Residual heat generated during laser processing of CFRP with picosecond laser pulses

Abstract

One of the major reasons for the formation of a heat-affected zone during laser processing of carbon fiber-reinforced plastics (CFRP) with repetitive picosecond (ps) laser pulses is heat accumulation. A fraction of every laser pulse is left as what we termed residual heat in the material also after the completed ablation process and leads to a gradual temperature increase in the processed workpiece. If the time between two consecutive pulses is too short to allow for a sufficient cooling of the material in the interaction zone, the resulting temperature can finally exceed a critical temperature and lead to the formation of a heat-affected zone. This accumulation effect depends on the amount of energy per laser pulse that is left in the material as residual heat. Which fraction of the incident pulse energy is left as residual heat in the workpiece depends on the laser and process parameters, the material properties, and the geometry of the interaction zone, but the influence of the individual quantities at the present state of knowledge is not known precisely due to the lack of comprehensive theoretical models. With the present study, we, therefore, experimentally determined the amount of residual heat by means of calorimetry. We investigated the dependence of the residual heat on the fluence, the pulse overlap, and the depth of laser-generated grooves in CRFP. As expected, the residual heat was found to increase with increasing groove depth. This increase occurs due to an indirect heating of the kerf walls by the ablation plasma and the change in the absorbed laser fluence caused by the altered geometry of the generated structures.

Deflection of particles of a laser erosion plume under the action of a high-voltage electrostatic field during ablation processing of titanium

“…Laser ablation of materials in a medium is a complex physical process that depends on the parameters of laser radiation, the properties of the working medium, and additional sources of physical impact. An additional source of influence can be both the thermal load caused by the action of the laser-induced plasma torch [1], which is formed above the treated surface, and the energy applied to the treatment area together with the laser beam [2][3][4][5]. The combination of various methods of exposure allows achieving a synergistic effect, and, as a consequence, increasing the efficiency of the ablation operation.…”

Study on the mechanism of inhomogeneous microdamage in short-pulse laser processing of carbon fiber reinforced plastic

“…Völkermeyer et al 4 discussed the influence of filling distance and cycle times on ablation depth and ablation amount and proved that the maximum value of material strength decreased significantly in the total processing time. Christian et al 5 studied the relationship between the residual heat in CFRP and the volume of the laser beam, the pulse overlap, and the depth of the lasergenerated groove. The results showed that the residual heat gradually increased with the increase of the groove depth.…”