Today’s advanced composite materials fall into three main classes: Ceramic Matrix Composites, Metal Matrix Composites, and the most common type – Polymer Matrix Composites or PMCs. Polymer composites are created by adding reinforcing fibers such as aramid, carbon, graphite, or glass to a thermosetting resin like epoxy or polyurethane. Although the material properties of individual fibers are not spectacular by themselves, the combination of fiber and resin properties along with the design of the fiber geometry within the composite combine to produce lightweight, durable materials that are quickly replacing metals, especially in the aerospace industry.

Because of their non-contact cutting method, CO₂ lasers are an ideal tool for cutting composites especially when specific shapes or profile cuts are required. For this test, all runs were made using 200 watts of power at cut speeds of 120–125 inches per minute (IPM). Beam delivery to the surface of the 1 mm (0.04”) thick PMC material was focused through a 2.5” positive meniscus lens, which provided a 100-micron (0.004”) spot with a 1.8 mm (0.07”) depth of focus.

The first photo shows a woven PMC material that was cut using 40-PSI air as the assist gas. The cut edge exhibits a light charring, which is typical of the chemical degradation cutting method where laser energy degrades the material to a point that the material is removed under pressure of an inert assist gas.

Marking Ceramic Surfaces

Surface mount components are used extensively in manufacturing electronic circuit boards due to their small size and compatibility with automated assembly processes. In this application, ceramic surface mount capacitors, measuring 2.5 mm x 3 mm, required an eight-digit identification mark.

To perform this task, we set up a Synrad CO₂ laser with an FH Series marking head and installed an 80 mm focusing lens, which provided a 116-micron (0.005”) diameter beam with a 0.8 mm (0.032”) depth of focus. Using our WinMark Pro^TM laser marking software, we created an eight-digit code using “Simple”, one of WinMark’s twelve built-in stroke fonts. For Power, we set a duty cycle percentage corresponding to nine watts and then set a marking Velocity of nine inches per second (IPS). With these parameters, the characters, measuring only 0.82 mm (0.032”) high, were marked in a cycle time of 0.35 seconds. 

Welding PMMA

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, depth, or weld path.

To accomplish this sample, we setup a rotating fixture to clamp the two discs in position underneath the beam. Remember that laser welding adds no additional material to fill gaps between pieces, so proper part fit up is crucial to achieving a strong mechanical bond. Our beam delivery consisted of a 2.5” focusing lens fixed in place over a rotating stage operating at 100 revolutions per minute (RPM). Typically, this positive meniscus lens provides a 100-micron (0.004”) focused spot with a 0.07” depth of focus, however in this instance we adjusted the Z-axis, essentially defocusing the beam, to create a 0.51 mm (0.02”) diameter weld beam. We choose air, at 10 PSI, as an assist gas.