Irregular-shape die

Abstract

A cross-section of a bearing orthogonal to a drawing direction has a pair of long sides having relative long side lengths and a pair of short sides having relatively short side lengths. In a cross section of a reduction on the long-side side, parallel to the drawing direction, the absolute value of the difference between a first reduction angle and a second reduction angle opposite the first reduction angle with respect to the drawing direction is 2° or less. In a cross section of the reduction on the short-side side, parallel to the drawing direction, the absolute value of the difference between a third reduction angle and a fourth reduction angle opposite the third reduction angle with respect to the drawing direction is 2° or less. The average value of the first reduction angle and the second reduction angle is greater than the average value of the third reduction angle and the fourth reduction angle.

Description

Irregular shaped dice

[0001] The present disclosure relates to a modified die. This application claims priority to Japanese Patent Application No. 2024-010950, filed on January 29, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] A profiled die is disclosed, for example, in International Publication No. WO 2018 / 123513.

[0003] International Publication No. 2018 / 123513

[0004] The irregular-shaped die of the present disclosure is a irregular-shaped die having, from the upstream side in the wiredrawing direction, a reduction and a bearing adjacent to the reduction with the smallest diameter. A cross section of the bearing perpendicular to the wiredrawing direction has a pair of relatively long sides and a pair of relatively short sides. In a cross section of the reduction parallel to the wiredrawing direction and intersecting the long sides, the absolute value of the difference between a first reduction angle with respect to the wiredrawing direction and a second reduction angle opposite to the first reduction angle is 2° or less. In a cross section of the reduction parallel to the wiredrawing direction and intersecting the short sides, the absolute value of the difference between a third reduction angle with respect to the wiredrawing direction and a fourth reduction angle opposite to the third reduction angle is 2° or less. The average value of the first reduction angle and the second reduction angle is greater than the average value of the third reduction angle and the fourth reduction angle.

[0005] FIG. 1 is a cross-sectional view of a deformed diamond die 10 according to embodiment 1, a diamond 1 constituting the deformed diamond die 10, a case 2 housing the diamond 1, and a sintered alloy 3 interposed therebetween. FIG. 2 is a front view of the diamond 1 in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. FIG. 5 is an enlarged cross-sectional view of a bearing 6d taken along line V-V in FIG. 3. FIG. 6 is a cross-section corresponding to FIG. 5, showing a corner portion 7a1 and a non-corner portion 7b1 in a reduction 6c. FIG. 7 is a diagram for explaining a method for measuring curl of a wire 201.

[0006] [Problem to be Solved by the Present Disclosure] With conventional irregular shaped dies, it has been difficult to draw wires having a flat shape.

[0007] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0008] Deformed wires with a square or similar cross section are often used for motor coils, etc. In recent years, the demand for deformed wires has increased due to the spread of hybrid and electric vehicles.

[0009] The irregular shaped wires used in these applications must have a uniform diameter, be free from curls, and have no scratches on the surface.

[0010] Scratches and defects on the wire surface may reduce the insulating properties of the coating applied after wiredrawing. In this type of deformed wire drawing process, a wire with a round cross section is passed through multiple deformed dies, and the cross section is successively plastically deformed into a deformed shape such as a square, to obtain a deformed wire of the desired shape.

[0011] Although some irregular dies have sides of the same length, the vast majority have sides of different lengths, making it difficult to uniformly plastically deform all sides. In particular, irregular dies with long and short sides of different lengths have the problem that, because the cross-sectional shape is deformed using each of the irregular dies, stress applied to the entering metal wire is less uniform than with round dies. This results in differences in the contact distance between the wire and the inner surface of the die hole and in the load during wire drawing, depending on the location on the inner surface of the die hole, making the wire more susceptible to curling and scratches on the surface of the wire.

[0012] The irregular-shaped die of the present disclosure has, from the upstream side in the wiredrawing direction, a reduction and a bearing with the smallest diameter adjacent to the reduction. A cross section of the bearing perpendicular to the wiredrawing direction has a pair of relatively long sides and a pair of relatively short sides. In a cross section of the reduction parallel to the wiredrawing direction and intersecting the long sides, the absolute value of the difference between a first reduction angle relative to the wiredrawing direction and a second reduction angle opposite the first reduction angle is 2° or less. In a cross section of the reduction parallel to the wiredrawing direction and intersecting the short sides, the absolute value of the difference between a third reduction angle relative to the wiredrawing direction and a fourth reduction angle opposite the third reduction angle is 2° or less. The average value of the first reduction angle and the second reduction angle is greater than the average value of the third reduction angle and the fourth reduction angle.

[0013] In the irregular-shaped die configured in this manner, the average value of the first and second reduction angles on the long sides is greater than the average value of the third and fourth reduction angles on the short sides, so that the reduction angles are matched to the shape of the wire entering the reduction, thereby preventing scratches from occurring on the surface of the wire.

[0014] Preferably, the ratio (D2 / D1) of the length D2 of the short side to the length D1 of the long side is 1 / 11 or more and 4 / 5 or less. Within this range, a high-quality profiled wire can be most effectively produced. More preferably, D2 / D1 is 1 / 10 or more and 4 / 5 or less.

[0015] Preferably, the first reduction angle and the second reduction angle are equal to or greater than 5° and equal to or less than 20°.

[0016] Preferably, the length D2 of the short side is 10 μm or more and 10 mm or less. Preferably, the irregular shaped die contains polycrystalline diamond.

[0017] Preferably, the absolute value of the difference between the first reduction angle and the second reduction angle is 0.5° or less, and the absolute value of the difference between the third reduction angle and the fourth reduction angle is 0.5° or less. The smaller the absolute value of the difference between the first and second reduction angles and the absolute value of the difference between the third and fourth reduction angles, the more preferable it is. However, setting the absolute value of the difference to 0 increases the cost. If this difference is 0.5° or less, a shaped wire of the same high quality as when the difference is 0° can be produced.

[0018] (Structural Overview) The outline of a diamond die for deformed wire drawing will be explained using the drawings. Figure 1 is a cross-sectional view of a deformed diamond die 10 according to an embodiment, a diamond 1 constituting the deformed diamond die 10, a case 2 for housing the diamond 1, and a sintered alloy 3 interposed therebetween. Figure 1 is a cross-sectional view of the die case in a usable state. The diamond 1 is housed in the case 2. The diamond 1 is attached to the case 2 using the sintered alloy 3. In the deformed diamond die 10 as a deformed die, the portion for processing wire material is constituted by, for example, the diamond 1.

[0019] Fig. 2 is a front view of the diamond 1 in Fig. 1. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 2.

[0020] As shown in Figures 2 to 4, diamond 1 has a polycrystalline diamond 5 surrounded by a cemented carbide support ring 4. The center is composed of a hole inner surface 6, through which the wire to be drawn passes while in contact, and a processing hole 7. The hole inner surface 6 is further subdivided, the details of which are shown in Figure 3. The hole inner surface 6 is divided into a bell 6a, an approach 6b, a reduction 6c, a bearing 6d, a back relief 6e, and an exit 6f, and as shown in Figure 2, its shape when viewed from the front resembles a rectangle. The bearing 6d is the region of the processing hole 7 that includes the smallest diameter part.

[0021] The diamond 1 is a polycrystalline diamond consisting essentially of diamond, that is, a binderless diamond 1. A typical example is a diamond produced by directly converting non-diamond carbon into diamond under ultra-high pressure and temperature, which is known as a binderless diamond.

[0022] The diamond 1 is not limited to a binderless diamond, but may be a diamond 1 having a binder. Furthermore, the diamond 1 may contain unconverted carbon components. Furthermore, the diamond 1 may be replaced with a hard material such as cemented carbide or cubic boron nitride.

[0023] Of the inner surface 6 of the hole formed by the drilled hole 7, at least the surface from the bell 6a to the bearing 6d is formed as a smoothly curved surface in the thickness direction of the diamond. That is, unlike a case in which the bell 6a, approach 6b, reduction 6c, and bearing 6d are each formed linearly and each boundary portion is rounded, each portion is formed as a smoothly curved surface as a whole. This curved surface is formed as a curved surface with a single radius or a curved surface with a compound radius, and the boundaries between them are not clearly distinguishable.

[0024] The diameter of the wire material after wire drawing with the deformed diamond die 10 is, for example, less than 0.5 mm, which is a thin wire diameter. When drawing such a thin wire, if the surface from the bell 6a to the bearing 6d is formed as a smoothly curved surface, there is no significant change in wire drawing resistance, and even an extremely thin wire is less likely to break. Furthermore, in terms of supplying lubricant, a smoothly curved surface results in good lubrication conditions.

[0025] The polycrystalline diamond 5 around the machining hole 7 is a single polycrystalline diamond that is continuous in the circumferential direction of the machining hole 7. Because the polycrystalline diamond 5 around the machining hole 7 is a single polycrystalline diamond that is continuous in the circumferential direction of the machining hole, it has higher strength than divided diamonds. As a result, the precision of the machining hole is high and the surface roughness of the wire after wiredrawing can be reduced.

[0026] A pair of long sides 71, 72 of the bearing 6d face each other. A pair of short sides 73, 74 of the bearing 6d face each other. The length D1 of the long sides 71, 72 is the distance between the opposing short sides 73, 74. The length D2 of the short sides 73, 74 is the distance between the opposing long sides 71, 72.

[0027] The corners where the long sides 71, 72 and the short sides 73, 74 intersect may or may not be rounded.

[0028] (Method for Identifying the Shape of the Die Hole 7) To measure and identify the shapes of the bell 6a, approach 6b, reduction 6c, bearing 6d, back relief 6e, and exit 6f, the die hole 7 is filled with a transfer material (for example, RepliSet, manufactured by Struers Corporation). This creates a replica onto which the shape of the die hole 7 is transferred. This replica is examined using a tool microscope with transmitted illumination to clarify the outline of the die hole 7, thereby obtaining a cross-sectional view of the die hole 7, such as the die hole 7 in Figures 3 and 4.

[0029] In the cross-sectional view, the cylindrical portion with the narrowest inner diameter is designated as bearing 6d. The distance between short sides 73, 74 of bearing 6d is designated as D1. In the cross-sectional view, the portion adjacent to bearing 6d and located upstream of bearing 6d, with an inner dimension RD (parallel to D1) on the long side satisfying D1 < RD ≦ 1.500 D1, is designated as reduction 6c. In the cross-sectional view, the portion adjacent to bearing 6d and located downstream of bearing 6d, with an inner dimension BD (parallel to D1) on the long side satisfying D1 < BD ≦ 1.100 D1, is designated as back relief 6e.

[0030] To measure the reduction angles C and D on the short sides 73 and 74 in Figure 3, tangents 103 and 104 are drawn on both sides of the reference region (RD = 1.500D1) of the reduction 6c in the cross section of the die hole 7. The angle between the tangent 103 and the axis 100 is defined as reduction angle C. The angle between the tangent 104 and the axis 100 is defined as reduction angle D.

[0031] To measure the reduction angles A and B on the long sides 71 and 72 in Figure 4, tangents 101 and 102 are drawn on both sides of the reduction 6c in the reference region (RD = 1.500D1) in the cross-sectional view of the die hole 7. The angle between the tangent 101 and the axis 100 is defined as reduction angle A. The angle between the tangent 102 and the axis 100 is defined as reduction angle B.

[0032] [Correction based on Rule 91 16.09.2025] (Corner Radius R) Figure 5 is an enlarged cross-sectional view of the bearing 6d taken along line VV in Figure 3. Figure 6 is a cross-section corresponding to Figure 5, showing the corner portion 7a1 and the non-corner portion 7b1 of the reduction 6c.

[0033] The drawn wire is used for motor windings, etc. In such applications, high density winding is required, so the smaller the radius R of the corners of the wire, the better.

[0034] Therefore, it is preferable that the radii R and R1 of the corner portions 7a and 7a1 of the quadrangles of the bearing 6d and reduction 6c are small.

[0035] Reducing the difference in the angle of the reduction 6c on the opposing surfaces of the die hole 7 reduces the difference in the contact angle with the wire, which in turn reduces the difference in wire drawing resistance and the difference in the stress applied to the wire between the opposing surfaces of the hole, making the wire less likely to curl.

[0036] Furthermore, by increasing the reduction angle of the long sides 71 and 72, where the wire contact surface is larger, relative to the reduction angle of the short sides 73 and 74, the shape of the wire after drawing can be made closer to the target cross-sectional shape of the wire. As a result, when the wire contacts the next die, the timing at which the wire starts to contact the reduction 6c at the long sides 71 and 72 and the short sides 73 and 74 becomes closer. As a result, the difference in the axial wire contact distance at each side becomes smaller, the difference in stress applied to the wire becomes smaller, and the occurrence of wire scratches can be reduced.

[0037] The wire to be drawn can be made of various metals such as copper, silver, iron, gold, and aluminum.

[0038] The deformed diamond die 10 as a deformed die has, from the upstream side in the wiredrawing direction indicated by the arrow 110, a reduction 6c and a bearing 6d with the smallest diameter adjacent to the reduction 6c. A cross section of the bearing 6d perpendicular to the wiredrawing direction (FIG. 2) has a pair of long sides 71, 72 that are relatively long, and a pair of short sides 73, 74 that are relatively short.

[0039] In a cross section of the reduction 6c (FIG. 4) that is parallel to the wire-drawing direction and intersects with the long sides 71 and 72, the absolute value of the difference between the first reduction angle A relative to the wire-drawing direction and the second reduction angle B opposite to the first reduction angle A is 2° or less.

[0040] [Correction under Rule 91 16.09.2025] In a cross section of the bearing 6d (Figure 3) parallel to the wire-drawing direction and intersecting the short sides 73, 74, the absolute value of the difference between the third reduction angle C relative to the wire-drawing direction and the fourth reduction angle D opposite to the third reduction angle C is less than or equal to 2°.

[0041] The average value of the first reduction angle A and the second reduction angle B is greater than the average value of the third reduction angle C and the fourth reduction angle D.

[0042] [Details of the embodiment of the present disclosure] (Example) (Test item numbers 1 to 8)

[0043]

[0044] Test specimens Nos. 1 to 8 shown in Table 1 were prepared with various numerical values ​​set.

[0045] The irregularly shaped diamond dies of test piece numbers 1 to 8 were produced by the following method: First, a pilot hole was drilled in the polycrystalline diamond by laser processing, then rough processing was performed by electrical discharge processing, and then finishing processing was performed by lapping.

[0046] A copper square wire with a cross-sectional dimension of 550 μm × 550 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated. The results are shown in Table 1.

[0047] To evaluate line scratches, the surface of the square wire was observed under a microscope. Scratches with a depth of less than 10 μm or no scratches were rated "A," scratches with a depth of 10 μm or more but less than 20 μm were rated "B," and scratches with a depth of 20 μm or more were rated "C." Evaluations A and B were considered acceptable, and evaluation C was considered unacceptable.

[0048] FIG. 7 is a diagram illustrating a method for measuring the curl of wire 201. Wire 201, which is a rectangular wire, is hung vertically downward from fixed part 200. If wire 201 is linear, it will be located at the position indicated by the dotted line. When wire 201 is hung from fixed part 200 and no force is applied to wire 201, wire 201 will curl. As a result, lower end 201e of wire 201 moves upward by a vertical distance X from the position indicated by the dotted line. Regarding the evaluation of curl, assuming that wire 201 has a length of 1 m, if distance X is 5 cm or less, it is evaluated as "A," if distance X is more than 5 cm but not more than 10 cm, it is evaluated as "B," and if distance X is more than 10 cm, it is evaluated as "C." Evaluations A and B were considered acceptable, and evaluation C was considered unacceptable.

[0049] (Test item numbers 11 to 18)

[0050]

[0051] Deformed diamond dies 10 with test piece numbers 11 to 18 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 500 µm, the length D2 of the short sides 73 and 74 was 200 µm, and the radius R of the corner portion 7a was 30 µm.

[0052] First, a pilot hole was drilled in the polycrystalline diamond by laser processing, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were changed in various ways for test pieces 11 to 18.

[0053] A copper square wire with a cross-sectional dimension of 550 μm × 550 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 2.

[0054] [Correction based on Rule 91 16.09.2025] From Table 2, it can be seen that if the angle variation |A-B| is equal to or less than the angle variation |C-D|, the grade will be "C" for either line scratches or curls.

[0055] (Test item numbers 21 to 32)

[0056]

[0057] Deformed diamond dies 10 with test piece numbers 21 to 32 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 500 µm, the length D2 of the short sides 73 and 74 was 200 µm, and the radius R of the corner portion 7a was 30 µm.

[0058] First, a pilot hole was drilled in the polycrystalline diamond by laser processing, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were changed in various ways for test pieces 21 to 32.

[0059] A copper square wire with a cross-sectional dimension of 550 μm × 550 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 3.

[0060] From Table 3, it was found that when either the angle variation |A−B| or the angle variation |C−D| was 3° or more, the evaluation of either the line scratch or the curl was "C."

[0061] It was found that when the average value of reduction angles A and B was greater than the average value of reduction angles C and B, a grade of "B" or higher was obtained in the evaluation of line scratches and curl.

[0062] It was found that if the sum of the angle variation |AB| and the angle variation |CD| was 3° or less, a rating of "A" could be obtained in the evaluation of line scratches and curls.

[0063] (Test item numbers 41 to 52)

[0064]

[0065] Deformed diamond dies 10 with test piece numbers 41 to 52 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 500 µm, the length D2 of the short sides 73 and 74 was 400 µm, and the radius R of the corner portion 7a was 30 µm.

[0066] First, a pilot hole was drilled in the polycrystalline diamond by laser machining, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were changed in various ways for test pieces 41 to 52.

[0067] A copper square wire with a cross-sectional dimension of 550 μm × 550 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 4.

[0068] From Table 4, it was found that when either the angle variation |A−B| or the angle variation |C−D| was 3° or more, the evaluation of "C" was given for either line scratches or curl.

[0069] It was found that when the average value of reduction angles A and B was greater than the average value of reduction angles C and B, a grade of "B" or higher was obtained in the evaluation of line scratches and curl.

[0070] It was found that if the sum of the angle variation |AB| and the angle variation |CD| was 3° or less, a rating of "A" could be obtained in the evaluation of line scratches and curls.

[0071] (Test item numbers 61 to 72)

[0072]

[0073] Deformed diamond dies 10 with test piece numbers 61 to 72 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 700 µm, the length D2 of the short sides 73 and 74 was 100 µm, and the radius R of the corner portion 7a was 30 µm.

[0074] First, a pilot hole was drilled in the polycrystalline diamond by laser machining, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were changed in various ways for test pieces 61 to 72.

[0075] A copper square wire with a cross-sectional dimension of 900 μm × 150 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 5.

[0076] From Table 5, it was found that when either the angle variation |A−B| or the angle variation |C−D| was 3° or more, the evaluation of "C" was given for either line scratches or curls.

[0077] It was found that when the average value of reduction angles A and B was greater than the average value of reduction angles C and B, a grade of "B" or higher was obtained in the evaluation of line scratches and curl.

[0078] It was found that if the sum of the angle variation |AB| and the angle variation |CD| was 3° or less, a rating of "A" could be obtained in the evaluation of line scratches and curls.

[0079] (Test item numbers 81 to 92)

[0080]

[0081] Deformed diamond dies 10 with test piece numbers 81 to 92 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 1000 µm, the length D2 of the short sides 73 and 74 was 100 µm, and the radius R of the corner portion 7a was 30 µm.

[0082] First, a pilot hole was drilled in the polycrystalline diamond by laser machining, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were changed in various ways for test pieces 61 to 72.

[0083] A copper square wire with a cross-sectional dimension of 1200 μm × 150 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 6.

[0084] From Table 6, it was found that when either the angle variation |A−B| or the angle variation |C−D| was 3° or more, the evaluation of "C" was given for either line scratches or curls.

[0085] It was found that when the average value of reduction angles A and B was greater than the average value of reduction angles C and B, a grade of "B" or higher was obtained in the evaluation of line scratches and curl.

[0086] It was found that if the sum of the angle variation |AB| and the angle variation |CD| was 3° or less, a rating of "A" could be obtained in the evaluation of line scratches and curls.

[0087] (Test item numbers 101 to 112)

[0088]

[0089] Deformed diamond dies 10 with test piece numbers 101 to 112 were produced. The deformed diamond dies 10 had the structure shown in Figures 1 to 6. The length D1 of the long sides 71 and 72 was 1100 µm, the length D2 of the short sides 73 and 74 was 100 µm, and the radius R of the corner portion 7a was 30 µm.

[0090] [Rule 91 Amendment 16.09.2025] First, a pilot hole was drilled in the polycrystalline diamond by laser machining, then rough machining was performed by electrical discharge machining, and then finishing was performed by lapping. During this process, the reduction angles A to D (Figures 3 and 4) relative to the axis were varied for test pieces 101 to 112.

[0091] A copper square wire with a cross-sectional dimension of 1300 μm × 150 μm was drawn in a lubricant (drawing speed: 10 m / min) for 1 hour to obtain a square wire with a length of 600 m. A 1 m long sample (a sample near the end of the 600 m wire) was extracted from the square wire after 1 hour of drawing, and the wire scratches and curl were evaluated in the same manner as in Table 1. The results are shown in Table 7.

[0092] From Table 7, it was found that when either the angle variation |A−B| or the angle variation |C−D| was 3° or more, the evaluation of "C" was given for either line scratches or curl.

[0093] It was found that when the average value of reduction angles A and B was greater than the average value of reduction angles C and B, a grade of "B" or higher was obtained in the evaluation of line scratches and curl.

[0094] It was found that if the sum of the angle variation |AB| and the angle variation |CD| was less than 1°, a rating of "A" was obtained in the evaluation of line scratches and curl.

[0095] It was found that scratches or curling are likely to occur when the ratio of the length of the long sides 71, 72 to the length of the short sides 73, 74 is 11 and there is a difference between the reduction angles A and B and between the reduction angles C and D on the opposing surfaces.

[0096] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0097] 1 Diamond, 2 Case, 3 Sintered alloy, 4 Carbide support ring, 5 Polycrystalline diamond, 6 Hole inner surface, 6a Bell, 6b Approach, 6c Reduction, 6d Bearing, 6e Back relief, 6f Exit, 7 Die hole, 7a, 7a1 Corner portion, 7b1 Non-corner portion, 71, 72 Long side, 73, 74 Short side, 100 Axial center, 101, 102, 103, 104 Tangent, 200 Fixed portion, 201 Wire rod, 201e Lower end.

Claims

1. An irregular die having, from the upstream side in the wiredrawing direction, a reduction and a bearing with the smallest diameter adjacent to the reduction, wherein a cross section of the bearing perpendicular to the wiredrawing direction has a pair of long sides with relatively long sides and a pair of short sides with relatively short sides, in a cross section of the reduction parallel to the wiredrawing direction and intersecting with the long sides, the absolute value of the difference between a first reduction angle with respect to the wiredrawing direction and a second reduction angle opposite to the first reduction angle is 2° or less, in a cross section of the reduction parallel to the wiredrawing direction and intersecting with the short sides, the absolute value of the difference between a third reduction angle with respect to the wiredrawing direction and a fourth reduction angle opposite to the third reduction angle is 2° or less, and the average value of the first reduction angle and the second reduction angle is greater than the average values ​​of the third reduction angle and the fourth reduction angle.

2. The irregular-shaped die according to claim 1, wherein the ratio (D2 / D1) of the length D2 of the short side to the length D1 of the long side is 1 / 11 or more and 4 / 5 or less.

3. A profile die according to claim 1 or 2, wherein the first reduction angle and the second reduction angle are between 5° and 20°.

4. A modified die according to claim 1 or 2, wherein the length D2 of the short side is 10 μm or more and 10 mm or less.

5. The irregular die according to claim 1 or 2, wherein the irregular die comprises polycrystalline diamond.

6. A profile die according to claim 1 or 2, wherein the absolute value of the difference between the first reduction angle and the second reduction angle is 0.5° or less, and the absolute value of the difference between the third reduction angle and the fourth reduction angle is 0.5° or less.

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