Method and apparatus for producing container body end countersink

Abstract: A method and press are disclosed for forming a container end piece (410) which is attachable to an open end of a container body. The method comprises the steps of: providing a blank (434) between first and second axially-aligned cooperating inner dies (530,550) and between first and second axially-aligned cooperating outer dies (510,520) which coaxially surround the first and second inner dies, respectively; moving the outer dies axially relative to the inner dies in one direction (B) so that a flange (412) of the end piece is formed in the blank between the outer dies and so that a chuckwall of the end piece is formed by stretching the blank in a gap between the second inner die (550) and a die surface (514) of the first outer die (510); and moving the outer dies axially relative to the inner dies in the opposite direction (D) so that the blank flexes and an inner panel wall of the end piece is formed in the blank against a die surface (540) of the first inner die (530) which is inclined relative to the die surface of the first outer die, so that the curved portion of the end piece is formed between the inner panel wall and the chuckwall, and so that the portion of the blank between the inner dies provides the central panel of the end piece.

Description: The present invention generally relates to a method of forming a container end piece which is attachable to an open end of a container body, and to a press for performing such a method, as described in the pre-characterising portion of claims 1 and 5 resp.. Metal containers typically have at least one end piece which is separately attached to the container to seal the same. In a two-piece design, the container body is drawn and ironed to have an integrally formed bottom and sidewall such that only a single end is necessary to seal the container body. In a three-piece design, a sheet of metal is rolled into a cylindrical configuration and joined along a seam which extends along the entire length of the container body such that there are two open ends, each of which is sealed by separately attaching an end thereto. Metal container designs must meet some types of strength requirements. For instance, in the case of beverage containers, which are typically of the two-piece design, often the containers are subjected to relatively high internal pressures. Moreover, the container must be able to withstand handling during shipping when containers are often dropped. The or each end which is separately attached to the container body is one part of the container which must meet these types of strength requirements. Balanced with the need for stronger containers, and including container ends, are economic and environmental considerations, such as reducing the amount of metal used to manufacture container ends which reduces material and transportation costs and the amount of raw materials used in can manufacture. Even a slight change in the gauge or thickness of the container or container end can result in significant economic and material usage savings due to the enormous volume of containers and container ends produced yearly. As such, there is a continued need to utilise thinner and thinner materials to form container bodies and container ends which still meet specified strength requirements. A first aspect of this invention relates in particular to a method of forming a container end piece which is attachable to an open end of a container body and which comprises a central panel, an annular groove disposed about a perimeter of the central panel and having a curved portion extending between and integrally joining a chuckwall and an inner panel wall of the annular groove, and a flange disposed about the annular groove, the method comprising the steps of: providing a blank between first and second axially-aligned cooperating inner dies and between first and second axially-aligned cooperating outer dies which coaxially surround the first and second inner dies, respectively; moving the outer dies axially relative to the inner dies in one direction to an intermediate position so that the flange of the end piece is formed in the blank between the outer dies, so that the chuckwall of the end piece is formed by stretching the blank in a gap between the second inner die and a die surface of the first outer die, so that the central panel is provided between the inner dies and so that an intermediate portion is formed between the chuckwall and the central panel; and moving the outer dies axially relative to the inner dies in the opposite direction from the intermediate position to a final forming position so that the intermediate portion flexes to form the inner panel wall of the end piece against a die surface of the first inner die which is inclined relative to the die surface of the first outer die and to form the curved portion of the end piece between the inner panel wall and the chuckwall. Such a method is known from patent document EP-A-0153115. In that known method, in the intermediate position (Fig. 7 of EP-A-0153115), the bulk of the intermediate portion is shown and described to be generally flat, with a first small radiussed portion joining the flat portion to the chuckwall and a second small radiussed portion joining the flat portion to the central panel. During the second moving step, it is stated in EP-A-0153115 that the generally flat part of the intermediate portion is deformed progressively and without restraint, guidance or confinement into an annular chamber between the first inner and outer dies until the final curved portion is fully formed. The final radius of the curved portion is not stated in EP-A-0153115, but from the drawings and other dimensions that are given in that document, it can be estimated that the final radius of the curved portion is about 635 µm (0.025 "). The method of the first aspect of the invention is characterised in that: before the step of moving in said opposite direction, the intermediate portion has a continuously arcuate portion curving between the direction of the chuckwall and the direction of the central panel, with the convex side of the arcuate portion facing towards the first outer die; and upon completion of the step of moving in said opposite direction, the curved portion of the end piece has a radius of less than about 250 µm (0.010"). Preferably, before the step of moving in said opposite direction, the arcuate portion stops short of the first outer die. Preferably, the arcuate portion is formed, during the step of moving in said one direction, by a continuously rounded portion of the second inner die. Preferably, upon commencement of the step of moving in said opposite direction, the distance along the intermediate portion from a central position on the arcuate portion to the first inner die is less than the distance along the intermediate portion from the central position to the first outer die. A second aspect of the invention relates to a press for forming such a container end piece. The press comprises: first and second axially-aligned cooperating inner dies for receiving a blank therebetween; first and second axially-aligned cooperating outer dies which coaxially surround the first and second inner dies, respectively, for receiving the blank therebetween; means for moving the outer dies axially relative to the inner dies in one direction to an intermediate position so that the flange of the end piece is formed in the blank between the outer dies, so that the chuckwall of the end piece is formed by stretching the blank in a gap between the second inner die and a die surface of the first outer die, so that the central panel is provided between the inner dies and so that an intermediate portion is formed between the chuckwall and the central panel; and means for moving the outer dies axially relative to the inner dies in the opposite direction from the intermediate position to a final forming position so that the intermediate portion flexes to form the inner panel wall of the end piece against a die surface of the first inner die which is inclined relative to the die surface of the first outer die and to form the curved portion of the end piece between the inner panel wall and the chuckwall. Such a press is known from EP-A-153115. The press of the invention is furthermore characterised in that: the second inner die has a continuously rounded portion for engaging the blank when the dies are moving to the intermediate position so that when the dies have been so moved to the intermediate position, the intermediate portion has a continuously arcuate portion curving between the direction of the chuckwall and the direction of the central panel, with the convex side of the arcuate portion facing towards the first outer die; and said die surfaces of the first outer die and the first inner die bear on the curved portion so that when the dies have been so moved to the final forming position, the curved portion of the end piece has a radius of less than about 250 µm (0.010"). A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which Figures 1 to 6 show an apparatus for producing a can end in a blank and form station in fragmentary cross-sectional views of a can end at various points in the process. Container ends having an annular groove with a radius within the desired range of less than about 250 µm (0.010"), and preferably from about 76 µm (0.003") to about 180 µm (0.007"), may be produced directly from the container end forming process. Specifically, a container end having an annular groove within the noted range may be produced as the annular groove of the container end itself is being formed, as opposed to reforming or reworking the annular groove of an end piece. For instance, a container end with the noted desired radius may be produced in the blank and form stage of a container end press. One embodiment of a method and apparatus for directly achieving a container end with an annular groove of a radius of less than about 0.25 mm (0.010 inches), and preferably from about 0.08 mm (0.003 inches) to 0.18 mm (about 0.007 inches), is illustrated in Figs. 1-6. These figures progressively illustrate the formation of a container end having this type of radius in what is commonly characterized and a blank and form station. In the blank and form station 400, a generally circular blank or disk-like member is blanked out from a metal sheet 430 or other appropriate feed stock. This blank 434 is then drawn into a container end by the interaction of various dies discussed below. An annular groove with the above-described desired radius is achieved directly from this drawing procedure. Referring to Figs. 1-6, the blank and form station 400 includes first and second blanking dies 560, 570 and a support base 600 which is disposed radially outwardly of the blanking dies 560, 570. The metal sheet 430 is disposed on the support base 600 and below the first blanking die 560 and above the second blanking die 570. Subsequent axial movement of the blanking die 560 in the direction of the arrow A illustrated in Fig. 1 and relative to the stationary support base 600 produces the blank 434 from the metal sheet 430. As illustrated in Fig. 1, the blank 434 is disposed above the second inner die 550 at this time. The second blanking die 570 is movable in the direction of the arrow A but is biased in a direction which is generally toward the first blanking die 560 or opposite to the direction of arrow A. This may be affected by having the second blanking die 570 be spring loaded and this spring (not shown) would then be compressed during the noted movement of the first blanking die 560 such that the second blanking die 570 would also move in the direction of the arrow A during this blanking operation. Other "movably biased" mechanisms could be used, such as an air system. Although the outer perimeter 442 of the blank 434 is disposed between the first and second blanking dies 560, 570 at this time, the blank 434 is able to "slide" or move relative to the first and second blanking dies 560, 570 which facilitates the formation of the flange 412 of the can end piece 410 (e.g., the blank 434 is able to slide between the first blanking die 560 and the second blanking die 570 during formation of the flange 412). The flange 412 is formed during a first portion of the drawing procedure in which the blank and form station 400 further utilizes first and second outer dies 510, 520 and first and second inner dies 530, 550. The first blanking die 560 continues to move in the direction of the arrow A as illustrated in Fig. 1. The blank and form station 400 also exerts an annular, axially-directed force on an outer portion 438 of the blank 434 with the first outer die 510. In this regard, the first outer die 510 is moved axially relative to the blank 434 in the direction of the arrow B illustrated in Fig. 1. The second outer 520 is movable in the direction of the arrow B, but is biased in a direction which is generally toward the first outer die 510 or opposite to the direction of the arrow B. This may be affected by having the second outer die 510 die be spring loaded and this spring (now shown) would then be compressed such that the second outer die 520 would also move in the direction of the arrow B illustrated in Fig. 1. other "movably biased" mechanisms could be used, such as an air system. After a certain amount of movement of the first and second outer dies 510, 520 and the first and second blanking dies 560, 570 relative to the support 600, the central portion of the blank 434 engages the second inner die 550 which is illustrated in Fig. 2. Once this engagement is established, further movement of the first and second outer dies 510, 520 in the direction of the arrow A and of the first and second blanking dies 560, 570 in the direction of the arrow B causes a certain amount of sliding-like movement of the blank 434 relative to both the blanking dies 560, 570 (e.g., by sliding between the dies 560, 570), a certain amount of sliding-like movement between the blank 434 and the outer dies 510, 520 (e.g., by sliding between the dies 510, 520), and/or a stretching of the blank 434. Achieving the noted sliding-like movement is facilitated by having the first inner die 530 compressively engage the blank 434 against the second inner die 550 which has occurred prior to the position illustrated in Fig. 2. About the time that the blank 434 is about to become disengaged with the blanking dies 560, 570 by the sliding-like movement as illustrated in Fig. 2, further movement of the first blanking die 560 and therefore the second blanking die 570 in the direction of the arrow B is terminated. The movement of the outer dies 510 and 520 in the direction of the arrow A continues for a time after the blank 434 becomes disengaged with the blanking dies 560, 570 and results in corresponding portions of the blank 434 being forced to generally conform to the shape of the surfaces 512 and 514 of the first outer die 510 as illustrated in Fig. 3. This is provided by sliding-like movements of portions of the blank 434 within the gap between the second blanking die 570 and the first outer die 510 and within the gap between the first outer die 510 and the second inner die 550. Once the first outer die 510 reaches its bottom dead center position which is shortly after the position illustrated in Fig. 3, the flange 412 is completely formed. As can be seen in Fig. 3, while the outer dies 510 and 520 continue their movement in the direction of the arrow B, some time after becoming disengaged with the blank 434 the blanking dies 560 and 570 move in the direction of the arrow C as a result of the bias of the second blanking die 570. The annular groove 420 is formed after formation of the flange 412 utilizing, inter alia , a first die surface 540 of the first inner die 530 which engages at least a part 450 of an intermediate portion 436 of the blank 434, the second die surface 514 of the first outer die 510 which cooperates with the first die surface 540, and the second outer die 520 which conformingly engages the flange 412. The first die surface 540 and the second die surface 514 are both inclined relative to a vertical reference axis. In one embodiment, the first die surface 540 is inclined at an angle ranging from about 30° to about 60° relative to this vertical reference axis and in the illustrated embodiment is about 45° relative to vertical, while the second die surface 514 of the first outer die 510 is inclined at an angle ranging from about 10° and about 15° relative to this vertical reference axis. The vertical portion of the first inner die 530 has a length of about 1.5 mm (0.060 inches) in the illustrated embodiment, and the first surface has a length of about 1.1 mm (0.045 inches) in the illustrated embodiment. In order to form the annular groove 420 from the intermediate portion 436 of the blank 434, an annular, axially-directed force is exerted on the newly formed flange 412 to effectively flex the intermediate portion 436 into the annular groove 420. Referring to Fig. 4, the second outer die 520, as a result of its bias, exerts an axially-directed force on f lange 412 generally in the direction of the arrow D as its associated spring transmits a force on the die 520. This may be due to the driving force on the first outer die 510 being disengaged or reversed so as to axially drive the first outer die 510 in the direction of the arrow D, or alternatively to simply removing the force from the die 510 which initially drove the die 510 in the direction of the arrow B as described above. Note that the first outer die 530 remains in a substantially fixed position to forcibly retain the central portion of the drawn blank 434 against the second inner die 550. As a result of this retention of the drawn blank 434 and the force being exerted on the flange 412 by the second outer die 520 due to its expanding spring or other biasing mechanism, the intermediate portion 436 begins to flex away from the surface of the second inner die 550 as illustrated in Fig. 4. Continued application of the noted axially-directed forces on the flange 412 by the second outer die 520, as well as the interaction of the second die surface 514 of the first outer die 510 with the blank 434, forces the intermediate portion to flex into conformance with the first die surface 540 of the first inner die 530 and for the base of the annular groove 420 to be disposed in the gap between the first inner die 530 and the first outer die 510, all as illustrated in Fig. 5. As illustrated in Figs. 1-6, for purposes of accommodating formation of the annular groove 420 from the intermediate portion 436 of the blank 434, a gap 460 exists between the first outer and first inner dies 510, 530. In addition, formation of the annular groove 420 is accommodated by the second die surface 514 of the first outer die 510, which exerts an inwardly-directed force on and relative to the intermediate portion 436 during formation of the annular groove 420. In this regard, as the biased (e.g., springloaded) second outer die 520 pushes the flange 412 upwardly relative to the first and second inner dies 530, 550, the intermediate portion 436 of the blank 434 is further:flexed into the gap 460 to form a generally concave groove 420. As shown in Fig. 5, as the second outer die 520 continues to exert an axial force on the flange 412 to push the flange 412 upwardly, a part 450 of the intermediate portion 436 engages and is pushed against the first die surface 540 of the first inner die 530. In this regard, the first die surface 540 exerts an outwardly-directed force on and relative to the part 450 of the intermediate portion 436 as the flange 412 is moved upwardly relative to the first die surface 540. Thus, as the second outer die 520 continues to apply an axial force on the flange 412 to move the flange 412 upwardly relative to the first die surface 540 and the part 450, the second die surface 514 of the first outer die 510 and the first die surface 540 of the first inner die 530 cooperate to form the annular groove 420 as the upper portion 424, adjacent the part 450, is flexed therebetween, wherein the part 450 substantially conforms to the first die surface 540. In this regard, an annular groove 420 having a radius in the upper portion 424 of less than about 0.25 mm (0.010 inches), and more preferably ranging from about 0.08 mm (0.003 inches) to about 0.18 mm (0.007 inches), is formed in the blank and forming stage. The gap 460 is approximately 0.5 mm (0.02 inches) to about 0.8 mm (0.03 inches) wide at least at a point located above the first die surface 540. Once the first outer die 510 becomes disengaged from the container end 410, the first inner die 530 may be moved in the direction of the arrow E illustrated in Fig. 6 such that the end 410 may be removed from the station 400. EXAMPLE 1 End pieces formed according to principles of the present invention were tested in order to determine whether end pieces formed according to principles of the present invention exhibited improved strength characteristics (e.g., resistance to buckling). In this regard, end pieces configured according to the present invention having a gauge of 0.224 mm (0.0088 inches) and 0.218 mm (0.0086 inches) (formed group) were tested and compared to conventional end pieces having a gauge of 0.224 mm (0.0088 inches) and 0.218 mm (0.0086 inches) (control group). End pieces configured according to principles of the present invention exhibited improved strength characteristics. Formed group end pieces having a gauge of 0.218 (0.0086 inch) buckled at an average of 705 kN/m 2 (102.2 psi), while control group end pieces having a gauge of 0.218 mm (0.0086 inches) buckled at an average of 653 kN/m 2 (94.7 psi). Similarly, the formed group end pieces having a gauge of 0.224 mm (0.0088 inches) exhibited improved strength characteristics over the control group. Formed group end pieces having a gauge of 0.224 mm (0.0088 inches) buckled at an average of 734 kN/m 2 (106.4 psi), while control group end pieces having a gauge of 0.224 mm (0.0088 inches) buckled at an average of 684 kN/m 2 (99.2 psi). The container ends in accordance with principles of the present invention thereby clearly exhibit increased strength. This allows for a reduction in the thickness of the sheet metal used to form the container ends which not only reduces material costs, but also preserves our natural resources. Although reducing the gauge of the sheet metal typically dictates a loss of strength, by utilizing principles of the present invention at least some of this strength is recovered such that the container ends will still meet the various container body strength specifications.

Claims: A method of forming a container end piece (410) which is attachable to an open end of a container body and which comprises a central panel, an annular groove (420) disposed about a perimeter of the central panel and having a curved portion (424) extending between and integrally joining a chuckwall and an inner panel wall of the annular groove, and a flange (412) disposed about the annular groove, the method comprising the steps of: providing a blank (434) between first and second axially-aligned cooperating inner dies (530,550) and between first and second axially-aligned cooperating outer dies (510,520) which coaxially surround the first and second inner dies, respectively; moving the outer dies axially relative to the inner dies in one direction (B) to an intermediate position: so that the flange of the end piece is formed in the blank between the outer dies, so that the chuckwall of the end piece is formed by stretching the blank in a gap between the second inner die (550) and a die surface (514) of the first outer die (510), so that the central panel is provided between the inner dies and so that an intermediate portion is formed between the chuckwall and the central panel; and moving the outer dies axially relative to the inner dies in the opposite direction (D) from the intermediate position to a final forming position so that the intermediate portion flexes: to form the inner panel wall of the end piece against a die surface (540) of the first inner die (530) which is inclined relative to the die surface of the first outer die and to form the curved portion of the end piece between the inner panel wall and the chuckwall; characterised in that : before the step of moving in said opposite direction, the intermediate portion has a continuously arcuate portion curving between the direction of the chuckwall and the direction of the central panel, with the convex side of the arcuate portion facing towards the first outer die; and upon completion of the step of moving in said opposite direction, the curved portion of the end piece has a radius of less than about 250 µm (0.010"). A method as claimed in claim 1, wherein, before the step of moving in said opposite direction, the arcuate portion stops short of the first outer die. A method as claimed in claim 1 or 2, wherein the arcuate portion is formed, during the step of moving in said one direction, by a continuously rounded portion of the second inner die. A method as claimed in any preceding claim, wherein, upon commencement of the step of moving in said opposite direction, the distance along the intermediate portion from a central position on the arcuate portion to the first inner die is less than the distance along the intermediate portion from the central position to the first outer die. A press for forming a container end piece (410) which is attachable to an open end of a container body and which comprises a central panel, an annular groove (420) disposed about a perimeter of the central panel and having a curved portion (424) extending between and integrally joining a chuckwall and an inner panel wall of the annular groove, and a flange (412) disposed about the annular groove, the press comprising: first and second axially-aligned cooperating inner dies (530,550), for receiving a blank therebetween; first and second axially-aligned cooperating outer dies (510,520) which coaxially surround the first and second inner dies, respectively, for receiving the blank therebetween; means for moving the outer dies axially relative to the inner dies in one direction (B) to an intermediate position: so that the flange of the end piece is formed in the blank between the outer dies, so that the chuckwall of the end piece is formed by stretching the blank in a gap between the second inner die (550) and a die surface (514) of the first outer die (510), so that the central panel is provided between the inner dies and so that an intermediate portion is formed between the chuckwall and the central panel; and means for moving the outer dies axially relative to the inner dies in the opposite direction (D) from the intermediate position to a final forming position so that the intermediate portion flexes: to form the inner panel wall of the end piece against a die surface (540) of the first inner die (530) which is inclined relative to the die surface of the first outer die and to form the curved portion of the end piece between the inner panel wall and the chuckwall; characterised in that : the second inner die has a continuously rounded portion for engaging the blank when the dies are moving to the intermediate position so that when the dies have been so moved to the intermediate position, the intermediate portion has a continuously arcuate portion curving between the direction of the chuckwall and the direction of the central panel, with the convex side of the arcuate portion facing towards the first outer die; and said die surfaces of the first outer die and the first inner die bear on the curved portion so that when the dies have been so moved to the final forming position, the curved portion of the end piece has a radius of less than about 250 µm (0.010").

Inventors: FARLEY TODD W, NGUYEN TUAN A, FARLEY, TODD W., NGUYEN, TUAN A.
Applicants: BALL CORP, BALL CORPORATION
Application year: 1997
Main classification: B21D51
IPC codes: B21D51