All About Abrasive Jet Machining (AJM)

Abrasive Jet Machining (AJM) is a non-conventional machining process where the material is removed by the application of a high-velocity stream of abrasive particles carried in gas/air or liquid medium onto the work surface.

Introduction

Abrasive Jet Machining (AJM) uses the high-velocity stream of abrasive particles to remove material from metallic/non-metallic workpieces. It is mostly used for machining of hard and brittle materials which are sensitive to heat and have low thermal conductivity like glass, ceramics, quartz etc. AJM does not produce thermal or chemical changes in the workpiece.

Working Principle

• In AJM, the kinetic energy of abrasive particles is utilized to remove the material.
• The abrasive particles strike the work surface at high velocity and material removal takes place due to micro-cutting action as well as brittle fracture of workpiece surface.
• The high velocity stream of abrasive particles is carried by carrier gas or liquid. Common carrier gases used are air, CO2, nitrogen etc.

Process Parameters

• Abrasive - Silicon carbide, aluminum oxide, glass beads etc.
• Abrasive size - Around 50 μm. Fine abrasive for smooth surface finish.
• Abrasive flow rate
• Nozzle design - Material is tungsten carbide mostly. Orifice dia 0.25-1.5mm.
• Pressure - 1-6 bar for gas, up to 400 MPa for liquid jet.
• Standoff distance - 1-25mm.
• Traverse speed - Depends on application.

Advantages

• No heat affected zone
• No thermal or chemical changes
• Very fine surface finish
• No burrs at edges
• Ability to machine complex shapes
• No micro-cracks

Disadvantages

• Low material removal rate
• High equipment and operational cost
• Sensitivity to work surface orientation
• Taper formation in machined holes

Applications

• Machining of heat sensitive materials like glass, quartz, ceramics etc.
• Drilling holes in hard and brittle materials
• Cleaning and finishing operations
• Shaping of polymer matrix composites
• Deburring and polishing

FAQ

Which type of materials can be machined using abrasive jet machining?

Abrasive jet machining can be used to machine almost all types of materials like metals, alloys, composites, glass, ceramics etc. It is especially useful for machining hard and brittle materials.

How is the material removed in abrasive water jet machining?

In abrasive water jet machining, material is removed by the kinetic energy and micro-cutting action of the fine abrasive particles as they strike the work surface at very high velocities.

What is the grain size of abrasive particles, which are often used for abrasive water jet machining?

The grain size of abrasive particles used is generally around 50 μm. Very fine abrasives are used to get smooth surface finish.

Which of the following material/s cannot be used for making of nozzle in abrasive jet machining?

Carbon steel cannot be used for making the nozzle in abrasive jet machining due to its low wear resistance. Materials like tungsten carbide, sapphire, ruby etc are commonly used.

What is the value of stand-off distance in abrasive water jet machining?

The typical stand-off distance in abrasive water jet machining ranges from 1mm to 25mm. Lower stand-off distance results in greater material removal rate but poor surface finish.

When was abrasive water jet machining developed first?

Abrasive water jet machining technology was first developed in early 1970s for commercial use. However, the use of sand laden fluid streams for cutting has been known since ancient times.

Which of the following carrier gases is generally used in abrasive jet machining?

Air, carbon dioxide and nitrogen are generally used as carrier gases in abrasive jet machining.

Which of the following components influence the material removal rate in abrasive jet machining?

Abrasive flow rate, particle size and velocity, stand-off distance and traverse speed influence the material removal rate in abrasive jet machining.

By using abrasive jet machining, how much amount of hardening does the materials experience?

Abrasive jet machining does not cause any thermal damage or hardening of the machined surface, unlike other thermal processes. The workpiece retains its original metallurgical structure.

In abrasive water jet machining, intensifier is used to deliver which type of pressure?

In abrasive water jet machining, the intensifier pressurizes the water to ultra-high pressures up to 400 MPa before it exits via the nozzle.

In summary, Abrasive Jet Machining is a versatile non-conventional machining process suitable for hard and brittle materials. It offers many advantages like absence of heat affected zone, high precision and finesse of cut. With continuous research and development, AJM promises to find wider applications in machining difficult-to-cut materials.