Tube forming technologies based on internal forming pressures, such as hydroforming or hot tube gas forming, are state of the art to manufacture complex closed profile geometries. However, materials with excellent specific strengths and chemical properties, such as titanium alloys, are often challenging to shape due to their limited formability. In this study, the titanium alloy Ti-3Al-2.5V was processed by superplastic hot tube gas forming to manufacture a helically shaped flex tube. The forming process was investigated in terms of process simulation, forming tool technology and process window for the manufacturing of good parts. Within a simulation study, a strain rate optimized forming pressure–time curve was defined. With the newly developed tool design, forming temperatures up to 900 °C and internal forming pressures up to 7 MPa were tested. A process window to manufacture good parts without necking or wrinkling has been successfully identified. The experiment data showed good agreement with the numerical simulations. The detailed study of the process contributes to an in-depth understanding of the superplastic forming of Ti-3Al-2.5V during hot tube gas forming. Furthermore, the study shows the high potential of superplastic hot tube gas forming of titanium alloys for the manufacturing of helical flex tubes and bellows.
Within the framework of investigations, an exhaust gas component made of Titanium Grade 2 was produced by means of Hot Metal Gas Forming (HMGF) at the Fraunhofer IWU in Chemnitz, Germany. The semi-finished products were two-fold bent, thermal joined, calibrated and pre-formed tubes. So far, a three-stage internal high-pressure forming process at room temperature plus two necessary intermediate heat treatments were used to produce the component. Due to its complexity as well as the limited forming ability of Titanium Grade 2 at room temperature an one step Hot Metal Gas Forming was developed to replace the former procedure
Front cover by Krbetschek and Ullmann: SEM micrographs of the Mg97Y2Zn1 alloy in the as‐cast state showing the α‐Mg matrix with block‐like LPSO structures. https://doi.org/10.1002/eng2.12380
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