Prediction of Extent of Heat Affected Zone in Laser Grooving of Unidirectional Fiber-Reinforced Plastics

Laser has been widely used in various industrial applications including machining. However, in shaping operation of composite material after curing, thermal damage associated with laser energy can be produced. It leads to poor assembly tolerance and long-term performance deterioration. The current research investigates the anisotropic formation of the heat affected zone (HAZ) in unidirectional fiber-reinforced plastics induced by laser grooving. Preliminary analytical and experimental analysis reveal that the laser energy per unit length and fiber orientation-dependent thermal conductivity primarliy determine the induced thermal damage. The extent of HAZ is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the fibers, and the HAZ shape is thus affected by the beam scanning direction relative to fiber orientation. The study investigates the grooving of laminated unidirectional carbon/epoxy, which demonstrates clear thermal damage in 90 degree (i.e., perpendicular grooving), 60 degree, 30 degree, and 0 degree (i.e., parallel grooving) relative to the fiber axis. A theoretical analysis based on moving point heat source is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. Mirror Image Method is used for specimen of finite thickness. Considerations of temperature-dependence of thermal conductivity and the emmerged heat source further improve the prediction of HAZ. While HAZ in grooving along the principal material axes can be solved analytically, conductivity ellipsoid and finite difference can calculate the extent of HAZ induced by grooving in any direction relative to fiber axis.