Abrasive jet machining
Encyclopedia
Abrasive jet machining (AJM), also known as abrasive micro-blasting, pencil blasting and micro-abrasive blasting, is an abrasive blasting
machining
process that uses abrasive
s propelled by a high velocity gas to erode material from the workpiece. Common uses include cutting heat-sensitive, brittle, thin, or hard materials. Specifically it is used to cut intricate shapes or form specific edge shapes.
es. Pressures for the gas range from 25 to 130 psig (170–900 kPag) and speeds can be as high as 300 m/s.
before entering the mixing chamber, and then exits through a convergent nozzle. The nozzle can be hand held or mounted in a fixture for automatic operations.
Nozzles must be highly resistant to abrasion and are typically made of tungsten carbide
or synthetic sapphire. For average material removal, tungsten carbide nozzles have a useful life of 12 to 30 hours, and sapphire nozzles last about 300 hours. The distance of the nozzle from the workpiece affects the size of the machined area and the rate of material removal.
One of the main disadvantages is its slow material removal rate; for this reason it is usually used as a finishing process. Another disadvantage is that the process produces a taper
ed cut.
Abrasive blasting
Abrasive blasting is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface, or remove surface contaminants. A pressurized fluid, typically air, or a centrifugal wheel is used to...
machining
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...
process that uses abrasive
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away...
s propelled by a high velocity gas to erode material from the workpiece. Common uses include cutting heat-sensitive, brittle, thin, or hard materials. Specifically it is used to cut intricate shapes or form specific edge shapes.
Process
Material is removed by fine abrasive particles, usually about 0.001 in (0.00254 cm) in diameter, driven by a high velocity fluid stream; common gases are air or inert gasInert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
es. Pressures for the gas range from 25 to 130 psig (170–900 kPag) and speeds can be as high as 300 m/s.
Equipment
AJM machines are usually self-contained bench-top units. First it compresses the gas and then mixes it with the abrasive in a mixing chamber. The gas passes through a convergent-divergent nozzleNozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
before entering the mixing chamber, and then exits through a convergent nozzle. The nozzle can be hand held or mounted in a fixture for automatic operations.
Nozzles must be highly resistant to abrasion and are typically made of tungsten carbide
Tungsten carbide
Tungsten carbide is an inorganic chemical compound containing equal parts of tungsten and carbon atoms. Colloquially, tungsten carbide is often simply called carbide. In its most basic form, it is a fine gray powder, but it can be pressed and formed into shapes for use in industrial machinery,...
or synthetic sapphire. For average material removal, tungsten carbide nozzles have a useful life of 12 to 30 hours, and sapphire nozzles last about 300 hours. The distance of the nozzle from the workpiece affects the size of the machined area and the rate of material removal.
| Abrasive material | Grit size (μin) | Orifice diameter (in) |
|---|---|---|
| Aluminum oxide | 10 - 50 | 0.005 - 0.018 |
| Silicon carbide Silicon carbide Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive... |
25 - 50 | 0.008 - 0.018 |
| Glass beads | 2500 | 0.026 - 0.05 |
Advantages and disadvantages
The main advantages are its flexibility, low heat production, and ability to machine hard and brittle materials. Its flexibility owes from its ability to use hoses to transport the gas and abrasive to any part of the workpiece.One of the main disadvantages is its slow material removal rate; for this reason it is usually used as a finishing process. Another disadvantage is that the process produces a taper
Taper
In cymbal making, taper refers to the gradual change in thickness from the bell to the rim of the cymbal. It is one of the key features that determines the tone of the cymbal....
ed cut.