Abrasive jet machining uses high velocity (100 – 300m/s) jet of fine grain abrasives mixed with pressurized carrier gas to remove material from work surface by impact erosion. Such high velocity jet is obtained by transforming static pressure of carrier gas to kinetic energy. Therefore, this carrier gas is first dehumidified and then compressed to very high pressure (10 – 20bar) with the help of air compressor. Abrasives, maintained at atmospheric pressure, are then mixed with carrier gas as per mixing ratio inside a vibratory mixing chamber. This mixture is then fed to a nozzle, which then converts pressure energy into kinetic energy before discharging it for striking the work surface. Basic functions of carrier gas in abrasive jet machining are discussed below.
- Effects of carrier gas on abrasive jet machining performance.
- Can pure oxygen be used as a carrier gas in AJM?
Functions of carrier gas in abrasive jet machining (AJM)
- It accelerates tiny abrasive particles.
- It helps forming abrasive jet.
- It blows away eroded metal particles and used grits from machining zone.
Function-1: Accelerating abrasive particles
Tiny abrasive particles are usually kept in a chamber (abrasive feeder) maintained in atmospheric pressure. These abrasives are then mixed with pressurized carrier gas in the vibratory mixing chamber. A predefined Mixing Ratio determines the volume or mass of abrasive to be mixed per unit volume of carrier gas. During mixing, momentum transfer takes place and abrasives start flowing with carrier gas through the pipeline until it reaches nozzle. As abrasives possessing zero velocity are mixed with abrasive-gas mixture, its pressure becomes less than that for carrier gas alone. Final pressure of mixture depends on mixing ratio, carrier gas pressure before mixing and also momentum loss during mixing.
Function-2: Forming abrasive jet
A nozzle is used to convert the pressure energy of gas-abrasive mixture to kinetic energy and thus high velocity jet is obtained. Since abrasives are incompressible, so without presence of one carrier medium it is impossible to form a high velocity jet. Carrier gas serves this purpose and carries the abrasives until it strikes the work surface for eroding material.
Function-3: Blowing away removed metal particles
Once abrasive jet strikes the work surface at a particular angle from a suitable stand-off distance, it erodes material in the form of tiny metal particles. If these metal particles as well as used abrasive grits are allowed to stay in the machining zone, they will collide with fresh jet and will reduce jet velocity. Carrier gas blows away these unwanted materials from machining zone and thus protects fresh jet from losing its kinetic energy.
- Paper: N. Ramachandran and N. Ramakrishnan (1993); A review of abrasive jet machining; Journal of Materials Processing Technology; Vol. 39; pp. 21-31.
- Modern Machining Processes by P. C. Pandey and H. S. Shan (Mcgraw Higher Ed.).