Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
1999-12-09
2001-08-21
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
Reexamination Certificate
active
06276185
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method and apparatus for drawing high strength steel in a conventional forming press.
BACKGROUND OF THE INVENTION
It is known in the art of metal forming to form deep drawn three dimensional sheet metal structures for automobile body components and the like using a conventional forming press and drawing dies working with low carbon steels of an adequate gauge or thickness.
In order to provide lighter structures for forming or supporting body components, it has long been desired to utilize high strength steels of thinner gauge to replace the components currently formed from low carbon steel. However, the use of high strength steels has not previously been successfully accomplished where significant drawing of the metal is required since the resulting product is deformed due to internal stresses in the high strength steel which are not relieved in the forming process.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for successfully drawing high strength steel to form relatively light weight structural members for automobile bodies and the like with a high degree of accuracy in the resulting component. The invention involves a two-step process wherein a blank, which may be flat or preformed to a desired shape, is first partially drawn in a forming press while binder edge portions of the blank are drawn across flow restricting beads in a press binder to allow drawing of metal into a die cavity by an associated punch to form a partially completed structure. The process is completed by forcing the beads further into associated die cavities to lock the binder edges of the blank so that the final portion of the forming process is limited to working the metal of the blank by stretching it into the final shape, sufficient working being accomplished to develop yielding of the metal which avoids subsequent warping or distortion of the finished component upon removal from the die.
The forming apparatus includes mating upper and lower dies, the lower die assembly including a binder having novel flow lock beads. In an initial predetermined portion of the stroke of the press, the beads are positioned to apply a restraining force while allowing metal from the binder edges to flow into the die cavity. Upon further movement of the press toward the final forming position, the beads are forced upward into associated
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cavities. This locks the edges of the blank against further flow, causing the final forming step to stretch the metal so that it yields and forms a smooth drawn structure with stresses relieved to avoid subsequent distortion of the part.
In a preferred embodiment, the apparatus includes a drawing die with a mating punch and binder, the die and binder having opposing binder edge engaging portions. The die includes a bead recess opposing a bead carrying pocket in the binder. At least one adjustable bead is received in the pocket, having an initial metal restraining position. Transfer means in the binder move the bead to a second position during relative motion of the die and punch to lock the associated binder edge of the blank in position for final forming and working of the metal to a smooth stress relieved component.
REFERENCES:
patent: 58-181432 (1983-10-01), None
patent: 64-27726 (1989-01-01), None
patent: 3-71932 (1991-03-01), None
General Motors Corporation
Larson Lowell A.
Leahy Charles E.
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