Modeling of Tow-to-spot Diameter Ratio for Laser Cutting of Single-layer Carbon Fiber Reinforced Plastics (CFRP)

Abstract

Carbon fiber reinforced plastics (CFRP) is a kind of advanced composite material with resin as matrix and carbon fiber as reinforcing phase. Laser cutting is considered as a high-efficiency and high-quality processing method of CFRP because of its high removal rate, narrow slit and no cutting force. Due to the differences in physical properties between carbon fiber and resin in CFRP, the whole composed of these two phases in different arrangement is a typical anisotropic material, which leads to the high complexity of its laser cutting process compared with isotropic materials. In order to study the influence of material anisotropy on energy conduction in laser cutting CFRP, taking single-layer CFRP as the research object, based on the heat conduction theory and the mixing rate of composite materials, the three-dimensional finite element models of single fiber arrangement with tow-to-spot diameter ratio of 1:1, 1:2, 1:5 and 1:10 are established by using the commercial software ANSYS. Through the numerical simulation of the same direction laser cutting process, the material temperature field and cross-section temperature gradient are analyzed. The results show that with the increase of fiber arrangement density (tow-to-spot diameter ratio approaching 1:10), the width of heat affected zone decreases, but the maximum temperature increases, which means that the temperature gradient increases. Therefore, it is speculated that when laser cutting with large spot diameter is used, i.e. K < 1:10, CFRP can be treated as homogeneous composite. In order to verify the effectiveness of the model, a slit aperture is used to control the tow-to-spot diameter ratio at about 1:7, and a CO2 continuous laser is used for cutting experiments. By fitting the experimental measurements with the width of carbon fiber ablation area and heat affected zone in the numerical simulation results, it is found that there is a logarithmic correlation between both of the width and the tow-to-spot diameter ratio. There are 3.37% and 1.92% deviations between the experimental result and the theoretical value, respectively. The agreement is relatively good, which can prove the effectiveness of the model. In conclusion, the establishment of tow-to-spot diameter ratio model reveals the response characteristics of anisotropic materials to energy input and conduction in the process of laser cutting, especially the difference of radial and axial conduction efficiency. The influence mechanism of fiber arrangement mode (mainly density in this work) on temperature field and cutting effect is clarified, which provides important theoretical support and experimental basis for laser precision cutting method of CFRP materials.