page 413

Application

Precision measurement of length surveying and alignment rangefinding

drilling cutting welding opthamology

pollution detection holography communications

monochromatic

low divergence

single or low order mode

coherence

X X X

XX X

X X

X X

X X

X X X

X X X X X X

high output power

efficiency

Laser normally used

He-Ne

He-Ne

X Nd:YAG, GaAs

X X Ruby, Nd:YAG

X X CO2

XX CO2, ruby, Nd:YAG Ruby, argon ion Dye, GaAs

Ruby, Nd:YAG, Argon ion, He-Ne

He-Ne, GaAs

• Efficiency of lasers is often about 0.1% for gas, but CO2 can be as high as 18%.

64.1.1 References

Harry, J. E., Industrial Lasers and Their Applications, McGraw-Hill, London, 1974.

Hugel, H., Lasers in Manufacturing, Proceedings of the 5th, International Conference, Sept., 1988, Stuttgart, West Germany.

Ready, J. F., Lasers in Modern Industry, Society of Manufacturing Engineers, Dearborn Michigan, 1979.

Soares, O. D. D., and Perez-Amor, M., Applied Laser Tooling, Martinus Nijhoff Publishers, Lancaster UK, 1987.

64.2 LASER CUTTING

• Good for,

page 414

-thin work pieces that would be greatly effected by contact force (e.g. soft or brittle)

-parts that are too complex for saws and other cutters

-materials normally too hard to machine with traditional methods. The laser effects the thermal, not hardness cutting conditions.

•Used for,

-cutting

-welding

-scribing

-drilling

-heat treating

•Results,

-less part deformation

-reduced part grinding and deburring

-lighter fixtures

•Can be used for 2D or 3D workspace.

•The cutters typically have a laser mounted, and the beam is directed to the end of the arm using mirrors.

Mirror

Laser

Lens

Focal Point

•Mirrors are often cooled (water is common) because of high laser powers.

•The light focuses on the surface, and vaporizes it. The basic process is,

1.Unheated material.

2.Heating begins and metal becomes reflective.

page 415

3.Heating continues and reflectivity decreases.

4.A molten zone is established.

5.Material vaporizes, consuming most of the laser energy. Very little energy goes into heating the surrounding material.

6.Outgoing vapor is struck by the laser and further energizes, producing plasma.

•The cuts look like,

laser

s = thickness of material delta s = .15 for s<2mm

.2 mm for s>=2mm

M = measuring range to determine alpha and u

	delta s	w
		R2
		r
	M	u
	s
		alpha
		r
	delta s

R2 = surface roughness

u = rectangular and inclination tolerances alpha = flank angle

r = radius of cutting edge (upper/lower side)

w = kerf width (upper/lower/middle as measured by M)

•Dross is metal that has been collected on the underside of the sheet and protrudes as a burr would.

•Laser cutting is often assisted with a gas,

-oxygen is used to help when cutting metals. This happens because the oxygen initiates the exothermic reactions to increase cutting rates, and it cools surrounding material. The user must be aware that the oxygen reacts with the heated metals and forms an oxide layer on the cutting edge.

•Gas flow tends to “blow” vaporized metal away from the cutting zone, and minimize the beam absorption in the vapor.

page 416

•Slag-collectors and vacuums are used to clear debris and vapors in these systems.

•Cutting speeds are related to material thickness, and laser power.

•Typical laser components are,

-laser tube/laser power supply/controls

-mirrors to direct laser to end of tool

-focusing optics

-nozzle with optics, gas delivery, etc.

-workpiece fixture

-nozzle/fixture positioner

-fume extractors for vapors

-slag collectors

-enclosure

-safety interlock system

•Additional laser cutter components are,

-CNC machine/robot

-diagnostic software/sensors for beam condition

-beam splitter for multiple operations.

operator controls

CNC controls

page 417

power supply

laser

beam transmission

beam forming

focus			gas

positioning		workpiece

suction

•The major design decisions are,

a)Move the workpiece and maintain fixed optics.

b)Move the “flying optics” and keep the workpiece steady. Large parts are easier to deal with when they don’t move, but the changes in the optics system can cause focussing problems.

•Laser speed example

- 5KW laser, 5mm thick carbon steel cut at 1m/min.

page 418

WL = 5KW
		W
RL	= 1000	----------------
		mm3
		min
		----------

V = ( 0.01m) ( 5m) ( 0.01m) = 0.0005m3

Q =

WL

=

5KW

= 5

10

–9

m3

-------RL

min---------

W

1000

----------------

mm3

min

----------

t =

V

=

0.0005m3

= 10

–5

min

---

-----------------------------------

3

Q

5

10

–9 m

min---------

• Some commercial specifications for the Trumpf L5000 are given below,

page 419

Positioning	Work Volume	118 by 78 by 29.5 in.
	Single Pallet Size	59 by 78 in.
	Double Pallet Size	118 b 78 in.
	X Axis Travel	126 in.
	Y Axis Travel	78 in.
	Z Axis Travel	29.5 in.
	B Axis Orientation	±120°
	C Axis Orientation	n(360°) continuous rotation
	Range of Auto Focus	± 0.200 in.
	Traverse Speed	1200 in./min., 180°/sec.
	Resolution	±0.001 in., ±0.01°
	Accuracy	±0.004 in.
	Repeatability	±0.002 in.
Machine Size	Width	284 in.
	Depth	472 in.
	Height	158 in.
	Table Height	28 in.
	Weight	33,000 lbs.
Laser	Laser Type	CO2 Gas
	Performance	750W continuous wave
	Adjustment Range	40-750 W continuous wave
	Beam Mode	TEMoo
	Pulse Frequency	100Hz - 10 KHz
	CO2 Consumption	0.06 ft3/hr.
	He Consumption	0.56 ft3/hr.
	N2 Consumption	0.25 ft3/hr.
	O2 Consumption	53-106 ft3/hr.
Services	Electrical Supply	460V, 60 Hz, 39 KVA
	Pneumatic Supply	0.75 ft3/hr.

•Summary of Laser machining;

-mechanics of material removal - melting, vaporization

-medium - normal atmosphere

-tool - high power laser

-maximum mrr = 5 mm3/min

-specific power consumption 1000W/mm3/min

-critical parameters - beam power intensity, beam diameter, melting temperature

-material application - all materials