Optimization of laser-remote-cutting of CFRP by means of variable exposure delay times – simulation and validation

The growing interest in carbon-fiber-reinforced-plastics (CFRP) leads to a rising demand for cost-efficient, alternative production methods, such as laser-remote-cutting. Since the cycle times, particularly in the automotive industry, represent a significant cost factor, this paper presents a method for reducing the heat-affected zone (HAZ) in the CFRP-laminate while maximizing the cutting speed. In pursuing this goal, in this paper, a comparison is made between a multi- and a single-mode laser system. In addition, simulation is used to investigate which mechanisms contribute to the formation of the HAZ and the effect of the delay times between the exposures on the HAZ. For the comparison of the beam sources, attempts are made with regard to the required cumulative energy per unit length to achieve a complete cut. The developed numerical simulation takes into account the thermal decomposition of the plastic matrix as well as the fibers, the heat conduction in the laminate, the flow of the gaseous decomposition products in the kerf and the heat transfer by forced convection on the cutting edge, the layer setup, the material properties as well as the laser parameters power, scanning speed, exposure number, and the delay times between the exposures. By means of Monte-Carlo-simulation, an optimization of the HAZ or the sum of all delay times is carried out. The experiments show that a complete cut with the single-mode laser requires a higher energy than the multi-mode system. It can be shown by the simulation that the primary target conflict in laser beam cutting of CFRP with several exposures exists between the average width of the heat-affected zone and the sum of the delay times between the exposures. The sum of the delay times is decisive in particular for the effective cutting speed. The simulation also shows that as a rule at least 50% of the width of the heat-affected zone is caused by the flow of the gaseous process emission within the kerf. The optimization could be used to calculate and validate that a skillful selection of the delay times results in a reduction of the HAZ or the sum of all delay times. By comparison of the beam sources, it can be seen that the aspect ratio between laser beam diameter and laminate thickness must be optimized. In addition to the optimization of the delay times, it is also necessary to adjust the laser power and the scanning speed from exposure to exposure.