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The influence from shape and size of tool surface defects on the occurrence of galling in cold forming of aluminium
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterials group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterials group)
2011 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2517-2524Article in journal (Refereed) Published
Abstract [en]

Aluminium alloys are shaped in cold condition in a large number of industrial applications. Simple geometries can be produced to net shape in a single operation. Galling is an important factor limiting the tool life, the complexity of the shapes and the number of processing steps. A selection of ceramic coatings gives a strongly reduced tendency to galling, even without lubricant, as long as the coating surface is smooth. With rough coating surfaces there is no significant improvement compared to the conventionally used uncoated tool steels. The present investigation concentrates on the character of the surface roughness and its influence on galling. Here, surface defects including pyramidal indents and elongated scratches are introduced in a controlled manner and then characterised with optical microscopy and electron microscopy. After testing, the transfer of work material to the tool is studied using electron microscopy and surface analysis. The influence of the various types of local defects is studied with respect to galling tendencies and friction. The shape and extent of the surface roughness is important for galling resistance. Single indents, symbolizing occasional dents in the coating, initially pick up more aluminium than the surrounding coating but do not influence the galling and friction in total. This implies that the forming tools need fine polishing and gentle handling to avoid dents and initial aluminium pick up. The overall surface roughness level is of higher importance for galling and friction.

Place, publisher, year, edition, pages
2011. Vol. 271, no 9-10, p. 2517-2524
Keywords [en]
Galling, Surface preparation, Friction, Tool steel, Ceramic coating, Aluminium alloy
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-162393DOI: 10.1016/j.wear.2011.01.077ISI: 000294590200167OAI: oai:DiVA.org:uu-162393DiVA, id: diva2:460437
Available from: 2011-11-30 Created: 2011-11-30 Last updated: 2017-12-08Bibliographically approved
In thesis
1. On Transfer of Work Material to Tools
Open this publication in new window or tab >>On Transfer of Work Material to Tools
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Uppsaliensis, 2012. p. 68
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 894
Keywords
Tribology, Friction, Forming, Cutting, Galling, Material transfer, Tribological coatings, Surface finish, Micro mechanisms, Aluminium
National Category
Engineering and Technology
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-165828 (URN)978-91-554-8261-9 (ISBN)
Public defence
2012-03-02, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Supervisors
Available from: 2012-02-10 Created: 2012-01-10 Last updated: 2013-04-08

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Heinrichs, JannicaJacobson, Staffan

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