Thin-walled 2024 aluminum alloys tubes with big-diameter round section are often used in machines as light-weight flexible shaft. However, the axis of a tube is inevitably bent during fabrication process, so it is necessary to straighten the bent tube before it could be used.
After analyzing previous papers and books, this paper presents and explains the related concepts of straightening, and study the straightening process in the way of a combination of experiments and theories. Firstly, the engineering definition of straightness is introduced. Meanwhile, the principle of measuring and calculating the bending of tube are given. Secondly, under the frame of materials mechanics and elastic-plasticity mechanics, we build up the model of tension-leveling and three-point pressing straightening. As for the tension-leveling model, it deals with the relationship between the bending of tubes and the magnitude of tension, meanwhile, it gives an analytical solution of the axis variation under particular bending based on the premise of bar and beam bending. In the model of three-point pressing straightening, the paper mainly focuses on the study about how the bending of tubes changes with the reduction amount, and gives a common rule to determine the pivots and pressing point. At the same time, the roundness of a particular tube section is also investigated. Later, the quantitative formulation is put forward to calculate the reduction amount. Finally, after comparing the weakness and strength of tension leveling and three-point pressing straightening, the paper proposes a straightening process combining the advantages of the above two straightening methods. In this new straightening process, it first straightens the tube into reverse bending by a combination of tension leveling and three-point pressing straightening, and then makes the tube straighten by tension leveling with small tension. A quantitative model is also given to determine the related processing parameters.
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