| Stainless steel is the main substrate of flexible display due to its low thermal expansion coefficient,water and oxygen isolation.The surface of stainless steel is usually required to achieve global planarization by grinding and polishing,but machining often produces damage which has great infiuence on the removal amount of subsequent processing and the performance of stainless steel substrate.The processing efficiency and the damage of the surface / sub-surface of 304 stainless steel polishing process were studied in this paper.The specific contents are as follows :(1)Detection scheme on surface / subsurface damage of 304 stainless steelThe surface / subsurface damage layer thickness of 304 stainless steel was observed by metallographic microscope,3D surface profilometer and scanning electron microscope.The residual stress of 304 stainless steel was measured by sin2? method and the surface / subsurface damage detection policy was determined.It was surface morphology inspection,processing surface polishing and residual stress detection,mosaic pattern,cross section grinding and polishing,corrosion,observation and detection.(2)Detection on surface / subsurface damage of 304 stainless steel lapped by free abrasiveIt is difficult to preserve high efficiency and low damage.Under high pressure,high rotating speed,large abrasive grains and short time working condition,the removal rate of grinding can surpass1?m/min.With low pressure,low rotating speed,large abrasive grains and long time,the surface roughness is lower than 0.336 ?m and the surface damage layer thickness is less than 4.677 ?m.Under the condition of high rotation speed and small grain size,the residual stress of the subsurface is low,which is lower than – 179.49 ± 9.01 MPa.Under low pressure,low speed and long time working conditions,thethickness of subsurface damage layer is less than 8 ?m.The damage layer thickness of 304 stainless steel subsurface lapped by free abrasive grains is larger than that of the surface.(3)Detection on surface / subsurface damage of 304 stainless steel lapped by fixed abrasiveBoth high efficiency and low damage are preserved difficultly.Under high pressure,high rotating speed and short time working condition,the removal rate of grinding can reach more than 1?m/min.With high rotating speed,small abrasive grains,surface roughness is lower than 47.51 nm and surface damage layer thickness is less than 1.259 ?m.Under the condition of low pressure,high rotation speed and small grains,the residual stress of the subsurface is lower than – 440.49 ± 9.01 MPa.Under high speed and small grains condition,the thickness of subsurface damage layer is less than 2.5 ?m.The 304 stainless steel surface roughness and the surface damage layer thickness of fixed abrasive lapping are smaller than that of free abrasive.The residual stress in the subsurface of fixed abrasive lapping is larger than that of free abrasive.The 304 stainless steel subsurface damage layer thickness of fixed abrasive lapping is larger than that of the surface,and is also smaller than that of free abrasive.The total damage of fixed abrasive lapping is less than that of free abrasive.(4)Detection on surface/subsurface damage of chemical mechanical polishing 304 stainless steelHigh efficiency and low damage are difficult to be together.With high pressure,high rotation speed,short time,the removal rate is above 0.7?m/min.Under high speed and small grains condition,the surface roughness is lower than 13.02 nm and the thickness of surface damage layer is less than 1.676 ?m.The residual stress of subsurface is lower than-220.99 ± 3.01 MPa with low speed,large grains and long time.Under high rotating speed and small grains condition,the subsurface damage layer thickness is less than 1?m.The surface roughness of chemical mechanical polishing 304 stainless steel is smaller than thatof fixed abrasive lapping,but the thickness of surface damage layer is opposite,and both are less than that of free abrasive lapping.Due to chemical corrosion,the subsurface residual stress of chemical mechanical polishing 304 stainless steel is between the free abrasive lapping and the fixed abrasive lapping.The damage layer thickness of stainless steel subsurface produced by chemical mechanical polishing is similar to that of surface damage layer,and is smaller than subsurface damage layer thickness produced by free abrasive and fixed abrasive.The overall damage of 304 stainless steel produced by chemical mechanical polishing is less than that of fixed abrasive and free abrasive.(5)Optimize the process of 304 stainless steelThe thickness range of stainless steel surface/subsurface damage layer lapped by free abrasive is4.677~16.69?m and 8~35?m respectively,as well as the change is big.The thickness range of stainless steel surface/subsurface damage layer lapped by fixed abrasive is 1.259~ 2.945 ?m and 2.5~ 10 ?m respectively,and the change is similar.The surface/subsurface damage layer thickness of chemical mechanical polishing stainless steel is 1.676~ 3.027 ?m and 1~ 5?m respectively,which change is small.The optimized finishing process of 304 stainless steel is obtained.First,the surface of 304 stainless steel is lapped by fixed abrasive pad with technological parameters(The pressure is 5psi,the speed is 85r/min,and the grains is 7?m.)in chapter 4 to realize high efficiency lapping and a quick smooth surface,it will be needed 1.45 h.Then the surface of 304 stainless steel is processed by chemical mechanical polishing(Process parameters are the same as above.)in chapter 5,it will be required 0.31 h to remove the maximum damage of fixed abrasives.Finally,it will take 1.7h which stainless steel is polished by the polishing method in chapter 2.In the end,it will need 6h to realize the global smooth planarization. |
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