Wire Drawing Dies

Abstract

A wire drawing die 1 that comprises a non-diamond material, is provided with a die hole 1h, and has a reduction 1c and a bearing 1d that is positioned downstream of the reduction 1c. The reduction angle γ, which is the opening angle of the die hole 1h at the reduction 1c, is no more than 17°, and the surface roughness Ra of the die hole 1h within ±20 μm from a specific position inside the bearing 1d in a circumferential direction of the die hole 1h that is perpendicular to the wire drawing direction is no more than 0.025 μm.

Description

[Technical field]

[0001] This disclosure relates to a wire drawing die. This application claims priority to Japanese Patent Application No. 2020-140863, filed on August 24, 2020. The entire contents of said Japanese Patent Application are incorporated herein by reference. [Background technology]

[0002] Conventionally, wire drawing dies have been disclosed in, for example, JP 2-6011 A (Patent Document 1), JP 2-127912 A (Patent Document 2), JP 4-147713 A (Patent Document 3), WO 2013 / 031681 A (Patent Document 4), JP 2014-34487 A (Patent Document 5), and JP 56-98405 A (Patent Document 6). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-6011 [Patent Document 2] Japanese Patent Application Publication No. 2-127912 [Patent Document 3] Japanese Patent Application Publication No. 4-147713 [Patent Document 4] International Publication No. 2013 / 031681 [Patent Document 5] JP 2014-34487 A [Patent Document 6] Japanese Patent Application Publication No. 56-98405 Summary of the Invention

[0004] The wiredrawing die disclosed herein is made of a non-diamond material, is provided with a die hole, and has a reduction and a bearing located downstream of the reduction, wherein the reduction angle, which is the opening angle of the die hole at the reduction, is 17° or less, and the surface roughness Ra of the die hole within a range of ±20 μm from a specific position in the bearing in the circumferential direction of the die hole perpendicular to the wiredrawing direction is 0.025 μm or less. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a cross-sectional view of a wire drawing die according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a diagram for explaining a method for measuring the surface roughness inside the bearing 1d. [Figure 4] FIG. 4 is a cross-sectional view showing a die hole 1h and a replica 300 filled in the die hole 1h. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] There has been a demand for improving the lifespan of conventional wire drawing dies.

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

[0008] The wiredrawing die disclosed herein is a wiredrawing die made of a non-diamond material, provided with a die hole, and having a reduction and a bearing located downstream of the reduction, wherein the reduction angle, which is the opening angle of the die hole at the reduction, is 17° or less, and the surface roughness Ra of the die hole within a range of ±20 μm from a specific position in the bearing in the circumferential direction of the die hole perpendicular to the wiredrawing direction (a total range of 40 μm) is 0.025 μm or less.

[0009] The non-diamond material may be CBN or a nitride or carbide of at least one element selected from the group consisting of titanium, silicon, aluminum and chromium.

[0010] The CBN may be binderless CBN, which does not contain a binder, or may be CBN with a binder. The non-diamond material may be a mixture of CBN and compressed hBN (hexagonal boron nitride). Here, "compressed hexagonal boron nitride" refers to a material that has a similar crystal structure to normal hexagonal boron nitride and has a smaller interplanar spacing in the c-axis direction than normal hexagonal boron nitride (0.333 nm).

[0011] The die hole generally has a circular cross section perpendicular to the wire drawing direction, but may have a rectangular cross section.

[0012] The wire drawing die has, from the upstream side, a bell, an approach, a reduction, a bearing, a back relief, and an exit.

[0013] The reduction angle, which is the opening angle of the die hole in reduction, is 17° or less. In a cross-sectional view of the die hole parallel to the wiredrawing direction, two first tangents are drawn on both side surfaces at the portion where the reduction diameter RD is 1.050D, and the reduction angle is the angle between the two first tangents. If the reduction angle exceeds 17°, the life of the wiredrawing die will be shortened. More preferably, the reduction angle is 6° or more and 15° or less.

[0014] The surface roughness Ra in the range of ±20 μm from a specific position in the bearing in the circumferential direction of the die hole perpendicular to the wire drawing direction is 0.025 μm or less. If the surface roughness exceeds 0.025 μm, the surface roughness of the wire deteriorates and the lifespan is shortened. Preferably, the surface roughness Ra is 0.005 μm or more and 0.025 μm or less.

[0015] Preferably, the length of the bearing is 200% D or less, where D is the diameter of the bearing. If the length of the bearing is more than 200% D, the bearing will become too long and there is a risk of the bearing's lifespan being shortened. Note that "likely" means that there is a slight possibility that this will happen, and does not mean that there is a high probability that this will happen.

[0016] The area reduction rate is preferably 5% or more. If the area reduction rate exceeds 5%, the bearing may become more susceptible to wear. The area reduction rate is calculated by (cross-sectional area of ​​wire before drawing - cross-sectional area of ​​wire after drawing) / (cross-sectional area of ​​wire before drawing) x 100.

[0017] Preferably, the wire is initially contacted with the die during reduction, and the die is in contact with the wire over a length of 50% D or more, including the bearing. In this case, the wire can be processed by the bearing more reliably.

[0018] Preferably, the thermal conductivity of the wire drawing die is 100 to 300 W / (m·K). In this case, heat generated by friction between the wire and the wire drawing die can be easily dissipated to the outside.

[0019] If the shape specifications of CBN dies are not set appropriately, mechanical wear will significantly shorten the die's lifespan. CBN has a Knoop hardness of about 40-50 GPa, which is only half that of diamond (70-130 GPa), and is therefore disadvantageous in terms of mechanical wear. Therefore, by setting the reduction shape, etc. within an appropriate range, the die surface pressure can be prevented from becoming excessively high, and mechanical wear can be suppressed.

[0020] Compared to diamond dies, CBN dies are more susceptible to defects on the inside of the die, which affects the quality of the wire after drawing. As mentioned above, CBN has a low hardness, so defects on the inside of the die occur when the inside is ground, which has a significant effect on the quality of the wire after drawing.

[0021] The wire drawing die of the present disclosure has a long service life by solving the above problems. Fig. 1 is a cross-sectional view of a wire drawing die according to an embodiment. As shown in Fig. 1, a wire drawing die 1 according to the embodiment has a die hole 1h. The die 1 has, in order from the upstream side, a bell 1a, an approach 1b, a reduction 1c, a bearing 1d, a back relief 1e, and an exit 1f.

[0022] Bell 1a is located at the most upstream side of die hole 1h. The angle α formed by tangents 12a, 13a to the side surface of die hole 1h that defines bell 1a is the bell angle. Bell 1a corresponds to the entrance for the wire to be drawn and the lubricant.

[0023] Approach 1b is provided downstream of bell 1a. At the boundary between bell 1a and approach 1b, the inclination of die hole 1h may change continuously or discontinuously. Angle β between tangents 12b and 13b of the side surface of die hole 1h that defines approach 1b is the approach angle.

[0024] The reduction 1c is provided downstream of the approach 1b. At the boundary between the approach 1b and the reduction 1c, the inclination of the die hole 1h may change continuously or discontinuously. The angle γ of the side surface of the die hole 1h that defines the reduction 1c is the reduction angle.

[0025] The bearing 1d is provided downstream of the reduction 1c. At the boundary between the reduction 1c and the bearing 1d, the inclination of the die hole 1h may change continuously or discontinuously. The diameter D of the die hole 1h that defines the bearing 1d is constant. The bearing 1d has a cylindrical shape. The bearing 1d is the part of the die hole 1h with the smallest hole diameter.

[0026] The back relief 1e is provided downstream of the bearing 1d. At the boundary between the bearing 1d and the back relief 1e, the inclination of the die hole 1h may change continuously or discontinuously. The angle θ of the side surface of the die hole 1h that defines the back relief 1e is the back relief angle.

[0027] Exit 1f is provided downstream of back relief 1e. At the boundary between back relief 1e and Exit 1f the inclination of die hole 1h may change continuously or discontinuously. Exit 1F The angle φ of the side surface of die hole 1h that defines [it] is the exit angle.

[0028] If the diameter of reduction 1c is RD, then between RD and D, the relationship D < RD ≤ 1.050D holds. Therefore, the portion having the diameter RD of the above relationship is reduction 1c. The cross-sectional area of reduction 1c is more than 100% and 110% or less of the cross-sectional area of bearing 1d.

[0029] The length of bearing 1d is L. Between L and D, the relationship 0 < L ≤ 200%D holds.

[0030] To measure the shapes of bell 1a, approach 1b, reduction 1c, bearing 1d, back relief 1e, and exit 1f, a transfer material (for example, Repliset manufactured by Stollas Co., Ltd.) is filled into die hole 1h to produce a replica in which the shape of die hole 1h is transferred. This replica is cut in a plane including center line 1p to obtain a cross-sectional view of die hole 1h like die hole 1h in FIG. 1. Based on this cross-sectional view, the shape of each part can be measured. When bearing 1d has a sufficiently large diameter, the replica in which die hole 1h is transferred can be pulled out from die hole 1h by elastically deforming it. When bearing 1d has a small diameter and the replica cannot be pulled out from die hole 1h even by elastically deforming the replica, the replica is cut near exit 1f and the shape of the portion other than exit 1f is reproduced using the replica. Further, a transfer material is filled into die hole 1h to create a replica, this replica is cut near bell 1a, and the shape of the portion other than bell 1a is reproduced using the replica. By combining these, the cross-section of die hole 1h can be obtained.

[0031] In measuring the reduction angle γ, tangents 12c, 13c are drawn on both sides of the reduction 1c at the reference point 11c (RD=1.050D) in the cross-sectional view of the die hole 1h, and the angle between the two tangents 12c, 13c is defined as the reduction angle γ.

[0032] [Details of the embodiment of the present disclosure] Example 1 (Basic wire drawing evaluation of BL (binderless) CBN dies) In order to confirm the effect of different die materials on performance, the following three types of dies with the same shape were prepared and evaluated.

[0033] Dice Material Three types of dies were prepared: A. single crystal diamond die, B. binderless PCD die, and C. CBN die. The CBN die contains 99% by mass or more of CBN and less than 1% by mass of hBN. This composition was measured by the following method. The contents (volume %) of cubic boron nitride, compressed hexagonal boron nitride, and wurtzite boron nitride in the CBN die can be measured by X-ray diffraction. The specific measurement method is as follows. The CBN die is cut with a diamond grinding wheel electrodeposited wire, and the cut surface is used as the observation surface.

[0034] An X-ray spectrum of the cut surface of the CBN die is obtained using an X-ray diffraction device (MiniFlex600 (product name) manufactured by Rigaku Corporation). The conditions of the X-ray diffraction device at this time are, for example, as follows.

[0035] Characteristic X-ray: Cu-Kα (wavelength 0.154nm) Tube voltage: 45kV Tube current: 40mA Filter: Multi-layer mirror Optics: Concentration method X-ray diffraction method: θ-2θ method.

[0036] In the obtained X-ray spectrum, the following peak intensities A, B, and C are measured.

[0037] Peak intensity A: The peak intensity of compressed hexagonal boron nitride obtained by subtracting the background from the peak intensity around the diffraction angle 2θ = 28.5° (the peak intensity at the diffraction angle 2θ = 28.5° in the X-ray spectrum).

[0038] Peak intensity B: Peak intensity of wurtzite boron nitride obtained by subtracting the background from the peak intensity around the diffraction angle 2θ = 40.8° (peak intensity at a diffraction angle of 40.8° in the X-ray spectrum).

[0039] Peak intensity C: The peak intensity of cubic boron nitride obtained by subtracting the background from the peak intensity around the diffraction angle 2θ = 43.5° (the peak intensity at the diffraction angle 2θ = 43.5° in the X-ray spectrum).

[0040] The content of compressed hexagonal boron nitride is obtained by calculating the value of peak intensity A / (peak intensity A+peak intensity B+peak intensity C). The content of wurtzite boron nitride is obtained by calculating the value of peak intensity B / (peak intensity A+peak intensity B+peak intensity C). The content of cubic boron nitride polycrystal is obtained by calculating the value of peak intensity C / (peak intensity A+peak intensity B+peak intensity C). Compressed hexagonal boron nitride, wurtzite boron nitride and cubic boron nitride all have similar electronic weights, so the above X-ray peak intensity ratio can be regarded as the volume ratio in the CBN die. If the respective volume ratios are known, the density of compressed hexagonal boron nitride (2.1 g / cm 3 ), density of wurtzite boron nitride (3.48 g / cm 3 ), and the density of cubic boron nitride (3.45 g / cm 3 ) these mass ratios can be calculated.

[0041] The crystal grain size D50 of CBN is 200 to 300 μm. D50 refers to the diameter at which, when particles are divided into two at a certain particle size, the number of larger particles is equal to the number of smaller particles.

[0042] D50 was measured as follows. A CBN die was cut using wire electric discharge machining and diamond grinding wheel electrodeposited wire, and ion milling was performed on the cut surface. The measurement point on the CP processed surface was observed using an SEM ("JSM-7500F" (product name) manufactured by JEOL Ltd.) to obtain an SEM image. The size of the measurement field of view was 12 μm × 15 μm, and the observation magnification was 10,000 times. With the grain boundaries of the crystal grains observed in the measurement field of view separated, the aspect ratio of each crystal grain, the area of ​​each crystal grain, and the distribution of the circle equivalent diameter of the crystal grains were calculated using image processing software (Win Roof ver. 7.4.5). The results were used to calculate D50.

[0043] Die shape: (Dice A to C are all the same) Reduction angle γ: 13 degrees (opening angle: All reduction angles below are listed as opening angles) Bearing 1d length L: 30%D Die hole 1h diameter D: 0.18mm (reduction rate set to 16%) Surface roughness Ra of bearing 1d in a circumferential length of 40 μm: 0.015 μm The surface roughness Ra of the bearing 1d is measured as follows.

[0044] It is known that the surface roughness Ra of the bearing 1d is determined by the tool and polishing conditions used to polish the bearing 1d. First and second dies of the same material and dimensions are prepared. The first and second dies are polished with the same polishing tool and polishing conditions. As a result, the bearings 1d of the first and second dies have the same surface roughness Ra. Polishing methods include ultrasonic polishing using a polishing needle and free abrasive grains, and polishing by laser processing.

[0045] In order to observe the cross-sectional shape of the die hole 1h of the first die, the side of the die 1 is ground by a surface grinder to remove 50% or more of the die hole diameter D.

[0046] 2 is a cross-sectional view taken along the line II-II in FIG. 1. In FIG. 2, the shape of the die before grinding is shown by a dotted line. The amount of grinding of the die hole 1h is indicated by a point 501. from The distance to the center line 1p is 50% D or more. The distance from the center line 1p to the point 502 is 50% D or less.

[0047] The exposed die hole 1h is degreased and cleaned with alcohol etc. to remove dirt from the bearing 1d. The following equipment is used for the measurement. Measuring device: Olympus MEASURING LASER MICROSCOPE OLS4000 Image size (pixels): 1024 x 1024 Image size: 258×258μm Scanning mode: XYZ high precision + color Objective lens: MPLAPONLEXT x50 DIC: Off Zoom: x1 Evaluation length: 40μm Cutoff λc: 8μm Filter: Gaussian Analysis parameters: Roughness parameters Magnification: x100 Cutoff: 8μm Using the above measuring device, an image including the surface roughness measurement area is taken under the above shooting conditions. At this time, an image as bright as possible is obtained without the image being reflected by scratches, etc. When taking the image, the die grinding surface 1z is set so that it is parallel to the microscope.

[0048] Fig. 3 is a diagram for explaining a method for measuring the surface roughness inside a bearing 1d. The captured image is displayed on a screen, and a line 1y is drawn at a position equidistant from the wall surfaces 31 and 41 at both ends of the die hole 1h in Fig. 3. This line 1y approximately coincides with the center line 1p of the die hole 1h.

[0049] A line 101 perpendicular to the line 1y is displayed. The shape of the inner peripheral surface of the die hole 1h at the position of the line 101 (a circle that constitutes a plane perpendicular to the center line 1p and that includes the line 101) is shown as a circular arc curve 201.

[0050] Line 101 is translated, for example, in the upward direction as indicated by arrow 110 to the position of line 102. Accordingly, the shape of the inner peripheral surface of die hole 1h at the position of line 102 (a circle that constitutes a plane perpendicular to center line 1p and including line 102) is shown as a circular arc curve 202. The radius of circular arc curve 202 is larger than the radius of circular arc curve 201.

[0051] Line 101 is translated downward as indicated by arrow 120, for example, to the position of line 103. Accordingly, the shape of the inner circumferential surface of die hole 1h at the position of line 103 (a circle that is perpendicular to center line 1p and forms a plane including line 103) is displayed as a circular arc curve 203. The radius of circular arc curve 203 is smaller than the radius of circular arc curve 201. In this manner, line 101 is translated upward as indicated by arrow 110 and downward as indicated by arrow 120, to display the inner circumferential surface at each position, and the position where the radius of the circular arc curve is the smallest, i.e., the position where the circular arc curve is highest, is found. That position is bearing 1d.

[0052] A circular arc curve 204 corresponding to the line 104 of the bearing 1d indicates the shape of the inner peripheral surface of the bearing.

[0053] The bottom of the arc curve 204 (Fig. 3 So, line A range of 20 μm to the left and right (40 μm in total) from the intersection 210) of 104 and line 1y is set as the roughness measurement range, and the surface roughness Ra in this range is defined as the surface roughness of bearing 1d. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. The shape of the die before grinding is shown by a dotted line in Figure 2. The amount of grinding of die hole 1h is 50%D or more of the distance from point 501 to center line 1p. The distance from center line 1p to point 502 is 50%D or less.

[0054] The first die and the second die had the same surface roughness Ra of the bearing 1d, and the wire drawing was performed using the second die.

[0055] Wire drawing conditions Wire rod: SUS316L Linear speed: 500m / min Lubrication: oil-based Wire drawing distance: 30km The results are shown in Table 1.

[0056] [Table 1]

[0057] In judging the "life" in Table 1, the time when the surface roughness Ra of the wire after drawing became 0.100 μm or more was judged to be the end of the life.

[0058] "Ring wear" refers to annular wear near the reduction 1c on the inner peripheral surface of the die.

[0059] The magnitude of the ring wear was determined by the following method. A transfer material (for example, RepliSet, manufactured by Struers Corporation) was filled into the die hole 1h to create a replica in which the shape of the die hole 1h was transferred. This replica was cut along a plane including the center line 1p to obtain a cross-sectional view of the die hole 1h, such as the die hole 1h in FIG. 1. FIG. 4 is a cross-sectional view showing the die hole 1h and the replica 300 filled into the die hole 1h. As shown in FIG. 4, the replica 300 has a shape that follows the die hole 1h. The shape of the inner surface of the die hole 1h was transferred to the outer surface of the replica 300. Ring wear 304a, 304b was formed on the reduction 1c. The replica 300 was photographed with a transmission microscope, and the areas of the ring wear 304a, 304b were calculated using image analysis software (WinRoof, ImageJ, etc.), and the larger area was taken as the result of the ring wear. In Fig. 4, ring wear 304a and 304b are formed on the left and right sides of the replica 300. The areas of the ring wear 304a and 304b are calculated, and the larger area is taken as the result. The area of ​​the part surrounded by the straight line connecting the upper end 301 and the lower end 302 of the ring wear 304a and the ridge line 303 is taken as the area of ​​the ring wear 304a. If this area is 50 μm 2 If the area was 10μm or more, the ring wear was deemed large. 2 The ring wear was considered small when the area was less than 10 μm 2 More than 50μm 2 Ring wear was considered to be medium in the following cases:

[0060] "Change in wire diameter" indicates the difference between the wire diameter of the wire after drawing at the start of drawing and the wire diameter of the wire after drawing at the end of its life or after 30 km of drawing, whichever comes first.

[0061] "Uneven wear" refers to the deformation of the bearing 1d into a shape other than circular. Wear of single crystal diamond depends on the plane orientation of the single crystal diamond. Therefore, it wears more easily in one direction than in another. As a result, uneven wear occurs. Binderless PCD and CBN are polycrystalline, so they wear equally in all directions and therefore do not suffer from uneven wear.

[0062] "Pulling force" is the increase in pulling force at 30 km compared to 15 km for binderless PCD and CBN. For single crystal diamond, it is the increase in pulling force at 20 km compared to 15 km.

[0063] "Wire surface roughness Ra" refers to the roughness Ra of the wire surface at the end of its life or after 30 km of drawing, whichever comes first. Ra is defined by JIS B 0601 (2001) and was measured using a MEASUREING LASER MICROSCOPE OLS4000 manufactured by Olympus.

[0064] The single crystal diamond die reached the end of its life when the wire was drawn for 20 km, due to a deterioration in the surface roughness of the wire. Observation of the die after drawing revealed that uneven wear and ring wear had progressed rapidly, causing unevenness on the inner surface of the die, which was presumably transferred to the wire and thus reaching the end of its life.

[0065] The binderless PCD die had ring wear at the 15 km drawing stage. At the 30 km drawing stage, the ring wear was the deepest among the three types of dies. It was also confirmed that the progression of ring wear increased the pulling force by about 10%, suggesting that the wire is more susceptible to breakage.

[0066] Even after 30 km of wire drawing, the CBN die showed significantly less ring wear than the other dies, and there was almost no change in wire diameter or drawing force, demonstrating good wire drawing performance.

[0067] Example 2 (Basic evaluation of binderless CBN die shape dependency) In order to compare the shape dependency due to differences in die materials, the following dies were prepared and evaluated. The specifications other than the wire drawing evaluation conditions and reduction angle were the same as in Example 1.

[0068] Dice Material Three types of dies were prepared, the same as in Example 1: A. single crystal diamond die, B. binderless PCD die, and C. CBN die. The CBN die contains 99% by mass or more of CBN and less than 1% by mass of hBN. The crystal grain size D50 of the CBN is 200 to 300 μm.

[0069] Die shape: (Dice A to C are all the same) Reduction angle: 18 degrees Bearing 1d length: 30%D Surface roughness Ra of bearing 1d in a circumferential length of 40 μm: 0.015 μm Die hole 1h diameter D: 0.18mm (reduction rate set to 16%) Wire drawing conditions Wire rod: SUS316L Linear speed: 500m / min Lubrication: oil-based The results are shown in Table 2.

[0070] [Table 2]

[0071] The CBN die reached the end of its life at 13 km, so the evaluation was discontinued at that point. Unlike when the reduction angle was 13°, the CBN die had the shortest life.

[0072] It can be seen that ring wear occurs in the single crystal diamond and binderless PCD dies. On the other hand, although the CBN die does not have ring wear, the inner surface is very rough from reduction 1c to bearing 1d, and the wire diameter also expands more than the other diamond dies. For this reason, although the effect of suppressing ring wear is the same regardless of shape, it is thought that due to its relatively low hardness compared to diamond, it was unable to fully demonstrate its performance in high-angle dies where surface pressure tends to increase.

[0073] Example 3 The performance of CBN dies was investigated when the reduction angle was changed.

[0074] Wire drawing conditions Die hole size: 80μm Wire rod: SUS316L Wire drawing distance: 60km Linear speed: 500m / min Back tension: 5cN Die specifications: See Table 3 Die material: CBN dies only. CBN dies contain 99% or more by mass of CBN and less than 1% by mass of hBN. The CBN grain size D50 is 200 to 300 μm.

[0075] The same measurements were carried out as in Example 1. The results are shown in Table 3.

[0076] [Table 3]

[0077] The lifespan of die number 4 is rated as 1, with a lifespan of 1 or more being rated as A, and a lifespan of 0.8 or more but less than 1 being rated as B. was rated B, and a lifespan of less than 0.8 was rated C.

[0078] As in the first and second embodiments, the "bearing surface roughness Ra" is the surface roughness Ra within a range of 40 μm in the circumferential length of the bearing 1d.

[0079] Regarding the wire drawing results, the linear change is 0.5μm or less. surface A roughness Ra of 0.05 μm or less was acceptable, a roundness of 0.3 μm or less was acceptable, and a life span of A or B was acceptable. Overall, if all four of these items were acceptable, the wire drawing die was deemed to be of good quality (accepted).

[0080] In order to determine the wire drawing performance resulting from differences in the shape of the CBN die, experiments were conducted with five different reduction angles. The results showed that when the reduction angle was 17 degrees or less, ring-shaped die wear was less likely to occur, and the wire surface roughness, roundness, and change in wire diameter tended to be smaller.

[0081] On the other hand, when the reduction angle exceeded 17 degrees, the wear of the ring and the bearing progressed rapidly, and problems such as deterioration of the wire surface roughness and enlargement of the wire diameter occurred. Based on the above results, it is recommended that the appropriate reduction angle for CBN dies is 17 degrees or less.

[0082] Example 4 The performance of the CBN die was investigated when the bearing length was changed.

[0083] A CBN die having the bearing length shown in Table 4 was prepared, and a wire drawing test was carried out under the same conditions as in Example 3. The results are shown in Table 4.

[0084] [Table 4]

[0085] The lifespan of die number 4 was assigned a rating of 1, with a lifespan of 1 or more assigned an A, a lifespan of 0.8 or more but less than 1 assigned a B, and a lifespan of less than 0.8 assigned a C.

[0086] The pass criteria were the same as in Example 3. When the bearing length was less than 400% D, almost no ring wear occurred even after wire drawing, and the wire quality (diameter change, roughness, roundness) remained good.

[0087] When the bearing length was 400% D, the wire quality was good, but there was a tendency for breakage to occur somewhat easily. However, good drawability (no breakage) was achieved by lowering the wire speed. From the above results, the CBN die bearings perform best when they are 200% D or less.

[0088] Example 5 The effect of the initial surface roughness of the CBN die hole 1h on wire drawing performance was investigated. Roughness The performance of the CBN die was investigated when the temperature was changed.

[0089] A CBN die having the bearing length shown in Table 5 was prepared, and a wire drawing test was carried out under the same conditions as in Example 3. The results are shown in Table 5.

[0090] [Table 5]

[0091] The lifespan of die number 4 was defined as 1, and a lifespan of 1 or more was rated as A, a lifespan of 0.8 or more but less than 1 was rated as B, and a lifespan of less than 0.8 was rated as C. The pass criteria were the same as in Example 3.

[0092] The initial roughness of the inner surface of the die does not have a significant effect on the amount of change in wire diameter or roundness during wire drawing. However, it was found that the initial roughness of the die has a significant effect on wire quality. For these reasons, it is desirable for the inner surface roughness of the die to be 0.025 μm or less.

[0093] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the claims, not by the embodiments described above, and is intended to include the equivalent meanings of the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0094] 1 die, 1a bell, 1b approach, 1c reduction, 1d bearing, 1e back relief, 1f exit, 1h die hole, 1p,1y center line, 101,102,103,104 lines, 1z die grinding surface, 11a,11b,11c reference point, 12a,12b,12c,13a,13b,13c tangent line, 31,41 wall surface, 110,120 arrow, 201,202,203,204 arc curve, 210 intersection, 501,502 points.

Claims

1. A wire drawing die made of a non-diamond material, the non-diamond material being CBN, having a circular die hole, a reduction and a bearing located downstream of the reduction, a reduction angle, which is an opening angle of the die hole during the reduction, is 17° or less, and a surface roughness Ra of the die hole within a range of ±20 μm in a circumferential direction of the die hole perpendicular to the wiredrawing direction from a specific position in the bearing is 0.025 μm or less, When the diameter of the bearing is D, the length L of the bearing is 200% D or less, A wire drawing die having an area reduction rate of 5% or more.

2. 2. The wire drawing die according to claim 1, wherein the base wire and the die come into initial contact during the reduction, and the die comes into contact with the wire over a length of 50% D or more including the bearing.

3. 3. The wire drawing die according to claim 1 or 2, having a thermal conductivity of 100 to 300 W / (m·K).

4. A wire drawing die as described in any one of claims 1 to 3, wherein the wire drawing die contains 99% by mass or more CBN and less than 1% by mass hBN.

5. A wire drawing die as described in any one of claims 1 to 4, wherein the CBN crystal grain size D50 is 200 to 300 μm.

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