Study On Tool Wear Mechanism During Drilling CFRP/Ti Stack

Carbon fiber reinforced plastics(CFRP)and titanium alloy both have a series of advantages such as the light quality,high specific strength,fatigue resistance and corrosion resistance etc.Therefore,using these two materials can greatly increase aircrafts' life,reduce structural weight and fuel consumption,and save the maintenance costs.The usage amount of composite and titanium alloy has already become one factor of the significant technical index on the aircraft evaluation.They have been widely used in aviation,aerospace,marine,automotive and other high-tech fields.It is easy for carbide cemented tool to occur adhesive wear and even the failure phenomenon of edge chipping during the drilling processing of CFRP/Ti stack and titanium alloy.Therefore,the most prominent problem are short tool life and poor hole quality.By means of theoretical analysis and experiment,the variation of mechanical properties of work piece material and tool material at different temperatures,the selection of process parameters of drilling CFRP/Ti stack using carbide cemented tool,the failure mechanism of tool edge chipping and tool failure prediction had been analyzed.Firstly,the Vickers indentation test and friction coefficient test about work piece material and tool material at different temperatures were established.The results show that the hardness of the carbide cemented will gradually decrease with the drilling temperature increasing.As the drilling temperature increases,the friction coefficient between the work piece material and tool material will gradually decrease.Secondly,Influence of cutting parameters on drilling temperature and thrust force and torque of CFRP/Ti stacks were analyzed.Test results show that drilling temperature rise with the increase of spindle speed and the decrease of feed speed.The influence of the spindle speed is greater than the feed speed on the drilling temperature.The thrust force and torque rise with the increase of feed speed while they decline with the increase of spindle speed.The influence of the feed speed is greater than the spindle speed on thrust force.When the drilling processing is carried out at the interface of the CFRP/Ti stack and the exit hole of titanium alloy,the work piece and the tool are strongly vibrated,and the vibration frequency increases with the feed rate increasing.The vibration amplitude at the interface is stronger than at the exit hole of titanium alloy.Then,the affinity interaction between titanium alloy with carbide cemented and thermal residual stresses are the two critical factors for tool edge chipping.The adhesive wear on the carbide cemented tool causes WC grains shedding on the rake face.It results that shear stress perpendicular to the rake face is generated in the vicinity of the cutting edge.The crack propagates along the WC grains at rake face,then expands to the flank face,and eventually results in the tool edge chipping.The phenomenon of crack and tear occur inside the binding phases or at the phase boundary between hard phases with binder phases.Comparing to machining titanium alloy,it is feasible to delay the edge chipping during drilling CFRP/Ti stack owing to the CFRP plate.But it is can't be avoided the occurrence of chipping failure.Finally,a failure prediction model of edge chipping is established,based on the failure mechanism of carbide cutting tool.The failure time of carbide cemented tool in the process of drilling CFRP/Ti stack is calculated theoretically,and the results are consistent with the results of actual drilling experiment.It is reasonable that using the model to predict the failure time of tool edge chipping.The computer software system is established to predict the failure time of tool edge chipping and to choose the drilling parameters suitably.