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Technology trends for today’s material processing needs

Pulsed Nd:YAG Laser Welding. Technology trends for today’s material processing needs. SHG Nd:YAG 532 nm. 10 -6 m. 10 -9 m. 10 -12 m. 10 -3 m. 1m. GAMMA. XRAY. UV. VISIBLE. INFRARED. MICRO- WAVE. TV. RADIO. Excimer Laser (Gas) 93 – 358 nm. CO 2 Laser (Gas) 10,600 nm.

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Technology trends for today’s material processing needs

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

  2. SHG Nd:YAG 532 nm 10-6m 10-9m 10-12m 10-3m 1m GAMMA XRAY UV VISIBLE INFRARED MICRO- WAVE TV RADIO Excimer Laser (Gas) 93 – 358 nm CO2 Laser (Gas) 10,600 nm Red Laser Diode, HeNe Laser (Gas) 630 – 670 nm Electromagnetic SpectrumNd:YAG radiation is in the near infrared, is invisible to the human eye Nd:YAG 1064 nm

  3. Laser Rod (Neodymium Doped) 0.730-0.810 mm Absorption Band 50% Front Mirror 99.3% reflecting Rear Mirror Inside Pulsed Nd:YAG Lasers Output Beam 1.064 mm Emission Wave Length Light amplification takes place between the mirrors Flash Lamp (White Light - multiple wavelengths)

  4. Fiber Optic Delivery Fiber Input Coupler Focusing Head CCTV Camera Collimated beam from laser resonator Fiber Optic Cable 0.3 to 1.0mm Dia. Collimating Lens Focusing Lens Protective Cover Slide Part

  5. Effect of Beam Delivery Optical Spot Size = (F.L. Focus Lens / F.L. Collimating Lens) X Fiber Diameter • Long collimating lens = smaller spot size • Short focus lens = smaller spot sizes • Smaller spot size increases power density Fiber F Collimating Lens F Focus Lens Spot

  6. Effect of Beam Delivery Laser Beam Focusing Lens Minimum Spot Diameter (0.4mm Fiber, 70 mm Collimator Focal Length 0.28 mm 50 mm 0.40 mm 70 mm 0.57 mm 100 mm 0.68 mm 120 mm

  7. 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

  8. 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)

  9. PR HR Feedback YAG Waveform lamp Power Detector Lamp Power Supply Power Monitor Input Coupling Assembly VOUT = 1V/kW Reference DSP Waveform Comparator Laser Control - Power Feedback • State of the art “set and forget” output control:

  10. Open Loop Laser Feedback Laser Laser Control - Power Feedback Example of Power Feedback

  11. 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

  12. Where can Pulse Shaping help? • Gold and Aluminum (reflective) • Pin holes and cracking • Weld splatter Pulse shape to eliminate pin holes Pulse shape for reflective materials

  13. Laser Control - Power Ramping • Example of Power Ramping: Without Power Ramping With Power Ramping

  14. 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

  15. Your Parts and Laser Welding Getting ready to weld

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

  17. Butt Joint Configurations • For best results- NO GAP! • Rule of Thumb: 10% gap of the thinnest material • Butt • Edge • Fillet Lap Fillet

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

  19. 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 Excess penetration does not contribute to the weld Penetration is to light, weld not bonding to lower material Good penetrating lap weld

  20. Fillet Weld • Weld angle is 20-70 degrees • Deep penetration not necessary Fillet weld to thin wall tube Good Fillet Weld Deep penetration adds little to the weld

  21. 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

  22. 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

  23. Part Alignment Nominal Values +/-0.003” • Variance in: • X direction is critical • Y is travel direction • Z is forgiven due to large focusing tolerance +/-0.010” Includes Part Tolerances

  24. Cover Gas: Off Axis Weld travel into cover gas Part Travel Low flow for best coverage Gas Types: Argon, Helium

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

  26. Weld Mechanics Understanding the weld

  27. 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

  28. Keyhole Welding Laser Beam • 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 Keyhole Weld pool

  29. Typical Pulsed Weld • Typical pulsed welds have both conduction and keyhole welding Conduction Mode Keyhole Mode

  30. Weld Video

  31. SO 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

  32. Seam Welding Hermetic Barrier Actual Penetration 50% Overlap Hermetic Barrier Actual Penetration 85% Overlap

  33. Seam Welding

  34. Developing Laser Welds Optimizing the Process

  35. Typical Peak Power Density vs. Material

  36. Effect of Laser Settings 3 • Pulse Energy = Pulse Width x Peak Power 2 5J Pulse Energy Peak Power (kW) 1 4 5 1 3 2 Pulse Width (msec)

  37. 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

  38. 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

  39. Peak Power Optimization kW 0.9 1.1 1.5 2.2 4.5 ms 5.0 4.0 3.0 2.0 1.0 4.5J Stainless Steel

  40. 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 Undercut Porosity

  41. 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

  42. 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 Last pulse cracking Solidification cracking Small crack

  43. 532nm Laser Welding Breaking new ground

  44. Excimer Laser (Gas) 0.093 to 0.358mm Electromagnetic SpectrumGreen Laser is in the Visible Region LW2AG 532nm Nd:YAG1064nm 10-6m 10-12m 10-9m 10-3m 1m GAMMA XRAY UV VISIBLE INFRARED MICRO- WAVE TV RADIO CO2 Laser (Gas) 10.6 mm HeNe Laser (Gas) 0.632mm

  45. Green Welder Specifications

  46. Resonator Layout Fiber Optic Fiber input unit 100% at 1064 nm 0% at 532nm Nd:Yag Rod Focus Head Resonator Mirror Flashlamp Frequency Doubling Crystal 532 nm 1064 nm Resonator Mirror

  47. 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

  48. Spectral Response

  49. 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.

  50. Copper to Stainless • 532 nm wavelength • .3mm SI fiber • CCTV 70/70 focus head • Material • Plate: .004” Stainless Steel • Terminal: .004” gold plated copper

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