Laser beam welding

Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.

Operation

Like electron beam welding (EBW), laser beam welding has high power density (on the order of 1 Megawatt/cm²(MW)) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized when the focal point is slightly below the surface of the workpiece.

A continuous or pulsed laser beam may be used depending upon the application. Milliseconds long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds.

LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry. [Cary and Helzer, p 210] [Weman, p 97]

Some of the advantages of LBW in comparison to EBW are as follows: the laser beam can be transmitted through air rather than requiring a vacuum, the process is easily automated with robotic machinery, x-rays are not generated, and LBW result in higher quality welds.

A derivative of LBW, laser-hybrid welding, combines the laser of LBW with an arc welding method such as gas metal arc welding. This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced. [Weman, p 98]

Equipment

*The two types of lasers commonly used in are solid-state lasers and gas lasers (especially carbon dioxide lasers and lasers).
*The first type uses one of several solid media, including synthetic ruby and chromium in aluminum oxide, neodymium in glass (Nd:glass), and the most common type, crystal composed of yttrium aluminum garnet doped with neodymium (Nd:YAG).
*Gas lasers use mixtures of gases like helium, nitrogen, and carbon dioxide (CO2 laser) as a medium.
*Regardless of type, however, when the medium is excited, it emits photons and forms the laser beam.

olid state laser

Solid-state lasers operate at wavelengths on the order of 1 micrometer, much shorter than gas lasers, and as a result require that operators wear special eyewear or use special screens to prevent retina damage. Nd:YAG lasers can operate in both pulsed and continuous mode, but the other types are limited to pulsed mode. The original and still popular solid-state design is a single crystal shaped as a rod approximately 20 mm in diameter and 200 mm long, and the ends are ground flat. This rod is surrounded by a flash tube containing xenon or krypton. When flashed, a pulse of light lasting about two milliseconds is emitted by the laser. Disk shaped crystals are growing in popularity in the industry, and flashlamps are giving way to diodes due to their high efficiency. Typical power output for ruby lasers is 10–20 W, while the Nd:YAG laser outputs between 0.04–6,000 W. To deliver the laser beam to the weld area, fiber optics are usually employed.

Gas laser

Gas lasers use high-voltage, low-current power sources to supply the energy needed to excite the gas mixture used as a lasing medium. These lasers can operate in both continuous and pulsed mode, and the wavelength of the laser beam is 10.6 μm. Fiber optic cable absorbs and is destroyed by this wavelength, so a rigid lens and mirror delivery system is used. Power outputs for gas lasers can be much higher than solid-state lasers, reaching 25 kW. [Cary and Helzer, p 209]

ee also

* Laser cladding

References

*Cary, Howard B. and Scott C. Helzer (2005). "Modern Welding Technology". Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
*Weman, Klas (2003). "Welding processes handbook". New York: CRC Press LLC. ISBN 0-8493-1773-8.
*Kalpakjian, Serope and Schmid,Steven R.(2006). "Manufacturing Engineering and Technology"5th ed. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-148965-8

External links

* [http://files.aws.org/wj/supplement/10-2002-XIE-s.pdf Dual beam laser welding; research article from the 2002 Welding Journal]
* [http://files.aws.org/wj/supplement/11-2002-XIE-s.pdf Weld morphology and thermal modeling in dual-beam laser welding; research article from the 2002 Welding Journal]
* [http://www.industrial-lasers.com/laser-welding/index.html Laser welding articles from the Industrial Laser Solutions Magazine]
* [http://www.fraunhofer.de/fhg/Images/magazine1-2005-36f_tcm6-14041.pdf Laser-beam welding makes aircraft lighter;] Fraunhofer Society [http://www.iws.fraunhofer.de/e_welcome.html Material and Beam Technology - IWS] , Dresden, Germany (1 January 2005)
* [http://www.twi.co.uk/content/laser_welding.html Laser welding of thick sections, aluminium, plastics etc.]

Notes