TPT January 2009

In the first step, the flower pattern and respective roll tool design was created (picture 12) and various downhill strategies were investigated (picture 13, 14). The following step was to verify each rollforming (tubemaking) process and investigate the respective performances. It showed that there were no optimum results from either the ‘linear downhill strategy’ (or constant centre of gravity), or the strategy according to minimized longitudinal strain values. The latter showed that these processes do not match the ‘natural forming’ behaviour (which is essential in the straight edge forming method due to high amount of air bending), with regard to tube diameter, thicknesses, forming length and material.

 Picture 15 : Vertical cross sectional cut through the cage forming section. The green arrow indicates the direction where the 90º bent tube tends to move to. The blue arrow shows the route of the tube according to the cage roll positions However, the ‘linear downhill’ method showed problems where the tube leaves the cage forming section and enters the subsequent fin stations. It was discovered that there was a constant bottom point of tube profile. Picture 15 clearly shows that this effect already starts within the cage. The picture shows a vertical cross sectional FE drawing at a position where the tube is already formed to a 90° angle. The tube has already got such a stiffness that is cannot be pushed upward any further in order to run smoothly into the following bottom roll in the forming cage without getting damaged. Instead, the forming was set to take place ‘on top’ by means of the upper rollers and a kind of ‘free and natural’ bending, while the forming cage would be aligned accordingly. As a conclusion we ended up in a combination of both methods – a linear downhill strategy in the beginning and a style of uphill forming in the second part of the cage in order to achieve a smooth and natural forming. It has to be pointed out that the bottom rolls are supposed to bear only low forces and contribute to the forming process in a minor way.

 Picture 11 : Copra FEA RF allows for a detailed evaluation of the forming process of the tube forming method – including straight edge system

 Picture 12 : The standard design of roll tooling with Copra (tube mill module, cage design functions) with constant centre of gravity

 Picture 13 : Downhill forming according to ‘minimum longitudinal strain’ values

data M Software GmbH – Germany Fax : +49 8024 640 300 Email : datam@datam.de Website : www.datam.de CSoft – Russia

 Picture 14 : Linear downhill forming method

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J anuary 2009

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