Abrasive Jet Machining

• Aluminum or Silicon carbide abrasive grains contained in gas or air – for heavy cleaning

• Magnesium carbonate for light cleaning

• Sodium bicarbonate for light cutting

Introduction

• Oxygen never should be used

• Mixing chamber vibrates at 50 Hz

• Abrasive velocity 150 to 300 m/s

• Application dictates the size and the type of abrasive• Aluminum oxide and silicon carbide- cleaning,

cutting, and debarring• Magnesium carbonate – light cleaning and etching• Sodium bicarbonate – fine cleaning and cutting of

soft material • Glass beads – Polishing and de-flashing• Foundry Sand (Garnet is 30% more effective than

sand)• Size of abrasives range from 10 to 50 micrometer• Powders should be free from silica dust which is

hazardous• re-usability?

Abrasives

Process Characteristics

Masks are used to control the location of abrasives in restricted areas

Material Removal Mechanism

Tiny Brittle Fracture

• The material removal rate is mainly dependent on the flow rate and size of abrasives.

• Larger grain sizes produce greater removal rates.

AWJM

• Harder materials such as glass, ceramics, concrete, and tough composites can be cut by adding abrasives to the water jet during abrasive water jet machining

• AWJM cuts 10 times faster than the conventional machining methods of composite materials

• Abrasive water jet is hundreds, if not thousands, of times more powerful than the pure water jet

The Machining System

The Machining System

The basic machining system of AWJM incorporates the following elements:

Water delivery Abrasive hopper and feeder Intensifier Filters Mixing chamber Cutting nozzles Catcher

Processing Parameters

Ice Jet Machining• Drawback of WJM and AWJM

is low efficiency of energy transfer.

• Mixing of water and abrasives limits the minimum jet diameter that can be used

• Abrasives are replaced by ICE• Low MRR compared to

AWJM, however economy and environmental impact is high

• IJM is used in the food, electronic, medical, and space industries where contamination is not permitted

• Abrasive water jet can machine many materials that laser can not. (Reflective material such Al, copper)

• Abrasive jet do not heat your part therefore no thermal distortion or hardening of material

• Much faster than EDM

• Abrasive jet provide much nicer edge finish without heating a part comparing to flame cutting

Comparison With Other Processes

• Gas (air, Ni, Co2, inert gas) supply at 700-850 KPa• Jet velocity 100-350 m/s• Nozzels – WC and Sapphire

AJM System

• For glass-typical MRR are 16 mm3/min• For metals MRR range from 1.6-4.1 mm3/min• For hard ceramics MRR are 50% more than for glass

0 3 6 9 12 15 18 21 24 27 300

3

6

9

12

15

18

21

24

MRR v/s Powder Flow Rate

Powder flow rate, g/min

MRR

, mg/

min

0 5 10 15 20 250

5

10

15

20

25

30

35MRR v/s Abrasive size

10 micron 27 micron 50 micron

Flow rate, g/min

MRR

, mg/

min

Process Characteristics

• Drilling and cutting small sections of glass, ceramics, or hardened metals

• Engraving• De-burring on metals and plastics• Frosting glass• Cutting intricate pattern in hard and brittle materials• Cleaning oxides from metal surfaces• Cleaning and trimming of electronic components• Removing smudges and films from documents and

museum artifacts• Machining of superhard materials• It is typically used to ut,clean, peen, deburr, deflash, and

etch glass, ceramics, or hard metals.

Applications

• Drilling holes, cutting slots, cleaning hardsurfaces, deburring, polishing, and radiusing

• Deburring of cross holes, slots, and threads in small precision parts that require a burr-free finish, such as hydraulic valves, aircraft fuel systems, and medical appliances

• Machining intricate shapes or holes in sensitive, brittle, thin, or difficult-to-machine materials

• Insulation stripping and wire cleaning without affecting the conductor

• Micro-deburring of hypodermic needles• Frosting glass and trimming of circuit boards, hybrid circuit

resistors, capacitors, silicon, and gallium• Removal of films and delicate cleaning of irregular

surfaces because the abrasive stream is able to follow contours

Applications

Advantages

• Best suited for machining brittle and heat-sensitive materials like glass, quartz, sapphire, and ceramics.

• The process is used for machining superalloys and refractory materials.

• It is not reactive with any workpiece material.• No tool changes are required.• Intricate parts of sharp corners can be machined.• The machined materials do not experience hardening.• No initial hole is required for starting the operation as required by wire EDM.

• Material utilization is high.• It can machine thin materials.

Limitations

• The removal rate is slow.• Stray cutting can’t be avoided• The tapering effect may occur especially when drilling

in metals.• The abrasive may get impeded in the work surface• Suitable dust-collecting systems should be provided• Soft materials can’t be machined by the process• Silica dust may be a health hazard• Ordinary shop air should be filtered to remove

moisture and oil

Advanced AWJM

CAD drawing

Computer determines the starting and end points and the sequence

of operations

Material type and tool offset

Modules to optimize the processing

CATIA, AUTOCAD, IGES

Feed rate and performs cutting

• No material restrictions such as electric conductivity, magnetic properties, opaqueness etc. Very suitable for hard and brittle nonmetals such as glass, silicon, tungston and ceramics.

• As the tool is not shaped to conform to the produced feature, it is mainly for cutting or slitting or drilling and not for profiling or surface generation.

• It is however used for polishing and etching. Very low MRR in polishing, i.e., < 0.015 cm3/min.

• An entry hole is required.

Application/Process Capability

Water Jet Machining

Water Jet Machining

The hydraulic pump is powered from a 30- kilowatt (kW) electric motor and supplies oil at pressures as high as 117 bars in order to drive a reciprocating plunger pump termed an intensifier (4 bar to 3800 bar).

MACH-3 Velocity

Water Jet Machining

The accumulator maintains the continuous flow of the high- pressure water and eliminates pressure fluctuations. It relies on the compressibility of water (12 percent at 3800 bar) in order to maintain a uniform discharge pressure and water jet velocity, when the intensifier piston changes its direction.

Processing Parameters

Operating SummaryFluid Type : Water or water with additives

Additive : Glycerin, Polyethylene Oxide or long chain polymer

Pressure : 100 to 1000 MPa

Jet Velocity : 300 to 1000 m/min

Power : Up to 40 Kw

Metal Removal Rate : 0.5 mm3/s for metals and alloys, 20 mm3/s for Elastomers

Nozzle Material : Hardened steel, WC synthetic sapphire

Water Jet Cutting Rates

• It has multidirectional cutting capacity.• No heat is produced.• Cuts can be started at any location without the need for

predrilled holes.• Wetting of the workpiece material is minimal.• There is no deflection to the rest of the workpiece.• The burr produced is minimal.• The tool does not wear and, therefore, does not need

sharpening.• The process is environmentally safe.• Hazardous airborne dust contamination and waste

disposal problems that are common when using other cleaning methods are eliminated.

Advantages

• There is multiple head processing.• Simple fixturing eliminates costly and complicated tooling,

which reduces turnaround time and lowers the cost.• Grinding and polishing are eliminated, reducing

secondary operation costs.• The narrow kerf allows tight nesting when multiple parts

are cut from a single blank.• It is ideal for roughing out material for near net shape.• It is ideal for laser reflective materials such as copper and

aluminum.• It allows for more accurate cutting of soft material.• It cuts through very thick material such as 383 mm in

titanium and 307 mm in Inconel.

Advantages

• Low MRR• Stray cutting• Abrasive particles embedding• Taper on cut geometry

Disadvantages

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