Superplastic forming of titanium alloy sheet can be divided into the following three methods :(1) vacuum forming;(2) pneumatic forming (blow molding);(3) molding (coupling molding).The first two methods are commonly used to form plastic (or glass) products.Because the superplastic forming of titanium plate belongs to viscous or semi-viscous flow deformation, low pressure forming can be used.Pneumatic forming can also be used in combination with vacuum forming.
1. Vacuum forming
Vacuum forming method can be divided into two kinds: punch method and die method.
Punch method is a forming method that adsorbs the heated wool on the punch with the inner shape of the part. It is used to form parts with high precision of inner dimension.Die law is to heat the wool, adsorption on the shape of the parts of the form force method, used to require the shape of the size of high precision parts forming.Generally speaking, the former is used for forming deeper containers, while the latter is used for forming shallower containers.
Vacuum forming is also a kind of pneumatic forming, but the forming pressure can only be one atmosphere.Therefore, for the titanium plate, can only be formed thin thickness, simple shape, curvature and gentle parts, not suitable for forming thicker, more complex shape and deformation more rapid parts.
2. Pneumatic forming (blow molding)
This is a special bulging process.
The traditional bulging process is achieved by mechanical, hydraulic or explosive bulging method, using high pressure and energy, and due to the limitation of plastic materials, deformation is generally not too large.Blow molding is a low energy, low pressure can get a large amount of deformation forming, is a different from the traditional technology concept of sheet metal forming technology.Since the metal is free in the process of deformation, almost all the power is consumed in the deformation work, the friction loss is small (for free blow molding, there is no friction loss), which is essentially different from other stamping.
Blow molding can be divided into two categories: free blow molding and mold blow molding.The characteristics of blow molding are semi-die forming, which is similar to vacuum forming.The difference is that the forming pressure can be greater than one atmosphere, and the pressure can be adjusted through the air source system, so that parts with complex shapes and large curvature variations can be made.
(1) free blow molding
This is the simplest form of blow molding.It is characterized by the use of no mold, the typical blown parts are spherical parts.
(2) punch forming method
This method is to make the outside of the titanium plate wool, the formation of a closed pressure space, titanium plate heated to the superplastic temperature, under the pressure of compressed gas, the wool produces superplastic deformation, gradually close to the mold surface, until the mold fully fit, make the same parts with the mold surface.The inner surface size of the forming parts is high precision, the shape is accurate, the depth and width of the larger, mold processing is easier, but more difficult to demold, the cost of raw materials.The bottom of the parts formed by this method is thicker than the sides.
(3) die forming method
Different from punch forming method, a closed pressure space is formed on the inside of titanium plate wool during forming.The surface size of the forming parts is high, the shape is accurate, the parts are easy to demould, the raw materials are less, but the depth and width are smaller, the mold processing is more difficult.The bottom of the parts formed by this method is thinner than the sides.
3. Molding method
Coupling mode is adopted.Different from the ordinary pressure is the high temperature, the mold speed is much slower.
Because it is difficult to manufacture the metal coupling mold that can withstand the superplastic temperature of titanium plate, the matching precision is difficult to be guaranteed (especially for the mold of complex shape), so the superplastic forming of titanium plate is seldom used.