Laser welding: a joining process used for fuel injector fabrication

1. Laser welding: a joining process used for fuel injector fabrication Ing. M. Muhshin Aziz Khan

2. What shall we discuss in this seminar? • Facts about laser • Laser basics • Laser quality and its effects • Primary adjustable or controllable parameters and their effects • Facts about lasers for welding • CO2 laser • Nd3+:YAG laser • Lamp-pumped • LD-pumped • Disk laser • Diode laser • Fiber laser • Why do we need lasers for welding • Laser beam welding • Types • Laser welding unit • Laser beam welding: Fuel Injector Perspective • Fuel injector section • VS-VB weld configuration and power profile • Seat to valve body assembly process steps • Weld quality requirements • A case study: Laser beam welding of martensitic stainless steels in constrained overlap configuration • Experimental procedure and conditions • Results and discussion • Weld bead profile aspect • Parametric effects on weld bead chararcteristics • Problem associated with inappropriate parameter selection

3. Facts About Laser:Laser Basics • Laser Components Lasing Medium:Provides appropriate transition and Determines the wavelength (it must be in a metastable state) • Pump:Providesenergy necessary for populationinversion • Optical Cavity:Provides opportunity for amplification and Produces a directional beam (with defined length and transparency) Light Amplification by Stimulated Emission of Radiation • Properties of Laser • Coherent (synchronized phase of light) • Collimated (parallel nature of the beam) • Monochromatic (single wavelength) • High intensity (~1014W/m2)

4. Facts About Laser:Laser Basics Light Amplification by Stimulated Emission of Radiation

5. Facts About Laser:Laser Quality and Its Effect Effects of Beam Quality Beam Quality • A measure of Lasers’ capability to be • propagatedwith low divergenceand • focused to a small spot by a lens or mirror • Beam Quality is measured by M2 or BPP (Beam Product Parameter, mm.mrad) • Ratio of divergence of actual beam to a theoretical diffraction limited beam with samewaist diameter • M2= 1; Ideal Gaussian Beam, perfectly diffraction limited • Value of M2 tends to increase with increasing laser power • Smaller focus at constant aperture and focal length • Longer working distance at constant aperture and spot diameter • Smaller aperture (‘slim optics’) at constant focal diameter and working distance A higher power density by a smaller spot size with the same optics, or The same power density at lowerlaser power

6. Facts About Laser:Primary Adjustable Parameters and Their Effects Change in Pulse Duration Primary Controllable Parameters • Laser Beam Energy Output Characteristics (i) Voltage (ii) Pulse Duration • Laser Focus Characteristic (iii) Laser Beam Diameter Increased pulse duration results in deeper and wider melting Change in Voltage Change in Voltage and Pulse Duration Increased voltage results in deeper physical penetration with less melting due to physical pressure Simultanous increase in voltage and pulse duration results in deeper melting Change in Beam Diameter Increased beam diameter results in shallow soft penetration and wide, but soft melting

7. Facts about lasers for welding Laser Characteristics, Quality and Application • Typical commercial lasers for welding • CO2 Laser • Nd3+:YAG Lasers • Lamp-pumped • LD-pumped • Disk Laser • Diode Laser • Fiber Laser CO2 Laser: M2 values [CW]

8. Facts about lasers for Welding: YAG Laser Laser Characteristics, Quality and Application YAG Laser: M2 values [CW & PW]

9. Facts about lasers for welding: Disk Laser Laser Characteristics, Quality and Application Recent Development(Mann 2004; and Morris 2004): • Commercially available disk laser system: 1 and 4 kW class • Beam delivery with 150 and 200µm diameter fiber • Even a 1 kW class laser is able to produce • a deepkeyhole-type weld bead • extremely narrow width in stainless steel and aluminum alloy

10. Facts about lasers for welding: Fiber Laser Laser Characteristics, Quality and Application Recent Development(Thomy et.al. 2004; and Ueda 2001): • Fiber lasers of 10kW or more are commercially available • Fiber lasers of 100kW and more are scheduled • Fiber laser at 6.9kW is able to provide deeply penetrated weld at high speed • Fiber laser is able to replace high quality (slab) CO2 laser for remote or scanning welding

11. Facts about lasers for welding Comparison of different laser systems Correlation of Beam Quality toLaser Power (Katayama 2001; O’Neil et. al. 2004; Shiner 2004; Lossen 2003): • Overlaid with condition regimes • Beam quality of a laser worsens with an increase in power • LD-pumped YAG, thin disk, CO2 and fiber lasers can provide high-quality beams • The development of higher power CO2 or YAG lasers is fairly static and, hence Main focus on development: i. high-power diode, ii. LD-pumped YAG, iii. disk and/or iv. fiber lasers

12. Facts about lasers for welding Wavelengths of some important laser sources for materials processing CO2 Laser Expanded portion of the electromagnetic spectrum showing the wavelengths at which several important lasers operate

13. Why do we need laser for welding? • Traditional welding: • Natural limitations to speed and productivity • Thicker sections need multi-pass welds • A large heat input • Results in large and unpredictable distortions • Very difficult to robotize Laser beam welding: • High energy density input process • single pass weld penetration up to ¾ inch • High aspect ratio • High scanning speeds • Precisely controllable (close tolerence: ± 0.002 in.) • Low heat input produces low distortion • Does not require a vacuum (welds at atmospheric pressure) • No X-rays generated and no beam wander in magnetic field. • No filler metal required (autogenous weld and no flux cleaning) • Relatively easy to automate • Materials need not be conductive

14. Lasers Beam Welding: Types of LBW Conduction Welding • Description • Heating the workpiece above the melting temperature without vaporizing • Heat is transferred into the material by thermal conduction. • Characteristics • Low welding depth • Small aspect ratio (depth to width ratio is around unity) • Low coupling efficiency • Very smooth, highly aesthetic weld bead • Applications • Laser welding of thin work pieces like foils, wires, thin tubes, enclosures, etc.

15. Lasers Beam Welding: Types of LBW Keyhole Welding • Description • Heating of the workpiece above the vaporization temperature and forming of a keyhole • Laser beam energy is transferred deep into the material via a cavity filled with metal vapor • Hole becomes stable due to the pressure from vapor generated • Characteristics • High welding depth • High aspect ratio (depth to width ratio can be 10:1) • High coupling efficiency

16. Beam Delivery Unit Laser Processing Optics Workpiece Positioning Unit Lasers Beam Welding: Laser welding unit Schematic Diagram Beam Delivery unit

17. Specimen Holder Specimen Shielding Gas Nozzle Laser Head Lasers Beam Welding: photographic view of laser welding unit

18. Joint overlap at full power to ensure hermetic enclosure of joint Post heating to remove micro cracks from joint surface Lasers Beam Welding:Fuel Injector Perspective XL2 injector: VB-VS Welding Configuration and Power Profile Valve Body-Valve Seat Welding Configuration

19. LASER BEAM WELDING OF MARTENSITIC STAINLESS STEELS IN A CONSTRAINED OVERLAP JOINT CONFIGURATION A Case Study

20. Experimental Procedure and Conditions

21. Experimental Procedure and Conditions: Mechanical Characterization: Weld X-Section Characterization of welding cross-section (W: Weld width, P: Weld penetration depth, S: Weld resistance length)

22. (b) Punch Expeller Specimen Holder Specimen Experimental Procedure and Conditions: Mechanical Characterization: Shearing Test Photographic views of the experimental set-up for shearing test

23. Results and Discussion: Weld profile Aspect • Curvature of the keyhole profile is closely related to welding speed. • The higher the welding speed the larger the curvature of the keyhole. • Keyhole is nearly cone-shaped • Its vertex angle decreases as the keyhole depth increases Shape of the keyhole changes from conical to cylindrical

24. Results and Discussion: Effects of Individual Process Parameters AA: laser power BB: welding speed CC: fiber diameter

25. Results and Discussion: Interaction Effects of Process Parameters on Weld Width

26. Results and Discussion: Interaction Effects of Process Parameters on Penetration Depth

27. Results and Discussion: Interaction Effects of Process Parameters on Penetration Depth Energy density is frequently used as process parameter in energetic term: LP : laser power describing the thermal source, WS : welding speed determining the interaction time φSpot : focal spot diameter defining the area through which energy flows into the material

28. Results and Discussion: Interaction Effects of Process Parameters on Resistance Length

29. Results and Discussion: Interaction Effects of Process Parameters on Resistance Length

30. Results and Discussion: Interaction Effects of Process Parameters on Shearing Force

31. Results and Discussion: Interaction Effects of Process Parameters on Shearing Force

32. Results and Discussion: Interaction Effects of Process Parameters on Shearing Force

33. Results and Discussion: Effects of Shielding Gas on Penetration Depth

34. Thank You for Patience Hearing