FEATURED ARTICLE Laser Cutting of CFRP Using a 30 kW Fiber Laser
BY DIRK HERZOG, MATTHIAS SCHMIDT-LEHR, MARTEN CANISIUS, MAX OBERLANDER, JAN-PHILIPP TASCHE AND CLAUS EMMELMANN
Today, industrial usage of Carbon Fiber Reinforced Plastic (CFRP) is steadily increasing, with an amount of 67,000 t/year. Latest products such as the Boeing 787 and Airbus A350 in the aerospace sector, as well as the BMW i3 from the automotive industry, consist of more than 50 percent of CFRP in their structural weight. At the same time these products also have comparatively high production volumes, in the five-digit range per year in the case of the BMW i3. Therefore, a higher degree in automation and cost-efficiency is needed in production. Due to the highly abrasive carbon fibers, conventional machining processes result in short tool life and high costs.
For that reason laser cutting of CFRP as a wear-free alternative has become the focus of several research groups. Two different approaches are commonly chosen: Cutting by short- and ultra- short pulsed laser systems to reach a process regime of cold ablation, and cutting with continuous wave (cw) lasers at high cutting speeds. For the latter approach, it has already been shown that by increasing power and cutting speed, the heat affected zone (HAZ) can be reduced due to less time allowed for heat conduction.
A new approach presented here uses an ultra-high power fiber laser system of 30 kW to cut CFRP laminates in order to allow for highest-speed and lowest HAZ.
Material and Set-up The material for the process was chosen to specifications from typical automotive applications of CFRP. 2D specimens were manufactured using vacuum infusion technology, consisting of a total of six layers of non-crimp carbon fabrics and an epoxy resin.
A high power Yt:YAG fiber laser was used in combination with a special optical system that can handle the high intensities needed for the experiments. The laser beam was directed to the manufacturing cell in a 300 µm process fiber and then collimated and focused by an optical system with an image scale of 1:1.2 to achieve a theoretical focal diameter of 250 µm.
Normally in laser materials processing, relative movement is realized either by movement of the workpiece or the beam with the means of a linear axis, or alternatively by scanner systems. Commercially available scanner systems operate already with comparably high feed rates of several m/s. In order to allow for a detailed investigation on the influence of the number of passes in a multi-pass cutting strategy, the achievable feed rate should be high enough to enable a cutting process with n ≥ 30 passes at highest possible intensity. Calculations of the required feed rate based on the necessary intensity for the sublimation of the carbon fibers yield a requirement for the relative movement system of 80 m/s, which is not achievable by today’s scanner technology. To achieve these feed rates, a rotary plate was
Figure 1. Overview of high-speed rotary plate and laser system 10 LIATODAY FOCUS: LASERS IN MANUFACTURING JULY/AUGUST 2015
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