Laser beam welding is a technique in manufacturing whereby two or more pieces of material (usually metal) are joined by together through use of a laser beam.

The laser beam is a coherent (single phase) light of a single wavelength (monochromatic). The laser beam has low beam divergence and high energy content and thus will create heat when it strikes a surface.

Lasers are utilized in metalworking for:

• Seam tracking and inspection
• Surface heat treating
• Welding
• Cutting (metallic and non-metallic materials)

Laser types

There are two primary types of lasers used in welding and cutting:

• Gas lasers (CO₂ type)
• Solid state lasers (Nd:YAG type)

Carbon dioxide lasers use a mixture of high purity carbon dioxide with helium and nitrogen as the lasing medium. Here are some of the key characteristics for CO₂ lasers:

• Infrared (10.6 micrometres)
• Beam transmission by mirror only (not fibre optic)
• Cutting lasers are typically from 0.5 to 10 kW
• Difficulties in cutting/welding reflective materials (e.g., aluminum or copper)
• Can cut non-metallic materials
• High cutting speed possible

YAG lasers use a solid bar of yttrium aluminum garnet doped with neodymium as the lasing medium. Here are some of the key charateristics for Nd:YAG lasers:

• Infrared (1.06 micrometres)
• Beam transmission by optical fiber possible
• Available to 4 kW
• Wavelength absorbed well by metallic materials (including Al and Cu)
• Not suitable for cutting non-metallic materials
• Good for fine work, but cutting speeds are generally lower than CO₂

Both CO₂ and Nd:YAG lasers can operate in either continuous or pulsed operating modes.

Laser beam welding (LBW)

Nd:YAG lasers are being more commonly utilized in automotive parts manufacturing using robotic delivery. CO₂ laser welding using a 10 kW system can produce a single pass autogenous weld in ¾” thick stainless steel at 20 ipm (8 mm/s). Systems producing up to 50 kW have been built. Keyhole welding is a method of laser welding in which a high power continuous-wave laser is focused on the metal to be welded, forming a capillary channel (keyhole) filled with a partially ionized metallic gas. This vapor interacts with the laser beam and the melt pool, causing different effects. As the beam moves across the work-piece the molten material flows around the keyhole and solidifies to form a continuous weld.

Laser beam cutting (LBC)

CO₂ Lasers are most popular for 2D profile cutting of steel plates up to ~3/4” thick (1/2” for stainless, 3/8” for aluminum). Approximate CO₂ laser cutting speeds for steel of different thicknesses:

• 350 ipm (0.15 m/s) - 20 gauge (0.95 mm)
• 100 ipm (0.04 m/s) - ¹⁄₄ in (6.4 mm) thick
• 35 ipm (0.015 m/s) - ⁵⁄₈ in (15.9 mm) thick

Nd:YAG systems are more common on thinner gauge materials using robotic delivery systems.

Assist gases are used to help expel the molten metal, protect the lenses, and in the case of oxygen on steels—to provide chemical cutting action.

See also

• American Welding Society, Welding Handbook, Volume 2 (8th Ed.)

Welding

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