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Pipe bending , bend the outside wall thickness thinning , thickening of the medial wall thickness , wall thickness difference may be more than 30 % , it will follow-up pre- forming and hydroforming have a huge impact . This paper analyzes fittings hydroforming process , due to bending lead to uneven distribution of the initial wall thickness brought the hydroforming regular different . In this paper the dynamic explicit finite element program LS- DYNA diameter 55mm, wall thickness 1.75mm Low carbon steel tube NC bending numerical simulation analysis in the form of a mandrel , the mandrel protrusion amount , r value of elbow -section shape and wall thickness distribution ; and CNC bending experimental study , and elbow -sectional shape and the wall thickness distribution law . The results showed that the the NC rotational paraboloid mandrel bending smaller projecting amount of the mandrel and the r value greater material elbow thinned smaller . Bending axis of the rectangular cross-section parts CNC bending , preforming and hydroforming numerical simulation analysis of the relative bending radius , parting ways , the amount of collapse , tube internal hydroforming wall thickness distribution , equivalent strain distribution the impact . The results show that the appropriate increase in the relative bending radius , medial flattening volume and the horizontal parting ways , resulting hydroforming pieces smallest wall thinning . CNC bending , bending sedan chassis before Liang , numerical simulation of the pre - forming and hydroforming process , studied the influence of the material properties and friction on the forming , analysis of the condition and location of the crack defects , given the typical sectional wall thickness distribution and forming pressure fillet radius relationship . The results show that under the in using materials MS264 billets and MOLYKOTE lubricant conditions , it is possible to obtain a qualified parts .
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