Study On The Defect Formation Mechanism And Diameter Control Of Double-stepped Hole In CFRP/Titanium Alloy Stacks

In drilling process of CFRP/titanium alloy stacks,due to the different physical and mechanical properties of CFRP and titanium alloy,there are significant differences in the value of hole diameter measured in two materials under the same drilling condition,this phenomenon referred to as double-stepped hole defect.This defect seriously affects the service and safety performance of aircraft structural parts.In this article,the high efficiency and precision automatic assembly requirements of new generation of aircraft is aimed,the double-stepped hole defects is around,the overall study ideas of“ from the exploration of defects formation mechanism to the precision control of hole diameter ” is adhered,the study method of theoretical analysis and experimental test is used,three aspects of the formation mechanism of double-stepped hole defects under the influence of multi-factor,the hole diameter control of step variable parameter drilling in stacks,and the hole diameter control of low-frequency vibration drilling in stacks arestudied,the main research contents and results are as follows:(1)The factors with potential influence on double-stepped hole defects were analyzed and screened,the multi-condition drilling tests instackswere carried out.Based on the experimental data and theoretical analysis,the law and mechanismof influence of drilling sequence,drilling parameters,tool vibration,chip morphology,drilling temperature and tool wear on the holediameter in stacks were investigated.On this basis,the formation mechanism of double-steppedhole defects under the influence of multi-factors was revealed,and the reasonable measures to restrain defects were also put forward.(2)The drilling experiment study of step variable parameter is carried out.Based on the experimental data,the change of drilling force,hole making quality and hole diameter precision at different step positions were compared,and the optimal step position is determined.By means of mathematical statistics including intuitive analysis,variance analysis and residuals test,the primary and secondary relationshipsrelationship and law of influence of process parameters of step variable parameter drillingon the holediameter in stacks were analyzed,and the optimization scheme of process parameters for hole diameter control was also proposed.(3)Through theoretical derivation,the kinematics analysis of the low-frequency vibration drilling process are carried out,and the theoretical conditions for tool intermittent machining weregiven.The drilling experiment study of low-frequency parameter was carried out.Based on the experimental data,the variation of drilling force,chip morphology and hole diameter precision between traditional drilling and low-frequency vibration drilling technology was compared.By means of mathematical statistics including intuitive analysis,variance analysis and residuals test,the primary and secondary relationships relationship and law of influence of process parameters oflow-frequency vibration parameter drilling on the holediameter in stacks were analyzed,and the optimization scheme of process parameters for hole diameter control was also proposed.