Forming method and application of titanium and titanium alloy bellows

- Nov 22, 2018 -

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.