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Standard metal cutting processes: laser cutting vs. plasma 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.

Plasma (arc) cutting was developed in the 1950s for cutting of metals that could not be flame cut, such as stainless steel, aluminum and copper. The plasma arc cutting process uses electrically conductive gas to transfer energy from an electrical power source through a plasma cutting torch to the material being cut. The plasma gases include argon, hydrogen, nitrogen and mixtures, plus air and oxygen.

Normally, a plasma arc cutting system has a power supply, an arc starting circuit, and a torch. The power source and arc starter circuit are connected to the cutting torch through leads and cables that supply proper gas flow, electrical current flow, and high frequency to the torch to start and maintain the process. The arc and the plasma stream are focused by a very narrow nozzle orifice

The temperature of the plasma arc melts the metal and pierces through the workpiece while the high velocity gas flow removes the molten material from the bottom of the cut, or the kerf. In addition to high energy radiation (Ultraviolet and visible) generated by plasma arc cutting, the intense heat of the arc creates substantial quantities of fumes and smoke from vaporizing metal in the kerf..

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

Fundamental process differences

Subject

CO2 laser

Plasma cutting

Method of imparting energy

Light 10.6 µm (far infrared range)

Gas transmitter

Source of energy

Gas laser

DC power supply

How energy is transmitted

Beam guided by mirrors (flying optics); fiber-transmission not
feasible for CO2 laser

Electrically charged gas

How cut material is expelled

Gas jet, plus additional gas expels material

Gas jet

Distance between nozzle and material and maximum permissable tolerance

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

0.010" to 0.02"

Physical machine set-up

Laser source always located inside machine

Working area, shop air and plasma torch

Range of table sizes

8' x 4' to 20' x 6.5'

8' x 4' to 20' x 6.5'

Typical beam output at the workpiece

1500 to 2600 Watts

Not applicable to this process


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Typical process applications and uses

Subject

CO2 laser

Plasma cutting

Typical process uses

Cutting, drilling, engraving, ablation, structuring, welding

Cutting

3D material cutting

Difficult due to rigid beam guidance and the regulation of distance

Not applicable to this process

Materials able to be cut by the process

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

All metals can be cut

Material combinations

Materials with different melting points can barely be cut

Possible materials with different melting points

Sandwich structures with cavities

This is not possible with a CO2 laser

Not possible for this process

Cutting materials with liminted or impaired access

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

Rarely possible due to small distance and the large torch head

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

~0.12" to 0.4"

Common applications for this process

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

Cutting of flat sheet and plate of greater thickness


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Initial investment and average operating costs

Subject

CO2 laser

Plasma cutting

Initial capital investment required

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

$120,000+

Parts that will wear out

Protective glass, gas
nozzles, plus both dust and the particle filters

The cutting nozzles and electrodes

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

300 amp Plasma

Electrical power use:
55kW


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Precision of process

Subject

CO2 laser

Plasma cutting

Minimum size of the cutting slit (kerf width)

0.006", depending on cutting speed

0.002"

Cut surface appearance

Cut surface will show a striated structure

Cut surface will show a striated structure

Degree of cut edges to completely parallel

Good; occasionally will demonstrate conical edges

Fair, will demonstrate non-parallel cut edges with some frequency

Processing tolerance

Approximately 0.002"

Approximately 0.02"

Degree of burring on the cut

Only partial burring occurs

Only partial burring occurs

Thermal stress of material

Deformation, tempering and structural changes may occur in the material

Deformation, tempering and structural changes may occur in the material

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

Gas pressure poses
problems with thin
workpieces, distance
cannot be maintained

Gas pressure poses problems with thin
workpieces, distance cannot be maintained


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Safety considerations and operating environment

Subject

CO2 laser

Plasma cutting

Personal safety
equipment requirements

Laser protection safety glasses are not absolutely necessary

Protective safety glasses

Production of smoke and dust during processing

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

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

Noise pollution and danger

Very low

Medium

Machine cleaning requirements due to process mess

Low clean up

Medium clean up

Cutting waste produced by the process

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

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


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