A Beginner’s Guide to Abrasive Water Jet Polishing

Abrasive Water Jet Polishing is a process that involves using a mixture of a polishing liquid and fine abrasive particles. The mixture is sprayed at high speed from a nozzle onto the surface of the workpiece, causing the abrasive particles to collide with the material at high speed, resulting in the grinding and removal of material through the shearing action.

Abrasive Water Jet Polishing

The surface roughness of the workpiece is quantitatively improved by adjusting process parameters such as pressure, angle, and injection time during the slurry spray process.

Working principle

When compressed air is expelled at high speed through the nozzle of a spray gun, a negative pressure is created at the nozzle, causing the slurry containing fine abrasive particles mixed in the liquid tank to be drawn into the spray gun through the inlet pipe. This results in a high-speed jet that is then directed at the workpiece surface.

The high-speed collision of abrasive particles with the workpiece surface concentrates the local stress field and rapidly changes it, leading to erosion and shearing, and ultimately removing material. The high-speed abrasive particles act like a flexible cutting tool during the polishing process.

The surface shape of the workpiece can be corrected by controlling parameters such as pressure, angle, and time of injection to achieve material removal and polishing. The used polishing liquid can be recycled by returning it to the container through the recovery device.

When the abrasive water jet strikes the workpiece at a certain angle, the impact force of the abrasive can be decomposed into a horizontal and vertical component. The horizontal component creates a flattening effect on the convex peaks on the workpiece, while the vertical component compresses the working surface and causes it to cool.

At the start of the polishing process, some of the abrasive water jet mixture is retained in the valleys of the workpiece surface, forming a film. The peaks exposed outside of the film are the first to be removed by the abrasive impact, leading to a noticeable smoothing of the surface. This is called primary polishing, or coarse polishing, and a larger abrasive material is required to remove a significant amount of material. The material removal mechanism is believed to be similar to that of general abrasive water jet processing.

There are two main mechanisms for abrasive removal of surface material from the workpiece in the abrasive water jet polishing process. One is due to the plastic deformation mechanism, where the impact of the abrasive on the workpiece surface causes the material to bulge to the side. This does not directly cause material cutting, but the material is detached under the abrasive particles’ action to form secondary chips. At the same time, the abrasive particles also cut the workpiece surface through processes like planing, which directly removes material and creates chips.

The other mechanism is the collision impact and shear scribe action of the polishing liquid mixed with abrasive particles. After rough polishing, only small peaks remain on the workpiece surface. At this stage, the horizontal impact component is reduced, and the vertical impact component is increased, enhancing the abrasive’s pressing effect on the working surface. This is referred to as secondary polishing, or fine polishing, and requires finer particle abrasives to remove smaller amounts of material. The material removal mechanism at this stage is still under research. Some scholars believe that when the material removal scale is at the nanometer level, plastic flow becomes the main way of material removal since the removal depth is less than its critical depth of cut. The effect of nano-scale abrasives on the workpiece is mainly extrusion grinding.

Main feature

(1) Abrasive jet processing is distinct from sandblasting, as the former uses abrasive grains to cut material, while the latter is used primarily to clean surfaces. The grain size of the abrasive used in abrasive jet processing is smaller than that in sandblasting. This process allows for precise control over grinding and polishing, thanks to the high-speed jet of abrasive particles.

(2) Compared to traditional polishing methods, abrasive jet processing utilizes a liquid “machining tool,” which eliminates the issue of abrasive wear. The constant removal function and easy-to-control surface accuracy result in a high surface brightness without sacrificing the original dimensional accuracy of the workpiece.

(3) The polishing head is a small liquid column that can be used to polish a variety of holes, profiles, and complex surfaces such as gears, impellers, molds, and precision mechanical parts. The position of the workpiece does not affect the polishing characteristics, making this method suitable for a wide range of applications. It can be used on both metal and non-metallic materials.

(4) Abrasive water jet polishing is a cold processing method that does not generate heat, making it ideal for processing heat-sensitive materials. There is no spark during cutting and no thermal deformation or heat affected zone on the workpiece. Additionally, the polishing liquid continuously circulates during processing, which automatically removes any debris.

(5) Processing and cleaning with abrasive water jet polishing is safe for the environment and the operator, as there are no toxic gases or dusts produced. The polishing liquid is non-depleting, can be reused, and has a long lifespan.

(6) The abrasives used in this process are high-speed, high-pressure liquid flows, which do not become dull during processing. This reduces the time needed for grinding tool sharpening, increasing efficiency. The nozzle does not make mechanical contact with the machined surface during high-speed machining.

(7) The equipment is easy to maintain, operate, and offers flexible starting point and location selection for machining. Complex shapes can be machined automatically with numerical control.

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