10. laser beam weldingdantn/wt/wt1-c10.pdf · 2020. 8. 6. · 10. laser beam welding 129 the term...

2003

10.

Laser Beam Welding

10. Laser Beam Welding 129

The term laser is the abbreviation for

,,Light Amplification by Stimulated

Emission of Radiation”. The laser is

the further development of the maser

(m=microwave), Figure 10.1. Al-

though the principle of the stimulated

emission and the quantum-

mechanical fundamentals have al-

ready been postulated by Einstein in

the beginning of the 20th century, the

first laser - a ruby laser - was not

implemented until 1960 in the Hughes

Research Laboratories. Until then

numerous tests on materials had to

be carried out in order to gain a more

precise knowledge about the atomic

structure. The following years had

been characterised by a fast devel-

opment of the laser technology. Already since the beginning of the Seventies and,

increasingly since the Eighties when the first high-performance lasers were available,

CO2 and solid state lasers have been used for production metal working.

The number of the

annual sales of la-

ser beam sources

has constantly in-

creased in the

course of the last

few years, Figure

10.2.

The application ar-

eas for the laser

beam sources sold

br-er10-01e.cdr

History of the Laser

1917 postulate of stimulated emission by Einstein

1950 physical basics and realisation of a maser (Microwave Amplification by Stimulated Emission of Radiation) by Towens, Prokhorov, Basov

1954 construction of the first maser

1960 construction of the first ruby laser (Light Amplification by Stimulated Emission of Radiation)

1961 manufacturing of the first HeNe lasers and Nd: glass lasers

1962 development of the first semiconductor lasers

1964 nobel price for Towens, Prokhorov and Basov for their works in the field of masers construction of the first Nd:YAG solid state lasers and CO gas lasers

1966 established laser emission on organic dyes

since increased application of CO and solid state laser1970 technologies in industry

1975 first applications of laser beam cutting in sheet fabrication industry

1983 introduction into the market of 1-kW-CO lasers

1984 first applications of laser beam welding in industrial serial production

work out of

2

2

2

Figure 10.1

br-er10-02e.cdr

3

10 €

2

1.5

1

0.5

0

9

Japan and South East AsiaNorth AmericaWest Europe

1986 1988 1990 1992 1994 1996 1998 2000

Figure 10.2


in 1994 are shown in Figure 10.3. The main application areas of the laser in the field

of production metal working are joining and cutting jobs.

The availability of

more efficient laser

beam sources

opens up new ap-

plication possibili-

ties and - guided

by financial con-

siderations - makes

the use of the laser

also more attrac-

tive, Figure 10.4.

Figure 10.5 shows the characteristic properties of the laser beam. By reason of the

induced or stimu-

lated emission the

radiation is coher-

ent and mono-

chromatic. As the

divergence is only

1/10 mrad, long

transmission paths

without significant

beam divergences

are possible.

br-er10-03e.cdr

inscribe20,5%

microelectronics

5,4%

welding18,7%

drilling1,8%

others9,3%

cutting44,3%

Figure 10.3

br-er10-04e.cdr

lase

r po

wer

CO2

Nd:YAG

diode laser0

1

2

3

4

5

10

20

kW

40

1970

1975

1980

1985

1995

1990

2000

Figure 10.4


Inside the resonator, Figure 10.6, the laser-active medium (gas molecules, ions) is

excited to a higher energy level (“pumping”) by energy input (electrical gas dis-

charge, flash lamps).

During retreat to a lower level, the energy is released in the form of a light quantum

(photon). The wave length depends on the energy difference between both excited

states and is thus a characteristic for the respective laser-active medium.

A distinction is made between spontaneous and induced transition. While the spon-

taneous emission is non-directional and in coherent (e.g. in fluorescent tubes) is a

laser beam gener-

ated by induced

emission when a

particle with a

higher energy level

is hit by a photon.

The resulting pho-

ton has the same

properties (fre-

quency, direction,

phase) as the excit-

ing photon (“coher-

ence”). In order to

maintain the ratio of

the desired induced

emission I sponta-

neous emission as

high as possible,

the upper energy

level must be con-

stantly over-

crowded, in com-

parison with the

lower one, the so-

called “laser-

© ISF 2002br-er10-05e.cdr

Characteristics of Laser Beams

light bulb Laser

E2

E1 exitedstate

groundstate

polychromatic

incoherent

large divergence

(multiple wave length)

(not in phase)

0,46"

0,94"

monochromatic

coherent

small divergence

(in phase)

induced emission

Figure 10.5


Laser Principle

energy source

energy source

resonator

fully reflecting mirror

R = 100%

partially reflectingmirrorR < 100%

las

er b

ea

m

active laser medium

Figure 10.6


inversion”. As result, a stationary light wave is formed between the mirrors of the

resonator (one of which is semi-reflecting) causing parts of the excited laser-active

medium to emit light.

In the field of production metal working, and particularly in welding, especially CO2

and Nd:YAG lasers are applied for their high power outputs. At present, the devel-

opment of diode lasers is so far advanced that their sporadic use in the field of mate-

rial processing is also possible. The industrial standard powers for CO2 lasers are,

nowadays, approximately 5 - 20 kW, lasers with powers of up to 40 kW are available.

In the field of solid state lasers average output powers of up to 4 kW are nowadays

obtainable.

In the case of the

CO2 laser, Figure

10.7, where the

resonator is filled

with a N2-C02-He

gas mixture, pump-

ing is carried out

over the vibrational

excitation of nitro-

gen molecules

which again, with

thrusts of the sec-

ond type, transfer

their vibrational

energy to the car-

bon dioxide. During

the transition to the

lower energy level,

CO2 molecules

emit a radiation

with a wavelength

of 10.6 µm. The

helium atoms, fi-


Energy Diagram of CO Laser2

0,6

eV

0,4

0,3

0,2

0,1

0

ener

gy

0,288 eV

2

1 001 0,290 eV

100

002

LASER = 10,6 µmλ

transmission ofvibration energy

thrust of second type

thrust of first type

∆E = 0,002 eV

transition withoutemission

discharge through thrust with helium

N2 CO2

0000

Figure 10.7

br-er10-08e.cdr

radio frequency high voltage exitaion

laser beam

cooling water cooling water

laser gas

gas circulation pump

vakuum pumplaser gas:CO : 5 l/hHe: 100 l/hN : 45 l/h

2

2

Figure 10.8


nally, lead the CO2

molecules back to

their energy level.

The efficiency of up

to 15%, which is

achievable with

CO2 high perform-

ance lasers, is, in

comparison with

other laser sys-

tems, relatively

high. The high dis-

sipation component

is the heat which must be discharged from the resonator. This is achieved by means

of the constant gas mixture circulation and cooling by heat exchangers. In

dependence of the type of gas transport, laser systems are classified into longitudi-

nal-flow and transverse-flow laser systems, Figures 10.8 and 10.9.

With transverse-flow laser systems of a compact design can the multiple folding

ability of the beam reach higher output powers than those achievable with longitudi-

nal-flow systems, the beam quality, however, is worse. In d.c.-excited systems

(high voltage), the

electrodes are po-

sitioned inside the

resonator. The in-

teraction between

the electrode mate-

rial and the gas

molecules causes

electrode burn-off.

In addition to the

wear of the elec-

trodes, the burn-off

br-er10-09e.cdr

Cooling water

cooling water

laser gas:CO : 11 l/hHe: 142 l/hN : 130 l/h

2

2

laser gasend mirror

turningmirrors

gas circulationpump

mirror(partially reflecting)

gas discharge

laser beam

Figure 10.9


Laser Beam Qualitiy

0<K<1

with d d. d. =c.σ σ 0. 0 F FΘ = Θ = Θ

ΘF

d0

unfocussed beam focussed beam

f2,57"

dF

K = .2 1 λπ dσ σΘ

Figure 10.10


also entails a contamination of the laser gas. Parts of the gas mixture must be there-

fore exchanged permanently. In high-frequency a.c.-excited systems the electrodes

are positioned outside the gas discharge tube where the electrical energy is

capacitively coupled. High electrode lives and high achievable pulse frequencies

characterise this

kind of excitation

principle. In diffu-

sion-cooled CO2

systems beams of

a high quality are

generated in a

minimum of space.

Moreover, gas ex-

change is hardly

ever necessary.

The intensity distribution is not constant across the laser beam. The intensity distribu-

tion in the case of the ideal beam is described by TEM modes (transversal elec-

tronic-magnetic). In the Gaussian or basic mode TEM00 is the peak energy in the

centre of the beam weakening towards its periphery, similar to the Gaussian normal

distribution. In practice, the quality of a laser beam is, in accordance with DIN EN

11146, distinguished

by the non-

dimensional beam

quality factor (or

propagation factor)

K (0...1), Figure

10.10. The factor

describes the ratio of

the distance field

divergence of a

beam in the basic

mode to that of a

br-er10-11e.cdr

resonator

LASER

work piece manipulator

absorber

partiallyreflecting

mirror

shutter

work piece

endmirror

beam creationfocussing system

beam divergence mirror

beam transmissiontube

Figure 10.11

Figure 10.12

© ISF 2002br-er10-12e_f.cdr

CO Laser Beam Welding Station2


real beam and is

therefore a meas-

ure of a beam fo-

cus strength. By

means of the beam

quality factor, dif-

ferent beam

sources may be

compared objec-

tively and quanti-

taively.

The CO2 laser beam is guided from the resonator over a beam reflection mirror sys-

tem to one or several processing stations, Figures 10.11 and 10.12. The low diver-

gence allows long transmission paths. At the processing station is the beam, with the

help of the focussing optics, formed according to the working task. The relative mo-

tion between beam and workpiece may be realised in different ways:

- moving workpiece, fixed optics

- moving (“flying”) optics

- moving workpiece and moving optics (two handling facilities).

In the case of the

CO2 laser, beam

focussing is normally

carried out with mir-

ror optics, Figure

10.13. Lenses may

heat up, due to ab-

sorption, especially

with high powers or

contaminations. As

the heat may be dis-


Focussing Optics

reflective90°-mirror optic

α

Figure 10.13


Principle Layout of Solid State Laser

laser rod

laser beam

partially reflectingmirror (R < 100%)

flash lamps

end mirror (r = 100%)

Figure 10.14


sipated only over the holders, there is a risk of deformation (alteration of the focal

length) or destruction through thermal overloading.

In the case of solid state laser, the normally cylindrical rod serves only the purpose

to pick up the laser-active ions (in the case of the Nd:YAG laser with yttrium-

aluminium-garnet crystals dosed with Nd3+ ions), Figure 10.14. The excitation is, for

the most part, carried out using flash or arc lamps, which for the optimal utilisation of

the excitation energy are arranged as a double ellipsoid; the rod is positioned in their

common focal point. The achieved efficiency is below 4%. In the meantime, also di-

ode-pumped solid

state lasers have

been introduced to

the market. The

possibility to guide

the solid-state laser

beam over flexible

fibre optics makes

these systems des-

tined for the robot

application,

whereas the CO2

laser application is

restricted, as its

necessary complex

mirror systems may

cause radiation

losses, Figure

10.15.

Some types of opti-

cal fibres allow, with

fibre diameters of ≤

1 mm bending radii

of up to 100 mm.

With optical

© ISF 2002

Nd:YAG Laser Beam Welding Station

br-er10-15e_f.cdr

Figure 10.15

© ISF 2002br-er10-16e_f.cdr

Diode Laser

Figure 10.16


switches a multiple utilisation of the solid state laser source is possible; with beam

splitters (mostly

with a fixed splitting

proportion) simulta-

neous welding at

several processing

stations is possible.

The disadvantage

of this type of beam

projection is the

impaired beam

quality on account

of multiple reflec-

tion.

The semiconductor or diode lasers are characterised by their mechanical robust-

ness, high efficiency and compact design, Figure 10.16. High performance diode la-

sers allow the welding of metals, although no deep penetration effect is achieved. In

material processing they are therefore particularly suitable for welding thin sheets.

Energy input into the workpiece is carried out over the absorption of the laser

beam. The absorption coefficient is, apart from the surface quality, also dependent

on the wave length

and the material.

The problem is that

a large part of the

radiation is re-

flected and that, for

example, steel

which is exposed

to wave lengths of

10.6 µm reflects

only 10% of the

impinging radia-

br-er10-17e.cdr

abso

rptio

n A

0,30

0,25

0,20

0,15

0,10

0,05

0

wave lenght λ0,1 0,2 0,3 0,5 0,8 1 2 4 5 8 10 µm 20

AlCu

Ag

Mo

Fe

Stahl

Nd:YAG-laser

CO -laser

2

Figure 10.17

Figure 10.18

br-er10-18e.cdr

10 10 10 10 s 10-8 -6 -4 -2 0

10

W/cm

10

10

10

10

10

10

10

2

8

7

6

5

4

3

po

wer

den

sity

acting time

energy density [J/cm²]

drilling102

100

104

106

remeltingcoating

glaze

shock hardening

weldingcutting

martensitic hardening


tion, Figure 10.17. As copper is a highly reflective metal with also a good heat con-

ductivity, it is frequently used as mirror material.

Intensity adjust-

ment at the work-

ing surface by the

focal position with

a simultaneous

variation of the

working speed

make the laser a

flexible and con-

tactless tool, Fig-

ure 10.18. The

methods of welding

and cutting de-

mand high intensi-

ties in the focal point, which means the

distance between focussing optics and

workpiece surface must be maintained

within close tolerances. At the same

time, highest accuracy and quality

demands are set on all machine com-

ponents (handling, optics, resonator,

beam manipulation, etc.).

Steel materials with treated surfaces

reflect the laser beam to a degree of

up to 95%, Figures 10.19 - 10.22.

When metals are welded with a low-

intensity laser beam (I ≤ 105 W/cm2),

just the workpiece surfaces and/or

edges are melted and thus thermal-


Principle of Laser Beam Welding

heat conductingwelding

deep penetrationwelding

laser beam

molten poolsoldifiedweld metal

laser beam

keyhole(vapour-/plasma cavity)

metal vapourblowing away

laser-inducedplasma

molten pool

soldifiedweld metal

Figure 10.19


Reflection and Penetration Depthin Dependence on Intensity

10 10 W/cm 105 6 2 7

laser intesity I

pen

etra

tion

dep

th t

refl

ecti

on

R

100

%

60

40

20

0

4

mm

2

1

0

Figure 10.20


conduction welding with a low deep-

penetration effect is possible. Above

the threshold intensity value (I ≤ 106

W/cm2) a phase transition occurs and

laser-induced plasma develops. The

plasma, whose absorption character-

istics depend on the beam intensity

and the vapour density, absorbs an

increased quantity of radiation.

A vapour cavity forms and allows the

laser beam to penetrate deep into the

material (energy input deep beyond

the workpiece surface); this effect is

called the “deep penetration effect”.

The cavity which is moved though the

joining zone and is prevented to close

due to the vapour pressure is sur-

rounded by the largest part of the mol-

ten metal. The residual material vaporises and condenses either on the cavity side

walls or flows off in an ionised form. With suitable parameter selection, an almost

complete energy input into the workpiece can be obtained.

However, in de-

pendence of the

electron density in

the plasma and of

the radiated beam

intensity, plasma

may detach from

the workpiece sur-

face and screen off

the working zone.

The plasma is

heated to such a


Calculated Intensity Threshold forProducing a Laser-Induced Plasma

10 10 10 s 10-10 -8 -6 -2

lase

r in

ten

sity

I

radiation time t

10

W/cm

10

10

10

10

10

2

8

7

6

5

steel

r = 100 µm = 10.6 µm

F

λ

A = 0,1

A = 1

working zone

plasma threshold

plasma shielding

Figure 10.21


Interaction Between Laser Beam and Material

Transformation of electromagnetic energy into thermal energywithin nm range at the surface of the work piece by

stimulation of atoms to resonant oscillations

"normal" absorption: "abormal" absorption:

−

−−−−

−−

depandent on laser beam intensity: I < 10 W/cm²

dependent on wave length

dependent on temperature

dependent on material

absorption at solid or liquid surface: A < 30%

formation of a molten bath with low

penetration depth

6 −

−

−

−

dependent on laser intesity: I 10 W/cm²

heating up to temperature of evaporation and formation of a metal

vapour plasmaalmost complete energy entry through absorption by plasma: A > 90%formation of a vapour cavity

≥ 6

heat conducting welding deep penetration welding

Figure 10.22


high degree that only a fraction of the beam radiation reaches the workpiece. This is

the reason why, in laser beam welding, gases are applied for plasma control. The

gases’ ionisation potential should be as high as possible, since also the formation of

“shielding gas plasmas” is possible

which again decreases the energy in-

put.

Only a part of the beam energy from

the resonator is used up for the actual

welding process, Figure 10.23. Another

part is absorbed by the optics in the

beam manipulation system, another

part is lost by reflection or transmission

(beam penetration through the vapour

cavity). Other parts flow over thermal

conductance into the workpiece.

Figure 10.24 shows the most important

advantages and disadvantages of the

laser beam welding method.

Penetration

depths in depend-

ence of the beam

power and welding

speed which are

achievable in laser

beam welding are

depicted in Figure

10.25. Further rele-

vant influential

factors are, among

others, the material

br-er10-23e.cdr

Scheme of Energy Flow

beam energy

diagnostics

beam transmissionfocussing system

reflection

transmission

heat convectionheat conductionmetal vapourplasma

recombination

work piece

fusion energy

0-2,5%

2,5-12,5%

ca. 5%

ca. 10%

ca. 40%

85-95%

10-15%ca. 30%

Figure 10.23


Advantages and Disadvantagesof Laser Beam Welding

advantages disadvantages

process

work piece

installation

- high power density- small beam diameter- high welding speed- non-contact tool- welding possibleatmosphere

- high reflection at metallic surfaces- restricted penetration depth ( 25 mm)

- minimum thermal stress- little distortion- completely processed components- welding at positions difficult to access- different materials weldable

- expensive edge preparation- exact positioning required- danger of increased hardness- danger of cracks- Al, Cu difficult to weld

- expensive beam transmission and forming- power losses at optical devices- laser radiation protection required- high investment cost- low efficency (CO -Laser: < 20%, Nd:YAG: < 5%)2

- short cycle times- operation at several stations possible- installation availability > 90%- well suitable to automatic function

Figure 10.24


(thermal conductivity), the design of

the resonator (beam quality), the

focal position and the applied optics

(focal length; focus diameter).

Figure 10.26 shows several joint

shapes which are typical for car body

production and which can be welded

by laser beam application.

The high cooling rate during laser beam welding leads, when transforming steel

materials are used, to significantly increased hardness values in comparison with

other welding

methods, Figure

10.27. These are a

sign for the in-

creased strength at

a lower toughness

and they are par-

ticularly critical in

circumstances of

dynamic loads.

br-er10-25e.cdr

Penetration Depths

pene

trat

ion

dept

hpe

netr

atio

n de

pth

welding speed

welding speed

28

mm

20

16

12

8

4

0

15

mm

5

0

0 0,6 1,2 1,8 m/min 3,0

0 1 2 3 4 5 6 7 m/min 9

laser power:

0,2% C-steelCO -laser2

(cross flow)

X 5 CrNi 18 10CO -laser2

(axial flow)

laser power:

15 kW

8 kW

1,5 kW

6 kW4 kW

6 kW4 kW2 kW1 kW

10 kW

Figure 10.25

br-er10-26e.cdr

butt weld

lap weld at overlap joint

fillet weld at overlap joint

flanged weld at overlap joint

Figure 10.26


The small beam diameter demands the very precise manipulation and positioning of

the workpiece or of

the beam and an

exact weld prepa-

ration, Figure

10.28. Otherwise,

as result, lack of

fusion, sagged

welds or concave

root surfaces are

possible weld de-

fects.

Caused by the high cooling rate and, in connection with this, the insufficient de-

gassing of the molten metal, pore formation may occur during laser beam welding

of, in particular, thick plates (very deep welds) or while carrying out welding-in works

(insufficient degassing over the root), Figure 10.29.

However, too low a weld speed may also cause pore formation when the molten

metal picks up gases from the root side.

The materials that

may be welded

with the laser reach

from unalloyed and

low-alloy steels up

to high quality tita-

nium and nickel

based alloys. The

high carbon con-

tent of the trans-

forming steel mate-

rials is, due to the

br-er10-27e_f.cdr

laser beam weld

submerged arc weld

hard

ness

distance from the weld centre

weld submerged arc weld

MAZ

MAZ MAZ

MAZWMA

0 12

500HV 0,4

Figure 10.27


Welding Defects

edge preparation misalignment

gap mispositioning

(e 0,1 x plate thickness)≤

(a 0,1 x plate thickness)≤

beam

Figure 10.28


high cooling rate, to be considered a critical influential factor where contents of C >

0.22% may be stipulated as the limiting reference value. Aluminium and copper

properties cause problems during energy input and process stability. Highly reactive

materials demand, also during laser beam welding, sufficient gas shielding beyond

the solidification of the weld seam. The sole application of working gases is, as a

rule, not adequate.

The application of laser beam welding may be extended by process variants. One is

laser beam welding with filler wire, Figures 10.30 and 10.31 which offers the following

advantages:

- influence on the mechanic-technological properties of the weld and fusion zone

(e.g. strength, toughness, corrosion, wear resistance) over the metallurgical composi-

tion of the filler wire

- reduction of the demands on the accuracy of the weld preparation in regard to edge

misalignment, edge preparation and beam misalignment, due to larger molten pools

- “filling” of non-ideal, for example, V-shaped groove geometries

- a realisation of a defined weld reinforcement on the beam entry and beam exit side.


Porosity

v = 0,7 m/minw v = 0,9 m/minw v = 1,5 m/minw

material: P460N (StE460), s = 20 mm, P = 15 kw

Figure 10.29


The exact positioning of the filler wire is a prerequisite for a high weld quality and a

sufficient dilution of the molten pool through which filler wire of different composition

as the base can reach right to the root. Therefore, the use of sensor systems is indis-

pensable for industrial application, Figure 10.32. The sensor systems are to take over

the tasks of

- process control,

- weld quality as surance

- beam positioning and joint tracking, respectively.

br-er10-30e.cdr

backward wire feedingforward wire feeding

welding direction

filler wire filler wirelaser beam laser beam

gas gas

plasma plasma

work piece work pieceweld metal weld metal

molten pool molten poolkeyhole keyhole

Figure 10.30

br-er10-31e.cdr

without filler wire with filler wire

filler wire: Sg2d = 0,8 mmw

gap: 0 mmv = 1,6 m/minw

gap: 0,5 mmwire: SG-Ni Cr21 Fe18 Mo

v = 1,0 m/mind = 1,2 mm

w

w

weld zoneweld zone

increase of gapbridging ability

material: gap:

S380N (StE 380)0,5 mm

P = 8,3 kWV = 3 m/minE = 166 J/mins = 4 mm

L

W

S

Possibility ofmetallurgical influence

material combination:10CrMo9-10/ X6CrNiTi18-10P = 5,0 kWL

Figure 10.31


The present state-of-the-art is the further development of systems for industrial appli-

cations which until now have been tested in the laboratory.

Welding by means of solid state lasers has, in the past, mainly been applied by

manufacturers from the fields of precision mechanics and microelectronics. Ever

since solid state lasers with higher powers are available on the market, they are ap-

plied in the car industry to an ever increasing degree. This is due to their more vari-

able beam manipulation possibilities when comparing with CO2 lasers. The CO2 laser

is mostly used by

the car industry and

by their ancillary

industry for welding

rotation-

symmetrical mass-

produced parts or

sheets. Figure

10.33 shows some

typical application

examples for laser

beam welding.

br-er10-32e.cdr

0.1 mm 0.2 mm 0.3 mm 0.4 mm 0.5 mm 0.6 mm

with sensing device; fill factor 120 %

without sensing device; wire speed v = 4 m/min constantD

KB 4620/1220:1

10/92

Probe OS1-6A

KB 4621/720:1

10/92

Probe OS1-1B

KB 4621/1520:1

10/92

Probe OS1-4C

KB 4620/1720:110/92

Probe OS1-5C

KB 4621/920:1

10/92

Probe OS1-2B

KB 4621/1220:1

10/92

Probe OS1-3B

KB 4620/920:1

10/92

Probe MS1-6C

KB 4620/620:1

10/92

Probe MS1-5A

KB 4620/3820:1

10/92

Probe MS1-1C

KB 4620/420:110/92

Probe MS1-4C

KB 4620/020:110/92

Probe MS1-3A

KB 4620/4120:110/92

Probe MS1-2B

1 mm

Figure 10.32

Practical Application Fields


plant and apparatus engineering- seal welds at housings- measurement probes

aerospace industry

- engine components- instrument cases

automotive industry- gear parts - body-making

- engine components

(cog-wheels, planet gears)

(bottom plates, skins)

(tappet housings, diesel engine precombustion chambers)

medical industry

- heart pacemaker cases- artificial hip joints

electronic industry

- PCBs- accumulator cases- transformer plates- CRTs

steel industry

- pipe production- vehicle superstructures- continuous metal strips- tins

Figure 10.33

10. laser beam weldingdantn/wt/wt1-c10.pdf · 2020. 8. 6. · 10. laser beam welding 129 the term...

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