1. Technical Field
The present invention relates to seals for tools that use fluid to form a part against a rigid forming surface.
2. Background Art
Fluid forming processes generally include processes in which a workpiece is formed in a tool where one side of the tool is provided by a liquid. The other side of the tool is generally a rigid die against which the part is formed. Examples of fluid forming processes include hydro-forming, bladder press forming, super-plastic forming, electro-hydraulic forming, and explosive forming.
Traditional seals for such applications include elastomeric seals, such as O-rings. Elastomeric seals used in hydro-forming applications may feature an O-ring inserted in a circumferential groove that is pushed inside the tube that is to be hydro-formed. Such O-ring seals have a short useful life in hydro-forming applications. In sheet forming applications, sealing requirements are more stringent. Elastomeric seals resist drawing the flange of the sheet across the seal.
Metal-to-metal seals are used in hydro-forming applications that include a mandrel that includes a conical surface that is inserted into the tube that is to be hydro-formed. The mandrel is axially moved to provide additional material for the forming process. This approach is not adaptable to sheet forming processes to permit the outer edge of the flange of the sheet metal blank to be drawn into the forming die.
In hydro-mechanical drawing operations, metal-to-metal surface contact has been proposed in which ribs formed on the die directly contact the metal blank. This approach suffers from considerable leakage of fluid from the die cavity. With this approach, the pressure level used in the forming process must be limited. A disadvantage of this approach is excessive wear of the ribs formed on the die.
In super-plastic forming operations, seals are used in which metal-to-metal contact is obtained by indenting seating elements or ribs into the body of the blank. With this approach, only minimal movement of the blank across the sealing line is permitted.
In electro-hydraulic forming processes, elastomeric sealing elements, such as O-ring seals, are utilized. In electro-hydraulic forming, elastomeric seals have lives that are limited to forming several dozen parts and, in any event, are certainly not expected to exceed several hundred parts. As a result, electro-hydraulic forming is limited to low volume applications. The sealing requirements for electro-hydraulic forming are more stringent than for hydro-forming because the sealing system must be able to preserve the vacuum between the blank and the die, and another seal must be provided on the side of the blank facing the fluid filled chamber to contain the fluid.
The above problems relating to sealing in fluid forming applications are addressed by Applicants' development as summarized below.