Laser (Light Amplification by Stimulated Emission of Radiation) beaming is an entirely non-contact process. You access the point of welding from one side and use the intense laser light to heat up the metal or other material quickly. It takes milliseconds to achieve the desired result.
The single-phase (coherent) beam of light is monochromatic (one color because it comprises only a single wavelength). Because the beam has high energy content and low beam divergence it is capable of creating heat when it hits a surface.
In the cutting and welding industry, a handful of different laser beams are used:
- Diode Lasers: These comprise one or several laser diodes. Semiconductor lasers spring to mind when referring to diode lasers. However, some of them in the semiconductor laser category do not need a diode to work. These obviously do not fall under this classification.
- Solid State Lasers: Not only do these operate at 1-micrometer wavelengths, they can function either continuously or in pulses. The latter results in joints that look rather similar to spot welds only with full penetration. It utilizes 1-100 joules of pulse energy and lasts 1-10 milliseconds.
- Gas Lasers: Using nitrogen or helium, even carbon dioxide, these lasers (named after the gases they use) rely on a high voltage power source and low current to work via a lasing medium to excite the gas atoms.
They too can operate either continuously or in pulse mode. Consider carbon dioxide lasers. They use a mixture of high purity CO2 with nitrogen and helium making up the lasing medium. This gas type laser is most often used in dual beam laser welding; the beam splits into two beams of equal power.
Why Lasers ?
If a metal or material proves troublesome or difficult to weld – and there are indeed several such instances – other methods cannot be relied upon.
For instance, very small components or objects with hard to access areas need laser welding methods. If you are working with reactive materials, inert gas shielding will be required, or laser beam welding can become a bit too tricky.
Laser Welding – The Basics
Using a highly concentrated coherent light beam to generate heat, you can coalesce or merge materials via the process of laser beam welding. The beam hits the exact spot where the metals or materials need to be joined.
Of all known sources of usable energy, a focused laser beam produces the highest energy concentration.
Without any divergence, electromagnetic energy (aka light) can be shot forth and brought to bear on a fine point.
- The single frequency beam is coherent and when working with coherent gases (nitrogen, helium, or carbon dioxide) is ideally suited to use the coherent radiation given off by these gases in the optical resonant cavity.
- You can continuously operate gas lasers using low levels of power. With innovations in technological processes, higher power outputs and continuous laser operations are possible because gases in the laser can now be cooled.
- High radio frequency generators are responsible for exciting the gas atoms to a good enough energy level. This results in Lasing. 2000-watt carbon dioxide laser systems are ideal for this with higher-powered versions in development. For instance, a 6-kw laser for automotive welding applications and a 10-kw one for research projects are already underway.
- You can focus and/or reflect coherent laser light much like normal light. Sundry lenses control the size of the focus spot; these can be as small as 0.003 inches (welding and cutting purposes) to ten times that size (heat treating purposes). The distance from the base metal also determines how efficiently you can focus or reflect the laser.
High-powered lasers can be shockingly expensive. With newer and newer improvements to the technology, you can expect the cost to go down. Researchers are working to incorporate fiber optic techniques into laser beam transfer. This will surely enhance laser use in metal welding processes.
Why Not Use Arc Welding Instead?
Laser beam welding and arc welding show different rates of energy transfer.
- Laser energy absorption by a material or metal is influenced by several factors (incident power density, laser type, and surface condition of base metal).
- Not only can lasers work outside a vacuum they can work with any kind of material, unlike arcs. You will also not see any x-rays being produced where laser welding is concerned.
Because it is not electrical in nature, laser welding does not need an electric current for it to progress. You will consequently find no magnetism effects while also working with different materials; they do not have to be electrically conductive.
Metals Compatible With Laser Welding:
• Carbon steels
• Stainless steels
• High-strength low-alloy steels
Advantages To Laser Welding:
- Deep and narrow welds are quite possible.
- Does not pose a hassle when working with high-alloy metals.
- No direct contact with materials required.
- Lasers can weld dissimilar metals together.
- You can perform this technique in open air without the need for a vacuum.
- No filler metals are required.
- Thin and/or small components can easily be welded.
- With minimal power loss, laser energy can be transmitted across a distance.
- There is little to no weld distortions.
- You do not need any secondary finishings.
- The heat-affected region is rather narrow.
- Not only can you perform high quality welds the process itself is very accurate.
- The total thermal input is quite low.
Disadvantages To Laser Welding:
- High maintenance expenses.
- Equipment is quite costly.
- Some metals can crack under rapid cooling rates used in certain laser welding sub-techniques.
- The laser’s optical surface is not strong and can be easily damaged.
Specialized Laser Welding Techniques:
- Soldering & Brazing: where a filler is melted by the laser beam via edge wetting of the joint without melting the base material. The leads in electronic boards have been joined using this technique (founded in the 1980’s).
- Twin Beam Welding: where two laser beams are simultaneously used to gain access to two possibilities, namely controlling weld bead shape and weld pool geometry. High reflectivity materials like copper and aluminum showed better coupling with the combination of an eximer and CO2 laser beam.