How does it work?• Fine particles (0.025mm) are accelerated in a gas

stream (commonly air at a few times atmospheric pressure).

• The particles are directed towards the focus of machining (less than 1mm from the tip).

• As the particles impact the surface, it causes a small fracture, and the gas stream carries both the abrasive particles and the fractured (wear) particles away.

 

 

 

Factors affecting the process

• Material removal rate. • Geometry of cut.• Roughness of surface produced.• The rate of nozzle wear.

Material removal rate (mmr).

These factors are in turn affected by,

•The abrasive

Composition; strength; size; mass flow rate.

•The gas

Composition, pressure and velocity.

•The nozzle

Geometry; material; distance to work; inclination to work.

Abrasive.

• Materials - Aluminum oxide (preferred); silicon carbide.

• The grains should have sharp edges.• Material diameters of 10-50 micro m 15-20 is

optimal.• Should not be reused as the sharp edges are worn

down and smaller particles can clog nozzle.

Gas jet.

• Mass flow rate of abrasive is proportional to gas pressure and gas flow.

• Pressure is typically 0.2 N/mm² to 1N/mm²• Air, N2 & CO2 can be used.

Nozzle.

• Must be hard material to reduce wear by abrasives: WC (lasts 12 to 30 hr); sapphire (lasts 300 hr).

• Cross sectional area of orifice is 0.05-0.2 mm².

• Orifice can be round or rectangular.

 

•Head can be at right angle, or straight.

Summary of AJM.• Mechanics of material removal - Brittle fracture

by impinging abrasive grains at high speed.• Media - Air, CO2.• Abrasives: Al2O3, SiC, 0.025mm diameter,

2-20g/min mass flow rate, non-recirculating • Velocity = 150-300 m/sec • Pressure = 2 to 10 atm. • Nozzle - WC, sapphire, orifice area 0.05-0.2 mm²,

life 12-300 hr., nozzle tip distance 0.25-0.75 mm.

Summary of AJM.

• Critical parameters - abrasive flow rate and velocity, nozzle tip distance from work surface and abrasive grain size.

• Materials application - hard and brittle metals, alloys, and nonmetallic materials (e.g., germanium, silicon, glass, ceramics, and mica) Specially suitable for thin sections.

• Applications- drilling, cutting, deburring, etching, cleaning.

Applications of AJM.

                                                                                    

             Above: A spring machined from 1/8" brass.

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             Above: Company name machined from a file. The abrasive jet machines from hardened steel as easily as the soft stuff, without almost no decrease in speed.

                                                                                    

             Above: A rack and a gear machined with an abrasive jet. Material is 1/2" (13mm) steel.

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Above: Some sort of friction plate made from 1/4" (6mm) stainless. The circle pattern was etched into the material using the abrasive jet with a feed rate so rapid that it would not cut all the way through.

                                                                                    

             Above: 2" (50mm) thick concrete. It's pink

because there was a pigment added to the concrete.

Advantages of AJM.

• The abrasive jet can be used to cut any material. Even diamonds have been cut, using diamond dust as the abrasive.

• Make all sort of shapes with only one tool.• Virtually no heat is generated in the work

piece.• No mechanical stress.• Fast set up.

Disadvantages of AJM.

• Because of the very small stream of abrasive particles, the material removal rate is low.

• The abrasive powders cannot be reused since the points and edges get worn down. However, the cost of most abrasives is relatively low.

• Because of its nature, AJM usually requires some type of dust-collecting system.