JP2002120031A - Method and tool for forming smooth neck for thin-walled can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of defective forming such as wrinkles and dents when performing smooth neck-in operation in an opening end part of a thin-walled can. SOLUTION: A necking die 14 in second and subsequent operations is relatively moved in the axial direction of the can to contract a neck part, and a connection point of a curvature part to an inclined part in the can 10 is faced to a forming surface for a connection part in the axial direction of the can 10 and the necking die 14 in the second and subsequent operations is relatively moved in the axial direction of the can 10 further. The curvature part already formed in the previous step is formed in an extended shape to the opening end side of the inclined part, the angle of the tangential line at the point on the forming surface for the connection part facing the connection point with respect to the axis of the can 10 is set to be larger than the angle of the inclined part already formed in the previous step with respect to the axis of the can 10, and the forming is performed by the necking die 14 in the second and subsequent operations.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for molding an open end portion of a can such as a beverage can into a small diameter, and a molding tool used for performing the method.
The present invention relates to a technique for forming a smoothly tied neck-in portion having a continuously changing diameter in multiple steps.

[0002]

2. Description of the Related Art Since a neck-in portion formed at an open end of a can body has a small diameter with respect to a can body, a can lid attached to the open end can be reduced in diameter, and as a result, it is used. This has the effect of saving lid material. Therefore, recently, a smooth neck which is smoothly connected from a shoulder to a neck, where a neck-in portion can be formed with a shorter neck length, has been increasing. As a method for forming a smooth neck, a spinning method and a multi-step die method (for example,
No. 0) is known, but the multi-step die method is more advantageous in terms of the quality of the can, such as having less adverse effect on the coating film on the inner and outer surfaces of the can.

On the other hand, squeezing and ironing cans for beverages are containers developed for gas beverages such as beer and carbonated beverages, which have a positive pressure inside the filled cans. Since the depression is suppressed, the side wall can be made thinner, that is, the weight of the container can be reduced, and the container is widely used as a container capable of saving resources and energy. Also, non-gas beverages such as teas and sports drinks can be used by applying the liquid nitrogen filling method.

[0004] The thickness of the side wall of a commercially available drawn ironing can is, for example, 0.140 to 0.150 mm in the case of a steel can, for example, in a thick portion, that is, a planned neck-in portion. Cost reduction and material saving have become more important than ever, and further weight reduction, that is, thinning of the material and side walls, is desired. However, when the neck-in expected portion is made thinner than the conventional one, there is a problem that the conventional smooth neck molding tends to cause molding defects such as wrinkles and depressions in the neck-in portion.

More specifically, as shown in FIGS. 8A to 8C, when the opening end of the can body 1 is inserted into the necking die 2 and processed into a small diameter, the can body 1 inserted into the necking die 2 is processed. The tip portion of the neck is formed along the inner surface shape of the necking die 2, and the neck at the start of necking where the opening end portion formed in the previous necking step is inserted into the necking die 2 and applied to the knockout punch 15. The tip of the part 11 is curved inward to some extent and reduced in diameter. At this time, a portion which is convex on the outer peripheral side, that is, a falling portion 6 (the average inclination angle θB is smaller than the necking angle θneck) is formed.

As shown in FIG. 8 (B), as the necking die 2 moves relatively in the axial direction of the can body 1, the necking forming progresses, and the fall-down portion 6 having a convex shape on the outer peripheral side is formed. Approaching the inclined portion 5 having the necking angle θneck formed in the previous necking step.

In the final step shown in FIG. 8 (C), since the average inclination angle .theta.B is smaller than the necking angle .theta.neck, a falling part 6 is formed. When the falling part 6 remains inside the can until the final step, this falling part The extra thickness of 6 causes a compressive stress in the circumferential direction, and there is a problem that molding defects such as wrinkles and depressions are likely to occur in the neck-in portion 3.

The inventor of the present invention has already proposed a shape of a necking die for solving such a molding failure in the Journal of the Japan Society for Technology of Plasticity “Plasticity and Processing”, Vol. 39, No. 444. The content of the proposal here is to form a first machining surface having an inclination angle substantially equal to the necking angle following the cylindrical portion on the tip end side of the necking die, and to form the first machining surface following the first machining surface. Is provided with a larger second processing surface, and the cylindrical portion and the first processing surface, and the connecting portion between the first processing surface and the second processing surface are formed in a necking die shape having an arc surface so that no edge is generated. is there.

[0009]

Problems to be Solved by the Invention JP-A-6-25 mentioned above.
The shape of the necking die described in No. 4640 is
In order to prevent the buckling of the trunk, even if the positional accuracy of the necking die and the height accuracy of the neck portion vary, the necking die and the can body neck-in forming part are The shape is such that a gap is formed between them. However, the shape described in this publication does not include a portion that acts to eliminate the molding defect caused by the so-called collapsed portion described above.
It is difficult to reliably eliminate molding defects such as wrinkles and depressions generated in the final stage of neck-in processing.

In the necking die shape proposed by the present inventor, the neck-in expected portion is 0.140 to
0.150mm, the diameter reduction of the opening per process is ΔD
= 0.9 to 1.0 mm, it is possible to suppress molding defects. However, in order to reduce the number of steps and reduce equipment costs, the diameter of each step is increased or the neck is reduced. When the in-scheduled portion is thinned, molding defects such as wrinkles and depressions may still occur, and there is room for further improvement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems, and prevents molding defects such as wrinkles and depressions caused by the neck portion falling down at the start of smooth necking molding, and reduces the necking speed. Even if it is fast, it makes it difficult for the torso to buckle, and furthermore, the planned neck-in part is thinned,
Another object of the present invention is to provide a smooth neck molding method capable of preventing molding defects such as wrinkles even when the diameter reduction amount per process ΔD is increased to 1.20 mm, and a molding tool used in the method. It is.

[0012]

Means for Solving the Problems and Action There are three major steps in forming a smooth neck-in part whose diameter gradually changes in the opening end of a can body by using a necking die in a processing step. be able to. The first step is a neck forming initial step from the time when the open end of the can body comes into contact with the necking die to the time when it comes into contact with the knockout punch, and the second step is to carry out the neck-in part following the first step. The process of extending in the direction parallel to the axis of the can body,
The third step is a step in which the neck-in portion being formed following the second step is smoothly joined to the neck inclined portion formed up to the previous necking step. Attention is paid to the fact that wrinkles and depressions may occur in the third step, that is, in forming the joint portion, even when no trouble occurs in the first and second steps, and a method for suppressing the molding failure is eagerly studied. As a result of research, the present invention has been accomplished.

That is, in the first aspect of the present invention, a relative axial movement is caused between the bottomed cylindrical can and the first necking die to reduce the open end of the bottomed cylindrical can. After the neck-in portion is formed by diameter reduction, the neck-in portion is subjected to diameter reduction processing from the opening end side by the second and subsequent necking dies, so that the neck portion at the opening end side has a curvature portion, an inclined portion, and a shoulder. In the method for forming a smooth neck for a thin-walled can, in which the portions are smoothly formed continuously, the necking die for the second and subsequent rounds is formed continuously with a cylindrical portion having an inner diameter smaller than the neck-in portion and in the axial direction of the cylindrical portion. And the inner diameter of the can gradually increases and becomes convex toward the center axis side of the can. Convex to the center axis side Becomes formed in a shape and a connecting portion for working surface including the second convex arc portion of the small radius of curvature than the radius of curvature of the first convex arcuate portion, the distal end portion of the neck,
A first step of contacting the knockout punch after contacting the first convex arc portion, and a second step of relatively moving the necking die of the second and subsequent times in the axial direction of the can to reduce the diameter of the neck. The second and subsequent necking dies in a state where the connection point between the curvature portion and the inclined portion in the can is opposed to the joint surface in the axial direction of the can. A third step of forming the curvature portion, which has already been formed in the previous step, into an extended shape toward the opening end side of the inclined portion by moving the curvature portion relatively further in the direction, and facing the connection point. The angle of the tangent to the central axis of the can at the point on the joint surface processing surface is larger than the angle of the inclined portion already formed in the previous step with respect to the central axis of the can. A smooth neck molding method for thin cans and performing processing by necking dies.

Therefore, according to the first aspect of the present invention, the second
In the case of performing the joint forming by the second or later necking process, of the neck-in portion formed by the first necking die, the cross-section passing through the center axis of the first necking die has a convex inside the can near the reduced diameter neck portion. In the step of shaping the portion having the curvature portion so that the inclined portion located between the central axis of the necking die, the shoulder portion of the neck-in portion, and the curvature portion is extended, the tip of the neck portion is formed by the joint forming in the third process. A point where the portion contacts the necking die of the first convex arc portion and an outwardly convex curved portion formed when the tip portion of the neck contacts the necking die of the first convex arc portion and is reduced in diameter, that is, The falling portion moves while contacting the first convex arc portion, and the radius of curvature of the second convex arc portion formed following the first convex arc portion is smaller than that of the first convex arc portion. Back to the axial direction of Since the degree of is larger than the first projected circular-section, the inclination angle of the tilting part (typically an angle corresponding to a half of the die half angle of necking die is)
However, it is possible to quickly approach the angle of the already formed inclined portion, and at the end of the joint forming, the connecting portion between the falling portion and the inclined portion is smoothly formed. Further, a tangent angle at a point located on the second convex arc portion opposite to a connection point between the curvature portion and the inclined portion of the neck-in portion is a can center axis of the inclined portion formed in the previous necking step. And the inclination angle of the falling part generated during the joint forming in the third process gradually increases, and in the final stage of the joint forming, the inclination angle becomes the can center of the already formed inclined part. Since the angle formed with the axis, that is, the angle of the inclined portion, is substantially the same, the falling portion is not pushed inward by the already formed inclined portion, so that molding defects such as wrinkles and depressions of the neck-in portion are made. Is suppressed or prevented.

According to a second aspect of the present invention, in the first aspect of the present invention, the angle formed between the tangent line and the central axis of the can is 1.degree. Of the angle of the inclined portion with respect to the central axis of the can.
A smooth neck forming method for thin cans, characterized in that the ratio is 5 to 2.7 times.

According to the second aspect of the present invention, the tangent angle is 1.5 to 2.7 times the angle formed by the inclined portion and the center axis of the can. Can be caused up to the angle formed by the inclined part and the center axis of the can, so that the inclined part can be gradually enlarged, and the inclined part is located inside the already formed inclined part. Since it is not pushed in, it can be formed into a smooth neck-in shape even when the thickness of the neck-in expected portion is small.

If the tangent angle is smaller than 1.5 times,
It is not preferable because wrinkles and the like easily occur at the end of the joint forming due to the influence of the falling part generated at the neck-in start part.
On the other hand, if the tangent angle is larger than 2.7 times, the tangent angle substantially exceeds 90 degrees, which is not preferable.

According to a third aspect of the present invention, there is provided a bottomed cylindrical can and a first can.
A neck-in portion is formed by causing a relative axial movement between the neck-in portion and the necking die to reduce the diameter of the open end portion of the bottomed cylindrical can. A smooth neck forming tool for a thin-walled can formed by performing a diameter reducing process with a necking die of the second and subsequent times from the neck on the opening end side so as to smoothly and continuously form a curved portion, an inclined portion, and a shoulder portion, A connecting portion processing surface for reducing the diameter of a connecting portion extending from the neck portion to the inclined portion; the connecting portion processing surface is formed in a cylindrical portion into which the neck portion is inserted, and the cylindrical portion is formed continuously in the axial direction; A first convex arc portion that is convex toward the central axis side of the can by gradually increasing the inner diameter, and a shape that is convex toward the central axis side of the can following the maximum outer diameter portion of the first convex arc portion. Formed and of the first convex arc portion The smaller radius of curvature than the rate radius 2
A smooth neck forming tool for a thin can, comprising a convex arc portion.

According to the third aspect of the present invention, the curved portion protruding inside the can near the reduced diameter neck is shaped so that the inclined portion located between the shoulder of the neck-in portion and the curved portion is extended. In the joint forming, the outwardly convex curved portion formed when the tip portion of the neck portion is reduced in diameter by contacting the necking die of the first convex arc portion, that is, wrinkles or depressions of the neck-in portion due to the falling portion. By suppressing the occurrence of such factors, the amount of diameter reduction per smooth neck molding process can be increased, and thus the number of processes can be reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described based on a specific example shown in the drawings. FIG. 1 is a partial cross-sectional view showing a shape of a necking die in a smooth neck forming tool, and FIG. 2 is a partial cross-sectional view schematically showing a state of joint forming when a smooth neck forming tool is used.

The can 10 molded by the molding tool of the present invention is, for example, a DI can having a shape shown in FIG. FIG. 3 (B) shows a can in the middle of molding in which the neck portion 11 and the neck-in portion 13 are formed by reducing the diameter of the opening end portion, and FIG. 3 (C) shows the molding through a plurality of necking molding steps. Fig. 6 shows a smooth neck molded can having a smoothed neck portion 11C and a smooth neck portion 13C. And
The present invention forms a smooth neck portion 13C having a smoothly continuous, smoothly wrinkled or stepless connecting portion from a neck portion 11C connecting the neck portion 11C and a so-called main body side wall portion 12 of the can 10. The present invention relates to a method for forming a smooth neck for thin cans and a forming tool used for the method.

The smooth neck molding of the can shown in FIG. 3 (C) uses the necking die 14 and the knockout punch 15 shown in FIG. It is carried out after being transformed. The forming tool according to the present invention is used in the second and subsequent necking moldings, and is characterized by the shape of the processing surface of the necking die 14.

FIGS. 1 and 4 schematically show a method of forming a smooth neck for a thin-walled can and a main part of a forming tool used for the method. The inner periphery of a necking die 14 into which the open end of the can 10 is inserted. A knock-out punch 15 is disposed in which the open end of the can 10 is brought into contact with the side and the molded can 10 is pushed out from the necking die 14. The knockout punch 15 has a portion corresponding to a core 16 that is inserted into the open end of the can 10 and regulates the inner diameter of the open end of the can 10.

On the opening end side of the can 10 formed in the previous necking step, as shown in FIGS. 3B and 4, a substantially cylindrical neck portion 11 in the middle of forming is formed. The subsequent neck-in portion 13 is inclined so as to be gently connected from the shoulder portion 21 to the neck portion 11 having the neck portion 22 reduced in diameter. The necking die 14 includes a cylindrical portion 17 forming the neck portion 11 and a cylindrical portion 17.
To the section along the generating line, ie, the necking die 14
A first convex arc portion 18 whose cross section on a plane passing through the central axis is curved convexly toward the center line side, and a second convex arc portion 19 following the first convex arc portion 19 are provided as described later. This second convex arc portion 19
The section along the generatrix, that is, the section passing through the central axis is convex toward the center line and inscribed in the first convex arc portion 18 to form an arc surface whose inner diameter gradually increases, and has a radius of curvature. R2 is the radius of curvature R of the first convex arc portion 18.
Radius less than 1.

The inner diameter of the first convex arc portion 18 is
7 and is connected to the cylindrical portion 17 at the end on the minimum diameter side. The inner diameter of the first convex arc portion 18 is such that the cross section along the generating line is an arc-shaped processed surface having a predetermined radius of curvature R1. The first convex arc portion 18 and the subsequent second convex arc portion 19 have a center angle θ1 set to a predetermined angle (30 degrees in this example).
The first convex arc portion 18 and the second convex arc portion 19 are inscribed at the position, and the two arc-shaped machining surfaces are formed as smooth neck portion machining surfaces, that is, joint portion machining surfaces.

Further, as shown in FIG. 1, the tangent angle θ2 at a point K of a predetermined size r2 (which will be described later) in the radial direction from the inner surface of the cylindrical portion 17 in the second convex circular arc portion 19 is determined. The curvature radius R of the second convex arc portion 19 is set to be larger than the necking angle θneck (the inclination angle of the neck-in portion 13 formed in the previous necking step).
2 is defined.

As described above, in the process of extending the neck-in molding portion in the axial direction, at the start of neck-in, the average inclination angle with respect to the center axis is determined by the necking die 1.
The inventor of the present invention has already published in the Journal of the Japan Society for Technology of Plasticity “Plasticity and Processing” Vol. 39, No. 444, but has conducted further studies. As a result, the point at which the tangent angle begins to become smaller than the angle θneck formed with the center axis of the inclined portion 20 that has been subjected to necking up to the diameter of the neck-in portion 13 formed at the previous stage, that is, the diameter of the neck-in portion 13 formed at the previous necking step. Q, in other words, the cylindrical portion 17 at a point Q corresponding to a connection point between the curvature portion P and the inclined portion 20 that protrude inward in the neck-in portion 13.
If the radial distance from the inner surface of the cylindrical portion 17 is r2, the tangent angle .theta.2 at the point K at the machining surface of the second convex arc portion 19 at the radial distance r2 from the inner surface of the cylindrical portion 17
It was found that it was important to make the necking angle larger than the necking angle θneck in forming the smooth neck. It is important to set these angle ratios (θ2 / θneck) in the range of 1.5 to 2.7, and preferably 2.0 to 2.1. When the angle ratio is smaller than 1.5, the influence of the so-called fall-down portion 6 generated at the neck-in start portion as shown in FIG. 8 tends to remain until the end of the joint forming as the third step of the neck-in forming, In the case of a steel thin can having a thickness of, for example, 0.120 mm or an aluminum thin can having a thickness of 0.130 mm at the neck-in expected portion, molding defects such as depression and wrinkles are likely to occur in the smooth neck-in portion. Also,
On the other hand, since the necking angle of the can is 28 to 33 degrees, which is preferably used from the viewpoint of moldability and buckling resistance,
When the tangent angle θ2 of the joint processing surface at the end of the smooth neck forming joint forming operation is larger than 2.7 times the necking angle θneck, the tangent angle θ2 of the joint processing surface of the smooth neck forming tool is substantially 90.
This is not only impractical, but also makes it difficult to shape the curvature portion P formed in the previous necking step so that the inclined portion 20 is extended in the third step of forming the joint portion, so that the neck portion becomes difficult. It is not preferable because traces of molding become conspicuous in the in-portion. Therefore, in order to smoothly perform the joint forming, the tangent angle θ2 of the processing surface at the time when the joint forming of the necking die 14 is completed needs to be set to 1.5 to 2.7 times the necking angle θneck. Yes, if the thickness of the neck-in planned part is thin,
Preferably, it is 2.0 times to 2.1 times.

Here, the relationship between the above dimensions and angles is as follows. First, the radial distance A between the portion of the circular arc of the second convex circular arc portion 19 closest to the central axis and the inner surface of the cylindrical portion 17 is as follows: A = R1 -R2-(R1 -R2) cos θ1 = r2- Since R2 (1−cos θ2), the radius of curvature R2 of the second convex arc portion 19 is R2 = {r2−R1 (1−cosθ1)} / (cosθ1−co)
sθ2). Since r2 is r2 = .DELTA.D / 2 + R1 (1-cos .theta.neck) (.DELTA.D is the amount of diameter reduction per process), the radius of curvature R1 of the first convex circular arc portion 18 and the common tangent of each convex circular arc portion 18, 19 are obtained. , The center angle θ1 of the first convex arc portion 18 and the necking angle θneck, and the tangent angle θ2 at the point r2 in the radial direction from the inner surface of the cylindrical portion 17 in the second convex arc portion 19.
Then, the radius of curvature R2 of the second convex arc portion 19 is obtained by giving the diameter reduction amount ΔD per process.

As shown in FIGS. 5 to 7, the necking die 14 is relatively moved in the axial direction of the can 10, so that the neck-in portion 13 formed in the previous necking step is formed.
As shown in FIG. 6, the tip of the neck portion contacts the knock-out punch 15 after contacting the first convex arc portion 18, and the falling portion 6 having a convex shape on the outer peripheral side generated at that time is formed by neck forming as shown in FIG. 6. The process proceeds to reach a step (FIG. 7) of connecting the fallen portion 6 to the inclined portion 20 of the neck-in portion 13 already formed in the previous necking step. In that case, the falling part 6 approaches the inclined part 20 of the necking angle θneck formed in the previous necking step, and finally,
It is raised and shaped on the outer peripheral side so as to become the inclined portion 20 of the necking angle θneck. In the above necking die 14 according to the present invention, the second convex arc portion 1 facing the point Q
9 at the point K is the necking angle θnec
Since k is 1.5 times to 2.7 times k, as shown in the middle of the forming in FIG. 6, when the falling portion 6 is formed on the processing surface of the first convex arc portion 18 of the necking die 14. Then, the falling portion 6 is gradually caused to become the inclined portion 20 of the neck-in portion 13 formed in the previous necking step. At that time, the contact point (the point at which the tip of the neck contacts the necking die 14 of the first convex arc portion 18) moves from the first convex arc portion 18 to the second convex arc portion 19, so that the falling portion 6 Since the average inclination angle θB can be made closer to the angle of the already formed inclined portion 20, the average inclination angle θB of the falling part 6 can be raised up to the necking angle θneck. That is, the rise of the average inclination angle θB can be increased. FIG. 7 shows the necking angle θneck and the average inclination angle θB of the falling part 6.
Are the same as in the last stage in which the falling part 6 disappears. In the final stage of forming the joint part in the third process, the average inclination angle θB of the falling part 6 is gradually raised to the necking angle θneck. The second convex arc portion 19
Is retracted from the inclined part 20 of the neck-in part 13, so that the rising of the falling part 6 can be increased. Therefore, in the final stage of forming the connecting portion, the fall-in portion 6 can be eliminated from the neck-in portion 13, so that the neck-in portion 1 in which the fall-in portion 6 is already formed is formed.
No longer being pushed into the can from the inclined portion 20 of 3, the molding defects such as wrinkles and depressions are suppressed or prevented at the neck-in portion.

In the embodiment of the present invention, the forming of the connecting portion in the third stroke is performed by the first convex arc portion 18 and the second convex arc portion 19.
The processing surface is simplified by performing the processing with the following configuration. However, the present invention is not limited to this, and a straight line portion is partially formed between the first convex circular arc portion 18 and the second convex circular arc portion 19. A similar purpose can be achieved even if the processing surface includes the processing surface or the processing surface including the second convex arc portion 19 having a plurality of radii of curvature.

Next, examples and comparative examples performed to confirm the effects of the present invention will be described.

[Example 1] The steel thickness of the neck-in expected portion is 0.1
A can having a nominal diameter of 211 (outer diameter of the tightening portion when the can lid is directly tightened is 2 + 11/16 inches) which is drawn and ironed to a height of 30 mm and trimmed to a predetermined height can be smoothly processed according to the present invention. Nominal 2 in 7 steps using a neck forming tool
06 diameter (the outer diameter of the tightened part when the can lid is tightened is 2 + 6 /
Die smooth neck-in processing was attempted up to 16 inches). Molding was possible without forming defects such as wrinkles and depressions.

[0032]

Example 2 The steel thickness of the neck-in expected portion is 0.1
Using a smooth neck forming tool of the present invention, a can body with a nominal diameter of 211 mm, which was drawn and ironed to 30 mm and trimmed to a predetermined height, was subjected to die smooth neck-in processing to a nominal diameter of 204 in nine steps. Was. Molding was possible without forming defects such as wrinkles and depressions.

[0033]

Embodiment 3 The steel thickness of the neck-in expected portion is 0.1
Using a smooth neck forming tool of the present invention, a can body having a nominal diameter of 211 mm, which is drawn to an iron diameter of 30 mm and trimmed to a predetermined height, is subjected to die smooth neck-in processing to a nominal diameter of 202 in 11 steps. Was. Molding was possible without forming defects such as wrinkles and depressions.

[0034]

Embodiment 4 The steel thickness of the neck-in expected portion is 0.1
Using a smooth neck forming tool of the present invention, a die with a nominal diameter of 211 mm, which was drawn and ironed to 20 mm, trimmed to a predetermined height, and attempted die smooth neck-in processing to a nominal diameter of 206 in 7 steps. Was. Molding was possible without forming defects such as wrinkles and depressions.

[0035]

[Embodiment 5] The steel thickness of the neck-in expected portion is 0.1.
Using a smooth neck forming tool of the present invention, a can body having a nominal diameter of 211 mm, which was drawn and ironed to 20 mm and trimmed to a predetermined height, was subjected to die smooth neck-in processing to a nominal diameter of 204 in nine steps. Was. Molding was possible without forming defects such as wrinkles and depressions.

[0036]

Embodiment 6 The steel thickness of the neck-in expected portion is 0.1
Using a smooth neck forming tool of the present invention, a can body having a nominal diameter of 211 mm trimmed to a predetermined height by drawing-ironing to 20 mm and attempting die-smooth neck-in processing to a nominal 202 diameter in 11 steps. Was. Molding was possible without forming defects such as wrinkles and depressions.

[0037]

[Comparative Example 1] The steel thickness of the neck-in expected portion is 0.1
A can body having a nominal diameter of 211 and trimmed to a predetermined height by drawing-ironing to 20 mm, and the tangent angle at the point where the joining is completed is 1.3 of the necking angle θneck.
Using a 5 times smooth neck forming tool, die smooth neck-in processing was attempted to a nominal 202 diameter in 11 steps.
As a result, depressions in the neck-in portion and wrinkles in the neck portion were scattered, and good moldability was not obtained.

[0038]

As described above, according to the method for forming a smooth neck for a thin-walled can of the present invention and the forming tool used in the same, even if the planned neck-in portion is considerably thin, the diameter of the neck-in process can be reduced. Is large, it is possible to satisfactorily perform smooth neck molding without generating defects such as wrinkles and depressions in the neck-in portion. Therefore, according to the present invention, material resources can be further reduced by reducing the thickness of the planned neck-in portion and reducing the diameter of the neck-in portion.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a shape of a necking die in a smooth neck forming tool according to the present invention.

FIG. 2 is a partial cross-sectional view schematically showing a state of joint forming when the smooth neck forming tool according to the present invention is used.

FIG. 3 is a view showing a shape of a can body before neck-in processing and a shape of a can body subjected to smooth neck-in processing.

FIG. 4 is a schematic partial cross-sectional view showing one of the processing steps of the smooth neck-in processing.

FIG. 5 is a partial cross-sectional view schematically showing an initial state of a working process by the necking die of the present invention.

FIG. 6 is a partial cross-sectional view schematically showing an intermediate state in a processing process by the necking die of the present invention.

FIG. 7 is a partial cross-sectional view schematically showing a final state of a working process by the necking die of the present invention.

FIG. 8 is a partial cross-sectional view schematically showing a state of molding failure caused by a conventional necking die.

[Explanation of symbols]

10: can, 11: neck, 12: body, 1
3 ... neck-in part, 14 ... necking die, 17 ... cylindrical part, 18 ... first convex arc part, 19 ... second convex arc part,
R1... (Radius of curvature of the first convex arc portion) R2.
The radius of curvature (of the convex arc).

Claims (3)

[Claims] 1. A neck-in part by causing relative axial movement between a bottomed cylindrical can and a first necking die to reduce the diameter of the open end of the bottomed cylindrical can. After forming, the neck-in portion is reduced in diameter by the second and subsequent necking dies from the opening end side, so that the curvature portion, the inclined portion, and the shoulder portion are smoothly continued from the neck on the opening end side. In the method for forming a smooth neck for a thin-walled can, the second and subsequent necking dies are formed continuously with a cylindrical portion having an inner diameter smaller than the neck-in portion and in the axial direction of the cylindrical portion, and the inner diameter gradually increases. A curved surface processing surface comprising a first convex arc portion which becomes convex on the central axis side of the can by doing, and a convex on the central axis side of the can following the maximum outer diameter portion of the first convex arc portion. Formed into a shape A connecting surface including a second convex arc portion having a radius of curvature smaller than the radius of curvature of the first convex arc portion; and a knockout punch after the tip of the neck is brought into contact with the first convex arc portion. A second step of relatively moving the second and subsequent necking dies in the axial direction of the can to reduce the diameter of the neck; and a curvature section and the inclination in the can. By further moving the second and subsequent necking dies relatively in the axial direction of the can in a state where the connection point with the part faces the processing surface for the connecting portion in the axial direction of the can, And a third step of forming the curvature portion, which has already been formed, into an extended shape toward the opening end side of the inclined portion, wherein a tangent line at a point on the joint portion processing surface facing the connection point is formed. On the center axis of the can A smooth neck forming process for the thin-walled can, characterized in that the angle of the inclined portion formed in the previous step is made larger than the angle with respect to the center axis of the can, and the second and subsequent necking dies are used for the processing. Method. 2. An angle between the tangent and the central axis of the can is 1.5 to 2.7 times the angle of the inclined portion with respect to the central axis of the can.
The method for forming a smooth neck for a thin-walled can according to the above. 3. A neck-in part by causing a relative axial movement between the bottomed cylindrical can and the first necking die to reduce the diameter of the open end of the bottomed cylindrical can. After forming, the neck-in portion is reduced in diameter by the second and subsequent necking dies from the opening end side, so that the curvature portion, the inclined portion, and the shoulder portion are smoothly continued from the neck on the opening end side. In a smooth neck forming tool for a thin can that is formed by molding, a connecting portion processing surface for reducing the diameter of a connecting portion extending from the neck portion to the inclined portion, the connecting portion processing surface is a cylindrical portion into which the neck portion is inserted, A first portion which is formed in the cylindrical portion in the axial direction and which is convex toward the central axis of the can by increasing the inner diameter gradually;
A second portion having a convex arc portion and a radius of curvature smaller than the radius of curvature of the first convex arc portion, the second arc portion being formed to be convex toward the center axis side of the can following the maximum outer diameter portion of the first convex arc portion; A smooth neck forming tool for thin cans, comprising a convex arc portion.