Study On Drills Of Vibration Assisted Drilling CFRP/TC4 Stacks

Carbon fiber reinforced plastics(CFRP)and titanium alloy are widely used in aerospace manufacturing.Bolts and rivets are commonly used to connect these two materials when they are assembled into CFRP/Titanium stacks.The quality of the assembly holes directly affects the quality and service life of the aircraft parts.In order to ensure assembly precision and processing efficiency,assembly holes of both materials should be finished in the same process.However both CFRP and titanium alloys are difficult to be machined,and the processing performances of the two materials are very different.The defects such as CFRP hole entrance tear,hole wall scratching,material burn or titanium alloy hole exit burr are easy to occur during the drilling of stacks.The vibration drilling can periodically change the feed rate during drilling and the cutting process is discontinuous.So,stable geometric chip breaking and better machining performance are achieved.In this article,CFRP/TC4 stacks are machined with low frequency axial vibration drilling process.Based on the research of the formation mechanism of hole defects in the stacks drilling,the effects of the vibration process on operating angle are analyzed and drills with different structures are designed to study the influence of the drill geometric parameters on the vibration drilling hole quality with drilling tests.The main research contents and conclusions are as follows:(1)By the analysis of the formation mechanisms of CFRP hole entrance tear and TC4 hole exit burr,it is determined that the formation of defects is related to the thrust force and the geometric parameters of the tool.The differences of thrust force,CFRP hole wall roughness and drilling temperature between vibration drilling and conventional drilling are studied with contrast tests.(2)The influences of the change of the drill structure on the processing effects are studied by geometric analysis to determine the tool parameter range for CFRP and TC4.Drills suitable for vibration drilling of CFRP/TC4 stacks are designed on the basis of the influence of vibration drilling on drill operating angle.(3)According to thrust force,drilling temperature,CFRP entrance tear and TC4 exit burr,the influences of drill point angle,helix angle and relief angle on the process and quality of vibration drilling are studied by single factor tests.The drill with 120° point angle,25° helix angle and 20° relief angle is more suitable for the vibration drilling of the CFRP/TC4 stacks.