10355 r of in Fine Welding With Laser

8/10/2019 10355 r of in Fine Welding With Laser

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Fine Welding with Lasers

Michael Mller


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Lasers and Systems

Welding principle

Weld types and tolerances

Material selection

Influencing factors / Advanced process approaches

ISO Standards

!a"le of contents

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Notation according EN ISO 1145 : 1994

Laser source

Laser

Supply cabinet(power,cooling)

Work piece

Handling system(positioning, movement,clamping, gas supply)

Beam formingBeam guiding system

Process gas supply

Laser Working Station

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Fi( Optics

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Advantages

fast positioning

fle(i"le in terms of part

geometry

easy to use software

Suita"le for fi"er and direct

"eam delivery

)ision system through the lense

'alvo head

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*

Laser material interaction

AbsorptionIn a thin surface layer +optical penetration depth depends on

material , -. nm0

Generation o heat1y transition of the energy of the light +photons0 to the

electrons of the material within the optical penetration depth

Heat transport1y heat conduction from the optical penetration depth into

"ul2 material +temperature gradient0

t

t.

Laser "eam

Laser "eam

!aterials reactionSolid state3, li4uid state3, vapour phase processes

+e5 g5 recristallisation, anealing, hardening, melting,5550

depending on power density and interaction time

*

Laser As a !hermal !ool

Laser beam

Laser beam

Isotherme


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The absorbtivity of materials at room temperature and perpendicular incidence angle

of low intensity laser radiation is strongly depending on the wave length

St

Fe

Mo

Cu

Au

AgAl

30

25

20

15

10

5

Absorption

Abso

rptionin%

Wave length in m

0.1 0.2 0.4 0.8 1 2 4 6 8 10 20

Nd:YAG1,06 m

CO2

10,6 m

Laser 1eam A"sorption

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Heat cond"ction weldingThe material is heated above meltingtemperature but there is no vaporization.

aspect ratio appro(5 .

ma(5 penetration appro(5 56 mm )ery smooth surface

#rocess types conduction welding

.0 Molten material70 Weld depth

.0

80

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Applications#

Welding of thin wor2pieces, cosmetic welding

of enclosures


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$eep % &eyhole weldingHeating of the material above vaporization

temperature and formation of a keyhole

aspect ratio appro(5 99 .

:eyhole diameter appro(5 spot

diameter

;w% ma(5 penetration depending on

laser power

#w% ma( penetration appro(5 < mm

.0 #lasma cloud

70 Molten material


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=(ample%

Spot diameter 58 mm, #ower 7 W 39 I > .5? ( .@ W/cm

Spot diameter 57 mm, #ower 7 W 39 I > ?5< ( .6 W/cm

#ower density BW/cmC

DepthBmmC

;onduction

mode

:eyhole

mode

;riticalintensity

power

.6 .? .@ .E

#lasma

shielding

#O;=SS !=S


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=

! > ./

#A)

##:

##uls

Power P

'ime t

.5 #ea2 power ##:75 #ulse power ##uls ##ulsG

#A) > = G =nergy too high

=nergy too low

##ulse

process threshold

Spot welding

Laser #arameters 3 pulsed

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1) Increase of peak power (W)

2) Increase of pulse duration (ms)

3) Increase of spot size (mm)

1000 W-2 ms-Focus 0,4 mm 2000 W-2 ms-Fokus 0,4 mm 3000 W-2 ms-Fokus 0,4 mm

1000 W-2ms-Fokus 0,4 mm 1000 W-10ms-Fokus 0,4 mm 1000 W-50 ms-Fokus 0,4 mm

1000 W-2 ms-Fokus 0,4 mm 1000 W-2 ms-Fokus 0,8 mm 1000 W-2 ms-Fokus 1,2 mm

=ffect of #arameter ;hanges #ulsed Laser

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(1))* overlap+)*

!he overlap indicates which

percentage of a pulse is covered "y

the following pulse5

From overlap, spot diameter and

velocity the necessary fre4uency can

"e calculated5

!he overlap in pulsed laserwelding is usually in the range of 6 to * H5

!o achieve good strentgh a little more than 6 H are sufficient5 If hermetic

sealing is re4uiered the overlap needs to "e @6 H or more5

;ross section

70 % 50 %

#ulsed Welding 3 Overlap

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Laser parameters 3 cw

=

#A) > ##:

'ime t

process threshold

Power P

cw - Laser

#ea2 power > average power in cw mode, pea2 power of a

modulated puls is as ma(imum the ma(5 average power

#ulse width% 58 ms 3 . ms or cw mode

Fre4uency% cw +up to .@ 2J in modulated mode0

#ower density +#/+K/8D00 has to "e a"ove process threshold

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=ffects of !emperature ;ycle

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Laser welding has the following characteristics%

,ery high gradients and heating3 +9. :/s0 and cooling rates +. 55 Some

. :/s05 es"lt# high state o stress5

Material areas close to the molten Jone are heated up close to the solidus

temperature5

!he formation of "alanced microstructures is nearly impossi"le5 !ypically we

find coarse grained, hard and "rittle microstructures in the A5


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1utt

weld

Lap Noint

Fillet

weld

!hin material should "e on top

Incidence angle of the laser"eam

as much in Noint direction as possi"le

Weld Noint types

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.oint types / 0"tt Weld

20

0"tt weld

Advantages%

optimum distri"ution of forces

optimum solution for light weight structures

no pro"lems at welding coated material

Disadvantages%

high re4uirements on tolerances high re4uirements on clamping and positioning


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.oint types / Lap .oint

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Lap oint

Advantages%

low re4uirements in tolerances and positioning accuracy

low distortion indistri"ution of forces

more than 7 layers possi"le

Disadvantages%

risc of crevice corrosion

difficult degassification

#lease note% !hin material should "e on top5


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.oint types / 2illet Weld

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2illet weld

Advantages%

easy to clamp

good distri"ution of forces

Disadvantages%

high re4uirements on clamping and positioning

#lease note% Angle of weld follows incidence angle of laser"eam

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Butt weld

Lap joint

< 0,15 d

< 0,1 d

d

< 0,1 d d = 0.75 mm

d

'olerances

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Spot si3es

24

600 m 30 m


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Without gas $itrogen Argon

Goal#

#revent o(idation

Improve seam 4uality

Sol"tion# 4se protection gas

$itrogen cheap

Argon "etter seam 4uality

elium difficult to handle

5mportant#

Laminar flow At ? mm noJJle diameter

. l/min are reasona"le

#rotection 'as

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Welda"ility of a material is given, if in production due to the chemical,metallurgical and physical properties a weld according to the re6"irements can

"e done5

from% DI$ E67E !eil .

Possible re6"irements#

P static strength

P dynamic strength

P heremtical sealing

P electrical conductivity

P reproduca"ility

P process sta"ility

Welda"ility is no

material specific value5

Due to this most often

tests need to "e done5

Welda"ility of Materials

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Material Selection

!aterial Comment

Carbon steel Welds well5 If car"on content 9 57 H "rittle welds5

Stainless steel


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#lating Issues

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9inc coating 1oiling issues have to "e considered

'in May cause "rittle intermetallic phases with ;u

;ickel =lectroless 39 leads to crac2ing due to # in plating process

=lectrolytic 39 to "e preferred Gold

Often with $i underplating , avoid electroless $i plating ShinyT Au more difficult than dullT Au

Silver

!ends to spatter


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!he welda"ilty of steel depends strongly on the following material

characteristics%

chemical composition metallurgical processes at melting and solidification

physical properties

Material composition limits% ;3 content - ,7 H

S3 and #3content as small as posi"le + usually 5


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non- and low alloyed steel General str"ct"ral steel#

hardening in A possi"le5

'o"gh at s"b3ero steel and heat resisting str"ct"ral steel# Welda"ilty good "esides martensitic heat resisting structural steel 5

Case hardening-: nitriding heat treatable steel%

good welda"ility for ;= > ;QMn/7QMo/.6Q$i/8Q;r/.Q)/.Q;u/7QSi/76 - ,


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Stainless steel 2erritic chrome steel 71< * = Cr = 1+*: C = ):1 *8#

welda"ility has to "e proved5

!artensitic chrome steel 71) * = Cr = 1>*: ):1 * = C = 1:< *8# Danger of cold crac2ing, increase of hardness and "rittleness5 welda"ility has to "e proved5 welda"ility for martensitic chrome nic2el steel with . H - $i - ?H and ; - ,6 H is

"etter5

A"stenitic chrome / nickel 7-molybden"m8-steel# mainly good welda"ilty5

A"stenitic erritic steel 7d"ple? steel8# ;ool down time not sufficient for complete change of microstructure5

Steel Welda"ility Stainless steel

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Welda"ility of aluminium depends

strongly on the composition of the

alloy5

#ure aluminium is for e(ample well

welda"le5

When using Al alloys containing Si, Mg

and ;u care should "e ta2en to avoidthe pea2 of hot crac2 sensitivity5

Aluminium Welding 3 1asics

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Sol"tion#

Filler wire, increase fle(i"ilty inmaterial selection "ut difficult

handling

;hoose the material of one of the

parts to weld in a way that the

resulting microstructure in the weldseam is not critical5 +e5 g5% 667 and

88@0


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1 2 3 4 5 6 7

Felative;rac2

Sensitivity

#ercentage Alloying =lement BWeight HC

Al-Li

Al-Cu

Al-Mg2-Si

Al-Mg

Al-Si

Aluminium Welding ot ;rac2ing

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Series

;on-heat-treatable alloys.(((


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Weld Depth #ulsed Laser

38

,6

.

.,6

7

7,6

10355 r of in Fine Welding With Laser

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