The superplastic forming method of the plate in titanium machining can be roughly divided into the following three types: (1) vacuum forming; (2) air pressure forming (blow forming); (3) compression forming (coupling mold forming). The first two methods are commonly used methods for forming plastic (or glass) products. The superplastic forming of titanium plate is viscous or semi-viscous flow deformation, so low pressure forming can be used. Air pressure forming can also be combined with vacuum forming.
1, vacuum forming method
Vacuum forming method can be divided into two types: convex mold method and concave mold method.
The punch method is a forming method in which heated wool is adsorbed on a punch with the inner shape of the part, and is used to form parts that require high inner dimensional accuracy. The die method is a forming force method in which heated wool is adsorbed on a die with the shape of the part. It is used for the forming of parts that require high dimensional accuracy. Generally speaking, the former is used for forming deeper containers, and the latter is used for forming shallower containers.
Vacuum forming is also a kind of air pressure forming, but the forming pressure can only be one atmosphere. Therefore, for the titanium plate, only parts with thin thickness, simple shape, and gentle curvature can be formed, and it is not suitable for forming parts with thicker thickness, more complicated shape and severe deformation.
2, air pressure forming method (blow forming method)
This is a special bulging process.
The traditional bulging process is realized by mechanical, hydraulic bulging or explosive bulging. The pressure and energy used are relatively high, and due to the limitation of material plasticity, the amount of deformation is generally not too large. Blow molding is a kind of forming that can obtain large deformation with low energy and low pressure. It is a sheet metal forming technology that is different from the traditional process concept. Since the metal is free during the deformation process, almost all the power is consumed in the deformation work, and the friction loss is small (for free blow molding, there is no friction loss), which is essentially different from other stamping forming .
Blow molding can be divided into two types: free blow molding and mold blow molding. Mold blow molding is characterized by half-mold molding. Similar to vacuum molding, it is also divided into two types: convex molding and concave molding; the difference is that the molding pressure can be greater than one atmosphere, and it is also suitable for air supply system. The pressure can be adjusted so that parts with complex shapes and large curvature changes can be manufactured.
(1) Free blow molding method
This is the simplest form of blow molding. Its characteristic is that there is no mold, and the typical parts blown are spherical parts.
(2) Punch forming method
This method is to form a closed pressure space on the outside of the titanium sheet wool. After the titanium sheet is heated to superplastic temperature, the wool will undergo superplastic deformation under the action of the compressed gas pressure, and gradually approach the mold surface until it is the same as the mold. Completely fit, make the same parts as the mold surface. The inner surface of the formed part has high dimensional accuracy, accurate shape, large depth and width ratio, and easy mold processing, but it is difficult to demold and raw materials are more expensive. The bottom of the part formed by this method is thicker than the surrounding.
(3) Concave mold forming method
is different from the punch forming method in that a closed pressure space is formed inside the titanium sheet wool during the forming process. The outer surface of the formed part has high dimensional accuracy, accurate shape, easy part demolding, less raw materials, but the depth and width are relatively small, and the mold processing is also difficult. The bottom of the part formed by this method is thinner than the surrounding.
3, compression molding method
Using coupling mode. The difference from ordinary pressing is that the temperature is high and the molding speed is much slower.
Since it is difficult to manufacture metal coupling molds that can withstand the superplastic temperature of titanium plates, and the matching accuracy is difficult to ensure (especially for molds with complex shapes), superplastic forming of titanium plates is rarely used.