Patent Publication Number: US-6702538-B1

Title: Method and apparatus for forming a can end with minimal warpage

Description:
FIELD OF THE INVENTION 
     The present invention relates to ends for can-type containers. More specifically, the invention pertains to a method and an apparatus for manufacturing a relatively thin can end with minimal warpage. 
     BACKGROUND OF THE INVENTION 
     Can-type containers used for the storage of food products often comprise a body and two ends fixed to the body. Manufacturers of can ends, in general, make substantial efforts to reduce the thickness of the can ends which they produce. Reducing the thickness of a can end lowers the amount of material needed to manufacture the can end, and thereby leads to cost savings. For example, thickness reductions as small as one-thousandth of an inch or less can yield substantial cost savings over time due to the relatively large production volumes of typical can ends. Hence, the ability to manufacture can ends from relatively thin sheets of material offers substantial benefits. For example, the use of double-reduced steel in the manufacture of can ends is particularly advantageous because double-reduced steel provides a favorable combination of thinness, tensile strength, hardness, and resistance to elongation. 
     Reducing the thickness of a can end, however, increase the potential for the can end to warp during manufacture. Can ends manufactured from materials formed by rolling, e.g., double-reduced steels, are particularly susceptible to such warpage. In particular, the rolling operation induces a direction-dependent non-uniformity in the mechanical properties of the can end, i.e., rolling causes the mechanical properties of the can end to vary in different directions. This non-unifornity induces a tendency in the can end to warp. Warpage of a can end inhibits the effective mating of the can end and the can body. In addition, warpage can interfere with the automated transfer (feeding) of the can end during subsequent processing operations, e.g., lining of the can end. Hence, can-end warpage is highly undesirable and should be minimized or eliminated. 
     Warpage of a can end can be reduced by coining an annularly-shaped area on the can end. Coining substantially reduces the directional non-uniformity in the mechanical properties of the coined area, and thereby lowers or eliminates the tendency of the can end to warp. Coining, however, usually increases the diameter of the can end. In particular, the coining operation causes material within the coined area to be displaced. The displacement of material in this manner usually causes an increase in the chuck-wall diameter of the can end. Increases in chuck-wall diameter can inhibit the effective mating of the can end and the can body. Furthermore, increases in the chuck-wall diameter can prevent a proper fit between the can end and the seaming chuck utilized to join the can end to a can body. Hence, increases in chuck-wall diameter resulting from the coining operation should be minimized or eliminated. 
     The above-described increase in chuck-wall diameter is illustrated in FIGS. 13A and 13B. FIG. 13A shows a can end  100  having a chuck wall  102  and a panel  104 . FIG. 13A depicts the can end  100  before the panel  104  is coined. The panel  104  has an initial length denoted by the symbol “L 1 .” The can end  100  has an initial chuck-wall diameter represented by the symbol “D 1 .” 
     FIG. 13B depicts the can end  100  after the panel  104  has been coined. The material displaced by the coining operation increases the overall length of the coined panel  104  by an amount represented by the symbol “Δ 1 .” Hence, the overall length of the panel  104  after the coining operation equals the initial length (L 1 ) plus the increase in the length of the panel  104  caused by the coining operation (Δ 1 ). The increase in the length of the panel  104  causes a corresponding increase in the chuck wall diameter of the can end  100 . Specifically, the chuck-wall diameter after the coining operation is approximately equal to the initial chuck-wall diameter (D 1 ) plus the change in the length of the panel  104  (Δ 1 ). 
     The above discussion illustrates the current need for a method and an apparatus for manufacturing a relatively thin can end with minimal warpage. More particularly, a method and an apparatus are needed for reducing the tendency of thin can ends to warp during manufacture, without substantially affecting the chuck-wall diameter of the can ends. The present invention is directed to these and other goals. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method of forming a can end with minimal warpage. In accordance with this object, a presently-preferred method of forming a can end comprises the step of forming a substantially circular metal blank having a periphery and a center panel. The method also comprises the step of forming a substantially annular recessed panel in the blank. The recessed panel has a first depth in relation to a substantially annular portion of the blank contiguously formed with the recessed panel. The method further comprises the step of coining the substantially annular portion of the blank while re-forming the recessed panel to a second depth in relation to the substantially annular portion of the blank, with the second depth being greater than the first depth. 
     Further in accordance with the above-noted object, another presently-preferred method of forming a can end comprises the step of forming a substantially circular metal blank having a periphery and a center panel. The method also comprises the step of forming a substantially annular recessed panel in the blank. The recessed panel has a depth in relation to a substantially annular portion of the blank contiguously formed with the recessed panel. The method further includes the step of coining the substantially annular portion of the blank while the recessed panel is being formed, and after the depth of the recessed panel reaches a predetermined value. 
     Another object of the present invention is to provide a method for minimizing warpage of a can end. In accordance with this object, a presently-preferred method of minimizing warpage of a can end comprises the step of partially forming a substantially annular recess in the can end and then fully forming the recess while coining a substantially annular area of the can end bordering the recess. 
     A further object of the present invention is to provide an apparatus for forming a can end with minimal warpage. In accordance with this object, a presently-preferred embodiment of a die for forming a can end comprises an annular cut edge having an inner circumferential surface. The die also comprises a punch coaxially disposed with the cut edge. The punch and the cut edge are adapted to form a metal blank having a periphery and a center panel. 
     The die further comprises means for forming an annular recessed panel in the blank. The recessed panel has a first depth in relation to a substantially annular portion of the blank contiguously formed with the recessed panel. The die also comprises means for coining the substantially annular portion of the blank while re-forming the recessed panel to a second depth in relation to the substantially annular portion of the blank. The second depth is greater than the first depth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of a presently-preferred embodiment, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, the drawings show an embodiment that is presently preferred. The invention is not limited, however, to the specific instrumentalities disclosed in the drawings. In the drawings: 
     FIG. 1 is a top view of a can end formed in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of the can end shown in FIG. 1 before the can end is fixed to a can body; 
     FIG. 3 is a cross-sectional view of the can end shown in FIGS. 1 and 2 configured to engage a lip of a can body (not shown); 
     FIGS. 4A through 4E are cross-sectional views of a metal blank being progressively formed into the can end shown in FIGS. 1 through 3; 
     FIG. 5A is a magnified view of the area designated “ 5 A” in FIG. 4D; 
     FIG. 5B is a magnified view of the area designated “ 5 B” in FIG. 4E; 
     FIG. 6A is a cross-sectional view of the can end shown in FIGS. 1 though  5 B prior to being coined in accordance with the present invention; 
     FIG. 6B is a cross-sectional view of the can end shown in FIGS. 1 through 6A after being coined in accordance with the present invention; 
     FIG. 7 is a cross-sectional view of a die for forming the can end shown in FIGS. 1 through 6B; 
     FIG. 8 is a cross-sectional view of the die shown in FIG. 7 prior to forming a blank from a metal sheet positioned on the die; 
     FIG. 9 is a cross-sectional view of the die shown in FIGS. 7 and 8 after a blank is cut from the metal sheet shown in FIG. 8; 
     FIG. 10 is a cross-sectional view of the die shown in FIGS. 7 through 9 as a seaming-panel is formed in the metal blank shown in FIG. 9; 
     FIG. 11 is a cross-sectional view of the die shown in FIGS. 7 through 10 as stiffening beads are formed in the metal blank shown in FIGS. 9 and 10; 
     FIG. 12A is a cross-sectional view of the die shown in FIGS. 7 through 11 as a coined panel and a recessed panel are formed in the metal blank shown in FIGS. 9 through 11; 
     FIG. 12B is a cross-sectional view of the die shown in FIGS. 7 through 12A as a coined panel and a recessed panel are re-formed in the metal blank shown in FIGS. 9 through 12A; 
     FIG. 13A is a cross-sectional view of a can end prior to being coined using a method in accordance with the prior-art; and 
     FIG. 13B is a cross-sectional view of the can end shown in FIG. 13A after being coined using the method in accordance with the prior-art. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention provides a method and an apparatus for forming a can end with minimal warpage. A can end  10  produced in accordance with the present invention is shown in FIGS. 1 through 6B. The figures are referenced to a common coordinate system  11  denoted in each illustration. The can end  10  is described in detail herein for exemplary purposes only. The invention is equally applicable to the formation of can ends having structural features that differ from those of the exemplary can end  10 . 
     The can end  10  is used in conjunction with a can body  12  (a limited portion of the can body  12  is shown in FIG.  3 ). Specifically, one of the can ends  10  is fixed to a top of the can body  12 , and another of the can ends  10  (not shown) is fixed to a bottom of the can body  12 . The can ends  10  and the can body  12  form a container that may be used, for example, to store vacuum-packed food products. 
     The exemplary can end  10  is formed from double-reduced steel such as DR8 65-pound continuous-annealed steel (the invention can also be used in conjunction with batch-annealed steel, and with 55-pound (or lower) steel). FIG. 2 is a detailed view of an outermost portion of the can end  10  before the can end  10  is joined to the can body  12 . FIG. 3 shows the same portion of the can end  10  after the can end  10  is joined to the can body  12 . 
     The thickness of the can end  10  is approximately 0.0072 inch (0.18 mm), except where otherwise noted below (this value is based on the use of DR8 65-pound steel). The can end  10  comprises a substantially circular center panel  16 . The center panel  16  is substantially flat, i.e., the center panel  16  lies substantially in the x-y plane denoted in the figures. The can end  10  further includes an annular first angled panel  18 . The first angled panel  18  is contiguously formed with the center panel  16 , i.e., the first angled panel  18  adjoins the center panel  16 . The first angled panel  18  slopes downward, i.e., in the z −  direction, as it extends radially outward from the center panel  16 . A second angled panel  20  is contiguously formed with the first angled panel  18 . The second angled panel  20  is annular, and slopes upward as it extends radially outward from the first angled panel  18 . The first and the second angled panels  18  and  20  form a downwardly-extending stiffening bead  22 . 
     The can end  10  also includes a third angled panel  24 . The third angled panel  24  is contiguously formed with the second angled panel  20 . The third angled panel  24  is annular, and slopes downward as it extends radially outward from the second angled panel  20 . The second and the third angled panels  20  and  24  form an upwardly-extending stiffening bead  26 . 
     In accordance with the present invention, a coined panel  28  is contiguously formed with the third angled panel  24 . The coined panel  28  extends radially outward from the third angled panel  24 . The coined panel  28  is substantially flat, i.e., the coined panel  28  lies substantially in the x-y plane denoted in the figures. The coined panel  28  has an upper surface  28   a  and an opposing lower surface  28   b , as is most clearly shown in FIGS. 5A and 5B (FIGS. 5A and 5B respectively show the coined panel  28  in its initial (uncoined) and final (coined) states). The panel  28  has a thickness of approximately 0.0072 inch (0.18 mm) before the panel  28  is coined. The panel  28  preferably has a thickness within the range of approximately 0.0062 inch to 0.0068 inch (0.16 mm to 0.17 mm) after the coining operation (these values are based on the use of DR8 65-pound steel). The width (radial dimension) of the coined panel  28  is approximately 0.060 inch (1.5 mm) after the panel  28  is coined. The function of the coined panel  28  is described below. 
     Further in accordance with the present invention, a recessed panel  30  is contiguously formed with the coined panel  28 . The recessed panel  30  has an upper surface  30   a  and a lower surface  30   b , as is most clearly shown in FIGS. 5A and 5B. The recessed panel  30  has a substantially arcuate cross-section. The upper surface  30   a  of the recessed panel  30  preferably has a radius of curvature R 1  within the range of approximately 0.035 inch to 0.039 inch (0.89 mm to 0.99 mm) when the recessed panel  30  is fully formed (see FIG.  2 ). The recessed panel  30  initially curves downward as it extends radially outward from the coined panel  28 . The recessed panel  30  eventually curves upward as the panel  30  continues to extend radially outward from the coined panel  28 . 
     The recessed panel  30  preferably has a depth of approximately 0.0030 inch (0.076 mm) when the recessed panel  30  is fully formed. The depth of the fully-formed recessed panel  30  is denoted by the symbol “D 4 ” in FIG.  5 B. The depth D 4  represents the vertical (z-axis) distance between the bottom surface  28   b  of the coined panel  28  and the lowest point on the bottom surface  30   b  of the recessed panel  30 . The upper surface  30   a  of the recessed panel  30  defines a recess  31  (see, e.g., FIGS.  5 A and  5 B). The significance of the recess  31  and the recessed panel  30  are explained in detail below. 
     The can end  10  further includes an annular chuck wall  32 . The chuck wall  32  is contiguously formed with the recessed panel  30  and extends substantially in the vertical (z) direction. The chuck wall  32  defines a chuck-wall diameter. The chuck-wall diameter of the fully-formed can end  10  is denoted by the symbol “D 2 ” in FIG.  3 . The chuck-wall diameter D 2  of the exemplary can end  10  is within the range of approximately 3.882 inches to 3.886 inches (98.60 mm to 98.70 mm). 
     A seaming panel  34  is contiguously formed with the chuck wall  32 . The seaming panel  34  is utilized to join the can end  10  to the can body  12  through a conventional seaming operation. The seaming panel  34  includes a first portion  34   a  and a second portion  34   b  contiguously formed with the first portion  34   a . The seaming panel  34  also includes a third portion  34   c  contiguously formed with the second portion  34   b.    
     The seaming panel  34  has the following structural characteristics before the seaming panel  34  is joined to the can body  12 . The first portion  34   a  of the seaming panel  34  has a substantially arcuate cross section, and extends upward and radially outward from the chuck wall  32 . The first portion  34   a  preferably has a radius of curvature of approximately 0.043 inch (1.1 mm). The second portion  34   b  has a substantially arcuate cross section, and extends primarily radially outward from the first portion  34   a . The second portion  34   b  preferably has a radius of curvature of approximately 0.259 inch (6.58 mm). The third portion  34   c  extends downward and radially outward from the second portion  34   b . The cross section of the third portion  34   c  is substantially arcuate where the third portion  34   c  meets the second portion  34   b . The cross section of the third portion  34   c  becomes substantially straight as the third portion  34   c  continues to extend away from the second portion  34   b  (see FIG.  2 ). The arcuate section of the third portion  34   c  preferably has a radius of curvature of approximately 0.029 inch (0.74 mm). 
     The seaming panel  34  is joined to the can body  12  by placing the seaming panel  34  over a cover hook  12   a  disposed along an upper (or lower) edge of the can body  12  (see FIG.  3 ). The third portion  34   a  of the seaming panel  34  is subsequently deformed downward and radially inward so that the seaming panel  34  is secured around the lip  12   a . This action secures the can end  10  to the can body  12 . The can end  10  preferably has a diameter within the range of approximately 4.266 inches to 4.274 inches (108.4 mm to 108.6 mm) after the can end  10  has been joined to the can body  12 . 
     Details relating to the formation of the can end  10  are as follows. FIGS. 4A through 4E show the successive stages of the geometry of the can end  10  as the can end  10  is formed according to the current invention. The process of forming the can end  10  commences with the cutting of a substantially circular metal blank  50  from a sheet of metal such as DR8 65-pound continuous-annealed steel (the invention can also be used in conjunction with batch-annealed steel and 55-pound (or lower) steel, as noted previously). The blank  50  includes the center panel  16 , as shown in FIG.  4 A. The blank  50  is then stamped along its outer periphery to form the seaming panel  34  (see FIG.  4 B). The stiffening beads  22  and  26  are subsequently formed radially outward of the center panel  16 , as shown in FIG.  4 C. 
     The recessed panel  30  and the coined panel  28  are initially formed on a substantially simultaneous basis after the stiffening beads  22  and  26  have been formed (see FIGS.  4 D and  5 A). Specifically, the area on the blank  50  directly inward of the recessed panel  30  is stamped so as to lie substantially flat in relation to the x-y plane. In addition, the recessed panel  30  is formed to an initial depth (this action also initially forms the recess  31 ). The initial depth of the recessed panel  30  is denoted by the symbol “D 3 ” in FIG.  5 A. The depth D 3  represents the vertical (z-axis) distance between the bottom surface  28   b  of the initially-formed coined panel  28  and the lowest point on the bottom surface  30   b  of the recessed panel  30 . The initial depth D 3  of the recessed panel  30  is preferably approximately 0.0025 inch (0.064 mm). 
     In accordance with the present invention, the panel  28  is coined after the recessed panel  30  and the panel  28  have been initially formed in the above-noted manner (see FIGS.  4 E and  5 B). The coining operation reduces the thickness of the coined panel  28 . (The reduction in the thickness of the coined panel  28  is exaggerated in FIG. 5B for clarity.) The thickness of the panel  28  is approximately 0.0072 inch (0.18 mm) before the coining operation, as noted previously. The coining operation reduces the thickness of the panel  28  to its final value within the range of approximately 0.0062 inch to 0.0068 inch (0.16 mm to 0.17 mm). 
     The recessed panel  30  is re-formed into its final configuration on a simultaneous basis with the coining operation, i.e., the recessed panel  30  is formed to its final depth D 4  as the panel  28  is coined (this action also re-forms the recess  31  into its final configuration). (Differences between the initial depth D 3  and the final depth D 4  of the recessed panel  30  are exaggerated in FIGS. 5A and 5B for clarity). The can end  10  is fully formed at this point, and is ready to be joined to the can body  12  through a conventional seaming operation. 
     The above-described series of steps form the can end  10  with minimal warpage. In particular, the coining operation substantially reduces the direction-dependent nature of the mechanical properties of the can end  10  in the coined area. This direction-dependence, as noted previously, is a result of the rolling operation used to form the blank  50 . The direction-dependent properties induce a tendency in the can end  10  to warp. Hence, reducing the direction-dependence of these properties reduces the warpage experienced by the can end  10  as it is formed. 
     In addition, forming the can end  10  in the above-described manner allows the panel  28  to be coined with little or no increase in the chuck-wall diameter of the can end  10 . Applicants have found that initially forming the recessed panel  30  before the coining operation, and then forming the remainder of the recessed panel  30  during the coining operation, minimizes the effect of the coining operation on the chuck-wall diameter. More specifically, coining the area contiguous with the recessed panel  30  while simultaneously forming the recessed panel  30  to its final depth D 4  causes substantially all of the material displaced by the coining operation to be driven into the recessed panel  30 . The displaced material thereby increases the overall length of the recessed panel  30 . The arcuate cross section of the recessed panel  30  allows the recessed panel  30  to undergo such an increase in length without substantially affecting the chuck-wall diameter of the can end  10 . In particular, the arcuate cross-section of the recessed panel  30  causes a substantial portion of the displaced material to be driven downward, rather than outward, as the coined panel  28  and the recessed panel  30  are simultaneously formed into their final configurations. Hence, the material displaced by the coining operation adds minimally to the chuck-wall diameter of the can end  10 . 
     The above-described changes in the geometry of the can end  10  are illustrated in FIGS. 6A and 6B. FIG. 6A depicts the can end  10  before the panel  28  is coined. The panel  28  and the recessed panel  30  have an initial combined length denoted by the symbol “L 2 ” in FIG.  6 A. The can end  10  has an initial chuck-wall diameter represented by the symbol “D 5 .” 
     FIG. 6B depicts the can end  10  after the panel  28  has been coined, i.e., FIG. 6B shows the fully-formed can end  10 . The material displaced by the coining operation increases the combined length of the coined panel  28  and the recessed panel  30  by an amount represented by the symbol “Δ 2 .” Hence, the combined length of the panels  28  and  30  after the coining operation equals the initial length (L 2 ) plus the increase in length caused by the coining operation (Δ 2 ). The length increase Δ 2  does not cause a corresponding increase in the chuck-wall diameter of the can end  10  due the geometry of the recessed panel  30 , as explained above. In particular, the increase in the chuck-wall diameter is less than the length increase Δ 2  because a substantial portion of the material displaced by the coining operation is driven downward as a result of the geometry of the recessed panel  30 . 
     Applicants have produced the exemplary can end  10  using the above described process. The increase in the chuck-wall diameter of the can end  10  caused by coining the panel  28  was approximately 0.002 inch (0.05 mm), and warpage of the fully-formed can end  10  was approximately 0.015 inch (0.38 mm). These values are both within acceptable limits for production can ends  10 . Applicants have also produced a comparable can end without the recessed panel  30 . The chuck-wall diameter of this can end increased by approximately 0.006 inch (0.15 mm) as a result of the coining operation. Hence, the use of the invention reduced the change in the chuck-wall diameter of the exemplary can end  10  by approximately two-thirds in relation to a conventionally-formed can end. 
     The can end  10  can be formed in a die  60  shown in FIGS. 7 through 12B. The die  60 , in general, is of a type commonly known to those skilled in the art of making can ends such as the can end  10 . Hence, the die  60  will not be described in detail except where necessary for an understanding of the invention. 
     Structural details of the die  60  are as follows. The die  60  comprises anannular cut edge  62  and a punch  64 . The cut edge  62  and the punch  64  are coaxially disposed. The cut edge  62  remains stationary as the can end  10  is formed. The punch  64  is adapted to translate downward, i.e., in the z −  direction, through the cut edge  62 . In particular, the punch  64  and the cut edge  62  are sized so that an outer circumferential surface  64   a  of the punch  64  slides vertically along an inner circumferential surface  62   a  of the cut edge  62  (see FIGS.  8  and  9 ). 
     The die  60  further comprises an annular pressure ring  66 . The pressure ring  66  is substantially aligned with the punch  64  in the vertical (z) direction. The pressure ring  66  is biased upward, i.e., in the z +  direction, by a pneumatic pressure of approximately 40 psi. 
     The die  60  also includes an annular lower form  68 . The lower form  68  is coaxially and translatably disposed within the pressure ring  66 . The pressure ring  66  and the lower form  68  are sized so that an inner circumferential surface  66   a  of the pressure ring  66  slides vertically along an outer circumferential surface  68   a  of the lower form  68  (see FIG.  10 ). The lower form  68  has an upper face  68   b . The geometric profile of the upper face  68   b  substantially matches the profile of the seaming panel  34  before the seaming panel  34  is joined to the can body  12 . The significance of this feature is explained below. 
     The die  60  further comprises a pressure-ring knock-out  70 . The pressure-ring knock-out  70  is coaxially and translatably disposed within the punch  64 . The punch  64  and the pressure ring knock-out  70  are sized so that an inner circumferential surface  64   b  of the punch  64  slides vertically along an outer circumferential surface  70   a  of the pressure-ring knock-out  70  (see FIG.  10 ). The pressure-ring knock-out  70  is substantially aligned with the lower form  68  in the vertical direction. The pressure-ring knock-out  70  is biased downward by a pneumatic pressure of approximately 50 psi. 
     The die  60  also includes a lift-out lower coin ring  72 . The lift-out lower coin ring  72  is coaxially and translatably disposed within the lower form  68 . The lift-out lower coin ring  72  is sized so that an outer circumferential surface  72   a  of the ring  72  slides vertically along an inner circumferential surface  68   c  of the lower form  68  (see FIG.  10 ). The lift-out lower coin ring  72  is biased upward by a pneumatic pressure of approximately 10 psi. The lift-out lower coin ring  72  has an upper surface  72   b . The upper surface  72   b  includes a substantially flat portion  72   c  and an adjoining curved portion  72   d  (see FIGS.  12 A and  12 B). The significance of these features is explained below. 
     The die  60  further comprises an annular upper punch form  74 . The upper punch form  74  is coaxially and translatably disposed within the pressure-ring knock-out  70 . The upper punch form  74  is sized so that an outer circumferential surface  74   a  of the upper punch form  74  slides vertically along an inner circumferential surface  70   b  of the pressure-ring knock-out  70  (see FIGS.  10  and  11 ). The upper punch form  74  has a lower surface  74   b . The lower surface  74   b  includes a substantially flat portion  74   c  and an adjoining curved portion  74   d  (see FIGS.  12 A and  12 B). The curved portion  74   d  of the lower surface  74   b  has a curvature that is substantially similar to the curvature of the recessed panel  30  of the can end  10 . Hence, the curved portion  74   b  has a radius of curvature within the range of approximately 0.035 inches to 0.039 inches (0.89 mm to 0.99 mm). The substantially flat portion  74   c  and the curved portion  74   d  of the upper punch form  74  are substantially vertically aligned with the flat portion  72   c  and the curved portion  72   d , respectively, of the lift-out lower coin ring  72 . 
     The die  60  also comprises a first lower bead ring  76  and a second lower bead ring  78  (see FIG.  11 ). The first and the second lower bead rings  76  and  78  remain stationary as the can end  10  is formed. The second lower bead ring  78  is coaxially disposed within the first lower bead ring  76 . In particular, an outer circumferential surface  78   a  of the second lower bead ring  78  is fixed to an inner circumferential surface  76   a  of the first lower bead ring  76  (see FIG.  11 ). Furthermore, the first lower bead ring  76  is sized so that an inner circumferential surface  72   e  of the lift-out lower coin ring  72  slides along an outer circumferential surface  76   b  of the first lower bead ring  76 . The first lower bead ring  76  includes an upper surface  76   c  having a curvilinear portion  76   d  and a substantially flat portion  76   e . The second lower bead ring  78  includes an upper surface  78   b  having a substantially flat profile. The second lower bead ring  78  also includes a rounded corner  78   c  that adjoins the upper surface  78   b.    
     The die  60  further comprises an inner upper-form-ring  80  (see FIG.  11 ). The inner upper-form-ring  80  is coaxially disposed within the upper punch form  74 . Specifically, an outer circumferential surface  80   a  of the inner upper-form-ring  80  is fixed to an inner circumferential surface  74   e  of the upper punch form  74 . The inner upper-form-ring  80  includes a lower surface  80   b  having a curvilinear portion  80   c . The curvilinear portion  80   c  is substantially vertically aligned with the substantially flat portion  76   e  of the first lower bead ring  76 . 
     Functional details relating to the die  60  are as follows. The process of forming the can end  10  on the die  60  begins by placing a metal sheet  82  on the die  60  (ss FIG.  8 ). In particular, the metal sheet  82  is placed on the die  60  so that the metal sheet  82  is substantially supported by the pressure ring  66  and the cut edge  62 . The punch  64  subsequently translates downward, into the cut edge  62 . (The directions of translation for the various components of the die  60  are denoted by arrows  84  included in the figures.) The movement of the punch  64  into the stationary cut edge  62  cuts the substantially circular blank  50  from the metal sheet  82 . More specifically, the punch  64  forms the metal sheet  82  downward. The resulting interference between the metal sheet  82  and the punch  62  cuts (shears) the metal sheet  82  along the inner periphery of the cut edge  62 , thereby forming the blank  50  (see FIG.  9 ). The pressure ring  66  is pushed downward, against its pneumatic bias, in response to the downward movement of the punch  64  as the blank  50  is cut. 
     The punch  64  continues its downward movement after cutting the blank  50 . In addition, the upper punch form  74  translates downward on a simultaneous basis with the punch  64  (see FIG.  10 ). Furthermore, the pressure ring knock-out  70  applies downward pressure to the blank  50  as a result of its pneumatic bias. The lower form  68  remains stationary, and thereby resists the downward bias of the pressure ring knock-out  70 . Hence, a portion of the blank  50  is secured between the pressure ring knock-out  70  and the lower form  68 . 
     The downward movement of the punch  64  and the upper punch form  74  in relation to the lower form  68  stamps the outer periphery of the blank  50  in the manner shown in FIG.  10 . In particular, the profile of the upper surface  68   b  of the lower form  68  is stamped into the outer periphery of the blank  50 . The profile of the upper surface  68   b  substantially matches the profile of the seaming panel  34 , as noted previously. Hence, the noted interaction between the punch  64 , the pressure ring knock-out  70 , the upper punch form  74 , and the lower form  68  forms the seaming panel  34  in the blank  50 . 
     The upper punch form  74  continues its downward movement after the seaming panel  34  is formed. The inner upper-form-ring  80  is fixed to the upper punch form  74 , as stated above (see FIG.  11 ). Hence, the inner upper-form-ring  80  translates downward on a simultaneous basis with the upper punch form  74 . The continued downward movement of the upper punch form  74  and the inner upper-form-ring  80  urges the blank  50  downward. The downward movement of the blank  50  causes the blank  50  to deform around the curvilinear portion  76   d  of the first lower bead ring  76  and the rounded corner  78   c  of the second lower bead ring  78 . This deformation forms the stiffening beads  22  and  26 . 
     The continued downward movement of the upper punch form  74  forms the blank  50  into the lift-out lower coin ring  72 . The upper punch form  74  and the lift-out lower coin ring  72  act in conjunction to form the coined panel  28  and the recessed panel  30 . The coined panel  28  and the recessed panel  30  are formed substantially in two stages, as depicted in FIGS. 12A and 12B. More particularly, the recessed panel  30  and the coined panel  28  are initially formed as shown in FIG.  12 A. The recessed panel  30  and the coined panel  28  are subsequently re-formed into their final configurations as depicted in FIG.  12 B. 
     The recessed panel  30  and the coined panel  28  are initially formed as the upper punch form  74  forms the blank  50  into the lift-out lower coin ring  72 . Specifically, the downward movement of the upper punch form  74  causes a portion of the blank  50  to become sandwiched between the respective upper surfaces  74   b  and  72   b  of the upper punch form  74  and the lift-out lower coin ring  72 . The continued downward movement of the upper punch form  74  drives the lift-out lower coin ring  72  downward, against its pneumatic bias. The lift-out lower coin ring  72  eventually reaches the end of its range of movement. The resistance of the lift-out lower coin ring  72  to further downward movement causes the respective surface portions  74   c  and  72   c  of the upper punch form  74  and the lift-out lower coin ring  72  to substantially flatten the portion of the blank  50  disposed therebetween (see FIG.  12 A). This action forms the panel  28  into its initial configuration. Furthermore, a curvilinear profile is imposed on the portion of the blank  50  disposed between the respective curved portions  74   d  and  72   d  of the upper punch form  74  and the lift-out lower coin ring  72 , thereby forming the recessed panel  30  and the recess  31 . 
     The continued downward movement of the upper punch form  74  re-forms the panel  28  and the recessed panel  30  into their final configurations. Specifically, the downward movement of the upper punch form  74 , in conjunction with the resistance offered by the lift-out lower coin ring  72 , coins the panel  28 . In addition, the curved portion  74   d  of the upper punch form  74  urges the recessed panel  30  downward until the recessed panel  30  contacts the curved portion  72   d  of the lift-out lower coin ring  72 . The recessed panel  30  and the recess  31  are fully formed at this point. This step takes place simultaneously with the coining operation on the panel  28 . Applicants have found that re-forming the recessed panel  30  to its final depth D 4  while simultaneously coining the panel  28  minimizes any increase in the diameter of the chuck wall  32  resulting from the coining operation, as explained in detail above. 
     The invention provides substantial advantages in relation to the prior art. For example, the use of the invention allows can ends such as the can end  10  to be manufactured from relatively thin sheets of material. More particularly, the use of the invention substantially reduces the potential for unacceptable warpage in can ends manufactured from relatively thin sheets of rolled metal. The invention thereby facilitates the manufacture of can ends from thinner sheets of material than is feasible with common manufacturing techniques. The use of thinner sheets of material can lead to substantial cost savings due to the large production volumes of typical can ends. In particular, the invention facilitates the use of double-reduced steel in the manufacture can ends such as the can ends  10 . Double-reduced steel, as noted previously, provides a favorable combination of thinness, tensile strength, hardness, and resistance to elongation. 
     Furthermore, reducing or eliminating warpage in a can end such as the can end  10  enhances the fit between the can end  10  and the can body to which the can end is fixed, thereby reducing the potential for leakage into or from the assembled can. The reduction or elimination of warpage also enhances the fit between the can end  10  and the seaming chuck utilized to join the can end  10  to the can body. In addition, reducing or eliminating warpage facilitates the automated transfer (feeding) of the can end  10  during subsequent processing operations, e.g., application of a lining to the can end  10 . Other advantages include the ability to implement the invention through relatively minor tooling changes to conventional can-manufacturing equipment. Also, the use of the invention adds little or no time or expense to the manufacturing process for can ends such as the can end  10 . In addition, the coining operation enhances the structural integrity the can end  10 . In particular, coining the can end  10  increases the overall strength and stability of the can end  10 . 
     It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of the parts, within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.