ABRASIVE JET MACHININGABRASIVE JET MACHINING

• An unconventional machining process.An unconventional machining process.

• It is the process of removal of materials by impact It is the process of removal of materials by impact erosion through the action of a concentrated, high erosion through the action of a concentrated, high velocity of the grit abrasives entertained in a high-velocity of the grit abrasives entertained in a high-velocity gas stream. velocity gas stream.

WHY ABRASIVE JET MACHINING ?WHY ABRASIVE JET MACHINING ?

• Since it is an unconventional machining Since it is an unconventional machining process, so it is used where conventional process, so it is used where conventional machining processes cannot be used, like in machining processes cannot be used, like in machining of hastalloy, nitralloy, nimonics,etc.machining of hastalloy, nitralloy, nimonics,etc.

• Also it differs from conventional sand blasting Also it differs from conventional sand blasting process for its fineness of particle size and process for its fineness of particle size and controllable machining parameters.controllable machining parameters.

SCHEMATIC SET UP OF ABRASIVE JET SCHEMATIC SET UP OF ABRASIVE JET MACHINING PROCESS:-MACHINING PROCESS:-

PROCESS DESCRIPTION:-PROCESS DESCRIPTION:-

• In this process, a gas (nitrogen or carbon dioxide or In this process, a gas (nitrogen or carbon dioxide or air), is supplied under pressure (2-8kg/sq.cm) is air), is supplied under pressure (2-8kg/sq.cm) is supplied and after filter and regulator, it is passed supplied and after filter and regulator, it is passed to a mixing chamber (containing abrasive particles) to a mixing chamber (containing abrasive particles) vibrating at 50c/sec.vibrating at 50c/sec.

• From the mixing chamber , the gas along with the From the mixing chamber , the gas along with the abrasive particles of size 10-50 micro-mt. passes on abrasive particles of size 10-50 micro-mt. passes on to a nozzle having its tip of tungsten carbide and to a nozzle having its tip of tungsten carbide and diameter around 0.45mm , with a velocity of 150-diameter around 0.45mm , with a velocity of 150-300m/sec.300m/sec.

• The air consumption is of the order of 0.6 The air consumption is of the order of 0.6 cu-m/hr.cu-m/hr.

• The nozzle tip distance is of the order of 0.81mmThe nozzle tip distance is of the order of 0.81mm

• The abrasive powder feed rate is controlled by the The abrasive powder feed rate is controlled by the amplitude of vibration of the mixing chamber.amplitude of vibration of the mixing chamber.

• The relative motion between the nozzle and the The relative motion between the nozzle and the work piece is obtained by cams,pantographs to work piece is obtained by cams,pantographs to control size and shape of cut.control size and shape of cut.

• Dust removal equipment is also incorporated to Dust removal equipment is also incorporated to protect the environment.protect the environment.

OPERATING PRINCIPLES IN ABRASIVE OPERATING PRINCIPLES IN ABRASIVE JET MACHINING:-JET MACHINING:-

• Carrier gasCarrier gas

• Shape of cut Shape of cut

• Nozzle designNozzle design

• Work materialWork material

• Type of abrasive Type of abrasive

• Stand-off distanceStand-off distance

• Size of abrasive grainSize of abrasive grain

• Velocity of abrasive jetsVelocity of abrasive jets

• Mean of abrasive particle/unit volume of the carrier gasMean of abrasive particle/unit volume of the carrier gas

EFFECT OF VARIOUS PARAMETERS EFFECT OF VARIOUS PARAMETERS ON MATERIAL REMOVAL RATEON MATERIAL REMOVAL RATE

ABRASIVES USED IN ABRASIVE ABRASIVES USED IN ABRASIVE JET MACHININGJET MACHINING

ABRASIVESABRASIVES::

1.1. Alumina Alumina

2.2. Silicon carbideSilicon carbide

3.3. Sodium bicarbonateSodium bicarbonate

4.4. DolomiteDolomite

5.5. Glass beadsGlass beads

GRAIN GRAIN SIZE(micron)SIZE(micron)

10,27,5010,27,50

-do--do-

2727

6666

0.635-1.27mm0.635-1.27mm

CHARACTERISTICS OF THE CHARACTERISTICS OF THE PROCESS:-PROCESS:-

1.1. Size of abrasiveSize of abrasive Around 25 micro-mt.Around 25 micro-mt.

2.2. Flow rateFlow rate 3-20 g/min.3-20 g/min.

3.3. Life of nozzleLife of nozzle WC(12-30 hrs),sapphire(300 hrs).WC(12-30 hrs),sapphire(300 hrs).

4.4. ToleranceTolerance + or – 0.05mm + or – 0.05mm

5.5. Surface roughnessSurface roughness 0.15-0.2 micro-m with particles of size 10micro-0.15-0.2 micro-m with particles of size 10micro-m, 0.4-0.8 micro-m. m, 0.4-0.8 micro-m.

6.6. Work materialWork material Hard and brittle materials like glass, ceramics, Hard and brittle materials like glass, ceramics, mica, etc.mica, etc.

7.7. Machining operationsMachining operations Drilling , cutting , deburring , cleaning.Drilling , cutting , deburring , cleaning.

APPLICATIONS OF THE PROCESS:-APPLICATIONS OF THE PROCESS:-

• Used for abrading and frosting glass more Used for abrading and frosting glass more economically as compared to etching or grinding.economically as compared to etching or grinding.

• For cleaning of metallic smears on ceramics, oxides on For cleaning of metallic smears on ceramics, oxides on metals, resistive coatings, etc.metals, resistive coatings, etc.

• Cutting and machining of fragile material like Ge, Si, Cutting and machining of fragile material like Ge, Si, etc.etc.

• For deburring small hole in hypodermic needles and For deburring small hole in hypodermic needles and for small milled slots in hard metallic components.for small milled slots in hard metallic components.

• Register treaming can be done very easily and micro-Register treaming can be done very easily and micro-module fabrication for electrical contact, module fabrication for electrical contact, semiconductor processing can also be done effectively.semiconductor processing can also be done effectively.

ADVANTAGES OF THE PROCESS:-ADVANTAGES OF THE PROCESS:-

• Ability to cut fragile, brittle or heat sensitive Ability to cut fragile, brittle or heat sensitive material without damage.material without damage.

• Ability to cut intricate holes in materials of Ability to cut intricate holes in materials of any hardness.any hardness.

• Low capital cost.Low capital cost.

• Can cut materials without damage because Can cut materials without damage because there is no heating of the working surface.there is no heating of the working surface.

DISADVANTAGES OF THE DISADVANTAGES OF THE PROCESSPROCESS

•Slow material removal rate.Slow material removal rate.

•Low accuracy (0.1mm) due to stray Low accuracy (0.1mm) due to stray cutting.cutting.

•Abrasives get embedded on the Abrasives get embedded on the material surface, if it is soft.material surface, if it is soft.

•Abrasives powder cannot be Abrasives powder cannot be refused.refused.

FUTURE PROSPECTS OF THE FUTURE PROSPECTS OF THE PROCESSPROCESS

• This process can be used in future in those This process can be used in future in those places where there is intricacy and costly places where there is intricacy and costly machining, so this process can be used to machining, so this process can be used to remove both of these difficulties.remove both of these difficulties.

• Also, due to cost-effectiveness of the set of Also, due to cost-effectiveness of the set of AJM, this process can be used in small-scale AJM, this process can be used in small-scale industries.industries.

REFERENCESREFERENCES

• Production technology- R.K.JainProduction technology- R.K.Jain

• Non-conventional machining- P.K.MishraNon-conventional machining- P.K.Mishra

• GoogleGoogle

• WikipediaWikipedia