Effects Of Shim Matrix-stiffness And Structure-stiffness On Wear And Damage Behaviors Of The Insert

Microcracks can form on the surface or inside an insert during forming or cutting processes.These microcracks tend to expand rapidly under impact loading,eventually leading to tool fracture and failure.Fracture and breakage of inserts cause significant limitations to the improvement of processing efficiency and safe production.As an important part of indexable cutting tools,the shim is in direct contact with the insert and the tool body,often playing a role in protecting the tool body and determining the position of the insert.In this paper,mechanical impact finite element simulation and experimental analysis are performed under a shim-insert system equipped with different material stiffness(Young’s modulus)and surface structure stiffness of shims to explore the effect of shim stiffness on insert wear resistance and breakage behavior.For shims with different material stiffness,insert stress intensity factor,maximum principal stress,strain,contact stress between insert and shim,crack extension deflection angle and breakage are analyzed.For shims with different surface structure stiffness,contact stress,maximum principal stress of the insert,strain,contact stress,wear and breakage are analyzed.which provided a theoretical basis for in-depth understanding of the mechanism of insert stress distribution by shim material stiffness and surface structure stiffness when subjected to impact forces,as well as providing a theoretical basis for correctly designing and selecting inserts and shims for indexable tools.the main research contents and conclusions of this thesis are as follows:Firstly,the effects of shim stiffness on the stress distribution in the insert and at the crack tip under static and dynamic(impact)loading conditions was investigated.The extended finite element method(XFEM)was used to develop a 3D simulation model for an insert–shim system.The model was used to study crack initiation and expansion in the insert for different rigid shims under static and dynamic loading.Analyses of the crack tip stress intensity factor,the maximum principal stress,the strain,the contact stiffness,and the angle and direction of crack deflection were performed.it was concluded that a weakly rigid shim reduced the crack tip stress intensity factor,the maximum principal stress and the contact stress.the stiffness of the shim has no effect on the angle of crack deflection on the insert surface.The weakly rigid shim increases the deflection angle as the crack expands inside the insert,thereby reducing the downward fracture length.Secondly,the surface structure of the shim is designed according to the influence of the material stiffness of the flat structure shim on the fracture of the insert,and design several types of shims in two categories: area gradient and height gradient.A threedimensional simulation model of the insert-shim system is established to study the effects of different shim surface structure parameters on the maximum principal stress,strain and contact stress of cemented carbide and ceramic inserts.It was concluded that the experimental results of cemented carbide and ceramic inserts are basically the same.The cylindrical boss structure height gradient shim and the stepped boss structure area gradient shim are effective in reducing the maximum principal stress and strain of the insert.The four boss structure height gradient shim and the four boss structure area gradient shim are the second most effective in reducing the maximum principal stress and strain on the insert.The stepped boss structure area gradient shim has little effect in reducing the maximum principal stress and strain on the insert.The cylindrical boss structure area gradient shim increases the maximum main stress and strain of the insert,which was not conducive to reducing insert fracture.Finally,cemented carbide inserts were subjected to interrupted cutting experiments under the conditions of four plane structured shims with different material stiffnesses.The wear and breakage during the cutting process were counted and the fracture morphology was analyzed to study the effect of shim material stiffness on the wear and breakage of cemented carbide inserts.Interrupted cutting experiments were conducted with cemented carbide and ceramic inserts equipped with different TC4 titanium alloy surface gradient structure shims.The wear and breakage during the cutting process were counted and analyzed to investigate the effect of different shim surface gradient structure stiffness on the wear and breakage of cemented carbide and ceramic inserts.The experimental results show that for four different material plane structured shims,the strong rigid shim increases the probability of insert fracture,reduces the crack deflection angle of the rear blade surface,and then increases the fracture length of the rear blade surface.The experimental results show that for four different material plane structured shims,weakly rigid shim increases the deflection angle as the crack expands inside the insert,thereby reducing the downward fracture length.Proper design of the shim surface structure has a significant effect on inhibiting insert fracture.