Saturday, 21 November 2015

Abrasive Jet Machining (AJM)

In abrasive jet machining (AJM) material removal occurs on account of impact of high velocity air / gas stream of abrasive particles on the workpiece. The abrasives are propelled by a high velocity gas to erode material from the workpiece. As an outcome of impact of the abrasive particles on the workpiece, tiny brittle fractures occur at the surface of the workpiece and the carrier gas carries away the fractured fragments. AJM is also called as abrasive blasting process. It is also known by several other names such as abrasive micro-blasting, pencil blasting and micro-abrasive blasting. AJM is an effective machining method for hard and brittle materials such as glass, silicon, tungsten and ceramics. Typically the process is used for cutting intricate shapes or forms of specific edges. The process is inherently free from chatter, vibration and heat problems because the tool never touches the substrate. The schematic of AJM process set up is shown in Figure

Principle of AJM

The principle of machining / cutting by abrasive jet process is explained through the
following steps:

1. Abrasive particles of size between 10 m to 50 m (depending upon the requirement of either cutting or finishing of the work piece) are accelerated in a gas stream (commonly used gas stream is air at high atmospheric pressures).
2. The smaller abrasive particles are useful for finishing and bigger are used for cutting operations.
3. The abrasive particles are directed through the nozzle, towards the work piece surface where-ever cutting or finishing is to be done. The distance between the tip of the nozzle and the work surface is normally within 1 mm.
4. As the abrasive particles impact the surface of the work piece, it causes a small fracture at the surface of the work piece. The material erosion occurs by the chipping action.
5. The erosion of material by chipping action is convenient in those materials that are hard and brittle.
6. As the particles impact the surface of
7. The abrasive particles once used, cannot be re-used as its shape changes partially and the work piece material is also clogged with the abrasive particles during impingement and subsequent flushing by the carrier gas.

 AJM process is a highly flexible process wherein the abrasive media is carried by
a flexible hose, which can reach out to some difficult areas and internal regions.
 AJM process creates localized forces and generates lesser heat than the conventional machining processes.
 There is no damage to the workpiece surface and also the process does not have tool-workpiece contact, hence lesser amount of heat is generated.
 The power consumption in AJM process is low. Disadvantages
 The material removal rate is low
 The process is limited to brittle and hard materials
 The wear rate of nozzle is very high
 The process results in poor machining accuracy
 The process can cause environmental pollution
Metal working:
 De-burring of some critical zones in the machined parts.
 Drilling and cutting of the thin and hardened metal sections.
 Removing the machining marks, flaws, chrome and anodizing marks.
 Cutting of the optical fibers without altering its wavelength.
 Cutting, drilling and frosting precision optical lenses.
 Cutting extremely thin sections of glass and intricate curved patterns.
 Cutting and etching normally inaccessible areas and internal surfaces.
 Cleaning and dressing the grinding wheels used for glass.
 Cleaning the residues from diamond wheels, dressing wheels of any shape and size.

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