Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
1999-08-27
2001-03-06
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
Reexamination Certificate
active
06196043
ABSTRACT:
TECHNICAL FIELD
This invention relates to lockbeads and to lockbead retaining and forming means for restraining the edges of sheet metal blanks against inward motion during forming of the blanks into stampings in a forming press.
BACKGROUND OF THE INVENTION
It is known in the art relating to press forming of a sheet metal blank into a stamping, in particular stretch forming processes, to provide a lockbead around edges of the blank to hold the blank edges against inward motion during forming of the blank in a press. A conventional lockbead comprises a trapezoidal or nearly rectangular protrusion of the blank material upward or downward from the associated flange or edge portion of the blank.
The bead is usually formed in the press by engagement of the blank by one of upper and lower dies in the press and an associated binder (also called a cushion ring or blank holder). These members have opposed blank holding surfaces for engaging opposite sides of the blank adjacent its edges or periphery in what may be called the outer flange area of the blank. One of the opposing die and binder members is provided with a protruding bead of rectangular, square or trapezoidal cross section lying generally parallel to the blank edge. The other of the members has formed therein a mating bead recess or slot into which the protruding bead of the first member extends when the blank holding surfaces of the members are forced against opposite sides of the blank. This forms a nearly square, rectangular or trapezoidal bead in the blank running along its edges and trapped in the mating beads of the associated die and binder members.
A conventional bead, formed by a square protrusion forcing the blank into a parallel sided slot with small clearance, forms a nearly square sided bead in the blank having four sequential bends in the bead of nearly 90 degrees each, but slightly less because of the clearance required for bead forming. In stretch forming of sheet metal blanks, for example, the bead is usually capable of restraining the blank edges against inward motion if the angles of the four bends total 340 degrees or more (for example 85 degrees for each bend). This works well for horizontally disposed blank edge flanges but is less or not at all satisfactory where the blank edges are disposed at an angle, such as 45 degrees from horizontal. In such a case, the requirement that the slot edges remain vertical for entry of the protruding bead during a vertical motion of the press causes the bends in the bead to be substantially less than 90 degrees. The resulting sum of the bends then falls to significantly less than 340 degrees and sometimes less than 300 degrees, resulting in inadequate restraint of the flanges, or blank edges, against slipping, or inward motion during forming.
SUMMARY OF THE INVENTION
The present invention provides a novel form of double V or similar form of lockbead and lockbead retaining and forming means. Lockbeads and their retaining means according to the invention provide restraint which is less dependent upon clamping surface angle and is able to provide 340 degrees or more of total bending while using less of the blank edge material than a conventional lockbead. In a preferred embodiment, the double V lockbead includes three alternately angled sharp bends forming in cross section the double V configuration. Two additional sharp bends of about 45 degrees each connect the double V bead with the adjacent portions of the clamped flange of the blank. The sum of the five angles thus totals at least 340 degrees, nearly 90 degrees each from the three bends of the double V and nearly 45 degrees each for the two connecting bends. Because of their shape and the possibility of using slightly shorter legs between the bends than with a conventional bead, the double V bead uses less material of the blank flanges for bead formation. Thus, a substantial saving of sheet metal is accomplished which provides cost savings for the double V bead as opposed to conventional beads.
In various alternative embodiments, the bend angles may vary and total more or less than 340 degrees as is required for the particular application, material and forces developed in the forming process being used. For example the sum of the alternately angled and connecting bends could be as little as 300 degrees with the alternately angled beads contributing only 225 degrees to the total. Each of the alternately angled bends could vary in a range of from 75 to 120 degrees. If desired, the double section could be increased by adding an additional bend, or two which would form a triple V bead. Then lesser bend angles might be adequate for forming loads or greater loads could be accommodated. In the unusual case of near vertical blank holding surfaces, the double V bead of this invention could still be used but one of the connecting bends would approach 90 degrees while the other side of the double V would have a nearly straight, connection. The legs or sides of the V elements may have unequal lengths but negative die angles or back draft cannot exist.
As to the lockbead retaining means or beads formed in one die and an associated binder, forming the bead surfaces with 90 degree angles would allow cutting the beads with a standard end mill. However, other bead surface angles can also be formed which could range from 105 to 60 degrees, comparable to the 75 to 120 degree bend angles mentioned above and considered reasonable for normal use. Other angles may, of course, be appropriate for various particular forming conditions.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
REFERENCES:
patent: 2285903 (1942-06-01), Clark
patent: 3299689 (1967-01-01), Dolney et al.
patent: 3664172 (1972-05-01), Cyacho
patent: 3789649 (1974-02-01), Clowes
patent: 4833903 (1989-05-01), de Smet
patent: 5372026 (1994-12-01), Roper
patent: 5572896 (1996-11-01), Story
patent: 5644943 (1997-07-01), Lanz
patent: 5701777 (1997-12-01), Yamanaka et al.
patent: 1438207 (1976-06-01), None
General Motors Corporation
Larson Lowell A.
Leahy Charles E.
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