Metal deforming – By application of fluent medium – or energy field – With actuated tool engaging work
Reexamination Certificate
2001-03-30
2001-10-23
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
With actuated tool engaging work
C072S212000, C029S421100
Reexamination Certificate
active
06305202
ABSTRACT:
TECHNICAL FIELD
This invention relates to the art of superplastically forming heated metal sheet material into profiled parts and more particularly to new and improved superplastic forming equipment and processes featuring advanced construction and processes for mechanically stuffing the heated sheet material into an optimized preform position with respect to a forming profile of the equipment during a superplastic forming cycle.
BACKGROUND OF THE INVENTION
Prior to the present invention, various constructions and methods have been devised to improve the operations of superplastic and quick plastic forming equipment in the forming of high quality parts from sheets of aluminum alloy or other superplastic metal alloys. For example, in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Sanders et al for Superplastic Forming Process, assigned to the assignee of this invention and hereby incorporated by reference, a heated sheet of superplastic forming metal alloy is positioned on a preforming block mounted on a lower die platen. A forming die is then lowered into a preforming position in which the peripheral lower edges thereof surround the block thereof and contact the outer edge portions of the heated sheet. These lower edges in conjunction with the preform block act as stuffer unit to pull the material inwardly into an intermediate or preform position as the forming die reaches its closed or seated position. With the heated sheet in the preform or intermediate position in which more sheet material has been pulled into a preform, low pressure inert gas is injected into the interface between the preformed sheet and the preform block to stretch the sheet material into the desired shape as defined by the profile of the forming die. After part forming, the die can be opened so that the part can solidify and be handled and removed without damage thereto.
SUMMARY OF THE INVENTION
While such existing stuffing devices are simple static devices that effect mechanical deformation of the metal sheet material and that effectively gathers more sheet material into the die set, high friction forces between the stuffer and sheet material may cause the physical tearing of the material as the forming dies are closed. Such material tearing results in part defects and limits the amount of material that can be stuffed into the die set. With limited amounts of material that can be drawn into the die set, there may be insufficient material to make an optimized part. More particularly, there may be insufficient material for optimizing shapes and the wall thickness, and the part may have tears or voids resulting in part rejection. Such tearing or flaws reduce the production effectiveness and efficiency of the equipment.
Accordingly, a gentle or cushioned low-friction material contact or stuffing unit is needed for optimizing the engagement between the contact and the sheet to optimize the quantity of material that is drawn into the forming die for improved part forming.
These problems and requirements have been worked out in the present invention by providing a stuffer having a freedom of rotation to effectively reduce the friction between the stuffer and the superplastic forming blank and to provide a better material distribution in the formed part. The reduced friction allows for improved intermediate deformation of the blank sheet of superplastic forming material into an optimized preform with more material pulled into the die set. This ensures that there will be minimized thinning or tearing and resultant part rejection when the equipment is operated to superplastically form a part.
In the preferred embodiment of this invention, at least one rotatable stuffer is mounted in a chambered upper tool of the superplastic forming equipment which is offset from the forming profile of the lower steel or forming die. This ensures that the profile of the forming die and stuffer do not physically contact one another in the stuffing or intermediate forming operation. The rotatable stuffer, however, physically contacts portions of a blank sheet of superplastic forming material as the upper tool is lowered and, with low rolling resistance or friction therebetween, effectively pulls the sheet material into the working area and around portions of the profile of the forming die equipment in the intermediate phase of forming operation. With the sheet intact and pulled into an optimized preform position around the forming die, sufficient material is present within the working chamber so that the part can be fully formed without wall thinning or tearing when the chamber is charged with pressure gas. The rotating contact of the stuffer importantly results in reduced friction between the stuffer and the blank sheet. The reduced friction allows more deformation of the forming blank and therefore more material in the die set.
REFERENCES:
patent: 1032907 (1912-07-01), Hyde
patent: 2317869 (1943-04-01), Walton
patent: 2783727 (1957-03-01), Hoffmann
patent: 5819572 (1998-10-01), Krajewski
patent: 5974847 (1999-11-01), Saunders et al.
General Motors Corporation
Grove George A.
Jones David
Sedlar Jeffrey A.
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