Developments in Wire-EDM for the Manufacturing of Fir Tree Slots in Turbine Discs Made of Inconel 718

Klocke, Fritz; Welling, D.; Dieckmann, Jens; Veselovac, D.; Pérez, Rebeca

doi:10.4028/www.scientific.net/kem.504-506.1177

Cited by 39 publications

(28 citation statements)

References 10 publications

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“…11. In recent years, milling and wire electrical discharge machining (WEDM), as more flexible machining techniques, have been intensively discussed in turbo machinery industries as alternatives other than broaching for the production of complex slots on turbine engine components [33,34]. More introduction with respect to the process of WEDM will be given in the next Section 4.2.…”

Section: Turning and Millingmentioning

confidence: 99%

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Chen¹

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Gas turbines are widely used in e.g., power generation, and aero-industries. Due to global warming, the demand for more efficient gas turbines has increased. A way to achieve this is by increasing the operating temperature of gas turbines. Therefore, nickel-based superalloys have been developed to withstand these extreme temperatures and loads, especially in the hot sections.Today, the way of operating land-based gas turbines is changing. Instead of running for long periods of time, the operation is becoming more flexible, with everincreasing cyclic loads and number of start and stop cycles. To handle the increased stress and cycles, component resistance to fatigue failure needs to be improved.Surface integrity is critical to fatigue performance, since fatigue cracks are normally initiated at surfaces. Nickel-based superalloys are difficult-to-machine materials, primarily due to their high strength, high tendency for work-hardening, and low thermal conductivity. The machining process changes the surface integrity of the alloys which can result in worse fatigue resistance.The work presented in this Ph.D. thesis was conducted in collaboration with Siemens Industrial Turbomachinery AB in Finspång, Sweden. Surface integrity changes which are induced during machining and their effects on fatigue performance have been studied on alloy Inconel 718. Inconel 718 is a widely-used nickel-based superalloy for high temperature applications in modern gas turbines.Broaching, milling, and wire electrical discharge machining, related to component manufacturing in turbo machinery industries, were included in this study. Surface irregularity and defects induced by machining provide preferential sites for fatigue crack initiation which influence the fatigue performance of the alloy. If compressive residual stresses are induced during machining, they benefit the fatigue life by retarding fatigue crack initiation away from surface regions. Shot peening was performed on machined Inconel 718, by which high compressive residual stresses are deliberately induced. It results in increased fatigue performance. The high iv temperatures in gas turbines generally deteriorate the surface integrity. For instance, recrystallization often occurs in the highly plastically-deformed surface layer. Microstructural degradation, in a form of α-Cr precipitates, have also been observed in the deformed surface and sub-surface microstructure when subjected to thermal exposure. Oxidation at elevated temperatures was found to degrade the surface integrity and thereby also the fatigue performance. Fatigue cracks are preferably initiated at oxidized surface carbides, if thermal exposure has been made prior to the test, and a reduced fatigue life is often obtained. It is even worse when high temperatures relax the beneficial compressive residual stresses induced by shotpeening and thereby lowering the fatigue resistance. This increases the interest for research regarding how to optimize the shot peening process in order to enhance the thermal stability o...

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Section: Turning and Millingmentioning

confidence: 99%

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Chen¹

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“…Thus, KLOCKE ET AL. derived a set of EDM parameters optimizing the surface integrity for the manufacturing of nickel-based alloy turbine blades [8]. With this set of parameters negative surface modifications are reduced to a minimum [6].…”

Section: Wire Electrical Discharge Machiningmentioning

confidence: 99%

“…The machine uses an oil-based dielectric and has implemented an up-to-date digital generator which enables high cutting rates. According to preliminary work processing Ti6Al4V [10] and Inconel718 [8], wire EDM was performed using brass wire electrode with a diameter of 0.25 mm in two cuts. The roughing-cut (generator setting E7 -roughing: open circuit voltage V = 200 V, discharge duration A = 0.05 μs, pulse interval time B = 5.40 μs, discharge current I = 4.0 A, offset G = 0.143 mm, cutting rate V w = 200 mm 2 /min) was used to cut out blocks and to separate the specimens at economical parameters (see Fig.…”

Section: Specimen Manufacturingmentioning

confidence: 99%

“…The effect of EDM and MHP parameters on surface integrity has already been studied by the authors. The authors derived suitable EDM-parameters using either Inconel 718 with regard to surface integrity [8] and fatigue [9] or Ti6AL4V [10] as well as investigated the MHP indentation force [11] and influence of MHP-parameters on residual stresses and strain hardening [12]. However, the impact of improved surface integrity on fatigue strength under cyclic loading is insufficiently researched.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the surface integrity and fatigue strength of Inconel718 after wire EDM and machine hammer peening

et al. 2015

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Highly stressed turbine blades made of Inconel718 (DIN NiCr19NbMo (2.4668); ASTM B637; UNS N07718) have to satisfy stringent requirements regarding durability and reliability. The impact of surface integrity on the fatigue strength of the workpiece material has proven to be of significant importance. An optimization of the surface integrity after wire EDM of Inconel718 can be achieved using the surface finishing process machine hammer peening. Machine hammer peening is an incremental forming process which has the potential to induce residual compressive stresses and strain hardening while smoothing surface asperities. As the effect of machine hammer peening on surface integrity has not yet been completely investigated, this paper deals with its description and modeling of the unknown impact of machine hammer peening on the fatigue strength of Inconel718. Wire EDM and machine hammer peening parameters maximizing the fatigue strength are presented. Experimental measurements are performed to quantify the surface integrity, especially surface roughness, compressive residual stresses and strain hardening, after wire EDM and subsequent machine hammer peening. The evaluation of the effect of surface integrity on the fatigue strength is carried out using a bending fatigue strength testing machine. Additionally, a finite element model is developed to analyze the surface integrity under load and to reveal the effects of difficult-to-measure properties on the fatigue strength. Based on the new knowledge gained during this work, a model to predict the fatigue strength using similitude theory is presented. Along with the previously analyzed correlations between surface integrity and fatigue strength, this allows a constructive setting of machine hammer peening parameters. Thereby, a significant new contribution to knowledge about the influence of machine hammer peening on surface integrity and fatigue strength of Inconel718 is made. The presented approach can be easily transferred to other materials and workpiece geometries

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“…An overview of achievable surface integrities was given by Aspinwall et al [4] and Li et al [5]. Klocke et al [6] presented slot qualities that exhibit geometry tolerances within t ± 5 μm, surface roughness values Ra < 0.8 μm and recast layer thicknesses which tend to zero in thickness. Even the resulting dynamic component strength of produced parts by Wire-EDM was shown to be in the same magnitude as broaching by Welling [7].…”

Section: Introductionmentioning

confidence: 98%

Quality Assessment through In-process Monitoring of Wire-EDM for Fir Tree Slot Production

et al. 2014

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Against the background of an increased importance of in-process quality measurement -especially for manufacturing of safety critical jet engine componets -this paper deals with the development of a process monitoring tool for process quality assessment and correlating surface integrity evaluation of Wire-EDM for fir tree slot production. For the last trim cut, which is the relevant cut for the final surface integrity, a correlation between process data and surface integrity aspects is set up. The process data are read out from the machine tool's controlling device to obtain a position depending signal of mean gap voltage for the quality assessment. Two demonstration runs showed the work capability of the monitoring tool for cutting the often applied nickel-based turbine alloy Inconel 718. On the one hand a failure free slot machining process and on the other hand a manipulated machining process with enforced short circuits were conducted. For the manipulated process these instabilities were successfully detected. A cross section view analysis of both fir tree slots results in best surface integrity qualities for the first run, which shows the potential to machine fir tree slots by Wire-EDM, and failures in the surface of the manipulated run due to short cuts. These failures were additionally correlated with the position depending signal. With the developed monitoring tool a first approach was designed to build up an in-process and position oriented quality assessment for the production of fir tree slots by Wire-EDM.

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Developments in Wire-EDM for the Manufacturing of Fir Tree Slots in Turbine Discs Made of Inconel 718

Cited by 39 publications

References 10 publications

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Investigation of the surface integrity and fatigue strength of Inconel718 after wire EDM and machine hammer peening

Quality Assessment through In-process Monitoring of Wire-EDM for Fir Tree Slot Production

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