Optimisation par éléments finis des trajectoires de chauffage par induction pour un traitement thermique robotisé in situ

Abstract

Post-welding heat treatments are used during the hydraulic turbine manufacturing process to restore mechanical properties and relieve internal stress caused by welding. For many aging turbines, such treatments are needed to ensure high quality repairs. However, dismantling and bringing such large equipment into a furnace is not feasible. As a solution, Hydro-Quebec’s Research Institute (IREQ) developed a new robotic process to perform local induction heat treatment in situ. Heat is generated by moving an induction coil following a back and forth trajectory over a specific area. A critical part of the process is to make temperature profile uniform within a precise range. For CA6NM turbine wheel, this range is as narrow as ±10 °C. This thesis proposed a method, combining finite element and optimization, to set heating and trajectory optimal parameters. A conjugated gradient algorithm is combined to the thermal solver of an in-house finite element software. The temperature field calculation is computed using an averaging heat input source. Computed temperatures with this model show good agreement with measured temperatures, on a plane and a curve instrumented plate. First, pancake coil and interpass distance are optimized to get the most uniform lateral temperature profile. Results show that an internal radius of 13 mm, an external radius of 37 mm and an interpass distance of 70 mm are optimal. The inner radius is not determined by the optimization but by the coil manufacturing process. The selection of the outer diameter is constrained by the manufacturing process and must represent a fixed number of turns. The selection of the outer diameter is also constrained by the manufacturing process and must represent a fixed number of turns. Moreover, the optimal interpass distance is found to be about 95 % of the external coil diameter. Second, the output power along the path is optimized to get a more uniform longitudinal temperature profile. Third, the coil orientation is optimized to improve the lateral and longitudinal temperature profile uniformity. Optimal angles found are 4,3 ° in the straight portion of the path 14 ° and in the curve portion. Experiments show that the model is representative of reality. The average difference between the calculated and measured temperatures is 1,5 %. In addition, successful results were obtained upon heat treatment after welding performed in the laboratory.

Date	16 Oct 2013
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Henri Champliaud (Supervisor) & Tan Pham (Co-supervisor)