| TC4 titanium alloy is an alloy composed of other elements based on titanium.It has a series of advantages such as excellent corrosion resistance,low density,high specific strength,good toughness and weldability.Because TC4 titanium alloy is a difficult-to-process material,the improvement effect of the surface quality of the workpiece after barrel polishing is limited,and it is difficult to achieve the desired surface roughness.Research shows that the surface quality of the workpiece is closely related to its service performance.When the surface roughness of the TC4 titanium alloy workpiece drops below 0.250?m,the fatigue strength is not affected by the roughness value.At the same time,cryogenic treatment enhances the workability of the workpiece,and the physical and mechanical properties are also improved to varying degrees.In order to make the surface roughness of TC4 titanium alloy reach 0.250?m or less after processing,this paper combines cryogenic treatment with barrel finishing,using EDEM discrete element analysis software for simulation,and experiment research on barrel finishing technology.Different test methods analyze the surface integrity of the workpiece before and after cryogenic treatment,and explore the mechanism of the influence of cryogenic treatment on the barrel finishing of TC4 titanium alloy.The main research contents are as follows:(1)Through the EDEM discrete element simulation analysis software,the simulation is carried out to analyze the processing position of the workpiece in the drum during the barrel polishing and the changes in the force and speed of the workpiece before and after the cryogenic treatment.It is found that the position of the workpiece in the vertical direction is basically unchanged during processing,and the horizontal direction performs regular reciprocating motion;the magnitude of the tangential force before and after the cryogenic treatment is basically the same,and the force on the normal direction increases by 20.08%;There is no obvious change in the size and cycle of the speed of the workpiece in the processing medium.(2)The orthogonal experiment was used to study the influence of centrifugal barrel finishing process parameters on the surface roughness of TC4 titanium alloy.Orthogonal experiment results show that the diameter of the grinding block has the greatest influence on the processing effect during the machining process,followed by the rotating speed of the drum,type of the grinding block and the processing time.Analysis of the material removal rate found that the white ceramic abrasive block is more suitable for processing TC4 titanium alloy.The better experimental level combination for range analysis is: drum speed 350r/min,grinding block diameter 4mm,grinding block type is white ceramic,and processing time is 20 min.The analysis of variance shows that the diameter of the grinding block have a significant effect on the surface roughness of the workpiece.(3)Single factor experiments are used to analyze the effects of cryogenic treatment in different time periods on barrel finishing and the influence of different barrel finishing parameters on the workpiece after cryogenic treatment.The experimental results found that the surface roughness of TC4 titanium alloy workpieces treated by cryogenic treatment for 11 hours decreased the most compared with other time periods.The single-factor experiment was used to compare and analyze the surface roughness of non-cryogenic and cryogenic workpieces after rolling and finishing.It was found that cryogenic treatment can further reduce the surface roughness of the workpiece.The single factor experiments of the drum speed,the diameter of the grinding block and the type of the grinding block respectively concluded that: 350r/min,4mm,white ceramics,which are consistent with the results obtained by the orthogonal experiment.(4)Analyzing the physical and mechanical properties of TC4 titanium alloy,it is found that the cryogenic treatment causes the TC4 titanium alloy to recrystallize,and the ? phase is transformed into the secondary ? phase.After the cryogenic treatment,the content of the ?phase is 1.51 times that before the cryogenic treatment.The strong internal stress makes the TC4 titanium alloy recrystallize.The organization is more uniform and the density increases.The microhardness test shows that cryogenic treatment can slightly increase the microhardness of TC4 titanium alloy,and when treated for 11 h,the microhardness value reaches the maximum,which is 3.47% higher than that of the workpiece without cryogenic treatment.Residual stress test shows that both cryogenic treatment and barrel polishing process increase the residual compressive stress on the surface of the workpiece.The residual stress on the surface of the workpiece after cryogenic treatment and processing makes 26.26% of the untreated workpiece.Compared with the effect of cryogenic treatment on residual stress,centrifugal Rolling and finishing can increase the residual compressive stress on the surface even more.(5)Scanning electron microscopy analyzed the surface morphology of the workpiece under different processing parameters.It was found that the surface milling traces of the workpiece after the cryogenic treatment for 11 h basically disappeared,and the surface roughness was stabilized below 0.250?m.Combined with the analysis of friction and wear experiments,it can be known that cryogenic treatment changes the wear mechanism of the workpiece,from adhesion wear and abrasive wear without cryogenic treatment to abrasive wear.Adhesive wear is mechanical wear caused by the material migration between the grinding block and the surface of the workpiece.During processing,the grinding block particles fall off and adhere to the surface of the workpiece,making the surface of the workpiece adhere to a layer of tumble polishing block particles.Direct contact with the surface of the workpiece affects the processing effect of the workpiece.After cryogenic treatment,the wear mechanism of the workpiece changes,only abrasive wear exists.The surface of the workpiece is always in direct contact with the tumbling grinding block during the processing,which is more conducive to the centrifugal barrel polishing and finishing of the workpiece. |
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