Simulating roll forming Analysis and prediction of roll forming

Automotive Applications

Corus Research, Development & TechnologyAutomotive Applications3H-36P.O. Box 10.0001970 CA IJmuidenThe Netherlands

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Driving materials excellence

Simulating roll forming

Analysis and prediction of roll forming processesUsing simulation techniques the behaviour of metal sheet during roll forming and profiling can be analysed. To this end different methods are used: a simple analytical method that is fast but not too accurate, and the more accurate but slower and more complex Finite Element method.

Analysis with COPRA® DesignCOPRA® Design, a product of data M software, is a computer programme for designing and calculating the roll forming process in order to increase quality as well as efficiency. COPRA® can unfold the product to a plane metal strip, and it is possible to look at influences on longitudinal strains, which is the most significant parameter in roll forming. By doing so, COPRA® offers the possibility to optimise the shaping process of the section before making new rolls.

Simulation with COPRA® FEA RFThe finite element roll forming model is more accurate than the COPRA® analysis, but takes more time in running. It is based on the MSC.MARC/MENTAT software enhanced with a shell to facilitate input and to set up the calculation parameters.

The COPRA® FEA RF model calculates, based on input data like strip and roll properties, the stresses, strains and geometrical data in the roll formed product.

Visit our defects cataloguewww.rollformdefects.com

november 2007



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+31 (0)251 498276+31 (0)251 470432

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Analysing roll forming

Longitudinal strain calculations with COPRA® softwareWhen considering the forming of newly designed profiles on existing production lines the number of roll forming passes must be sufficient to produce acceptable products. COPRA®, a programme of Data M, can calculate the longitudinal strain level between the passes, which is one of the most significant parameters in roll forming technology. By doing so, COPRA® offers the possibility to analyse and optimise newly designed roll forming processes before making new forming rolls.

Principle of longitudinal elongationThe theoretical flow of the material between two roll forming passes can be represented as follows. The longitudinal elongation EF developed in the material path DF has to be ‘compressed’ back at point F. This can cause distortion problems in the roll formed product.

Set-up of the COPRA® flowerFrom an initial sketch, the flower design is reconstructed and entered into the COPRA® programme. When the cross sections of all the forming passes are combined into one figure, the so-called ‘flower’ appears.

Analysis of the initial flower designThe longitudinal elongation can be calculated for each individual forming pass. Strain levels that exceed the red limit line of elastic elongation consequently contain plastic strain components. The strain distribution between the forming passes can also be analysed from the presentation of calculated maximum strain levels. Both the strain diagram and the strain level presentation show a rather irregular and critical strain distribution in the profile concerned.

Optimisation of the flower designBy adaptation of the critical forming passes a more favourable flower with the same number of forming steps can be obtained. This gives longitudinal strain levels that do not exceed the elasticity limit. Consequently no plastic elongation occurs in the lengthwise direction of the profile. The calculated maximum strains between the forming passes also show a very regular distribution.


november 2007



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+31 (0)251 498276+31 (0)251 470432

[email protected]


Defects in roll forming products

3D finite element analysis with COPRA® FEA RF softwareSometimes roll formed products suffer from defects caused by distortion of the profiles’ edges or webs. Some of these defects can be attributed to the set-up of the roll forming passes. One of them is the occurrence of ‘wavy edges’ in light gauge profiles. A 3D finite element analysis offers the possibility to visualise these defects and show the effects of countermeasures against the defect concerned.

Defects catalogueEarlier research has shown that the occurrence of wavy edges in a profile results from the presence of too much compressive strain in the longitudinal direction of the flange edge of the profile. For example, an insufficient number of forming passes can introduce plastic elongation of the sheet edge, which will produce edge buckling when compressed in the subsequent forming stages.

Flower designIn order to evaluate the influence of the process set-up, three different flowers were designed with the COPRA®

Design programme. These flowers consist of 3, 4 and 6 forming steps to produce the final flange geometry, which result, respectively, in an extreme, a rough and a smooth forming process. At the 3-step and 4-step processes, the longitudinal strain levels contain some plastic deformation; the strains at the 6-step process are only elastic.


Finite element analysisA 3D numerical simulation with the finite element software COPRA® FEA RF was performed for each flower. The outcome of these simulations is presented as the geometrical shape of the roll formed profile. The pictures of the simulated profiles clearly show that the presence and the amount of plastic deformation in the flange edge lead the formation of wavy edges.

Extreme forming

3-steps process

Rough forming

4-steps process

Smooth forming

6-steps process

november 2007



PHONEFAXEMAILWWW

+31 (0)251 498276+31 (0)251 470432

[email protected]


roll

displacement

of the sheet

sheet

sheet edge

sheet section roll

displacement

of the sheet

sheet

sheet edge

sheet section

Panel production support

Characterising shape defects in sandwich panelsCorus RD&T can assist customers to characterise various process steps of their panel production lines in order to identify critical areas for the origin of shape defects in sandwich panels.

3D laser scanning and digitisingLaser scanners allow accurate, non-contact 3 dimensional geometry measurements of objects. This technology can be applied to digitise and check the geometry of roll forming tools providing a quick and accurate measure of tool wear. The portable equipment allows these measurements to be made in-line or off-line. The results can also be used to produce CAD files for the manufacturing of new rolls.

Analytical calculationsCorus RD&T has generated experience in the field of sheet metal forming analysis and simulation. Using analytical calculations Corus can quantify different issues such as panel waviness, depths of embossments, thermal expansion and contraction following pre-heating or hot bonding steps, etc.

Analysis of the roll forming flowerFor each individual forming pass the longitudinal elongation can be calculated with the COPRA® program. Strain levels that exceed elastic elongation consequently contain plastic strain components, which may introduce shape deviations of the produced

panels. Using COPRA® critical roll forming steps can be predicted.

FE modelling of process stepsLatest numerical simulation software can be applied to analyse forming operations such as ridge rolling and roll forming. From the simulations, product shape, spring back and strain distribution in different directions can be derived.

Customer supportThis brochure gives examples of our expertise in characterisation of critical process steps, which can introduce shape defects in sandwich panels. For advice regarding your specific process, please contact the Automotive Applications Department of Corus Research, Development & Technology.


november 2007

Documents

Simulating roll forming Analysis and prediction of roll forming