Study On Resistance Welding Of Diamond Grits Pre-bonded By Ni-Cr-P Alloy

In the process of high-efficiency and heavy-load processing,the high grits exposure of brazed large-size diamond tools will lead to grits fracture and fall off,which reduce the machining accuracy and service life of the brazed diamond tools.However,this problem cannot be solved by the existed dressing methods of diamond tools.As a pressurized local heating process,resistance welding can solve the problem of repairing damaged grits in diamond tools.Therefore,the processes of pre-bonding and resistance welding are adopted to“replant”the intact diamond grits at the positions of damaged grits so as to restore the function of brazed large-size diamond tools with less work and to improve the service life of the tools.The following works of theoretical demonstration with innovation were completed by experimental analysis:（1）The research results of the pre-bonded diamond grits indicated that good metallurgical bonding between diamond grits and Ni-Cr-P alloy was achieved by the pre-bonding process of 1000℃for 2min.Meanwhile,the grinding performance of diamond grits was maintained to a great extent.The compounds of Cr₃C₂ and Cr₇C₃ were generated at the interface between diamond grits and pre-bonded layer.The diamond grits still maintained good sharpness and there was no thermal damage on the surface.The pre-bonded diamond grits were subjected to compressive stress,and the value of the compressive stress gradually decreased from the surface to the core.The minimum value of the compressive stress was 0.597GPa and the maximum value of the compressive stress was 0.739GPa.Compared with the original diamond grits,the impact toughness of the pre-bonded diamond grits decreased by about 29.6%.（2）The research results of the resistance welded diamond grits showed that the diamond grits could be exposed to a certain extent and maintain a good sharpness in the optimal welding parameters（I=0.67k A;F=0.2MPa;t=50ms）.Meanwhile,the pre-bonded grits fused with the substrate by resistance welding.The welded diamond grits were subjected to compressive stress.The minimum value of the compressive stress was0.692GPa,and the maximum value of the compressive stress was 0.829GPa.Compared with the pre-bonded diamond grits,the impact toughness of the welded diamond grits only decreased by 3.75%.Resistance welding had no thermal effect on the diamond grits around the welded grits.（3）The results of the grinding test showed that when the spindle speed,the sharpening depth and the sharpening time were 10000r/min,80μm and 8s,respectively,the edges and corners of the sharpened grits were intact,and the grits were exposed from the pre-bonded layer,the effect of sharpening was better.After sharpening,the top of the diamond grit was subjected to tensile stress of 0.377GPa,while the bottom of the diamond grit was subjected to compressive stress of 0.783GPa.The area expansion rate of top worn platform of the diamond grits welded by resistance welding and the material reduction amounts of marble removed by diamond grits welded by resistance welding were better than those of the brazed diamond grits.The average surface roughness R_a of marble grinded by resistance welded diamond grits was 1.670μm,while the average surface roughness R_a of marble grinded by brazed diamond grits was 1.478μm.The maximum temperature in the grinding arc zoon of the resistance welded diamond sample was 44.26℃,which was about 7.24℃lower than that of the brazed diamond sample.