Stretch-drawing of titanium sheets

Stretch-drawing is a type of the popular deep-drawing process, which utilizes a sharp die shoulder of less than three times the sheet thickness, whereas the conventional process adopts about eight times. When the sheet slides over the die shoulder it is subjected to a strong bending under tension and thus the sheet becomes thinner to yield a deeper cup. Titanium is paid much attention to for its lightness and property of anti-rust. Here, its ability and behavior in the stretch-drawing process is investigated in detail. Two kinds of pure titanium and one of its alloys are tested, of which the thickness is commonly 0.5 mm. It is evidenced that the merit of stretch-drawing or bending under tension is remarkable for titanium sheets as much as for other metals. The variation of the cup wall thickness with the die profile radius, and the relationship between the blank diameter and the depth of formed cups are clarified. The shape quality of the formed cups is also inspected, especially regarding the roundness and the three-dimensional radius distribution of the cup wall cross-section. The former indicates the level of deviation of any cup cross-section from an exact circle, and the latter the global distortion pattern of the cup. The shape quality of a stretch-drawn cup is confirmed to be better than that of a deep-drawn cup. Furthermore, the measurement of the shape implies that its feature depends on the planar anisotropy of the sheets tested.