JP4573985B2 - Smooth neck molding method and tool for thin-walled cans - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molding method for molding an opening end portion of a can such as a beverage can into a small diameter and a molding tool used for executing the method, and in particular, the diameter is connected smoothly and continuously. The present invention relates to a technique for forming a neck-in portion in multiple steps.
[0002]
[Prior art]
Since the neck-in portion formed at the opening end of the can body is small in diameter relative to the can body, the can lid attached to the opening end can be reduced in diameter, thereby saving the lid material to be used. effective. For this reason, recently, the number of smooth necks that are gently connected from the shoulder to the neck where a neck-in portion can be formed with a shorter neck length has increased. As a method for forming a smooth neck, a spinning method and a multi-step die method (for example, a method described in JP-A-6-254640) are known, but the multi-step die method is more suitable for coating the inner and outer surfaces of the can body. This is advantageous in terms of the quality of the can, such as having a small adverse effect.
[0003]
On the other hand, squeezed and squeezed cans for beverages have been developed for gas beverages where the inside of cans after filling such as beer and carbonated beverages has a positive pressure, and in this type of cans, the depression inside the side walls is suppressed by the pressure inside the cans. Therefore, the side wall can be thinned, that is, the container can be reduced in weight, and is widely used as a container that can save resources and energy. It can also be used for non-gas beverages such as teas and sports drinks by applying the liquid nitrogen filling method.
[0004]
In the case of a steel can, the side wall thickness of a squeezed iron can that is currently on the market is, for example, 0.140 to 0.150 mm at a thick portion, that is, a neck-in planned portion. Material saving has become more important than ever, and further weight reduction, that is, thinner material and sidewalls, is desired. However, when the neck-in planned 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.
[0005]
That is, as shown in FIGS. 8A to 8C, when the opening end of the can 1 is inserted into the necking die 2 and processed into a small diameter, the tip of the neck of the can 1 inserted into the necking die 2 The portion is formed along the inner surface shape of the necking die 2, and when the necking start point when the opening end portion formed in the previous necking step is inserted into the necking die 2 and applied to the knockout punch 15 is started. The tip is curved inward to some extent and is reduced in diameter. A convex portion on the outer peripheral side generated at that time, that is, a tilted portion 6 (average inclination angle θB is smaller than necking angle θneck) is formed.
[0006]
As shown in FIG. 8B, when the necking die 2 moves relatively in the axial direction of the can body 1 and the necking molding proceeds, the collapsed portion 6 that protrudes toward the outer peripheral side is It approaches the inclined portion 5 of the necking angle θneck formed in the necking step.
[0007]
In the final process shown in FIG. 8 (C), the average tilt angle θB is smaller than the necking angle θneck, so that a collapsed portion 6 is formed. If the collapsed portion 6 remains inside the can until the final process, the remaining portion of the collapsed portion 6 is left. There is a problem that compressive stress is generated in the circumferential direction due to the meat, and molding defects such as wrinkles and depressions are likely to occur in the neck-in portion 3.
[0008]
The present inventor has already proposed the shape of a necking die for eliminating such a molding defect in the Journal of Plasticity Processing, Vol. 39, No. 444.
The content of the proposal here is to form a first machining surface having an inclination angle substantially the same as the necking angle following the cylindrical portion on the tip portion side of the necking die, and to provide an inclination angle following the first machining surface. Is a necking die shape in which a larger second machining surface is provided, and the connecting portion between the cylindrical portion and the first machining surface and between the first machining surface and the second machining surface is an arc surface so that no edge is generated. is there.
[0009]
[Problems to be solved by the invention]
The shape of the necking die described in the above-mentioned Japanese Patent Application Laid-Open No. 6-254640 is the case where the neck portion is buckled even when the position accuracy in which the necking die is pushed to the maximum and the height accuracy of the neck portion vary. In order to prevent this, a shape in which a gap is generated between the necking die and the can body neck-in molded part is formed. However, the shape described in this publication does not have a portion that acts to eliminate the molding defects caused by the so-called collapsed portion described above, so molding such as wrinkles and depressions that occur in the final stage of neck-in processing. It is difficult to reliably eliminate the defects.
[0010]
Further, in the necking die shape already proposed by the present inventor, the neck-in planned portion is 0.140 to 0.150 mm in the conventional case, and the diameter reduction amount per step of the opening is ΔD = 0.9 to 1.0 mm. If it is so small, molding defects can be suppressed, but in order to reduce the number of processes and reduce equipment costs, when the diameter reduction amount for each process is increased or when the neck-in scheduled part is thinned However, molding defects such as wrinkles and depressions still occurred, and there was room for further improvement.
[0011]
The present invention has been made paying attention to the technical problems described above, and prevents molding defects such as wrinkles and depressions caused by the collapse of the neck portion that occur at the start of smooth necking molding, even if the necking speed is high. Smooth neck that makes it difficult to buckle the body part, and that can reduce molding defects such as wrinkles even if the neck-in planned part is thinned and the diameter reduction per process ΔD is increased to 1.20 mm. An object of the present invention is to provide a forming method and a forming tool used in the forming method.
[0012]
[Means for Solving the Problem and Action]
Using a necking die, the process of forming a smooth neck-in portion in which the diameter gradually changes in a sequential processing step at the opening end portion of the can body can be roughly classified into three. The first stroke is a neck forming initial stroke from when the open end of the can body contacts the necking die until it contacts the knockout punch, and the second stroke is the neck-in portion following the first stroke. The process of extending in a direction parallel to the axial direction of the can body, the third process smoothly connects the neck-in part being formed to the neck inclined part formed up to the previous necking process following the second process. In the smooth neck molding of thin-walled cans, the present inventor may cause wrinkles and depressions in the third stroke, that is, the joint molding, even if no problems occur in the first and second strokes. As a result of diligent research on a method for suppressing molding defects, focusing on a certain point, the present invention has been achieved.
[0013]
That is, according to the first aspect of the present invention, a relative axial movement is generated between the bottomed cylindrical can and the first necking die, and the opening end portion of the bottomed cylindrical can is reduced in diameter. After the neck-in portion is formed, 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 curvature portion, the inclined portion, and the shoulder portion are gently formed from the neck portion on the opening end side. In the smooth neck molding method for thin-walled cans that are continuously molded, the second and subsequent necking dies are formed continuously with the cylindrical portion having an inner diameter smaller than the neck-in portion, and the axial direction of the cylindrical portion. Is increased to the central axis side of the can, and the curved surface of the first convex arc portion is convex to the central axis side of the can, and the maximum outer diameter portion of the first convex arc portion is followed by the central axis side of the can. In a shape that becomes convex And a machining surface for a linking part including a second convex arc part having a radius of curvature smaller than the curvature radius of the first convex arc part, the tip part of the neck part being brought into contact with the first convex arc part A first stroke to be brought into contact with the knockout punch later, a second stroke in which the necking die after the second time is moved relatively in the axial direction of the can to reduce the diameter of the neck, and the curvature portion in the can And further moving the second and subsequent necking dies relatively in the axial direction of the can in a state where the connection point between the inclined portion and the inclined portion faces the work surface for the connecting portion in the axial direction of the can. A point on the work surface for the joint portion that is formed by a third step of forming the curved portion already formed in the previous step into an extended shape of the inclined portion toward the opening end side, Of the tangent of the can Smoothing for thin-walled cans, characterized in that the angle with respect to the center axis is made larger than the angle with respect to the central axis of the can of the inclined portion that has already been formed in the previous step, and the second and subsequent necking dies are used for processing. This is a neck forming method.
[0014]
Therefore, according to the first aspect of the present invention, in the case where the joining is formed by the second or subsequent necking, in the section passing through the central axis of the first necking die among the neck-in portions formed by the first necking die. In the process of shaping the portion having a curvature portion that protrudes inside the can near the reduced diameter neck portion so that the inclined portion located between the central axis of the necking die and the shoulder portion and the curvature portion of the neck-in portion extends. When the tip of the neck comes into contact with the necking die of the first convex arc part and the tip of the neck comes into contact with the necking die of the first convex arc part in the joint forming of the third step, and the diameter is reduced. The outwardly convex curved portion, that is, the falling portion moves while contacting the first convex arc portion, but the curvature radius of the second convex arc portion formed subsequent to the first convex arc portion is Smaller than the first convex arc Since the degree of retraction with respect to the axial direction of the can is larger than that of the first convex arc portion, the inclination angle of the falling portion (generally an angle corresponding to half the die half angle of the necking die) is It becomes possible to quickly approach the angle of the already formed inclined portion, and the connecting portion between the falling portion and the inclined portion is smoothly formed at the end of the connecting forming. Further, the tangent angle at the point located on the second convex arc portion facing the connection point between the curvature portion and the inclined portion of the neck-in portion is the can center axis of the inclined portion formed in the previous necking step. Therefore, the inclination angle of the fold-down portion generated during the joint molding in the third stroke is gradually increased, and the inclination angle is the center of the can of the already-formed slope portion at the final stage of the joint molding. Since the angle formed with the axis, that is, the angle of the inclined portion is almost the same, the collapsed portion is not pushed inward by the already formed inclined portion, so molding defects such as wrinkles and depressions in the neck-in portion Is suppressed or prevented.
[0015]
According to a second aspect of the present invention, in the first aspect of the present invention, an angle formed by the tangent line and the central axis of the can is 1.5 times to 2.7 times an angle of the inclined portion with respect to the central axis of the can. It is a smooth neck molding method for thin-walled cans characterized by being doubled.
[0016]
According to the invention of claim 2, since the tangential angle is 1.5 to 2.7 times the angle formed by the can center axis of the inclined portion, the collapse occurs during the joint molding in the third stroke. The inclination angle of the part can be caused to the angle formed by the can center axis of the inclination part, so that the falling part can be gradually increased, and the falling part is pushed inward from the already formed inclined part. Therefore, even if the neck-in planned portion is thin, it can be formed into a smooth neck-in shape.
[0017]
If the tangential angle is smaller than 1.5 times, wrinkles are likely to occur at the end of joining molding due to the influence of the fall-down portion generated at the neck-in start portion, which is not preferable. On the other hand, when the tangent angle is larger than 2.7 times, the tangential angle substantially exceeds 90 degrees, which is not preferable.
[0018]
According to a third aspect of the present invention, a relative axial movement is generated between the bottomed cylindrical can and the first necking die, and the opening end portion of the bottomed cylindrical can is reduced in diameter. After forming the in part, by applying a diameter reduction process to the neck in part from the opening end side with the necking die for the second and subsequent times, the curvature part, the inclined part and the shoulder part from the opening end side gently It is a smooth neck forming tool for thin-walled cans that is formed continuously, and has a connecting portion processing surface for reducing the diameter of the connecting portion from the neck portion to the inclined portion, and the connecting processing surface inserts the neck portion. A cylindrical portion, a first convex arc portion formed on the cylindrical portion continuously in the axial direction and projecting toward the central axis side of the can as the inner diameter gradually increases, and a maximum outer diameter of the first convex arc portion Convex to the center axis side of the can It is smooth neck molding tool thin cans, characterized in that a second projected circular portions of small radius of curvature than the radius of curvature of the formed in a shape and the first projected circular portion.
[0019]
According to the invention of claim 3, at the time of joint molding in which the curved portion convex toward the inside of the can near the reduced diameter neck portion is shaped so that the inclined portion located between the shoulder portion and the curved portion of the neck-in portion extends. When the tip of the neck is brought into contact with the necking die of the first convex arc portion and the diameter thereof is reduced, an outwardly convex curved portion, that is, occurrence of wrinkles or depression of the neck-in portion accompanying the falling portion Since the amount of diameter reduction per one smooth neck forming step can be increased by suppressing the number of steps, the number of steps can be reduced.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described based on specific examples shown in the drawings. FIG. 1 is a partial cross-sectional view showing the 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.
[0021]
A can 10 formed with the forming tool of the present invention is a DI can having a shape shown in FIG. 3A, for example, and is a cylindrical body with a bottom. FIG. 3B shows a can in the middle of forming the neck portion 11 and the neck-in portion 13 by reducing the diameter of the opening end portion, and FIG. 3C shows the molding through a plurality of necking molding steps. A smooth neck molded can having a neck portion 11C and a smooth neck portion 13C. And this invention changes smoothly smoothly from the neck part 11C which connects the neck part 11C and what is called the main body side wall part 12 of the can 10, and the smooth neck part 13C which has a smooth joint part without a wrinkle and a step. The present invention relates to a method for forming a smooth neck for thin-walled cans and a forming tool used therefor.
[0022]
The smooth neck forming of the smooth neck forming can shown in FIG. 3 (C) uses the necking die 14 and the knockout punch 15 shown in FIG. 1, and the opening end portion of the can 10 is gradually deformed to a small diameter in a plurality of times. Done. The forming tool according to the present invention is used in the second and subsequent necking forming, and is characterized by the shape of the processed surface of the necking die 14.
[0023]
FIG. 1 and FIG. 4 schematically show the smooth neck forming method for thin-walled cans and the main part of the forming tool used therefor, and the can is formed on the inner peripheral side of the necking die 14 into which the opening end of the can 10 is inserted. A knockout punch 15 that pushes out the molded can 10 from the necking die 14 by bringing the opening end of 10 into contact is disposed. The knockout punch 15 has a portion corresponding to the core 16 that is inserted into the opening end of the can 10 and regulates the inner diameter of the opening end of the can 10.
[0024]
On the opening end side of the can 10 formed in the previous necking process, as shown in FIGS. 3B and 4, a substantially cylindrical neck portion 11 is formed in the middle of forming, and the neck following the neck portion 11 is formed. The in part 13 has an inclined shape that is gently connected from the shoulder part 21 to the neck part 11 having the neck part 22 having a reduced diameter. The necking die 14 has a cylindrical portion 17 that forms the neck portion 11, and a cross section along the generatrix line, that is, a cross-section in a plane that passes through the central axis of the necking die 14, is convex toward the center line side. A curved first convex arc portion 18 and a subsequent second convex arc portion 19 are provided as will be described later. The second convex arc portion 19 has an arc surface in which a cross section along the generatrix, that is, a plane passing through the central axis is convex toward the center line side, is inscribed with the first convex arc portion 18 and gradually increases in inner diameter. This is a portion to be formed, and its radius of curvature R2 is smaller than the radius of curvature R1 of the first convex arc portion 18.
[0025]
The inner diameter of the first convex arc portion 18 is minimum on the cylindrical portion 17 side, and is connected to the cylindrical portion 17 at the end portion on the minimum diameter side. Further, the inner diameter of the first convex arc portion 18 is an arc-shaped processed surface having a predetermined radius of curvature R1 in the cross section along the generatrix. The first convex arc 18 and the subsequent second convex arc 19 have a central angle θ1 set to a predetermined angle (30 degrees in this example), and the first convex arc at the position of the central angle θ1. The portion 18 and the second convex arc portion 19 are inscribed, and two arc-shaped machining surfaces are formed as a smooth neck portion machining surface, that is, a connecting portion machining surface.
[0026]
Further, as shown in FIG. 1, the tangent angle θ2 at a point K of a predetermined dimension r2 (which will be described later) in the radial direction from the inner surface of the cylindrical portion 17 in the second convex arc portion 19 is the necking angle. The radius of curvature R2 of the second convex arc portion 19 is determined so as to be larger than θneck (inclination angle of the neck-in portion 13 formed in the previous necking step).
[0027]
As described above, in the process of extending the neck-in molded portion in the axial direction, a collapsed portion 6 is generated in which the average inclination angle with respect to the central axis is ½ of the tangential angle θ2 of the necking die 14 at the time of neck-in start. Has already been published in the Journal of the Japan Society for Technology of Plasticity, “Plastics and Processing” Vol. 39, No. 444. As a result of further research, it was molded in the previous stage, that is, molded in the previous necking process. The point Q at which the tangent angle starts to become smaller than the angle θneck formed with the central axis of the inclined portion 20 that has been necked to the diameter of the neck-in portion 13, in other words, the curvature that protrudes inward at the neck-in portion 13. When the radial direction distance from the inner surface of the cylindrical portion 17 of the point Q corresponding to the connection point between the portion P and the inclined portion 20 is r2, the cylindrical portion on the machining surface of the second convex arc portion 19 It has been found that it is important for smooth neck formation to make the tangent angle θ2 at the point K separated from the inner surface of FIG. 17 by the radial distance r2 larger than the necking angle θneck. 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. If the angle ratio is smaller than 1.5, the influence of the so-called collapsed portion 6 that occurs at the neck-in start portion as shown in FIG. 8 is likely to remain until the end of the joining process, which is the third step of neck-in molding, In the case of a steel thin can having a thickness of, for example, 0.120 mm and a thin aluminum can having a thickness of 0.130 mm, molding defects such as depressions and wrinkles are likely to occur in the smooth neck-in portion. On the other hand, since the necking angle of the can is preferably 28 to 33 degrees from the viewpoint of formability and buckling resistance, the tangent angle of the processed surface of the joint at the end of the joint formation of smooth neck molding If θ2 is larger than 2.7 times the necking angle θneck, the tangent angle θ2 of the joint surface of the smooth neck forming tool will substantially exceed 90 degrees, which is not practical and is not practical. In the third stroke, it is difficult to shape the curvature portion P formed in the previous necking process so that the inclined portion 20 extends, and the trace of molding becomes conspicuous in the neck-in portion, which is not preferable. Therefore, in order to perform the joining portion forming more smoothly, it is necessary to set the tangent angle θ2 of the processed surface at the time when the joining portion forming of the necking die 14 is finished to 1.5 times to 2.7 times the necking angle θneck. In addition, when the plate thickness of the neck-in scheduled portion is thin, it is preferable to make it 2.0 times to 2.1 times.
[0028]
Here, it is as follows when the relationship of said each dimension and angle is shown. First, the distance A in the radial direction between the portion closest to the central axis in the arc of the second convex arc portion 19 and the inner surface of the cylindrical portion 17 is:
A = R1-R2- (R1-R2) cos [theta] 1
= R2-R2 (1-cosθ2)
Therefore, the radius of curvature R2 of the second convex arc portion 19 is
R2 = {r2-R1 (1-cos [theta] 1)} / (cos [theta] 1-cos [theta] 2)
It is represented by And r2 is
r2 = .DELTA.D / 2 + R1 (1-cos .theta.neck) (.DELTA.D is the amount of diameter reduction per process)
Therefore, the radius of curvature R1 of the first convex arc portion 18 and the angle with respect to the central axis of the common tangent of each of the convex arc portions 18 and 19, that is, the central angle θ1 of the first convex arc portion 18 and the necking angle θneck, the second convexity The radius of curvature R2 of the second convex arcuate part 19 is obtained by giving the tangential angle .theta.2 at the point r2 in the radial direction from the inner surface of the cylindrical part 17 in the arcuate part 19 and the diameter reduction amount .DELTA.D per process.
[0029]
As shown in FIGS. 5 to 7, the necking die 14 moves relatively in the axial direction of the can 10, so that the tip of the neck portion of the neck-in portion 13 formed in the previous necking step becomes the first convex portion. As shown in FIG. 6, when the arcuate portion 6 comes into contact with the knockout punch 15 and contacts the knockout punch 15, the collapsed portion 6 that protrudes toward the outer peripheral side proceeds as shown in FIG. 6. The process (FIG. 7) which connects with the inclination part 20 of the neck-in part 13 already shape | molded by the necking process is reached. In that case, the falling portion 6 approaches the inclined portion 20 of the necking angle θneck formed in the previous necking step, and finally is shaped to be formed on the outer peripheral side so as to become the inclined portion 20 of the necking angle θneck. Is done. In the necking die 14 according to the present invention, since the tangent angle θ2 at the point K on the second convex arc portion 19 facing the point Q is 1.5 to 2.7 times the necking angle θneck, As shown in the middle of the molding in FIG. 6, when the falling portion 6 is formed on the processed surface of the first convex arc portion 18 of the necking die 14, the neck-in portion 13 formed by the previous necking process is formed. It is gradually caused to become the inclined part 20. At that time, the contact point (the point at which the tip of the neck comes into contact with 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; Since the average inclination angle θB can be brought close to the angle of the already formed inclined portion 20, the average inclination angle θB of the falling portion 6 can be caused to the necking angle θneck. That is, it is possible to increase the rise of the average inclination angle θB. FIG. 7 shows the final stage in which the necking angle θneck is equal to the average inclination angle θB of the falling part 6 and the falling part 6 disappears. In the final stage of forming the connecting part of the third stroke, the falling part is shown. The rise of the fall-down portion 6 is increased by retreating the outer surface of the second convex arc portion 19 from the inclined portion 20 of the neck-in portion 13 so as to cause the average inclination angle θB of the portion 6 gradually to the necking angle θneck. Can do. Therefore, since the fall-down portion 6 can disappear from the neck-in portion 13 at the final stage of forming the joint portion, the fall-down portion 6 is pushed into the can from the inclined portion 20 of the neck-in portion 13 that has already been formed. In other words, molding defects such as wrinkles and depressions are suppressed or prevented at the neck-in portion.
[0030]
In the embodiment of the present invention, the processing surface is simplified by forming the connecting portion in the third step on the processing surface constituted by the first convex arc portion 18 and the second convex arc portion 19. However, the present invention is not limited to this, and a processing surface including a part of a straight line between the first convex arc portion 18 and the second convex arc portion 19 or the second convex arc portion 19 with a plurality of radii of curvature. The same purpose can be achieved even with the structured working surface.
[0031]
Next, Examples and Comparative Examples conducted for confirming the effects of the present invention will be shown.
[Example 1]
Nominal 211 diameter (drawn and ironed so that the steel wall thickness of the planned neck-in part is 0.130 mm and trimmed to a predetermined height (the outer diameter of the tightened part when the can lid is wrapped as it is is 2 + 11) / 16 inch) can be smoothly necked in by using the smooth neck forming tool of the present invention to a nominal 206 diameter in 7 steps (the outer diameter of the tightened portion when the can lid is tightened is 2 + 6/16 inch). I tried processing. Molding was possible without causing molding defects such as wrinkles and depressions.
[0032]
[Example 2]
Drawing and ironing so that the steel wall thickness of the planned neck-in portion is 0.130 mm, and then trimming the can body with a nominal diameter of 211 diameters to a predetermined height using the smooth neck forming tool of the present invention in 9 steps. Die smooth neck-in processing was attempted up to a nominal diameter of 204. Molding was possible without causing molding defects such as wrinkles and depressions.
[0033]
[Example 3]
Using a smooth neck forming tool of the present invention, the can body having a nominal diameter of 211 is drawn and ironed so that the steel wall thickness of the planned neck-in portion is 0.130 mm and trimmed to a predetermined height in 11 steps. Die smooth neck-in processing was attempted to a nominal diameter of 202. Molding was possible without causing molding defects such as wrinkles and depressions.
[0034]
[Example 4]
Drawing and ironing is performed so that the steel wall thickness of the planned neck-in portion is 0.120 mm, and a can body having a nominal diameter of 211 diameter trimmed to a predetermined height is formed in 7 steps using the smooth neck forming tool of the present invention. Die smooth neck-in processing was attempted to a nominal 206 diameter. Molding was possible without causing molding defects such as wrinkles and depressions.
[0035]
[Example 5]
Drawing and ironing is performed so that the steel wall thickness of the planned neck-in portion is 0.120 mm, and the can body having a nominal diameter of 211 diameter trimmed to a predetermined height is formed in 9 steps using the smooth neck forming tool of the present invention. Die smooth neck-in processing was attempted up to a nominal diameter of 204. Molding was possible without causing molding defects such as wrinkles and depressions.
[0036]
[Example 6]
Using a smooth neck forming tool according to the present invention, the can body having a nominal diameter of 211 is drawn and ironed so that the steel wall thickness of the planned neck-in portion is 0.120 mm and trimmed to a predetermined height in 11 steps. Die smooth neck-in processing was attempted to a nominal diameter of 202. Molding was possible without causing molding defects such as wrinkles and depressions.
[0037]
[Comparative Example 1]
Necking angle θneck is the tangential angle at the point where splicing is completed on a can body with a nominal diameter of 211 diameter that has been drawn and ironed so that the steel wall thickness of the planned neck-in portion will be 0.120 mm. Using a smooth neck forming tool of 1.35 times, a die smooth neck-in process was attempted to a nominal diameter of 202 in 11 steps. As a result, the depression of the neck-in portion and the wrinkles of the neck portion were scattered, and good moldability was not obtained.
[0038]
【The invention's effect】
As described above, according to the smooth neck molding method for thin cans and the molding tool used therefor according to the present invention, even if the neck-in planned portion is considerably thin, the diameter reduction amount of neck-in processing is large. However, smooth neck molding can be performed satisfactorily without causing defects such as wrinkles and depressions in the neck-in portion. Therefore, according to the present invention, material resources can be further saved by reducing the thickness of the neck-in planned portion and reducing the diameter of the neck-in portion.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing the 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 joining forming when the smooth neck forming tool according to the present invention is used.
FIG. 3 is a diagram 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 smooth neck-in processing.
FIG. 5 is a partial cross-sectional view schematically showing an initial state of a processing process by the necking die of the present invention.
FIG. 6 is a partial cross-sectional view schematically showing an intermediate state of the 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 machining process by the necking die of the present invention.
FIG. 8 is a partial sectional view schematically showing a state of molding failure caused by a conventional necking die.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Can, 11 ... Neck part, 12 ... Main part, 13 ... Neck-in part, 14 ... Necking die, 17 ... Cylindrical part, 18 ... First convex arc part, 19 ... Second convex arc part, R1 ... (first Radius of curvature of one convex arc, R2 ... radius of curvature of the second convex arc.

Claims (3)

After causing a relative axial movement between the bottomed cylindrical can and the first necking die, and reducing the diameter of the open end portion of the bottomed cylindrical can to form a neck-in portion, A thin-walled can that is formed by continuously reducing the diameter, curvature, and shoulder from the neck on the opening end side by reducing the diameter of the neck-in portion from the opening end side with the second and subsequent necking dies. In the smooth neck molding method for
The second and subsequent necking dies are formed in a cylindrical portion having an inner diameter smaller than the neck-in portion, and are formed continuously in the axial direction of the cylindrical portion, and are projected toward the central axis side of the can as the inner diameter gradually increases. The first convex arc portion is formed into a shape that is convex toward the central axis side of the can following the processing surface for the curvature portion composed of the first convex arc portion and the maximum outer diameter portion of the first convex arc portion. A connecting portion processing surface including a second convex arc portion having a curvature radius smaller than the curvature radius of
A first stroke in which the tip of the neck is brought into contact with the knockout punch after being brought into contact with the first convex arc portion;
A second stroke in which the necking die after the second time is relatively moved in the axial direction of the can to reduce the diameter of the neck;
The second and subsequent necking dies are relative to the axial direction of the can in a state in which the connection point between the curvature portion and the inclined portion of the can is opposed to the processing surface for the connecting portion in the axial direction of the can. And the third step of forming the curved portion already formed in the previous step into an extended shape toward the opening end of the inclined portion,
The angle of the tangent line at the point on the processing surface for the connecting portion facing the connection point with respect to the central axis of the can is made 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-walled cans, wherein the second and subsequent necking dies are used. 2. The thin can according to claim 1, wherein an angle formed between the tangent and the central axis of the can is 1.5 to 2.7 times an angle of the inclined portion with respect to the central axis of the can. Smooth neck forming method. After causing a relative axial movement between the bottomed cylindrical can and the first necking die, and reducing the diameter of the open end portion of the bottomed cylindrical can to form a neck-in portion, A thin-walled can that is formed by continuously reducing the diameter, curvature, and shoulder from the neck on the opening end side by reducing the diameter of the neck-in portion from the opening end side with the second and subsequent necking dies. For smooth neck forming tools,
A connecting portion processing surface for reducing the diameter of the connecting portion from the neck portion to the inclined portion;
The connecting surface is a cylindrical portion into which the neck portion is inserted, and a first convex arc portion that is formed in the cylindrical portion continuously in the axial direction and is convex toward the central axis side of the can as the inner diameter gradually increases. A second convex arc portion formed in a shape convex toward the central axis side of the can following the maximum outer diameter portion of the first convex arc portion and having a radius of curvature smaller than the curvature radius of the first convex arc portion; A smooth neck forming tool for thin-walled cans.

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