Abrasive water jet polishing is performed by using a polishing liquid mixed with fine abrasive particles sprayed at a high speed from a nozzle orifice to the surface of the workpiece, and grinding and removing the material by high-speed collision shearing action of the abrasive particles.
The surface roughness of the workpiece is quantitatively corrected by controlling process parameters such as pressure, angle, and injection time when the slurry is sprayed.
When the compressed air is ejected at a high speed through the nozzle orifice of the spray gun, a negative pressure is generated at the nozzle, so that the slurry containing the fine abrasive particles stirred in the liquid tank is sucked into the spray gun through the inlet pipe, thereby forming a high-speed jet and ejecting to the workpiece surface.
By means of the high-speed collision of the abrasive particles with the surface of the workpiece, the local stress field stress on the workpiece is concentrated at a high speed and changes rapidly, thereby causing erosion and shearing, thereby achieving the purpose of material removal.
During the polishing process, the high-speed abrasive particles are like a flexible turning tool to cut the surface of the workpiece.
The surface shape of the surface of the workpiece is quantitatively corrected by controlling parameters such as pressure, angle and time of the injection to achieve the purpose of removing the material and polishing.
After the polishing liquid is ejected, it can be returned to the container containing the polishing liquid through the recovery device and recycled.
When the abrasive water jet impacts the workpiece at a certain angle, the impact force of the abrasive on the workpiece can be decomposed into a horizontal component and a vertical component.
The horizontal component force produces a convex and flattening action on the convex peak on the workpiece, and the vertical component force squeezes the working surface to cause a chilling effect on the surface of the workpiece.
At the beginning of polishing, a portion of the abrasive water jet mixture is retained in the valleys of the workpiece surface to form a film.
The peaks exposed outside the film are first removed by the impact of the abrasive, resulting in a noticeable smoothing of the working surface.
Usually the surface roughness is on the order of microns, a process commonly referred to as primary polishing (ie, coarse polishing).
In this process, the amount of material removed is large, and a larger abrasive material is required.
The material removal mechanism is considered to be similar to the general abrasive water jet processing mechanism.
In the abrasive water jet polishing process, there are two main mechanisms for the abrasive to remove the surface material of the workpiece.
One is caused by the plastic deformation mechanism.
The impact of the abrasive on the surface of the workpiece causes the material to bulge to the sides.
This process does not directly cause the cutting process of the material, but the material is detached under the action of the abrasive particles to form secondary chips.
At the same time, the 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 collision impact and shear scribe action of the polishing liquid mixed with the abrasive particles.
After rough polishing, only a small peak is left on the surface of the workpiece.
At this time, the horizontal impact component is reduced, and the vertical impact component is increased, so that the pressing effect of the abrasive on the working surface is enhanced.
This process is often referred to as secondary polishing, or fine polishing.
In this process, the amount of material removed is small and fine particle abrasives are required.
The removal mechanism of the material at this stage is still in the research stage.
Some scholars believe that when the material removal scale is nanometer, since the removal depth is less than its critical depth of cut, plastic flow becomes the main way of material removal.
The effect of nano-scale abrasives on the workpiece is mainly extrusion grinding.
(1) Abrasive jet processing is different from sandblasting.
The main purpose of the blasting process is to clean the surface of the workpiece.
Abrasive jet processing is the use of abrasive grains to cut the processed material;
The abrasive grain size used in the sandblasting process is larger than the abrasive grain size in the jet abrasive processing;
The high-speed jet of abrasive particles can be ground and polished under tight control.
(2) Compared with the conventional polishing technique, its “machining tool” is liquid, and there is no problem of abrasive wear.
The removal function remains constant and the surface accuracy is easy to control.
High surface luminosity can be achieved without destroying the original dimensional accuracy of the part.
(3) The polishing head is a small liquid column that can be used for polishing various types of holes, profiles and various special complicated surfaces such as gears, impellers, various molds, precision mechanical parts.
The polishing characteristics are not affected by the position of the workpiece, and the application range is wide.
It can be used to process both metal and non-metallic materials.
(4) Abrasive water jet polishing belongs to the category of cold processing, and there is no thermal influence on the material during processing.
There is no spark during cutting, and the workpiece does not produce thermal deformation and heat affected zone, which is especially beneficial for processing heat sensitive materials.
At the same time, since the polishing liquid continuously circulates during the processing, the processed debris can be automatically removed.
(5) Processing and cleaning, no toxic gases and dusts that are harmful to human health, no pollution to the environment, and improve the safety of operators.
The polishing liquid is basically non-depleting, can be reused, and has a long life.
(6) Processing “abrasives” is a high-speed high-pressure liquid flow, which will not become dull during the processing, reducing the time required for grinding tools, sharpening, etc., and in high efficiency.
The nozzle has no mechanical contact with the machined surface for high speed machining.
(7) The equipment is easy to maintain and easy to operate, and the starting point and location of the machining can be flexibly selected.
Automatic machining of complex shapes can be easily performed by numerical control.
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