Model-based temperature monitoring for broaching safety-critical aero engine components
Cutting temperatures are the main factor adversely affecting the product quality and limiting the productivity in the manufacture of safety-critical aero engine components. At present, a system for monitoring the temperature field in the cutting zone is not existent. This work presents the development of a monitoring solution enabling the detection of critical process conditions and therewith allows manufacturers to adapt processes appropriate to the situation. The system is developed using the example of broaching fir tree slots in nickel-based turbine discs, which is considered one of the most critical processes in aero engine manufacture. Investigations of the generated surfaces and subsurfaces have been made in order to validate the temperature as the main critical variable in the regarded case. As a temperature measurement is not possible under industrial conditions to date, a model-based approach was employed to compute the temperature field in the cutting zone. Thereby the cutting force vector, which is determined using a machine-integrated force dynamometer, serves as a representative for the momentary process energy. Within the scope of the thesis, the analytical thermal model proposed by Komanduri and Hou was first-time validated by means of calibrated in-process high-speed thermography recordings and later modified to meet the conditions of the broaching process. Finally, suggestions for an industrial implementation and an outlook to a temperature controlled process are given. The presented solution provides the possibility to either focus the temperature field in the cutting edge with the aim of an optimized tool deployment or in the workpiece enabling the prediction of thermal defects as a consequence of unfavorable thermo-mechanical conditions. Due to its analytical nature, the model-based solution is especially robust and requires very short calculation times allowing for an online application. Furthermore, the transferability to other machining operations is ensured.
Zugl.: Aachen, TH, Diss., 2015