Drilling of CFRP with reduced and non-directional heat-affected zone by using 3-kW CW single-mode fiber laserThursday (25.06.2020) 08:40 - 09:00 Room 2
As the lightweight and high-strength material, the demand for carbon fiber reinforced plastic (CFRP) is growing in aviation and automotive industries. It is well known that mechanical processing is a general method for trimming and drilling formed CFRPs. However, tools are easily damaged and it leads to the degradation of the processing quality and the frequent replacement of the tools. Laser processing is one of the most promising candidates for a wear-free cutting method of CFRP. The challenge in laser processing is how to suppress heat-affected zone (HAZ). Although the processing by short-pulsed laser is a good solution for reducing HAZ, it takes relatively long processing time. The combination of single-mode fiber laser and galvanometer scanner is an effective way to achieve the short processing time and the small HAZ simultaneously. We have reported the high speed cutting of CFRP by using the 3-kW single-mode fiber laser and the galvanometer scanner. The 3-mm thick CFRP plate was successfully cut at the effective cutting speed of 7.8 m/min and the small HAZ of less than 100 μm.
In this paper, we demonstrate the drilling of the thermoset CFRP with the thickness of 2 mm by using the same setup as the high speed cutting of CFRP. The CFRP plate consists of 7 layers made from unidirectional fabric layers with fiber orientations of (0°/90°)s. As the heat conductivity of the carbon fiber is relatively high, HAZ tends to spread in a direction of the carbon fiber. Therefore, it is difficult to suppress the HAZ in all directions in the laser drilling of the CFRP. We carried out the drilling demonstration at the scanning speed of 10 m/s. In order to suppress HAZ, we adopted the multi-pass scanning strategy with the time interval of 20 ms between each scan. N2 gas was coaxially supplied for cooling the surface of the plate and removing the deposition of the carbon fiber in the kerf. The hole of 6.4 mm diameter was successfully achieved with 110 scans. Figure 1 (a) shows the microscopic image of the processed sample and Fig. 1 (b) shows the maximum size of the HAZ in each area. The HAZ is suppressed to around 100 μm in most areas and to 160 μm even at the worst point. The spread of the heat was well suppressed even in the direction of the carbon fiber. The processing time was about 3 seconds, which is equivalent to that in mechanical drilling.