Research On Formation And Suppression Of Surface Damage In Milling Of CFRP

Carbon fiber reinforced polymer(CFRP)has outstanding advantages such as high specific strength,high specific stiffness,performance designability and simultaneous manufacturing of materials and structures.It has become the preferred material for weight reduction and efficiency improvement of high-end equipment in aerospace.During the manufacture of components from CFRP,a large number of edges,blind windows,profiled contours,etc.are required to be milled after curing in order to meet the required tolerances and to manufacture fitting and joining surfaces.However,due to the macroscopic anisotropy and lamination characteristics of CFRP,the material removal form is significantly affected by the direction,and the surface material is in a severely weakly constrained state.This results in the formation of burrs,tears and other damage on the surface of CFRP during milling,which seriously affects the bearing performance of the components.Aiming at this problem,this paper studies the formation and inhibition of CFRP surface damage from two aspects: fiber cutting angle in the horizontal direction and the constraint state of the surface material in the vertical direction.Firstly,aiming at the factor affecting damage in the horizontal direction-fiber cutting angle,the global distribution law of surface damage with respect to fiber cutting angle and cutting edge radius has been obtained through the slotting experiment of CFRP unidirectional laminates,and the comprehensive influence mechanism of fiber cutting angle,cutting edge radius and milling cutter movement on the surface damage in CFRP milling has been elucidated from two aspects of transient cutting and dynamic cutting.It is found that fiber cutting angle and cutting edge radius are the key factors affecting the distribution range and existence form of surface damage.The milling cutter movement induces a continuous dynamic change of fiber cutting angle,and the damage is dynamically accumulated in the interval where it is easy to form,and finally the degree of damage is determined.Reasonable selection of milling method is a way to effectively suppress surface damage in trimming CFRP.Secondly,aiming at the factor affecting damage in the vertical direction-the constraint state of surface material,the corresponding model for cutting a single fiber with one-sided constraint has been established and the influence of the concentrated force direction in the model has been analyzed.The axial force is used to replace the concentrated force,and the difference of the constraint state and damage of the surface material in different axial force directions during milling has been analyzed.Studies have shown that the one-sided weak constraint state is the root cause of surface damage.The direction of the concentrated force has a significant influence on the degree of damage.By changing the tool structure to apply axial restraint at the surface material,the purpose of strengthening the constraint state can be achieved,and surface damage can be effectively suppressed.Finally,the interaction between fiber cutting angle and surface constraint state has been further explored.Based on the fiber/resin interface crack length at the minimum radius of curvature,the fiber bending direction in different fiber cutting angles has been obtained,and the degree of damage inhibition caused by axial restraint in different fiber cutting angles has been discussed.In addition,the effect of feed per tooth has been analyzed experimentally.Studies have shown that the fibers in the acute angle zone are mainly bent in the layer,and the fibers in the obtuse angle zone are mainly bent outside the layer.The degree of damage inhibition by the surface constraint for the obtuse angle region is better than that for the acute angle region.In addition,an increase in the feed per tooth will attenuate damage inhibition by the constraint.In actual machining,the milling quality can be improved by reducing the feed per tooth.The above researches have been revealed the causes and processes of surface damage formation in CFRP milling.The research result has certain reference value for the further study of CFRP damage formation mechanism.At the same time,it provides a certain guiding significance for the comprehensive selection of the structure and parameters of the tool,the milling method and the cutting amount in the actual processing,which can realize the low-damage processing of CFRP.