Cutting Carbon Fibre Composite

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 fibres such as aramid, carbon, graphite, or glass to a thermosetting resin like epoxy or polyurethane. Although the material properties of individual fibres are not spectacular by themselves, the combination of fibre and resin properties along with the design of the fibre geometry within the composite combine to produce lightweight, durable materials that are quickly replacing metals, notably in the aerospace industry.

Because of their non-contact cutting method, CO2 lasers are the ideal tools for cutting composite materials, 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 3.0–3.2 meters per minute (120–125 inches/minute). Beam delivery to the surface of the 1 mm (0.04”) thick PMC material was focused through a 63.5 mm (2.5”) positive meniscus lens, which provided a 100-micron (0.004”) spot with a 1.8 mm (0.07”) depth of focus. Woven PMC material cut using a 40-PSI air assist.

The first photo shows a woven PMC material that was cut using 2.8 bars (40 PSI) of clean, dry 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. Because edge quality was important in this particular application, the assist gas set-up was modified for high-pressure nitrogen. As seen in the second photo, the use of a high-pressure (12.4 Bars or 180 PSI) nitrogen assist gas significantly reduced edge charring on the PMC material. Changing the assist gas to 180 PSI high-pressure nitrogen reduces edge charring significantly.

It is important to note that although gas consumption increased by 355% using high-pressure nitrogen (an N2 flow rate of 2.73 CFM @ 180 PSI versus 0.77 CFM @ 40 PSI for air), the relative costs of high-purity nitrogen and breathing grade air means that gas costs increase by only 200% in achieving substantially better cut edge quality.

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