Manufacturing Technologies for Fir Tree Slots: A Technological and Economic Evaluation

Abstract

Fir tree slots in engine disks pose a great challenge to the production process, especially due to the use of increasingly filigree geometries. Broaching with high-speed steel (HSS) as cutting tool material has been established as the state of the art process. However, this manufacturing process obtains the disadvantages of high tool costs and long waiting times in case of geometry adaptations. Alternative manufacturing technologies, namely electrochemical machining (ECM) and wire electrical discharge machining (WEDM) offer the potential to replace broaching. Because of their removal mechanism being independent of the mechanical properties of the material, these processes are not hindered by increasingly higher thermomechanical material properties. Furthermore, the tool in WEDM is not specific to geometry, allowing fast adaptations. Nevertheless, the technology specific white layer may reduce the mechanical integrity of the engine disk. ECM in contrast has no negative impact on the rim zone of the workpiece but the tool is still specific to the slot geometry. Consequently, this paper experimentally investigates the three different manufacturing technologies in order to evaluate their capability to manufacture fir tree slots with respect to geometric accuracy and surface integrity. Subsequently, the technology specific manufacturing costs are considered to outline the economic potential of each process while taking into account the influence of the batch size.

A brief review on the status of machining technology of fir-tree slots on aero-engine turbine disk

“…29 Vogtel et al put forward a broach structure of carbide inserts, optimized the shape of broach tooth for superalloy materials, and further improved the machining efficiency and ability for turbine disk slots. The experimental results showed that the processing efficiency of cemented carbide broaching tool was 4–10 times that of HSS broaching tool, the broaching force was reduced by nearly 35%, the thickness of the deformed layer of machined surface was reduced by about 50%, 30,31 as shown in Figure 6. Meanwhile, the wear law of surface coated and uncoated carbide broach inserts were preliminarily studied, which provided important experimental data reference for the popularization and application of high-speed broaching technology for turbine disk slots.…”