How laser types, marking goals, and material choice affect metal marking.
Laser engraving metals with barcodes, serial numbers, and logos are very popular marking applications on both CO2 and fiber laser systems.
Thanks to their long operational life, lack of required maintenance and relatively low cost, fiber lasers are an ideal choice for industrial marking applications. These types of lasers produce a high-contrast, permanent mark that does not affect part integrity.
When marking bare metal in a CO2 laser, a special spray (or paste) is used to treat the metal prior to engraving. The heat from the CO2 laser bonds the marking agent to the bare metal, resulting in a permanent mark. Fast and affordable, CO2 lasers can also mark other types of materials – such as woods, acrylics, natural stone, and more.
Both fiber and CO2 laser systems manufactured by Epilog can be operated from almost any Windows-based software and are exceptionally easy to use.
Because different types of lasers react differently with metals, there are some considerations to be made.
More time is required for marking metals with a CO2 laser, for instance, because of the need for coating or pre-treating with a metal marking agent. The laser must also be run at a low-speed, high-power configuration to allow the marking agent to adequately bond with the metal. Users sometimes find that they are able to wipe off the mark after lasering – an indication that the piece should be run again at a lower speed and higher power setting.
The advantage of metal marking with a CO2 laser is that the mark is actually produced on top of the metal, without removing material, so there is no impact on the metal’s tolerance or strength. It should also be noted that coated metals, such as anodized aluminum or painted brass, do not require pre-treatment.
For bare metals, fiber lasers represent the engraving method of choice. Fiber lasers are ideal for marking many types of aluminum, brass, copper, nickel-plated metals, stainless steel and more – as well as engineered plastics such as ABS, PEEK and polycarbonates. Some materials, however, are challenging to mark with the laser wavelength emitted by the device; the beam can pass through transparent materials, for instance, producing marks on the engraving table instead. While it’s possible to achieve marks on organic materials such as wood, clear glass and leather with a fiber laser system, that’s not really what the system is best suited for.
Types of Marks
In order to best suit the type of material being marked, a fiber laser system offers a range of options. The basic process of engraving involves the laser beam vaporizing material from the surface of an object. The mark is often a cone-shaped indentation, due to the shape of the beam. Multiple passes through the system can create deep engraving, which eliminates the possibility of the mark being worn in harsh-environment conditions.
Ablation is similar to engraving, and is often associated with removing a top coating to expose the material underneath. Ablation can be performed on anodized, plated and powder-coated metals.
Another type of mark can be made by heating the surface of an object. In annealing, a permanent oxide layer created by exposure to high temperature leaves a high-contrast mark, without changing the surface finish. Foaming melts the surface of a material to produce gas bubbles that get trapped as the material cools, producing an elevated result. Polishing can be achieved by quickly heating a metal surface to change its color, resulting in a mirror-like finish. Annealing works on metals with high levels of carbon and metal oxide, such as steel alloys, iron, titanium and others. Foaming is typically used on plastics, although stainless steel can also be marked by this method. Polishing can be done on just about any metal; darker, matte-finish metals tend to yield the most high-contrast results.
By making adjustments to the laser’s speed, power, frequency and focus, stainless steel can be marked in various ways – such as annealing, etching and polishing. With anodized aluminum, fiber laser marking can often achieve much higher brightness than a CO2 laser. Engraving bare aluminum, however, results in less contrast – the fiber laser will create shades of gray, not black. Still, deep engraving combined with oxidizers or color fills can be used to produce a black etch on aluminum.
Similar considerations must be made for marking titanium – the laser tends to create shades from light gray to very dark grey. Depending on the alloy, however, marks of various colors can be achieved through adjusting frequency.
Best of Both Worlds
Dual-source systems can allow companies with budget or space limitations to increase their versatility and capabilities. It should be noted, however, that there is a drawback: when one laser system is in use, the other is unusable.
For more information on marking metal with a laser machine, contact us to set up a demonstration with the distributor in your area.