Laser processing of carbon fiber reinforce plastic (CFRP) is a very promising method to solve a lot of the challenges for large-volume production of lightweight constructions in automotive and airplane industries. However, the laser process is actual limited by two main issues. First the quality might be reduced due to thermal damage and second the high process energy needed for sublimation of the carbon fibers requires laser sources with high average power for productive processing. To achieve thermal damage of the CFRP of less than 10μm intensities above 108 W/cm² are needed. To reach these high intensities in the processing area ultra-short pulse laser systems are favored. Unfortunately the average power of commercially available laser systems is up to now in the range of several tens to a few hundred Watt. To sublimate the carbon fibers a large volume specific enthalpy of 85 J/mm³ is necessary. This means for example that cutting of 2 mm thick material with a kerf width of 0.2 mm with industry-typical 100 mm/sec requires several kilowatts of average power. At the IFSW a thin-disk multipass amplifier yielding a maximum average output power of 1100 W (300 kHz, 8 ps, 3.7 mJ) allowed for the first time to process CFRP at this average power and pulse energy level with picosecond pulse duration. With this unique laser system cutting of CFRP with a thickness of 2 mm an effective average cutting speed of 150 mm/sec with a thermal damage below 10μm was demonstrated.
Carbon fibre reinforced plastics (CFRP) have a large potential in the automotive lightweight construction due to their
low density and high mechanical stability. Compared with today’s laser processing methods of metals the main issues in
laser processing of CFRP are the very differing thermal, optical and mechanical properties of the components. To
understand the process in detail, the ablation process of CFRP with ultrashort laser pulses was investigated. The shock
wave and the vapor resulting from processing with single laser pulses were recorded. Shadow photography and
luminescence photography with an ultra-high-speed camera was used to show the ablation process with a temporary
resolution of up to 3 ns. The field of view was 250 μm × 250 μm. An ultrashort laser pulse with pulse duration of 4 ps
and a wavelength of 800 nm was focused onto the workpiece. The energy content of the shock wave was calculated from
the resulting images. The energy content of the shock wave was about 20 % of the incident energy and the speed of
propagation of the shock wave was more than 2000 m/s. The high intensities in the range of 1013 W/cm2 lead to
formation of a plasma plume which was clearly seen in the shadow photography images.