Abrassive jet machining
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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.
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Abrassive jet machining
- 1. 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.
- 3. Factors affecting the process • Material removal rate. • Geometry of cut. • Roughness of surface produced. • The rate of nozzle wear.
- 4. Material removal rate (mmr).
- 5. 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.
- 6. 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.
- 7. 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.
- 8. 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.
- 9. •Head can be at right angle, or straight.
- 10. 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.
- 11. 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.
- 12. Applications of AJM. Above: A spring machined from 1/8" brass.
- 13. ! Above: Company name machined from a file. The abrasive jet machines from hardened steel as easily as
- 14. Above: A rack and a gear machined with an abrasive jet. Material is 1/2" (13mm) steel.
- 15. 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
- 16. Above: 2" (50mm) thick concrete. It's pink because there was a pigment added to the concrete.
- 17. 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.
- 18. 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.