Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Patent
1990-04-02
1991-09-17
Larson, Lowell A.
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
B21D 2222
Patent
active
050483170
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing a draw-formed container, and more specifically to a method of manufacturing a draw-formed container having excellent appearance characteristics and corrosion resistance without the occurrence of creases from a metal foil or sheet having a coated surface.
PRIOR ART
A laminate produced by coating the surface of an aluminum foil or a surface treated steel foil with a coated layer or a resin film has heretofore been widely used in the field of food packaging containers because of its light weight or of the easiness of its disposal. Attempts have long been made to manufacture a cup-shaped container comprised of a tapered or cylindrical side wall portion, a closing bottom portion connected to its under part and a sealing flange portion connected to its upper part by draw-forming this laminate. However, creases occur in the side wall portion, particularly that part of the side wall portion to which the flange is attached, and give rise to a problem of impairing its appearance characteristics and sealing property.
As a solution to this problem, Japanese Patent Publication No. 4408/1982 describes that a male mold consisting of a rigid core and surrounding the rigid core, a sleeve made of an elastic material having a larger outside diameter than the inside diameter of a die cavity in the die shoulder portion with its tip portion composed of the above rigid core is used, and the outside surface of the material to be processed which is in contact with the die shoulder portion is draw-formed while this outside surface is being pressed by the elastic material.
U.S. Pat. No. 4,562,717 describes that in a similar draw-forming, the same tool as in the above prior art is used, but a space is provided between the rigid core and the elastic sleeve, and the elastic sleeve is increased in diametrical sectional area from its tip as it is directed to the rear side.
The invention of the above first prior art is considered to have a great significance in that it discloses a technique in which a male mold having an elastic sleeve is used, and by applying an elastic pressure of the material to be processed, the occurrence of creases is inhibited. In the second prior art, a space is provided between the elastic sleeve and the rigid core and adjusted so that immediately before the stroke end (bottom dead point) the amount of space becomes zero. Thus, the deformation of the elastic material in the radial direction is performed to a greater extent that its axial deformation to improve the maximum formable draw ratio.
However, when a coated metal sheet is actually draw-formed by using these forming methods, it frequently happens that the elastic sleeve is worn, or the coated metal sheet undergoes breakage. Specifically, these prior art methods have no sufficient recognition of the relation between the femal mold and the elastic sleeve of the male mold used, and this is believed to have resulted in these inconveniences.
SUMMARY OF THE INVENTION
The present inventors have found that the ratio between the inlet diameter (D) of the female mold and the maximum diameter (d.sub.2) of the elastic sleeve and axial load which the female mold undergoes at the bottom dead point (d) per unit area of the circumferential area of the female mold when the male mold and the female mold are mated without a coated metal sheet are what act effectively for the inhibition of the occurrence of creases in the draw-forming of thin coated metal sheet, and that by selecting these values within certain fixed ranges, the occurrence of creases during forming can be inhibited effectively while preventing the wear of the elastic sleeve and the breakage of the coated metal sheet.
It is an object of this invention to provide a method by which a draw-formed container having a combination of excellent appearance characteristics, corrosion resistance and sealing performance can be manufactured with high productivity and at low costs while completely inhibiting the occurrence of creases duri
REFERENCES:
patent: 3724247 (1973-04-01), Page
Hirota Kazumi
Matsuoka Kikuo
Larson Lowell A.
Toyo Seikan Kaisha Ltd.
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