standard metal cutting processes

7/30/2019 Standard Metal Cutting Processes

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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 manufacturingprocesses compete both technically and economically with conventional and nonconventionalmanufacturing processes such as mechanical and thermal machining, arc welding,electrochemical, and electric discharge machining (EDM), abrasivewater jet cutting, plasmacutting, andflame cutting.

Plasma (arc) cutting was developed in the 1950s for cutting of metals that could not be flamecut, such as stainless steel, aluminum and copper. The plasma arc cutting process useselectrically conductive gas to transfer energy from an electrical power source through a plasmacutting torch to the material being cut. The plasma gases include argon, hydrogen, nitrogen andmixtures, 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 andcables that supply proper gas flow, electrical current flow, and high frequency to the torch tostart and maintain the process. The arc and the plasma stream are focused by a very narrownozzle orifice

The temperature of the plasma arc melts the metal and pierces through the workpiece while thehigh velocity gas flow removes the molten material from the bottom of the cut, or the kerf. Inaddition to high energy radiation (Ultraviolet and visible) generated by plasma arc cutting, theintense 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 processand plasma cutting process in industrial material processing.

Fundamental process differences Typical process applications and uses Initial investment and average operating costs Precision of process Safety considerations and operating environment

Fundamental process differences

Method of impartingenergy

Light 10.6 m (farinfrared range)

Gas transmitter

Source of energy Gas laser DC power supply

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

How cut material isexpelled

Gas jet, plus additionalgas expels material

Gas jet

Distance between nozzleand material andmaximum permissabletolerance

Approximately 0.2" 0.004", distance sensor,regulation and Z-axisnecessary

0.010" to 0.02"

Physical machine set-up Laser source alwayslocated inside machine

Working area, shop airand 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 theworkpiece

1500 to 2600 Watts Not applicable to thisprocess

Typical process applications and uses

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

Cutting

3D material cutting Difficult due to rigid beamguidance and theregulation of distance

Not applicable to thisprocess

Materials able to be cut bythe process

All metals (excludinghighly reflective metals),all plastics, glass, andwood can be cut

All metals can be cut

Material combinations Materials with differentmelting points can barelybe cut

Possible materials withdifferent melting points

Sandwich structures withcavities

This is not possible with aCO2 laser

Not possible for thisprocess

Cutting materials withliminted or impairedaccess

Rarely possible due tosmall distance and thelarge laser cutting head

Rarely possible due tosmall distance and thelarge torch head

Properties of the cut Absorption characteristics Material hardness is a key
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Cut surface appearance Cut surface will show astriated structure

Cut surface will show astriated structure

Degree of cut edges tocompletely parallel

Good; occasionally willdemonstrate conical edges

Fair, will demonstratenon-parallel cut edgeswith some frequency

Processing tolerance Approximately 0.002" Approximately 0.02"

Degree of burring on thecut

Only partial burringoccurs

Only partial burringoccurs

Thermal stress of material Deformation, temperingand structural changesmay occur in the material

Deformation, temperingand structural changesmay occur in the material

Forces acting on materialin direction of gas orwater jet duringprocessing

Gas pressure posesproblems with thinworkpieces, distancecannot be maintained

Gas pressure posesproblems with thinworkpieces, distancecannot be maintained

Safety considerations and operating environment

Personal safetyequipment requirements

Laser protection safetyglasses are not absolutelynecessary

Protective safety glasses

Production of smoke anddust during processing

Does occur; plastics andsome metal alloys mayproduce toxic gases

Does occur; plastics andsome metal alloys mayproduce toxic gases

Noise pollution anddanger

Very low Medium

Machine cleaningrequirements due toprocess mess

Low clean up Medium clean up

Cutting waste produced bythe process Cutting waste is mainly inthe form of dust requiringvacuum extraction andfiltering

Cutting waste is mainly inthe form of dust requiringvacuum extraction andfiltering
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standard metal cutting processes

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