Acrylic (also known as Lexan, Plexiglas, Lucite, Acrylite, Optix) is an awesome plastic for laser cutting. It comes in a variety of colors, finishes, and opacity. It's also pretty easy to work with, so with a little heat or a bit of a welding chemical, you can form it into almost any shape you'd like. You can also get specialty acrylic with mirror finishes, metallic finishes, and fluorescent colors. That being said, working with acrylic for custom laser services is much different than using a laser for etched wood. Using acrylic for laser cut signage opens up a ton of creative options when laser cutting signs as you can see in our portfolio.
One of the reasons we bought one of the biggest CO2 laser cutters (Kern HSE) is that it can cut up to 1.25" acrylic with a smooth as glass flame polished edge. That being said, working with acrylic takes a bit of practice. Laser engraving acrylic can produce mixed results if you don't do it properly, and laser cutting acrylic can be even more difficult.
These are a few things we've learned along the way.
Flashback is the term used to describe when the laser beam cuts through the material but hits the laser bed causing heat to reflect onto the back of your work surface. This can produce a haze on the backside of your acrylic, which is especially pronounced with clear acrylic. In a worst case scenario, the flash can get so hot during laser cutting (something we have to be mindful of with our 500-watt laser cutter) that it can cause a fire. The easiest solution for avoiding flashback is to raise the acrylic off the laser bed. Kern sells these great, cone-shaped standoffs that raise the acrylic up a bit off the bed. By the time the laser beam hits the bed, it has come out of focus enough not to cause much heat build up. Additionally, the cone shape of the standoff reflects the laser beam away from the backside of the acrylic, so your laser beam is harmlessly reflected into the bed. If you don't want to shell out the money for milled standoffs, you can also use golf tees (Yep, we've used them) or small blocks of wood (we have a bag of 1/2" wood spacers right next to our lasers). You just place them underneath the acrylic in places where it won't touch the cutting path of the laser.
Additionally, when cutting materials that are translucent, we'll also leave the paper (or plastic) protective film on the bed-side of the acrylic to provide a little additional protection. Just be mindful to watch for flare-ups as the paper backing is flammable.
One of the great things about our big laser is because it is so powerful that when we are laser cutting of acrylic, the edges come out great. However, you can get an even better result if you slow the laser down so that heat builds up in the cutting kerf. So, if we normally would just cut the acrylic at 75 power and say 2 inches per second, we would slow the lasercutting speed down to half of that. That allows the cut to build up a bit more heat, effectively melting the laser cut surface. For lower power lasers (like our Epilog Helix 50w), you can get close to flame polished edges by slowing down the laser cutting speed below the recommended cutting settings from the manufacturer. You won't really get flame polished edges, but it will still look pretty good!
Lastly, you can buy a MAP torch and do it yourself after the acrylic is cut. Just do a google search on how to flame polish acrylic with a MAP torch and you'll see what I mean.
Probably the most important tip is never to leave acrylic to cut unattended. Recently a friend of ours had their laser catch on fire when they left some acrylic cutting unattended. Acrylic is combustible, so you must keep a close eye on it when it's cutting. Any fire we've ever experienced was during an acrylic cutting job. We will keep a compressed air line close to the laser so that if it starts to flare up, we can blast it with high-pressure air to put the flame out before it gets out of control. If you have your workpiece on standoffs, even better as you can blow the air under the piece to put out any flare-ups on the backside. For a closed system where this isn't possible, keep a Halotron extinguisher close, and never leave the system unattended.
Most lasers come supplied with a device to properly set your laser focal depth. Our Epilog Laser has the added bonus of an autofocus plunger that makes things even easier. Whenever we engrave or laser etch acrylic for signs or laser engraved artwork, we'll focus the lens, then back it off about .2". This spreads out the 'hot spot' of the beam, melting the acrylic as it etches (a bit). This gives you a much smoother engraving and has the added bonus of cutting down on dust from acrylic engraving.
CO2 laser engravers can engrave with insane detail. This is called DPI (dots per inch). The higher the DPI, the more detailed the laser engraving. Typically when laser etching acrylic, you'll want to run at 600 dpi. If you run at this resolution and blur your lens a bit, you'll get a much cleaner engraving. If detail isn't super important (say for business signs that just have text or simple graphics), you can run at 300dpi, but we never recommend going any lower. With a lower dpi, your laser is laying down fewer "dots" so the job will run much more quickly.
There are two types of acrylic, cheap extruded acrylic (like you would get at a home center) and higher quality cast acrylic. We always use cast acrylic as it cuts much better and looks fantastic when engraving. Extruded acrylic looks horrible. Cast acrylic is a bit more expensive, but the end result is worth the extra expense!
Thanks for reading, if you have any questions or need any acrylic laser cut, hit us up through our contact page.