The Milling Chip Forming Mechanism And Surface Integrity Studies Of Nickel-based Single Crystal Superalloy DD5

As being a new kind of material used in the aviation sector,Nickel-based single crystal superalloy has a better performance than traditional forging superalloys in strength,ductility and thermal fatigue resistance under high temperature conditions and can be applied to the manufacture of engines and gas turbines.In the process of cutting nickel base single crystal superalloy,due to cutting force,cutting temperature,cutting speed,tool wear and other different material compositions,after the cutting process,the material surface roughness,work hardening,plastic deformation degree will be great different.Due to the unfavorable processing parameters,grain refinement may occur in the affected layers after material processing,seriously affecting the physical and mechanical properties of the single crystal superalloy.In this paper,nickel-based single crystal superalloy DD5 was used as the research object.During DD5 milling chip cutting process the evolution of chip morphology,and the changes cutting force and cutting temperature was studied through experimental study and the finite element modeling methods Processing conditions under the surface of the integrity of the law of changes in the analysis and research to achieve high-efficiency,high-quality single crystal superalloys processing preliminary exploration.First of all,through DD5 milling chip,the variation of chip shape with cutting speed during milling process was analyzed to determine the critical cutting speed of DD5 high-speed cutting.Based on the finite element model of DD5 milling process,the periodic variation of stress field,strain field and temperature field in cutting area was analyzed.According to the theory of lamellar structure slippage,the forming process of the chip burrs formed by the growth of chip edge micro-cracks was analyzed.Then the cutting force and cutting temperature was analyzed.The relationship curves between cutting force,cutting temperature and various factors were plotted.It was found that in the conventional cutting stage,the cutting heat flow was nearly not affected by the cutting speed.After entering the high-speed cutting stage,a large amount of cutting heat was taken away by the chips.When the cutting depth got larger,the cutting heat tended to concentrate on the chips.The rake angle increased and the cutting heat collected on the rake face.The heat transfer coefficient had no influence on the cutting temperature.After that,the surface integrity of the machined surface was analyzed.The relationship curves between surface roughness,work hardening degree,burr morphology and various factors were plotted,and it was found that with the increasing of cutting depth,the burr was changed from burr I to burr II.Finally,based on finite element models of burr ? and burr ? forming,it was determined that burr I was formed because of the unbroken chip left on the surface after the bending,and burr II was formed because of the extension of the connecting area between the chip and the workpiece.