| Titanium alloy and superalloy are widely used in aerospace field because of their high strength,good corrosion resistance and high heat resistance.As a typical difficult-to-machining material,the machining accuracy,machining quality and fatigue life of titanium alloy and superalloy parts have always been the focus of attention in the field of machining.In this paper,the anti-fatigue manufacturing technology of titanium alloy and superalloy materials is taken as the starting point,and the surface roughness is controlled at a low level through the selection of processing parameters.On the basis of this,the influence law and mechanism of machining methods and process parameters on surface plastic deformation and fatigue life of specimens in finishing machining are studied,and a new idea is put forward for improving the fatigue life of parts of difficult-to-machining materials such as titanium alloy and superalloy.It also provides a certain experimental basis for the selection and optimization of machining parameters.Firstly,effect of turning and milling on the surface plastic deformation and fatigue life of TC4 titanium alloy were studied.Machining experiments were carried out by using the single factor control variable method,and fatigue test of specimens was carried out.By measuring the data index of the machined surface and fatigue life of specimens,it is found that fatigue life of specimens in milling is significantly higher than that of specimens by turning,and the main influencing factor is the fibrosis direction of the surface plastic deformation layer.Among them,the direction of tissue fibrosis on the surface of specimens in milling is consistent with the direction of fatigue loading,and the direction of tissue fibrosis on the surface of specimens by turning is perpendicular to the direction of fatigue loading.In order to study the effect of the depth of surface plastic deformation layer on fatigue life of specimens,experiments of turning TB6 titanium alloy were carried out in this paper.First of all,after consulting the relevant literature,the selection range of common machining parameters is determined,and several groups of machining parameters are selected to carry out the turning experiment of surface integrity.Surface integrity data(surface roughness and surface micro-hardness)of specimens were measured.Then,according to the measured results,appropriate machining parameters are selected by the control variable method,and effect of tool flank wear on the surface plastic deformation and fatigue life of specimens are carried out by using the single factor variable method.It is found that fatigue life of specimens in turning is sensitive to the change of surface roughness R_a.Only when surface roughness R_a is lower than a critical value,fatigue life of specimens will rise with the increase of the surface plastic deformation depth,otherwise it will decrease rapidly.In order to study the effect of the surface plastic deformation depth on fatigue life of specimens during side milling,experiments of GH4169 superalloy of specimens in milling were also carried out in this paper.Experimental steps of milling are basically the same as that of turning.After the completion of machining and fatigue testing experiments,through the analysis and summary of the data of surface roughness,surface plastic deformation index and fatigue life of specimens,it is found that fatigue life of specimens in milling rises obviously with the increase of the depth of surface plastic deformation,and fatigue life of specimens decreases rapidly when surface roughness R_a reaches a large critical value.However,in general finishing,surface roughness of specimens will be lower than the critical value,so that fatigue life of the specimens can be improved by increasing the depth of surface plastic deformation.The experimental idea of this paper is also of great significance to the progress of aviation parts technology. |
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