03-09-2014, 10:35 AM
Abrasive Jet Machining (AJM)
Abrasive Jet.ppt (Size: 1.73 MB / Downloads: 12)
Introduction
A stream of abrasive grains (Al2O3 or SiC) is carried by high pressure gas or air (compressed).
Impinges on the work surface at very high velocity through a nozzle of 0.3 to 0.5 mm diameter.
Sand Blasting (SB) - a similar process
The major differences between are SB and AJM
smaller diameter abrasives
a more finely controlled delivery system
Material removal – by mechanical abrasion action of the high velocity abrasive particles.
Best suited for hole drilling in superhard materials.
Typically used to cut, clean, peen, deburr, deflash and etch glass, ceramics and other hard materials.
Machining System – Contd
A gas (Nitrogen, CO2 or air) is supplied at 2 – 8 kg/cm2
Oxygen should never be used. (because, it causes violent chemical action with the workpiece chips or abrasive particles).
Gas passes through a mixing chamber after filtration and regulation.
In the mixing chamber, abrasive particles (10 – 40 m) are present and vibrated at 50 Hz.
Amplitude of vibration – to control the feed rate of abrasives.
(Gas + abrasives) - passed through a 0.45 mm diameter tungsten carbide nozzle at a speed of 150 – 300 m/s.
The nozzle is directed over the area to be machined.
Relative motion between nozzle and workpiece – can be manual
Or automatically controlled using cam drives, tracer mechanisms or using computer controlled according to the cut geometry required.
Masks of copper, glass or rubber – can be used to concentrate the jet stream of abrasives to a confined area on the workpiece.
Intricate and precise shapes can be produced using masks with corresponding contours.
Dust removal or collecting equipment must be incorporated to protect the environment.
Applications
Drilling holes, cutting slots, cleaning hard surfaces, deburring, polishing,
and radiusing.
Deburring of cross holes, slots, and threads in small precision parts that require a burr-free finish, such as hydraulic valves, aircraft fuel systems, and medical appliances.
Machining intricate shapes or holes in sensitive, brittle, thin, or difficult-to-machine materials.
Insulation stripping and wire cleaning without affecting the conductor.
Micro-deburring of hypodermic needles.
Frosting glass and trimming of circuit boards, hybrid circuit resistors, capacitors, silicon, and gallium.
Removal of films and delicate cleaning of irregular surfaces because the abrasive stream is able to follow contours.