Setup requires the import of a graphic file; the machine generates the marking program.Click image to enlargeShop Metalworking Technology discusses laser marking with Thomas Burdel, national sales manager for TRUMPF Inc., Farmington, CT.

How does laser marking differ from industrial laser cutting?
Laser cutting uses a tremendous amount of power–several thousand watts is not uncommon–to melt a narrow line in sheet steel or aluminum. The molten material is then ejected through the bottom of the kerf using compressed air or gas, separating the finished workpiece from the raw material. With laser marking, you don’t cut through the part, so the power levels are far lower, typically 50 watts or less is sufficient. Both processes may use solid state lasers, but marking generally employs wavelengths of 355,532, or most often 1064 nanometers (ultraviolet and green light) compared to a laser cutter’s 1064 nm infrared wavelength only. Finally, almost all laser markers use pulsed light rather than continuous wave, and are much smaller, stand-alone devices, roughly the size of a shoebox.

What materials can be laser marked?
Simply put, nearly everything. Laser marking works on metal, plastic, silicon, glass, rubber, textiles, and even organic material such as paper and wood. Depending on the amount of power being applied and its duration, it’s possible to remove substantial amounts of material, or touch it only gently enough to change its colour. For example, laser light can be used to bleach or blacken a wide range of polymers. There’s no heat or ink involved, and it’s extremely fast. The colour change is similar to what happens when plastic is left in sunlight for a long period of time, except here it’s instantaneous. Annealing is a similar process, one that is frequently used on metal. The workpiece is heated enough to create a colour change, but there is no material removal, leaving the surface smooth. Apply slightly more power and ablation occurs, which removes a thin top layer of material. This works very well on parts that have been painted or anodized. Engraving removes even more material. By using a high power laser (or moving slowly with a low power one), very deep marks are possible. Some less common processes include foaming, which uses a laser to create small gas bubbles beneath the surface of a plastic workpiece to create a raised mark, and surface conditioning, where marking lasers are used to remove rust and corrosion from various materials.

 

Who uses laser marking, and why?
Anyone that wants to mark something quickly and needs it to be difficult to remove. Compared to inkjet markers, laser marking is far more permanent. Mechanical marking is noisy and limited to metals. Lasers are the perfect tools for marking nearly anything. Many of our systems are used for placing an identification mark–a logo or serial number, for example–on medical components. These might be for pacemakers, or knee and hip implants, and are typically low volume applications, so are done on stand-alone stations. Another medical example is pharmaceuticals, where testing kits or pill bottles are sold to large retail chains and must be marked with a data matrix for traceability. This is a perfect use for laser coloring on an automated packaging line, since it is very fast and has no impact on the base material. Of course, we also provide systems to aerospace and defense companies, consumer products manufacturers, and especially the automotive industry, where cost effective solutions are always an important concern.

 

How much do they cost, and what should I know before buying one?
It all comes down to what you’re marking, and how fast you need to mark it. Laser power is probably the first question. You can engrave most any metal with a very low power laser, but it won’t be very fast. Higher power lasers, however, cost more. For simple applications such as basic marking of metal or plastic, you’re probably looking at $30,000 for a basic system. For those doing special marking, say the UV colour changing mentioned previously, it could get up in the $150,000 range. Integration to a high volume production system may cost substantially more than that. Granted, these are substantial investment amounts, but offsetting that are the very low operating costs down the road, often just a few dollars per hour. As for any application concerns, there really aren’t any. Some aerospace suppliers may be anxious over the heat affected zone (HAZ) associated with laser use, but even deep engraving operations create only a small amount of annealing.

 

Aren’t lasers difficult to operate?
Lasers were once considered “laboratory only” instruments, but that viewpoint has changed considerably over the past 30 to 40 years. Cutting lasers today require some small amount of maintenance and a higher skill level to operate, but laser markers are very simple; they’re almost like using a laser printer. These machines are shipped with predetermined operating parameters for different materials, so setup requires little more than an import of the desired graphic file such as a DXF, JPG, or PDF, and then generate the marking program. It’s very quick. About the only maintenance that’s required is to keep the operating area and the workpieces fairly clean. There’s no motor or moving parts to worry about, and the laser typically has a lifetime of at least 35,000-50,000 hours. Unless there is some accidental physical damage to the lens, there’s really nothing to ever fix.

 

What does the future hold for laser marking technology?
The market is really growing, pretty much across the board. Automotive, medical, electronics–everybody wants their parts marked cleanly and easily. Companies used to get by with labeling their products, but found that counterfeiters were peeling them off and replacing the labels with their own brand name. And the US FDA has some new requirements about unique part identification, where every part in an assembly had to be identified, rather than just the entire part. We have injection moulding companies that serialize their parts as they pop out of the mould. That’s all done with lasers. The market growth is really fueled by two things: the need, some of which I’ve just described, and the fact that lasers are getting smaller, less expensive, and more flexible. Some of the newer systems have adjustable focal points, making it easy to mark multiple levels on a workpiece. And they’re very easy to integrate with other systems. Considering the increased need for traceability, accountability, and foolproof product information, laser marking has a bright future. SMT

 

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