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Design and application of experimental methods for steel sheet shearing
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-7535-5250
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Utveckling och tillämpning av experimentella metoder för klippning av stålplåt (Swedish)
Abstract [en]

Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools.

Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations.

In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry.

In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed.

Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance.

Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material.

A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles.

In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.

Place, publisher, year, edition, pages
Luleå University of Technology, 2016.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-59863ISBN: 978-91-7583-733-8ISBN: 978-91-7583-734-5 (pdf)OAI: oai:DiVA.org:ltu-59863DiVA: diva2:1039069
Public defence
2016-12-20, E231, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2016-10-24 Created: 2016-10-21 Last updated: 2016-11-28Bibliographically approved
List of papers
1. Design and validation of a sheet metal shearing experimental procedure
Open this publication in new window or tab >>Design and validation of a sheet metal shearing experimental procedure
2014 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, 2468–2477- p.Article in journal (Refereed) Published
Abstract [en]

Throughout the industrial processes of sheet metal manufacturing and refining, shear cutting is widely used for its speed and cost advantages over competing cutting methods. Industrial shears may include some force measurement possibilities, but the force is most likely influenced by friction losses between shear tool and the point of measurement, and are in general not showing the actual force applied to the sheet. Well defined shears and accurate measurements of force and shear tool position are important for understanding the influence of shear parameters. Accurate experimental data are also necessary for calibration of numerical shear models. Here, a dedicated laboratory set-up with well defined geometry and movement in the shear, and high measurability in terms of force and geometry is designed, built and verified. Parameters important to the shear process are studied with perturbation analysis techniques and requirements on input parameter accuracy are formulated to meet experimental output demands. Input parameters in shearing are mostly geometric parameters, but also material properties and contact conditions. Based on the accuracy requirements, a symmetric experiment with internal balancing of forces, is constructed to avoid guides and corresponding friction losses. Finally, the experimental procedure is validated through shearing of a medium grade steel. With the obtained experimental set-up performance, force changes as result of changes in studied input parameters are distinguishable down to a level of one percent.

Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-4180 (URN)10.1016/j.jmatprotec.2014.05.013 (DOI)215c89f7-cce9-449f-979f-da31efba57d9 (Local ID)215c89f7-cce9-449f-979f-da31efba57d9 (Archive number)215c89f7-cce9-449f-979f-da31efba57d9 (OAI)
Note
Validerad; 2014; 20140522 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-10-21Bibliographically approved
2. Experimental study on the effects of clearance and clamping in steel sheet metal shearing
Open this publication in new window or tab >>Experimental study on the effects of clearance and clamping in steel sheet metal shearing
2016 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, 172–180- p.Article in journal (Refereed) Published
Abstract [en]

Shear cutting is common within several sheet metal industry processing steps, e.g. in cut to length lines, slitting lines, end cropping. Shearing is fast and cheap relative to competing cutting methods like laser and plasma cutting, but involves large forces on the equipment that increase with increased sheet material strength. Accurate shear experiments are a prerequisite to increase the knowledge of shearing parameters, improve industrial shearing, and provide data for validation of numerical shear models. Here, the two shear parameters clearance and clamp configuration, identified as important to the shear results, were studied in an experimental set-up with well defined tool movement and high measurability of tool position and force. In addition to force measurements, the sheared edge geometry was characterized. Steels of low, medium, and high strength were selected for the study. Throughout the experimental study, the shear tool penetration before fracture decreased with increased material strength. The required shear force decreased and the force attempting to separate the two shear tools increased when one side of the sheet was left unclamped and free to move. Further, the maximum shear force increased with decreased clearance. Clearance changes were small and moreover continuously measured during all shear experiments.

Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-8674 (URN)10.1016/j.jmatprotec.2015.09.004 (DOI)737ed041-de8c-40ed-b298-67e548cfdbee (Local ID)737ed041-de8c-40ed-b298-67e548cfdbee (Archive number)737ed041-de8c-40ed-b298-67e548cfdbee (OAI)
Note
Validerad; 2015; Nivå 2; 20150907 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-10-21Bibliographically approved

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