Research On Delamination Suppression Of CFRP In Bidirectional Drilling

Carbon fiber reinforced composite(CFRP)is a new type of composite material with high specific strength and specific modulus,which is widely used in aerospace,transportation,medical and other fields.The application of CFRP material requires a large number of connection holes to be processed during the assembly process.At present,drilling accounts for more than half of the total follow-up machining,of which about 60% of the scrap of composite components is caused by drilling damage.Drilling damage mainly includes delamination,tearing and burrs,among which delamination damage is the interlaminar failure phenomenon caused by the multi-layer structure of composite materials during the drilling technology.It will not only increase the assembly error of the component and reduce the support strength of the assembly hole but also damage the long-term working performance of the component under the continuous action of fatigue load,which has the greatest impact on the drilling quality.In view of these problems,this thesis proposes a process method for bidirectional drilling of CFRP,which can effectively suppress delamination.The specific research contents are as follows:1)The delamination mechanism of CFRP drilling was studied.The removal process of twist drill drilling CFRP laminate was analyzed and a two-dimensional cutting model of twist drill drilling CFRP laminate was obtained.Aiming at the further analysis of the process of adding the support plate and the bidirectional drilling technology,the causes of the delamination damage under different processing technology are explained in principle.An experimental platform for bidirectional drilling of CFRP was built and the drilling technology experiment of twist drill was carried out.By analyzing the process of delamination damage under unidirectional and bidirectional drilling,the delamination mechanism under traditional drilling and bidirectional drilling is obtained,which provided a theoretical basis for the proposal of delamination control methods.2)The critical thrust force of CFRP drilling was studied.The force distribution of unidirectional and bidirectional drilling of CFRP was analyzed,and a critical thrust force model for twist drills was established based on the brittle fracture theory and classical shell theory of CFRP materials.A measurement platform for thrust force was built and a static pressure experiment was designed.Comparative experiments verified the accuracy of the layered model and the effectiveness of the bidirectional drilling technology.Comparing the experimental results and model data,it is found that the average relative error between the model prediction data and the experimental data is 6.55%,so it can be considered that the critical thrust force model of bidirectional drilling has a good prediction effect on the critical thrust force,and the model is reliable.The critical thrust force in the bidirectional drilling technology is significantly larger than that in the unidirectional drilling,which indicates that the bidirectional drilling can increase the critical thrust force and suppress the delamination of the outlet.3)The delamination damage suppression of common tools in bidirectional drilling was studied.Based on the occurrence mechanism and of CFRP delamination damage in tool drilling,and using the experimental platform built in the first two chapters,the variable parameters of twist drill and nest drill under different tool feed speeds and different spindle speeds were designed.By comparing the experiments,the experimental results of the delamination damage morphology,cutting force,and delamination damage area under different machining tools was obtained.Through the experimental results,the force cutting characteristics and delamination shape of the machining tool is further analyzed,and the delamination damage is evaluated.The processing characteristics of twist drill and nesting drill are obtained,which provides a new process idea for different tools to process CFRP.This thesis starts from the drilling theory of CFRP and combines the theoretical model with the experimental research,and then the delamination damage occurrence process,delamination damage suppression mechanism,thrust force characteristics,and delamination control method of the bidirectional drilling CFRP laminate process are carried out.Finally,the two-dimensional cutting model for the delamination process of twist drill drilling CFRP laminate,the critical thrust force model of unidirectional drilling and bidirectional drilling of twist drill drilling CFRP laminate,and the common tool in bidirectional drilling are obtained.It provides guidance and reference for the bidirectional drilling CFRP process method to suppress the exit delamination.