Research On Defect Suppression Helical Milling Technology On CFRP

Carbon fiber reinforced plastics(CFRP)is a laminated heterogeneous material composed of carbon fiber and resin material,which is widely used in aerospace and military industry for its excellent characteristics such as high specific modulus,high specific strength,corrosion resistance,fatigue resistance and so on.Thus the application proportion of CFRP has become one of the important symbols to evaluate the progressiveness of aerospace vehicles and other products.To meet the assembly requirements in the practical application of CFRP components,a large number of riveting and bolting are needed.So hole making process is the most commonly used processing technology in the manufacture of CFRP components.The cutting mechanism of CFRP is different from that of metal due to the anisotropy,which can easily lead to a series of defects in hole making,such as delamination,burrs,tearing,etc.These defects cause the overall strength decline of the component and leave undetectable safety hazards,which have an unrecoverable destruction on the high reliability and long-life service of the component,and restrict the wide application of CFRP components.Due to the high hardness of carbon fiber,the tool wear seriously in the hole making process,resulting in low processing efficiency at the same time.Therefore,in order to achieve high quality and efficiency,the research of CFRP hole making technology has always been a research focus at domestic and abroad,and it is also a recognized problem in the manufacturing field.In recent years,as a new method applied to CFRP hole making,helical milling shows many advantages such as high machining accuracy,good quality and low cost compared with traditional drilling.However,due to insufficient research on machining mechanism and special tools,as well as less practical experience,there still is a huge space for improving the hole making quality.Taking research on the tool design for high-quality hole making in helical milling as the starting point,this paper studies the CFRP low defect helical milling technology.And the article studies the cutting force and cutting temperature characteristics of the novel tool in the process of CFRP helical milling,and comes up with damage suppression method in efficient machining of CFRP helical milling to improve quality and efficiency.The main research contents of this paper are as follows:Firstly,on the basis of studying the characteristics of helical milling,a new tool for defect reduction helical milling of CFRP is developed.The machining process,cutting force and cutting temperature of CFRP helical milling are analyzed,and the delamination formation at the exit of CFRP helical milling is studied.The influence of technological parameter such as cutting parameters,tool diameter and ratio of milling to drilling on the hole making effect in helical milling are researched experimentally.A novel tool for defect reduction helical milling of CFRP is proposed,which can realize the composite machining process of helical milling and multiple reaming,the upward thrust force in the reaming process inhibits the generation and expansion of delamination and tearing at exit in principle.Secondly,the cutting force characteristics of the novel tool are studied.Based on the analysis of the tool motion in helical milling,the calculating of the width and thickness of undeformed chip in helical milling is presented.Considering the effects of undeformed chip shape,cutting edge and cutting parameters,an helical milling force model is established on the basis of the instantaneous rigid force model,and the validity of the model is verified.Combined with the machining characteristics of the novel tool,the cutting force model of defect reduction helical milling is established based on the cutting force model of helical milling.The characteristics of the cutting force in defect reduction helical milling are analyzed,and the experimental results show that the novel tool can effectively reduce the thrust force in CFRP hole making.Then,the prediction of cutting temperature field in the process of CFRP defect reduction helical milling is studied.The influence of cutting temperature on the quality of CFRP helical milling is explored through the experiment of preheating workpiece.According to the cutting theory,the heat source model of CFRP cutting is established,and the heat flux in the processing of end mill and novel tool is analyzed.According to the movement of the tool and the diffusion of heat in helical milling,the prediction model of temperature field distribution in three dimensional polar coordinate is established,and the correctness of the temperature field model is verified.The temperature rises of traditional end mill and novel tool at different cutting speeds are compared by experiments,which verify that the novel tool for CFRP defect reduction helical milling can effectively reduce the machining temperature.Finally,the machining performance of novel tool is analyzed and the damage suppression method in efficient machining is studied.Under the same condition,the quality of exit,entrance,hole wall and tool life of traditional end mill and novel tool are compared and analyzed.In order to further improve the efficiency of helical milling,a damage suppression method in efficient machining of CFRP is proposed,and a depthoriented high-efficiency damage suppression processing control system is built,and the high-quality,high-efficiency CFRP helical milling technology is realized with the adjustment of feed rate allocation strategy.