ABRASIVE JET MACHINE

Pallavi Priyambada Badajena Guided By

Debashish Bose Rajendra Kumar Mohanty

Deepak Kumar Mohanty Lecturer

Dillip Kumar Sahoo Dept.Of Mechanical Engg.

Debesh Jena

Introduction

History

Working Principle

Diagram

Equipments

Process Parameters

Process Characteristics

Schematic Diagram

Types of Abrasive

Market Price Of Compressor

Abrasive Particle

Carrier Gas

Nozzle And Jet Velocity

Stand-off Distance

Design Of AJM In Autocad

Material Removal Rate

Accuracy

Surface Finish

Application

Advantages

Disadvantages

References

There are many situations where the processes of manufacturing we’ve learned cannot produce the required dimensional accuracy and or surface finish.

Fine finishes on ball/roller bearings, pistons, valves, gears, cams, etc.

The best methods for producing such accuracy and finishes involve Abrasive Jet Machining

Abrasive Jet Machining, It is an unconventional machining process based on mechanical energy for cutting, deburring and cleaning hard and brittle materials.

In 1979, Dr. Mohamed Hashish working at Flow Research, began researching methods to increase the cutting power of the abrasive jet so it could cut metals, and other hard materials.

Dr. Hashish, regarded as the father of the abrasive jet, invented the process of adding abrasives to the plain abrasive jet. He used garnet abrasives, a material commonly used on sandpaper. With this method, the jet (containing abrasives) could cut virtually any material.

Abrasive Jet Machining helps in removing materials from the brittle and heat sensitive materials by the application of high speed stream of abrasive particles.

Micro-abrasive particles are propelled by inert gas at velocities of upto 300 m/sec, which result in erosion

The material removal is due to erosive action of a high

pressure jet.

In particular drilling of holes of minimum diameter and maximum depth with greater accuracy and surface finish.

Material is removed by fine abrasive particles, usually about 0.001 in (0.025 mm) in diameter.

Pressures for the gas range from 25 to 130 psig (170–900 kPag) and speeds can be as high as 300 m/s.

High pressure gas supply source

Powder mixing chamber

Control valve

Nozzle

Hood

Exhaust systems

A filter and water separator unit

The abrasive powder is held in a hopper, which is fed to the mixing chamber to mix with carrier gases.

A jet stream of abrasive forms as the mixture comes out of the nozzle.

At the working table a dust collection hood is provided, with a vacuum dust collector.

Nozzle Nozzle tips are made of hard materials like tungsten

carbide or sapphire.

Tungsten carbide nozzles give a life of about 15 hours with silicon carbide abrasive.

The nozzle diameter is in the range of 0.13 to 1.25 mm

MRR, machining accuracy, surface roughness and nozzle wear are influenced by Size and distance of the nozzle.

Composition, strength, size, and shape of abrasives

Flow rate

Composition, pressure, and velocity of the carrier gas.

The mass flow rate of the gas decreases with an increase in the abrasive flow rate

Hence the mixing ratio increases and causes a decrease in the removal rate because of the decreasing energy available for material removal

High nozzle pressures result in a greater removal rate, but the nozzle life is decreased

Refractory-Powder

Refractory-Loose Grit Sand

Bonded Abrasives

Coated Abrasives

Blasting/Lapping/Polishing Abrasives

The market price of air compressor vary over a wide range.

Its value depends on the pressure with which the abrasive particle is to be bombarded on the workpiece(Glass).

20-25cfm – Rs70,000

10-12cfm – 35,000

Material – Al2O3 / SiC / glass beads

Shape – irregular / spherical

Size – 10 ~ 50 μm

Mass flow rate – 2 ~ 20 gm/min

Composition – Air, CO2, N2

Density – Air ~ 1.3 kg/m3

Velocity – 500 ~ 700 m/s

Pressure – 2 ~ 10 bar

Flow rate – 5 ~ 30 lpm

Material – WC / sapphire

Diameter – (Internal) 0.2 ~ 0.8 mm

Life – 10 ~ 300 hours

Velocity – 100 ~ 300 m/s

Stand-off distance – 0.5 ~ 5 mm

Impingement Angle – 600 ~ 900

• The metal removal rate depends upon The diameter of nozzle

Composition of abrasive-gas mixture

Jet pressure

Hardness of abrasive particles and that of work material

Particle size

Velocity of jet

Distance of work piece from the jet

• In AJM, tolerances in the region of ±0.05 mm can be achieved for precision works.

• In normal production jobs tolerance up to 0.1mm are possible.

• The corner radius can be up to 0.1 mm, while taper is about 0.05 mm per 10 mm of depth.

Surface finish in AJM is in the range of 0.4 to 1.2 mm depending upon the abrasive particle size.

There is no heat affected zone, since the surface while machining remains at room temperature, as the carrier gas acts as the coolant.

The effect of impact on the surface is less than 2 μm

AJM can be used conveniently for fragile materials like glass.

Its applications include removing oxides from metal surfaces, deburring, etching patterns, drilling and cutting of thin sections.

The process is not suitable for cutting soft materials since the abrasive particles may get embedded into the soft material.

Cutting action is shock less.

Ability to cut fragile and heat sensitive materials without damage.

Ability to cut intricate hole shapes in materials of any hardness and brittleness.

No variation due to surface irregularities and tool wear as in conventional machining.

Low capital cost.

AJM units are easy to operate and maintain

It is not suitable for mass material removal.

It needs a dust control system.

The abrasives may get embedded in softer material.

The nozzle life is limited.

The cutting motion is to be properly controlled.

Boothroyd, Geoffrey; Knight, Winston A. (1989),Fundamentals of machining and machine tools(2nd ed.), Marcel Dekker, pp. 478–479,

Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes Reference Guide, Industrial Press Inc., pp. 2–5, .

Chastagner, Matthew W.; Shih, Albert J. (2007), "ABRASIVE JET MACHINING FOR EDGE GENERATION", Transactions of NAMRI/SME35: 359–366