Tube/tube joining technology by using rotary swaging forming method

• Rotary swaging can be utilized as a joining by forming method for connecting tubes.
• The concave arc joint type plays an important role on the joining strength of the tubes.
• The joining strength of the tubes is high enough by rotary swaging.

With the development of the manufacturing technology, a challenge has been proposed on the joining of difficult welding materials and the poor connection interface of materials. In this paper, rotary swaging technology is utilized as a joining by plastic deformation forming method to join tube/tube parts with different diameters. Experimental set-up of rotary swaging forming was designed and fabricated, in which the forging energy can be adjusted by changing the rotation speed of AC server motor. The rotary swaging model and tension testing model are established by using FE simulation software Forge 2D. The effects of forming parameters on the tension strength of the joined tubes and the joining mechanism are investigated. The results show that a concave arc joint can be formed at the overlapping parts of the tubes. To obtain the high joining strength, the distance from the end of the inner tube to the center of the hammer die need to exceed a certain value. The maximum strain and stress occur at the concave arc joining region in which the thickness variation of the two joined tubes is small. To exam the joining strength, the tension test was performed. The two tubes tend to slide out during tension process and the maximum stress occurs at the relative sliding region. The ratio on tensile load of the joined tubes to the maximum tensile load of the single tube can reach to 68% for the inner tube and 47% for the outer tube. Therefore, the joining strength of the tube/tube parts, formed by using rotary swaging method, is enough high.