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Enhanced heat transfer and tool wear in high-pressure coolant assisted turning of alloy 718
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-0895-3303
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Förbättrad värmeavledning och verktygsslitage vid högtryckskyld svarvning av legering 718 (Swedish)
Abstract [en]

Heat generated in a machining process is a common and critical obstacle faced in today's manufacturing industries. The heat generated in the cutting zone has adirect negative influence on the tool life, which, in turn contributes to increasing the manufacturing costs. Especially in the machining of Heat Resistant Superalloys, HRSA, this is a very limiting factor. HRSA are capable of retaining their mechanical strength and hardness at elevated temperatures. This property is advantageous for applications such as aero-engines, but also a disadvantage, since it also lowers the machinability significantly.This work is an attempt to improve the heat transfer from the cutting zone, which would lead to an increase in the tool life. To achieve this goal, the effect of cooling the flank face (tertiary shear zone) with high-pressure is studied; furthermore, the cutting tool has been modified to create an improved interface between the high pressure coolant and the tool where high-temperature gradient exists.Three main generations of inserts have been designed and investigated. Firstly, an insert with surface texture features created with the purpose of increasing the available surface area for heat dissipation: First generation, Gen I. Secondly, GenI+, a modified rake design of Gen I, for improved frictional conditions on the tool-chip contact. Thirdly, Gen II was designed as a further improvement of GenI. Here, several channel features on the rake face were added, reaching out from the contact zone to the near proximity of the cutting edge. This has the purpose of improving access of the coolant closer to the cutting edge.The experiments were conducted in facing operations of Alloy 718 with uncoated round carbide inserts. All experiments were carried out with high-pressure coolant, with a maximum available pressure of 16 MPa on the rake face and 8MPa on the flank face, respectively. The three generations of inserts, Gen I, I+and II, were experimentally evaluated by tool wear analysis in comparison with a regular insert. The results shows that the tool life increased significantly for the Gen I insert, compared to catastrophic failure of the regular insert at the same conditions. Regarding the Gen II insert, an increase in tool life by approximately30-40 percent, compared to Gen I inserts was observed. XRegarding the coolant-boiling phenomenon, results revealed the existence in form of dark region (Ca precipitate) below the flank wear land. The location and size of the coolant-boiling region is interrelated between flank wear, cutting zone temperature, coolant pressure and vapour pressure of the coolant at the investigated coolant pressure levels. The coolant applied at a pressure lower than the vapour pressure of the coolant itself will cause the "Leidenfrost effect" to appear that will effectively act as a coolant barrier region. However, most importantly, this effect led to the observation of a new wear mechanism present "Cavitation Wear". This type of wear appears in the form of erosion pits on the flank surface of the insert and it is observed for flank pressure conditions of 4and 8 MPa. It is a new phenomenon in tool wear to be seen on uncoated WC cutting tools during machining operations with high-pressure coolant.

Place, publisher, year, edition, pages
Trollhättan: University West , 2019. , p. 118
Series
PhD Thesis: University West ; 31
Keywords [en]
Alloy 718; Cavitation; Coolant-boiling; High-pressure coolant; Heat dissipation, Leidenfrost effect; Textured insert; Tungsten carbide; Tool life; Tool wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-14663ISBN: 978-91-88847-42-3 (print)ISBN: 978-91-88847-41-6 (electronic)OAI: oai:DiVA.org:hv-14663DiVA, id: diva2:1366717
Public defence
2019-11-22, Albertssalen, 10:00 (English)
Opponent
Supervisors
Available from: 2019-10-30 Created: 2019-10-30 Last updated: 2019-10-30Bibliographically approved
List of papers
1. Effects of high pressure cooling in the flank and rake faces of WC tool on the tool wear mechanism and process conditions in turning of alloy 718
Open this publication in new window or tab >>Effects of high pressure cooling in the flank and rake faces of WC tool on the tool wear mechanism and process conditions in turning of alloy 718
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2019 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 434-435, article id 102922Article in journal (Refereed) Published
Abstract [en]

The exceptional properties of Heat Resistant Super Alloys (HRSA) justify the search for advanced technologiesthat can improve the capability of machining these materials. One such advanced technology is the applicationof a coolant at high pressure while machining, a strategic solution known for at least six decades. The aim is toachieve extended tool life, better chip control and improved surface finish. Another aim is to control the temperature in the workpiece/tool interface targeting for optimum cutting conditions. In most of the existing applications with high-pressure coolant media, the nozzles are positioned on the rake face side of the insert andthey are directed towards the cutting edge (the high-temperature area). The coolant is applied at high-pressureto improve the penetration of the cooling media along the cutting edge in the interface between the insert andworkpiece material (chip) as well as to increase chip breakability. However, the corresponding infusion ofcoolant media in the interface between the flank face of the insert and the work material (tertiary shear zone) hasbeen previously only scarcely addressed, as is the combined effect of coolant applications on rake and clearancesides of the insert. The present work addresses the influence of different pressure conditions in (flank: 0, 4 and8 MPa; rake: 8 and 16 MPa) on maximum flank wear, flank wear area, tool wear mechanism, and overall processperformance. Round uncoated inserts are used in a set of face turning experiments, conducted on the widely usedHRSA "Alloy 718" and run in two condition tests with respect to cutting speed (45 (low) and 90 (high) m/min).The results show that an increase in rake pressure from 8 to 16 MPa has certainly a positive impact on tool life.Furthermore, at higher vc of 90 m/min, cutting edge deterioration: due to an extensive abrasion and crack in thewear zone were the dominant wear mechanism. Nevertheless, the increase in coolant pressure condition to16 MPa reduced the amount of abrasion on the tool compared to 8 MPa. At the lower cutting speed, no crack orplastic deformation or extensive abrasion were found. When using 8 MPa pressure of coolant media on the flank,the wear was reduced by 20% compared to flood cooling conditions. Application of high-pressure cooling on theflank face has a positive effect on tool life and overall machining performance of Alloy 718.

Keywords
Alloy 718, Cemented tungsten carbide, High-pressure coolant, Tool wear mechanism, Crack, Coolant-boiling
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14330 (URN)10.1016/j.wear.2019.05.037 (DOI)000487194500001 ()2-s2.0-85070612386 (Scopus ID)
Funder
Knowledge Foundation, 20140130Region Västra Götaland
Note

Funders:ESIF , EU Operational Programme Research , Development and Education; the Centre of Advanced Aerospace Technology ( CZ.02.1.01/0.0/0.0/16_019/0000826 )

Available from: 2019-08-26 Created: 2019-08-26 Last updated: 2019-12-11Bibliographically approved
2. Influence of Surface Features for Increased Heat Dissipation on Tool Wear
Open this publication in new window or tab >>Influence of Surface Features for Increased Heat Dissipation on Tool Wear
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2018 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 5, article id E664Article in journal (Refereed) Published
Abstract [en]

The critical problems faced during the machining process of heat resistant superalloys, (HRSA), is the concentration of heat in the cutting zone and the difficulty in dissipating it. The concentrated heat in the cutting zone has a negative influence on the tool life and surface quality of the machined surface, which in turn, contributes to higher manufacturing costs. This paper investigates improved heat dissipation from the cutting zone on the tool wear through surface features on the cutting tools. Firstly, the objective was to increase the available surface area in high temperature regions of the cutting tool. Secondly, multiple surface features were fabricated for the purpose of acting as channels in the rake face to create better access for the coolant to the proximity of the cutting edge. The purpose was thereby to improve the cooling of the cutting edge itself, which exhibits the highest temperature during machining. These modified inserts were experimentally investigated in face turning of Alloy 718 with high-pressure coolant. Overall results exhibited that surface featured inserts decreased flank wear, abrasion of the flank face, cutting edge deterioration and crater wear probably due to better heat dissipation from the cutting zone.

Keywords
Alloy 718, carbide insert, high-pressure coolant, machining, textured inserts, tool-chip contact area
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12274 (URN)10.3390/ma11050664 (DOI)000434711700014 ()29693579 (PubMedID)2-s2.0-85046275282 (Scopus ID)
Funder
Knowledge FoundationRegion Västra Götaland
Note

Funders: EDS

Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2019-11-18Bibliographically approved
3. Investigation of micro-textured cutting tools used for face turning of alloy 718 with high-pressure cooling
Open this publication in new window or tab >>Investigation of micro-textured cutting tools used for face turning of alloy 718 with high-pressure cooling
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2019 (English)In: Journal of manufacturing processes, ISSN 1526-6125, Vol. 37, p. 606-616Article in journal (Refereed) Published
Abstract [en]

There is an increasing demand to improve the service life of cutting tools during machining of heat resistant superalloys (HRSA). Various studies showed that textured cutting tools improved the tribological properties and reduced cutting forces, temperature, and tool wear. Surface texturing can be seen as a futuristic design to improve the performance of the cutting tool and to increase productivity. However, only limited research has been conducted in machining superalloys with textured inserts and high-pressure coolant. In this work, three different micro texture designs on both rake and flank face are investigated in combination with high-pressure coolant in machining Alloy 718. Due to better tool life predictability, carbide cutting tools are used in machining components made from superalloys. However, the disadvantage is that machining can only be done at lower cutting speed/feed rate/depth of cut with high tool wear rates. The experimental investigation using different tool wear analysis methods showed that the combination of a cylindrical dimple on the rake and the square pyramid texture on the flank surface improved the wear resistance of the tool. An increase in tool life of about 30% was achieved as compared with a regular insert for the investigated cutting conditions. Different levels of adhering workpiece material were observed on the rake face of textured tools. Furthermore, the chip backside showed imprints from the tool textures. The tool textures on the rake face have influenced the tool-chip friction conditions during cutting.

Keywords
Alloy 718Face turningHigh-pressure coolantNext generation cutting toolsTextured insertsTool wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13430 (URN)10.1016/j.jmapro.2018.12.023 (DOI)000465052000058 ()2-s2.0-85060085875 (Scopus ID)
Funder
Region Västra GötalandKnowledge Foundation, 20140130
Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-12-12Bibliographically approved
4. EDS Analysis of Flank Wear and Surface Integrity in Machining of Alloy 718 with Forced Coolant Application
Open this publication in new window or tab >>EDS Analysis of Flank Wear and Surface Integrity in Machining of Alloy 718 with Forced Coolant Application
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2016 (Swedish)In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 45, p. 271-274Article in journal (Refereed) Published
Abstract [en]

There has been extensive research on forced coolant application, usually known as high pressure coolant, in machining heat resistant super alloys. This technology has shown to improve the tool life, chip segmentation, surface integrity and reduce the temperature in the cutting zone. A number of studies have been done on hydraulic parameters of the coolant. This study has been focused on residues on the flank face of the insert and residual stress on the workpiece surface generated by regular and modified cutting inserts. To identify any residual elements, analysis were done by energy dispersive X-ray spectrometer, EDS, on regular as well as modified inserts in combination with forced coolant application on both rake and flank face. The investigations have shown that the temperature gradient in the insert has changed between the regular and modified cutting inserts and that the tool wear and surface roughness is significantly affected by the modified cutting tool.

Keywords
EDS; Heat zone; Surface roughness; Residues; Facing; Forced coolant application; Residual stress
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10031 (URN)10.1016/j.procir.2016.02.144 (DOI)2-s2.0-84978639847 (Scopus ID)
Conference
3rd CIRP Conference on Surface Integrity,
Funder
Region Västra Götaland
Available from: 2016-10-21 Created: 2016-10-21 Last updated: 2019-12-03Bibliographically approved
5. Flank wear characteristics of WC-Co tools when turning Alloy 718 with high-pressure coolant supply
Open this publication in new window or tab >>Flank wear characteristics of WC-Co tools when turning Alloy 718 with high-pressure coolant supply
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2017 (English)In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 30, no Supplement C, p. 116-123Article in journal (Refereed) Published
Abstract [en]

In the present study, the tool wear mechanisms of uncoated cemented tungsten carbide (WC-Co) tools during machining Alloy 718 with high-pressure coolant supply are investigated. Worn flank faces are analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). With increasing spiral cutting length, larger areas on the tool surface are subjected to erosion of Co-binder by the coolant jet impact. Moreover, the amount and morphology of workpiece-precipitates adhered on worn flank surfaces are influenced significantly by the extent of flank wear land (due to increasing spiral cutting length). The reasons for the obtained results are addressed with respect to the underlying mechanisms. Possible implications for the tool wear behavior are discussed.

Place, publisher, year, edition, pages
Dearbord, Mich.: Society of Manufacturing Engineers, North American Manufacturing Research Institution, 2017
Keywords
Wear mechanisms, High-pressure jet assisted machining, Cemented tungsten carbide, Alloy 718, Erosion, Co-capping
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11802 (URN)10.1016/j.jmapro.2017.09.017 (DOI)000418212100011 ()2-s2.0-85029704988 (Scopus ID)
Funder
Region Västra Götaland
Note

Available online 22 September 2017.

Funders: Area of Advance Production at Chalmers University of Technology

Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2019-11-18Bibliographically approved

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