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Selection of milling strategy based on surface integrity investigations of highly deformed Alloy 718 after ceramic and cemented carbide milling
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. RISE IVF AB, Argongatan 30, Mölndal, 431 53, Sweden. (PTW)ORCID iD: 0000-0003-2991-2911
GKN Aerospace Sweden AB, Trollhättan, 461 81, Sweden.
RISE IVF AB, Argongatan 30, Mölndal, 431 53, Sweden.
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-0976-9820
2020 (English)In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 58, p. 193-207Article in journal (Refereed) Published
Abstract [en]

High speed milling with ceramic indexable inserts is a current practice for manufacturing of gas turbine components in superalloys since it allows for high material removal rates. Ceramic milling is used for rough milling, which is followed by cemented carbide semi- and finish milling. The tool motion play an important role on the resulting surface integrity. The machining strategy of up or down milling will induce different degree of residual stresses and deformations. Increased knowledge of selecting the machining strategy with lowest impact will promote improved productivity by using ceramic milling to a greater extent based on the affected depth. The main objective in this work has been to correlate the residual stresses and deformations to promote a greater utilization of ceramic milling while still producing surfaces with acceptable properties. Prior investigations have shown that ceramic milling induce very high tensile stresses in the surface, exceeding the material’s nominal yield strength. A second objective has been to explain these stress levels by thorough investigations of the deformation after milling. In this study, milling tests with new and worn ceramic and cemented carbide inserts have been performed in Alloy 718. The topography, residual stresses, deformation and hardness have been investigated for up, centre and down milling. Residual stress measurements were performed using X-ray diffraction, followed by evaluation of hardness and deformation, using hardness testing, light optical microscopy as well as electron back scattering diffraction (EBSD). These results have been used to determine an appropriate milling strategy based on lowest possible impact in respect to residual stresses and deformation. The results show a high degree of deformation after milling that differs for the up, centre and down milling. Based on these results, it is shown that up milling is preferable for new inserts but as the inserts wear out, down milling becomes more suitable since a lower degree of deformation and residual stress impact was observed. EBSD and hardness testing showed that the milling, especially ceramic milling, caused severe deformation of the surfaces resulting in grain refinement to a nano-crystalline level. This is most likely the explanation for the prevalence of the high tensile stresses without distorting or causing failure. © 2020 The Authors

Place, publisher, year, edition, pages
2020. Vol. 58, p. 193-207
Keywords [en]
Backscattering; Carbide tools; Carbides; Ceramics industry; Deformation; Grain refinement; Hardness; Hardness testing; Nanocrystalline materials; Petroleum reservoir evaluation; Residual stresses; Tensile stress; Topography; Well testing, Degree of deformations; Electron backscattering diffraction; Light optical microscopies; Machining strategy; Material removal rate; Milling strategies; Nominal yield strength; Severe Deformation, Milling (machining)
National Category
Other Materials Engineering Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-15771DOI: 10.1016/j.jmapro.2020.08.010ISI: 000583414900017Scopus ID: 2-s2.0-85089503058OAI: oai:DiVA.org:hv-15771DiVA, id: diva2:1464117
Funder
Vinnova, 2015-06047Available from: 2020-09-04 Created: 2020-09-04 Last updated: 2020-12-17Bibliographically approved
In thesis
1. High volumetric machining strategies for superalloy gasturbine components: Comparing conventional and nonconventional machining methods for efficient manufacturing
Open this publication in new window or tab >>High volumetric machining strategies for superalloy gasturbine components: Comparing conventional and nonconventional machining methods for efficient manufacturing
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is a strong industrial driving force to find alternative manufacturing technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies, as well as enhanced utilisation of today's high volumetric manufacturing, allows taking a leap to increase the material removal rate and the productivity. However, the final goal is to meet there quirements set for today's machined surfaces.The objective with the present work has been performed to show how the conventional, Milling, and the non-conventional machining methods, Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. This knowledge can beused to define and optimise different manufacturing alternatives for existing orfuture production.The results show that it is possible to use the rough milling to a greater extent if the impact on residuals stresses and deformation is used when determine the machining allowance. This could have a great impact on the productivity.

However, further improvement of the productivity requires an alternative method. For this reason, EDM and AWJM was evaluated and shown to be suitable alternatives to today's manufacturing methods, but both methods require post processing. The results showed that a combination of two post processes is required for addressing issues with residue, topography and residual stresses.The most promising and effective manufacturing strategy would be EDM or AWJM for rough machining followed by post processing either by finish millingor post processing by means of High-Pressure Water Jet Cleaning and shot peening. If EDM and AWJM are to be considered as finish machining operations, further development of the two methods are required.

Place, publisher, year, edition, pages
Trollhättan: University West, 2020. p. 121
Series
PhD Thesis: University West ; 40
Keywords
Alloy 718, High volumetric machining, Conventional and Nonconventional machining, Material removal rate, Post processing, surface integrity, Residual stress, Microstructure, Deformation
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16010 (URN)978-91-88847-75-1 (ISBN)978-91-88847-74-4 (ISBN)
Public defence
2020-11-04, Albertssalen, 10:00 (English)
Opponent
Supervisors
Available from: 2020-11-11 Created: 2020-11-10 Last updated: 2020-11-10Bibliographically approved

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Holmberg, JonasBeno, Tomas

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