JP2018164936A - Punching mold and punching method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a punching mold having excellent abrasion resistance and adhesion resistance, which is suitable for punching electromagnetic soft iron.SOLUTION: A punching mold for electromagnetic soft iron contains 6 mass% or less of Co and is composed of WC-based sintered material. Preferably, the punching mold is provided with a hard film containing Al, Cr, and N, on its surface. The punching mold can be applied to a punching method for electromagnetic soft iron.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a punching die and a punching method using the die. In particular, the present invention relates to a punching die suitable for electromagnetic soft iron punching and a punching method using the die.

  Iron-based electromagnetic materials are used in iron cores such as transformers and motors, armatures (movable iron pieces) of electromagnetic relays, etc. by utilizing their excellent soft magnetic properties.

  An armature that is a component of an electromagnetic relay is required to have excellent electromagnetic characteristics. Therefore, pure iron-based electromagnetic soft iron having high magnetic flux density, magnetic permeability, and small coercive force is used as the material. When manufacturing an armature from a plate material, stamping is used. A plate member made of electromagnetic soft iron is punched out to obtain a member (blank material) having a predetermined shape. After that, it is common to manufacture an armature for a small relay having a predetermined shape by performing a scouring process for finishing the shearing surface and the fracture surface of the obtained member.

  In the punching process, two types of molds, a punching mold and a shaving mold, are used. In the present specification, the punching die and the shaving die are collectively referred to as “a punching die”. Since the punching die is violently rubbed with the workpiece, it is worn as the number of machining increases, and the clearance between the punch and the die also increases. If processing is continued with the mold worn out, the shear surface ratio of the product end face decreases, the fracture surface ratio increases, and the fracture surface properties change and the burr height increases, resulting in shape defects. Cause it. For this reason, the mold that has been worn out is replaced or re-polished. Frequent replacement causes a decrease in productivity and increases manufacturing costs.

  A die for punching is required to have a high hardness and a high wear property, so that a cemented carbide is often used. The cemented carbide is a material mainly composed of WC, and is obtained by mixing and sintering WC powder and Co powder as a binder. In order to suppress the loss of WC, the amount of Co in the binder is included at about 10% by mass.

  Regarding punching of electromagnetic materials, for example, in Patent Document 1, in a punching method for high silicon steel sheets of Si: 4.0 to 7.0 wt%, a cemented carbide alloy having an average particle size of hard phase of 3 μm or less is used. A tool that suppresses tool wear and chipping and extends tool life by using a punching tool is described.

Japanese Patent Laid-Open No. 11-319981

  Unlike the silicon steel sheet of Patent Document 1, electromagnetic soft iron used in electromagnetic parts has a composition close to that of pure iron, so it is a material with relatively low mechanical strength and requires a high load for punching. do not do. However, when punching is performed, an adhesion phenomenon may occur in which a part of the workpiece (electromagnetic soft iron) sticks to the surface of the cemented carbide mold. A part of the work material adhered to the mold surface is missing from the mold together with the mold material attached at the time of the punching process, which is a factor for promoting the wear of the mold. In the punching process of electromagnetic soft iron, this adhesion occurs, resulting in severe wear of the mold and short mold life. Therefore, there has been a problem that the manufacturing cost increases and the productivity is lowered.

  An object of the present invention is to provide a die for punching which is suitable for punching electromagnetic soft iron and has excellent wear resistance and adhesion resistance. Another object of the present invention is to provide a punching method for punching electromagnetic soft iron using the mold.

  As a result of studying to solve the above problems, the present inventors have found that by reducing the amount of Co in the cemented carbide of the mold, it is possible to suppress electromagnetic soft iron from adhering to the mold surface, The present invention has been reached. Specifically, the present invention provides the following.

(1) The present invention is a die for punching electromagnetic soft iron, comprising a sintered member mainly containing WC, containing 6% by mass or less of Co.

(2) The present invention is the electromagnetic soft iron punching die according to (1), wherein a hard film containing Al, Cr and N is provided on the surface of the die.

(3) The present invention is a punching method in which electromagnetic soft iron is punched using the mold described in (1) or (2).

  According to the present invention, even if punching is performed, electromagnetic soft iron is prevented from adhering to the mold surface. Therefore, the wear of the mold due to adhesion is suppressed, the mold life is extended, the productivity of the punching process is improved, and the manufacturing cost is reduced.

It is a figure for demonstrating the punch test in an Example. It is a figure which shows the external appearance of the metal mold | die after the punching process in an Example. It is a figure for demonstrating the measuring method of the abrasion loss in an Example. It is a figure for demonstrating the measurement location of the abrasion loss in the punch tip in an Example, (a) is a figure which shows the measurement location of a right side part, (b) is a figure which shows the measurement location of a corner part. It is. It is a schematic diagram which shows the measuring apparatus of the friction coefficient in an Example. It is a figure which shows the time change of the friction coefficient in an Example.

  Hereinafter, embodiments of the present invention will be described. The present invention is not limited by the following description.

  The punching die according to the present invention is composed of a sintered member mainly containing WC, containing 6% by mass or less of Co. The sintered member used in the mold is made of a cemented carbide manufactured by mixing and sintering WC powder with Co as a binder. The punching process is a processing mode in which a punch is pushed into a workpiece, a crack is generated in the workpiece by the shearing action of the punch and the die, and the workpiece is further sheared and broken by pressurization. When punching is performed, intense friction occurs between the mold (punch, die) and the workpiece, and the workpiece may adhere to the mold surface.

  In the punching die according to the present invention, the Co content of the die material is regulated to 6% by mass or less. When electromagnetic soft iron is punched using a cemented carbide mold with a reduced amount of Co, the phenomenon of electromagnetic soft iron adhering to the mold can be suppressed.

  Although the reason for this is not clear, the adhesion of electromagnetic soft iron in a conventional cemented carbide mold is assumed to be due to the affinity between the Co element contained in the mold material and the Fe element of electromagnetic soft iron. In the mold according to the present embodiment, the content of Co bonded to Fe is reduced, so that it is considered that the adhesion of electromagnetic soft iron is suppressed.

  The punching die according to the present invention preferably includes a hard film containing Al, Cr, and N on the surface of the die. By providing the hard film on the mold surface, direct contact between the electromagnetic soft iron and the mold is prevented, so that the wear resistance and adhesion resistance of the mold are improved. Further, when the mold surface becomes high temperature due to processing heat generation, the hard coating may be denatured and peeled off. Therefore, the hard coating is preferably an AlCrN coating that hardly oxidizes at a high temperature and has excellent seizure resistance, which contributes to further improving the wear resistance of the mold.

  Examples according to the present invention will be described below. The present invention is not limited by the following description.

(Test Example 1) Evaluation of wear state by punching test As described above, in the process of manufacturing a member such as an armature by punching, the punching die and the die for shaving die have a friction with the plate material. It is repeating. Therefore, the punching test in this example is for punching by repeating the operation of applying a shaving die to the punched surface of the punched hole after punching a hole in the plate material by the punching die. The mold performance and surface condition were evaluated.

  FIG. 1 shows an outline of a punching test using a punching die 1 including a punching die 2 and a shaving die 3 according to this embodiment. As shown in FIG. 1, after the workpiece 4 is punched by the punching die 2 to form the processed hole 5, the processed hole 5 is transferred in the feed direction 7. Next, the punched surface of the processed hole 5 is finished with the shaving mold 3 to form the processed hole 6.

  The punching die 1 includes a punch and a die. FIG. 1 shows a punch. The punch tip surface of the punching die 2 corresponds to the shape and dimensions of the machining hole 5 of the workpiece 4 shown in FIG. 1, and the tip surface of the punching die 2 has a size of 4.0 mm × 4.0 mm. Have. As shown in FIG. 1, the shaving die 3 is formed with a processing hole 6 at one end of the processing hole 5 so as to take a cutting allowance of 2.0 mm × 0.5 mm. It has a shape and dimensions of × 4.5 mm.

  A die (not shown) having an opening is provided on the opposite side of the punch across the workpiece 4. The opening in the die has a dimension that is larger than the punch dimension by a clearance. The clearance in this example was set to 0.06 mm (5%) for the punching die and 0.02 mm (1.7%) for the shaving die.

The punching die is a test die No. having a different die material. 1. Test mold No. 2 was prepared and subjected to a punching test.
Test die No. 1: WC-6 mass% Co cemented carbide material (example of the present invention)
Test die No. 2: WC-13 mass% Co cemented carbide material (comparative example)

  The test mold was produced by a known production method. Specifically, raw materials were prepared from commercially available WC powder and Co powder. The average particle size of the WC powder is determined according to the mold no. 1 is 0.5 to 5.0 μm, No. of Comparative Example. 2 used 0.5-1.5 micrometers (comparative example). The raw material powder is weighed to a prescribed composition, inserted into a stainless steel pot together with an acetone solvent and a cemented carbide ball, the ball content and grinding time are adjusted, mixed and ground, then dried and mixed A powder was obtained. These mixed powders were pressure-molded to form powder compacts, and then sintered by heating for 1 hour at a temperature of 1300 to 1400 ° C. in a vacuum of 10 Pa. The surface of the obtained cemented carbide material was polished so as to have a predetermined dimension to obtain a test mold.

  The plate material of 1.2 mm thick electromagnetic soft iron (SUYP-1) was punched by a 400 kN press using the punching die of the present invention example and the comparative example. As shown in FIG. 1, after punching out a 4.0 mm × 4.0 mm rectangular hole of electromagnetic soft iron 4 with a punching die 2, a shaving die is used to reduce the cutting allowance to 2.0 mm × 0.5 mm. A shaving process was performed. This series of punching processes was performed a total of 20,000 punching tests at a processing speed of 300 spm.

  FIG. 2 shows an appearance of a shaving die (punch) after 20,000 times of shaving. This appearance shows the surface of the punch having a length of 2.0 mm. As shown in FIG. As for 2, the white part was observed on the surface. This part is a place where a part of electromagnetic soft iron has adhered. In particular, many adhesions were observed at the corner (Rc portion) of the mold. On the other hand, the test mold No. No. 1 was a degree in which slight adhesion was observed in the corner portion, and almost no adhesion occurred on the entire surface.

  Next, the amount of wear at the tip of the punch was measured. The measuring method is as follows. As shown in FIG. 3, the outer shape of the punch body is set as reference lines 21 and 22, and intersection points 25 of lines extending from the side reference line 21 and the end face reference line 22 are set. Then, the distances 26 and 27 from the points 23 and 24 where the outer shape of the punch tip portion starts to deviate from the reference lines 21 and 22 to the intersection 25 are measured, and the distance is defined as the wear amount. According to the measurement surface of the wear amount, a side wear amount 26 measured on the side surface of the punch tip and an end face wear amount 27 measured on the end surface of the punch tip are obtained. For example, the side surface wear amount 26 corresponds to the distance from the portion 23 that deviates from the side surface reference line 21 of the punch body to the intersection 25.

  In this test, the side surface wear amount 26 in the side surface direction 31 and the end surface friction amount 27 in the end surface direction were measured at the front end portion of the punch at the straight side portion shown in FIG. 4A, and shown in FIG. At the corner portion, the side surface wear amount 26 in the side surface direction 33 and the end surface wear amount 27 in the end surface direction 34 were measured. The measurement results of the amount of wear (mm) are shown in Table 1.

  As shown in Table 1, the amount of wear in the right side portion of the inventive example was reduced to about 14% of the comparative example in the side surface direction 31 and to about 60% of the comparative example in the end surface direction 32, respectively. The amount of wear at the corners was about the same as that of the comparative example in the end surface direction 34, but was reduced to about 66% of the comparative example in the side surface direction 33. Thus, in the mold of the present invention example containing 6% by mass or less of Co, the wear amount of the mold in the punching of electromagnetic soft iron was greatly reduced due to the reduction of the Co content. In the punching of electromagnetic soft iron, it has been found that reducing the Co content of the mold is effective in improving adhesion resistance and wear resistance.

  The reason for the above test results is not clear. Due to the affinity between Fe and Co, in the conventional mold using a cemented carbide with a high Co content, Fe in the electromagnetic soft iron and Co in the mold are bonded during processing, and the mold surface It is thought that this resulted in adhesion.

(Test Example 2) Measurement of friction coefficient Next, the change in the friction coefficient of the mold due to the sliding time was measured by the pin-on-disk test method using the test molds of the present invention example and the comparative example. . FIG. 5 shows an outline of the friction coefficient measuring apparatus. A test piece (70 mm × 70 mm) having a plate thickness of 5.0 mm made of a test mold material was fixed on the turntable 41. A pin-shaped contact 46 made of electromagnetic soft iron was attached to a support 45 provided on the load sensor 44 side. The contact 46 was brought into contact with the position on the test piece 42 at a radius of 10 mm from the center of rotation. Thereafter, while applying a load with a load weight 43 of 100 g, the turntable was rotated at a speed of 9.6 rpm, and the contact 46 was slid on the same circumference on the test piece 42. In consideration of heat generated during punching, a heating device was arranged around the measuring device, and the test temperature was 200 ° C. Then, the friction force was measured by the load sensor 44 to obtain a friction coefficient (= friction force / load).

  The measurement results are shown in Table 2. The coefficient of friction is measured with the sliding time. The measured values of the coefficient of friction shown in Table 2 are average values over 5 minutes.

  FIG. 6 illustrates the measurement results of Table 2. As shown in FIG. 6, in the mold of the example of the present invention, the friction coefficient 0.24 before the test decreased with the sliding time, and shifted to almost constant around 0.13 after 20 minutes or more. On the other hand, in the mold of the comparative example, the friction coefficient 0.26 before the test increased with the sliding time, and shifted to almost constant around 0.33 after 10 minutes or more. It has been found that the coefficient of friction of the cemented carbide mold decreases as the sliding time increases due to the reduction of the Co content.

  The reason is not clear. In the comparative mold, due to the affinity between Fe in the electromagnetic soft iron and Co in the cemented carbide, Fe adhesion occurs on the mold surface due to sliding between the mold and the electromagnetic soft iron. Further, it is presumed that the friction coefficient of the mold increased with the sliding time because the adhesion was promoted by generation of frictional heat. On the other hand, in the metal mold of the present example containing 6% by mass or less of Co, the occurrence of adhesion is suppressed by reducing Co, and it is presumed that the wear induced by the adhesion is also suppressed. . And since the unevenness | corrugation (surface roughness) of the metal mold | die surface was shaved and smoothed by the friction of sliding, it is thought that a friction coefficient fell with progress of sliding time.

(Test Example 3) Evaluation of surface coating Test mold No. 1 is a test mold No. 1 coated with TiAlN by PVD. 3 and test mold No. 1 coated with AlCrN. 4 was produced. Using these molds, the punching process similar to that of Test Example 1 was performed, and then the appearance of the punch was observed. All showed surface properties with suppressed adhesion. Compared in detail, the mold no. In No. 1, slight adhesion occurred at the corners on the entire surface. In contrast, mold No. having a coating of TiAlN. 3 and mold No. 3 having a coating of AlCrN. In No. 4, no adhesion was observed on the entire surface including the corner.

  On the other hand, mold no. In No. 3, the surface changed to black in a wide range near the blade edge, and the progress of wear was observed. This is presumed that the TiAlN coating is oxidized and deteriorated by processing heat generation, and as a result, the coating is partially peeled off at the corner portion where the sliding is particularly intense, resulting in intensive wear. In contrast, mold no. The coating of AlCrN No. 4 is a coating material that hardly oxidizes even at high temperatures and has excellent seizure resistance. No significant damage was observed in 4. Therefore, it was confirmed that the die used for electromagnetic soft iron punching can further improve the die life by the AlCrN coating.

1 Punching die 2 Punching die 3 Shaving die punch 4 Work material (electromagnetic soft iron)
5 Processed hole by punching 6 Processed hole by shaving mold 7 Feed direction 21 Side reference line 22 End face reference line 23 Deviation (side)
24 Deviation (end face)
25 Intersection of the reference line 26 Side wear amount 27 End face wear amount 31 Side direction (long side)
32 End face direction (long side)
33 Side direction (corner part)
34 End face direction (corner part)
41 rotating table 42 test piece 43 load weight 44 load sensor 45 support tool 46 contactor

Claims (3)

  A die for punching electromagnetic soft iron, comprising a sintered member mainly containing WC, containing 6% by mass or less of Co.   2. The electromagnetic soft iron punching die according to claim 1, wherein a hard coating containing Al, Cr and N is provided on a surface of the die. 3.   A punching method for performing electromagnetic soft iron punching using the mold according to claim 1.