Longitudinal deformation process is uneven, in the previous frame, steel strip edges extension is greater than the central part of the extension, reach a closed hole before two, central part of the extension and extension is greater than the edges.But the overall result after forming for cylinder, edge length is L 'is greater than the original length L.The difference between the two delta L = L '- the greater the L, the greater the corresponding tensile stress.If tensile stress exceeds a certain value, the residual deformations of edge, prompted a crease, tube cone part seriously affect the tube billet precision forming.Therefore, in order to ensure the quality of the forming of stable, must ensure that the longitudinal deformation of elastic deformation zone of tensile tube billet edge relative extension control within the scope of 0.1% or less, or alpha 1 or less DHS ~ 1 DHS '25.So for the unit to meet the maximum product diameter deformation zone length is required for L = on3dmax (40 ~ 57).

(2) the lateral deformation.Cross section deformation after forming, sizing and straightening, steel tube wall thickness and strip thickness changes before forming.Thick wall tube forming side wall thickness change is not obvious, when thin-walled tube forming when the wall thickness than the strip thickness on the one hand small thickening.For ∅ 76 mm x 2.5 mm 66 groups of data of automobile transmission shaft tube for determination of the regression equation
Y = 0.92 + 0.22
In the type - strip steel thickness
Y - pipe wall thickness
When χ = 2.5 mm, Y = 2.52 mm, thickening of the wall thickness of 0.02 mm.
On the other hand, the same cross section of the wall thickness uneven distribution regularly.Edges of the wall thickness is less than the part at the bottom of the tube wall thickness, this is due to the results of the edge.

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