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Gustafsson, E. (2016). Design and application of experimental methods for steel sheet shearing. (Doctoral dissertation). Luleå University of Technology
Open this publication in new window or tab >>Design and application of experimental methods for steel sheet shearing
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Utveckling och tillämpning av experimentella metoder för klippning av stålplåt
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:nbn:se:ltu:diva-59863 (URN)978-91-7583-733-8 (ISBN)978-91-7583-734-5 (ISBN)
Public defence
2016-12-20, E231, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2016-10-24 Created: 2016-10-21 Last updated: 2017-11-24Bibliographically approved
Gustafsson, E. (2013). Experiments on sheet metal shearing (ed.). (Licentiate dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Experiments on sheet metal shearing
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Within the sheet metal industry, different shear cutting technologies are commonly used in several processing steps, e.g. 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.Numerical models to predict forces and sheared edge geometry for different sheet metal grades and different shear parameter set-ups are desirable. For new sheet metal grades, numerical shear models are efficient for finding appropriate shear parameters without the need for time consuming and expensive live tests in the production. In order to allow for validation of numerical models, accurate experimental data is wanted.Many industrial equipments for shearing give some measure of applied force, but due to machinery friction losses, measured forces are always higher than the forces acting on the sheet. Shearing also generates a force that attempts to separate the two shear tools with changed shear conditions through increased clearance between the shear tools as result. Clearance is also the most common shear parameter to adjust, depending on material grade and sheet thickness, in order to moderate the required force and to control the final sheared edge geometry.Sheared edges have four characteristic zones, rollover, shear, fracture and burr zones. Burrs and rough fracture zones complicate the following processing through inadequate tolerances that may imply additional machining and sharp edges that may damage equipment or even cause injuries. Well defined shears and accurate measurements are important for the understanding of shear parameters. In this work, an experimental procedure with high measurability and consistent and predictable output, is designed, built and evaluated. Important shear parameters and demands on the experimental set-up are identified in a perturbation analysis performed with use of finite element method.Considering the perturbation analyses results, experimental set-up requirements are formulated. Based on magnitude of the force changes obtained as result of perturbed input parameters in the analyses, force measurements with one percent accuracy are considered necessary. Since a clearance change of one percentage point results in approximately one percent change in forces, the target experimental clearance stability is an order of magnitude lower, i.e. the clearance should remain within 0.1% or 5μm at the sheet thicknesses sheared.With respect to high clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the shear tools, is constructed. Besides a stable clearance, the experiment features high accuracy force measurements without external friction losses through 20 strain gauges mounted on the set-up.Since clearance and clamping of the sheet are identified as important to the shear results, these parameters are selected for further experimental studies through shearing of three material grades with various strength. Judging by the result, shear tool penetration before fracture decreases with increased material strength. When one side of the sheet is left unclamped and free to move, the required shear force decreases but instead the force attempting to separate the two shear tools increase. Further, the maximum shear force increases and the rollover decreases with decreased clearance. In general terms, results from the study are promising for use in validation of numerical shear models.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2013
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-17805 (URN)54d1c713-062d-485b-968a-323ff512dc1e (Local ID)978-91-7439-622-5 (ISBN)978-91-7439-623-2 (ISBN)54d1c713-062d-485b-968a-323ff512dc1e (Archive number)54d1c713-062d-485b-968a-323ff512dc1e (OAI)
Note

Godkänd; 2013; 20130430 (emigus); Tillkännagivande licentiatseminarium 2013-05-16 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Emil Gustafsson Ämne: Hållfasthetslära/Solid Mechanics Uppsats: Experiments on Sheet Metal Shearing Examinator: Professor Mats Oldenburg, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Doktor Magnus Eriksson, SINTEF Materials and Chemistry, Structural Mechanics, Trondheim, Norge Tid: Torsdag den 30 maj 2013 kl 10.00 Plats: E246, Luleå tekniska universitet

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7535-5250

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