Fibre laser cutting of CFRP thin sheets by multi-passes scan technique

In the present work, the employment of multi-passes laser scan technique in cutting of CFRP thin sheets is investigated using a 30 W MOPA Q-switched pulsed Yb:YAG fibre laser. In this technique a laser beam, moved by a galvanometric mirrors system is used to groove the material surface. The absence of cutting head and assistance gas, as well as the low pulse energy only allow to remove small amounts of material in a single beam travel scan. Therefore, the through cut can be obtained by repeating the beam travel more than once. The main advantages of this technique are represented by the low cost of the equipment, compared to a traditional CNC, and the possibility to cut small and complex shapes due to the very narrow beam spot. The aim of this paper is to determine how the process performs in terms of effective cutting speed, kerf geometry and Heat Affected Zone (HAZ) extent. Experimental tests were carried out at the maximum average power, by changing the laser beam scan speed and pulse power. Two experimental testing series were performed. First, for each process condition, the number of repetitions required to obtain a through cut and the effective cutting speeds were determined. Then, cutting tests were executed using the same process parameters and the number of repetitions required to completely cut the laminate. On the obtained samples, kerf geometry and HAZ extent were measured by optical microscopy. The experimental results pointed out that the effective cutting speed depends on scanning speed and pulse power, whereas the kerf geometry is mainly affected by scanning speed and the HAZ extent is influenced by scanning speed as well as pulse power.