstanding comprehensive performance.However,due to its intrinsic characteristics of low thermal conductivity,elevated temperature exists in the machining zone resulting in tool wear and poor surface finishing.Therefore,Ti-6Al-4V is a difficult-to-machine material.Furthermore,the additive/subtractive hybrid manufacturing technology changes the material processing conditions due to no coolant involved and residual heat induced by additive manufacturing.These greatly increases the milling temperature,resulting in low tool life and poor workpiece surface integrity.Therefore,it is of a great significance to study the milling temperature.In this study,three heat sources in the machining zone are assumed spiral-line heat source based on the principle of milling.A model is proposed to predict the milling temperature by integration method.The workpiece is simplified as an infinite heat conductor by using mirror-image heat source,and thus the temperature of workpiece at any point at any time is calculated.A heat flux equation including milling heat coefficients is deduced by milling force and milling speed.A calibration method of milling heat coefficients,similar to calibration method of the milling force coefficients,is proposed to obtain the heat flux density under different processing conditions in the milling of titanium alloy forged and AMed parts.This study offers a theoretical basis for subsequent milling temperature prediction.A finite element model based on the actual cutting and a finite element model based on heat load are established to predict the milling temperature.The model based on the actual cutting is used to predict the milling temperature in the milling of titanium alloy forged parts.The heat flux density of finite element model based on heat load is calculated by milling heat coefficients.The model based on heat load is used to predict the milling temperature in the milling of titanium alloy forged and AMed parts.The milling temperature in the machining zone is measured by the semi-artificial thermocouples.The predicted and the experimental temperatures under different milling conditions with different milling width of forged part,the feed rate and the initial temperature of the AMed parts are obtained,and the prediction model is validated.The temperature prediction model and the experimental method of milling temperature proposed in this thesis can be applied to other materials and processing technology.The results can offer theoretical basis for the parameter optimization in machining processes with regard to tool wear and surface integrity.