Mid plate process and equipment for the superplastic forming of parts from plural sheets

#Prior to the present invention, various types of superplastic forming equipment and processes have been developed for shaping blanks of metallic sheet material into a wide range of items. The forming dies of such equipment and processes are generally mounted in presses that are capable of maintaining elevated temperatures in the dies and metal sheet material necessary for superplastic forming. More specifically, such temperature elevation enhances the capacity of the metal to tolerate strain-induced deformation without tearing and importantly diminishes the force required for deformation. A time controlled compressed air charge is typically delivered to the forming equipment to apply the force on the heated metal blank to superplastically form the metal on the forming die.

#In more specific detail relative to the present invention, superplastic forming involves the employment of a ductile sheet of superplastic metal alloy positioned between dies in a press whose temperature is increased by the heat energy maintained in the press. The heated sheet is stretched by the force of the compressed air into forming cavities or onto forming surfaces of heated forming dies to produce high-quality, lightweight parts such as panels for automotive vehicles. Often such sheets are quite large and components such as trunk lids, engine hoods and these or other large panels can be precisely formed in one piece by such superplastic forming.

#Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Sanders et al. for Superplastic Forming Process and U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to P. E Krajewski for Lubricating System For Hot Forming, both assigned to the assignee of this invention and both hereby incorporated by reference.

#These and other objects, advantages and features of the invention will become more apparent from the following detailed description of one preferred embodiment of the invention and drawing in which:

#FIG. 1 is a pictorial view of superplastic forming equipment according to this invention for simultaneously forming pairs of sheet metal blanks into plurality of formed parts;

#FIG. 2A is a pictorial view of spaced upper and lower forming dies with a mid plate diagrammatically shown therebetween;

#Turning now in greater detail to the drawing, FIG. 1 illustrates a forming press 10 comprising a base member 12 supporting a lower bolster plate 14 on which lower tool or forming die 16 is mounted. The press additionally has an upper carrier plate 18 operatively mounted for reciprocating movement on upstanding rails 19 extending from the base. The carrier plate 18 securely mounts the upper tool or forming die 20, which projects downwardly therefrom. Both plates 14 and 18 are electrically heated to establish the required heat energy levels in the upper and lower dies and the upper and lower sheet metal blanks 22, 24 loaded therein for super plastic forming.

#The upper carrier plate 18 of the press is cycled by hydraulic cylinders 26 from the illustrated open position shown in FIG. 1 for loading of the two sheet metal blanks 22, 24 to the closed position shown in FIG. 3 for the superplastic forming of the blanks into two discrete parts and then back to the open position for removal of the formed parts from the hot forming dies. A second pair of blanks can then be loaded into the forming dies for another cycle to form additional parts.

#The upper and lower blanks 22, 24 utilized with this invention may be flattened rectilinear sheets of aluminum alloy coated with a dry lubricant such boron nitride to function as an agent to enhance the stretching and forming of the parts 28, 30 during super plastic forming operation and to prevent the formed parts 28, 30 from adhering to the associated forming dies. These blanks and formed parts may be identical to one another or may be of differing designs, dimensions and materials depending on part specifications.