Product identification made by fiber lasers.

High-contrast marks made by a fiber laser.


Fast-paced developments have increased the power levels and improved the beam quality of fiber lasers, and are expanding their range to include high-contrast, indelible marking — computer-generated text, graphics and bar codes — on metals.

Laser marking uses lamp-pumped lasers, diode lasers or fiber lasers, and has distinct advantages over other marking methods:

  • The process is fast, sharp and accurate.
  • Marks can be changed quickly by computer without re-tooling.
  • It does not add excessive heat to the product.
  • And, as a non-contact application, it generates no physical deformation or chemical change to the product.

The most commonly used laser marking techniques, engraving and ablating, are used to produce computer-generated vector or bitmap patterns on metals, and leave minor amounts of debris.

Engraving typically is done at high power densities that require high energy, pulsed laser systems. The laser's power density is intense enough to partially vaporize metals, developing a colorless impression on the material. However, this process produces debris — fine metallic particles — that can be detrimental because unwanted material is deposited on sensitive parts such as electronics, medical devices, or metal bearing housings.

Control Micro Systems Inc. (www.cmslaser.com) says it has solved this problem by using a 100W continuous wave/modulated, water-cooled fiber laser manufactured by SPI Lasers UK Ltd. (www.spilasers.com) in Control Micro's customers use to engrave metal bearing housings.

Bearing manufacturers have stringent requirements for process debris because of the damage the debris can cause to bearings. Because of that potential for damage, marking bearing housings with lasers traditionally combines a "minimal" engraving process with an induced change in surface color. Until recently, Control Micro Systems provided Nd:YAG lasers to do this.

Recently it found that it could use a fiber laser more commonly designated for welding and cutting tasks and apply it to metal marking. Control Micro Systems says its 100W SPI fiber laser produces the same thermally induced, high-contrast mark on the bearing housing but without the amount of debris generated by the Nd:YAG lasers.

The company says the 100W SPI fiber laser also costs less, requires less maintenance and is more reliable.

Advantages of fiber lasers
Several types of lasers now are used in many materials processing applications, but it is fiber lasers that have revolutionized many of these applications through a combination of improved optical performance, better systems flexibility, high component yield, long uptime and improved reliability.

The spot size of fiber lasers is small, predictable and consistent at all power levels across all pulse sequences and during the entire life of the laser — a feature critical to many marking applications.

Fiber lasers can produce better results faster and at lower power levels because of their small spot size and high beam quality. Beam quality is determined by a ratio of the beam width and divergence angle of the actual beam to that expected for a perfect beam.

The focused beam treats a small area of material consistently, and little heat is generated in the surrounding area. This means that high quality precision marking and welding and cutting can be performed to within 0.1 mm of intricate component parts without causing distortion or potential damage to the other parts.

Speed of technology advances
Improvements that have been made in the lifespan of diodes are indicative of the speed at which laser technology is advancing. In 2005, the Welding Institute reported that fiber lasers could operate 100,000 hours before the laser diode pump needed maintenance or failed. In 2006, SPI Lasers says the individual diodes of its 100W, continuous wave/modulated, watercooled fiber laser have a life of 400,000 hours, and that the combined optical system can operate 30,000 hours without maintenance.

Compact size
Fiber lasers also are compact. For instance, a 7-kW Ytterbium-fiber laser can have a footprint of 10.76 sq. ft., making it easily transportable. Fiber lasers now are being used for mobile applications such as in-field pipe welding and remote site cladding. However, TWI reports that fiber lasers and air-cooled diode lasers are more sensitive to ambient temperature than lamppumped lasers, so cooling devices may be needed when fiber lasers are being used and the ambient temperature exceeds 93 degrees F.

Laser-helper

TherMark Holdings Inc. (www.thermark.com) has a different approach to laser marking. The company's process for high-contrast, permanent, highresolution marks on metals combines lasers with inks that form a permanent, chemical bond to a surface after laser fusing.

Specially formulated black or dark grey ink in liquid or paste forms is brushed, sponged or air sprayed onto metal surfaces and allowed to dry. A laser is used to fuse the paint to the surface. After fusing, any excess ink is cleaned from the surface by rinsing it with water.

Different colors are available to mark glass, ceramics, porcelain, crystal, plastics, marble and granite.

The company says the marks produced by its system are highly resistant to mechanical and chemical abrasion, high temperatures, corrosion, sea water and salt spray, deep space and other environmental elements.


The word "laser" is an acronym for light amplification by stimulated emission of radiation. Fiber lasers are solid-state lasers that use optical fibers doped with a rare earth element as the lasing medium, reports G. Verhaeghe of the The Welding Institute Inc. (www.twi.co.uk). Laser diodes stimulate the lasing medium to emit photons — called pumping — at a wavelength specific to the lasing medium. Lowrefractive-index material surrounds the doped fiber to act as a waveguide for the pumping light and to ensure optimum transfer of the energy to the lasing medium.