From Event: SPIE LASE, 2019
Combustion chambers of helicopter engines experience high temperature during combustion of the kerosene spray. Improving the efficiency and reducing the NOx produced by these engines, requires to further increase the temperature within the combustion chamber. However the latter tackles the fusion of the used metallic alloys. Nowadays to sustain such high temperature, the combustion chamber is coated with refractory ceramics and it is drilled with thousands of holes through which compressed air is flowing. Lasers are largely used to drill the holes in the combustion chamber. However drilling sub-millimetric holes with a well-controlled profile in ceramic coated metal alloys with no defects (delamination, formation of cracks…) remains a difficult task. In this presentation, we will detail the technique we developed to drill holes in such ceramic coated combustion chamber using sub-millisecond pulses delivered by high power fiber laser. This technique was made possible thanks to the numerical model we developed using COMSOL. By solving Maxwell’s equations this model account for the propagation of the laser beam within the hole during the drilling process. To test its validity, we drilled a series of holes in 800 µm thick cobalt alloy (KCN22W) coated with a 400 µm thick zirconium oxide (ZrO2) ceramic using an IPG Ytterbium fiber laser (YLS-1200-12000-QCW) and a Precitec drilling head (YK52). Experimental and numerical data are found to be in very good agreement. Moreover, Raman measurements indicate the ceramic alloy is not affected by this drilling process. Further improvements of this technique will be discussed.
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Minh-Hoang Nguyen, Cyrille Delor, and Eric Freysz, "High power fiber laser drilling process for ceramic coated helicopter combustion chambers (Conference Presentation)," Proc. SPIE 10911, High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VIII, 109110O (Presented at SPIE LASE: February 07, 2019; Published: 8 March 2019); https://doi.org/10.1117/12.2505812.6011730401001.