For the aerospace industry, X-ray tomography inspection and in-depth analysis of cooling holes would provide a better understanding of the influence of laser drilling parameters on the manufacture of combustion chambers, as well as helping to improve manufacturing techniques. The inspection would also make it possible to establish the link between laser hole geometry and the quality criterion currently used in industry, i.e. the mass flow rate passing through the chamber. This thesis presents the development of an X-ray tomography inspection method for the analysis of effusion holes. The method developed measures the angle of the hole, the entry and exit surface area variation and the volume of material removed during laser drilling. It also makes it possible to correlate the metrics measured by the method with the corresponding cooling rate. This research may be of great interest to combustion chamber manufacturers, such as aircraft engine designers, in the rejection or acceptance of these components. An automated inspection method was developed using Dragonfly 3D World software (Comet Group, V. 2024.1), measuring geometric metrics resulting from the laser drilling process.
In the first part of this work, a comparison between X-ray tomography and conventional metallographic analysis was carried out in order to evaluate the accuracy of angle and diameter measurements. The experimental results confirmed the possibility to quantify the differences between the two methods, establishing differences of around 0.55° for angles and between 47 and 72 μm for diameters. The second part of the work focused on studying the material removal mechanism as a function of pulse energy and the drilling side (metal vs. ceramic). The analysis showed that the direction of drilling significantly influences material expulsion, thereby altering the geometry of the hole entrances and exits as well as the volume of the cavities formed, with differences of more than 33%. Finally, the third part characterized the impact of laser parameters (drilling angle, focal position, and drilling direction) on the cooling mass flow rate. Tests performed on a specialized test bench showed significant variations. In fact, there was a difference of approximately 20% in flow rate between drilling at 35° and 20°, a reduction of nearly 35% linked to a focal shift of 7.6 mm compared to 0 mm, and a difference of approximately 25% between drilling on the metal side and the ceramic side. In addition, the inlet surfaces were consistently larger than the outlet surfaces, confirming the influence of the drilling angle on the morphology of the holes. This research highlights the effectiveness of X-ray tomography as a fast and reliable method for inspecting micro-holes smaller than one millimeter in diameter, reducing analysis time from nearly three hours (conventional methods) to less than one hour. These results pave the way for further optimization of laser drilling processes applied to advance cooling systems.
Renaud, P. (Author),
Demers (Supervisor) &
Brailovski (Co-supervisor),
19 Dec 2025Student thesis: Master's thesis › Master in Engineering: Mechanical Engineering