Assessment of process monitoring systems for tool wear in broaching of fir-tree slots

The engine represents a safety-critical component of the aircraft. Design modifications that result in ecological and economic improvements require the implementation of changes to the manufacturing process. The turbine disks located in the low-pressure section are made of nickel-based superalloys that resist elevated temperatures. To facilitate the connection of the turbine blades to the disk, fir-tree slots are machined by broaching. The broaching process enables the attainment of high geometrical accuracy and the generation of reliable rim zone properties. One of the challenges during machining of nickel-based alloys is the rapid progression of tool wear. Thus, a tool change or regrinding of the cutting edge is necessary after manufacturing of a few turbine disks. In particular, the tool geometry involved in finishing operations is highly complex, resulting in extensive production and regrinding times and costs. Consequently, there is a need to maximize tool life. However, due to the broaching process located at the end of the manufacturing chain of the turbine disk, any damage to the workpiece during this process leads to significant costs. Therefore, it is essential to investigate the factors influencing the tool wear and the development of wear along the tool life in order to enhance process reliability. As part of the work, the correlation between indirect process data and tool wear was demonstrated, in particular using a wattmeter and a Hall sensor, and a Pearson coefficient greater than 0.6 was determined.