Theoretical And Experimental Study On Surface Modification Of Cylindrical Sample By Mixed Water Jet

Surface modification is a key process in anti-fatigue manufacturing.Water jet has become a promising surface modification technology due to its high energy density and high modification efficiency.In this paper,the related research work on water jet modification of 18CrNiMo7-6 carburized steel cylindrical sample is carried out.The relationship between modified process parameters and modification effect is studied by using the modified surface integrity as the evaluation index.The important factors influencing the surface integrity index were discussed.On this basis,an opptimized modification process for cylindrical sample was proposed.Following is the main research work:1.In the theoretical research,the momentum theorem is used to calculate the impact force of the water jet by analyzing the formation process of the injection water jet,and the introduction mechanism of the residual stress is discussed.2.Through the theory and experiment,the conditions of the full coverage of the surface of the round bar sample by water jet are studied,and the critical ratio of the moving speed of the nozzle to the rotational speed of the sample is obtained: the ratio is the coverage width of the jet on the surface of the sample.3.Using variable analysis test methods,the effects of sample rotation speed,nozzle moving speed,pump pressure and rounds of treatments on the modification effect of the sample were studied.It was found that the particles and water will cause some erosion and wear on the surface of the sample,and the surface morphology of the sample is changed after the injection water jet peening.The surface roughness,surface residual stress and hardness of the sample decrease with the increase of the sample rotation speed and the nozzle movement speed,and increase with the increase of the pump output pressure and the round of treatments.When the sample rotation speed n=100r/min,the nozzle movement speed v=50mm/min,the pump pressure p=300MPa,the number of treatments N=1,the maximum residual stress is about-1176.25 MPa,and the maximum hardness is 64 HRC,which is 6.7% higher than that of the original sample.4.The influence of the injection water jet peening on the surface of the original sample and the modified sample surface was studied when the nozzle axis was offset from the axis of the cylindrical sample.It was found that the surface roughness surface,the residual stress and hardness of the sample decreased with the increased of offset distance.But it has little effect on the residual stress and hardness of the modified sample surface;The jet produces a turning effect when the offset distance is large enough to approach the round radius of the round bar sample section,and the effect on the modified surface roughness is not obvious.