Forming method and application of titanium and titanium alloy bellows
Titanium and titanium alloys have become a new type of bellows material due to their superior mechanical properties, certain shape memory function and excellent corrosion resistance. Titanium and titanium alloy bellows have wide application prospects in aviation, aerospace, marine, atomic and chemical industries due to their advantages of non-magnetic, thermal radiation and electromagnetic shielding, light weight, high sensitivity and strong corrosion resistance. However, it is still used less in China. The reason is that titanium and titanium alloy materials are more expensive. Second, titanium and titanium alloys have low elastic modulus (only 1/2 of stainless steel), and the yield ratio is high (0). 8～ 0. 84), cold working deformation has large rebound, high deformation strengthening rate, and is not suitable for cold working. Therefore, the processing skill at room temperature is not good, and it is very difficult to manufacture titanium and titanium alloy bellows. Therefore, titanium and titanium are currently The use of titanium alloy bellows is greatly limited. In view of the current literature on the introduction of titanium and titanium alloy bellows, this paper briefly introduces the forming method, performance, application status and prospects of titanium and titanium alloy bellows.
There are six types of forming methods for titanium and titanium alloy bellows: hydroforming, roll forming, spin forming, expansion forming, welding forming, and superplastic forming.
1. 1 hydroforming
Hydroforming is suitable for processing pure titanium bellows, which is the medium pressure (oil or water) injected into the tube blank by the pump, forcing the tube blank to bulge in the limiting module, and then removing the positioning support between the modules, using a hydraulic press or other related For similarly acting equipment, the tube blank is compressed to the desired final length, and the module is removed to form a bellows. The feature of hydroforming is that during the forming process, the tube blank is evenly pressed and the amount of thinning is moderate. Hydroforming is divided into two modes: multi-wave primary forming and single-wave continuous forming.
1. 2 roll forming
Roll forming is to place the tube blank in the forming machine. By the rotation of the working wheel, friction is generated on the contact surface between the working wheel and the tube blank, and the whole tube blank is driven by the force, and then the direction of the working wheel is used. The lower feed, that is, the bulge is gradually formed on the tube blank, that is, the initial wave. At the same time, the shaping wheel gradually closes axially, corresponding to the slow-feeding working wheel, and finally a U-shaped corrugation is rolled in the circumferential direction of the tube blank. Roll forming can be rolled into one or more corrugations each time, which is suitable for processing titanium bellows with larger diameters. However, due to the difficulty in production of large diameter seamless titanium tubes, the forming method is less applied. This method also allows the work wheel to be placed outside the tube for reduction in diameter and is suitable for machining titanium bellows with a diameter of <100 mm.
1. 3 spin forming
Spin forming is currently the most used titanium bellows production method, mainly used to produce spiral bellows. Its mold is composed of a working diaphragm and a spacer. After the tube blank enters the rotating mold, under the action of the diaphragm and the spacer, the tube blank is subjected to a certain compression in the radial direction and the axial direction to cause plastic deformation, and is gradually formed into a spiral bellows. This method generally produces a small titanium bellows, for example, a titanium bellows having a diameter of 9.52 mm to 28.6 mm, a wall thickness of 0.3 mm to 0.77 mm, and a length of 6 m or less. .
1. 4 inflation molding
The expansion molding is pre-installed with a circular inner mold in the tube blank. The mold is composed of a plurality of split-valve modules. The center of the inner mold has a cone that pushes up and down by the oil cylinder. When the cone descends, side pressure is generated on the block. Under the force, the module causes the tube blank to be expanded and formed into a wave shape, and the module is reset by the spring force after the cone is ascended.
The above four methods are all cold working methods, and basically only a pure titanium corrugated pipe with good plasticity can be formed. Since a seamless titanium pipe is required as a blank, the diameter of the formed bellows is also limited.