“When you get into laser marking on plastics, you’re stepping into a tricky realm,” says laser applications guru Josh Christley. “In many ways, it’s totally different from marking metals. Metals are relatively straightforward. But plastics are complex; that’s what makes them so versatile. And with that complexity you get a touch of uncertainty.”

We answer you most frequently asked questions about laser engraving on plastics and what laser engraving/marking machines work best for marking plastics.

TOP TAKEAWAYS

Laser marking can be one of the most successful ways to mark or engrave plastics -- over labels, printing, and other alternatives -- when you are using the right type of laser marking machine for your application.

One of the key features that makes plastics so difficult to mark successfully is the wide variety of compounds available, including polycarbonate, polyethylene, and silicone; furthermore, common fillers, extenders, and additives as well as colors can alsp affect marks on plastics.

To find the best way to laser mark plastics and other materials for manufacturers, the MECCO team uses an evidence-based process to define the requirements, assess technical feasibility, and design a custom solution.

EXPERT Q&A: LASER ENGRAVING PLASTICS

Q: So, laser marking IS a practical solution for plastic parts?

Josh: Oh, of course. It’s been a reliable workhorse across a whole spectrum of industries for decades. Aerospace, medical instruments and devices, semiconductors, automotive manufacturing … every week I see new sub-sectors integrate laser marking with their production lines to engrave plastic parts with text (like serial numbers and part numbers); machine-readable data (barcodes, Unique ID codes, 2D codes); or graphics (logos and other branding marks).   

Compared to lasers, other direct marking techniques like dot peen don’t always play well with plastic shapes and surfaces. And both printing and adhesive labels fall short in terms of cost (think of the consumables), environmental impact, permanence, visibility, speed, flexibility, and maintenance. So laser marking makes a lot of sense, for plastics as well as other materials.

“Accept the fact that no two applications are exactly the same. View any blanket statement about laser marking on plastics with caution.  Realize that your situation is unique, and that it will take some deep analysis to get the right solution.” 

- Josh Christley, Applications Manager, MECCO

Q: But there’s no one-size-fits-all approach for laser-marking plastics, is there?

Josh: Correct. That’s true when you’re marking metals, as well. The same ground rules apply any time you’re looking for a laser system to match your application: For a smooth, low-risk transition to a new technology, the first priority is to connect with a vendor who’s willing to help you deep-dive into your processes, goals, and business. That’s how you get a system that’s going to work for you.

Those are the fundamentals for working with any material. It’s when the material is a polymer or a composite that things start to get interesting.

Q: You’ve said marking metals is relatively straightforward. What makes plastics marking so complicated?

Josh: It’s like the difference between checkers and chess.

To begin, we custom-design every system we build to match the properties of the production material as closely as 21st-century science and engineering allow. Nothing is off-the-shelf. That means we have to know a lot more about your raw material than you might imagine.

Just look at the variety of resins in common use. All the polys: polyamide, polycarbonate, polyethylene, polypropylene, polyoxymethylene, polyarylsulfone, polyether ketone,  polyimide, polystyrene, polymethylmetacrylate, polyester, polyethylene terephthalate. Then you have Delrin, silicone, olefins, butadiene, styrene, and so on. Each behaves in its own way, and each will respond differently to variations in laser type, power setting, and pulse duration.

Another twist: Any of those compounds can behave differently from batch to batch, especially if re-ground resins go into the mix.

Furthermore, material from one resin manufacturer may vary, in some subtle way, from another maker’s nominally similar product. That’s why, when our manufacturing partners change suppliers, I always advise them to ship us a sample run of parts made from the new material. Our Quality Assurance lab will test the new parts under the same conditions that applied when we designed the customer’s system, and raise a flag if any concerns arise. Later on, our archive of physical samples and consistent test data can help your in-house troubleshooters track down causes and cures for any production-line irregularities that might pop up.

Q: But that just covers the pure resin. What about fillers, extenders, and other additives that efffect marking on plastic?

Josh: For reasons unrelated to marking, resins usually contain additives selected for the specific part, product, process, and price point. Not uncommonly, production materials contain 50 percent or more of fillers like calcium carbonate, calcium metasilicate, talc, mica, or gypsum, or even glass fibers. All of the above —and more — can affect the interaction of laser and plastic. Additives optimize the material for its purpose, but they also present the laser system designer with another set of variables.

Have I mentioned color yet? Let me give you just two examples: A fiber laser, for instance, can’t effectively mark white Delrin or clear polypropylene because the fiber wavelength — 1,064 nm — passes right through the material. The same laser can, however, put a legible, khaki-colored mark on Delrin that’s been pigmented with light-absorbing carbon black. 

Another solution might be to coat a white or transparent part with a clear, nanoparticle-bearing polymer film that selectively absorbs the appropriate wavelength.

Color is hardly ever a trivial issue, however. Factors like customer specs or pre-existing FDA approvals can make a color change impractical. Instead, you and your laser tech partner may rethink your choices of power setting, laser type, or marking effect.

Q: What do you mean by “rethink your choice of marking effect” when marking on plastics?

Josh: Depending on the wavelength of the light, the delivered wattage, and the composition of the surface itself, laser markers work by producing a variety of controlled changes in color or texture on or in plastic surfaces. The effects include:

Ablation or vaporization

Foaming or frothing

Chemical or molecular alteration

Charring

Engraving

Melting

Engineering or esthetic considerations may dictate the best marking effect for the job, although certain combinations of laser technology and surface materials may narrow the range of options.

Q: What type of laser marking machine should manufacturers use to mark or engrave plastics?

Josh: There’s no single class of lasers that’s ideal for all applications. For marking plastics, the MECCO team usually recommends a system built around an industry-tested technology. 

Laser Marking Plastics? Learn About Plastic Engraving Machines 

CO2 Laser Marking Machine: Rliable, cost-effective performance and high-quality marking for plastics and a wide range of other materials. CO2 marking is a low-risk solution when you’re replacing other marking technologies, such as dot peen or non-permanent methods like ink jet or labeling.

Green Laser Marking Machine: Best for materials too thin or heat sensitive for a CO2 laser. Green lasers operate at 532 nm, and with this lower wavelength you get a higher absorbtion rate than you would with a CO2 laser. That means they are less likely to burn the surrounding material because they produce less heat. And the SMARTmark Green Laser is capable of reaching a maximum power output of 20W, more than three times that of other green laser marking technologies.

UV Laser Marking Machine : Well-suited for marking heat-sensitive materials, including a number of plastics, from HDPE and silicone to polycarbonate and polyethylene. With a wavelength of only 355 nm, this UV laser can create ultra-fine marks with high contrast. Medical device manufacturers like UV lasers for their ability to make hygienic marks, and automotive companies can use them for a wide variety of parts. 

Fiber Laser Marking Machines: When high contrast and minimal surface disruption are critical, conventional fiber and diode-pumped lasers are two proven alternatives.

Q: It sounds like the range of variables and possible solutions is staggering. How do you even begin to sort them out?

Josh: In some ways, it’s as simple as the first question most customers ask: “Can you mark my plastic?”  

In response, we’ve developed a system we call The MECCO Experience that leads our team and the customer through a logical decision-making process. We have a process for rigorously defining the requirements, assessing their technical feasibility, and designing a custom solution.

Every step is evidence-based. We not only test each customer’s material before we even think about selling a machine; we make a point of testing the exact product or part that will come down the production line. That means we have to find out how many resin vendors supply the project, and test samples from each vendor. With test results in hand, we may investigate possible changes in material composition or color for better performance.

Along the way, we’ll ask about things you may not have had on your radar. For example, how hot will your part be when it reaches the marking station? Odd as it may sound, temperature matters. Manufacturers often want to mark the part with a “born-on” date right away. But some plastics — say, in the molding industry — take time to cool down, cure, and stabilize. The room-temperature sample part we test in the lab may respond to marking differently from the same part right out of the mold.

Details, details. Anyway, whichever laser system vendor you work with should provide equivalent levels of service, analysis, and attention to detail.

Q: Anything you’d like to add to help de-mystify laser marking on plastics?

Josh: As I said: Yes, there are a lot of variables to consider. But the potential rewards of laser marking plastics — cost savings, productivity, reduced risk and down time — are huge.

Just being aware that there is complexity, and that there’s no such thing as a quickie, one-size-fits-all solution, is an important first step. Laying the groundwork, doing your homework, getting expert advice will pay off. It is do-able, one small step at a time.