Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
1999-11-10
2001-06-12
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
C072S350000
Reexamination Certificate
active
06244091
ABSTRACT:
BACKGROUND OF THE INVENTION
TECHNICAL FIELD
The invention relates to forming cup-shaped members such as container bodies from a blank of metal, and in particular to forming such bodies in a press which reduces the wrinkling and splintering of the peripheral edge of a blank disk as it is drawn around the draw forming radius and into the opening of a blank and draw die by providing the draw pad with an annular tapered relief area adjacent a central ram opening for reducing the clamping force on a peripheral edge of the disk blank as it moves around the draw forming radius of the blank and draw die and into the die opening.
BACKGROUND INFORMATION
It is well known in the container forming art to form two piece containers, that is containers in which the sidewalls and bottom of the container is a one piece member and the top or end closure is a separate piece by stamping disk shaped blanks from a strip of metal sheet then subsequently drawing the desired can body configuration into the disk blank in either a single or double acting press. Examples of such a method and apparatus are shown in numerous patents including U.S. Pat. Nos. 5,626,048 and 5,628,224. These patents as well as other prior art discloses that flat sheet material such as steel or aluminum, either in sheet or coil form, is initially blanked by an annular cutting edge and then drawn into a cup shape for subsequent redrawing into a final container in the same press or in subsequent presses and operations. Generally these prior art presses will simultaneously form a plurality of container bodies in the single stroke of the single or double acting press.
However, one problem that is encountered with these prior art presses is that the peripheral edge of the disk blank is excessively pinched as it moves around the inner radius of the die opening of the blank and draw die into which the metal of the disk blank is being drawn by the draw horn to form the cup-shaped member by the pressure exerted on the peripheral edge by the draw pad. In a double action press, the timing of the inner and outer rams is adjusted in an attempt to have the draw pad move upwardly in order to reduce the clamping pressure on the peripheral edge at the instant of time that the edge is moving around the radius and into the die opening. However, due to the extreme speeds that these presses operate and the metal thinness and tolerances between the parts of the die and press it is difficult to achieve the desired results. This excess pinching of the peripheral edge results in flattening the peripheral edge into an extremely sharp edge resulting in bits of metal splintering off from the disk and from a preapplied coating for certain strip materials. These splinters quickly accumulate and affect the operation of the press and require maintenance and repair problems.
This pinching problem of the peripheral disk blank edge is also critical in a single action press where the clamping pressure exerted on the disk blank remains generally constant until the metal has been pulled from between the clamping surfaces of the draw pad and blank and draw die by movement into the die opening by the draw horn and there is no mechanism for attempting to reduce the pressure on the draw pad at this critical instant in the forming operation as in a double acting press.
Many of these problems are eliminated by controlling the gap between the opposed clamping surfaces of the draw pad and the blank and draw die by providing an annular rib on an outer periphery of the draw pad as shown in pending application Ser. No. 09/093,250, filed Jun. 8, 1998. However, for certain applications the subject invention may provide a better solution than that of this referred to application.
Therefore, the need exists for an improved press and the apparatus therefor and to a method of forming a cup-shaped member which will enable the clamping pressure to be minimized on the peripheral edge of the disk shaped blank as it moves around the draw forming radius of the die as the metal is drawn into the die cavity by the draw horn to reduce excess pinching and with the resultant splintering of metal chips and slivers therefrom without requiring a substantial modification to the press or to its mode of operation.
SUMMARY OF THE INVENTION
Objectives of the invention include providing an improved apparatus and method for forming cup-shaped members such as container bodies, in either a single or double acting press from sheet metal material, wherein the material is formed into disk-shaped blanks and then drawn into a cylindrical cup-shaped configuration in a single stroke of the press, which automatically prevents excessive clamping pressure being applied to the peripheral edge of the disk blank as it moves around the radius of the die cavity or opening when being drawn into a cup shape by the draw horn.
Another objective is to provide such a method and apparatus which enables the desired amount of clamping pressure to be exerted on the disk blank as it is being drawn into the die cavity by the draw horn and which prevents the clamping pressure from excessively squeezing the peripheral edge of the blank disk into a pointed configuration with the resultant slivering of metal particles therefrom by providing the draw pad with an annular tapered relief area at the periphery of the ram opening or by providing a tapered or recessed relief area at the periphery of the blank and draw die opening adjacent the forming radius thereof, thereby limiting movement of the draw pad against the peripheral edge which heretofore had produced the pointed configuration and slivered particles.
Another objective of the invention is to provide such a method and apparatus which requires relatively minor adjustments to existing press and die constructions and operations thereof, thus avoiding complicated and expensive modifications for retrofitting existing presses.
These objectives and advantages are obtained by the improved apparatus of the invention for use in forming a cup-shaped member from a metal sheet in a press having at least one ram and a base wherein the general nature of said apparatus includes a draw pad and a draw horn carried by the ram and a blank and draw die carried by the base in opposed relationship to the draw pad and draw horn, said draw pad having a clamping surface and a central opening defined by an annular wall through which the draw horn is reciprocally moveable; the blank and draw die having a clamping surface opposed to the clamping surface of the draw pad for releasably clamping a disk blank therebetween; said die further having a die opening defined by an annular wall and a draw forming radius extending between said annular wall and the clamping surface; a cutting edge carried by the ram and surrounding the draw horn for cutting the disk blank from the metal sheet; and the draw pad having an annular tapered relief area extending from its clamping surface to the annular wall of the central opening for reducing the clamping force exerted on a peripheral edge of the disk blank as the draw horn advances into the die opening to form the cup-shaped member from the disk blank.
These objectives and advantages are further obtained by the improved method of the invention for forming a cup shaped member from a metal sheet in a press having a base and a blank and draw die mounted thereon, said die having a die spring and a forming radius at an entrance of said opening; and at least one ram for moving a draw pad, a draw horn and a cut edge toward said die; said method includes the steps of feeding the metal sheet between the die and the draw horn, draw pad and cut edge; providing the draw pad and the die with opposed clamping surfaces with the draw pad having a tapered relief area extending from the clamping surface thereof to a central opening formed in said draw pad for receiving the draw horn therein; advancing the cut edge, draw pad and draw horn toward the metal sheet and the die by movement of the ram; blanking a disk blank from the metal sheet by advancing the cut edge; initially clamping an outer an
McClung James A.
Rubalcava Manuel P.
Can Industry Products, Inc.
Larson Lowell A.
Sand & Sebolt
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