TPT January 2009

Designing tube mill rolls: state-of-the-art software technology for optimization of cage forming systems By Mr Albert Sedlmaier, managing director, Data M Software, Germany, and Mr Anton Skripkin, project engineer, CSoft, Russia

Introduction The development of a new set of tube mill rolls and the following production of accurate tubular sections might seem without serious considerations. However, there can be problematic hurdles such as down times of the tube mill, installation, startup and try-outs of roll sets. Internal strain and work hardening in the roll formed material might cause poor welding conditions or deformation of the end-product. For a number of years, data M Software GmbH, Germany, has been offering a virtual process chain for the design and validation of roll tooling for tube welding lines. The Copra ® RF (roll forming) software program family supports all steps in the development of open or closed profile cross-sections. This includes the design of the final cross-section to be produced, the definition of the various shaping steps (passes or flower), and the generation of technical documentation (ie production drawings, parts lists, CNC programs), and later inline quality control of profile cross-sections and roll tools. The latter works with optical instruments developed especially for the application (Copra ® RollScanner and Copra ® LaserCheck). This article describes how to perform a state-of-the-art roll tool engineering for the production of longitudinally welded tubes. It shows how to analyze and optimize a tube mill with integrated straight edge forming stands using advanced finite element computer simulation. In the past, the only way to create a properly functioning roll set was through practical experience and extensive trials on the machine. Today there is an alternative with effective design- and analysis software, which speeds up this time-consuming and costly process. Both the so-called ‘flower pattern’ and the roll tools are designed in Copra’s tube mill software module. The ‘flower pattern’ is the sequence of all subsequent tube forming steps; it is very important to properly define the ‘flower patttern’ as it influences the final tube quality. The material is formed at every roll station; this is the case not only for the intended method with round tube but also in a longitudinal direction due to the rollforming process. This can cause longitudinal strain and may, if the material gets strained beyond its linear elastic limit, inappropriately influence the material properties through effects like local work hardening. How to design tube forming rolls on the computer?

The principle of forming a strip into a tube in a tube welding line is shown in picture 1. A special software program can be used to determine the longitudinal strain values, taking into account the influencing parameters defined by the roll tool layout. The Copra ® tube mill software module is a dialogue driven software program that allows a parametric flower- and roll design for tube mill rolls. It is important to know that the software does not stipulate any specific tube mill or design strategy. It is completely free to define any forming strategy the designer wants to develop and is not restricted to any specific tube mill concept. This is important, as there is no ‘global’ valid strategy for making tubes. The method to be used always depends on the specific mill, material and tube data. In a first step the user defines a certain tube mill and therefore selects a number of standard forming stations from a catalogue (picture 2).  Picture 1 : Copra ® DTM (deformation technology module) calculates longitudinal plastic strain values resulting from the rollforming process in the tube mill

 Picture 2 : Mill definition in Copra ® tube mill roll design software

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J anuary 2009

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