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Friday, August 14, 2020
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Opinions

Tooling Costs

“Since we have been optimising our rolls with COPRA® DTM (Deformation Tecnology Module) we were able to reduce our tooling costs drastically”
(Matjas Knez - Alpos, Slowenia)

FEA in Tubemaking: Process Problems

“The FEA analysis that data M performed for us allowed us to see a visual representation of the process problem we were having, as well as providing a quantitative value to the stresses we were imparting to the product. The visual representation was described by the machine operator as <<exactly what I'm seeing coming out of the mill>>. This analysis showed us exactly where in the process our problems were occurring.”
(Duffy Armstrong - Webco Industries, USA)

Quality management in the design of roll form tooling

Development & Optimization of Cold Roll Forming Tool Sets

How to get roll forming up and going with all its efficiency?
Because of their large variety of applications, cold roll formed parts have become increasingly important in recent years, and made their way into whole new sectors like automotive industry. The reasons for this include the introduction of new types of materials and improved forming capabilities like shaping on flexible roll forming lines.
Cold Roll Forming is seen as a highly productive process for manufacturing steel sections through continuous shaping of sheet steel by driven rolls. Particular advantages of this process are the virtually unlimited variety of profile cross-sections, and the strain hardening of the material that results from the shaping, which can be turned to good advantage - in many cases. These are the benefits. But there are also drawbacks like, in some instances, the time-consuming design and production of roll tools, difficulties during installation of a new tool set and getting it into operation or unexpected deformation of the end-product due to, e.g. internal material strains. Which takes us straight to the subject of analysis and optimization software, presenting a whole lot of potential for remedying this situation. To get cold roll forming up and going with all its efficiency, you need to apply methods as early as the profile and tool design phase that can play a major role in improving the quality of the rolled section.

For some years now the firm data M Software GmbH, based in Bavaria, has been offering a virtual process chain for the design and validation of roll sets in roll forming production. The COPRA® RF (Roll Forming) software program supports all steps in the development of open or closed profile cross-sections: from design of the final cross-sections to be produced, through definition of the various shaping steps (passes or flower) to generation of technical documentation (production drawings, parts lists, CNC programs, etc.) and later quality control of profile cross-sections and roll tools.
The latter works with optical instruments specially developed for the application (COPRA® RollScanner and COPRA® Laser Check). Amultistage concept speeds up both the design and the analytical process, allowing for the needs of the designer who wants to create a tool set fast, as well as those of the production manager interested in checking out the later roll forming process as early as possible.

Fast simulation by deformation analysis
Taking the end-user's idea, a profile flower is created by a draft program – COPRA’s profile design module. The resulting CAD data goes into an analytical program – COPRA® DTM (Deformation Technology Module) – to design the shaping stations. Within a matter of seconds, this software program computes the theoretical (elastic as well as plastic) strains on the material during forming as a function of influencing variables like profile cross-section geometry, material gauge, roll configuration and roll diameter (an essential parameter in the forming process). In this way it is able to indicate where the material might be overstressed.

This fast simulation program enables you to run through a whole series of different shaping variants, and to correct the drafted flower or number of shaping stations and tool dimensions, as necessary, before starting the actual detailed work or even production of the roll tools. This is very time-saving, and it reduces the risk of having to rework the roll tools later at startup, or even having to make them afresh. In many cases, the major cause of poor profile quality is residual, local deformation of the sheet metal (internal strain) produced by (mostly longitudinal) elongation during roll forming. In addition to the theoretical figures for such elongation on the top and/or under side of the metal, COPRA® DTM predicts how the figures are distributed over the cross-section. Why this is so important is that there is still much talk about so called strip edge elongation, even though the majority of profile cross-sections that are produced are in fact stressed over their entire cross-section during roll forming. You can see this effect very clearly in prepunched material. The holes punched before the material goes onto the line are deformed by the plastic elongations caused by the roll stations. 

Once the design of the shaping flower and details of the roll set are firm, it is possible to generate the complete documentation for making the rolls, i.e. sawing lists, production drawings and CNC data, and to produce the roll tools. After this, the tool is set up on the forming plant. Without the kind of optimization of the shaping flower described above, extensive settings and adjustments will usually be necessary on the plant, sometimes even elementary modification of the tools, before a new section of the required quality comes off the line. Not so long ago, the only way to create a properly functioning roll set was through practical trials on the machine.

Today there is an alternative - a possibility of speeding up this time-consuming and costly process getting a new roll forming tool set into operation, and of avoiding reworking of the tools altogether - namely simulation by the finite element method (FEM).

FEM simulation of the roll forming process
Once a roll set has been ready designed, the data go into the FEM simulation program. COPRA® FEA RF (Finite Element Analysis for Roll Forming) simulates the roll forming process by a nonlinear, elastoplastic form of computation. The user can forget questions like definition of the finite element computing model, discrete data formulation, selection of suitable element types or application of boundary conditions. The software program fully integrated into the COPRA® process chain automatically considers these factors. Anumber of effective analytical functions predict for the user the ex-pected profile quality or material properties. Both the ready profile and the individual shaping steps are pre-sented in three-dimensional, colour images. Visualization of defects means that the empirical trials needed to date and adjustments to the forming mill can be dispensed with – a new tool set is ready optimised in the design phase.

An entire finite element computation cannot be performed within a matter of minutes, even on today's high-speed computer systems, so the dual-step solution described here, i.e. advance optimisation by a fast computing approach followed by validation of the complete tool set by the FE method, has proven extremely successful in actual practice. COPRA® FEA RF, however, provides the roll tooling engineer with a  lot of additional information allowing him to better understand to forming process.

The practical benefits in the roll forming of profiles go beyond reduced running in times for a new tool set and enhanced process control. The producer now derives significant expertise and experience in the roll forming process, putting him in a position to eliminate faults and problems in the leadup phase to new products.