Titanium sheet is widely recognized for its advantages such as high strength, light weight and good structural rigidity. The high-strength titanium alloy Ti-6Al-4V can be used not only in the aviation field, but also as an important candidate material for structural parts in other industrial fields such as automobiles and chemicals. The formability of Ti-6Al-4V alloy sheet at room temperature is very limited, and the springback after forming is very large, which brings many problems to traditional stamping and pressure forming. Although the forming limit of Ti-6Al-4V alloy sheet will be increased and the springback will be reduced at high temperatures, room temperature forming still has great advantages in terms of cost savings. Roll forming is a forming method that uses rotating rollers to gradually deform metal blanks to make workpieces. It is suitable for forming structural parts with high strength and limited formability. It is used more and more in the automotive industry. Used for forming ultra-high strength steel, high strength steel, etc. Because the springback angle of the material is small during the roll forming process and the springback can be compensated by a simple and easy method, roll forming is an effective method for forming Ti-6Al-4V alloy sheet at room temperature. To this end, Ossama et al. Conducted laboratory research on the forming and springback behavior of 2 mm thick high-strength Ti-6Al-4V alloy sheet after annealing at 820 ℃ at room temperature.
The original structure of the Ti-6Al-4V alloy plate selected for the experiment is composed of 93.86% equiaxed α phase and 6.14% β phase, and the average grain size is 1.3 μm ± 0.7 μm. The tensile test results at room temperature show that the anisotropy is relatively large. When the direction is 45 ° from the rolling direction, the sample has the lowest yield strength and high elongation. When the ultimate strength is reached, the sample will quickly break. . The forming limit test is completed on a device equipped with a hemispherical punch with a diameter of 60 mm. An optical strain measurement system “Autogrid Vario” equipped with 4 advanced CCD cameras is used to record the complete deformation history of each specimen. By designing different specimen shapes to test the deformation behavior of different strain paths. The experiment found that all the samples suddenly broke at the top of the hemispherical punch, and there was no obvious necking before breaking, indicating that the room temperature formability of the alloy is very limited. The deformation behavior of Ti-6Al-4V alloy sheet during bending and rolling at room temperature was compared and analyzed. The results show that the minimum bending radius of the pendulum bending test and the V-shaped bending test is 9 mm, while the minimum bending radius of roll forming is 7.51 mm, an increase of more than 15%. Roll forming can form smaller radius sizes and have less springback than simple bending. This is mainly because rolling forming is a multi-step cumulative deformation process. The gradual multiple deformations can suppress the growth of cracks, and at the same time make the deformation of the material more adequate than the ordinary one-time deformation. In addition, the shape defects that often occur in the rolling process of high-strength steel are relatively few in the rolling process of Ti-6Al-4V alloy. It can be seen that roll forming is a very promising process for forming high-strength titanium alloy sheets for aerospace and automotive structural parts at room temperature.
