Superplastic hot metal gas forming of titanium hollow profilesTuesday (05.11.2019) 14:20 - 14:40 Part of:
Tube forming technologies based on high internal forming pressures, like hydroforming or hot metal gas forming (HMGF), are state of the art to form complex closed profile geometries. Materials with excellent specific strengths and chemical properties, such as Ti-3Al-V2.5 (Grade 9), are often challenging to shape due to their limited formability. However, it is well known that titanium alloys with a microstructure consisting predominantly of globular grains become superplastic in a certain temperature range. In this study, the superplastic HMGF process for hollow profiles was investigated in terms of process simulation, forming tool technology, process window and microstructural analyses. As preforms seamless tubes with 0.4 mm wall thickness were used. The final geometry is challenging and resembles to a helical contour. The used tool was based on a HMGF tool with tempered forming dies. The evolution of the microstructure at specific positions before and after tube processing was analyzed by scanning electron microscopy and electron back-scattered diffraction analysis. With the newly developed tool design forming temperatures up to 930 °C and internal gas pressures up to 7 MPa were tested. In comparison to the simulated thinning of about 50 %, the manufactured good parts showed thinning up to 60 % in critical forming areas of the geometry. A process window to manufacture good parts without necking or wrinkling has been successfully identified. Microstructural analyses of several states of the process have shown that both the forming process and the simultaneous dynamic recrystallization influence the microstructure significantly. The detailed study of the process in correlation to the microstructure contributes to an in-depth understanding of the superplastic forming of Ti-3Al-V2.5 during HMGF. Furthermore, it shows the great potential of this forming technology for the production of complex titanium profile geometries.