Research status of the hottest abrasive water jet

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Research status of abrasive water jet polishing technology

1 introduction

abrasive water jet is a new technology that has developed rapidly since the 1980s. Compared with traditional processing technology, it has the advantages of no tool wear, no thermal effect, small reaction force and high processing flexibility. At present, it has been widely used in a variety of processing industries for processing ceramics, quartz, composite materials and other materials

abrasive water jet polishing technology is a new precision machining technology developed on the basis of abrasive water jet machining technology, which integrates hydrodynamics and surface technology. At present, there is little research on it at home and abroad. Only a few scholars have carried out exploratory experimental research, and have not yet formed systematic research results

Hashish has carried out exploratory experiments on the feasibility of polishing diamond films with abrasive liquid jet. Through the experiments, it is found that diamond films can be polished from 3% by using 600 mesh SiC abrasive μ M polished to 1.3 μ m。 When fahnle, Oliver W and others polished flat glass with liquid abrasive jet, the glass surface roughness decreased from the initial 475nm to 5nm. Booij, Silvia M. et al. Found that the material removal rate could be controlled within 1nm/min by adjusting the main process parameters (such as processing time, abrasive concentration, abrasive size and target distance) in the process of polishing glass with abrasive liquid jet. Booij, Silvia M., fanle, Oliver W. and others found through experiments that in the process of abrasive liquid jet polishing, by adjusting the trajectory of the nozzle, a plane with a surface accuracy of N10 can be obtained. Meselink and wilhelmus A. C. M. verified by experiments that abrasive liquid jet can pre polish and polish the spherical surface. The research results show that: in the polishing process, the material removal speed depends on the sharpness of the abrasive and the size of its kinetic energy. Through experimental research, Yang Qianhua and Liu Jiguang believed that the grinding and polishing of ferroalloy special-shaped curved surface by grinding fluid jet was feasible, and a more reasonable polishing scheme was obtained

2 abrasive water jet polishing mechanism

when abrasive water jet impacts the polished workpiece at a certain angle, the impact force of abrasive on the workpiece can be divided into horizontal component and vertical component. The horizontal component has a convex and flattening effect on the convex peak on the workpiece, and the vertical component has an extrusion effect on the working surface, which makes the workpiece surface cold and hard

at the initial stage of polishing, a part of the mixed liquid of abrasive water jet will remain in the valley of the workpiece surface, forming a thin film. The convex peaks exposed outside the film will be removed by the impact of abrasive first, so that the working surface can be obviously flat. Generally, the surface roughness is micron level, and this process is usually called primary polishing (i.e. rough polishing). In this process, the amount of material removed is large, and the abrasive with larger particles needs to be selected. Its material removal mechanism is currently considered to be similar to that of ordinary abrasive water jet machining. In the process of abrasive water jet polishing, there are mainly two mechanisms for the abrasive to remove the material on the workpiece surface. One is caused by the plastic deformation mechanism. The impact of the abrasive on the workpiece surface causes the material to bulge to both sides. This process does not directly cause the cutting process of the material, However, under the action of abrasive particles, the materials fall off and form secondary chips. As an important part of high technology, biomedical materials have entered a new stage of rapid development. At the same time, abrasive particles also have a cutting process on the surface of the workpiece, such as planing. This process can directly remove the material and form a chip. The other is to remove the material by the impact, shear and scoring of the polishing liquid mixed with abrasive particles on the workpiece

after rough polishing, only a small crest is left on the workpiece surface. At this time, the horizontal impact component is reduced and the vertical impact component is increased, which enhances the extrusion effect of abrasive on the working surface. This process is usually called secondary polishing, that is, fine polishing. In this process, the amount of material removed is very small, and fine-grained Abrasives need to be selected. At this stage, the material removal mechanism is still in the research stage. Some scholars believe that when the material removal scale is nano scale, because the removal depth is less than its critical cutting depth, plastic flow becomes the main way of material removal, and the role of nano scale abrasive on the workpiece is mainly extrusion grinding

3 influence of process parameters on polishing effect

when polishing with abrasive water jet, the processing quality is affected by many factors, such as jet pressure, jet nozzle diameter, target distance, inclination angle, diameter, shape and length of sand nozzle, action time, flow, size, shape and hardness of abrasive particles, and the properties of processed materials

(1) when the injection pressure is too high, the material removal is large, and the polishing effect is not ideal; The spraying pressure is too small, and the material is difficult to remove, so the polishing effect cannot be achieved. Therefore, the spray pressure should be optimized according to the properties and hardness of the material

(2) the abrasive particle size has a greater impact on the polishing effect. The smaller the abrasive particle size, the better the polishing quality, but the lower the polishing efficiency

(3) abrasive hardness has a significant impact on the polishing effect. In ordinary abrasive water jet machining, it is generally considered that the hardness of abrasive is higher than that of workpiece before machining the workpiece. However, in abrasive water jet polishing, due to its different processing mechanism and high requirements for surface quality, the larger the deformation of the abrasive itself, that is, the smaller the hardness of the abrasive, the better the polishing effect

(4) the processing time has no obvious influence on the polishing effect, but has a great influence on the amount of material removal. The longer the processing time is, the more material is removed

(5) there is an optimal range for the influence of target distance on polishing effect. The target distance is too small. For example, when polishing in the initial stage, the material removal rate is high, but the polishing effect on the workpiece is weak. The target distance is too large. If you choose to polish in the dissipation section of the jet, the material is basically not removed, and the polishing effect is also poor. It is generally believed that when polishing, the target distance should be selected so that the jet can polish the workpiece in the basic section

(6) the spray angle has the best relationship with the polishing effect. When polishing the workpiece with abrasive water jet, the polishing effect becomes better and better with the decrease of the spray angle. When it is reduced to a certain value, the polished surface quality reaches the best. When the spray angle is further reduced, the surface quality changes little, but the amount of material removal will become smaller and smaller with the decrease of the spray angle. If the spray angle is too small (for example, the jet polishes the workpiece in the direction parallel to the workpiece surface), then the material removal is too small or basically not removed, and the polishing effect is not ideal

(7) the diameter, shape and length of the sand nozzle affect the distribution of abrasive in the jet beam. When polishing, the ideal abrasive distribution is that the abrasive is evenly distributed in the jet beam

(8) under the same polishing conditions, the higher the hardness of the material, the lower the surface roughness, and the smaller the amount of material removal

4 the main problems of abrasive water jet polishing technology at present

the ideal abrasive water jet polishing results in small material removal and high surface quality. If you want to get ideal polishing results, you need to choose abrasive water jet with low pressure and small abrasive size, that is, micro abrasive water jet. However, at present, the theory of micro abrasive water jet is not mature, and the following main problems need to be solved:

(1) the formation of micro abrasive water jet. Ordinary abrasive water jet is formed by using the venturi effect to inject the abrasive into the water jet, but Miller found that when the jet diameter is less than 300 μ M, this way of making abrasive enter water jet can no longer be applied. At present, there are few reports on the mixing mechanism of micro abrasive water jet

(2) abrasive agglomeration. When the abrasive particles are nanometer, the surface energy of the abrasive is very large, and the abrasive particles tend to agglomerate during the formation of abrasive water jet. In abrasive water jet polishing, nano abrasive is needed, but the dispersion of nano abrasive in abrasive water jet has not been solved

(3) nozzle blockage occurs during micro abrasive machining. Due to the small size of micro abrasive water jet nozzle, it is very easy to block in the process of jet switching. Some scholars use the valve to control the time when the abrasive enters the spray and tighten the nozzle in time when the screw is found to be loose, but at the same time, the rapid wear and failure of the valve has become a new problem

(4) because the research on abrasive water jet polishing technology is just in its infancy, mature polishing technology and theory have not been formed from experiment to theory. In abrasive water jet polishing, the material removal mechanism is the micro removal mechanism, and the micro removal mechanism of various materials has not been finalized yet

(5) in abrasive water jet polishing (especially in fine polishing), the size of the selected abrasive is very small, and the size of the nozzle is difficult to be very small due to economic and technical reasons. At this time, the law of size effect caused by the large ratio of nozzle size to abrasive size is not clear

in conclusion, it can be seen that the research on abrasive water jet polishing technology is still in its infancy. In the future, the abrasive water jet polishing technology should be further studied from both theoretical and experimental aspects

5 conclusion

with the progress of science and technology, more and more new materials have been developed, and the requirements for the processing accuracy of materials are becoming higher and higher. As a new type of precision machining technology, abrasive water jet machining technology has its unique advantages, so that it can play a role in the processing of various difficult to machine materials. In particular, the development of micro abrasive water jet technology will promote the research of abrasive water jet polishing technology and the maturity of the process, which can guarantee the 100% pass of the processed sample gap. (end)

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