Abrasive-jet Machining (AJM)

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In abrasive-jet machining (AJM) material is removed by the impact of a high velocity stream of gases and abrasive mixture focused on to the workpiece. High Velocity impact of an abrasive particle causes a tiny brittle fracture on the work surface and the flowing gases carries away the dislodged small workpiece particle.

Abrasive-jet machining process is similar to convectional sand blasting, but differs in the way that the abrasive is much finer and the process parameters are effectively controlled.

Schematic diagram of abrasive jet machining

Schematic diagram of abrasive-jet machining

Features of Abrasive-jet Machining:

  • Size of abrasive particle is in the range from 10 to 50 µm.
  • Mechanism of material removal is due to brittle fracture by impinging abrasive grains at high speed.
  • This process is more suitable when the work material is brittle and fragile.
  • Normally number of grains per unit time is 2 to 20 g/min with non recirculation type and size of grains is 15 to 20µm.
  • Pressure of air/gas normally used is 2 to 10 MPa.
  • Nozzle is made by WC with orifice area of 0.05 to 0.2 mm2 and its life is 12 to 300 hours.

Materail Removal Rate (MRR) characteristics:

  • Nozzle is generally having contact with abrasives, so it should be made by very hard material to avoid wear.
  • Shape of orifice is circular or rectangular.
  • Nozzle tip distance is the distance between nozzle tip and work piece, it affects not only the MRR but also shape and size of cavity produced.
  • As the nozzle lip distance increases velocity of abrasive particles impinging on work surface increases due to their acceleration after they leave the nozzle, which in turn increases the MRR.
  • But with further increase in nozzle tip distance velocity decreases due to drag of the atmosphere.

Limitations:

  • Low MRR (40 mg/min) embedding of abrasive in workpiece, tapering of drilled holes.
  • Tapping is about 7° angle if the nozzle top distance is 15 mm.

Applications:

  • AJM is used for cutting, cleaning and for machining of semi-conductors such as silicon, gallium or germanium, for making holes and slots in glass, quartz, mica and ceramics.
  • A dimensional tolerance of 0.05 mm can be obtained with surface finish of 0.5 to 1.2 µm.
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All Comments

  • It is very useful for me

    franklin Feb 29, 2016 11:21 am Reply

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