Technology trends for today’s material processing needs

Technology trends for today’s material processing needs

Pulsed Nd:YAG Laser Welding

Electromagnetic SpectrumNd:YAG radiation is in the near infrared, is invisible to the human eye

Nd:YAG 1064 nm

GAMMA XRAY UV VISIBLE INFRARED MICRO-WAVE

TV RADIO

10-12m 10-9m10-6m

10-3m 1m

Red Laser Diode, HeNe Laser (Gas)630 – 670 nm

CO2 Laser (Gas)10,600 nm

Excimer Laser (Gas)93 – 358 nm

SHG Nd:YAG532 nm

Inside Pulsed Nd:YAG LasersOutput Beam1.064 mm Emission

Wave Length

Flash Lamp (White Light - multiple wavelengths)

50% FrontMirror99.3% reflecting

Rear Mirror

Laser Rod (Neodymium Doped)0.730-0.810 mm Absorption Band

Light amplification takes place between the mirrors

Fiber Optic Delivery

Part

Fiber OpticCable 0.3 to 1.0mm Dia.

FocusingHead

Fiber Input Coupler

Collimating Lens

Focusing Lens

Protective Cover Slide

CCTVCamera

Collimated beam from laser resonator

Long collimating lens = smaller spot size Short focus lens = smaller spot sizes Smaller spot size increases power density

Spot

F Focus Lens

F Collimating Lens

Fiber

Optical Spot Size = (F.L. Focus Lens / F.L. Collimating Lens) X Fiber Diameter

Effect of Beam Delivery

Laser Beam

Focusing Lens

Focal Length

Minimum Spot Diameter(0.4mm Fiber, 70 mm Collimator

50 mm

70 mm

100 mm

120 mm

0.28 mm

0.40 mm

0.57 mm

0.68 mm

Effect of Beam Delivery

Effect of Beam Delivery

Energy settings are the same Weld 1:

– 600µm fiber– 120/100 focus head– Spot: .6mm x 120/100 = .5 mm

Weld 2:– 400µm fiber– 120/ 70 focus head – Spot: = 0.4 x 120/100 = .23 mm

Laser Control - Power Feedback

“Real-time” optical power feedback.Benefits:– Programmed in peak power and time profile – Instantaneous output power is identical to

programmed pulse shape.– Automatically compensates for aging lamps– No “dummy shots” required to stabilize output– Output updated every 50 microseconds (20kHz)

Laser Control - Power Feedback State of the art “set and forget” output control:

YAG

HR PR

Lamp Power Supply

lamp

Comparator

PowerDetector

InputCouplingAssembly

Power MonitorVOUT = 1V/kW

DSPReference

Waveform

FeedbackWaveform

Laser Control - Power Feedback

Example of Power Feedback

Open Loop Laser Feedback Laser

Laser Control - Pulse Shaping

Pulse shaping permits the Operator to define a laser waveform over multiple segments or points.

Programming is accomplished by defining segments, in both amplitude (% of power) and duration (time).

Reference Actual

Where can Pulse Shaping help?• Gold and Aluminum

(reflective)

• Pin holes and cracking

• Weld splatter

Pulse shape for reflective materials

Pulse shape to eliminate pin holes

Laser Control - Power Ramping Example of Power Ramping:

Without Power Ramping With Power Ramping

Where can Power Ramping help?

Better Cosmetic Appearance Allows you to overlap a seam weld

without additional penetration to ensure hermeticity

Weld to the edge of thin material by “fading” into and out of the weld.

Last pulse cracking

Your Parts and Laser Welding

Getting ready to weld

Getting ready to weld

Process Considerations

Joint configurations Parts fit up Part alignment Cover gas Contamination Develop a wide weld process window while

meeting specifications

Joint Configurations

Lap

FilletButt

For best results- NO GAP! Rule of Thumb: 10% gap of the thinnest material

– Butt– Edge– Fillet

Butt Weld All of the penetration is along weld joint Increase penetration = increased strength Least amount of energy required for robust weld

Lap Weld Weld must pass through top material

to reach the joint Deeper penetration does not add to

strength Penetration must be at least 1.5x top

material thickness for robust weld

Good penetrating lap weld

Excess penetration does not contribute to the weld

Penetration is to light, weld not bonding to lower material

Fillet Weld

Weld angle is 20-70 degrees Deep penetration not

necessary

Fillet weld to thin wall tube

Deep penetration adds little to the weldGood Fillet Weld

Fillet Weld Due to angle of weld, the weld plume will be close to the part Will leave soot on part As angle becomes steep or shallow, some permanent discoloration

Angle Weld Welding at an angle

– Butt weld joint is obstructed by part, so beam comes in at a angle

Lopsided penetration Favor spot towards angle so deepest penetration is

along seam

Part Alignment Nominal Values

+/-0.003”

+/-0.010”

Includes Part Tolerances

Variance in:• X direction is critical• Y is travel direction• Z is forgiven due to

large focusing tolerance

Cover Gas: Off Axis

Part Travel

Low flow for best coverageGas Types: Argon, Helium

Weld travel into cover gas

Cover Gas: On AxisLaser Beam

Focusing LensProtective Lens

Cover Gas Nozzle Cover Gas Supply

Part

Weld Mechanics

Understanding the weld

Understanding the weld

Conduction Weld Low peak power Low penetration Laser acts as a point heat source Penetration spreads out in all directions Weld diameter large than optical spot size

Keyhole Welding High peak powers Deep penetrating A hole is formed in weld pool Laser is guided down hole to bottom to the

weld pool to drive penetration down Keyhole is highly dynamic

Laser Beam

Weld pool

Keyhole

Typical Pulsed Weld Typical pulsed welds have both conduction and keyhole

welding

Conduction Mode

Keyhole Mode

Weld Video

Welding Speed Seam weld is made by overlapping spot welds Speed (ips) = WD x (1-SO) x Hz

– WD = weld diameter– SO = spot overlap– Hz = laser repetion rate

Weld speed increases with higher average power Weld speed increases with less overlap

– 80% overlap for hermetic weld– 50% or less for structural weld SO

Hermetic Barrier

Actual Penetration

Hermetic Barrier

Actual Penetration

50% Overlap

85% Overlap

Seam Welding

Seam Welding

Developing Laser Welds

Optimizing the ProcessOptimizing the Process

Typical Peak Power Density vs. Material

Material Peak Power Density (MW/cm2)

Low Alloy Steel 1

Titanium 1

Kovar 1.5

Stainless Steel 2

Aluminum 3

Copper 4-5

Effect of Laser Settings

Pulse Energy = Pulse Width x Peak Power

5431 2

Pulse Width (msec)

Peak Power(kW)

3

2

1

5J Pulse Energy

Penetration at Constant Peak Power

The appropriate penetration for a given applications is achieved by increasing the pulse energy while maintaining a constant peak power

J 1.0 2.0 3.0 4.0 5.0

1.5kW Peak Power Stainless Steel

Peak Power Optimization Optimum peak power is defined as the peak power that creates

the deepest penetration at a given energy without material expulsion

Optimum peak power minimizes HAZ Low peak power produces shallow conduction welds Excess peak power produces drilling and cutting

4.5J

kW 0.9 1.1 1.5 2.2 4.5ms 5.0 4.0 3.0 2.0 1.0

Peak Power Optimization

Stainless Steel

Weld Evaluation Splatter and under cutting

– Peak power to high Porosity

– Weld solidifies to soon after keyhole closes

– Increase pulse width or decrease peak power

– Pulse shaping to slow solidification Weld Splatter

PorosityUndercut

Weld Evaluation Pin Holes

– Material contamination– Poor fit up– Material not compatible with laser welding

Small pin holes can be eliminated by parameter optimization or pulse shaping

Weld Evaluation Cracking

– Material contamination– Poor fit up– Material not compatible with laser welding– Small cracks may be eliminated by parameter optimization or

pulse shaping– Last pulse cracking can be eliminated by power ramping

Small crack Solidification cracking

Last pulse cracking

532nm Laser Welding532nm Laser Welding

Breaking new ground Breaking new ground

Electromagnetic SpectrumGreen Laser is in the Visible Region

GAMMA XRAY UV VISIBLE INFRARED MICRO-WAVE

TV RADIO

10-12m 10-9m 10-6m 10-3m 1m

HeNe Laser (Gas)0.632mm

CO2 Laser (Gas)10.6 mm

Excimer Laser (Gas)0.093 to 0.358mm

Nd:YAG 1064nmLW2AG 532nm

Green Welder Specifications

Wavelength 532 nm

Average Power 2 watts

Pulse Energy 2 J

Peak Power 1.5 kW

Pulse Width .2-3.0 msec (.02 msec/step)

Repetition Rate 1-12 pps

Minimum Fiber Diameter

.3 mm SI

Resonator Layout

100% at 1064 nm

0% at 532nmNd:Yag Rod

Frequency Doubling Crystal

Resonator Mirror

Resonator Mirror

Flashlamp

532 nm

1064 nm

Fiber input unit

Focus Head

Fiber Optic

Advantages of 532 nm Copper, Gold and Silver couple much better to the 532 nm

wavelength. – Lower energy is needed to weld– Penetration control of weld is much better– Not sensitive to surface conditions– Thin materials can be welded without damage to underlying

materials– Copper may be welded to dissimilar metals

Spectral Response

Copper to Kovar

532 nm wavelength– .4mm SI fiber– CCTV100/100 Focus head

Materials– Kovar– Copper

The energy needed to melt the copper is low, so the kovar does not blow out.

Copper to Stainless 532 nm wavelength

– .3mm SI fiber– CCTV 70/70 focus head

Material– Plate: .004” Stainless Steel– Terminal: .004” gold plated

copper

PCB Contact Welding

532 nm wavelength– .3mm SI fiber– CCTV 70/70 focus head

Material– Circuit board trace:

Copper with Gold plating– Contact: .004” copper

PCB Contact Welding Successfully welded to

trace without blowing through into the FR4.

Solar Cell Contact Welding 532 nm wavelength

– .3mm SI fiber– CCTV70/50 focus head

Material– Solar Cell: .002” stainless

steel over .001” kapton– Ribbon: .002” copper

Weld did not damage Kapton 532 nm wavelength needs

less power to couple into the copper so kapton is not damaged.

Small Spot Copper Welding 532 nm wavelength

– .3mm SI fiber– CCTV100/50 focus head

Material– Lead: .0025” copper

Ni/Au plated– Terminal: Copper, Ni/Au

plated Small spot size Wide process window

compared to current ultrasonic process

Copper Welding (cont)

Copper Component Welding

532 nm wavelength– .3mm SI fiber– CCTV50/50 focus head

Material– Lead: Copper gold tin plating– Wire: Copper

Copper Component Welding

Platinum to Nickel

532 nm wavelength– .3mm SI fiber– CCTV70/70 focus head

Material– Wire: .004” diameter

platinum– Wire: Nickel

532 nm wavelength can also do low power tradition applications.

Comparison of Welding Technologies

Why Laser Welding?Why Laser Welding?

Advantages of Laser Welding Weld quality

– Small Heat Affected Zone– Non-contact– No added material

Set up– No wear-out process items

Production– Fast beam positioning– Fast triggering

Comparison of Welding Technologies

Heat Input

Heat Affected Zone

Seam Weld Speed

Spot Weld Speed

Cost Operator skill level

Process maintenanceeffort

Pulsed Nd:YAG Laser

Low Small Medium Fast Medium Low Low

CW Nd:YAG Laser

High Large Fast Medium High Low Low

GMAW High Large Fast Slow Low Medium Medium

Advantage! - High Speed Battery Tab Welding

Spot Weld Tab to Battery– Tab: .004” thick Nickel 200– Battery: 304 Stainless Steel

Laser Settings– 4.0 mSec– 1.0 kW

Beam Delivery– 400 µm Fiber– 70/70 Focus Head

Advantage! – Medical Device Micro-Spot Welding

Sensor Wire Laser Settings

– 0.3 msec– 0.5 kW

Beam Delivery– 200 µm Fiber– 120/50 Focus Head

Spot Size: 200µm x 50/120 = 85µm

50µm Diameter wire

Advantage! - Heat Sensitive Battery Seam Welding

Al Battery Case Laser Settings

– 0.6 msec– 1.9 kW– 245 pps– 280 W, average power

Beam Delivery– 300 µm Fiber– 100/100 Focus Head

Speed: 33 mm/Sec

22 welds0.3 seconds

220um

240um

240um

150

195um

195um

40/100um

40/200um

40/200um

20/100um

20/200um

20/40um

20mm

6mm

(1)

(2)

(3)

(4)

Advantage! - High Speed Scan Head Welding of Suspension Bridge

Thank you!