Advanced Joining Processes - Laser Welding

Advanced Joining Processes - Laser, Plasma, and Electron Beam Welding

• Laser Welding (LW): A process used to join metals or thermoplastics using a laser beam to create a weld. High heat concentration allows for high welding speeds in thin materials, creating narrow, deep welds in square-edged thick parts.

Laser Welding - Introduction

• Process Characteristics: High quality welds at high power densities, high precision and speed; small heat affected zone; process flexibility; non-contact tool, free of wear; highly movable tool, suitable for automation.

Laser Welding - Basic Operation of a Laser

• LASER: Light Amplification by Stimulated Emission of Radiation. A laser emits light through controlled emission, amplification, and reflection. This controlled process is crucial in welding for precision and control of heat input.

Laser Welding - Laser Types and Applications

• Laser types and associated applications:

• Laser usage is dependent on beam intensity and exposure time: various applications are suited to varying intensities and exposure times.

Laser Welding - Process Parameters

• Key parameters affecting weld joint quality: Peak power, Pulse repetition rate, Wave length, Pulse shape, Pulse width, Spot diameter, Advance rate, Shielding gas, Shielding gas flow, Filler material.

• Laser power has a major influence on weld penetration: increasing power generally increases the depth of penetration through the material.

Laser Welding - Material-laser Interaction

• Different materials react differently to laser radiation. Levels of reflection, absorption, and transmission vary. This impacts the welding process and the need for different parameters, depending on the base material used.

Laser Welding - Defects

• Solidification cracking: High depth-to-width ratio in laser welds leads to high thermal stress where the solidification fronts meet. Full-penetration laser welds are less susceptible to this defect. Surface contamination can also lead to porosity.

• Porosity: This is a less critical defect, less problematic than solidification cracking, originating from surface contamination. Improper gas shielding can contribute.

Laser Welding - Operation Modes

• Conduction limited welding: Laser power density is lower (<10⁵ W/cm²), so the beam only interacts with the surface, creating a shallow weld.
• Deep penetration/keyhole welding: High power density (>10⁶-10⁷ W/cm²) leads to the melting and vaporization of the material, forming a 'keyhole', allowing the laser to penetrate deeper.
• Scanner/smart welding: Involves mobile mirrors which control precise targeting and coverage. The beam is guided with controlled movements for precision.
• Hybrid welding: Combining laser welding with other processes, such as MIG or TIG. This approach is often crucial for large areas or intricate pieces where the laser alone might not be sufficient.
• Soldering and brazing: Use of filler material for joints, where the melting point of the filler material is lower than the base materials. The process results in a smaller temperature gradient.

Laser Welding - Welding of Polymers

• Polymer Materials: Many thermoplastics are readily laser-weldable. Melting temperatures of dissimilar materials should ideally have a 50°C overlap.
• Glass Fiber Content: Polymers with high glass fiber content can result in brittle joints, due to exposed, isolated fibers.
• Polymer Welding Processes: Transmission welding, contour welding, simultaneous welding, and quasi-simultaneous welding are used depending on the complexity of the polymer parts.

Plasma Welding - Introduction

• Process: Similar to TIG welding, an arc is formed between a tungsten electrode and the workpiece, with a plasma column generated.
• Plasma Encapsulation: The plasma column is contained within a copper nozzle which constricts the arc.

Plasma Welding - Advantages

• High welding speed: Ideal for hard and thick materials. The tool to work distance does not affect arc formation.
• Lower power consumption: More efficient energy usage for welding same-sized parts.
• Stable arc: Increases welding accuracy and stability.
• High penetration and intense arc: Suitable for varied metals.

Plasma Welding - Disadvantages

• High equipment cost compared to alternative methods.
• Noisy operation and higher emission of radiation.
• High maintenance cost: specialized and demanding maintenance.

Plasma Welding - Applications

• Stainless steel piping for the petrochemical industry.
• Surgical instruments.
• Electrical relays.

Electron Beam Welding - Introduction

• Process: High-speed electrons are generated by an electron gun, accelerated by magnetic fields, and focused on the workpieces.

Electron Beam Welding - Advantages

• High precision and repeatability: Automation capabilities for precise welding.
• Strong and consistent joints: Allows more dependable welding for high-precision applications
• Precise weld penetration control: Precise targeting and control of the electron beam.
• Small heat affected zone (HAZ): Reduces distortion and shrinkage.

Electron Beam Welding - Disadvantages

• Vacuum requirement: The vacuum environment is crucial and expensive.
• Expensive equipment and maintenance.
• Slow component change: The vacuum environment creates downtime.

Electron Beam Welding - Applications

• Gearbox parts.
• Metal strip resistors.
• Piping and turbine blades.