Pressing die for an uncurled shell of a pressure-resistant easy open end

Abstract

A pressing die for an uncurled shell of a pressure-resistant easy open end, and the lower die mainly consists of a lower die base, a lower die core ring, a lower die core, a lower pressing ring and a lower blade; the upper die mainly consists of an upper die base, an upper die core, an upper inner forming ring, an upper outer forming ring and an upper blade, wherein: for the new easy open end type, the top of the lower die core ring of the lower die was designed to be the contour matching the new can end type, and the upper outer forming ring and the upper inner forming ring of the upper die were designed to the contour and suspended portion matching the lower die core ring of the lower die.

Claims

1. A pressing die for an uncurled shell of a pressure-resistant easy open end, the uncurled shell comprising a sealing portion, a countersink portion, a ferrule arc portion, an upward extension portion of ferrule and a center panel; a first annular recess being formed between the countersink portion, the ferrule arc portion and the upward extension portion of ferrule; the sealing portion being formed by a first straight portion, a first arc portion, a second arc portion, and a third arc portion; the countersink portion being formed by a second straight portion, a fourth arc portion, a fifth arc portion, a sixth arc portion and a third straight portion: the ferrule arc section being formed of a seventh arc portion: the upward extension portion of ferrule being formed a fourth straight line and an eighth arc portion; and the center panel being formed by a fifth straight line; the pressing die comprising a lower die and an upper die; wherein: the lower die comprises a lower die base, a lower die core ring, a lower die core, a lower pressing ring, and a lower blade, wherein: the lower die base is a cylinder with an upper opening; the lower die core ring is fixed in the lower die base and concentric with the lower die base; an acting part of the lower die core is a cylindrical body, which is embedded in the lower die core ring and slidably matched with the lower die core ring in upward and downward directions; a first air chamber is sealed and formed under the lower die core in the lower die core ring, and air pressure of the first air chamber supports the lower die core; the lower pressing ring is embedded between the lower die base and the lower die core ring, and a second air chamber is sealed and formed between the lower die base and the lower die core ring under the lower pressing ring, and air pressure of the second air chamber supports the lower pressing ring; and the lower blade is fixed on an edge of the upper opening of the lower die base, and a lower cutting edge is provided on an inner edge of a top of the lower blade; the upper die comprises an upper die base, an upper die core, an upper inner forming ring, an upper outer forming ring and an upper blade, wherein: the upper die base is a cylinder with a lower opening; an acting part of the upper die core is a cylindrical body, which is arranged in the upper die base and concentric with the upper die base, and the upper die core is slidably matched with the upper die base in the upward and downward directions; a third air chamber is sealed and formed above the upper die core in the upper die base, and air pressure of the third air chamber presses against the upper die core; the upper inner forming ring is embedded between the upper die core and the upper die base, and a fourth air chamber is sealed and formed between the upper die core and the upper die base and above the upper inner forming ring, and air pressure of the fourth air chamber presses against the upper inner forming ring; the upper outer forming ring is an embedded between the upper die base and the upper inner forming ring, and a fifth air chamber is sealed and formed between the upper die base and the upper inner forming ring and above the upper outer forming ring, and air pressure of the fifth air chamber presses against the upper outer forming ring; and the upper blade is fixed on an edge of the lower opening of the upper die base, and an upper cutting edge matched with the lower cutting edge is provided on an outer edge of a bottom of the upper blade; wherein: the upper outer forming ring and the upper inner forming ring of the upper die match with the lower die core ring of the lower die, wherein a top of the lower die core ring is provided with a contour corresponding to the first straight portion, the first arc portion, the second arc portion, the third arc portion, the second straight portion, the fourth arc portion, the fifth arc portion, the sixth arc portion and the third straight portion of the uncurled shell; an annular depression is formed at a top of the lower die core ring, the annular depression corresponding to the second straight portion, the fourth arc portion, the fifth arc portion and sixth arc portion of the uncurled shell; a bottom of the upper outer forming ring is provided with a contour corresponding to the second arc portion of the uncurled shell, and parts at the bottom of the upper outer forming ring corresponding to the first arc portion and the third arc portion of the uncurled shell are suspended relative to the top of the lower die core ring in a closed state; a bottom of the upper inner forming ring is provided with a contour corresponding to the fourth arc portion and the fifth arc portion of the uncurled shell, and parts at the bottom of the upper inner forming ring corresponding to the second straight portion, the sixth arc portion and third straight portion of the uncurled shell are suspended relative to the top of the lower die core ring in the closed state; the upper die core of the upper die matches with the lower die core of the lower die, a top of the lower die core is provided with a contour corresponding to the seventh arc portion, the fourth straight portion, the eighth arc portion and the fifth straight portion of the uncurled shell, and a second annular recess is formed on the top of the lower die core corresponding to the seventh arc portion, the fourth straight portion and the eighth arc portion of the uncurled shell; a bottom of the upper die core is provided with a contour corresponding to the fifth straight portion of the uncurled shell; and the bottom of the upper die core is provided with a downward raised fillet at an edge of the bottom of the upper die core, the raised fillet corresponding to the eighth arc portion of the uncurled shell, and parts at the bottom of the upper die core corresponding to the seventh arc portion and the fourth straight portion of the uncurled shell are suspended relative to the top of the lower die core in the closed state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the partial sectional view of the uncurled shell of the easy open end (new end type) produced by the present invention;

(2) FIG. 2 is the sectional view of a non-preformed pressing die in the embodiment 1 of the present invention, showing the separated state of the upper die and the lower die;

(3) FIG. 3 is the sectional view of a non-preformed pressing die in the embodiment 1 of the present invention, showing the state of the upper and lower dies at the lower dead center position under the press, that is, the state when the forward forming of the uncurled shell of the easy open end is completed;

(4) FIG. 4 is the sectional view of a non-preformed pressing die in the embodiment 1 of the present invention, showing the state of the upper and lower dies when the full forming of the uncurled shell of the easy open end is completed;

(5) FIG. 5 is the local enlarged view of pressing process 1 in the embodiment 1 of present invention;

(6) FIG. 6 is the local enlarged view of pressing process 2 in the embodiment 1 of present invention;

(7) FIG. 7 is the local enlarged view of pressing process 3 in the embodiment 1 of present invention;

(8) FIG. 8 is the local enlarged view of pressing process 4 in the embodiment 1 of present invention;

(9) FIG. 9 is the local enlarged view of pressing process 5 in the embodiment 1 of present invention;

(10) FIG. 10 is the local enlarged view of pressing process 6 in the embodiment 1 of present invention;

(11) FIG. 11 is the local enlarged view of pressing process 7 in the embodiment 1 of present invention;

(12) FIG. 12 is the local enlarged view of pressing process 8 in the embodiment 1 of present invention;

(13) FIG. 13 is the local enlarged view of pressing process 9 in the embodiment 1 of present invention;

(14) FIG. 14 is the local enlarged view of pressing process 10 in the embodiment 1 of present invention;

(15) FIG. 15 is the local enlarged view of pressing process 11 in the embodiment 1 of present invention;

(16) FIG. 16 is the sectional view of a preformed pressing die in the embodiment 2 of the present invention, showing the separated state of the upper die and the lower die;

(17) FIG. 17 is the local enlarged view of pressing process 2 in the embodiment 2 of present invention;

(18) FIG. 18 is the local enlarged view of pressing process 2 in the embodiment 2 of present invention;

(19) FIG. 19 is the local enlarged view of pressing process 3 in the embodiment 2 of present invention;

(20) FIG. 20 is the local enlarged view of pressing process 4 in the embodiment 2 of present invention;

(21) FIG. 21 is the local enlarged view of pressing process 5 in the embodiment 2 of present invention;

(22) FIG. 22 is the local enlarged view of pressing process 6 in the embodiment 2 of present invention;

(23) FIG. 23 is the local enlarged view of pressing process 7 in the embodiment 2 of present invention;

(24) FIG. 24 is the local enlarged view of pressing process 8 in the embodiment 2 of present invention;

(25) FIG. 25 is the local enlarged view of pressing process 9 in the embodiment 2 of present invention;

(26) FIG. 26 is the local enlarged view of pressing process 10 in the embodiment 2 of present invention;

(27) FIG. 27 is the local enlarged view of pressing process 11 in the embodiment 2 of present invention;

(28) In the above figures: 1. Upper die; 2. Lower die; 3. Lower die base; 4. Lower die core ring; 5. Lower die core; 6. Lower pressing ring; 7. Lower blade; 8. First air chamber; 9. Second air chamber; 10. Lower cutting edge; 11. Annular recess for supporting and limiting of the ferrule forming; 12. Upper die base; 13. Upper die core; 14. Upper outer forming ring; 15. Upper blade; 16. R fillet of upper die core; 17. Third air chamber; 18. Upper cutting edge; 19. Upper die core base; 20. Upper die core body; 21. Lower die core base; 22. Lower die core body; 23. Vent hole; 24. Vent hole; 25. Vent hole; 26. Uncurled shell when forward forming is completed; 27. Uncurled shell after complete forming; 28. Fourth air chamber; 29. First blocking limit face; 30. Uncurled shell blank; 31. Annular depression; 32. Upper inner forming ring; 33. Fifth air chamber; 40. Inlet port of upper inner forming ring; 41. Inlet port of upper inner forming ring; R1. First arc portion; R2. Second arc portion; R3. Third arc portion; R4. Fourth arc portion; R5. Fifth arc portion; R6. Sixth arc portion; R7. Seventh arc portion; R8. Eighth arc portion; L1. First straight portion; L2. Second straight portion; L3. Third straight portion; L4. Fourth straight portion; L5. Fifth straight portion.

SPECIFIC EMBODIMENT

(29) With reference to the accompanying drawings and embodiment, the present invention will be described in detail.

(30) The uncurled shell structure (new cover type) of a pressure-resistant easy open end in the embodiment of the present invention is shown in FIG. 1: On the cross section of the uncurled shell, it consists of a sealing portion, a countersink portion, a ferrule arc portion, an upward extension portion of ferrule and a center panel from periphery to center, and an annular recess is formed between the countersink portion, the ferrule arc portion and the upward extension portion of ferrule (shown in FIG. 1).

(31) The sealing portion consists of a first straight portion L1, a first arc portion R1, a second arc portion R2 and a third arc portion R3, wherein:

(32) One end of the first straight portion L1 is connected with the first end of the first arc portion R1, and the first straight portion L1 is tangent to the first arc portion R1; the second end of the first arc portion R1 is connected with the first end of the second arc portion R2, and the first arc portion R1 is tangent to the second arc portion R2; the second end of the second arc portion R2 is connected with the first end of the third arc portion R3, and the second arc portion R2 is tangent to the third arc portion R3.

(33) The countersink portion consists of a second straight portion L2, a fourth arc portion R4, a fifth arc portion R5, a sixth arc portion R6, and a third straight portion L3, wherein:

(34) The second end of the third arc portion R3 is connected with the first end of the second straight portion L2, and the third arc portion R3 is tangent to the second straight portion L2; the second end of the second straight portion L2 is connected with the first end of the fourth arc portion R4, and the second straight portion L2 is tangent to the fourth arc portion R4; the second end of the fourth arc portion R4 is connected with the first end of the fifth arc portion R5, and the fourth arc portion R4 is externally tangent to the fifth arc portion R5; the second end of the fifth arc portion R5 is connected with the first end of the sixth arc portion R6, and the fifth arc portion R5 is internally tangent to the sixth arc portion R6; the second end of the sixth arc portion R6 is connected with the first end of the third straight portion L3, and the sixth arc portion R6 is tangent to the third straight portion L3.

(35) The ferrule arc portion consists of a seventh arc portion R7, wherein:

(36) The second end of the third straight portion L3 is connected with the first end of the seventh arc section R7 and the second straight portion L2 is tangent to the seventh arc section R7.

(37) The upward extension portion of ferrule consists of a fourth straight portion L4 and an eighth arc portion R8, wherein:

(38) The second end of the seventh arc section R7 is connected with the first end of the fourth straight portion L4, and the fourth straight portion L4 is tangent to the seventh arc section R7; the second end of the fourth straight portion L4 is connected with the first end of the eighth arc portion R8, and the fourth straight portion L4 is tangent to the eighth arc portion R8.

(39) The center panel consists of a fifth straight portion L5, wherein:

(40) The second end of the eighth arc portion R8 is connected with the first end of the fifth straight portion L5, and the eighth arc portion R8 is tangent to the fifth straight portion L5.

Embodiment 1: A Pressing Die for an Uncurled Shell of a Pressure-Resistant Easy Open End (without Pre-Formed Pressing Die)

(41) As shown in FIGS. 1-3, the pressing die consists of two parts of a lower die 2 and an upper die 1 (see FIG. 2).

(42) The lower die 2 mainly consists of a lower die base 3, a lower die core ring 4, a lower die core 5, a lower pressing ring 6, and a lower blade 7 (see FIG. 2), wherein the lower die base 3 is a cylinder with an upper opening (see FIG. 2).

(43) The lower die core ring 4 is an annular body, which is fixed in the opening of the lower die base 3 through the locating pin and the bolt and concentric with the lower die base 3 (see FIG. 2).

(44) The lower die core 5 consists of a lower die core base 21 and a lower die core body 22 (see FIG. 2). The lower die core base 21 is fixedly connected with the lower die core body 22, and the action part of the lower die core 5 is the lower die core body 22. The lower die core body 22 is a cylindrical body, which is embedded in the lower die core ring 4 and works with the lower die core ring 4 in the up and down directions in a slidable way (see FIG. 2).

(45) A first air chamber 8 is sealed and formed under the lower die core 5 in the lower die core ring 4 (see FIG. 2) and the air pressure of the first air chamber 8 is used to support the lower die core 5.

(46) The lower die core body 22 is equipped with a vent hole 23 and a vent hole 24 (see FIG. 2), which are used for venting when pressing the uncurled shell.

(47) The lower pressing ring 6 is an annular body, which is embedded between the lower die base 3 and the lower die core ring 4 (see FIG. 2), and a second air chamber 9 is sealed and formed between the lower die base 3 and the lower die core ring 4 under the lower pressing ring 6, and the air pressure of the second air chamber 9 is used to support the lower pressing ring 6 (see FIG. 2).

(48) The lower blade 7 is an annular body, which is fixed on the edge of the upper opening of the lower die base 3, and a lower cutting edge 10 is provided on the inner edge of the top of the annular body.

(49) The upper die 1 mainly consists of an upper die base 12, an upper die core 13, an upper inner forming ring 32, an upper outer forming ring 14, and an upper blade 15 (see FIG. 2), wherein the upper die base 12 is a cylinder with a lower opening.

(50) The upper die core 13 consists of an upper die core base 19 and an upper die core body 20 (see FIG. 2). The upper die core base 19 is fixedly connected with the upper die core body 20 through a bolt and a spacer (see FIG. 2). The action part of the upper die core 13 is the upper die core body 20. The upper die core body is a cylindrical body, which is arranged in the upper die base 12 and concentric with the upper die base 12 (see FIG. 2).

(51) The upper die core 13 is slidably matched with the upper die base 12 in the upward and downward directions, and the lower die core body 12 is equipped with a vent hole 25 (see FIG. 2), which is used for venting when pressing the uncurled shell.

(52) The upper die core body 20 is equipped with a R fillet of the upper die core body at the bottom corner (see FIG. 2).

(53) A third air chamber 17 is sealed and formed above the upper die core 13 in the upper die base 12, and the air pressure of the third air chamber 17 is used to press against the upper die core 13.

(54) The upper inner forming ring 32 is an annular body, which is embedded between the upper die core 13 and the upper die base 12 (see FIG. 2), and a fourth air chamber 28 is sealed and formed between the upper die core 13 and the upper die base 12 above the upper inner forming ring 32 (see FIG. 2), and the air pressure of the fourth air chamber 28 is used to press against the upper inner forming ring 32, and the fourth chamber 28 is equipped with an inlet port of the upper inner forming ring 40 on the upper die base 12 (see FIG. 2).

(55) The upper outer forming ring 14 is an annular body, which is embedded between the upper die base 12 and the upper inner forming ring 32 (see FIG. 2), and a fifth air chamber 33 is sealed and formed between the upper die base 12 and the upper inner forming ring 32 above the upper outer forming ring 14 (see FIG. 2), and the air pressure of the fifth air chamber 33 is used to press against the upper outer forming ring 14, and the fifth chamber 33 is equipped with an inlet port of the upper inner forming ring 41 on the upper die base 12.

(56) The upper blade 15 is an annular body, which is fixed on the edge of the lower opening of the upper die base 12, and a upper cutting edge 18 matched with the lower cutting edge 10 is provided on the outer edge of the bottom of the upper blade 15.

(57) In order to solve the reliability and service life problems of the original pressing die for the uncurled shell of the easy open end on the basis of adapting to the easy open end type, the following parts have been improved in this embodiment:

(58) For the uncurled shell (shown in FIG. 1), the uncurled shell consists of a sealing portion, a countersink portion, a ferrule arc portion, an upward extension portion of ferrule and a center panel on the cross section from periphery to center, and an annular recess is formed between the countersink portion, the ferrule arc portion and the upward extension portion of ferrule; the sealing portion is formed by a tangent connection of a first straight portion L1, a first arc portion R1, a second arc portion R2, and a third arc portion R3; the countersink portion is formed by a tangent connection of a second straight portion L2, a fourth arc portion R4, a fifth arc portion R5, a sixth arc portion R6 and a third straight portion L3; the ferrule arc section is formed of a seventh arc portion R7; the upward extension portion of ferrule is formed by a tangent connection of a fourth straight line L4 and an eighth arc portion R8; the center panel is formed by a fifth straight line L5.

(59) The upper outer forming ring 14 and the upper inner forming ring 32 of the upper die 1 match with the lower die core ring of the lower die up and down, wherein the lower die core ring 4 is provided with a contour on its top corresponding to the first straight portion L1, the first arc portion R1, the second arc portion R2, the third arc portion R3, the second straight portion L2, the fourth arc portion R4, the fifth arc portion R5, the sixth arc portion R6 and the third straight portion L3 of the uncurled shell, wherein an annular depression 31 is formed at the top of the lower die core ring 4 corresponding to the position of the second straight portion L2, the fourth arc portion R4, the fifth arc portion R5 and sixth arc portion R6 of the uncurled shell (see FIG. 2).

(60) The upper outer forming ring 14 is provided with a contour on the bottom corresponding to the second arc portion R2 of the uncurled shell, while the parts at the bottom of the upper outer forming ring 14 corresponding to the first arc portion R1 and third arc portion R3 of the uncurled shell are suspended relative to the top of the lower die core ring 4 in a closed state.

(61) The upper inner forming ring 32 is provided with a contour on the bottom corresponding to the fourth arc portion R4 and the fifth arc portion R5 of the uncurled shell, while the parts at the bottom of the upper inner forming ring 32 corresponding to the second straight portion L2, the sixth arc portion R6 and third straight portion L3 of the uncurled shell are suspended relative to the top of the lower die core ring 4 in a closed state.

(62) The upper die core 13 of the upper die 1 matches with the lower die core 5 of the lower die 2 up and down, wherein the lower die core 5 is provided with a contour on its top corresponding to the seventh arc portion R7, the fourth straight portion L4, the eighth arc portion R8 and the fifth straight portion L5 of the uncurled shell, wherein an annular recess for supporting and limiting of the ferrule forming is formed on the top of the lower die core 5 corresponding to the seventh arc portion R7, the fourth straight portion L4 and the eighth arc portion R8 of the uncurled shell (see FIG. 2).

(63) The upper die core 13 is provided with a contour on its bottom corresponding to the fifth straight portion L5 of the uncurled shell.

(64) The parts at the bottom of the upper die core 13 corresponding to the seventh arc portion R7, the fourth straight portion L4 and the eighth arc portion R8 of the uncurled shell are suspended relative to the top of the lower die core 5 in a closed state.

(65) The uncurled shell pressing forming process of the embodiment 1 is shown in FIGS. 5 to 15, where FIG. 5 shows the pressing forming process 1. From FIG. 5, it can be seen that the upper die 1 moves downwards as a whole, and FIG. 30 shows the uncurled shell blank.

(66) FIG. 6 shows the pressing forming process 2. From FIG. 6, it can be seen that the upper blade 5 of the upper die and the lower blade 7 of the lower die 2 first cut to get the uncurled shell blanket 30, and then the upper blade 15 pushes the lower pressing ring 6 to move downward by the uncurled shell blanket 30.

(67) As the lower die core ring 4 is fixed on the lower die base 3, the upper outer forming ring 14 presses against the lower die core ring 4 to keep stationary by the uncurled shell blanket 30.

(68) FIG. 7 shows the pressing forming process 3. From FIG. 7, it can be seen that the uncurled shell blank 30 has deformation relative to FIG. 6.

(69) FIG. 8 shows the pressing forming process 4. From FIG. 8, it can be seen that the uncurled shell blank 30 between the upper blade 15 and the lower pressing ring 6 has slipped, the upper blade 15 directly contacts the lower pressing ring 6, and the upper inner forming ring 32 and the upper die core body 20 have started to contact the uncurled shell blank 30.

(70) FIG. 9 shows the pressing forming process 5. From FIG. 9, it can be seen that the upper die core body 20 pushes the lower die core body 22 to move downward by the uncurled shell blanket 30.

(71) FIG. 10 shows the pressing forming process 6. From FIG. 10, it can be seen that the upper die 1 and lower die 2 are in the state of the dead center position under the press, which is the state when the forward forming of the uncurled shell of the easy open end is completed. Refer to the uncurled shell 26 when the forward forming is completed in FIG. 10.

(72) FIG. 11 shows the pressing forming process 7. From FIG. 11, it can be seen that the upper die 1 moves upwards, while the lower pressing ring 6 and the lower die core body 22 also move upwards under the action of the corresponding first air chamber 8 and second air chamber 9.

(73) FIG. 12 shows the pressing forming process 8. From FIG. 12, it can be seen that the lower die core body 22 has moved to the upper dead center position and is not moving upwards. At this time, the upper and lower molds are in the state when the uncurled shell of the easy open end is fully formed, as shown in FIG. 12 when the uncurled shell 27 is fully formed.

(74) FIG. 13 shows the pressing forming process 9. From FIG. 13, it can be seen that the upper die core body 20 has left the fully formed uncurled shell 27.

(75) FIG. 14 shows the pressing forming process 10. From FIG. 14, it can be seen that the upper inner forming ring 32 has left the fully formed uncurled shell 27.

(76) FIG. 15 shows the pressing forming process 11. From FIG. 15, it can be seen that the fully formed uncurled shell 27 ejects out of the die.

Embodiment 2: A Pressing Die for an Uncurled Shell of a Pressure-Resistant Easy Open End (with Pre-Formed Pressing Die)

(77) As shown in FIG. 16, the pressing die consists of two parts of a lower die 2 and an upper die 1 (see FIG. 16).

(78) The difference between the embodiment 2 and the embodiment 1 is that: the bottom of the upper die core body 20 is different, and the bottom of the upper die core body 20 in the embodiment 1 is flat, and the parts at the bottom of the upper die core body 20 corresponding to the seventh arc portion R7, the fourth straight portion L4 and the eighth arc portion R8 of the uncurled shell are suspended relative to the top of the lower die core body 22 in a closed state.

(79) However, the bottom of the upper die core body 20 in the embodiment 2 is equipped with a downward raised R fillet at the edge (see FIG. 17), that is, the upper die core body 20 is provided with a contour on its bottom corresponding to the eighth arc portion R8 of the uncurled shell, while the parts at the bottom of the upper die core body 20 corresponding to the seventh arc portion R7 and the fourth straight portion L4 of the uncurled shell are suspended relative to the top of the lower die core body 22 in a closed state.

(80) The other structures of the embodiment 2 are the same as that in the embodiment 1, and will not be described repeatedly.

(81) The pressing forming process of the uncurled shell in the embodiment 2 is shown in FIGS. 17 to 27. The whole pressing forming process is similar to the embodiment 1, but there are differences in the forming method. The embodiment 1 is the forming method without pre-formed uncurled shell, while the embodiment 2 is the forming method with pre-formed uncurled shell.

(82) More detailed information can be obtained by comparing the pressing forming process drawings of the two embodiments, which will not be described in detail here.

(83) Compared with the forming method without pre-formed uncurled shell in the embodiment 1, the forming method with pre-formed uncurled shell in the embodiment 2 has the following advantages:

(84) 1. The working pressure of the upper outer forming ring 14 is 30-60 psi, and the working pressure of the upper inner forming ring 32 is 100-130 psi.

(85) During the pre-forming process and in the pressing forming process 5 (FIG. 21 in the embodiment 2 and FIG. 9 in the embodiment 1), the upper outer forming ring 14 and the lower die core ring 4 clamp the outer ring on the uncurled shell blank, while the annular bevel of the bottom end face of the upper inner forming ring 32 contacts the uncurled shell blank and has not yet clamped the middle ring on the uncurled shell blank with the lower die core ring 4.

(86) During the pre-forming process, only the upper outer forming ring 14 compresses the uncurled shell blank, while the upper inner forming ring 32 does not compress the uncurled shell blank. In this state, the material fluidity of the uncurled shell blank is good, so the uncurled shell blank will not become thin during the pre-forming process of the pressing forming process 5.

(87) 2. During the pressing forming process 6 (FIG. 22 in the embodiment 2 and FIG. 10 in the embodiment 1), at this point, both the upper forming ring 14 and the upper inner forming ring 32 compress the uncurled shell blank. In this state, the material fluidity of the uncurled shell blank is poor, and there will be slight thinning of the uncurled shell blank during the forming process.

(88) By adding the pre-forming process, the pre-forming is advanced during the pressing forming process 5, so the forming process of the pressing forming process 6 is reduced to improve the thinning of the uncurled shell blanket.

(89) 3. During the pressing forming process 7 (FIG. 23 in the embodiment 2 and FIG. 11 in the embodiment 1), the uncurled shell blank begins to be formed in reverse. If a structure without pre-forming is used, during the initial stage of reverse forming of the uncurled shell blank, the uncurled shell blank will exert a significant upward thrust on the upper inner forming ring 32.

(90) In order to ensure the stability of the entire forming process, the air pressure acting on the upper inner forming ring 32 shall always be available to make the upper inner forming 32 compress the uncurled shell blank, so a large amount of air pressure needs to be applied to the upper inner forming ring 32.

(91) If a pre-formed structure is used, when the uncurled shell blank starts reverse forming, a part of ferrule has been pre-formed. Throughout the entire reverse forming process, the uncurled shell blank will not exert significant upward thrust on the upper inner forming ring 32. Therefore, compared to the structure without pre-forming, the working pressure of the upper inner forming ring 32 with pre-formed structure is lower, and the lower working pressure can improve the thinning of the uncurled shell blank and increase the service life of the parts.

(92) 4. If a structure without pre-forming is used, during the reverse forming process of the uncurled shell blank, a small bending R fillet (R angular radius less than 0.25 mm) will be formed, ultimately causing slight cracks on the surface of the local area of the fourth straight portion L4 of the uncurled shell of the easy open end, thereby affecting the performance of the uncurled shell of the easy open end.

(93) For the pre-formed structure, the size of the initial bending R fillet during the reverse forming of the uncurled shell blanket can be set by the size of the R angle of the bottom end face of the upper die core body 20, in order to control the minimum bending R angle formed during the reverse forming of the uncurled shell blank, and ensure that the minimum bending R angular radius is greater than or equal to 0.25 mm, to solve the problem of slight cracks on the surface of the local area of the fourth straight portion L4 of the uncurled shell of the easy open end.

(94) It should be noted that the above-described embodiments are only for illustration of technical concept and characteristics of present invention with purpose of making those skilled in the art understand the present invention, and thus these embodiments shall not limit the protection range of present invention.

(95) The equivalent changes or modifications according to spiritual essence of present invention shall fall in the protection scope of present invention.