Abrasive jet machining (AJM), also known as abrasive micro-blasting, pencil blasting and micro-abrasive blasting, is an

abrasive blasting Sandblasting, sometimes known as 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 su ...

machining process that uses

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 by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

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 in diameter, driven by a high velocity fluid stream; common gases are air or

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

es. Pressures for the gas range from 25 to 130 psig (170–900 kPa or 4 bars) and speeds can be as high as 300 m/s (1,000 km/h).

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

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...

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 (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed int ...

or synthetic sapphire. For average material removal, tungsten carbide nozzles have a useful life of 12 to 30 hours, and sapphire nozzles last about 400 hours. The distance of the nozzle from the workpiece affects the size of the machined area and the rate of material removal.

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. Normally inaccessible portion can be machined with good accuracy. One of the main disadvantages is its slow

material removal rate Material removal rate (MRR) is the amount of material removed per time unit (usually per minute) when performing machining operations such as using a lathe or milling machine Milling is the process of machining using rotary cutters to remove m ...

; for this reason it is usually used as a finishing process. Another disadvantage is that the process produces a tapered cut.

References

{{DEFAULTSORT:Abrasive Jet Machining Abrasive blasting Industrial processes Machining