Today, in nearly every industry, there is an increasing demand for cost-effective metal marking solutions. Whether manufacturers need to mark parts with unique identification (UID) marks for tracking purposes, mark barcodes for serialization regulations, or even mark logos or text for branding initiatives, the need for convenient and effective metal marking solutions has never been greater.
While nd:YAG lasers were once the most highly sought-after equipment for marking bare metals, emerging technologies have brought to the table some very effective and, in some ways, better alternatives to this traditional method. One of the most popular alternatives to nd:YAG technology is fiber lasers.
First developed in the late 1980s for communication and military applications, the fiber laser is a relatively new class of laser used for marking applications. Essentially, it is a fiber optic cable that has been doped with Ytterbium. By pumping the fiber optic cable with light to excite the Ytterbium, the optic cable is able to act both as the laser source and as the delivery system for the laser beam.
A fiber laser emits a wavelength between 1,055 to 1,070 nanometers in the infrared range similar to YAG lasers. Until recently, the fiber laser was only available in a continuous-wave mode, not pulsed. Today, however, the high per-pulse energy of fiber lasers and the much smaller wavelength is what makes marking on metal feasible.
“Since Epilog brought our first fiber laser system to market in 2006, we’ve been harnessing that laser technology for commercial and industrial applications where metal marking capabilities are in high demand,” said Bob Henry, FiberMark product manager.
Metal marking techniques
While used for a myriad of purposes, Epilog has found that most metal marking is done through three techniques: etching, polishing and annealing. The differences between these different effects can be found in their speed, power and frequency settings dictated by the laser operator.
Etching is often used for industrial purposes – marking tools or parts with serial numbers, logos and bar codes. The etching process using fiber laser systems actually removes small amounts of material from the sample. Material is removed to create whatever mark the user desires. Essentially, it is a very shallow engraving that produces a high-contrast mark in the metal.
Polished metal, or ‘mirrored’ as it is sometimes called, is a laser effect where the laser beam heats the surface of a material and as it cools, the material takes on a different finish than the surround material. Most common on matte-finish metal, this technique creates marks that can look almost holographic. Unlike etching, no material is actually removed from the metal being marked – it is the heat that alters the finish of the metal. Since the polished look emits a sense of sophistication and distinction, it is often used in architectural signage or other applications where a unique or aesthetically pleasing mark is necessary. The mirrored finish produces a tone-on-tone look where the metal has been marked.
Annealing is the term used in the industry to describe a smooth, black mark on the surface of some metal materials. This marking process is achieved through changing the focal distance between lens and material, thereby working within a slightly wider spot of the laser beam. The resultant mark is actually a dense, black oxide layer that is created on the surface of the metal. By changing the frequency of laser output, some material will exhibit colors such as greens, blues and yellows.
Since no material is removed during this marking process, it is typically used in medical device marking applications. Depending on the metal type, annealing will generally produce the darkest fiber laser mark.
Streamlining the process
For over 25 years, Epilog has been designing and manufacturing CO2 laser systems that can engrave and cut wood, acrylic, plastic, fabric, rubber and many other non-metallic materials. During those years, the company cultivated a deep understanding of metal marking to drive technology that could streamline the process.
Because of the CO2 laser’s wavelength, it is difficult to mark directly on untreated metal, Henry explained. When using a CO2 laser for metal marking, the metal must first be coated with special metal marking material and then lasered. And though permanent marks can be produced using a CO2 laser, many users prefer the ease of direct marking that fiber lasers provide.
“That’s where the need for fiber lasers comes in,” said Henry. “The advanced, yet easy-to-use technology allows the laser to mark metals with no additional coatings and therefore increases the potential for product throughput. And what manufacturer can’t appreciate that?”
Overall, fiber-equipped laser systems allow users to quickly and effectively perform metal marking applications more easily than ever before. Epilog’s two fiber laser systems, the FiberMark and FiberMark Fusion, incorporate significant marking areas, 24-in. x 12-in. and 32-in. x 20-in., respectively. They also incorporate state-of-the-art fiber laser technology with flying optics beam delivery to create a system that is economical, intuitive and advantageous over traditional nd:YAG galvanometer-based beam delivery systems.