Acrylic is highly regarded as one of the most popular materials in the industry. It’s a beautiful material with high-end appeal, yet it is still an affordable option for many customers. The applications for this material are seemingly limitless and include product categories such as awards, gifts, signage and more. Take a look at catalogs from acrylic product suppliers and you will find pages and pages of unique designs that will appeal to high-end markets, such as corporate awards, as well as to more budget-conscious clients like school sports leagues. On top of that, acrylic engraves beautifully. Using a laser or a rotary engraving machine, you can achieve truly outstanding engraved images from intricate logos to the super fine details of a photograph.
You can choose from the always-popular clear acrylic or, for a different look, try something tinted with a color like sapphire (blue), jade (green), red or gold. Opaque colors are also available and include white, black, brown, blue, red, etc. Mirrored accents are also a very popular option. Manufacturers will laminate or glue mirrored material onto the top, bottom or sides of an acrylic product to create interesting, colorful reflections and accents that add a touch of distinction. Screen printing is another method used to add color to acrylic. This technique can be used to create colorful patterns, such as a black and blue marble, on the back of an award. Acrylic also looks stunning when paired with other materials, such as metal or wood bases or accents.
As mentioned, acrylic products can be personalized with a laser engraving machine or a rotary engraving system. Following is a look at both of these methods and some tips for getting the best results.
Acrylic is unique in that it is highly sensitive to absorbing certain wavelengths of light. One highly absorbed wavelength of light energy is 10.6 microns which, coincidentally, is the exact same output frequency of a CO2 laser. When exposed to a laser beam, acrylic acts like a sponge and essentially soaks up the laser energy. Even low watt lasers—as low as 10 watts—can produce excellent engraved results (albeit slowly) as the laser vaporizes the material.
Fine Tuning the Layout
Acrylic products can be engraved on the front or the back so the engraving can be viewed through the acrylic. Engraving the back of an acrylic piece is often preferred because it gives the item a dimensional quality that really enhances the look of the material. If you do this, however, remember that the graphics and text should be reverse-reading to make them read correctly from the front. You can use the “mirror” function in CorelDRAW (or your engraving software) to easily accomplish this. The difficult part is remembering to do it; it’s a much more common mistake than you might think. (Note: This is also true for rotary engraving.)
When setting up a job to be laser engraved, follow the old carpenter’s rule “measure twice, cut once,” especially when engraving expensive acrylic items. One way to check your layout skills is to apply a green-tinted polyester mask to the acrylic piece and use very low power, e.g. 5% power and 100% speed on a 30 watt laser system, to cut only the mask (not the acrylic). Once you are satisfied the image will engrave in the correct location, remove the mask and engrave at the correct power and speed settings for acrylic.
Fine Tuning the Laser Settings
Laser engraving acrylic is usually problem-free but you might, on occasion, run into some problems. A common complaint from people who laser engrave large fill areas is the appearance of horizontal “raster” lines that make the engraved areas appear coarse. These raster lines create a horizontal, linear pattern where the lasered dots slightly overlap. To reduce the appearance of raster lines, try enlarging the spot size of the focused laser. The focus lens creates a cone-shaped beam that gets larger the more distance there is from the optimum focus point. If you lower the engraving table by .020", the spot size of the laser is increased slightly which, in turn, increases the overlap of each of the raster strokes and creates smoother engraving.
Generally speaking, acrylic engraves best using high speed and low power. If you are engraving acrylic that is painted or screen printed on one side, use the same speed setting as you would for unpainted acrylic but turn up the power about 10%. That should allow the laser to cut cleanly through the paint.
On some occasions you may experience problems such as cracking, melting or hazing which usually indicates that there is too much heat present. To remedy this, try decreasing the power and/or increasing the engraving speed. Optimum power and speed settings will depend on the acrylic you are engraving and your laser system. Figure 1 shows some general starting guidelines.
A laser can also be used to cut completely through (profile) acrylic using an operation called “vector cutting” because the laser is set to move using an X-Y motion path. Vector cutting provides first-rate quality once you understand a few tricks of the trade. These tricks involve preparing the acrylic sheet, setting it up properly on the engraving table and adjusting some print driver settings.
All acrylic sheets come with a factory-applied paper mask designed to protect the polished surfaces during handling and fabrication. This brown paper, however, contains paraffin that can cause charring and excessive flame-ups during cutting that could damage the acrylic. To prevent this, always remove the mask and replace it with a medium tack paper mask (available from engraving suppliers). The paper mask protects the acrylic surface, cuts cleanly and can be easily removed after the acrylic is cut. Lightly misting the mask with water will also help draw heat away from the surface of the acrylic.
Next, it is a good idea to elevate the acrylic sheet above the worktable. The laser energy is not absorbed by the metal table of the laser system but instead, it reflects off of it which can burn the bottom side of the acrylic and cause pitting and distortion. Creating an air space between the acrylic and the table can dissipate this reflected light and thereby improve the cut.
You can use either shims or a vector cutting table to accomplish this. If you use shims, it’s a good idea to place a metal back-up plate beneath the material. This improves the quality of the cut and saves you from repeatedly cleaning the worktable. Vector cutting tables, available from laser manufacturers, are designed specifically for this purpose and are a good accessory to have if you do a lot of cutting with your laser. A vector cutting table is essentially a metal honeycomb grid that creates air space to dissipate the reflected beam and increase the air flow to reduce flame-ups.
Most laser machines also have an air assist feature, either as a standard feature or an option. An air assist system directs a constant stream of compressed air across the cutting surface which can reduce flaming, scorching and charring.
With regard to the machine settings, use a slow speed and a high power setting for vector cutting (profiling) acrylic. This allows the edges to melt and produces a flame-polished effect.
Keep in mind also that the laser beam does not emit a constant stream of light when it is cutting. In reality, it is being pulsed at a high frequency of up to 2,000 times per second. You can control the frequency that the laser switches on and off by adjusting the “rate” or “PPI” (pulses per inch) setting in your laser’s print driver. Using a high or maximum rate or PPI setting causes the laser to pulse more frequently and will give the effect of a fine-tooth saw blade, resulting in much smoother cuts (Fig. 2).
Depending on the wattage of your laser and the thickness of the acrylic sheet you are cutting, you might need to make more than one pass in order to achieve a clean edge cut. The higher the wattage on your laser, the deeper and quicker you can cut. For example, a 30 watt laser can cut through 1/4" thick acrylic in one pass, but a 50 watt laser can cut it faster and can also cut thicker pieces in one pass.
If you do need to make multiple passes, keep in mind the issue of focusing the laser. For example, if the laser is focused on the material surface during the first cutting pass, the beam may be out of focus during the second pass unless you refocus between passes. If the beam is out of focus, you have to burn through more material which takes more time and can cause a poor cut. Most of today’s laser engraving systems offer an auto-focus feature that takes care of this for you. The feature allows you to predefine focus depth changes from within the software in order to automatically cut thick materials in multiple passes with a focusing depth change between passes.
You can also use a rotary engraving machine to engrave acrylic with beautiful results. Unless you are profiling or making extra-deep cuts, standard tooling and engraving techniques (like what you would use on conventional plastic engraving stock) should work fine. You usually don’t need a coolant, and if you use a sharp carbide cutter, you can front- or reverse-engrave acrylic with stunning visual appeal and exceptional dimensional accuracy.
Cutter Selection & Engraving Depth
For conventional rotary engraving on acrylic, select a standard 60 degree included angle cutter and engrave at minimal depth. This creates an engraving with a “flat” look that is non-dimensional and appears flush with the material surface (Figs. 3 and 4). Keep in mind, though, that if you plan to color fill the characters, you need to engrave at least .006"-.008" deep (.010"-.012" is optimum).
If you want to achieve a more dimensional look in the characters and graphics, you will want to create V-grooved letters that have a smaller flat on the bottom and a wide groove at the mouth (Figs. 3 and 4). Front-engraved dimensional letters appear as deep V-grooves; reverse-engraved dimensional letters look as though they are raised when viewed from the front.
To create this look, choose a cutter with a 90 degree included angle and a small tip size. With this larger cutter angle, the deeper you engrave, the wider the mouth of the groove becomes. Even slight increases in depth can produce noticeable differences, so after you select the typestyle, set the depth to achieve the look you want.
If you have three-dimensional engraving capabilities, you will no doubt want to use them on acrylic. Three-dimensional designs look stunning on acrylic, especially when reverse engraved (Fig. 5).
For a slightly different effect, you might want to try using a slightly dull cutter to engrave acrylic. This produces bright white lettering and graphics that really stand out, similar to the look created by laser engraving.
Here are a few more tips to keep in mind when rotary engraving acrylic:
• If swirl marks are a problem in the bottoms of engraved grooves, try increasing the spindle speed and/or reducing the feed rate.
• Dwell marks (circular dots at the beginning and ending of character strokes) can usually be minimized by shortening the dwell time or, if your system has this feature, by “ramping” the cutter into and out of the material.
• If cutter strokes are visible between character strokes, try using a faster speed and/or a slower feed rate.
• If the depth nose is creating scratches and shadows around the characters, be sure you’re using light downward pressure and that the depth nose you are using is in good condition. Another option for minimizing shadow images is to use a plastic depth nose instead of a metal one.
A major advantage of rotary engraving is that it can also be used to profile acrylic. This technique can be used to create hole cutouts in products such as control panels or to cut out special shapes for custom badges, key tags and other merchandise. For the best results, you will need to modify your standard engraving technique somewhat. Here are a few tips:
• Use fast spindle speeds and slow feed rates.
• Always use a sharp, preferably carbide, cutter. A half-round cutter will work, although a better option might be a quarter-round cutter or a helical end mill, both of which tend to be stronger and produce better cuts.
• Use a tapered cutter for beveled edges and a parallel cutter for straight edges.
• Make sure the work is securely held on the table.
• If excess heat is a problem (if the plastic gums, sticks, stretches, tears, melts, etc.) try using a coolant. A good option for acrylic is dishwashing detergent mixed with water at a ratio of 10% detergent and 90% water.
• If the edge finish isn’t smooth enough, perform a finishing cut at full depth with a high spindle speed, e.g. 20,000 rpm.
One of the most recent innovations in personalizing acrylic products is AcryliPrint, a color imaging process introduced by Acrylic Idea Factory (AIF), Norcross, GA. What’s unique about this process is that it allows you to incorporate bright, vivid full-color photographs and graphics onto clear acrylic blanks to create truly stunning gifts and awards.
Previously, AcryliPrint products were only available through AIF’s in-house services where you sent them the artwork and they shipped your finished products. AIF still offers services for the trade but the company has since released its FusionProcessor and, more recently, the Junior FusionProcessor that allow you to bring the AcryliPrint process into your shop. The original FusionProcessor is a floor model unit that features a large 18"x24" production table whereas the Junior FusionProcessor is a scaled-down tabletop version with a smaller table (it can handle pieces up to 9"x12") and a smaller price tag.
In simple terms, the FusionProcessor is a sophisticated heat press. You simply create artwork using an inkjet printer (you can also use other types of printed artwork) and position it on the acrylic blank. AIF sells specially-coated, self-adhesive FusionBlank acrylic blanks and sheet stock designed specifically for this process.
After trimming the graphic, simply place it in the processor which fuses the artwork to the acrylic in about 11/2 minutes. The results are beautiful and colorful, and the crystal clear acrylic provides a unique dimensional quality. This process is well-suited for a variety of applications including photographs, gifts, awards, sign-
age, name badges, desk plates, promotional products, coasters, puzzles, key tags, point-of-purchase displays, clocks, etc. For more information, be sure to read “A Look at AIF’s AcryliPrint FusionProcessor” in the Feb. 2011 issue.
Cleaning & Polishing Acrylic
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