Freeform Bending of Aviation-Relevant Tubular Parts

Funding: BMWi/DLR
Project: 20W1514B
Contact: Stefan Gallus M. Sc.

In cooperation with PFW Aerospace GmbH, Incremental Tube Forming (ITF) is qualified for the production of aviation-compatible tube structures made of titanium and titanium alloys.

Incremental tube forming (see figure a) as a freeform bending process is very flexible so that the setup effort is low in comparison to conventional rotary draw bending, which is beneficial for small lot sizes such as in aviation. It is shown that the ovality and wall thinning of the outer tube bend is lower in incremental tube forming than in conventional rotary draw bending (see figure b). In addition, in a test setup (see figure c) the residual stresses are determined by means of x-ray diffraction on the outer surface of a bent tube and their distribution over the wall thickness is calculated with thermomechanical simulations (see figure d). The compensation of the residual stresses does not take place completely over the circumference, but partly over the wall thickness. It creates residual compressive stresses on the inner tube wall increasing the fatigue strength in tubes subjected to internal pressure.

a) Process principle, b) Ovality and wall thickness, c) Test setup, d) Residual stress at ITF