RESUMEN
This review article presents a summary of currently used and proposed methods of manufacturing fir tree slots of discs in turbine engines. The production of aircraft, including aircraft engines during times of overlapping global economic crises related to the COVID-19 pandemic or the war in Eastern Europe requires a quick response to the changing numbers of passengers and cargo. Similarly, the aviation industry must adapt to these conditions, and thus utilize flexible production methods allowing for a quick change in the design or type of a given part. Due to the constant adoption of new materials for the most critical aero engine parts and the necessity of complying with environmental regulations, it is necessary to search for new methods of manufacturing these parts, including fir tree slots. As an alternative to currently used expensive and energy-intensive broaching, many manufacturers try to implement creep feed grinding CFG or contour milling. However, other manufacturing methods, thus far rarely used for crucial machine parts such as WEDM, ECDM or AWJ, are gaining more and more popularity in the aviation industry. This article presents the advantages and shortcomings of these methods in the context of manufacturing fir tree slots.
RESUMEN
High feed Milling is a new milling method, which allows to apply high feed rates and increase machining efficiency. The method utilizes face cutters with a very small entering angle, of about 10°-20°. Thus, the cut layer cross-section is different than in traditional milling. In order to examine the high feed milling (HFM), experimental tests were conducted, preceded by an analysis of cutting zones when milling with an HF face cutter. The face milling tests of 42CrMo4 steel with the use of an HF cutter characterized by an entering angle, dependent on axial depth of cut ap and insert radius r values, as well as with a conventional face cutter with the entering angle of 45° were performed. The study focused on analyzing the vibration amplitude, cutting force components in the workpiece coordinate system, and surface roughness. The experimental tests proved, that when milling with constant cut layer thickness, the high feed cutter allowed to obtain twice the cutting volume in comparison with the conventional face cutter. However, higher machining efficiency resulted in an increase in cutting force components. Furthermore, the results indicate significantly higher surface roughness and higher vibration amplitudes when milling with the HF cutter.
RESUMEN
Servicing aircraft engines sometimes requires manufacturing only a single piece of a given part. Manufacturing a turbine disc using traditional methods is uneconomical. It is necessary to use a different machining method recommended for small lot production. One of the proposed methods is WEDM (wire electrical discharge machining). The article presents the results of the research on finishing WEDM of Inconel 718 turbine disc fir tree slots. The influence of infeed, mean gap voltage, peak current, pulse off-time, and discharge energy on the shape accuracy, surface roughness, microcracks, and the white layer thickness were determined. Mathematical models were developed based on the DoE (Design of Experiment) analysis. The statistical significance of the models was verified with the ANOVA (Analysis of Variance) test. The machining parameters control methods that allow achieving the required shape accuracy, surface roughness, and surface layer condition were presented. The obtained surface roughness was Ra = 0.84 µm, the shape accuracy of the slot in the normal-to-feed direction was Δd = 0.009 µm, the profile shape accuracy was Δr = 0.033 µm, and the thickness of recast (white) layer was approximately 5 µm.