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Standard metal cutting processes: laser cutting vs. water jet cutting

Laser 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.

The table that follows contains a comparison of metal cutting using the CO2 laser cutting process and water jet cutting process in industrial material processing.

Fundamental process differences

Subject

CO2 laser

Water jet cutting

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 not
feasible 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)


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Typical process applications and uses

Subject

CO2 laser

Water jet cutting

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


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Initial investment and average operating costs

Subject

CO2 laser

Water jet cutting

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, gas
nozzles, 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


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Precision of process

Subject

CO2 laser

Water jet cutting

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 poses
problems with thin
workpieces, distance
cannot be maintained

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


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Safety considerations and operating environment

Subject

CO2 laser

Water jet cutting

Personal safety
equipment 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


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