A brief overview of Abrasive Jet Machining (AJM)
In Abrasive Jet Machining (AJM), a focused stream of abrasive grains of Al2O3 or SiC carried by high pressure gas or air at high velocity is made to impinge on the work surface through a nozzle of 0.3–0.5 mm diameter. AJM has smaller diameter abrasives and a more finely controlled delivery system than sand blasting (SB). The workpiece material is removed by the abrasion action (A) of the high-velocity abrasive particles.
Abrasive Jet Machining Diagram
Abrasive Jet Machining working and process parameters
A gas (nitrogen, carbon dioxide, or air) is supplied under pressure of 2–8 kg/cm2. Oxygen should never be used because it causes a violent chemical reaction with the workpiece chips or the abrasives. After filtration and regulation, the gas is passed through a mixing chamber that contains abrasive particles and vibrates at 50 Hz. From the mixing chamber, the gas along with the entrained abrasive particles (10–40 μm) passes through a 0.45 mm diameter tungsten carbide nozzle at a speed of 150–300 m/s. Aluminum oxide (Al2O3) and SiC powders are used for heavy cleaning, cutting, and deburring. Magnesium carbonate is recommended for light cleaning and etching. Sodium bicarbonate is used for fine cleaning and cutting of soft materials. Commercial grade powders are not suitable because their sizes are not well classified and may contain silica dust, which can be a health hazard.
The abrasive powder feed rate is controlled by the amplitude of vibrations of the mixing chamber. The nozzle standoff distance is kept at 0.81 mm. The relative motion between the workpiece and the nozzle is manually or automatically controlled using cam drives, pantographs, tracer mechanisms, or computer control according to the cut geometry required. Masks of copper, glass, or rubber may be used to concentrate the jet stream of the abrasive particles to a confined location on the workpiece. Intricate and precise shapes are produced by using masks with corresponding contours. Dust removal equipment is incorporated to protect the environment.
Applications of Abrasive Jet Machining
- AJM machining is best suited for machining holes in super-hard materials.
- It is typically used to cut, clean, peen, deburr, and etch glass, ceramics, or hard metals.
Limitations or Disadvantages of Abrasive Jet Machining
- It is not practical to reuse the abrasive powder because contamination and worn grit cause a decline in the machining rate.
- The removal rate of materials is low.
- The tapering of hole mainly with more depth is unavoidable.
- A dust collecting chamber is a basic need to avoid atmospheric pollution that causes health problems.
- The abrasive particles might remain there on the work surface.
Advantages of Abrasive Jet Machining
- This process is significant for machining breakable, heat resistant materials like ceramic, glass, germanium, mica etc.
- It can be used for cutting, drilling, deburring, cleaning etc. the materials.
- The depth of surface damage is little.
- Holes of complex shapes could be produced efficiently.
- The surface machined has a good finish.
Enjoyed reading Abrasive Jet Machining, also read tool wear
Reference taken from Medium