Polymethyl methacrylate (PMMA), commonly called acrylic, is an exceptionally transparent thermoplastic sold under many trademarks including Plexiglas® and Lucite®. Bonding or welding PMMA is accomplished using chemicals (liquids such as methylene chloride or cyanoacrylate), ultrasonic welders, or by using CO2 lasers. Of the three, lasers provide the greatest flexibility for controlling weld width, weld depth, and weld path.

To accomplish the welding process, we set up a rotating fixture that clamps two 1.14 mm (0.045”) thick PMMA discs in position underneath the beam path. Because traditional laser welding does not introduce additional material to fill gaps between pieces, proper part fit up is crucial to achieving a strong mechanical bond.

Because laser degating is a non-contact process, lasers eliminate the need for knife or die replacement. The most important benefit however, is the laser’s ability to be reprogrammed quickly and easily to degate a new or redesigned part. In addition, laser degating is a thermal process that tends to produce a smooth cut edge versus mechanical methods that often leave a sharp edge at the trim point.

The photo shows the results of degating a small polycarbonate cover using a Firestar f201 laser and FH Series marking head. This galvanometer-based cutting method offers the added benefit of a familiar Windows®-based user interface and our easy-to-use WinMark Pro laser marking software. We equipped our FH head with an 80 mm focusing lens that provides a 116-micron (0.005”) spot size and a 0.8 mm (0.032”) depth of focus. At 200 watts of power, we cut through the 0.93 mm (0.0365”) thick sprue at a speed of 457 millimeters per second (18 inches/second) in a cycle time of 50 milliseconds (0.05) seconds per part. The degated edge is clean and smooth with no discoloration or polycarbonate residue seen on the part.