Ironing punch

Abstract

In the drawing and shrinking punch 1 used in the drawing and shrinking process of metal, dot-shaped recesses 3 are distributed on the outer peripheral surface 1a of the punch 1, and at least a portion of the periphery of the dot-shaped recesses 3 is formed with a raised portion 5.

Description

[Technical Field]

[0001] This invention relates to a shrink-forming punch for shrink-forming processing, and further, to a shrink-forming processing method for thinning a metal cylinder using the punch, and a shrink-forming tank obtained using the shrink-forming processing method. [Previous Technology]

[0002] Shrink forming is a rigorous plastic forming process performed to thin the walls of metal, suitable for manufacturing thin-walled, height-increasing metal cylinders (thin-walled metal cylinders), such as thin-walled seamless cans (also called shrink forming cans). This shrink forming process is performed by passing a hollow metal cylinder through a narrow space (mold space) enclosed by a rod-shaped punch and an annular mold. Specifically, the punch is inserted into the interior of the metal cylinder to be thinned, and the punch and the annular mold clamp the metal cylinder. In this state, the punch and the annular mold move relative to each other (slide), thereby thinning the walls of the metal cylinder. For example, Patent Documents 1 and 2 disclose a technique for manufacturing seamless cans (sometimes also called shrink forming cans or extruded shrink forming cans) using this shrink forming process.

[0003] However, in this type of drawing-out process, after the drawing-out process is completed, the punch must be pulled out of the thinned metal cylinder. The problem here is that during the drawing-out process, the inner surface of the main body of the metal cylinder, which is the workpiece, is pressed forcefully against the outer circumference of the punch. Therefore, there is significant frictional resistance, making it difficult to pull the punch out smoothly. This not only results in low productivity but also, depending on the situation, damage to the inner surface of the formed metal cylinder's main body due to the pulling process. The pullability of the punch in this type of drawing-out process has been almost entirely unstudied.

[0004] For example, Patent Document 3 discloses a seamless can, which is a seamless metal can with a thermoplastic resin layer formed on its inner surface, and the thermoplastic resin layer on its inner surface has a plurality of dot-shaped protrusions. In this technology, by forming dot-shaped protrusions, the molecular orientation of the thermoplastic resin layer generated by the shrinkage process is moderated, thereby suppressing the reduction in anti-dentation caused by the molecular orientation of the thermoplastic resin layer. That is, in Patent Document 3, in order to form dot-shaped protrusions on the thermoplastic resin layer on the inner surface of the can, a punch that forms dot-shaped recesses on the outer peripheral surface is used to perform the shrinkage process. It can be seen that Patent Document 3 also completely does not study the pullability of the shrinkage process punch. Prior Art Documents Patent Documents

[0005] Patent Document 1: WO2017 / 033791; Patent Document 2: Japanese Patent Application Publication No. 2018-69256; Patent Document 3: Japanese Patent Publication No. 3327137 [Summary of the Invention]

[0006] The problem the invention aims to solve

[0007] Therefore, the object of the present invention is to provide a shrink-forming punch with excellent drawability after shrink-forming. Another object of the present invention is to provide a shrink-forming method for thinning a metal cylinder using the above-described punch, and a shrink-forming can obtained using this shrink-forming method. Technical Means for Solving the Problem

[0008] After conducting numerous experiments on the pullability of the punch after shrinking, the inventors discovered that by using a hammering method to form multiple dot-shaped recesses on the outer surface of the punch, the pullability of the punch can be greatly improved, thus completing the present invention.

[0009] According to the present invention, a shrinking punch is provided for use in shrinking metal processing. The shrinking punch is characterized in that: dot-shaped recesses are distributed on the outer peripheral surface of the punch, and at least a portion of the periphery of the dot-shaped recesses is formed with a raised portion.

[0010] In the above-described drawing punch, depending on the hammering method used to form the above-described dotted recess, the following configuration can be adopted: (1) The above-described raised portion is formed on the entire periphery of the peripheral portion of the above-described dotted recess; or (2) The above-described raised portion is formed on a portion of the peripheral portion of the above-described dotted recess. In particular, as shown in (2) above, when the above-described raised portion is formed on a portion of the peripheral portion, the preferred configuration is: (2-1) The above-described raised portion (partial raised portion) is formed on the portion of the peripheral portion of the above-described dotted recess opposite to the front end of the punch; (2-2) When viewed in a cross-section along the axial direction of the punch, the shape of the above-described dotted recess is such that the deepest part is located on the side opposite to the front end of the punch; (2-3) The eccentricity of the deepest part is in the range of 30% to 100%.

[0011] According to the present invention, a shrink-forming process method is further provided, characterized in that: the shrink-forming punch is inserted into a metal cylinder, and the metal cylinder is subjected to shrink-forming process by passing through an annular mold; after the shrink-forming process is completed, the metal cylinder is thinned by pulling out the punch. In this shrink-forming process method, it is desirable that (3) the inner surface of the metal cylinder has an organic resin layer; and (4) the organic resin layer is formed of thermoplastic resin.

[0012] According to the present invention, a shrink-wrap can is further provided, which has a hollow cylindrical main body and a bottom that closes the lower end of the main body. The shrink-wrap can is characterized in that: dot-shaped protrusions are distributed on the inner circumferential surface of the main body, and when viewed in a longitudinal section along the axial direction, the apex of the dot-shaped protrusions is located in a direction opposite to the bottom. The shrink-wrap can is manufactured by shrink-wrap processing using a shrink-wrap processing punch that forms the protrusions (partial protrusions) as shown in (2) above. In the shrink-wrap can, preferably (5) an organic resin layer is laminated on the inner circumferential surface of the main body, and the dot-shaped protrusions are distributed on the surface of the organic resin layer. Effects of the Invention

[0013] The outer peripheral surface of the drawing punch of the present invention is provided with dot-shaped recesses, and its major feature is that at least a portion of the periphery of the dot-shaped recesses is formed with a raised portion. That is, if a punch with dot-shaped recesses of the above-described shape is used for drawing and forming a metal cylinder, as the wall thickness is achieved by the drawing and forming process, a raised portion corresponding to the dot-shaped recesses is formed on the inner peripheral surface of the metal cylinder. When the punch is pulled out after the drawing and forming process, the pressure between the outer surface of the punch and the inner peripheral surface of the metal cylinder is mitigated by the raised portion located at the periphery of the dot-shaped recesses. As a result, the drawing and forming punch is easy to pull out, thereby ensuring higher productivity.

[0014] The aforementioned raised portion is formed on the entire periphery of the dotted recess, or on a portion of the periphery, particularly on the opposite side of the punch tip (the side in the pulling direction of the punch). Depending on the shape of the raised portion, the punch for drawing and shrinking processing of the present invention can be divided into annular raised type and partial raised type, both types of punches have good pulling properties.

Implementation Method

[0016] <Contraction Processing>

[0017] Shrink forming is known as a representative method of plastic processing of metals, for example, in the widespread manufacture of seamless metal cans (also known as shrink forming cans) with high height and thin walls. As shown in Figure 1, in this shrink forming process, when the workpiece, i.e., the metal cylinder B, is moved in the processing direction by the shrink forming punch A, the shrink forming die C is pressed against the outer surface of the cylinder B and wiped, thereby achieving the thinning of the cylinder B's wall. Therefore, in this shrink forming process, the inner circumferential surface of the metal cylinder B is strongly pressed against the outer circumferential surface of the shrink forming punch A.

[0018] In this type of shrinkage process, when the thickness of the metal cylinder before shrinkage is set as t0 and the thickness after shrinkage is set as t1, the shrinkage rate is expressed by the following formula. The larger the shrinkage rate, the greater the surface pressure applied to the shrinkage die C and subsequently the punch A, thus ensuring precise forming. Shrinkage rate (%) = 100 × (t0 - t1) / t0

[0019] The drawing punch A has a tubular (cylindrical) shape and is generally formed of the same superhard alloy as the drawing die C described later, and is formed to be thicker in order not to cause deformation due to drawing. Moreover, a drive shaft S (not shown in Figure 1, but indicated by S in Figure 5) for moving the punch A in the processing direction is connected to the inner surface of one end of the punch A (upstream side in the processing direction of Figure 1).

[0020] Furthermore, the metal cylinder B used for the aforementioned shrinking process can be made of various metals or alloys, such as aluminum, copper, iron, or alloys containing these metals, or surface-treated steel sheets such as tinplate or chemically treated aluminum sheets. Moreover, the inner circumferential surface of the metal cylinder B (the surface in close contact with the outer circumferential surface of the shrinking punch A) can also be coated with a thermoplastic resin, such as polyethylene terephthalate or other polyester resin. This resin coating prevents corrosion and damage to the inner surface.

[0021] Furthermore, regarding the shrinkage die C, the higher the shrinkage rate, the significantly higher the surface pressure applied; therefore, it must be formed from a very hard material. Examples of such hard materials include, for instance, so-called superhard alloys obtained by sintering a mixture of tungsten carbide (WC) and a metal binder such as cobalt; cermets obtained by sintering a mixture of metal carbides such as titanium carbide (TiC), titanium compounds such as titanium carbonitride (TiCN), and metal binders such as nickel and cobalt; or hard ceramics such as silicon carbide (SiC), silicon nitride (Si3N4), alumina (Al2O3), and zirconium oxide (ZrO2). Furthermore, a carbon film, such as a diamond film, can be used to coat the processing surface (the surface in contact with the workpiece, i.e., the cylinder B) of this shrinkage die C. This carbon film can be formed by vapor deposition, such as CVD. <Shrinkage Processing Punch and Metal Cylinder of the Invention>

[0022] The above-mentioned shrinking punch and metal cylinder are closely joined during shrinking. However, the shrinking punch of the present invention has the following characteristics: a ring-shaped raised part formed in a ring shape on the entire periphery of the dot-shaped recess, and a partially raised arc-shaped part formed on a part of the periphery of the dot-shaped recess.

[0023] 1. Ring-shaped raised type shrink-forming punch; Please refer to Figure 2, which shows the longitudinal section of this type of shrink-forming punch and the thin-walled workpiece (metal cylinder), and Figure 3, which shows a partial enlarged rough planar development view of the punch.

[0024] In Figures 2 and 3, a plurality of dot-shaped recesses 3 are formed on the outer peripheral surface 1a of the drawing punch 1. The recesses 3 are recessed into cone shapes such as conical or pyramidal shapes, but a raised portion 5 is formed in a ring around the entire periphery of each of them (especially referring to Figure 3). That is, the raised portion 5 is a portion that protrudes from the outer peripheral surface 1a of the punch around the recesses 3.

[0025] Furthermore, please also refer to FIG4, which shows a planar development view of the inner circumferential surface of the metal cylinder that has been thinned by the drawing process. A dotted recess 3 is formed on the outer circumferential surface 1a of the drawing punch 1, resulting in a plurality of dotted protrusions 15 being formed on the inner circumferential surface 11a of the thinned metal cylinder 11. That is, the dotted protrusions 15 correspond to the dotted recesses 3 formed on the drawing punch 1 (especially refer to FIG3 and FIG4).

[0026] However, when the shrinking process is completed, the thinned metal cylinder 11 remains in the following state: a shrinking punch 1 is inserted inside it, and the outer peripheral surface 1a of the shrinking punch 1 is in close contact with the inner peripheral surface of the thinned metal cylinder 11. For example, in the state after the shrinking process is completed, the positional relationship between the shrinking punch and the thinned metal cylinder 11 is shown in Figure 5. This positional relationship is exactly the same as when using the arc-shaped shrinking punch 1 described later.

[0027] That is, the thin-walled metal cylinder 11 has a bottom 17, like a seamless can (shrink can). The shrinking punch 1 extends to the bottom 17 of the cylinder 11. The area Q where the outer peripheral surface 1a of the punch 1 contacts the inner peripheral surface of the metal cylinder 11 becomes the area that functions as the processing holding surface during shrinking. Generally, the drive shaft S is connected to the part of the punch 1 that is higher than the area Q. By driving the shaft S, the shrinking punch 1 is moved in the processing direction. After the shrinking is completed, the shrinking punch 1 is moved in the opposite direction to the processing direction, i.e., the pulling direction.

[0028] Therefore, after the drawing and shrinking process is completed, as shown in FIG5, the metal cylinder 11 is restricted from moving in the height direction of the punch 1 by the stop 20 through the pulling of the drawing and shrinking punch 1. Furthermore, as shown in FIG5, when the metal cylinder 11 has a bottom 17 like a can, the punch 1 is easily pulled out when the auxiliary gas is blown out simultaneously by using the drive shaft S for pulling. Moreover, when the metal cylinder 11 does not have a bottom 17 like a hollow pipe, it is formed as follows: the front end of one side of the cylinder 11 (the front end on the processing direction side) is formed with a small diameter so that the punch 1 can hold the metal cylinder 11 tightly and move it without the punch 1 coming off.

[0029] For example, when the drawing punch 1 is pulled out in the state after the drawing process is completed, if the outer peripheral surface of the drawing punch 1 and the inner peripheral surface of the metal cylinder 11 are completely in contact in the aforementioned region Q, the frictional resistance is extremely large, which makes the efficiency of the drawing operation worse. As a result, it is impossible to avoid a decrease in productivity, or the inner peripheral surface of the metal cylinder 11 becomes rough when it is pulled out (when the thermoplastic resin layer is formed, peeling occurs), or the drive shaft S and the like are subjected to a large load, causing problems such as a reduction in the life of the device. However, according to the present invention, as shown in Figures 2 and 3, a plurality of annular protrusions 5 are distributed around the periphery of the periphery of the plurality of dot-shaped recesses 3 formed on the outer peripheral surface 1a of the drawing punch 1. The upper end of the protrusions 5 is pressed against the inner peripheral surface 11a of the metal cylinder 11, and the slightly recessed recesses 12 corresponding to the protrusions 5 are formed in annular shape on the inner peripheral surface 11a of the metal cylinder 11. That is, the contact area between the outer peripheral surface 1a of the punch 1 and the inner peripheral surface 11a of the metal cylinder 11 is significantly reduced. As a result, in this invention, the frictional resistance during the pulling of the retracting punch 1 is greatly reduced, and the retracting punch 1 can be pulled smoothly without applying a large load, thereby enabling retracting processing to be carried out with extremely high productivity.

[0030] In this invention, the annular protrusion 5 formed on the outer peripheral surface 1a of the drawing punch 1 is formed by plastically deforming the outer peripheral surface 1a to form a recess 3. Specifically, a hammer-shaped jig with a rod-shaped tip having an axisymmetric tip is used to hammer the outer peripheral surface 1a of the drawing punch 1 in the vertical direction to form a recess 3, and at the same time, an annular protrusion 5 is formed around the recess 3. For example, in Patent Document 3 (Japanese Patent No. 3327137), ultrasonic processing, ion irradiation, laser processing, electron beam irradiation, etc., are described as means of forming a dot-shaped recess on the outer peripheral surface 1a of the drawing punch 1 (see paragraph 0064). These means cannot form a protrusion. The reason is that the recess is formed by cutting rather than plastic processing.

[0031] The size of this annular protrusion 5, such as the difference between the outer diameter D2 and the inner diameter D1 (corresponding to the diameter of the dotted recess 3) (D2-D1) and the height h, depends on the diameter D1 and depth d of the dotted recess 3 (see Figure 2). In order to make the protrusion 5 a size that will not break during the shrinkage process, the diameter D1 of the dotted recess 3 is preferably about 0.2 to 1.1 mm, and its depth d is preferably about 0.2 to 10.0 µm. Although it may vary slightly depending on the material of the punch 1, by setting the diameter D1 and depth d of the dotted recess 3 within the above range, the size (D2-D1) and height h of the protrusion 5 can be made appropriate, avoiding excessive forced pull-out, thereby allowing the punch 1 to be pulled out without causing unnecessary deformation of the metal cylinder 11, which is the workpiece.

[0032] For example, if the diameter D1 or depth d of the dot-shaped recess 3 is outside the above range, the size (D2-D1) and height h of the annular protrusion 5 will become larger or smaller than necessary, which will greatly increase the frequency of deformation (rollback) such as the upper opening of the metal cylinder 11 protruding outward due to the pulling of the punch 1.

[0033] That is, the ideal forming shape is as shown in Figure 6(a), where the upper opening of the metal cylinder 11 is in a straight line state. However, if the pulling of the punch 1 is a forced pull-out, as shown in Figure 6(b), the upper opening will roll back outward. By setting the diameter D1 or depth d of the dotted recess 3 to an appropriate range, the occurrence rate of this rollback can be reduced to approximately zero. When the diameter D1 and depth d are not within an appropriate range, or when the punch 1 with no raised portion 5 formed on the periphery of the dotted recess 3 is used for shrinkage processing, the rollback amount can easily reach 5.0 mm or more. The frequency of this large rollback may reach 20 to 30 per 100, or more.

[0034] Furthermore, regarding the annular protrusions 5, from the perspective of smooth drawing of the drawing punch 1, it is preferable that they be evenly distributed in the length direction and circumferential direction of the drawing punch 1 in the region Q of the drawing punch 1 described above. Furthermore, from the viewpoint of greatly reducing frictional resistance without significantly reducing the strength of the punch 1, it is desirable that the protrusions 5 be distributed in the region Q at an area ratio of 30 to 400 per cm2.

[0035] Regarding the metal cylinder (workpiece) 11 obtained by the shrinking process (thinning) using the aforementioned shrinking punch 1, as shown in Figures 2 and 4, corresponding to the aforementioned dotted recesses 3, dotted protrusions 15 are formed on its inner circumferential surface 11a. That is, when an organic resin coating is formed on the inner surface of the cylinder 11 by forming the protrusions 15, the orientation of the organic resin film can be sufficiently mitigated, improving dent resistance.

[0036] 2. Partially Raised Type Shrinkage Processing Punch; In this invention, regarding the partially raised type shrinkage processing punch, please refer to Figures 7 to 10. In this type of punch, a hammering fixture is hammered from an oblique direction (from the front end side to the root side) to form a dotted recess 3, thereby forming a raised portion 4 on a portion of the periphery of the dotted recess 3 (opposite to the front end of the punch 1). Moreover, the raised portion 4 can also be formed by hammering with a fixture having a front end with a shape consistent with the recess 3. This raised portion 4 is partially present on the periphery of the dotted recess 3. As described in the section on annular raised type punches, the raised portion 4 cannot be formed by cutting means such as ultrasonic processing and laser processing.

[0037] Referring to Figures 7 and 8, the shape of the recess 3 formed by the hammering described above is such that the deepest part P (equivalent to the apex of the cone shape) is offset to the side opposite to the front end 1b of the punch 1 (the side of the pulling direction of the punch 1). That is, because the impact mark forms the shape of the recess 3, a raised part 4 is formed on the side of the deepest part P of the recess 3 that is off-center. For example, the raised part 4 has an arc-shaped or approximately arc-shaped shape. In the annular raised type, the deepest part of the recess 3 is not off-center, thus forming an annular raised part 5.

[0038] In the present invention, as shown in FIG7, in the recess 3 of the above-described shape, the side surface of the front end of the drawing punch 1 becomes a gently inclined surface 3a with a small inclination angle α, and the opposite side surface becomes a steeply inclined surface 3b with a large inclination angle β.

[0039] If the punch 1 with the above-described shape is used for the drawing process, as shown in FIG9, a protrusion 13 is formed on the inner circumferential surface of the metal cylinder 11, corresponding to the above-described dotted recess 3, with a shape having a vertex P' located on the opposite side of the processing direction (i.e., the punch tip 1b side). That is, because of the formation of this protrusion 13, when its inner surface is coated with organic resin, its orientation becomes gentler by the protrusion 13, which can suppress the reduction of anti-dent resistance. Moreover, this protrusion 13 has a shape corresponding to the above-described recess 3, so it has a gentle inclined surface 13a with a smaller inclination angle α' corresponding to the gentle inclined surface 3a of the recess 3, and a steeply inclined surface 13b with a larger inclination angle β' corresponding to the steeply inclined surface 3b of the recess 3.

[0040] When the shrinking process is completed, the thinned metal cylinder 11 remains in the following state: a shrinking punch 1 is inserted inside it, and the outer peripheral surface 1a of the shrinking punch 1 is in close contact with the inner peripheral surface of the thinned metal cylinder 11. That is, as shown in Figure 5 above, the shrinking punch 1 extends to the bottom 17 of the cylinder 11, and the area Q where the outer peripheral surface 1a of the shrinking punch 1 contacts the inner peripheral surface of the metal cylinder 11 becomes the area that functions as a processing holding surface during the shrinking process, as described above. For example, a drive shaft S is connected to a portion above the area Q of the shrinking punch 1, and by driving the shaft S, the shrinking punch 1 moves in the processing direction. After the shrinking process is completed, the shrinking punch 1 moves in the pulling direction, which is opposite to the processing direction. Therefore, due to the pulling of the shrinking punch 1, the stop 20 restricts the movement of the metal cylinder 11 in the pulling direction of the punch 1.

[0041] In the shrinking process using the partially raised shrinking punch 1 described above, a concave portion 3 with a deepest point P eccentrically formed is formed on the outer peripheral surface 1a. Correspondingly, a convex portion 13 with a vertex P' eccentrically formed is formed on the inner peripheral surface 11a of the thinned metal cylinder 11 (see Figure 9). Therefore, if the shrinking punch 1 is pulled out after the shrinking process is completed, as shown in Figure 10, the gently inclined surface 3a of the concave portion 3 of the shrinking punch 1 is pulled out while the gently inclined surface 13a of the convex portion 13 on the inner peripheral surface of the metal cylinder 11 is in contact with it. As a result, not only can the shrinking punch 1 be pulled out smoothly, but an arc-shaped convex portion 4 is also formed on the pulling direction side of the punch 1 (opposite to the front end of the punch). Therefore, the contact area between the outer peripheral surface 1a of the punch 1 and the inner peripheral surface 11a of the metal cylinder 11 is small, thereby making it easier to pull out the punch 1. As a result, it can more effectively avoid unnecessary deformation of the metal cylinder 11 during the pulling process.

[0042] For example, when the periphery of the recess 3 formed on the outer peripheral surface 1a of the drawing punch 1 does not form a raised portion 4, the deepest part P is not eccentric. When viewed in a cross section along the sliding direction, the recess 3 has a linearly symmetrical shape. When the punch 1 is pulled out, the inclination angle of the surface in contact becomes a larger surface. Therefore, the resistance to pulling out the punch 1 is greater, and the punch cannot be pulled out smoothly, resulting in reduced productivity. Moreover, the load applied to the drive shaft S and the like is also greater, and the life of the device tends to be reduced.

[0043] Moreover, when using this arc-shaped drawing punch 1, the drawing ability of the punch 1 is also improved, so that the occurrence rate of rollback as shown in FIG6(b) is approximately zero.

[0044] The eccentricity of the deepest part P of the recess 3 formed on the outer peripheral surface 1a of the above-mentioned drawing punch 1 is expressed by the following formula. Eccentricity = 100d / (1 / 2)D = (2d / D) × 100 Where, d is the distance between the vertex P and the center of the recess 3 (the eccentricity of the vertex P), and D represents the diameter of the recess 3.

[0045] In this invention, the eccentricity of the deepest part P is preferably in the range of 30% to 100%, and more preferably in the range of 75% to 95%. Experiments have confirmed that if the eccentricity is less than 30%, the inclination angle α of the gently sloping surface of the recess 3 becomes larger, which impairs the drawing ability of the punch 1. For example, the occurrence rate of large deformation with a rollback amount of 5.0 mm or more is about 30%. By setting the eccentricity to 30% or more, especially 75% or more, the occurrence rate of large deformation with a rollback amount of 5.0 mm or more can be made approximately zero. Moreover, if the eccentricity is close to 100%, the end of the recess 3 on the side opposite to the processing direction becomes a sharp corner, which tends to easily cause the drawing punch 1 to break.

[0046] Furthermore, the depth of the aforementioned recess 3 (corresponding to d in FIG2) is the same as that of the annular drawing punch 1 described above, preferably about 0.2 to 10.0 µm. If the depth (d) is too large, it may impair the drawing ability of the drawing punch 1. Moreover, if the depth (d) is too small, the protrusion 13 formed corresponding to the recess 3 becomes smaller. As a result, the orientation of the organic resin film is not sufficiently smoothed, which tends to impair the anti-dentation properties.

[0047] Furthermore, similar to the annular drawing and shrinking punch 1 described above, the recesses 3 are preferably evenly distributed in the length direction and circumferential direction of the drawing and shrinking punch 1, and preferably, the recesses 3 are distributed in the region Q at an area ratio of 30 to 400 per cm2.

[0048] In this invention, if the arc-shaped drawing punch 1 is used for drawing processing, a protrusion 13 with an eccentric vertex P' is formed on the inner circumferential surface 11a of the metal cylinder 11, corresponding to the recess 3. This greatly reduces the frictional resistance when drawing the drawing punch 1, extends the lifespan of the device, and improves productivity. Furthermore, when an organic resin coating is formed on the inner surface of the metal cylinder 11, the orientation of the organic resin film is sufficiently mitigated, improving dent resistance. <Morphology of the dotted recess 3>

[0049] In the above-described drawing-out punch 1 of the present invention, whether it is an annular raised type or a partially raised type, the planar shape of the dotted recess 3 is not particularly limited, and can be circular, elliptical, quadrilateral, etc. It does not possess anisotropy. From the perspective of being least likely to break during drawing, depending on the shape of the punch used to form the recess 3, it is particularly preferred to be circular. However, in the arc-shaped drawing-out punch 1, when the recess 3 is formed by hammering the fixture at an angle, as shown in FIG8, it is mostly a slightly deformed circle. <Stamping forming process using drawing-out processing>

[0050] The shrinking process using the shrinking punch 1 described above is used for thinning various metal cylinders 11, but it is best used for stamping to manufacture shrink-wrap cans (seamless cans) with thin walls and increased height. Figure 11 shows the manufacturing process of such a metal can.

[0051] In Figure 11, the raw sheet (e.g., aluminum sheet) 101 used in forming the metal can is first punched to obtain a round plate 103 for the metal can (see Figure 11(a)). An organic resin coating may also be laminated on one side of the raw sheet 101, especially the side that becomes the inner surface of the can. The thickness of the raw sheet 101 will vary depending on the type of metal, the purpose of the can, or its size, but generally, it is preferred to have a thickness of 0.10 to 0.50 mm. When it is a surface-treated steel sheet, it is preferred to have a thickness of 0.10 to 0.30 mm, and when it is a light metal sheet such as aluminum, it is preferred to have a thickness of 0.15 to 0.40 mm.

[0052] The organic resin coating is a coating made from acrylic coatings, polyurethane coatings, silicone coatings, fluorine coatings, or other coatings, or a thermoplastic resin. Previously, it was used for corrosion resistance and to suppress surface roughness during rigorous molding processes. In this invention, an organic resin coating formed from a thermoplastic resin is particularly preferred.

[0053] That is, the thermoplastic resin coating can be easily laminated onto the raw plate 101 by a laminating roller, and the molecular orientation is achieved by bending and stretching caused by extrusion or shrinkage processing, thereby improving the barrier properties against corrosive components and thus improving the heat resistance. On the other hand, as disclosed in Patent Document 3, due to the molecular orientation of the organic resin coating, there is a tendency for the resin to become fibrillated, which makes it easy for the can to break in the height direction due to impact, resulting in a tendency for poor dent resistance. However, in this invention, by using the shrinkage processing of the punch 1 with dotted recesses 3, dotted protrusions 15 (or 13) are formed on the inner surface of the can, and the molecular orientation is moderated by the protrusions 15 (or 13), which can prevent a decrease in dent resistance.

[0054] Moreover, examples of the above-mentioned thermoplastic resins include low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene or random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl chloride copolymers, polystyrene, acrylonitrile-styrene copolymers, ABS, α-methylstyrene-styrene copolymers, polyvinyl chloride, polyvinylidene fluoride, vinyl chloride-vinyl chloride copolymers, polymethyl methacrylate, polymethyl methacrylate and other polyethylene compounds, nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12 and other polyamides, polyethylene terephthalate, polybutylene terephthalate and other thermoplastic polyesters, polycarbonate, polyphenylene ether and other mixtures thereof. Among these thermoplastic resins, polyester resins are particularly preferred in terms of processability, corrosion resistance, and aroma retention of can contents.

[0055] In the punching process, a punch 105 with an outer diameter equivalent to the diameter of the circular plate 103 and a die 107 holding the raw plate 101 and having an opening equivalent to the diameter of the circular plate 103 are used. That is, the raw plate 101 held on the die 107 is hammered by the punch 105 to obtain a circular plate 103 of a specific size. Moreover, depending on the shape of the formed article manufactured by this manufacturing process, the raw plate 101 can also be hammered into other shapes (e.g., rectangular).

[0056] The circular plate 103 obtained in the above manner is subjected to extrusion processing to obtain an extrusion can (bottomed cylindrical body) 109 with a lower height (see Figure 11(b)). In this extrusion processing, the circular plate 103 to be hammered is held on the die 111, and the circular plate 103 is held around the periphery by an anti-wrinkle fixture 113. An opening is formed in the die 111, and the circular plate 103 is pressed into the opening of the die 111 by an extrusion punch 115, thereby obtaining the extrusion can 109. Moreover, an arc (curvature portion) is formed at the upper corner of the opening of the die 111 (the side holding the circular plate 103), so that the circular plate 103 is pressed into the opening of the die 111 quickly and without breaking. The outer diameter of the punch 115 is set to be smaller than the diameter of the opening of the die 111 by an amount equivalent to the approximate thickness of the circular plate 103. That is, in this extrusion processing, almost no thinning is performed. Moreover, extrusion processing is sometimes performed multiple times depending on the shape of the finished product.

[0057] Next, the extruded can 109 obtained above is subjected to a shrinkage process, thereby forming a metal can (thin-walled seamless can) 11 with a higher height and thinner wall (see Figure 11(c)). In this shrinkage process, the annular raised type or partially raised type shrinkage punch 1 of the present invention is inserted into the interior of the extruded can 109 obtained by the above extrusion process. While pressing the outer surface of the cylindrical body 109 against the inner surface of the annular shrinkage mold 121, the punch 1 is lowered, thereby thinning the side wall of the extruded can (cylindrical body) 109 by means of the mold 121. In this way, a metal can (thin-walled seamless can) 11 of the present invention with a thin wall and a height that increases according to the degree of thinning is obtained.

[0058] As can be understood from Figure 11, in the series of processes of punching, extrusion and shrinking, sliding is not required in punching, but as the process progresses from extrusion to shrinking, sliding between the die and the workpiece becomes increasingly necessary. In particular, in shrinking, sliding is most required because surface pressure exceeding the yield stress of the workpiece is applied. That is, a large surface pressure is also applied between the inner circumferential surface of the extrusion can 109 (the workpiece) and the outer circumferential surface 1a of the shrinking punch 1. Consequently, due to contact with the raised portion 5 in the annular raised shrinking punch 1 described above, an annular recess 12 and a dotted protrusion 15 are formed on the inner circumferential surface of the extrusion can 109 (metal can 11) (see Figure 2).

[0059] Moreover, the above-mentioned shrink-forming process can also be performed in multiple stages. For example, multiple shrink-forming dies can be arranged in the processing direction to perform multi-stage shrink-forming. In this way, a metal can 11 with increased shrink-forming rate, further thinning and increased height can also be obtained. Figure 12 shows an example of a procedure for performing multi-stage shrink-forming.

[0060] In the process of FIG12, along the processing direction, there are ring-shaped redrawing dies 111a and drawing dies 121a to 121c arranged in sequence. A guide ring 135 is arranged on the downstream side of the drawing die 121c, which is the most downstream side relative to the processing direction. A retaining ring 137 and a retaining rod 137a for bottom forming are arranged in sequence on the further downstream side.

[0061] Regarding the aforementioned shrinkage molds 121a to 121c, the more they are positioned downstream in the processing direction, the smaller their diameter and the more stringent the thin-wall treatment they undergo.

[0062] In this multi-stage shrinkage process (re-extrusion-shrinkage process), the extrusion can 109 is held on the re-drawing die 111a by the bracket 141. In this state, the shrinkage punch 1 of the present invention is inserted into the interior of the extrusion can 109. On the one hand, the outer surface of the extrusion can 109 is pressed against the inner surface (processing surface) of the re-drawing die 111a and the shrinkage dies 121a to 121c. On the other hand, the punch 1 is moved in the processing direction to perform re-extrusion and shrinkage processes, thereby obtaining a metal can 11 (metal cylinder) with thinner sidewalls and increased height of the extrusion can 109.

[0063] Furthermore, in Figure 12, three shrink molds are configured, but of course, two or more shrink molds can also be configured.

[0064] After the shrink-drawing process shown in Figures 11 and 12 is completed, as shown in Figure 5, a stop 20 is provided at the upper end of the metal can 11. Under the state of restricting its movement, the shrink-drawing punch 1 is pulled out. That is, in the present invention, the frictional resistance during the pulling is greatly reduced, and the production efficiency of the shrink-drawing process is improved.

[0065] The extrusion process and shrinkage process in the above-mentioned Figures 11 and 12 can be carried out under humid conditions while the coolant is flowing, or under dry conditions such as low lubrication mode using solid lubricant or no lubrication mode without using lubricant, without using coolant.

[0066] The metal can 11 (metal cylinder) after the pull-out and shrink-processing punch 1 is subjected to, for example, outer surface printing and shrink-processing, for sale. [Simplified Explanation of the Diagram]

[0015] [Fig. 1] is a diagram illustrating the thinning of the workpiece (metal cylinder) by the shrink-forming process. [Fig. 2] is a longitudinal section showing the shrink-forming punch (annular raised type) of the present invention and a partially enlarged rough longitudinal section of the thinned workpiece (metal cylinder). [Fig. 3] is a partially enlarged rough planar development view of the outer peripheral surface of the shrink-forming punch shown in Fig. 2. [Fig. 4] is a partially enlarged rough planar development view of the inner peripheral surface of the workpiece (metal cylinder) shown in Fig. 2. [Fig. 5] is a rough longitudinal section showing the joining relationship between the shrink-forming punch and the thinned seamless can at the end of the shrink-forming process when the workpiece is a seamless metal can. [Fig. 6] (a) and (b) are diagrams illustrating the roll-back shape caused by the pulling of the shrink-forming punch. [Fig. 7] is a longitudinal section (X section in Fig. 8) of the shrink-forming punch (partially raised type) of the present invention. [Fig. 8] is a partially enlarged rough planar development view of the outer peripheral surface of the shrink-forming punch shown in Fig. 7. [Fig. 9] is a partially enlarged side section view of the workpiece (metal cylinder) that has been thinned by shrink-forming using the shrink-forming punch of Fig. 7. [Fig. 10] is a diagram showing the joining relationship between the punch of Fig. 7 and the workpiece (metal cylinder) of Fig. 9 at the end of the shrink-forming process. [Fig. 11] (a) to (c) are diagrams showing an example of a stamping forming process using shrink-forming. [Fig. 12] is a diagram showing an example of a shrink-forming can forming process when performing multi-stage shrink-forming.

Claims

1. A shrinking punch for use in shrinking metal processing, characterized in that: dot-shaped recesses are distributed on the outer peripheral surface of the punch, and at least a portion of the periphery of the dot-shaped recesses is formed with a raised portion; the raised portion is formed on a portion of the periphery of the dot-shaped recesses.

2. The punch for the drawing and retracting process as claimed in claim 1, wherein the raised portion is formed on the side of the periphery of the dotted recess opposite to the front end side of the punch.

3. The punch for the drawing process as claimed in claim 2, wherein when viewed in cross-section along the axial direction of the punch, the shape of the aforementioned dotted recess is such that the deepest part is located on the side opposite to the front end of the punch.

4. For the shrink-forming punch of request item 3, wherein the eccentricity of the deepest part is in the range of 30% to 100%.

5. A shrink-forming process, characterized in that: a shrink-forming punch as claimed in claim 1 is inserted into a metal cylinder, and the metal cylinder is shrunk by passing through an annular mold; after the shrink-forming process is completed, the metal cylinder is thinned by pulling out the punch.

6. The shrink-forming method of claim 5, wherein the inner surface of the metal cylinder has an organic resin layer.

7. The shrink-forming process of claim 6, wherein the organic resin layer is formed of a thermoplastic resin.

8. A shrink tank having a hollow cylindrical main body and a bottom that closes the lower end of the main body, characterized in that: dot-shaped protrusions are distributed on the inner circumferential surface of the main body, and when viewed in a longitudinal section along the axial direction, the apex of the dot-shaped protrusions is located in a direction opposite to the bottom.

9. The shrink tank of claim 8, wherein an organic resin layer is laminated on the inner peripheral surface of the main body, and the aforementioned dotted protrusions are distributed on the surface of the organic resin layer.

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