JP2004009112A - Die assembly with step - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die assembly with steps capable of manufacturing easier than all-in-one dies with steps, and manufacturing the step shape as arranged, and corresponding to various heights and angles by only changing one part of die shapes. <P>SOLUTION: The die assembly has a cylindrical die holder and several dies in the die holder having different inner diameters and outer diameters which are engaged with the inner surface of the die holder and contacted concentrically one another, and the several dies are arranged for getting the outer diameters smaller from the enter side to the exit side by a drawing process. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stepped die assembly used for manufacturing a wire or a bar by a drawing process.
[0002]
[Prior art]
With the recent high performance of automobiles, precision instruments, and the like, lower costs and higher quality are also required in the production of wires and steel bars used as structural materials. The cold drawing method is suitable for the production of wires and steel bars with a relatively smooth outer periphery, and continuously obtains wires and bars by pulling out the tip of the material while restraining the material with a hollow die. is there.
[0003]
Conventionally, a cold drawing method of this type disclosed in JP-A-8-66715 has been known. Briefly described with reference to FIGS. 12 and 13, the die 21 has a through hole at the center of the die 21 through which the workpiece 20 passes. The through hole extends from the entry side where the workpiece 20 is fed to the exit side. A tapered approach portion A is provided, followed by a substantially straight bearing portion B. The approach portion A is a portion that actually reduces the diameter of the workpiece 20, and the bearing portion B is a portion that determines the final dimensions and finishes the outer surface. Here, the entrance side may be referred to as the front side of the die, and the exit side may be referred to as the rear side of the die.
[0004]
In the conventional example of FIG. 12, a ring-shaped concave portion 22 is formed near the contact portion of the tapered surface of the die 21 with the material, particularly near the joint portion between the approach portion A and the bearing portion B. Ironing is applied to the surface of the material to improve the surface roughness. In the example of FIG. 13, a ring-shaped mountain-shaped step portion 23 for reducing the inner diameter of the die is formed in the bearing portion B. Similarly, the outer surface of the material 20 is ironed by the step portion 23 to obtain a surface roughness. To improve.
[0005]
[Problems to be solved by the invention]
The conventional cold-drawing dies described above are subjected to ironing to concentrate the shear composition deformation at the concave portion or the step portion, so that the surface roughness can be reduced without post-processing such as polishing while the cold-drawing is performed. There is a certain effect in that small wires and bars can be obtained. However, since such a die is entirely formed of an integral member, it is difficult to form an accurate concave portion or a step portion having high dimensional accuracy in the middle of the die through-hole, and it takes a great deal of time to manufacture the die. Was required.
[0006]
Generally, in stepped dies, it is necessary to perform gradual processing to reduce the residual stress of steel bars, and to sharply reduce the diameter to smooth the surface.To satisfy such conflicting requirements simultaneously, Must be a multi-step die 24 as shown in FIG. In this case, the dimensions of the respective parts of the die are required to be extremely high in accuracy with each other. According to a study by the inventors, for example, in FIG. 14, the front bearing length Lf = 2 mm at the front of the die, the step height of the die center part ΔH = 40 μm, step angle α = 15 °, center bearing length Lc = 1 mm, step height at the rear of the die Δh = 10 μm, step angle β at the rear of the die = 7 °, back bearing length Lb = 2 mm. By doing so, it has been found that the residual stress can be reduced and the surface roughness can be improved.
[0007]
In such multi-step dies, the strictness in terms of processing accuracy increases as the number of steps increases, and when this is made of an integrated member, if the accuracy of a certain part is not satisfied, the entire die must be reworked. However, there is a problem that the whole die becomes defective due to a part of the accuracy being inferior or a part being damaged during use.
[0008]
The present invention solves such a problem, and is much easier to manufacture than an integrated stepped die, a stepped shape can be manufactured to required dimensions, and only by changing a part of the die shape. An object of the present invention is to provide a stepped die assembly that can support various stepped heights and stepped angles.
[0009]
[Means for Solving the Problems]
According to the present invention, a cylindrical die holder and a plurality of dies having different inner diameters, each having an outer diameter fitted to the inner peripheral surface of the die holder and being accommodated in the die holder in concentric contact with each other, A stepped die assembly, wherein the plurality of dies in the die holder are arranged so that their outer diameters are reduced as the workpiece is drawn from the entry side to the exit side by drawing. You.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described based on preferred embodiments with reference to the drawings.
[0011]
FIG. 1 is a schematic exploded perspective view of a stepped die assembly according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of the stepped die assembly according to the present invention, which is constructed by assembling the members shown in FIG. FIG. 3 and FIG. 3 are enlarged sectional views of a portion A in FIG. As shown in these drawings, the die assembly of this embodiment is configured such that a front die 2 and a back die 3 having the same outer diameter are housed in a cylindrical die holder 1 in a tightly fitted state, and a rod-shaped cover is provided. A processing material (not shown) is inserted from the front die 2 side, the tip of which is gripped by an appropriate chuck means (not shown) and pulled out from the rear part of the back die 3.
[0012]
The inner peripheral surface of the front die 2 is constituted by a tapered approach portion 4 on the entry side and a straight cylindrical front bearing portion 5 following the approach portion, as described in the conventional example of FIGS. There is no stepped portion that causes a sudden change in inner diameter.
[0013]
The back die 3 has a back bearing portion 6 having an inner diameter smaller than the inner diameter of the bearing portion 5 of the front die 2, and a tapered back relief portion 7 is formed following the bearing portion 6 on the back die exit side. Have been. 3, the inner diameter d of the opening edge of the front end face of the back die 3 in close contact with the rear end face 2a of the front die 2 is somewhat larger than the inner diameter D of the bearing portion of the front die 2. The opening edge is connected to the back bearing portion 6 in a tapered shape (reference numeral 8). The front end tapered portion 8 of the back die 3 and the back bearing portion 6 together form a stepped portion of the die assembly. The radial difference between the bearing portion 5 and the back bearing portion 6 of the front die 2 is defined as a stepped height Δh, and the taper angle of the front end tapered portion 8 of the back die 3 when viewed in a half section (FIG. 3). Is the step angle β. For example, when the length L of the back bearing portion (stepped portion bearing portion) 6 is L = 2 mm, Δh = 20 μm, β = 15 °, and when L = 5 mm, Δh = 30 μm, β = 30 °, and When L = 10 mm, Δh = 40 μm and β = 45 °. The opening edge of the front end face of the back die has a diameter about 0.01 mm larger than the bearing portion 5 of the front die 2 in the radial direction.
[0014]
The split type stepped die assembly according to the present invention can surely form the angle (stepped angle β) of the front end tapered portion 8 of the back die 3 connected to the rear end of the front die 2, and can form the tapered portion like an integrated die. Thus, a sharp edge is not formed at the connecting portion between the rear edge of the tapered portion and the back die bearing portion, and a wire and a steel bar product having extremely smooth surface properties can be obtained.
[0015]
FIG. 4 is a diagram showing the surface smoothness of a steel bar product manufactured by a conventional integrated stepped die at various stepped heights L (20 μm, 30 μm, 50 μm, 60 μm). The horizontal axis represents the diameter D of the bearing portion, and the vertical axis represents the surface smoothness Rz (μm). In the same figure, the symbol △ indicates the case of a normal integrated die having no stepped portion.
[0016]
FIG. 5 is a diagram showing the surface smoothness of a steel bar product in various stepped heights L (20 μm, 40 μm, 60 μm) in the split type stepped die assembly of the present invention. As in FIG. 4, the horizontal axis represents the diameter D of the bearing portion, and the vertical axis represents the surface smoothness Rz (μm). Further, in the same figure, the symbol △ indicates the case of a split die assembly having no stepped portion. Regarding the surface smoothing, the influence of the difference in step height can be confirmed even with a split die. As is apparent from these figures, in the case of the present invention, as the diameter D becomes smaller, the surface smoothness is remarkably improved as compared with the conventional case.
[0017]
FIG. 6 is a diagram comparing residual stress (σN / mm ² ) between the conventional integrated stepped die and the split type stepped die assembly of the present invention. In the figure, white circles indicate the conventional dies, and black circles indicate the case of the split-type stepped die of the present invention. According to this, it can be seen that the reduction of the residual stress is larger in the split type stepped die than in the integrated type.
[0018]
Next, the effect of the step angle will be described based on the experimental results. As for the surface smoothing, the smoothing proceeds as the step angle increases, but burn-in occurs at a step angle of 20 ° or more. For the purpose of smoothing, the step angle is preferably around 15 °. Regarding the reduction of the residual stress, the smaller the step angle, the lower the residual stress. At a step angle of 7 °, the residual stress is minimized.
[0019]
Explaining the effect of the step height on the basis of the experimental results, the surface smoothing proceeds as the step height increases, but the step height is 40 μm (1.58%) or more. Then, smoothing does not proceed. For the purpose of smoothing, the step height is preferably around 40 μm (1.58%). Regarding the reduction of residual stress, the smaller the step height, the lower the residual stress. According to the analysis results, the residual stress is smallest when the step height is 10 μm (0.399%). Depending on the experimental conditions, the residual stress is minimized at a step height of 40 μm (1.58%).
[0020]
The stepped die assembly according to the present invention can arrange the dies concentrically if the inner diameter accuracy of the die holder and the outer diameter accuracy of each split die such as a front die and a back die fitted with the die holder are ensured. However, as shown in the embodiment of FIG. 3, the inner diameter of the back die 3 is formed to be slightly larger (for example, about 0.01 mm) so that the opening edge of the front end surface contacts the rear end surface 2a of the front die 2. By doing so, even if the concentric state of the front die 2 and the back die 3 is slightly deviated, there is no protruding sudden step on the inner peripheral edge of the rear end face 2a of the front die 2, and the production is also easy in this respect. It becomes.
[0021]
FIG. 7 is a partial longitudinal sectional view of a multi-step die assembly according to another embodiment of the present invention. Dies 11, 12, and 13 divided into three bodies are concentrically accommodated in one cylindrical die holder 1 with their respective end faces in contact with each other. A first-stage center die 12 is arranged in connection with the entrance-side front die 11, and a second-stage back die 13 is arranged on the exit side following the center die 12. In the case of a die having a step, a micro-stepped structure is used as compared with that of the two dies. In particular, the center die 12 of the first step is a stepped die having a high surface roughness improving effect, and the second stepped die (back) The die 13 is a small stepped die that is effective in reducing residual stress. By doing so, the surface roughness can be improved and the residual stress can be reduced in one pass.
[0022]
To improve the surface roughness as a whole, the step height Δh is high (40 μm), the step angle is large (about 15 °), the length of the back bearing portion is short (2 mm), and the corner R of the step portion is improved. In order to reduce residual stress, the step height Δh is low (10 μm), the step angle is small (about 7 °), the length of the back bearing portion is long (5 mm), and the corner R is large.
[0023]
As an example, in a die divided into three bodies as shown in FIG. 7, the length Lf of the front bearing portion 14 is 2 mm, the step height of the center die 12 is Δh = 40 μm, the step angle β is 15 °, and the center bearing is The length Lc of the portion 15 is 1 mm, the step height of the back die 13 is Δh = 10 μm, the step angle β is 7 °, and the length Lb of the back bearing portion is 2 mm. In FIG. 4, the corner R of the first stepped portion (between the front die and the center die) is R ₁ = R ₂ = 0, and the corner R of the second stepped portion (between the center die and the back die) is R3 = 1.0 and R4 = 0.5.
[0024]
FIG. 8 shows the analysis result of the residual stress of the multi-step die assembly of FIG. 7 in which the center die 12 is interposed between the front die 11 and the back die 13, and FIG. 9 shows the analysis result of the shear strain. In both figures, the horizontal axis indicates the distance r (mm) from the center. The unit of the residual stress in FIG. 8 is σ (x) N / mm ² , and the unit of the shear strain in FIG. 9 is γ (xr)%. Further, the black circles in the figure indicate the case of a normal stepped die, and the white circles indicate the case of the multistaged die according to the present invention. As is evident from these figures, the residual stress by the multi-step die is equivalent to that of the general residual stress reducing die, and the shear strain is equivalent to that of the surface roughness improving die. Was. Thus, it can be seen that the multi-step die assembly of the present invention can reduce the residual stress and improve the surface roughness, which cannot be achieved by the step die alone, in one pass.
[0025]
In the multi-step die, as described above, both the reduction of the residual stress and the improvement of the surface roughness can be achieved at the same time. However, in the case of the multi-step die, seizure due to running out of the lubricating oil may occur. However, since the multi-stage stepped die assembly of the present invention is composed of divided die sets, a lubricating oil ring is interposed between the dies, for example, between the front die and the center die or between the center die and the back die. Can be forcibly supplied with the lubricating oil.
[0026]
FIG. 10 is an end view of the lubricating oil ring according to the present invention, and FIG. 11 is a partial longitudinal sectional view of the lubricating oil ring arranged in contact with the front surface of the back die. A lubricating oil supply groove 17 and a lubricating oil discharge groove 18 extending in the radial direction are formed on the surface of the ring 16 in contact with the back die 13. These grooves extend from the outer peripheral portion of the ring to the center hole as shown in FIG. 10, and the grooves exposed on the outer periphery are aligned with the radial oil passages 19 formed in the die holder 1, respectively. 1 is supplied to the workpiece 20 in the die through the oil passage 19 in the holder and the lubricating oil supply groove 17 of the lubricating oil ring 16 and through the lubricating oil discharging groove and the lubricating oil discharging oil passage in the die holder. Is discharged. The lubricating oil supply / discharge grooves 17 and 18 of the lubricating oil ring 16 may be formed not only on one side of the ring but also on both sides. Further, the lubricating oil ring 16 may be formed on the end surface of the back die or the front die without using the lubricating oil ring 16. A radial oil groove may be formed, or an oil groove may be formed on the end face of the center die, and these grooves may communicate with the radial oil passage of the die holder 1. For example, in FIG. 7, a lubricating oil supply / discharge groove may be provided between the front die 11 and the center die 12 and between the center die 12 and the back die 13. Since the concave groove is formed on the end face, the processing is extremely easy.
[0027]
【The invention's effect】
As described above, according to the present invention, dies can be easily manufactured, the processing accuracy of each stepped portion can be increased, and a part of dies among a plurality of dies can be manufactured as compared with the conventional integrated stepped dies. Even in the case where the die is damaged, only the die at that portion needs to be repaired or replaced, and an extremely efficient stepped die assembly can be obtained. Especially when a multi-step die is used, it can be manufactured with the same ease as the processing of a single step die, and both residual stress reduction and surface roughness improvement can be achieved simultaneously in one pass. Is brought.
[Brief description of the drawings]
FIG. 1 is a schematic exploded perspective view of a stepped die assembly according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of a stepped die assembly according to the present invention configured by assembling the members shown in FIG. 1;
FIG. 3 is an enlarged sectional view of a portion A in FIG. 2;
FIG. 4 is a diagram showing the surface smoothness of a steel bar product manufactured with a conventional integrated stepped die at various stepped heights.
FIG. 5 is a view showing the surface smoothness of a steel bar product in a split type stepped die assembly of the present invention at various stepped heights.
FIG. 6 is a diagram comparing residual stress (σN / mm ² ) between a conventional integrated stepped die and a split type stepped die assembly of the present invention.
FIG. 7 is a partial longitudinal sectional view of a multi-step die assembly according to another embodiment of the present invention.
8 is a diagram showing an analysis result of residual stress of the multi-step die assembly shown in FIG. 7;
9 is a diagram showing an analysis result of shear strain of the multi-step die assembly shown in FIG. 7;
FIG. 10 is an end view of the lubricating oil ring according to the present invention.
FIG. 11 is a partial longitudinal sectional view of a lubricating oil ring arranged in contact with a front surface of a back die.
FIG. 12 is a longitudinal sectional view of a conventional integrated die.
FIG. 13 is a longitudinal sectional view showing another conventional example of the integrated die.
FIG. 14 is a partial longitudinal sectional view of a conventional integrated-type multi-step die.
[Explanation of symbols]
Reference Signs List 1 die holder 2 front die 3 back die 4 approach portion 5 front bearing portion 6 back bearing portion 7 back relief portion 8 front end taper portion 12 center die 16 lubricating oil ring 17 lubricating oil supply groove 18 lubricating oil discharge groove 19 oil passage 20 Material

Claims (3)

A die holder having a cylindrical shape and a plurality of dies each having an outer diameter fitted to the inner peripheral surface of the die holder and having different inner diameters housed in the die holder in concentric contact with each other; The stepped die assembly, wherein the plurality of dies are arranged such that the outer diameter thereof decreases as the workpiece is drawn from the entry side to the exit side. 2. The stepped die assembly according to claim 1, wherein a front end inner diameter of a die located on the rear side of the adjacent dies is formed to be somewhat larger than a rear end inner diameter of the die located on the front side. . 3. The stepped die assembly according to claim 1, wherein a lubricating oil ring having a groove for supplying and discharging lubricating oil extending in a radial direction is interposed between adjacent dies.

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