Investigation into laser machining of carbon fiber reinforced plastic in a flowing water layer

Over-melting and vaporization of resin matrix are usually found along a cut in the laser machining of carbon fiber reinforced plastic (CFRP). This is considered as the heat-affected zone (HAZ) and it has to be minimized to avoid the delamination of CFRP laminates. This paper presents the use of water flow to cool down the CFRP during the laser machining process. A thin flowing water layer induced by the impingement of low-pressure waterjet was formed on the workpiece surface, where a laser beam performed the ablation underneath the water layer. With this technique, the excessive heat and cut debris can be carried away from the workpiece by water. In this study, the effects of laser traverse speed, orientation of carbon fiber, water flow rate, and flow direction on cut dimensions and HAZ size were experimentally investigated. Using high water flow rate can limit the expansion of HAZ and also assist the material removal. In addition, the water flow directed along the laser traverse direction can increase the cut depth. The groove aspect ratio produced by the presented technique was found to be the same level as the laser ablation in air but the HAZ size was 20% smaller than the dry ablation. A predictive model for cut depth based on energy balance was also developed and analyzed in this study. The experimental findings and theoretical model presented in this work could enable a better understanding of the laser ablation in the flowing water layer and highlight the potential use of this technique for processing CFRP and other similar materials.