关键词: 前混合, 磨料水射流, 缺口圆角半径, 残余应力, 粗糙度

Abstract: Conventional contact processes such as rolling and extrusion are difficult to handle notched materials with high hardness, are not prone to plastic deformation, and are difficult to introduce residual stress. Therefore, it is necessary to seek new methods for effective modification. Pre mixed jet is a new type of surface modification technology that combines high-pressure water jet technology with shot peening. It utilizes the speed of high-pressure water flow to propel shot particles into the target material at high speed, forming multiple covered craters on the surface of the part, achieving the goal of introducing residual stress and modification. The characteristic of this process is high energy concentration, and through the combination of high pressure and high-strength pellets, the hard surface after heat treatment can be modified. In addition, this method is flexible in operation and can achieve effective modification of various spatial surfaces and narrow grooves under certain nozzle size conditions and with the cooperation of relevant motion platforms. In order to investigate the effects of different process parameters on the radius size, residual stress, and roughness of the notch in the pre mixed abrasive water jet system, the general pattern of modified notch specimens was obtained and the optimal jet process parameters were determined. A pre mixed abrasive water jet system was used to modify the fatigue specimen with a notch radius R=0.6 mm of 18CrNiMo7-6 carburized alloy steel after heat treatment. A combination of theoretical and experimental methods was used to measure and analyze the notch radius size, residual stress, and roughness of the specimen under different pressures, workpiece speed, nozzle movement speed, and jet frequency using a three-dimensional morphology analyzer and residual stress analyzer, Summarized the variation law of the notch fillet radius of the modified sample and the construction law of the residual stress field. Research has found that under a certain material, the change in narrow size caused by abrasive water jet is mainly through the action of abrasive, while pure water has little effect on size change. As the pressure of the abrasive jet increases, the size of the notch fillet changes more and more, and as the pressure increases, a better residual stress field can be obtained, but at the same time, a higher roughness will also be generated at the root of the notch. Taking residual stress, roughness, and machining efficiency as evaluation indicators, a suitable ratio of 0.48 was obtained by comprehensively considering the ratio of workpiece speed and nozzle movement speed. Due to the influence of erosion, the increase in jet frequency leads to a decrease in residual stress values near the surface layer, but there will be a certain increase in residual stress layer depth, maximum residual stress value, and layer depth corresponding to the maximum stress value. Among them, the maximum stress value corresponds to a significant increase in layer depth, increasing by 20 μm and 30 μm respectively, which is 66.67% and 100% higher than that of a single jet. Due to different pressures, workpiece speeds, nozzle movement speeds, and jet frequency, the modification effect can be affected differently. Therefore, suitable jet modification process parameters can be selected based on actual processing needs.