TPT January 2009

and the comparability of results with the real production process. Various benchmarks performed at the author’s company as well as some industrial companies (tube producers, machine builders and steel companies) are comfirming the high accuracy of this software program. A practical example The objective is to investigate if a 24" tube can be formed on a cage forming mill that is actually designed to produce 20" tubes – and to determine the achievable tube quality. The material to be used is S355 (ST52) with a minimum wall thickness of 7.5mm and maximum of 21mm. The investigations described below were

 Picture 9 : A feature of Copra is the possibility to design and model any type of rolling cage – often referred to as straight edge forming method. Using this feature, respective rolls are not just modeled but also transferred to Copra’s integrated finite element software package Copra ® FEA RF and simulated respectively

However, in some cases the tube forming process does not happen as expected due to areas with reduced forming and punctiform force distribution. Copra ® FEA RF allows for a detailed evaluation of the forming process in a rollforming line or a tube mill. This includes, of course, the straight edge forming method. The user is able to create and look at cross sections at any desired position and compare between designed (intended) and simulated (produced) cross sections. It is possible to check for strip edge damages or waviness. An integrated report generator allows the user to document discoveries and ideas by means of screen shots, videos or comments in order to discuss these issues with colleagues and customers. The user also gets detailed information on stresses, strains and forces occurring during the tube making process. It is possible to evaluate any displacement of the formed strip and achieve extremely important information about what is actually happening in his tube mill. This possibility had previously been unfeasible. The computer simulation allows the user to look ‘inside’ the mill and extract respective information. This is impossible if a mill operator has to do some troubleshooting on the tube mill without knowing what is going on in the roll cage. Another aspect that is decisive for a successful computer simulation is the accuracy of the Copra EA RF software program

performed on the minimum wall thickness as this is the most sensitive dimension with regard to waviness effects. The maximum wall thickness, however, was taken for a final verification of roll tool adjustment and resulting forming forces. A forming cage for such a 24" tube is usually not shorter than 12m. However – as the cage available was limited to around 7m, several investigations and trials have to be undertaken. The way to solve such a project is carried out in some ‘optimization loops’. It is essential to start with a certain design based on the designer’s practical experience and analyze the forming process by means of finite element computer simulation. This determines any critical situation or material behavior. In this instance, it was decided to determine the optimum alignment of the tube in height. In other words, to define the optimum so-called downhill strategy. The target to achieve a 24" tube formed successfully on this mill could be achieved. A linear downhill strategy would have been one of the obvious solutions but was not possible due to the subsequent fin passes following the roll cage that were aligned to a constant tube bottom line. However, to predict the result, the distribution of the final individual cross sectional lowering along the cage was totally different. It is clear that any expert would have guessed this from experience.

 Picture 10 : Automated creation of the FEA model by means of Copra FEA RF

102 ›

J anuary 2009

www.read-tpt.com