Hydrofoming Of Bi-layered T-shape Thin-walled Tubes

Bi-layered T-shape tubes could achieve optimal properties of material on thepremise of reducing precious metal usage, with high strength, abrasion resistance,corrosion resistance and other excellent properties. They can work under theenvironment of complex loading, corrosion and friction and usually can be used inall kinds of pipelines in the field of civil and industrial. Bi-layered T-shape tubesformed by hydroforming technology have some advantages, such as reducing theprocess of welding and subsequent processing, meanwhile the parts possess a higherprecision and formality.The requirements of lightweight structure have led to the increase of applicationof thin-walled tubes, however, thin-walled tubes are more likely wrinkled thanthick-walled tube during hydroforming technology. The research on hydroformingbi-layered T-shape tubes has important significance for industrial production.Hydrofoming of bi-layered tubes, which consist of a thick-walled carbon outerpipe and a thin-walled stainless steel inner pipe, was investigated by simulation andexperiment. The formability of bi-layered T-shape tube with different internalpressures, axial feedings and withdrawal displacements of the counterpunch waspointed out by simulation. The effects of different parameters on wall thickness ofthe formed parts were analyzed and the reasonable proportion of internal pressureand axial feeding was obtained. Meanwhile, the effects of friction coefficients, ratiosof thickness and material combinations in the forming process were analyzed. Thewall thickness distribution can become more uniform by improving the conditions oflubrication, applying reasonable ratio of thickness and material combination, so thequalified part can be formed.The combination of those obtained reasonable parameters was also investigatedby experiment. With the analysis of wall thickness and strain distribution of typicalarea of the formed bi-layered T-shape tube, the deformation state of typical area ofbi-layered T-shaped tube during hydrofoming process was obtained.The moving trace and the stress-strain state of typical points on the thin-walledtubes in forming process were analyzed, the reason of bi-layered T-shape tubesalways fractured at the top of branch tube and wrinkled at the axis of main pipe areexplained from the perspective of the stress-strain state. This paper provided thetheoretic foundation for the study of bi-layered T-shape tubes in hydroformingprocess.