TPT January 2007

This is a case for the Copra ® FEA RF software package, which is set up on the commercial MSC.MARC solver (responsible for performing the numerical calculations). Generating an FE model of a complete rollforming installation will normally involve a considerable work investment, requiring specialists trained for the purpose. The geometry of every single forming roll must be imported as a curve, then rotated about its axis, and positioned in space. Following this each roll must be assigned material and contact information, with data entered detailing output variables (job results), time sequences (load cases), material and contact of the strip material and other partially time-dependent boundary conditions. It can easily take up to several days in order to undertake such a job. Copra ® RF relieves the user of all this. The program generates an FE model optimised for simulation of the rollforming process, and executes the computation within MSC.MARC 5 . Copra ® FEA RF uses cubic volume elements with assumed strain formulation for the generated FE model. The advantage of these volume elements is that they can map forces in all three directions in space as well as the resulting stresses and deformations. Shell elements are not able to do this in the direction of their surface normals. For example, if a rollforming process is to be realistically simulated and the influence of the roll gap analysed, there is no alternative to use for these volume elements 4 . As shown by the investigations conducted, approximation methods or two-dimensional simulation of the continuous rollforming process is inadequate 1 . The longitudinal stress appearing in the strip must not be neglected in an FE simulation 2 because it contributes, among other things, to changes in the wall thickness. A number of powerful analytical functions (postprocessor), present in Copra ® FEA RF, provide the user with dependable information about the profile quality or material properties to be expected. Both the final tube and single intermediate stages are presented in three- dimensional colour images. The visualisation of defects means that, for the most part, it is possible to dispense with the once necessary empirical trials and adjustments to the tube mill or rollforming line. Instead, a new tool set can be analysed and optimised in its design phase. fi Figure 3 : Multi-stage concept for design and verification of the tube making process: 1) Design of the tube to be produced 2) Design optimisation by COPRA ® Deformation Technology Module 3) Process verification by finite element analysis 4) Analysis and quality control of existing roll tooling by optical roll scanning

› Figure 2 : Copra ® DTM (Deformation Technology Module) calculates longitudinal plastic strain values resulting from the rollforming process in tube mills

data M have developed a mathematical model for fast estimation of the plastic strain occurring on strip edges during rollforming (Copra ® Deformation Technology Module – DTM). This means that a newly designed forming sequence, before it is trialed on a machine or even accurately verified by finite element analysis (FEA), can be speedily and reliably examined for such undesirable plastic strain. Any undesirable plastic strain can consequently be corrected. In addition to theoretical values for the longitudinal or transverse strain appearing on the upper or underside of the sheet metal, Copra ® DTM also shows how the values are distributed over the cross- section. This is important because in practice, one often only hears of strip edge strain, whereas rollforming can quite easily create higher strain in other regions of the strip, ie as is the case in what is called downhill forming. Copra ® DTM produces a three-dimensional presentation of the rollforming operation together with the roll tools. Thus, immediately after tool design, the user sees a clear 3D display of the later forming process. With this fast analytical tool it is possible to work through a whole number of different forming variants, and, if need be, to correct the drafted forming strategy or the number of forming passes used before actually getting down to the details or producing the roll tools. This saves time and reduces the risk of reworking. Simulation by the finite element method (FEM) offers the means of accelerating the time-consuming and costly tryout of a new roll set, thus avoiding the need to rework the roll tools. As a map of the real process, the finite element model of the rollforming process is determined (among other things) by factors such as the number of finite elements (discretization), the number and modelling of contacting bodies, the number and distribution of time increments, and possible use of existing symmetry relationships. In the numerical solution of a structurally mechanical problem by FEM, it is important to look for a balance between inner and outer forces. Once this is found, it is possible to calculate the displacements of the individual nodes and, in turn, the strain. Using the strain, the law of materials enables one to deduce stress and force. Finite element simulation of the rollforming process

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J ANUARY /F EBRUARY 2007