Punch for ironing and metal cylindrical body obtained by ironing using said punch.

Abstract

To provide a punch for ironing which is excellent in drawability after ironing.SOLUTION: In a punch 1 for ironing used for ironing of a metal, dot-shaped recesses 3 are distributed on an outer peripheral surface 1a of the punch 1. When a cross section along a slide direction of the punch is viewed, each dot-like recess 3 has a shape in which its deepest part P is eccentrically located at the opposite side of a tip of the punch.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ironing punch used in ironing, and further to a metal cylindrical body, such as a seamless can, obtained by ironing using this ironing punch. [Background technology]

[0002] Ironing is a severe plastic processing method used to thin metals and is used to manufacture thin-walled, high-height cylindrical metal bodies, such as thin-walled seamless cans. Ironing is performed by passing a hollow metal body through a narrow space between an annular die and a rod-shaped punch. Specifically, the punch is inserted into the metal body to be thinned, the metal body is sandwiched between the punch and the annular die, and the punch and the annular die are moved (slid) relative to each other in this state to thin the metal body. For example, Patent Documents 1 and 2 disclose techniques for manufacturing seamless cans (drawn and ironed cans) using this ironing method.

[0003] In this ironing process, the punch must be removed from the thinned metal cylindrical body after the ironing process is completed. The problem here is that in the ironing process, the metal cylindrical body, which is the workpiece, is pressed strongly against the outer circumferential surface of the punch, which creates a large frictional resistance and prevents the punch from being smoothly removed, resulting in low productivity and, in some cases, in problems such as deformation of the inner surface of the formed metal cylindrical body due to the removal of the punch. The reality is that little research has been done on the pullability of the punch during such ironing.

[0004] For example, Patent Document 3 discloses a seamless metal can having a thermoplastic resin layer formed on the inner surface, in which numerous dot-like protrusions are formed in the thermoplastic resin layer on the inner surface. This technology alleviates the molecular orientation of the thermoplastic resin layer caused by the ironing process by forming the dot-like protrusions, thereby suppressing a decrease in dent resistance caused by the molecular orientation in the thermoplastic resin layer. That is, in Patent Document 3, to form the dot-like protrusions in the thermoplastic resin layer on the inner surface of the can, the ironing process is performed using a punch having dot-like recesses formed on the outer periphery. As can be seen from this, Patent Document 3 also does not consider at all the pull-out properties of the ironing punch. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 033791 [Patent Document 2] Patent Publication No. 2018-69256 [Patent Document 3] Patent No. 3327137 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ironing punch that has excellent drawability after ironing. Another object of the present invention is to provide a metal cylindrical body having a unique shape obtained by ironing using the above ironing punch. [Means for solving the problem]

[0007] According to the present invention, there is provided an ironing punch for use in ironing metal, The punch for ironing is characterized in that a large number of dot-shaped recesses are distributed on the outer peripheral surface of the punch, and when viewed in a cross section along the sliding direction of the punch, each of the dot-shaped recesses has a shape in which its deepest portion is located on the opposite side to the tip of the punch. In such an ironing punch, the eccentricity of the deepest part is preferably in the range of 30 to 100%.

[0008] The present invention also provides a metal cylinder having a hollow cylindrical shape and obtained by ironing using the above-mentioned ironing punch, characterized in that a large number of dot-shaped protrusions are distributed on the inner surface thereof, and when viewed in a longitudinal cross section along the axial direction, each of the dot-shaped protrusions has a shape in which the apex is biased in the direction opposite to the processing direction. According to the present invention, the device further has a hollow cylindrical shape, A large number of dot-shaped recesses are distributed on the outer peripheral surface, and when viewed in a cross section along the sliding direction of the punch, each of the dot-shaped recesses has a shape in which its deepest portion is located on the opposite side to the tip of the punch, and The present invention provides a metal cylindrical body obtained by ironing using an ironing punch having a raised portion on the opposite side of the recessed portion from the tip of the punch, characterized in that an organic resin layer is laminated on the inner peripheral surface thereof, and a large number of dot-shaped protrusions are distributed on the surface of the organic resin layer, and when viewed in a longitudinal cross section along the axial direction, each of the dot-shaped protrusions has a shape in which the apex is biased in the direction opposite to the processing direction, and the metal cylindrical body is formed during the ironing process.

[0009] In the metal cylindrical body of the present invention, (1 )before The organic resin is a thermoplastic resin; (2) one end of the hollow cylindrical shape is closed to form a bottom, forming a seamless can, and the apexes of the dot-like convex portions are located on the side opposite to the can bottom; is preferred. [Effects of the Invention]

[0010] The ironing punch of the present invention has a major feature in that dot-shaped recesses are distributed on the outer peripheral surface, and when viewed in a cross section along the sliding direction of the punch, each of the dot-shaped recesses has a shape in which its deepest portion is unevenly distributed on the side opposite to the tip of the punch. When a metal cylindrical body is ironed using a punch having dot-shaped recesses of this type distributed thereon, convex portions corresponding to the dot-shaped recesses are formed on the inner peripheral surface of the metal cylindrical body as the wall is thinned by the ironing process, and the pullability of the punch after ironing is greatly improved. That is, in the recess having the deepest portion eccentric to the side opposite to the tip of the punch as described above, when viewed in a cross section along the sliding direction of the punch, the side surface of the punch toward the tip of the punch is gently inclined, and when viewed in a similar cross section (a cross section along the axial direction), the protrusion formed on the inner peripheral surface of the metal cylinder corresponding to the recess also has a side surface whose apex is toward the tip of the punch that is gently inclined. Therefore, when a punch having a recess that engages with the protrusion on the inner peripheral surface of the metal cylinder in this manner is withdrawn, the punch is withdrawn while the inclined surfaces meet, allowing for smooth withdrawal of the punch and ensuring high productivity. For example, deformation of the metal cylinder due to excessive punch withdrawal can be effectively prevented. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram for explaining thinning of a workpiece (metallic cylindrical body) by ironing. [Figure 2] 2 is a partially enlarged axial cross-sectional view (cross-sectional view taken along the line XX) of the ironing punch of the present invention. FIG. [Figure 3] 3 is a partially enlarged schematic plan view of the outer peripheral surface of the ironing punch shown in FIG. 2. [Figure 4] FIG. 2 is a partially enlarged cross-sectional side view of a thinned workpiece (metallic cylindrical body). [Figure 5] 1 is a schematic vertical cross-sectional view showing the positional relationship between the ironing punch and the thinned seamless can at the end of ironing when the workpiece is a metal seamless can. FIG. [Figure 6]10 is a diagram showing the engagement relationship between dot-shaped recesses formed on the punch and dot-shaped protrusions formed on the workpiece (metallic cylindrical body) when the punch is pulled out. FIG. [Figure 7] 10A and 10B are diagrams for explaining the form of rollback that occurs when the ironing punch is withdrawn. [Figure 8] FIG. 1 is a diagram showing an example of a press forming process using ironing. [Figure 9] FIG. 10 is a diagram showing an example of a forming process when ironing is performed in multiple stages. DETAILED DESCRIPTION OF THE INVENTION

[0012] <About ironing> Ironing is known as a representative technique for plastic processing of metals and is widely used, for example, to manufacture thick, thin-walled seamless metal cans. As shown in Figure 1, ironing involves moving a workpiece (metal cylindrical body B) in the processing direction with an ironing punch A, while pressing an ironing die C against and rubbing the outer surface of the cylindrical body B, thereby thinning the wall of the cylindrical body B. Therefore, in this ironing process, the inner surface of the metal cylindrical body B is firmly attached to the outer surface of the ironing punch A.

[0013] In this type of ironing process, the ironing rate is expressed by the following formula, where t0 is the thickness of the metal cylindrical body before ironing and t1 is the thickness after ironing. The higher this ironing rate, the greater the surface pressure applied to the ironing die C and punch A, resulting in severe forming. Squeezing rate (%) = 100 × (t0-t1) / t0

[0014] The ironing punch A has a tubular (cylindrical) shape, is generally made of the same cemented carbide as the ironing die C described below, and is formed with a relatively thick wall so as not to deform during ironing. A drive shaft S (not shown in FIG. 1, but indicated by S in FIG. 5) for moving the punch A in the processing direction is connected to the inner surface of one end of the punch A (the upstream side in the processing direction in FIG. 1).

[0015] The metal constituting the metal cylinder B subjected to the ironing process may be any of a variety of metals or alloys, such as aluminum, copper, iron, or alloys containing these metals, or may be a surface-treated steel sheet such as tin-plated steel sheet or aluminum sheet subjected to a chemical conversion treatment. The inner peripheral surface of the metal cylinder B (the surface that comes into close contact with the outer peripheral surface of the ironing punch A) may be coated with an organic resin. Such a resin coating can prevent corrosion and scratches on the inner surface.

[0016] Furthermore, the ironing die C must be made of a fairly hard material because the surface pressure increases significantly as the ironing rate increases. Examples of such hard materials include cemented carbides obtained by sintering a mixture of tungsten carbide (WC) and a metal binder such as cobalt; cermets obtained by sintering a mixture of a metal carbide such as titanium carbide (TiC) or a titanium compound such as titanium carbonitride (TiCN) with a metal binder such as nickel or cobalt; and hard ceramics such as silicon carbide (SiC), silicon nitride (Si3N4), alumina (Al2O3), and zirconia (ZrO2). Furthermore, the working surface of such an ironing die C (the surface that comes into contact with the workpiece, i.e., the cylindrical body B) can be coated with a carbon film such as a diamond film. Such a carbon film can be formed by vapor deposition, such as CVD.

[0017] <Ironing punch and metal cylinder of the present invention> The above-mentioned ironing punch (hereinafter simply referred to as ironing punch) and the metal cylindrical body are in close contact with each other during ironing, and with this in mind, please refer to FIGS.

[0018] 2 and 3, for example, an ironing punch 1 of the present invention, generally designated by 1, has a large number of dot-shaped recesses 3 formed on its outer peripheral surface 1a. The recesses 3 distributed in a dot pattern are recessed in a cone shape such as a circular cone or a pyramid shape (shown as a cone shape in the example of the figure), but their deepest part P (corresponding to the apex of the cone shape) is eccentric in the direction opposite to the tip 1b of the punch 1 (the direction in which the punch 1 is pulled out).

[0019] The recess 3 having such a shape is formed by striking using a punch having a tip corresponding to the shape of the recess 3. That is, the striking mark becomes the shape of the recess 3. As a result, an arc-shaped raised portion 4 is formed on the side where the deepest portion P of the recess 3 is eccentric. The recess 3 having the above shape can also be formed by techniques such as ultrasonic machining, laser machining, electron beam irradiation, and ion irradiation without using a punch. However, in this case, the surface of the punch 1 is removed, and therefore the raised portion 4 as described above is not formed. In the present invention, forming the recess 3 by striking using a punch is preferable because the recess 3 can be formed at low cost without using special devices or equipment.

[0020] In the present invention, in the recess 3 having the above-described configuration, as shown in FIG. 2, the side surface on the tip side of the ironing punch 1 is a gently inclined surface 3a with a small inclination angle α, and the opposite surface is a steeply inclined surface 3b with a large inclination angle β.

[0021] When ironing is performed using the punch 1 having the above-described configuration, as shown in Fig. 4, convex portions 13 are formed on the inner peripheral surface of the metal cylinder 11, with apexes P' offset in the direction opposite to the machining direction (i.e., toward the punch tip 1b), corresponding to the dot-shaped concave portions 3. That is, because such convex portions 13 are formed, when the inner surface is coated with an organic resin, the orientation of the resin is moderated by the convex portions 13, thereby preventing a decrease in dent resistance. Furthermore, since such convex portions 13 have a shape corresponding to the above-described concave portions 3, they have gently inclined surfaces 13a with a small inclination angle α' corresponding to the gently inclined surfaces 3a of the concave portions 3, and they have steeply inclined surfaces 13b with a large inclination angle β' corresponding to the steeply inclined surfaces 3b of the concave portions 3.

[0022] After the ironing process is completed, the ironing punch 1 is inserted into the thinned metal cylindrical body 11, and the outer peripheral surface 1a of the ironing punch 1 is held in firm contact with the inner peripheral surface of the thinned metal cylindrical body 11. For example, in the example shown in FIG. 5, the metal cylindrical body 11 has a bottom 17 like a seamless can, and the ironing punch 1 extends to the bottom 17 of the cylindrical body 11. A region Q where the outer peripheral surface 1a of the ironing punch 1 contacts the inner peripheral surface of the metal cylindrical body 11 functions as a holding surface during the ironing process. Generally, a drive shaft S is connected to the ironing punch 1 above region Q. Drive of this shaft S moves the ironing punch 1 in the processing direction, and after the ironing process is completed, the ironing punch 1 is moved in the withdrawal direction, which is the opposite direction to the processing direction.

[0023] Therefore, after the ironing process is completed, the movement of the metal cylindrical body 11 in the direction in which the ironing punch 1 is pulled out is restricted by the stopper 20 so that the ironing punch 1 can be pulled out. 5, when the metal cylinder 11 has a bottom 17, such as a can, assist air is blown in at the same time as the drive shaft S pulls it out, making it easy to pull out the ironing punch 1. When the metal cylinder 11 does not have a bottom 17, such as a hollow pipe, one end of the cylinder 11 (the end on the processing direction side) is formed with a small diameter so that the ironing punch 1 can firmly hold and move the metal cylinder 11, preventing the punch 1 from slipping out.

[0024] In the present invention, the outer peripheral surface 1a of the ironing punch 1 is formed with the recess 3, the deepest part P of which is eccentric, and correspondingly, the inner peripheral surface 11a of the ironed metal cylindrical body 11 is formed with the protrusion 13, the apex P' of which is eccentric. Therefore, when the ironing punch 1 is withdrawn after the ironing process is completed, as shown in Figure 6, the gently sloping surface 3a of the recess 3 of the ironing punch 1 comes into contact with the gently sloping surface 13a of the protrusion 13 on the inner peripheral surface of the metal cylindrical body 11 while being withdrawn. As a result, the ironing punch 1 can be withdrawn smoothly, effectively avoiding unnecessary deformation of the metal cylindrical body 11 during withdrawal.

[0025] For example, if the deepest part P of the recess 3 formed in the outer peripheral surface 1a of the ironing punch 1 is not eccentric, that is, if the recess 3 has an axisymmetric shape when viewed in a cross section along the sliding direction, the inclination angle of the surface that comes into contact with the punch 1 when it is withdrawn will be large, and the resistance to the withdrawal of the punch 1 will be large, preventing smooth withdrawal of the punch, reducing productivity, and also increasing the load on the drive shaft S and the like, which tends to shorten the life of the device.

[0026] Furthermore, the ideal shape of the metal cylindrical body 11 obtained by ironing is one in which the upper open end portion is straight, as shown in Figure 7(a), but if the punch 1 is forcibly removed, rollback, in which the upper open end protrudes outward, is likely to occur, as shown in Figure 7(b). In the present invention, by performing the ironing process using the ironing punch 1 having the recess 3 described above, the retractability of the punch 1 is improved, and the occurrence rate of such rollback can be reduced to almost zero.

[0027] The eccentricity of the deepest part P of the recess 3 formed on the outer peripheral surface 1a of the ironing punch 1 described above is expressed by the following formula. Eccentricity=100d / (1 / 2)D=(2d / D)×100 In the formula, d is the distance between the apex P and the center of the recess 3 (the eccentricity of the apex P), D indicates the diameter of the recess 3 . In the present invention, the eccentricity of the deepest portion P is preferably in the range of 30 to 100%, and particularly 75 to 95%. If the eccentricity is lower than 30%, the inclination angle α of the gently sloping surface of the recess 3 becomes large, impairing the pullability of the punch 1 and resulting in an occurrence rate of large deformations, for example, rollback amounts of 5.0 mm or more, of approximately 30%. However, experiments have confirmed that by setting the eccentricity to 30% or more, particularly 75% or more, the occurrence rate of large deformations, for example, rollback amounts of 5.0 mm or more, can be reduced to almost zero. Furthermore, if the eccentricity approaches 100%, the end of the recess 3 opposite the machining direction will have a sharp corner, which tends to make the ironing punch 1 more susceptible to breakage.

[0028] The depth t of the recesses 3 is preferably about 0.2 to 10.0 μm. If the depth t is too large, the retractability of the ironing punch 1 may be impaired, while if the depth t is too small, the protrusions 13 formed corresponding to the recesses 3 will be small, which will result in insufficient relaxation of the orientation of the organic resin film and a tendency to impair dent resistance. Furthermore, it is preferable for the ironing punch 1 to be smoothly pulled out if the recesses 3 are distributed in the region Q of the ironing punch 1 so as to be uniformly distributed in the longitudinal and circumferential directions of the ironing punch 1. Furthermore, from the viewpoint of greatly reducing the frictional resistance without significantly reducing the strength of the punch 1, it is preferable to distribute the recesses 3 in the region Q at a density of 30 to 400 recesses / cm. 2 It is desirable that the recesses 3 are distributed at an area ratio of .

[0029] According to the present invention, by forming a large number of recesses 3, each having an eccentric deepest point P, in a dot pattern on the outer peripheral surface of the ironing punch 1, protrusions 13, each having an eccentric apex P' corresponding to the recesses 3, are formed on the inner peripheral surface 11a of the metal cylindrical body 11 by the ironing process.As a result, frictional resistance when the ironing punch 1 is pulled out is greatly reduced, the life of the device is extended, and productivity is increased.

[0030] <Press forming process using ironing> The ironing process using the ironing punch 1 described above is used to thin the walls of various metal cylindrical bodies 11, but is most preferably used in press molding to produce thin-walled, high-height metal cans (seamless cans). Figure 8 shows the manufacturing process for such metal cans.

[0031] In Fig. 8, a blank (e.g., an aluminum plate) 101 used to form a metal can is first punched to obtain a disk 103 for the metal can (see Fig. 8(a)). The above-mentioned organic resin coating is laminated on one side of this blank 101. The thickness of the base plate 101 varies depending on the type of metal, the purpose or size of the can, but is generally preferably 0.10 to 0.50 mm. In particular, in the case of a surface-treated steel plate, the thickness is preferably 0.10 to 0.30 mm, and in the case of a light metal plate such as aluminum, the thickness is preferably 0.15 to 0.40 mm.

[0032] Organic resin coatings include coatings derived from paints such as acrylic paints, urethane paints, silicone paints, and fluorine paints, as well as those derived from thermoplastic resins, and have been used conventionally for corrosion resistance and to suppress surface roughness during severe molding processes, etc. In the present invention, organic resin coatings formed from thermoplastic resins are particularly suitable.

[0033] That is, the thermoplastic resin coating can be easily laminated onto the base sheet 101 using a laminating roll, and the molecular orientation occurs through bending and stretching by drawing and ironing, thereby improving the barrier properties against corrosive components and heat resistance. On the other hand, as disclosed in Patent Document 3, the molecular orientation of the organic resin coating tends to cause the resin to fibrillate, which makes the can more susceptible to cracking in the height direction upon impact and tends to deteriorate dent resistance. However, in the present invention, numerous dot-shaped protrusions 13 are formed on the inner surface of the can by ironing using a punch 1 having dot-shaped recesses 3, and these protrusions 13 mitigate the molecular orientation, preventing a decrease in dent resistance.

[0034] Examples of the thermoplastic resin include polyolefins such as low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, and random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene; ethylene-vinyl compound copolymers such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, and ethylene-vinyl chloride copolymer; styrene resins such as polystyrene, acrylonitrile-styrene copolymer, ABS, and α-methylstyrene-styrene copolymer; polyvinyl compounds such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, polymethyl acrylate, and polymethyl methacrylate; polyamides such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, and nylon 12; thermoplastic polyesters such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate; polyphenylene oxide; and mixtures thereof. Among these thermoplastic resins, polyester resins are particularly suitable in terms of processability, corrosion resistance, and ability to retain the flavor of the contents of the can.

[0035] The punching process uses a punch 105 having an outer diameter corresponding to the diameter of the disk 103, and a die 107 that holds the blank 101 and has an opening corresponding to the diameter of the disk 103. That is, the blank 101 held on the die 107 is punched out by the punch 105 to obtain a disk 103 of a predetermined size. Depending on the shape of the molded product to be produced in this manufacturing process, the blank 101 may be punched out into other shapes (for example, rectangular).

[0036] The disk 103 obtained as described above is subjected to drawing, thereby obtaining a low-height drawn can (bottomed cylindrical body) 109 (see FIG. 8(b)). In this drawing process, the punched disk 103 is held on a die 111, and the periphery of this disk 103 is held by a clamping jig 113. An opening is formed in the die 111, and by using a drawing punch 115 to push the disk 103 into the opening of the die 111, a drawn can 109 is obtained. The upper corner of the opening of the die 111 (the side holding the disk 103) is rounded (curved), so that the disk 103 can be pushed into the opening of the die 111 quickly and without breaking, and the outer diameter of the punch 115 is set smaller than the diameter of the opening of the die 111 by an amount roughly equivalent to the thickness of the disk 103. In other words, this drawing process hardly results in thinning. The drawing process may be performed multiple times depending on the shape of the molded product.

[0037] Next, the drawn can 109 obtained above is subjected to an ironing process, whereby a metal can (thin-walled seamless can) 11 with a large height and thin wall is formed (see FIG. 8(c)). In this ironing process, an ironing punch 1 according to the present invention is inserted into the drawn can 109 obtained by the above-mentioned drawing process, and the punch 1 is lowered while pressing the outer surface of the cylindrical body 109 against the inner surface of a ring-shaped ironing die 121, thereby thinning the sidewall of the drawn can (cylindrical body) 109 by the die 121. This results in a metal can (thin-walled seamless can) 11 according to the present invention that has been thinned and whose height has increased depending on the degree of thinning.

[0038] As can be seen from Figure 8, in this series of punching, drawing, and ironing steps, sliding properties are not necessary during punching, but as the process progresses from drawing to ironing, sliding properties become increasingly important between the die and the workpiece. Ironing, in particular, requires the greatest sliding properties because a surface pressure exceeding the yield stress of the workpiece is applied. This means that a large surface pressure is also applied between the inner surface of the workpiece (drawn can 109) and the outer surface 1a of the ironing punch 1. As a result, a convex portion 13 with an eccentric apex P' is formed on the inner surface of the drawn can 109, corresponding to the concave portion 3 with an eccentric deepest point P formed in the punch 1.

[0039] The ironing process can also be performed in multiple stages. For example, by arranging a plurality of ironing dies in the ironing direction and performing the ironing process in multiple stages, it is possible to increase the ironing rate and obtain a thinner-walled, taller metal can 11. Figure 9 shows an example of a process in which the ironing process is performed in multiple stages.

[0040] In the process shown in FIG. 9, a ring-shaped redraw die 111a and ironing dies 121a to 121c are arranged in this order along the processing direction, and a guide ring 135 is disposed downstream of the ironing die 121c, which is located furthest downstream in the processing direction, and a retaining ring 137 and a retaining rod 137a, which form the bottom portion, are disposed further downstream in this order.

[0041] The ironing dies 121a to 121c have smaller diameters as they are arranged downstream in the processing direction, so that more severe thinning can be performed.

[0042] In this type of multi-stage ironing process (re-drawing-ironing), the drawn can 109 is held on the redraw die 111a by a holder 141, and in this state the ironing punch 1 of the present invention is inserted into the inside of the drawn can 109. The punch 1 is moved in the processing direction while pressing the outer surface of the drawn can 109 against the inner surfaces (processing surfaces) of the redraw die 111a and ironing dies 121a to 121c, thereby performing the re-drawing and ironing processes, thinning the side walls of the drawn can 109 and producing a taller metal can 11 (metallic cylindrical body).

[0043] Although three ironing dies are arranged in FIG. 9, it is of course possible to arrange two ironing dies, or to arrange more than three ironing dies.

[0044] After the ironing process shown in Figures 8 and 9 is completed, a stopper 20 is placed on the top end of the metal can 11, and the ironing punch 1 is withdrawn while its movement is restricted, as shown in Figure 5. In other words, in the present invention, the frictional resistance during this withdrawal is greatly reduced, thereby improving the production efficiency of the ironing process.

[0045] The drawing and ironing processes in the processes shown in Figures 8 and 9 can be performed under wet conditions with a coolant flowing through them, or they can be performed under dry conditions without using coolant, such as a low-lubrication method using a solid lubricant or a no-lubrication method using no lubricant.

[0046] After the ironing punch 1 is pulled out, the metal can 11 (metallic cylindrical body) undergoes, for example, exterior printing or neck-in processing, and is then put up for sale. [Explanation of symbols]

[0047] A: Ironing punch B: Metal cylinder (molded object) C: Squeezing Dice 1: Squeezing Punch 1a: Outer surface of ironing punch 1 3: Dot-shaped recesses P: Deepest part of recess 3 11: Metal cylindrical body 11a: inner circumferential surface of metal cylindrical body 11 13: Dot-shaped convex part P': vertex of convex part 13

Claims

1. In ironing punches used in metal ironing, a plurality of dot-shaped recesses are distributed on the outer peripheral surface of the punch, and each of the dot-shaped recesses has a shape such that, when viewed in a cross section along the sliding direction of the punch, its deepest portion is located on the side opposite to the tip of the punch.

2. 2. The ironing punch according to claim 1, wherein the eccentricity of the deepest portion is in the range of 30 to 100%.

3. 3. A metal cylindrical body having a hollow cylindrical shape and obtained by ironing using the ironing punch according to claim 1 or 2, characterized in that a large number of dot-shaped protrusions are distributed on the inner peripheral surface thereof, and when viewed in a longitudinal cross section along the axial direction, each of the dot-shaped protrusions has a shape in which an apex is biased in the direction opposite to the processing direction side.

4. A metal cylinder obtained by ironing using an ironing punch having a hollow cylindrical shape and a large number of dot-shaped recesses distributed on its outer peripheral surface, each of which has a shape such that, when viewed in a cross section along the sliding direction of the punch, the deepest part of the dot-shaped recesses is biased toward the opposite side to the tip of the punch, and each of the recesses has a raised part on the opposite side to the tip of the punch; the metal cylinder has an organic resin layer laminated on its inner peripheral surface, and a large number of dot-shaped protrusions distributed on the surface of the organic resin layer, and each of the dot-shaped protrusions has a shape such that, when viewed in a vertical cross section along the axial direction, the apex of the dot-shaped protrusions is biased toward the opposite side to the processing direction, and is formed during the ironing process.

5. 5. The metal cylindrical body according to claim 4, wherein the organic resin is a thermoplastic resin.

6. A metal cylinder according to any one of claims 3 to 5, wherein one end of the hollow cylindrical shape is closed to form a bottom, making it a seamless can, and the apexes of the dot-shaped convex portions are located on the side opposite the can bottom.

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