Simulation And Experimental Study On Drilling Force Of TC4 Titani?m Alloy Micro-hole Machining

With the development of modern industry,the miniaturization and precision of products become one of the trends in manufacturing industry.Because of its high efficiency,high precision and so on,micro drilling has a unique advantage in micro-hole machining.TC4 titanium alloy has been widely used in aviation,medical,electronic,national defense and other fields due to its high specific strength and good biocompatibility.However,the micro drill bit is easily subject to wear and break in the process of micro drilling TC4 titanium alloy,a kind of difficult machined material.It has been found that the drilling force is the main factor that causes micro bit's wear and fracture and also provides the basis for the optimization for machining parameters.Therefore,it is more of importance to study the drilling force during the process of drilling TC4 alloy.Firstly,a kind of analytical numerical force mode,for the prediction of drilling force during TC4 titanium alloy micro machining,is established by differential method.Moreover,a numerical model for predicting drilling force of the same process is established by using the whole drill bit.Finally,a micro drilling test system is built to validate the above two models.The main contents are as follows:1.An analytical numerical force model is developed to solve micro drilling force.(1)After the paper makes a study on the structure of the micro drill bit,compares to the similarities and differences between the traditional twist drills bit and the micro drill bit,and probes into the drilling principle of micro-hole drilling,the micro drill is reduced to two connected inner circular turning tool.Moreover,the cutting lips and the chisel regions are treated as a series of oblique sections and orthogonal cutting units respectively by micro-element method,while the variation of the rake angle,clearance angle,tool cutting edge inclination angle,cutting speed in different cutting unit must be taken into consideration.(2)All the forces loaded by every section are simulated by DEFORM simulation soft,considering the size effect sufficiently.During the process of modeling,the strain gradient theory is used to study the specific scale effect in micro-hole drilling and modify the constitutive equation of Johnson-Cook of TC4 titanium alloy,thereby to establish a constitutive model suitable for micro-hole drilling.(3)The integral coordinate system of the whole bit and the local coordinate system of every cutting unit are built respectively,and each unit's cutting force is transformed into the bit of force.Then,the overall thrust force and drilling torque can be determined.(4)This method is used to simulate the force of the drill bit under different cutting parameters,and the influence of different cutting parameters on the force of the drill bit is studied.2.A numerical model for predicting drilling force of micro drilling of TC4 titanium alloy based on integral drilling bit.(1)SOLIDWORKS and DEFORM are used to carry out solid modeling and parametric modeling of micro drill bit respectively,and the final geometric model is picked out,which is more able to describe the actual drill bit,after comparing the similarities and differences between the two models.(2)During the process of drilling simulation,the mesh is quite easy to be distorted,and the parameters of the mesh and the mesh distortion are studied.Other parameter settings are the same as the first model.(3)The force of the drill bit is simulated under different cutting parameters,and the influence of different cutting parameters on the force of the drill bit is studied.(4)Under the same cutting parameters,the simulation results of the two models are compared,and the similarities and differences are analyzed.3.Before a test is made on the TC4 titanium alloy—axial force and torque taken as test indexes and rotation speed,feed per tooth,and the depth of hole selected as experimental factors,the micro drilling test system is set up.Based on the analysis of the test results,the correlation effect is obtained,and then saliency influence of each factor are acquired by two factor analysis of variance.Based on the above analysis,the theoretical basis is provided for selecting suitable drilling parameters aiming at perfect fit between axial force and torque.Moreover,after a series of simulations and experiments under the condition of different process parameter are performed,it is found that these two models can all predict micro drilling force during the process of drilling accurately.Lastly,the causes for the error of these results are analyzed in detail.