26-08-2014, 12:25 PM
Abrasive Jet Machining
Abrasive Jet.ppt (Size: 1.73 MB / Downloads: 10)
INTRODUCTION
A jet of inert gas consisting of very fine abrasive strikes the work piece at high velocity(200-400m/s)
This high velocity results in removal of material effectively on hard and brittle material but not in the soft material like Al ,rubber etc..
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
Best suited for hole drilling in superhard materials.
Typically used to cut, clean, peen, deburr, deflash and etch glass, ceramics and other hard materials.
GAS PROPULSION SYSTEM
Clean and dry air is supplied to propel the abrasive particles
A gas (Nitrogen, CO2 or air) is supplied at 2 – 8 kg/cm2
Avoid water and oil contamination of abrasive particles
The gas should be non toxic ,cheap and easily available
MACHINING CHAMBER
The machining chamber is well closed so that the concentration of abrasive particle on the work chamber does not reach the harmful limit
The chamber is equipped with vaccum dust collector.
Special consideration should given to the dust collector in case of machining toxic material (beryllium etc).
Amplitude of vibration (50Hz) – to control the feed rate of abrasives
Application
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
Limitations
The removal rate is slow.
Stray cutting can’t be avoided (low accuracy of 0.1 mm).
The tapering effect may occur especially when drilling in metals.
The abrasive may get impeded in the work surface.
Suitable dust-collecting systems should be provided.
Soft materials can’t be machined by the process.
Silica dust may be a health hazard.
Ordinary shop air should be filtered to remove moisture and oil.