BENDING MECHANISMS, EXPERIMENTAL-TECHNIQUES AND PRELIMINARY TESTS FOR THE CONTINUOUS 4-ROLL PLATE-BENDING PROCESS

The continuous four-roll bending of sheet is an efficient process, it produces large and medium diameter tube sections which are then welded to form a single seamed tube. A particular advantage of the process is to minimise the remaining straight section of a finished bent sheet, thus achieving better circularity of the seamed tube. This improvement in the bending process reduces waste material and the subsequent cost of machining. Unfortunately the understanding of the bending operational mechanisms is still in its infancy, and its operation, at the present stage, still depends heavily upon the skill of operators and ''trial and error'' methods. This restricts the full exploration of the capacity and the flexibility of the four-roll bender. Thus, the present research was initiated in order to optimise this bending process and to remove its dependency upon skilled labour. This paper discusses the principle mechanisms of the bending process and some preliminary test results in bending HP30 aluminium plates of 8mm, 10mm and 12mm thickness for (i) single pass bending and (ii) multipass bending, using a four-roll model bender. The test results relate the force on the rollers to the inner bend radius of the bent plate.