INVESTIGATION OF TUBE SHEET JOINING THROUGH HYDROFORGING PROCESS

Tube-to-sheet joint expansion has been successfully used in HVAC industry for many years to avail better heat exchange between tube and fins (sheet). Because this system transports fluids under pressure, joining tube and sheet in heat exchangers is critical for all processing industries. The tube-sheet connection's joining strength is critical because it directly affects plant safety. Tube-to-sheet joint strength is measured in terms of residual contact stress between the tube’s outer surface and the sheet’s hole surfaces. The joint integrity is affected by several design parameters, including the type of material and the initial radial clearance. The tube can be either deformed with or without an internal fluid pressure to create a joint. A commonly used process to deform the tube is hydroforming. However, hydroforming mostly uses the high pressure to deform the cross-section without dominantly use of axial length of the tube. In contrast, another category where the dominant use of axial length of the tube material is used to deform the section is termed as a hydroforging process. The use of a plastic deformation technique in hydroforging joining technology eliminates some of the limitations of existing joining technologies. The sheet deforms more strongly than the tube after the expansion tool is retracted. As a result, the tube and sheet come into direct contact. This method allows for the joining of dissimilar materials and is also environmentally friendly. Fastened joints, welded joints, and adhesive joints are all examples of methods of joining that are comparable to each other in terms of their advantages and disadvantages. In this paper a tube to sheet joint will be studied during the hydroforging process. While the tube is pressurized with low pressure, the axial force will be applied to buckle the tube outward and around sheet. In the second stage the buckling region was compressed to make a joint. Two setting will be studied: intermediate joint (named: mid joint) and end joint. For this work a two-dimensional (2D) axisymmetric finite element model will be developed. The axial compression to create a buckling/folding in the tube and later joining with the sheet were studied. The mechanics of the buckling/folding was analyzed during the axial compression. The stresses induced at the interface were studied and resulted.