Cold and warm flaring of thin-walled titanium tube using single-point incremental forming

Abstract

The flaring process of thin-walled tubes from light metal alloys such as titanium is very important in automotive and aerospace industries, which is usually carried out at high temperatures. As compared to conventional flaring processes of the tube end, the single-point incremental forming (SPIF) process has a great potential to form symmetric and asymmetric shapes without needing dedicated dies. In this research, the end flaring of the commercially pure grade 2 titanium (Ti-grade 2) tube is experimentally and numerically investigated at room and high temperatures. To this end, firstly, an appropriate fixture was designed and manufactured for the high-temperature SPIF of tubes. Effects of the angular step of the multistage deformation strategy and the forming temperature on the formability limit and surface defects are studied. Results of the conical flaring at room temperature show that the maximum expansion ratio at the tube edge is greatly dependent on the angular step, such that by increasing the angular step from 5° to 10°, the maximum expansion ratio increases by 63%. At the temperature of 400 °C, the expansion of the tube end into the vertical wall relative to the tube axis (i.e., the semi-angle of 90°) was successfully performed. While at room temperature, the conical flaring is limited to the semi-angle of 40° and 70° for the flange length of 33 mm using the angular steps of 5° and 10°, respectively. To extend the process capability of the tube end flaring, it is shown that the cylindrical, elliptical, and square flaring with specified dimensions, which are not possible at room temperature, can be successfully carried out at the temperature of 400 °C. The above results are analyzed in detail by investigating the deformation mechanics using the finite element modeling.