A punch for ironing and a metal cylinder obtained by ironing using the punch.

Abstract

The present invention provides a punch for ironing that exhibits excellent pull-out properties after ironing, and a metal cylindrical body obtained by ironing using the punch. [Solution] The metal cylinder has a hollow cylindrical shape and is obtained by ironing, wherein numerous dot-shaped protrusions are distributed on its inner circumferential surface, 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 toward the direction opposite to the processing direction.

Description

Technical Field

[0001] The present invention relates to a punching die for ironing used in ironing, and further relates to a metal cylindrical body obtained by ironing using this punching die for ironing, such as a seamless can.

Background Art

[0002] Ironing is a severe plastic working performed for thinning metal, and is applied to the production of a metal cylindrical body that has been thinned and has a high height, such as a thin-walled seamless can. Such ironing is performed by passing a hollow metal cylindrical body through a narrow space between an annular die and a rod-shaped punch. Specifically, a punch is inserted into the metal cylindrical body to be thinned, the metal cylindrical body is sandwiched between the punch and the annular die, and in this state, the punch and the annular die are relatively moved (slid) to thin the metal cylindrical body. For example, Patent Documents 1 and 2 disclose techniques for manufacturing a seamless can (drawn and ironed can) by applying such ironing.

[0003] By the way, in such ironing, after the ironing is completed, the punch must be pulled out from the thinned metal cylindrical body. Here, the problem is that in ironing, since the metal cylindrical body as the workpiece is strongly pressed against the outer peripheral surface of the punch, a large frictional resistance acts, and the punch cannot be smoothly pulled out, resulting not only in low productivity but also in problems such as deformation of the inner surface of the formed metal cylindrical body due to the pulling out in some cases. In fact, almost no consideration has been given to the drawability of the punch during such ironing.

[0004] For example, Patent Document 3 discloses a seamless metal can having a thermoplastic resin layer formed on its inner surface, wherein numerous dot-like protrusions are formed on the inner thermoplastic resin layer. This technology aims to mitigate the molecular orientation of the thermoplastic resin layer caused by ironing by forming dot-like protrusions, thereby suppressing the decrease in dent resistance caused by molecular orientation in the thermoplastic resin layer. Specifically, in Patent Document 3, ironing is performed using a punch with dot-like recesses formed on its outer surface in order to form dot-like protrusions on the thermoplastic resin layer on the inner surface of the can. As can be seen from this, Patent Document 3 also does not consider the pullability of the punch for ironing at all. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2017 / 033791 [Patent Document 2] Japanese Patent Publication No. 2018-69256 [Patent Document 3] Patent No. 3327137 [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the object of the present invention is to provide a punch for ironing that has excellent pull-out properties after ironing. Another object of the present invention is to provide a metal cylindrical body having a unique shape obtained by ironing using the ironing punch described above. [Means for solving the problem]

[0007] According to the present invention, a metal cylinder is provided which has a hollow cylindrical shape and is obtained by ironing, wherein a large number of dot-shaped protrusions are distributed on its inner circumferential surface, 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 toward the direction opposite to the processing direction. In the metal cylindrical body of the present invention, (1) An organic resin layer is laminated on the inner circumferential surface, and the dot-shaped protrusions are distributed on the surface of the organic resin coating layer. (2) The organic resin is a thermoplastic resin. This is preferable.

[0008] The present invention also provides a punch for ironing metal, characterized in that a large number of dot-shaped recesses are distributed on the outer surface of the punch, and when viewed in a cross-section along the sliding direction of the punch, there is an arc-shaped raised portion on the side opposite to the tip of the punch.

[0009] The present invention further provides a metal cylinder having a hollow cylindrical shape, obtained by ironing using the ironing punch described above, wherein a large number of dot-shaped protrusions are distributed on its inner circumferential surface, and when viewed in a longitudinal cross-section along the axial direction, the apex of each of the dot-shaped protrusions is offset in the direction opposite to the processing direction. [Effects of the Invention]

[0010] The ironing punch of the present invention has dot-shaped recesses distributed on its outer surface, but a key feature is that, when viewed in cross-section along the sliding direction of the punch, the deepest part of each dot-shaped recess is located on the side opposite to the tip of the punch. When ironing a metal cylinder is performed using a punch with dot-shaped recesses of this form, as the wall thickness is reduced by ironing, protrusions are formed on the inner surface of the metal cylinder corresponding to these dot-shaped recesses, and the pull-out performance of the punch after ironing is greatly improved. In other words, in a recess with a shape where the deepest part is eccentrically off-center from the punch tip, when viewed in a cross-section along the direction of the punch's sliding motion, the side surface on the punch tip side becomes a gently sloping surface. Similarly, when viewed in a cross-section (a cross-section along the axial direction), the apex of the protrusion formed on the inner surface of the metal cylinder corresponding to the recess also becomes a gently sloping surface on the side surface on the punch tip side. Therefore, when a punch having a recess that engages with a protrusion on the inner surface of the metal cylinder in this manner is withdrawn, the aforementioned sloping surfaces come into contact with each other as the punch is withdrawn, allowing for smooth punch withdrawal and ensuring high productivity. For example, deformation of the metal cylinder due to forced punch withdrawal can be effectively prevented. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram illustrating the thinning of a workpiece (metal cylinder) by ironing. [Figure 2] A partially enlarged axial cross-sectional view (XX cross-sectional view) of the ironing punch of the present invention. [Figure 3] Figure 2 shows a partially enlarged schematic plan view of the outer surface of the ironing punch. [Figure 4] A partially enlarged cross-sectional view of a thinned workpiece (metal cylinder). [Figure 5] A schematic longitudinal cross-sectional view showing the positional relationship between the ironing punch and the thinned seamless can at the end of the ironing process when the workpiece is a metal seamless can. [Figure 6] This diagram shows the engagement relationship between the dot-shaped recesses formed on the punch and the dot-shaped protrusions formed on the workpiece (metal cylinder) during punch withdrawal. [Figure 7] A diagram illustrating the rollback pattern generated by the withdrawal of a punch used for ironing. [Figure 8] A diagram illustrating an example of a press forming process utilizing ironing. [Figure 9] A diagram illustrating an example of a molding process when ironing is performed in multiple stages.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] <Regarding Ironing Process> Ironing is known as a typical method of plastic working of metals and is widely used, for example, in the manufacturing method of seamless metal cans with high height and reduced wall thickness. As shown in FIG. 1, in this ironing process, when the metal cylindrical body B as the workpiece is moved in the processing direction by the ironing punch A, the ironing die C is pressed against and rubbed on the outer surface of the cylindrical body B to reduce the wall thickness of the cylindrical body B. Therefore, in such an ironing process, the inner peripheral surface of the metal cylindrical body B will be firmly adhered to the outer peripheral surface of the ironing punch A.

[0013] In such an ironing process, the ironing rate is expressed by the following formula when the plate thickness t0 of the metal cylindrical body before ironing and the plate thickness after processing are t1. The larger this ironing rate, the greater the surface pressure applied to the ironing die C and further to the punch A, resulting in a more severe forming. Ironing rate (%) = 100×(t0 - t1) / t0

[0014] The ironing punch A has a tubular (cylindrical) shape and is generally formed of the same cemented carbide as the ironing die C described later, and is formed relatively thick so as not to be deformed by the ironing process. Further, a drive shaft S (not shown in FIG. 1 and 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 with respect to the processing direction in FIG. 1).

[0015] Also, the metal which is the constituent material of the metal cylindrical body B subjected to the above-described ironing process may be various metals or alloys, for example, aluminum, copper, iron, or alloys containing these metals, and further may be a surface-treated steel plate such as a tin-plated steel sheet like tinplate or an aluminum plate subjected to chemical conversion treatment. Further, the inner peripheral surface of the metal cylindrical body B (the surface in close contact with the outer peripheral surface of the ironing punch A) may be coated with an organic resin. By such resin coating, corrosion and damage of the inner surface can be prevented.

[0016] Furthermore, as the ironing rate increases, the ironing die C is subjected to significantly higher surface pressure, making it necessary to form it from a fairly hard material. Examples of such hard materials include so-called cemented carbide, 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) or titanium compounds such as titanium carbonitride (TiCN) with a metal binder such as nickel or cobalt; or hard ceramics such as silicon carbide (SiC), silicon nitride (Si3N4), alumina (Al2O3), and zirconia (ZrO2). In addition, the machined surface of such an ironing die C (the surface that contacts the cylindrical body B, which is the workpiece) 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] <The present invention: a punch and metal cylinder for ironing> The ironing punch (hereinafter simply referred to as the ironing punch) and the metal cylinder are in close contact during the ironing process. Please refer to Figures 2 to 6 with this in mind.

[0018] For example, referring to Figures 2 and 3, the ironing punch 1 of the present invention, shown as a whole as 1, has numerous dot-shaped recesses 3 formed on its outer surface 1a. The dot-shaped recesses 3 are concave in a conical shape, such as a cone or pyramidal shape (in the example shown in the figures, they are conical), 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 (towards the direction in which the punch 1 is pulled out).

[0019] A recess 3 of this shape is formed by striking with a punch having a tip that corresponds to the shape of the recess 3. That is, the indentation becomes the shape of the recess 3. As a result, a curved raised portion 4 is formed on the side where the deepest part P of the recess 3 is eccentric. Although it is possible to form a recess 3 of the above shape by methods such as ultrasonic processing, laser processing, electron beam irradiation, or ion irradiation without using a punch, in this case the surface of the punch 1 is removed, so the raised portion 4 described above is not formed. In the present invention, forming the recess 3 by striking with a punch is preferable because it can be formed at low cost without using special devices or equipment.

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

[0021] When ironing is performed using the punch 1 having the above-described shape, as shown in Figure 4, a convex portion 13 is formed on the inner circumferential surface of the metal cylinder 11, corresponding to the dot-shaped recess 3, with its vertex P' being offset in the direction opposite to the processing direction (i.e., the punch tip 1b side). That is, because such a convex portion 13 is formed, when the inner surface is coated with organic resin, its orientation is mitigated by the convex portion 13, thereby suppressing a decrease in dent resistance. Furthermore, since such a convex portion 13 has a shape corresponding to the recess 3 described above, it has a gently sloping surface 13a with a small inclination angle α' corresponding to the gently sloping surface 3a of the recess 3, and a steeply sloping surface 13b with a large inclination angle β' corresponding to the steeply sloping surface 3b of the recess 3.

[0022] Incidentally, when the ironing process is completed, the thinned metal cylinder 11 is held in a state where the ironing punch 1 is inserted inside and the outer surface 1a of the ironing punch 1 is firmly in contact with the inner surface of the thinned metal cylinder 11. For example, in the example in Figure 5, the metal cylinder 11 has a bottom 17 like a seamless can, and the ironing punch 1 extends to this bottom 17 of the cylinder 11. The region Q in which the outer surface 1a of the ironing punch 1 is in contact with the inner surface of the metal cylinder 11 functions as a processing holding surface during the ironing process. Generally, a drive shaft S is connected to the portion of the ironing punch 1 above region Q, and the ironing punch 1 moves in the processing direction by driving this shaft S. 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 stopper 20 restricts the movement of the metal cylindrical body 11 in the direction of pulling out the ironing punch 1, in order to withdraw the ironing punch 1. As shown in Figure 5, when the metal cylinder 11 has a bottom 17, like a can, assist air is blown in at the same time as the drive shaft S pulls it out, making it easier to pull out the ironing punch 1. When the metal cylinder 11 does not have a bottom 17, like a hollow pipe, one end of the cylinder 11 (the end on the processing direction side) is formed to be small in diameter so that the ironing punch 1 can firmly hold and move the metal cylinder 11, preventing the punch 1 from coming out.

[0024] In this invention, a recess 3 with an eccentric shape at its deepest point P is formed on the outer circumferential surface 1a of the ironing punch 1, and correspondingly, a convex portion 13 with an eccentric shape at its apex P' is formed on the inner circumferential surface 11a of the ironed metal cylinder 11. 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 is withdrawn while in contact with the gently sloping surface 13a of the convex portion 13 on the inner circumferential surface of the metal cylinder 11. As a result, the ironing punch 1 can be withdrawn smoothly, and unwanted deformation of the metal cylinder 11 that occurs during withdrawal can be effectively avoided.

[0025] For example, if the deepest part P of the recess 3 formed on the outer surface 1a of the ironing punch 1 is not eccentric, that is, if the recess 3 has a symmetrical shape when viewed in cross-section along the sliding direction, the angle of inclination of the surface that comes into contact with the punch 1 during withdrawal will be large. As a result, the resistance to withdrawing the punch 1 will be large, making it difficult to withdraw the punch smoothly, which will reduce productivity. In addition, the load on the drive shaft S and the like will increase, and the lifespan of the device will tend to decrease.

[0026] Furthermore, the ideal form of the metal cylindrical body 11 obtained by ironing is that the upper opening is straight, as shown in Figure 7(a). However, if the punch 1 is forcibly removed, rollback occurs, causing the upper opening to protrude outward, as shown in Figure 7(b). In the present invention, by performing ironing using the ironing punch 1 having the recess 3 described above, the ease of removing the punch 1 is improved, and the occurrence rate of such rollback can be reduced to almost zero.

[0027] The eccentricity ratio of the deepest part P of the recess 3 formed on the outer 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 vertex P and the center of the recess 3 (the eccentricity of the vertex P). D indicates the diameter of the recess 3. In this invention, it is preferable that the eccentricity of the deepest part P is in the range of 30 to 100%, 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 pull-out performance of the punch 1, and the occurrence rate of large deformations with a rollback amount of 5.0 mm or more becomes about 30%. However, experiments have confirmed that by setting the eccentricity to 30% or more, particularly 75% or more, the occurrence rate of large deformations with a rollback amount 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 to the processing direction becomes a sharp corner, which tends to cause damage to the ironing punch 1.

[0028] Furthermore, the depth t of the recess 3 is preferably about 0.2 to 10.0 μm. If this depth t is excessively large, the pull-out performance of the ironing punch 1 may be impaired, and if the depth t is excessively small, the protrusion 13 formed in correspondence with the recess 3 becomes small, resulting in insufficient orientation relaxation of the organic resin coating and a tendency for dent resistance to be impaired. Furthermore, it is preferable for the smooth withdrawal of the ironing punch 1 if the recesses 3 are distributed evenly in the longitudinal and circumferential directions of the ironing punch 1 in the aforementioned region Q of the ironing punch 1, and from the viewpoint of significantly reducing frictional resistance without significantly reducing the strength of the punch 1, the region Q should have 30 to 400 recesses / cm². 2 It is desirable that the recesses 3 are distributed in the area ratio shown.

[0029] According to the present invention, by forming a large number of dot-like recesses 3 having an eccentric deepest part P on the outer circumferential surface of the ironing punch 1, a convex portion 13 having an eccentric apex P' corresponding to the recess 3 is formed on the inner circumferential surface 11a of the metal cylindrical body 11 by ironing. As a result, the frictional resistance when withdrawing the ironing punch 1 is greatly reduced, the lifespan 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 can be used to thin various metal cylindrical bodies 11, but most preferably it is used for press forming to manufacture thin-walled, high-height metal cans (seamless cans). Figure 8 shows the manufacturing process for such a metal can.

[0031] In Figure 8, the base sheet (e.g., an aluminum sheet) 101 used for forming the metal can is first subjected to a punching process to obtain a disc 103 for the metal can (see Figure 8(a)). The aforementioned organic resin coating is laminated onto one side of this base sheet 101. The thickness of the base plate 101 varies depending on the type of metal, the intended use of the can, and its size, but it is generally preferable to have a thickness of 0.10 to 0.50 mm. Among these, surface-treated steel plates are preferable to have a thickness of 0.10 to 0.30 mm, and light metal plates such as aluminum are preferable to have a thickness of 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 coatings derived from thermoplastic resins. These have been conventionally used to provide corrosion resistance and suppress surface roughness during harsh molding processes. In the present invention, organic resin coatings formed from thermoplastic resins are particularly preferred.

[0033] In other words, the thermoplastic resin coating can be easily laminated onto the base plate 101 using a laminating roll, and furthermore, molecular orientation is achieved by bending and stretching through drawing and ironing processes, thereby increasing the barrier properties against corrosive components and also improving heat resistance. On the other hand, as disclosed in Patent Document 3, the molecular orientation of the organic resin coating causes a tendency for the resin to fibrillate, which makes it easier for cracks in the height direction of the can to occur due to impact, and tends to worsen dent resistance. However, in the present invention, by ironing using a punch 1 having dot-shaped recesses 3, a large number of protrusions 13 are formed in a dot shape on the inner surface of the can, and molecular orientation is mitigated by these protrusions 13, thereby avoiding a decrease in dent resistance.

[0034] Examples of the thermoplastic resins mentioned above 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, 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-based 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, methyl polyacrylate, 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 flavor retention of canned contents.

[0035] In the punching process, a punching punch 105 having an outer diameter corresponding to the diameter of the disc 103 and a die 107 that holds the raw sheet 101 and has an opening corresponding to the diameter of the disc 103 are used. That is, by punching out the raw sheet 101 held on the die 107 with the punch 105, a disc 103 of a predetermined size is obtained. Furthermore, depending on the form of the molded product manufactured in this manufacturing process, the base sheet 101 may also be punched out into other shapes (for example, rectangular).

[0036] The disc 103 obtained as described above is subjected to a drawing process to obtain a low-height drawn can (bottomed cylindrical body) 109 (see Figure 8(b)). In this drawing process, a punched-out disc 103 is held on a die 111, and the periphery of the disc 103 is held by a wrinkle-preventing jig 113. An opening is formed in the die 111, and a drawing can 109 is obtained by pressing the disc 103 into the opening of the die 111 using a drawing punch 115. Furthermore, a radius (curvature) is formed at the upper corner of the opening of the die 111 (the side that holds the disc 103), so that the disc 103 is quickly and without breaking into the opening of the die 111. 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 roughly equivalent to the thickness of the disc 103. In other words, thinning of the wall is hardly performed in this drawing process. Note that 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 ironing, thereby forming a metal can (thin-walled seamless can) 11 that is tall and thin-walled (see Figure 8(c)). In this ironing process, an ironing punch 1 according to the present invention is inserted into the ironed can 109 obtained by the above-mentioned drawing process, and the outer surface of the cylindrical body 109 is pressed against the inner surface of the ring-shaped ironing die 121 while the punch 1 is lowered, so that the side walls of the ironed can (cylindrical body) 109 are thinned by the die 121. As a result, a metal can (thinned seamless can) 11 of the present invention is obtained that is thinned and has an increased height depending on the degree of thinning.

[0038] As can be seen from Figure 8, in this series of processes of punching, drawing, and ironing, sliding is not required in punching, but as the process progresses from drawing to ironing, sliding between the die and the workpiece becomes more necessary. In particular, ironing requires the most sliding because a surface pressure exceeding the yield stress of the workpiece is applied. That is, a large surface pressure is applied between the inner surface of the drawing can 109, which is the workpiece, and the outer surface 1a of the ironing punch 1. Consequently, a convex portion 13 with an eccentric apex P' is formed on the inner surface of the drawing can 109, corresponding to the recess 3 with an eccentric deepest part P formed in the punch 1.

[0039] Furthermore, the ironing process described above can be performed in multiple stages. For example, by arranging multiple ironing dies in the processing direction and performing the ironing process in multiple stages, the ironing rate can be increased, resulting in a thinner metal can 11 with a higher height. Figure 9 shows an example of a process for performing the ironing process in multiple stages.

[0040] In the process shown in Figure 9, ring-shaped redraw dies 111a and wiping dies 121a to 121c are arranged in this order along the machining direction. A guide ring 135 is positioned downstream of the wiping die 121c, which is located furthest downstream in the machining direction, and further downstream, a retaining ring 137 and a retaining rod 137a for bottom forming are provided in this order.

[0041] The ironing dies 121a to 121c described above have smaller diameters the further downstream they are positioned in the machining direction, allowing for more extreme thinning of the material.

[0042] In this multi-stage ironing process (re-drawing-ironing), the drawing can 109 is held on the redraw die 111a by the holder 141. In this state, the ironing punch 1 of the present invention is inserted into the inside of the drawing can 109, and the outer surface of the drawing can 109 is pressed against the inner surface (processing surface) of the redraw die 111a and the ironing dies 121a-121c while the punch 1 is moved in the processing direction. This performs re-drawing and ironing, thinning the side walls of the drawing can 109 and resulting in a metal can 11 (metal cylinder) with a greater height.

[0043] Note that while Figure 9 shows three squeezing dies, it is certainly possible to use two dies, or even more than three.

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

[0045] The drawing and ironing processes in the processes shown in Figures 8 and 9 above can be carried out under wet conditions with coolant flowing, or under dry conditions such as a low-lubrication method using solid lubricants or a lubrication-free method without lubricants.

[0046] After the cutting punch 1 is removed, the metal can 11 (metal cylinder) is subjected to processes such as external printing or neck-in processing and then put up for sale. [Explanation of Symbols]

[0047] A: Punch for ironing B: Metal cylinder (molded object) C: Shigoki Dice 1: Scrubbing punch 1a: Outer surface of the cutting punch 1 3: Dot-shaped recesses P: Deepest part of recess 3 11: Metal cylindrical body 11a: Inner circumferential surface of the metal cylinder 11 13: Dot-shaped protrusions P': Vertex of convex part 13

Claims

1. A metal cylinder having a hollow cylindrical shape and obtained by ironing, characterized in that a large number of dot-shaped protrusions are distributed on its inner circumferential surface, and when viewed in a longitudinal cross-section along the axial direction, the apex of each of the dot-shaped protrusions is offset in the direction opposite to the processing direction.

2. The metal cylindrical body according to claim 1, wherein an organic resin layer is laminated on the inner circumferential surface, and the dot-shaped protrusions are distributed on the surface of the organic resin coating layer.

3. The metal cylindrical body according to claim 2, wherein the organic resin is a thermoplastic resin.

4. In a punch used for ironing metal, The punch for ironing is characterized in that a large number of dot-shaped recesses are distributed on the outer surface of the punch, and when viewed in a cross-section along the sliding direction of the punch, it has an arc-shaped raised portion on the side opposite to the tip of the punch.

5. A metal cylinder having a hollow cylindrical shape, obtained by ironing using the ironing punch described in claim 4, characterized in that a large number of dot-shaped protrusions are distributed on its inner circumferential surface, and when viewed in a longitudinal cross section along the axial direction, the apex of each of the dot-shaped protrusions is offset in the direction opposite to the processing direction.

Images