The anisotropic heat-affected zone in the laser grooving of fiber-reinforced composite material

A heat-affected zone is frequently associated with the laser processing of materials. In the shaping of composite material after curing, thermal damage is found, such as matrix recession, matrix decomposition, and delamination, which lead to poor assembly tolerance and long-term performance deterioration. The current study analyzes the peculiar growth of the heat-affected zone due to laser energy and the anisotropy of heat conductivity from the anisotropic arrangement of the fiber reinforcement in the composite material. It further applies the concept that the cut quality can be improved by reducing the resulting temperture of the workpiece. which leads to laser machining at low temperature. The paper investigates the cutting of unidirectional laminated carbon/epoxy composite perpendicular to and parallel to the fiber axis, using a cool nitrogen jet to reduce thermal damage. A theoretical analysis based on moving-point heat-source theory is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. The analytical solution is modified by the 'mirror image method' for a specimen of finite thickness. The range of the heat-affected zone is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the carbon fibers, the heat-affected zone shape thus being affected by the beam scanning direction relative to the fiber orientation.