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Evaluation of surface topography parameters for friction prediction in stamping
Chalmers University of Technology.
Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.ORCID iD: 0000-0001-8058-1252
2004 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 257, no 12, p. 1296-1300Article in journal (Refereed) Published
Abstract [en]

The continued globalisation of the automotive industry, leading to increasing demands for competitiveness and escalating legislative requirements, is the main driving force of research activities of steel sheet surfaces. Recent studies on the stamping process have been carried out among others within AUTOsurf, a project funded by the European Community, and by Wihlborg and Crafoord. The purpose of this study was to evaluate the viability of the proposed parameters for friction prediction. Seventeen different surface topographies were investigated. The sheet materials were either, hot-dip galvanised, electrogalvanised or galvannealed, and electron beam or electric discharged textures. The frictional response was measured in a bending under tension (BUT) test under mixed lubricated conditions. This BUT test simulates the conditions of the die radius in a stamping tool. The laboratory test differs from the experimental work performed in AUTOsurf which simulated the conditions of the holding-down plate. In spite of the differences in test equipments in AUTOsurf, e.g. the rotational friction tester (RTF), on a comparison the correlation of frictional response was significant. But neither of the proposed parameters could predict the frictional response with sufficient accuracy in this study. In addition, the friction model in AUTOsurf describes peak lubrication as a dragging phenomenon on sliding surfaces. The movement eased friction in inverse proportion to the average peak area. However, the trend in this study showed the opposite, movement eased friction proportionally to the average peak area. The result indicates a switch of dominant friction mechanism when the sliding velocity is increased, i.e. from a dragging phenomenon at low velocities to micro-hydrodynamic wedge effects at high velocities.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2004. Vol. 257, no 12, p. 1296-1300
Keywords [en]
Surface topography, Automotive industry, Bending (deformation), Friction, Galvanized metal, Metal stamping, Steel sheet, Tensile strength
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:hh:diva-3551DOI: 10.1016/j.wear.2004.05.026ISI: 000225750700017Scopus ID: 2-s2.0-10044298311OAI: oai:DiVA.org:hh-3551DiVA, id: diva2:284886
Available from: 2010-01-08 Created: 2009-12-01 Last updated: 2018-03-23Bibliographically approved
In thesis
1. Tribology of stamping: the influence of designed steel sheet surface topography on friction
Open this publication in new window or tab >>Tribology of stamping: the influence of designed steel sheet surface topography on friction
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tribology is the science of friction, wear, and lubrication; the interaction of surfaces in relative motion. The tribological conditions in sheet metal forming influences the flow of material in forming operations, the strain distributions of sheet material, extent of wear, and thereby the quality of products. The purpose of the thesis is to increase the knowledge of why and how sheet surface topography influence the frictional response in stamping, to characterise the geometrical properties, and make results applicable for industry. The frictional response of different surface topographies have been measured in a Bending Under Tension test under mixed lubricated conditions. The studied materials have been stainless steel sheets and uncoated and coated carbon steel sheets. The results did show the influence of roughness, skewness, and anisotropy of surface topography. The findings could be explained by the theory of pad bearings. A new functional 3D parameter (Sq>0) was developed for pressing performance that is sensitive to the effects of roughness and skewness. The texture-aspect ratio parameter (Str) was found to be correlated to the anisotropical behaviour of the frictional response. The results are very tangible and mean increased control of stamping operations. An initial step was taken to introduce more advanced tribological models in FE simulation of sheet metal forming operations. The aim is to decrease the trial-and-error time in the design process of dies and tools. A friction model considering surface topography (Sq>0), sliding velocity, lubricant viscosity, and apparent pressure, was successfully implemented. Simulations of a part were evaluated with real stamping tryouts. The results did show the potential of improving the precision in forming simulations with more advanced tribological models. Finally, theory and characterisation methods of active micro-oil pockets in the contact zone of tool and sheet were investigated. The real contact area was shown to be the critical feature to determine. Therefore, two topographical methods and one microscope-imaging processing technique were studied, but no method was found to be viable. However, the experimental results did not confirm the importance of microoil pockets in mixed lubricated regime.

Place, publisher, year, edition, pages
Göteborg: Chalmers tekniska högskola, 2006. p. 72
Series
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, ISSN 0346-718X ; 2526
Keywords
steel sheet, tribology, surface topography
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hh:diva-2010 (URN)2082/2405 (Local ID)91-7291-844-6 (ISBN)2082/2405 (Archive number)2082/2405 (OAI)
Public defence
(English)
Available from: 2008-10-06 Created: 2008-10-06 Last updated: 2018-03-23Bibliographically approved

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Wiklund, DanielRosén, Bengt-Göran

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