Hot Gas Pressure Forming of Tubular Parts From Titanium Alloy Ti6-4

Concentrated loads in airframe structures are often controlled by so-called “tie rods”. Tie rods are conventionally made from Al- and Steel alloys. Conventional way of manufacturing is swaging of a tube at the ends to create a section with a smaller diameter for the inner thread. These threads are made by forming and not by cutting for enhanced fatigue live. Fixation of the tie rods in the fuselage is guaranteed by the rod ends, which are screwed into said threads.

For A350 it was asked to produce a set of tie rods from Titanium alloys .

Ti- alloys have high tensile strength up to temperatures of ~380°C and show just ~50% of the steels´ density. Unfortunately the forming properties at ambient temperature are not suitable at all to create the necessary geometry. Furthermore forming of threads with big diameters in Ti6-4 is not yet state-of-the

Process chosen to give the middle section the required bigger diameter for stiffness reasons is by hot gas pressure forming.

R&D phase rapidly showed proper forming and suitable material properties. An industrialised process was developed to produce FAI parts and shortly afterwards the first production parts. Result of the qualification procedure is a fully certified product. Total commitment to the drawing, tolerances etc are achieved. Final machining gives the product suitable surface finish and tolerance In a second approach also the forming of the thread was successfully verified. The resulting endurance live limit advantage is more than 1 million cycles compared to ~300.000 cycles with the cut thread. The applied processes as hot forming and thread forming are fully qualified with the results of the FAI tests. Joined effort of the partners guarantees for an extraordinary product performance with some potential for further applications in aerospace and other related fields of technology.