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Coolant boiling and cavitation wear: a new tool wear mechanism on WC tools in machining Alloy 718 with high-pressure coolant
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-0895-3303
Chalmers University of Technology, Department of Industrial and Materials Science, Göteborg, Sweden.
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-0976-9820
Chalmers University of Technology, Department of Industrial and Materials Science, Göteborg, Sweden.
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2020 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 452-453, article id 203284Article in journal (Refereed) Published
Abstract [en]

In recent years, research interest in liquid coolant media applied to the tool–workpiece interface (the tertiary shear zone) has grown considerably. In particular, attention has increased for work where the media has been applied under high-pressure. This is most likely triggered by the positive results reported on similar applications, but with coolant media directed towards the rake face of the cutting tool (the secondary shear zone). The most typical applications have not surprisingly been related to the machining of Heat Resistant Super Alloys (HRSA) or other “difficult to machine” alloys where the main intention has been to extend tool life and improve surface finish through reduced shear zone temperatures. Concurrently, these achievements have revealed a knowledge gap and unlocked a new research area in understanding the effects and influences of coolant media applied on super-heated surfaces under high-pressure conditions. The aim of this study is to investigate the “coolant boiling and cavitation” phenomena that emerges during the application of coolant under high-pressure to the flank face of an uncoated WC tool while turning Alloy 718. The experimental campaign was conducted in three aspects: varying flank (coolant media) pressure; varying spiral cutting length (SCL); and varying cutting speed. The results revealed that the location and size of the coolant-boiling region correlated with flank wear, coolant pressure and vapour pressure of the coolant at the investigated pressure levels. Further, the results showed that coolant applied with a lower pressure than the vapour pressure of the coolant itself caused the “Leidenfrost” effect. This then acts as a coolant media barrier and effectively reduces the heat transport from the cutting zone. Further, erosion pits were observed on small areas of the cutting tool, resembling the typical signs of cavitation (usually found in much different applications such as pumps and propellers). The discovered wear mechanism denoted as “Cavitation Wear” was used as base for the discussion aimed to deepen the understanding of the conditions close to the sliding interface between the tool and the workpiece. Even though “Cavitation Wear” has been widely reported in hydraulic systems like pumps and water turbines, it is a new phenomenon to be seen on cutting tools while using high-pressure flank cooling. © 2020 The Authors

Place, publisher, year, edition, pages
Elsevier, 2020. Vol. 452-453, article id 203284
Keywords [en]
Alloy 718, Coolant boiling, Cavitation wear, High-pressure coolant, Tool wear mechanism, Tungsten carbide
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-15156DOI: 10.1016/j.wear.2020.203284ISI: 000539275700002Scopus ID: 2-s2.0-85083650341OAI: oai:DiVA.org:hv-15156DiVA, id: diva2:1427930
Funder
Knowledge Foundation, 20140130Region Västra GötalandAvailable from: 2020-05-04 Created: 2020-05-04 Last updated: 2020-09-10Bibliographically approved
In thesis
1. Enhanced heat transfer and tool wear in high-pressure coolant assisted turning of alloy 718
Open this publication in new window or tab >>Enhanced heat transfer and tool wear in high-pressure coolant assisted turning of alloy 718
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Förbättrad värmeavledning och verktygsslitage vid högtryckskyld svarvning av legering 718
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
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:nbn:se:hv:diva-14663 (URN)978-91-88847-42-3 (ISBN)978-91-88847-41-6 (ISBN)
Public defence
2019-11-22, Albertssalen, 10:00 (English)
Opponent
Supervisors
Available from: 2019-10-30 Created: 2019-10-30 Last updated: 2020-06-16Bibliographically approved

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Tamil Alagan, NageswaranBeno, Tomas

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