The near-infrared picosecond laser ablation characteristics (threshold, heat-affected zone (HAZ) and morphology) for graphitized carbon fiber-reinforced cyanate ester resin (M55/BS-4), a mesoscopically heterogeneous composite, were studied. The ablation threshold and its incubation effect for the composite were measured based on the diameter-regression method, with the single-pulse threshold derived from the incubation model. The influence of incident laser fluence (0.6-26J/cm2) and beam scanning speed (0.8-5m/s) on the ablation quality were analyzed. It was show that the ablation threshold, morphology and thickness of HAZ can be controlled by processing parameters for the composite. Well-defined groove with clear edge and minor HAZ, probably an indication of mesoscopically uniform removal for the material’s heterogeneous structure, was obtained by using a proper combination of scanning speed and incident fluence. A satellite-used carbon-fiber skin as large as 1m2 based on laser cutting was demonstrated by using further optimized processing parameters.
We carried out a comparative study on ablation threshold behavior of femtosecond laser twin double-pulse processing of typical transparent material, semiconductors and metallic materials. Based on the change of ablation area with pulse temporal separation (100 fs-15ps) under the same spatially distributed Gaussian beam, influence of pulse-separation on normalized double-pulse ablation threshold (which is normalized to the single-pulse ablation threshold) was demonstrated qualitatively. Special attention paid on the variation characteristics of normalized double-pulse ablation threshold in the sub-picosecond pulse-separation range, as well as its value in pulse-separations comparable or larger than the electron-phonon (or ion) coupling time. We show that the ablation threshold behavior of femtosecond laser twin double-pulse is strongly material-specie dependent, however, can be summarized in to several ones. The difference in ionization and/or deionization mechanisms for the non-metal compared is possibly the physical origins for the contrasted behavior of double-pulse ablation threshold.
Carbon fiber reinforced polymer(CFRP) is a typical hard to machine material. High modulus CFRP is one of the most widely used types in spacecraft structures. In this paper, the ultrafast laser precision cutting technology for two kinds of high modulus materials with different thermal conductivity is studied. The single factor ablation experiments are carried out on two kinds of plates with the thickness of 1mm. The threshold value of the two materials and the influence law of different laser fluence and scanning speed parameters on the entrance cutting size and heat-affected zone are obtained, and the physical mechanism of the above laws is described. The results show that the huge difference in the thermal conductivity of the two materials has a certain influence on the difficulty of processing the material and the selection of process parameters.
We carried out a comparative study on laser cutting of fiber-reinforced plastic and its honeycomb sandwich structure widely used in aeronautic industry. The influence of pulse duration (CW, ns, ps and fs), wavelength (MIR, NIR, and NUV) on cutting quality (characterized by the HAZ) and productivity was experimentally studied. It was demonstrated that for either the aramid fiber reinforced plastics/polymers (AFRPs) or high-modulus carbon fiber reinforced plastics/polymers (CFRPs) and its honeycomb sandwich structure, tradition laser cutting was unable to satisfy the requirements of the appearance qualities in the astronautic industry due to the thermal damage induced discoloration, in spite of the less extension of damage than the contact machining used currently. The pulse duration effects on HAZ, the wavelength effects on cutting quality and productivity, the differences and similarities for low-HAZ cutting of AFRPs and high-modulus CFRPs, was studied, and the possible physical origins was discussed.
High-volume SiCp/Al materials were processed by Laser-induced Oxidation assisted machining technology.We obtained the laser induced oxidation process and oxidation mechanism, through the analysis of the average laser power, scanning speed, scanning distance and other factors on the oxidation effect.The results show that:1) In an oxygen-rich environment, the oxide layer will eventually exist as mullite(2 Al2O3·SiO2)after sufficient reaction of the surface material. 2) When the average laser power is 6W, the laser scanning speed is 1 mm/s, and the laser scanning distance is 10 μm, the optimal combination of parameters is obtained. The results show that the thermal hardening layer and dense layer are the least and the hardness is low, which is suitable for high efficiency and precision milling; 3)The laser induced oxidation assisted milling technology can significantly improve the processing efficiency, the material removal rate is greater than 3000 mm3 /min, the surface roughness value after Precision machining is better than Ra0.4 μm.
Morphological evolution of ripple on nickel surface induced by temporally shaped femtosecond laser irradiation were studied and compared with titanium. It was revealed that the transformation of single-pulse irradiation into double-pulse irradiation can exert very different influence on ripple morphology evolution for different metals. For nickel, the double-pulse irradiation resulted in the growth in rippled area, ripple period and ripple contrast, compared with the single-pulse irradiation, while double-pulse processing of titanium leads to reductions in in rippled area and ripple period. The contrasted influence of Te on electron-phonon coupling factor (G) for the two metals was the primary factor for the different behaviors of ripple morphology evolution with temporal pulse shaping.
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