Unconventional Machining Process

UNCONVENTIONAL MACHINING PROCESS

ABRASIVE WATER JET MACHINING. . .

A Brief Study..

Abrasive water jet (AWJ) machined surfaces exhibit the texture typical of machining with high energy density beam processing technologies. It has a superior surface quality in the upper region and rough surface in the lower zone with pronounced texture marks called striations. The nature of the mechanisms involved in the domain of AWJ machining is still not well understood but is essential for AWJ control improvement. In this paper, the development of an AWJ machining simulation is reported on. It is based on an AWJ process unit event, which in this case represents the impact of a particular abrasive grain. The geometrical characteristics of the unit event are measured on a physical model of the AWJ process. The measured dependences and the proposed model relations are then implemented in the AWJ machining process simulation. The obtained results are in good agreement in the engraving regime of AWJ machining.

An Abrasive water jet cutter is a tool capable of slicing into metal or other materials using a jet of mixture of water and an abrasive substance.

The process is essentially the same as water erosion found in nature but accelerated and concentrated by orders of magnitude.

It is often used during fabrication or manufacture of parts for machinery and other devices. It has found applications in a diverse number of industries from mining to aerospace where it is used for operations such as cutting, shaping, carving, and reaming.

History

In the 1950s, forestry engineer Dr. Norman Franz experimented with an early form of water jet cutter to cut lumber. However, the technology did not advance notably

until the 1970s when Dr. Mohamed Hashish created a technique to add abrasives to the water jet cutter.[1]

Today the water jet is unparalleled in many aspects of cutting and has changed the way many products are manufactured. Many types of water jets exist today,

including plain water jets, abrasive water jets, percussive water jets, cavitation jets and hybrid jets.

•The cutter is commonly connected to a high-pressure water pump (a local water main does not supply sufficient pressure) where the water is then ejected from the nozzle, cutting through the material by spraying it with the jet of high-speed water.

•Additives in the form of suspended grit or other abrasives, such as garnet and aluminum oxide, can assist in this process. Because the nature of the cutting stream can be easily modified, water jets can be used to cut diverse materials, from prepared foods to metals.

•There are few materials that cannot be effectively cut with a water jet cutter; one of these is tempered glass, which shatters when cut, regardless of the cutting technology used. Certain ceramics are also resistant to water jet cutting.

•Water jet cuts are not typically limited by the thickness of the material, and are capable of cutting materials over twelve inches (30 cm) thick. The penetrating power of these tools has led to the exploration of their use as anti-tank weapons but, due to their short range and the advent of composite armor, research was discontinued.

•Water jet cutters are also capable of producing rather intricate cuts in material. The kerf, or width, of the cut can be changed by changing parts in the nozzle, as well as the type and size of abrasive.

•Typical abrasive cuts are made with a kerf in the range of 0.04" to 0.05" (1.016 to 1.27 mm), but can be as narrow as 0.02" (0.508 mm).

•Non-abrasive cuts are normally 0.007" to 0.013" (0.178 to 0.33 mm), but can be as small as 0.003" (0.076 mm), which is approximately the size of a human hair.

•These small cutters can make very small detail possible in a wide range of applications.

Benefits

An important benefit of the water jet cutter is the ability to cut material without interfering with the material's

inherent structure as there is no "heat-affected zone" or HAZ. Minimizing the effects of heat allows metals to be

cut without harming or changing intrinsic properties.

Availability

•Commercial water jet cutting systems are available from manufacturers all over the world,

in a range of sizes, and with water pumps capable of a range of pressures.

•Typical water jet cutting machines have a working envelope as small as a few square feet,

or up to hundreds of square feet. Ultra-high pressure water pumps are available from as low as 40,000 psi (276 MPa) up to 87,000 psi (600

MPa)

Latest news about Water Jet System..

GOLDSBORO, N.C., Dec. 29/PRNewswire/ --

Jet Edge, Inc., is pleased to announce that Reuel Inc. of Goldsboro, N.C., has installed Jet Edge's latest ultra-high pressure waterjet cutting system,

the Jet Edge Mid Rail Gantry. With its new waterjet system, Reuel is now capable of cutting complex

parts from virtually any material with water that has been pressurized to 60,000 psi. and mixed with an

abrasive.

Then How about comparing Abrasive Water Jet Machining

with Laser Cutting….

Standard metal cutting processes:

laser cutting vs. water jet cuttingLaser manufacturing activities currently include cutting, welding,

heat treating, cladding, vapor deposition, engraving, scribing, trimming, annealing, and shock hardening. Laser manufacturing

processes compete both technically and economically with conventional and nonconventional manufacturing processes such

as mechanical and thermal machining, arc welding, electrochemical, and electric discharge machining (EDM), abrasive water jet cutting,

plasma cutting, and flame cutting.Water jet cutting is a process used to cut materials using a jet of pressurized water as high 60,000 pounds per square inch (psi).

Often, the water is mixed with an abrasive like garnet that enables more materials to be cut cleanly to close tolerances, squarely and

with a good edge finish. Water jets are capable of cutting many industrial materials including stainless steel, Inconel, titanium, aluminium, tool steel, ceramics, granite, and armor plate. This

process generates significant noise.

Fundamental process differences

Method of imparting energy Light 10.6 µm (far infrared range)

Water

Source of energy Gas laser High-pressure pump

How energy is transmitted Beam guided by mirrors (flying optics); fiber-transmission notfeasible for CO2 laser

Rigid high-pressure hoses transmit the energy

How cut material is expelled Gas jet, plus additional gas expels material

A high-pressure water jet expels waste material

Distance between nozzle and material and maximum permissable tolerance

Approximately 0.2" ± 0.004", distance sensor, regulation and Z-axis necessary

Approximately 0.12" ± 0.04", distance sensor, regulation and Z-axis necessary

Physical machine set-up Laser source always located inside machine

The working area and pump can be located separately

Range of table sizes 8' x 4' to 20' x 6.5' 8' x 4' to 13' x 6.5'

Typical beam output at the workpiece

1500 to 2600 Watts 4 to 17 kilowatts (4000 bar)

Typical process applications and uses

Typical process uses Cutting, drilling, engraving, ablation, structuring, welding

Cutting, ablation, structuring

3D material cutting Difficult due to rigid beam guidance and the regulation of distance

Partially possible since residual energy behind the workpiece is destroyed

Materials able to be cut by the process

All metals (excluding highly reflective metals), all plastics, glass, and wood can be cut

All materials can be cut by this process

Material combinations Materials with different melting points can barely be cut

Possible, but there is a danger of delamination

Sandwich structures with cavities This is not possible with a CO2 laser Limited ability

Cutting materials with liminted or impaired access

Rarely possible due to small distance and the large laser cutting head

Limited due to the small distance between the nozzle and the material

Properties of the cut material which influence processing

Absorption characteristics of material at 10.6 µm

Material hardness is a key factor

Material thickness at which cutting or processing is economical

~0.12" to 0.4" depending on material ~0.4" to 2.0"

Common applications for this process

Cutting of flat sheet steel of medium thickness for sheet metal processing

Cutting of stone, ceramics, and metals of greater thickness

Initial investment and average operating costs

Initial capital investment required

$300,000 with a 20 kW pump, and a 6.5' x 4' table

$300,000+

Parts that will wear out Protective glass, gasnozzles, plus both dust and the particle filters

Water jet nozzle, focusing nozzle, and all high-pressure components such as valves, hoses, and seals

Average energy consumption of complete cutting system

Assume a 1500 Watt CO2

laser:

Electrical power use: 24-40 kW

Laser gas (CO2, N2, He):

2-16 l/h

Cutting gas (O2, N2):

500-2000 l/h

Assume a 20 kW pump:

Electrical power use: 22-35 kW

Water: 10 l/h

Abrasive: 36 kg/h

Disposal of cutting waste

Precision of process

Minimum size of the cutting slit 0.006", depending on cutting speed

0.02"

Cut surface appearance Cut surface will show a striated structure

The cut surface will appear to have been sand-blasted, depending on the cutting speed

Degree of cut edges to completely parallel

Good; occasionally will demonstrate conical edges

Good; there is a "tailed" effect in curves in the case of thicker materials

Processing tolerance Approximately 0.002" Approximately 0.008"

Degree of burring on the cut Only partial burring occurs No burring occurs

Thermal stress of material Deformation, tempering and structural changes may occur in the material

No thermal stress occurs

Forces acting on material in direction of gas or water jet during processing

Gas pressure posesproblems with thinworkpieces, distancecannot be maintained

High: thin, small parts can thus only be processed to limited degree

Safety considerations and operating environment

Personal safetyequipment requirements

Laser protection safety glasses are not absolutely necessary

Protective safety glasses, ear protection, and protection against contact with high pressure water jet are needed

Production of smoke and dust during processing

Does occur; plastics and some metal alloys may produce toxic gases

Not applicable for water jet cutting

Noise pollution and danger Very low Unusually high

Machine cleaning requirements due to process mess

Low clean up High clean up

Cutting waste produced by the process

Cutting waste is mainly in the form of dust requiring vacuum extraction and filtering

Large quantities of cutting waste occur due to mixing water with abrasives