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Wear mechanisms in galling: cold work tool materials sliding against high-strength carbon steel sheets
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. (Materialteknik)
Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. (Materials Engineering, Materials Science)ORCID iD: 0000-0002-9441-2502
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.ORCID iD: 0000-0001-6029-2613
2009 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 33, no 1, 45-53 p.Article in journal (Other academic) Published
Abstract [en]

Transfer and accumulation of adhered sheet material, generally referred to as galling, is the major cause for tool failure in sheet metal forming. In this study, the galling resistances of several tool steels were evaluated against dual-phase high-strength carbon steel using a SOFS tribometer, in which disc-shaped tools were slid against a real sheet surface in dry sliding test conditions. Three different frictional regimes were identified and characterized during sliding, and any transition in friction corresponded to a transition in wear mechanisms of the sheets. The performance of the tools depended on load, material and the particular frictional regime. Best overall performance was obtained by nitrogen-alloyed powder metallurgy tool steel.

Place, publisher, year, edition, pages
Springer, 2009. Vol. 33, no 1, 45-53 p.
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-3034DOI: 10.1007/s11249-008-9390-6OAI: oai:DiVA.org:kau-3034DiVA: diva2:126664
Available from: 2008-11-19 Created: 2008-11-19 Last updated: 2017-06-22Bibliographically approved
In thesis
1. Wear mechanisms in sheet metal forming: Effects of tool microstructure, adhesion and temperature
Open this publication in new window or tab >>Wear mechanisms in sheet metal forming: Effects of tool microstructure, adhesion and temperature
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of lubricants, in combination with the introduction of high and ultrahigh-strength sheet materials, continuously increases the demands on the forming tools. The major cause for tool failure during the forming process is transfer and accumulation of sheet material on the tool surfaces, generally referred to as galling. The adhered material creates unstable frictional conditions and scratching of the tool/sheet interface. To provide the means of forming new generations of sheet materials, development of new tool materialswith improved galling resistance is required, which may include tailored microstructures introducing specific carbides and nitrides, coatings and improved surface finish. In the present work, the galling wear mechanisms in real forming operations have been studied and emulated at a laboratory scale by developing a test equipment. The wear mechanisms, identified in the real forming process, were distinguished into a sequence of events. At the initial stage, local adhesive wear of the sheets led to transfer of sheet material to the tool surfaces. Successive forming operations resulted in growth of the transfer layer with initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated withgross macroscopic damage. The wear process was successfully repeated in the laboratory test equipment in sliding between several tool materials, ranging from cast iron and conventional ingot cast tool steels, to advanced powder metallurgy tool steel, sliding against medium and high-strength steel sheets. By use of the test equipment, selected tool materials were ranked regarding galling resistance. The controlling mechanism for galling in sheet metal forming is adhesion. The initial sheet material transfer was found to occur, preferably, to the metallic matrix of the tool steels. Hence, the carbides in the particular steels appeared less prone to adhesion as compared to the metallic matrix. Therefore, an improved galling resistance was observed for a tool steel comprising a high amount of small homogeneously distributed carbides offering a low-strength interface to the transferred sheet material.Further, atomic force microscopy showed that nanoscale adhesion was influenced by temperature, with increasing adhesion as temperature increases. A similar dependence was observed at the macroscale where increasing surface temperature led to initiation of severe adhesive wear. The results were in good agreement to the nano scale observations and temperature-induced high adhesion was suggested as a possible mechanism.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2008. 41 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:46
Keyword
Galling, sheet metal forming, wear, friction, adhesion, temperature
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-2911 (URN)978-91-7063-204-4 (ISBN)
Public defence
2008-12-12, Nyqvistsalen, 9C 203, Karlstads Universitet, Karlstad, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2008-11-20 Created: 2008-10-23 Last updated: 2011-11-24Bibliographically approved

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Gåård, AndersKrakhmalev, PavelBergström, Jens
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