Research On Low Temperature Assisted Small Holes Processing Technology For Carbon Fiber Reinforced Polymer

Carbon fiber reinforced polymer（CFRP）is a widely used advanced composite.It has high specific strength,high specific stiffness,good conductivity,thermal stability and corrosion resistance and other excellent properties.The diameter of carbon fiber is very small（usually around 10μm）,and the tensile strength of CFRP can reach 5 times that of steel,while the proportion is only 1/4 of steel,which can significantly improve the performance of high-end equipment such as aviation,aerospace and transportation.As CFRP is an anisotropic material,different from traditional metal materials,it is easy to produce serious machining damage such as delamination,burr and tear during processing.For example,in the aircraft assembly process,the proportion of parts scrapped due to processing defects is as high as 60%.Therefore,aiming at the processing of CFRP holes,this paper studies the cutting mechanism and process from the aspects of improving the processing quality and efficiency of CFRP.Firstly,combined with low temperature assisted cutting condition and helical milling technology,the low temperature assisted helical milling process is studied.The quality of CFRP holes under two cutting conditions（dry cutting condition and low temperature assisted cutting condition）is investigated by comparative experiment,and the influence of machining conditions on tool wear,delamination,burr height and surface morphology is revealed.The results show that the tool wear is relatively large under low temperature assisted cutting condition,but the delamination factor and burr height are relatively small,and the machining holes are more regular and better surface quality is obtained.Secondly,the mechanism of CFRP low temperature assisted helical milling process is studied.By analyzing the effects of low temperature assisted condition on the cutting performance of CFRP,the patterns of key process parameters(spindle speed n,axial feed per tooth f_za,pitch a_p)on the key performance indexes of cutting force,cutting temperature and aperture deviation in CFRP hole machining are investigated during the helical milling process.The results show that for the cutting force index,the axial feed per tooth f_za has the greatest influence.For the cutting temperature and aperture deviation indexes,the spindle speed n has the greatest influence.Then,based on the response surface method（RSM）,the cutting quality of CFRP low temperature assisted helical milling process is investigated.The patterns of key process parameters on the wall surface roughness,the maximum outlet burr length and the maximum outlet delamination factor of the key quality index of CFRP hole machining quality are clarified.By establishing the mathematical models is to optimize the process parameters of low temperature assisted helical milling,and the optimal process parameter combination of machining quality is determined.The verification test results show that the optimal combination of process parameters can well suppress the damage defects generated during the machining process and improve the surface quality.Finally,for the smaller size of 1 mm holes,the drilling experiment is carried out by using the superhard PCD tool independently developed by the research group.The experiment analyzes the cutting force,surface morphology,delamination,and aperture accuracy by different axial feed speeds v_f,and the process parameters combination with the best drilling effect is identified,and conducts tool wear verification experiment.The results show that under the guidance of the process parameters combination,the tool wear can be effectively reduced and the high efficiency and low damage machining of small holes drilling can be realized.This paper provides theoretical and technical support for the research of suppressing the frequently machining damage in CFRP hole making,and also provides process technology reference for efficient and low damage machining of other types of composite materials in the future.