The superplastic forming methods for titanium alloy plates can be broadly categorized into the following three types:
- Vacuum forming;
- Air pressure forming (blow molding);
- Molding (coupled mold forming).
The first two methods are commonly used in the molding of plastic (or glass) products. Titanium plate superplastic forming because of viscous or semi-viscous flow deformation, so you can use low-pressure forming. Pneumatic forming can also be used in combination with vacuum forming.
Vacuum forming method
Vacuum forming method can be divided into two types: convex mold method and concave mold method. Convex mold method is the heated material, adsorption in the parts with the inner shape of the convex mold forming method, used to form the inside of the requirements of high dimensional accuracy of the parts. The concave die method is a forming method in which the heated material is adsorbed on a concave die with the shape of the part, and is used to form parts requiring high dimensional accuracy of the shape. Generally speaking, the former is used to form deeper containers, and the latter is used to form shallower containers. Vacuum forming is also a kind of pneumatic forming, but the forming pressure can only be an atmospheric pressure. Therefore, for titanium plate, can only form thin thickness, simple shape, curvature degree and slow parts, not suitable for forming thicker, more complex shape and deformation of more dramatic parts.
Air pressure forming method (blow molding method)
This is a special expansion process. Traditional expansion process is to use mechanical, hydraulic expansion or explosion expansion method to achieve, the use of pressure and energy are relatively high, and due to the limitations of the plasticity of the material, the amount of deformation is generally not too large. Blow molding is a low-energy, low-pressure can be obtained with a large amount of deformation forming, is a kind of traditional process with a different concept of sheet forming technology. Because the metal is free in the deformation process, therefore, almost all the power is consumed in the deformation work, the friction loss is very small (for free blow molding, there is no friction loss), which is fundamentally different from the other stamping forming.
Blow molding can be divided into two categories: free blow molding and mold blow molding.
Mold blow molding is characterized by half-mold forming, and vacuum forming similarities, also divided into convex mold forming concave mold forming; the difference is that the molding pressure can be greater than an atmospheric pressure, but also through the gas system to regulate the pressure, and thus can manufacture complex shapes, curvature changes in large parts.
(1)Free blow molding method
This is the simplest kind of blow molding shape. It is characterized by the fact that no molds are used, and the typical parts blown are spherical parts.
(2) Convex molding method
This method is to make titanium plate material outside, the formation of a closed pressure space, titanium plate heated to the superplastic temperature, under the action of compressed gas pressure, the material produces superplastic deformation, and gradually close to the mold surface until the mold with the mold completely close to make the same parts with the mold surface. Formed parts of the inner surface of the high dimensional accuracy, accurate shape, depth and width of the larger, easier mold processing, but more difficult to remove the mold, the raw material is also more costly. The bottom of the part formed by this method is thicker than the surrounding area.
(3) Concave mold forming method
With the convex mold forming method is different, in the forming process so that the inside of the titanium sheet material to form a closed pressure space. Formed parts of the outer surface of the high dimensional accuracy, shape accuracy, parts off the mold is easier, the raw material is more economical, but the depth and width is relatively small, mold processing is also more difficult. The bottom of the part formed by this method is thinner than the surrounding area.
Molding method
The use of coupling mold. Unlike ordinary compression molding is a high temperature, molding speed is much slower.
Due to the superplastic temperature resistant titanium plate metal coupling mold manufacturing difficulties, with the precision is difficult to ensure (especially for complex shapes of the mold), so the titanium plate superplastic forming less used.
