1

SUBMITTED BY: MANJEET KUMAR PANDAY

ABRASIVE JET MACHINING

2

TABLE OF CONTENT

INTRODUCTIONWORKING PRINCIPLE OF AJMDIFFERENT COMPONENTS OF AJM SET UP PROCESS PARAMETERS & THEIR EFFECTSAPPLICATIONSADVANTAGESDISADVANTAGESRESULTS AND DISCUSSIONREFERENCES

3

INTRODUCTION

Abrasive jet machining is a process in which a focused stream of abrasive particles, carried by high pressure air or gas is made to impinge on the work surface through a nozzle.

The work material is removed by erosion with the help of high velocity abrasive particles.

4WORKING PRINCIPLE OF AJM

In Abrasive jet machining abrasive particles are made to impinge on work material at high velocity.

Jet of abrasive particles is carried by carrier gas(generally compressed air).

The high velocity stream of abrasives is generated by converting pressure energy of carrier gas to its Kinetic energy with the help of nozzle.

The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material.

5

Air-compressor

Pressure control valve

Drier

Filter

Abrasive feeder

Mixing Chamber

Nozzle

Work-piece

Table

Exhaust

Electro-magnetic shaker

Fig 1: Schematic Diagram Of Abrasive Jet Machining Set Up

6

DIFFERENT COMPONENTS OF AJM SET UP

Air compressor: It pressurizes the gas. Air filter: It filters the gas before entering the mixing chamber. Drier: It extracts extra moisture from the air coming through

compressor. Pressure regulator: It regulates the flow rate of abrasive jet. Mixing chamber: It is used to mix the gas and abrasive particles.Abrasive Feeder: It controls the abrasive powder feed rate in the

mixing chamber. Nozzle: It forces the abrasive jet over the work piece.

7

PROCESS PARAMETERS

Type of Abrasive & Size of Abrasive Grain

Carrier Gas

Mixing Ratio

Velocity of Abrasive Jet & Nozzle Pressure

Stand-off distance

Work piece Material & Shape of Cut

Nozzle Design

8

1.TYPE OF ABRASIVE GRAIN & ABRASIVE GRAIN SIZE

Aluminum oxide (Al2O3), Silicon carbide (SiC), Glass beads, crushed glass and sodium bicarbonate are some of abrasives used in AJM.

Selection of abrasives depends on MRR, type of work material, machining accuracy.

We can also see the effect of grain size on accuracy from the following table.

Particle size ( in microns) Surface roughness ( in microns)

10 0.152 to 0.20325 to 27 0.355 to 0.67550 0.965 to 1.27

9

Abrasives Grain Sizes ApplicationAluminum oxide(Al2O3) 12, 20, 50 microns Good for cleaning, cutting

and deburring

Silicon carbide (SiC) 25,40 micron Used for similar application but for hard material

Glass beads 0.635 to 1.27micron Gives matte finishDolomite - Etching and polishingSodium bi carbonate 27 micros Cleaning, deburring and

cutting of soft materialLight finishing below 500C

TABLE : TYPES OF ABRASIVES & GRAIN SIZE FOR DIFFERENT OPERATIONS

10

2. CARRIER GAS

Gas should be non-toxic, cheap, easily available.

Air, Nitrogen and carbon dioxide can be used.

Gas may be supplied either from a compressor or a cylinder.

In case of a compressor, air filter cum drier should be used to

avoid water or oil contamination of abrasive powder.

The carrier gas consumption is of order of 0.008 m3/min at a

nozzle pressure of 5 bar.

11

3. MIXING RATIO

• Mixing ratio – Volume flow rate of abrasives/Volume flow rate of gas.• Increased mass flow rate of abrasive beyond a limit will result in a decreased velocity of fluid and will thereby decreases the available energy for erosion and ultimately the MRR.

Fig.2 &3. Effect Of Abrasive Flow Rate & Mixing Ratio On MRR

12

4. Velocity of Abrasive Jet & Nozzle Pressure

The recommended velocity of gas abrasive mixture ranges between 100 meter per second to 300 meter per second depending upon the cutting or finishing operations.

The velocity of gas abrasive mixture is a function of nozzle design, nozzle pressure and abrasive flow rate.

.

FIG 3 & 4: Effect of jet velocity & Nozzle pressure

13

5. Stand-off distance

Effect of stand-off distance on MRR and accuracy can be seen from the following figures.

Stand-off distance

MRR

(a) (b) (c) (d)

(a)

(b)

(c)

(d)

FIG 5 & 6: Stand-off distance and its effects

14

6. Work piece Material & Shape of Cut

For ductile materials the cutting may not be very effective

rather there will be flow of material and actual material

removal will not take place.

Hence material should be brittle.

It may not be possible to machine components with sharp

corners because of stray cutting. Hence sharp corners

should be avoided.

15

7.NOZZLE DESIGN

Nozzle material, nozzle geometry, flow rate.The nozzle material should be such that it can withstand the

erosive action of the abrasive particles and should be wear resistant.

AJM nozzle is usually made of tungsten carbide or sapphire.The nozzle is made of either circular or rectangular cross section.It is so designed that loss of pressure due to the bends, friction

etc. is minimum possible.With increase in nozzle wear, the divergence of jet stream

increases resulting in more stray cutting and high inaccuracy.

16

APPLICATIONS

AJM is useful in manufacture of electronic devices. Micro-machining of brittle objects.

Making of nylon and Teflon parts, permanent marking on rubber stencils, cutting titanium foils.

Cutting of optical fibers without altering its wavelength is one of the most important applications of this process.

Deburring of some critical zones in the machined parts.Cutting, drilling and frosting of precision optical lenses.Cutting and etching of inaccessible areas and internal

surfaces can be done.Reproducing designs on a glass surface with the help of

rubber or copper masks.

17

ADVANTAGES

It has the capability of cutting holes of intricate shape in hard materials.

Thin sections of hard & brittle materials like germanium, mica, silicon, glass and ceramics can be machined.

Process is free from chatter and vibration as there is no contact between the tool and work piece.

Abrasive jet machining process creates localized forces and generates lesser heat than the conventional machining processes.

The power consumption in abrasive jet machining process is considerably low.

18

DISADVANTAGES

The accuracy of cutting is hampered by tapering of hole due to unavoidable flaring of abrasive jet.

Abrasive powders cannot be reused as the sharp edges are worn and smaller particles can clog the nozzle.

The mixing chamber and the nozzle are the two critical components and they need to be changed very frequently because of the wear.

Material removal rate in abrasive jet machining process is rather low(around 15 mm3/min for glass).

19

RESULTS & DISCUSSION

The effects of parameters of AJM on material removal rate (MRR, gm/sec) and during micro machining of Silicon glass.

For this experiment SiC abrasive with grit size 70μm is selected. A tungsten carbide nozzle having diameter 1.3mm, 1.5mm, 2.3mm is considered.

Another parameter ranges are Pressure 50psi, 55psi, 60psi, Stand-off distance 8mm, 10mm, 12mm is considered.

The effect of machining parameters pressure, nozzle tip distance, and nozzle diameter is evaluated using ANOVA.

MRR=(w1-w2)/t, where w1 & w2 are wt. before & after machining and t=time

20

Pressure (psi)

STD (mm)

Nozzle dia (mm)

Wt. before machinng (gm)W

Wt. after machining (gm)

Time (sec)

MRR (gm/s)

50 8 1.2 25.3 25.1 9 0.02255 8 1.5 29.2 29.0 7 0.02860 8 2.3 25.2 24.9 9 0.03355 10 2.3 25.5 25.3 9 0.02260 10 1.2 25.4 25.2 7 0.028

It is observed that MRR of glass, machining by AJM, is increased by increasing Pressure & also increased by decreasing Nozzle Diameter.The optimum value of MRR is obtained at Pressure 60psi, Stand-off distance 8mm and Nozzle Diameter 1.5 mm.

ANNOVA TABLE For The Experiment

21REFERENCES

Verma, A.P. and Lal, G.K,.(1983) “An Experimental study of abrasive jet machining”, International Journal of Machine Tool & Manufacturing.

Fan,J.M, Wang,C.Y. and Wang,J. (2009) “Modelling the erosion rate in micro abrasive, air jet machining of glasses” .

Kea,J.H. Tsaia,F.C. Hungb,J.C. and Yanc,B.W. (2012)“Characteristics study of abrasives in abrasive jet machining”.

“Analysis on Performance of Different Parameters during Abrasive Jet”, International Journal of Emerging Research in Management &Technology.

22

THANK YOU