Research On Large Diameter Hole Drilling Method Of CFRP And Titanium

A variety of holes need to be made during the assembly of aviation CFRP components,and large diameter more than 8 mm holes are called large hole,which is difficult to machine.CFRP has serious defects such as fiber breakage and material delamination during the conventional drilling of large diameter holes.This paper mainly focuses on the CFRP and Ti stacks,and studies the method of making holes for processing large diameter holes and the method of reducing processing damage.Firstly,this paper focuses on the processing principle and axial force of helical milling and prefabricated holes,and estimates the critical thrust force of drilling.In this paper,three methods of helical milling,pre-drilling with a pilot hole and without pilot hole drilling are used to establish the comparative experiment,and are analyzed thrust force,quality and temperature of processing for these three methods.The results show that the thrust force of drilling is mainly provided by the chisel edge of the twist drill bit,and thrust force is the main result of delamination.When the thrust force is less than the critical thrust force,the delamination is significantly reduced.The thrust force is reduced by 47% to 61% due to eliminate the influence of chisel edge.The delamination factor at the exit level is 76% lower than drilling without pilot hole.In terms of temperature,the pilot hole is greatly reduced in temperature due to the reduction in the amount of cutting.Therefore,the method of pre-drilling with a pilot hole is outstanding when manufacturing large-diameter holes.Then,the main objective of this study was to establish a better method of milling holes in CFRP/Ti stacks.Four strategies were studied experimentally and the results compared including thrust forces,delamination and temperatures.In the first and second strategies,it was found that composite laminate experience less damage when machined in the configuration CFRP/Ti compared to Ti/CFRP.The third and fourth strategies employed three steps to achieve the required diameter while alternating the composite-metal stack.It was found that a multistep milling strategy leads to the best quality holes as the subsequent steps eliminate the damage caused by the first step while only utilizing peripheral cutting thus minimum forces.Thrust forces were found to have an almost linear relationship with the feed rates and an inverse relationship with the spindle speeds for all the strategies studied.