Research On Process Optimization Of Helical Milling Variable Parameters For CFRP/Ti Alloy Stacks Material

Carbon fiber-reinforced polymer(CFRP)and titanium alloys have good stiffness and strength matching,and have good compatibility in electrochemical aspects.In aircraft manufacturing,CFRP parts are often assembled with titanium alloy parts by rivets or bolts.In order to ensure the position accuracy of the connection holes,the two parts are usually pre-mounted together and then drilled once.As CFRP and titanium alloys are all difficult to machine materials,the high-quality integrated hole making of stacked components becomes a major problem for aircraft manufacturing.As a new type of hole making method,the helical milling hole has obvious advantages in the hole making of CFRP material.However,CFRP and titanium alloys have very different material properties and it is difficult to use the same processing parameters to make holes in stacked components.For this reason,this paper studies the variable parameter helical milling hole method of CFRP/titanium alloy stack materials,and optimizes the processing parameters based on the multi-objective optimization method of grey relational and principal component analysis,and provides test data and techniques support for improving the quality of hole making.Through experiments,the axial force and milling temperature variation characteristics of helical milling holes in CFRP/titanium alloy stacks were studied.The results showed that when the tool was cut from the CFRP layer,the axial force immediately increased when entering the titanium alloy layer,and the axial force was reduced when the tool was completely cut into the titanium alloy layer.The cutting temperature also sharply rises as it cuts into the titanium alloy layer,and gradually increases throughout the cutting process.The variance analysis method was used to study the effect of processing parameters such as the rotation speed and feed rate on the aperture error,surface roughness,and delamination of CFRP materials.It was found that increasing the rotation speed was beneficial to reducing the surface roughness of the pore wall,but the pore size shrinkage of the CFRP layer was increased and the burn at the outlet was severe.In order to improve the quality of the hole making,it is necessary to reduce the spindle speed of the titanium alloy layer and use a variable parameter milling hole process.According to the material properties of CFRP and titanium alloys,larger spindlespeeds and feed rates are used in the milling of holes in the CFRP layer,and smaller processing parameters are used in the milling of holes in the titanium alloy layer.The test results show that reducing the length of the variable-parameter region and the number of parameter changes helps to improve the quality of the hole when the processing parameters are decreasing.However,due to the fact that this method has a high feed rate when cutting into the titanium alloy layer,it still causes a sharp increase in the axial force,and the spindle rotates at a higher speed,resulting in a higher cutting temperature.Therefore,the paper also studies the variable parameter helical milling process which reduces the machining parameter first and then increases.It is found that under this drilling technology,the axial force and cutting temperature of stacked area will be reduced,and the quality of drilling will be improved.The grey relational and principal component analysis methods were used to optimize the helical milling process of CFRP/titanium alloy stacks with variable parameters,so as to obtain the optimal variation of the processing parameters in the stack area.The machining results were analyzed from the aspects of axial force,cutting temperature,hole surface roughness,hole diameter error,CFRP layered damage,etc.It was found that the helical milling hole process with reduced and then increased processing parameters can obtain better quality of milling hole.