Study On Compound Polishing Method And Mechanism Of 3D Printing Titanium Alloy Inner Channel

The 3D printing internal channel parts have increasingly highlighted the advantages in design,manufacturing and structural performance,but the polishing problem of internal channel surface is still severe.Chemical polishing device is simple,high efficiency and low cost,but the polished metal surface is prone to pitting and can not significantly improve the roughness.Micro abrasive suspension jet polishing is a potential complex polishing method for internal channel,and has strong physical polishing power,but there is no systematic research and scientific report at home and abroad.In this paper,the chemical and micro abrasive suspension jet polishing were studied independently.Combined with the advantages and disadvantages of the two polishing methods,a compound polishing method for 3D printing TC4 titanium alloy inner channel was innovatively proposed.With the aid of chemical polishing,micro abrasive suspension jet polishing is the main polishing method,in order to realize high surface quality and controllable dimensional accuracy of 3D printing TC4 titanium alloy inner channel parts.In the study of chemical polishing;the effects of solution ratio,temperature,time and additives of hydrofluoric acid system and ammonium fluoride system on polishing rate were explored.The mathematical model of chemical polishing is established through the mucosal layer theory to reveal the relationship between the mucosal layer and the parameters in the chemical polishing system,and to achieve the goal of the highest chemical polishing rate and the minimum thinning rate.At the same time,the existing chemical polishing theory is enriched.Due to the chemical polishing will produce corrosion dissolution,the corrosion layer is too deep to be removed by subsequent physical polishing,chemical polishing needs to inhibit the increase of titanium alloy thinning and corrosion layer depth.Therefore,this goal can be achieved by adjusting the influence factors in the chemical solution system to control the mucosal thickness.The optimum chemical polishing system is ammonium fluoride nitrate system,the parameters are water:nitric acid:ammonium fluoride=100ml:20ml:3G/L,tackifier 0.21g/l,polishing for 10min under 40?,the surface roughness of titanium alloy sample can be reduced to 1.5?m.In the study of micro-abrasive suspension jet polishing,the tool texture and cutting speed in titanium alloy contact machining are used to design the abrasive shape and the jet flow velocity of the fluid.The effects of micro abrasive suspension j et on powder removal,surface morphology,surface roughness and dimensional accuracy of internal flow channel after polishing were investigated.The correlation between fatigue corrosion,scouring deformation and processing time of internal flow channel was analyzed.The results show that the fluid velocity can reach the high-speed cutting speed of titanium alloy under the fluid pressure of 1MPa,and the critical removal time of chemical corrosion layer is about 150min.Chemical polishing has the problem of limited surface corrosion and roughness improvement.Micro-abrasive suspension jet polishing has the problem of bending erosion deformation and fatigue corrosion for too long processing time.Compound polishing can solve their respective limitations,which can not only remove the chemical corrosion layer by physical polishing,but also reduce the time of physical polishing to inhibit the bending erosion deformation.At the same time,the surface quality of secondary compound polishing is very high.Combined with chemical polishing and micro-abrasive suspension jet polishing,two critical conditions of internal channel corrosion layer removal and micro-abrasive suspension jet critical deformation were determined.The compound polishing method was established under the critical conditions.Combined with metallographic,scanning and laser confocal microscope,the surface morphology,metallographic,surface roughness and size of 3D printing ?3,5,7 and 9 mm internal flow channels after compound polishing were analyzed respectively,which confirmed the feasibility and technical potential of compound polishing technology.