Laser machining has great potential regarding automation in fabrication of CFRP (carbon-fiber-reinforced plastics) parts, due to the nearly force and tool-wear free processing at high process speeds. The high vaporization temperatures and the large heat conductivity of the carbon fibers lead to a large heat transport into the sample. This causes the formation of a heat-affected zone and a decrease of the process speed. In the present paper, an analytical heat flow model was adapted in order to understand and investigate the heat conduction losses. Thermal sensors were embedded in samples at different distances from the kerf to fit the calculated to the measured temperatures. Heat conduction losses of up to 30% of the laser power were determined. Furthermore, the energy not absorbed by the sample, the energy for sublimating the composite material in the kerf, the energy for the formation of the HAZ, and the residual heat in the sample are compared in an energy balance.
NomenclatureCFRP carbon-fiber-reinforced plastics c p mass specific heat capacity c p,f mass specific heat capacity of the fibers c p,m mass specific heat capacity of the matrix d k,mean measured mean width of the kerf d MSZ,mean measured mean width of the matrix-sublimation zone E abs absorbed laser energy E cond energy conducted into the sample E L laser energy E not abs laser energy not absorbed by the sample E res residual energy in the sample E s,k energy for sublimating the composite material in the kerf E s.m, MSZ energy for sublimating the matrix material in the MSZ HAZ heat-affected zone h s thickness of the material k heat conductivity k * fitted heat conductivity of the composite material describing the global heat transport l c length of the cut L s latent heat of sublimation L s,f latent heat of sublimation of the fibers L s,m latent heat of sublimation of the matrix MDZ matrix damage zone MSZ matrix sublimation zone P laser power t time t HeatLoad total effective heat load time T Heat,1 temperature in the sample for 0 < t < t HeatLoad T Heat,2 temperature in the sample for t > t HeatLoad t hom time of homogenisation T sub sublimation temperature T sub,f sublimation temperature of the fibers T sub,m sublimation temperature of the matrix T 0 room temperature T D structure damage temperature T D,m structure damage temperature of the matrix material v cutting speed
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