New method of continuous-wave laser ablation for processing microgroove with variable cross-section

Abstract

Surface microgrooves can effectively reduce the drag and have unparalleled advantages in energy saving and environmental protection. In the fabrication of microgrooves, the laser processing has shown a broad prospect in the fabrication of microgrooves for the advantages of high processing efficiency, no tool wear, no processing stress, etc. However, under the given process parameters, the energy distribution of the laser spot is fixed, and it is difficult to achieve different cross-sectional shapes in a single microgroove, which may have better performance for the drag reduction. In this situation, the effect of variable cross-section microgrooves on the drag reduction is demonstrated and the drag reduction mechanism is analyzed through the fluid simulation. Further, a novel method, moving zoom laser processing, is proposed to realize the fabrication of microgrooves with variable width at equal depth. For orderly planning of the laser processing parameters, the continuous wave laser (CW laser) ablation model is established under ‘tight focusing’ arrangement with predicted microgroove profiles, and the prediction errors of the model for the width and depth are 4.53 μm and 6.77 μm, respectively. Then, the ablation model is extended to the defocusing condition, and the prediction errors of the width and the depth of the microgroove under defocus arrangement are less than 3 % and 9 %, respectively. Additionally, the planning method of the process parameters in the moving zoom laser processing is introduced. Finally, the feasibility of the proposed method is verified experimentally and the microgroove with a depth of 24 μm and a width of 165–231 μm is successfully fabricated by the proposed method. With the proposed processing strategies, a good and concerned reference is provided for drag reduction technology with surface microgroove.