| Carbon fiber reinforced plastics(CFRP)with high strength,high modulus,and high resistance of fatigue,corrosion and heat,is one of the most potential aerospace materials.However,its high hardness,poor thermal conductivity and low laminating shear strength that leads to delamination,burr and splitting.What is worse,the tool wears easily,and surface quality is bad.Those bad behaviors seriously restrict the application of CFRP.CFRP drilling has been the researching hotspots,in recent years,some scholars found that ultrasonic vibration assisted(UVA)drilling could significantly reduce the thrust force,processing heat and tool wear,which shows great potential in CFRP hole-machining field.On this basis,this paper put forward to further researching the longitudinal and torsional ultrasonic vibration assisted(L-T UVA)drilling,and studied the theory and force characteristics of drilling,then explored the influence of processing parameters on the machining quality,for sake of finding the optimal processing without defects.The main contents were as followed: 1.designed 35000 Hz single-excitation L-T horn and built the UVA drilling equipment.2.Based on the axial vibration drilling model,the L-T UVA drilling model was created,then analyzed the model by the combination of theory and experiments.3 Various CFRP plates were carried out on drilling experiment with self-developed L-T UVA drilling equipment,then analyzed effects of speed,feed rate,ultrasonic vibration and plate type.4.The effect of cutting parameters on the inlet and exit delamination of CFRP was analyzed through experiment.Through theoretical analysis and experimental study,it can be concluded that: 1.Under the condition of UVA drilling,the maximum instantaneous cutting speed of L-T mode is greater than that of axial mode,and the instantaneous impact force of the former is larger which means that the CFRP material could be removed with much more effectively;2.Under the same cutting parameters,L-T UVA drilling can effectively reduce the axial force.In the case where the axial force remains constant,UVA drilling method could choose a larger feed rate and a lower rotation speed than conventional drilling,indicating that UVA drilling could improve processing efficiency and increase the scope of versatility of the machine 3.For weaved CFRP,the ratio of the tangential velocity Vc to the axial feed rate Vf is exponentially distributed for the influence on the axial force.Whether by conventional drilling or L-T UVA drilling,the thrust force varies with ratio's changing,the ratio has the critical value,and L-T UVA method can reduce the critical value to a certain extent,finally improve the processing quality;4.For quasi-isotropic CFRP plate,the influence of processing parameters on delamination is that higher rotation speed and lower feed rate could leads to lower delamination factor,and the UVA drilling method can significantly reduce the factor. |
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