Characterization of Heat Affected Zone Generation in Laser Processing of Carbon Fiber Reinforced Plastics

In this study, we conducted an analysis and evaluation of the heat affected zone (HAZ), which serves as a measure of surface processing quality in laser machining of Carbon Fiber Reinforced Plastics (CFRP). Carbon fibers have two axes, horizontal or vertical, in the alignment direction of the fibers. When the optical energy of the laser is primarily conducted along the alignment direction of the carbon fibers and diffused into heat, the HAZ occurs on the surface of the CFRP, exhibiting anisotropic characteristics. In laser processing by pulse, the accumulation of residual heat energy within the carbon fibers induces evaporation and thermal deformation of the polymer at the carbon fiber boundaries, ultimately resulting in a permanent change in the properties of the CFRP, defined as the HAZ. To confirm the influence of process variables on HAZ formation in laser machining, ray tracing was applied to predict the thickness and length of the layer in which the laser beam is absorbed by the CFRP. Generally, it was confirmed that more than 90% of the laser beam is absorbed by three layers of fibers from the surface. Based on this, the temperature distribution of carbon fibers due to residual laser energy during laser machining was predicted. Through these results, the size of HAZ according to the arrangement direction of carbon fibers could be numerically predicted. Experimental results confirmed that process variables such as laser power density and scan speed affect the formation of HAZ. Additionally, the size of HAZ due to conduction along the arrangement direction of carbon fibers was experimentally verified, and quantitative comparison and analysis were conducted with numerical results from previous modeling. Through this analysis, it was possible to predict the size of HAZ affecting surface quality during laser machining of CFRP and validate optimized laser process variables.