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Surface integrity on post processed alloy 718 after nonconventional machining
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-2991-2911
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There is a strong industrial driving force to find alternative production 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 allows taking a giant leap to increase the material removal rate and thereby drastically increase the productivity. However, the end result is to meet the requirements set for today's machined surfaces.The present work has been dedicated to improving the knowledge of how the non-conventional machining methods Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. The aim has been to understand how the surface integrity could be altered to an acceptable level. The results of this work have shown that both EDM and AWJM are two possible candidates but EDM is the better alternative; mainly due to the method's ability to machine complex geometries. It has further been shown that both methods require post processing in order to clean the surface and to improve the topography and for the case of EDM ageneration of compressive residual stresses are also needed.Three cold working post processes have been evaluated in order to attain this: shot peening, grit blasting and high pressure water jet cleaning, HPWJC. There sults showed that a combination of two post processes is required in order to reach the specified level of surface integrity in terms of cleaning and generating compressive residual stresses and low surface roughness. The method of high pressure water jet cleaning was the most effective method for removing the EDM wire residuals, and shot peening generated the highest compressive residual stresses as well as improved the surface topography.To summarise: the most promising production flow alternative using nonconventional machining would be EDM followed by post processing using HPWJC and shot peening.

Place, publisher, year, edition, pages
Trollhättan: University West , 2018. , p. 92
Series
Licentiate Thesis: University West ; 20
Keywords [en]
Alloy 718, Non-conventional machining, post processing, surface integrity, Microstructure, Residual stress, Electron back scattering diffraction, Material removal rate
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-12191ISBN: 978-91-87531-72-9 (print)ISBN: 978-91-87531-71-2 (electronic)OAI: oai:DiVA.org:hv-12191DiVA, id: diva2:1187107
Presentation
2018-03-07, C120, Högskolan Väst, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2018-03-07 Created: 2018-03-02
List of papers
1. Evaluation of surface integrity after high energy machining with EDM, Laser Beam Machining and Abrasive Water Jet Machining of Alloy 718
Open this publication in new window or tab >>Evaluation of surface integrity after high energy machining with EDM, Laser Beam Machining and Abrasive Water Jet Machining of Alloy 718
(English)Manuscript (preprint) (Other academic)
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12189 (URN)
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
2. Surface integrity and fatigue of non-conventional machined Alloy 718
Open this publication in new window or tab >>Surface integrity and fatigue of non-conventional machined Alloy 718
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12190 (URN)
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
3. Grit Blasting for Removal of Recast Layer from EDM Process on Inconel 718 Shaft: An Evaluation of Surface Integrity
Open this publication in new window or tab >>Grit Blasting for Removal of Recast Layer from EDM Process on Inconel 718 Shaft: An Evaluation of Surface Integrity
2016 (English)In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 25, no 12, p. 5540-5550Article in journal (Refereed) Published
Abstract [en]

The heat generated during EDM melts the work material and thereby allows large amounts to be removed,but an unfavorable surface of a recast layer (RCL) will also be created. This layer has entirely different properties compared to the bulk. Hence, it is of great interest to efficiently remove this layer and to verify that it has been removed. The main objective of this work has been to study the efficiency of grit blasting forremoval of RCL on an EDM aero space shaft. Additionally, x-ray fluorescence (XRF) has been evaluated asa nondestructive measurement to determine RCL presence. The results show that the grit-blasting processing parameters have strong influence on the ability to remove RCL and at the same time introduce beneficial compressive stresses even after short exposure time. Longer exposure will remove the RCL fromthe surface but also increase the risk that a larger amount of the blasting medium will get stuck into the surface. This investigation shows that a short exposure time in combination with a short grit-blasting nozzle distance is the most preferable process setting. It was further found that handheld XRF equipment can be used as a nondestructive measurement in order to evaluate the amount of RCL present on an EDM surface.This was realized by analyzing the residual elements from the EDM wire.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Aerospace, EDM, Inconel 718, residual stress, shot blasting, surface integrity, XRF
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10098 (URN)10.1007/s11665-016-2406-8 (DOI)2-s2.0-84992397193 (Scopus ID)
Available from: 2016-10-31 Created: 2016-10-31 Last updated: 2018-03-02Bibliographically approved
4. Surface integrity after post processing of EDM processed Inconel 718 shaft
Open this publication in new window or tab >>Surface integrity after post processing of EDM processed Inconel 718 shaft
2018 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 95, no 5-8, p. 2325-2337Article in journal (Refereed) Published
Abstract [en]

Electrical discharge machining (EDM) is considered as an efficient alternative to conventional material removal concepts that allows for much higher material removal rates. However, EDM generates unwanted features such as re-cast layer (RCL), tensile residual stresses and a rough surface. In order to recover the surface integrity, different post processes has been compared: high-pressure water jet (HPWJ), grit blasting (GB) and shot peening (SP). Surface integrity has been evaluated regarding microstructure, residual stresses, chemical content and surface roughness. The results showed that a combination of two post processes is required in order to restore an EDM processed surface of discontinuous islands of RCL. HPWJ was superior for removing RCL closely followed by grit blasting. However, grit blasting showed embedded grit blasting abrasive into the surface. Regarding surface roughness, it was shown that both grit blasting and HPWJ caused a roughening of the surface topography while shot peening generates a comparably smoother surface. All three post processes showed compressive residual stresses in the surface where shot peening generated the highest amplitude and penetration depths. However, the microstructure close to the surface revealed that shot peening had generated cracks parallel to the surface. The results strongly state how important it is to evaluate the surface at each of the different subsequent process steps in order to avoid initiation of cracks.

Keywords
Surface integrity Inconel 718 Shot peening Abrasive water jet Grit blasting EDM
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-11894 (URN)10.1007/s00170-017-1342-6 (DOI)000426055600058 ()2-s2.0-85034646822 (Scopus ID)
Note

First Online: 22 November 2017

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2018-04-06Bibliographically approved

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Holmberg, Jonas

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