Technology trends for today’s material processing needs Pulsed Nd:YAG Laser Welding

Electromagnetic Spectrum Nd:YAG radiation is in the near infrared, is invisible to the human eye Nd:YAG 1064 nm GAMMAXRAYUVVISIBLEINFRAREDMICRO- WAVE TVRADIO m m m m1m Red Laser Diode, HeNe Laser (Gas) 630 – 670 nm CO 2 Laser (Gas) 10,600 nm Excimer Laser (Gas) 93 – 358 nm SHG Nd:YAG 532 nm

Inside Pulsed Nd:YAG Lasers Output Beam  m Emission Wave Length Flash Lamp (White Light - multiple wavelengths) 50% Front Mirror 99.3% reflecting Rear Mirror Laser Rod (Neodymium Doped)  m Absorption Band Light amplification takes place between the mirrors

Fiber Optic Delivery Part Fiber Optic Cable 0.3 to 1.0mm Dia. Focusing Head Fiber Input Coupler Collimating Lens Focusing Lens Protective Cover Slide CCTV Camera 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

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 Power Detector Input Coupling Assembly Power Monitor V OUT = 1V/kW DSP Reference Waveform Feedback Waveform

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

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

Joint Configurations Lap Fillet Butt 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 degrees Deep penetration not necessary Fillet weld to thin wall tube Deep penetration adds little to the weld Good 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 coverage Gas Types: Argon, Helium Weld travel into cover gas

Cover Gas: On Axis Laser Beam Focusing Lens Protective Lens Cover Gas Nozzle Cover Gas Supply Part

Weld Mechanics 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

Developing Laser Welds Optimizing the Process

Typical Peak Power Density vs. Material MaterialPeak Power Density (MW/cm2) Low Alloy Steel1 Titanium1 Kovar1.5 Stainless Steel2 Aluminum3 Copper4-5

Effect of Laser Settings Pulse Energy = Pulse Width x Peak Power Pulse Width (msec) Peak Power (kW) J 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 kW Peak PowerStainless 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 ms 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 Porosity Undercut

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 Welding Breaking new ground

Electromagnetic Spectrum Green Laser is in the Visible Region GAMMAXRAYUVVISIBLEINFRAREDMICRO- WAVE TVRADIO m10 -9 m m m1m HeNe Laser (Gas)  m CO 2 Laser (Gas) 10.6  m Excimer Laser (Gas) to  m Nd:YAG 1064nm LW2AG 532nm

Green Welder Specifications Wavelength532 nm Average Power2 watts Pulse Energy2 J Peak Power1.5 kW Pulse Width msec (.02 msec/step) Repetition Rate1-12 pps Minimum Fiber Diameter.3 mm SI

Resonator Layout 100% at 1064 nm 0% at 532nm Nd:Yag Rod Frequency Doubling Crystal 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?

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 CostOperator skill level Process maintenance effort Pulsed Nd:YAG Laser LowSmallMediumFastMediumLow CW Nd:YAG Laser HighLargeFastMediumHighLow GMAW HighLargeFastSlowLowMedium

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 welds 0.3 seconds 220um 240um um 40/100um 40/200um 20/100um 20/200um 20/40um 20mm 6mm (1) (2) (3) (4) Advantage! - High Speed Scan Head Welding of Suspension Bridge

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