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Mechanisms of transfer of aluminium to PVD-coated forming tools
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. (Tribomaterial)
2012 (engelsk)Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 46, nr 3, s. 299-312Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Cold forging is a group of methods effectively used in a number of industrial applications to form aluminium. Tool life and complexity of the possible shapes are mainly restricted by galling; the uneven tool surfaces caused by lumps of transferred material lead to surface damage on successive parts formed and/or problems in successive forming operations, and high stresses occurring when forming complex shapes. Earlier investigations have shown that improved surface roughness of an uncoated steel tool decreases the amount of adhered aluminium on the tool, but does not decrease the friction in the long run. Testing has also shown that when using conventional forming tools it is very important to have sufficient lubrication to avoid galling. Addition of an optimized low-friction PVD-coating decreases the galling tendency and increases the tolerance to insufficient lubrication and lubricant film breakthrough, as long as the coating surface is smooth, whilst other similar coatings have little or no effect. The present article further investigates the mechanism behind the transfer of aluminium to the coatings. All coatings were found to be intact after testing, and so the differences were concluded to lie in the chemical properties of the coating and, if these are favourable, then in surface roughness on the micro scale.

sted, utgiver, år, opplag, sider
2012. Vol. 46, nr 3, s. 299-312
Emneord [en]
Galling, Friction mechanisms, Friction-reducing coatings, Aluminium
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial; Teknisk fysik med inriktning mot materialvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-167057DOI: 10.1007/s11249-012-9952-5ISI: 000303876300009OAI: oai:DiVA.org:uu-167057DiVA, id: diva2:480630
Tilgjengelig fra: 2012-01-19 Laget: 2012-01-19 Sist oppdatert: 2017-12-08bibliografisk kontrollert
Inngår i avhandling
1. On Transfer of Work Material to Tools
Åpne denne publikasjonen i ny fane eller vindu >>On Transfer of Work Material to Tools
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Bulk forming and cutting are widely used to shape metals in industrial production. Bulk forming is characterized by large strains, extensive plastic deformation and large surface expansions. Cutting is characterized by high speeds, high pressures and high temperatures. The prevailing conditions during these processes lead to transfer of work material to tools. In bulk forming this is a significant problem. The transferred work material is hardened and becomes harder than the work material, causing galling. This leads to high friction and high forming forces, bad surface finish of the formed products and significant difficulties to produce complicated geometries. In cutting, transfer of work material can be desired for protection of the tool surface. However, the transfer film has to be of the correct type to provide a stable and predictive behaviour during operation.

In this thesis the influence from tool material and surface treatment on work material transfer has been studied for both applications, with the use of simplified laboratory test methods followed by extensive surface studies. Both the tendency to, appearance of and chemical composition of work material transfer is evaluated. The results are compared with real industrial examples, to ensure that the correct mechanisms are mimicked.

In forming, the problems arise when poor lubrication prevails, due to high forming forces or large surface expansions. The transfer of work material can then be avoided with the use of a galling resistant coating, offering low adhesion. However, the coating has to be as smooth as possible, to avoid activation of the work material and subsequent transfer.

In cutting, the desired transfer film can be obtained by choosing the correct cutting parameters. The geometry and material of the fabricated component is often predetermined, setting the general cutting conditions, but the cutting speed influences the formation of the transfer film. Too low speed or too high speed leads to an unstable cutting process and poor surface finish of the piece. The speed intervals for each mechanism are partly determined by the tool material and thus by the tool coating.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Uppsaliensis, 2012. s. 68
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 894
Emneord
Tribology, Friction, Forming, Cutting, Galling, Material transfer, Tribological coatings, Surface finish, Micro mechanisms, Aluminium
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-165828 (URN)978-91-554-8261-9 (ISBN)
Disputas
2012-03-02, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (svensk)
Veileder
Tilgjengelig fra: 2012-02-10 Laget: 2012-01-10 Sist oppdatert: 2013-04-08

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