High precision laser macrodrilling of carbon fiber reinforced plastics with a new nanosecond pulsed laser—Optimized toward industrial needs

Due to their outstanding strength-to-weight ratio, carbon fiber reinforced plastics (CFRP) are of high interest for lightweight construction. Within industrial fields requiring lightweight design and energy efficiency, the demand for CFRP increases continuously. Until now, machining of CFRP, as a crucial step in the production chain of composite parts, is mainly performed by conventional techniques such as drilling, milling, and abrasive water jet cutting. These techniques come with known drawbacks, including force input, handling of auxiliaries, and tool wear. The laser cutting of CFRP has already shown its high potential to be a practical alternative due to wear-free and contactless processing. However, if sufficient cutting rates are required, laser cutting has to overcome the challenge of either nonorthogonal cutting edges when using short pulsed high power lasers or heat input into the material when using continuously emitting (continuous wave) high power singlemode laser sources, as shown by Staehr et al. [J. Laser Appl. 28, 022203 (2016)]. Within this investigation, the machining with a novel short pulsed high power laser source by Trumpf Laser GmbH emitting at λ = 1030 nm will be examined. The lab-state laser source provides nanosecond pulses at t_p = 20 ns, at a maximum pulse energy of E_p = 100 mJ, and a maximum average power of P_avg = 1.5 kW, while maintaining a very good beam quality allowing for small focus diameters down to d_f = 84 μm with the focusing optics used. It was shown that processing with small focus diameters results in narrow cutting kerfs contributing to the cutting edge angle. In addition, the investigations revealed a minimized thermal load resulting from the short pulses. At the same time, challenges resulting from shielding effects when specific parameters are used will be displayed and discussed. Different processing strategies for adjusting the cutting edge angle toward orthogonality will be presented in this paper. This optimization procedure aims at the drilling of macroscopic holes with a diameter of Ø > 4 mm in CFRP laminates with a thickness of s ≥ 2 mm at very high precision.

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