JP2009061465A - Metallic mold for cold forging and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallic mold for cold forging which can suppress the galling of a formed product forged thereby by preventing a hardened film on the surface of thereof from wearing or exfoliating, and to provide its manufacturing method. <P>SOLUTION: The metallic mold 1 for cold forging is provided with a single layer or multi-layer hardened film 3 composed of one or more selected from groups, which is composed of; carbide, nitride or carbonnitride, containing one or more of group 4A (Ti,Zr,Hf), 5A group (V,Nb,Ta), 6A group (Cr,Mo,W) metals and the nitride containing one or more of 4A group (Ti,Zr,Hf), 5A group (V.Nb,Ta), 6A group (Cr,Mo,W) metals; and one or two of Si and Al on the metallic mold designed plane 2. The surface roughness Ra of the hardened film 3 is 0.05-0.50 μm even in the case of being measured in every direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cold forging die and a method for manufacturing the same, and more specifically, a molded product (for example, forged by a cold forging die by applying shot peening or coating to the cold forging die. The present invention relates to a technique for suppressing galling of (tensile steel plate).

In order to reduce the CO ₂ emissions of automobiles and ensure collision safety, it is necessary to reduce the weight and rigidity of the vehicle body, and the use ratio of high-tensile steel sheets is rapidly increasing. However, since the high-tensile steel plate has high strength, when the high-tensile steel plate is pressed by a cold forging die, the steel material causes intense friction with the cold forging die, resulting in oil film breakage. Small seizure of the steel material to the cold forging die occurs, and a defect called galling (streak-like wrinkles generated in a high-tensile steel plate as a molded product) is likely to occur. A molded product having such defects cannot be used as a product.
Therefore, in order to solve this problem, an attempt has been made to coat a cold forging die with a hard coating having a low affinity with iron by a PVD method or the like.

In addition to these, various techniques have been proposed as surface treatment techniques that can extend the life of the mold.
For example, in a hot forging die, nitriding treatment is performed on the die surface, and fine irregularities are formed on the nitrided die surface by a nitride compound layer. Then, at the time of hot forging, a lubricant is applied to the mold surface in order to suppress the wear of the mold. The lubricant is made by diluting a powder having a solid lubricating action such as graphite or BN with water, and the lubricant is applied to the mold surface by spraying the mold during hot forging.
The applied lubricant enters the fine irregularities formed by the nitride compound layer, and the lubricant that has entered the irregularities retains the lubricating action and suppresses wear of the mold. In addition, even if the nitride compound layer is peeled off, if the mold surface is oxidized by the heat during forging, fine irregularities are formed on the oxidized surface in the same manner as the nitride compound layer, and the lubricant is held by these irregularities. The Therefore, even if the nitride compound layer is peeled off, the wear of the mold is suppressed.

  However, in the case of unevenness due to the nitride compound layer, there is a problem that the effect of suppressing wear is not sufficient. Therefore, in recent years, in order to suppress wear of the mold, a technique for coating the mold surface with a hard film (CrN, TiAlN, etc.) harder than the nitride compound layer has been developed and put to practical use.

  As a technique for forming a CrN film, for example, in Patent Document 1, after adjusting the surface roughness of a mold base with diamond paste (# 3000 mesh), a nitride layer is formed, washed, and then multi-arced. A hot or warm working mold in which a hardened layer made of CrN is formed by a method is disclosed. Patent Document 2 discloses a casting mold in which a surface treatment film made of CrN is formed on the inner wall of a cavity for injecting molten metal.

Further, as another surface treatment technique that can extend the life of a mold, a technique for performing shot peening has been proposed.
For example, Patent Document 3 discloses a general shot peening size projection material (particles) having a specific gravity equivalent to that of an iron-based projection material on a die (SKD, SKH) subjected to heat treatment (meaning including nitriding treatment and carbonitriding treatment). A technique is disclosed in which a smooth mold surface is obtained and a maximum residual compressive stress value is obtained by projecting a diameter of 125 μm at 60 to 100 m / second.

  In Patent Document 4, shot peening is performed by forming a nitride layer or a TiN hard coating on a mandrel, a molding tool or the like, setting a shot particle size from 40 to 200 μm, and a shot injection speed of 100 m / sec. Thus, a technique for extending the life by suppressing the wear and hair crack of the mandrel is disclosed.

Japanese Patent Laid-Open No. 11-092909 JP-A-10-137915 JP2003-191166 JP 2003-253422 A

However, the hard coating with low affinity with iron coated on the above-mentioned cold forging die is subjected to strong friction, so that the hard coating on the cold forging die is worn and finally peeled off. It was caused and it was not possible to exhibit a sufficient effect for suppressing galling.
In addition, since the hard coating (CrN, TiAlN, etc.) for suppressing wear of the hot forging mold is uniformly coated on the underlying mold, the surface roughness after coating is machined or lapped. The surface roughness of the mold was almost the same (smooth state). Therefore, the lube of the lubricant is poor, the lubricant flows, and the holding power of the lubricant is low. Moreover, since this hard film has high oxidation resistance, the film is not easily oxidized. Accordingly, there is a problem that fine irregularities are not generated on the mold surface, the holding power of the lubricant is low, and wear is promoted due to insufficient lubrication.
In addition, the warm or hot forging die disclosed in Patent Document 1 is provided with a CrN hardened layer mainly for the purpose of preventing peeling of a hardened film and improving adhesion. In order to increase the adhesion, it is better that the surface is as smooth and flat as possible. Therefore, in the way of forming a hard coating to increase the adhesion, the holding power of the lubricant is also necessary from the viewpoint of wear resistance. However, the problem of accelerated wear due to insufficient lubrication was not solved.
Further, the casting mold disclosed in Patent Document 2 is provided with a CrN coating instead of a release material mainly for the purpose of reducing adhesion and deposition of casting material and reducing pulling force when releasing the casting. It was intended to obtain excellent mold release properties. In order to improve the releasability, it is desirable that the surface is as flat as possible without being uneven. In the first place, casting molds have completely different uses from forging molds.

  The shot peening techniques disclosed in Patent Documents 3 and 4 both perform shot peening after forming a hard layer such as nitriding on the mold surface. The shot peening techniques disclosed in Patent Documents 3 and 4 attempt to suppress surface cracking by applying compressive residual stress and improve fatigue strength. Therefore, when shot peening is performed from the top of the hard layer using the shot peening technique disclosed in Patent Documents 3 and 4 for the purpose of forming irregularities that can maintain the holding power of the lubricant satisfactorily, nitriding treatment or the like There was a problem that the formed hard layer cracked.

  The present invention has been made in view of the above circumstances, and its purpose is to prevent wear and delamination of a hard coating formed on the surface of a cold forging die, thereby providing a cold forging die. An object of the present invention is to provide a cold forging die capable of suppressing the galling of a molded product to be forged and a method for manufacturing the same.

  In order to solve the above problems, the present inventors have studied a method for preventing wear and peeling of the surface of the cold forging die and suppressing galling of the molded product, and hardened the mold design surface. The knowledge that the mold surface becomes hard when coated with a coating was obtained. In addition, when the present inventors form irregularities on the mold design surface by shot peening before coating the hard coating, the irregular shape is reflected in the hard coating when the hard coating is coated from above. As a result, it was found that the hard coating also has irregularities, and the irregularities due to such a hard coating can maintain the retention of the lubricant over a long period of time. As a result, it has been found that the wear and delamination of the surface of the cold forging die during press working can be largely prevented, and the galling of the molded product can also be suppressed.

  This invention is made | formed based on this knowledge, The die for cold forging which concerns on this invention is 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta) on the die design surface. ), Carbides, nitrides or carbonitrides containing one or more of group 6A (Cr, Mo, W) metals, and group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta) A single-layer or multi-layer coating composed of one or two or more selected from the group consisting of nitrides containing one or more of Group 6A (Cr, Mo, W) metals and one or more of Si and Al The film is characterized in that the surface roughness Ra is 0.05 μm or more and 0.50 μm or less even when measured from any direction.

  In this case, the film may have a thickness of 1 μm or more and 20 μm or less.

  In any of the above cases, the mold design surface may be nitrided with a hardened layer depth of 200 μm or less.

In any of the above cases, it is desirable that the coating film be formed after forming irregularities on the mold design surface by shot peening.
At this time, the media may be projected at a projection speed of 100 m / sec or less.

In order to solve the above problems, a method for manufacturing a cold forging die according to the present invention includes:
A concavo-convex forming step of forming concavo-convex so that the surface roughness Ra is measured from any direction on the mold design surface by shot peening so as to be 0.05 μm or more and 0.50 μm or less,
After performing the unevenness forming step, a kind of Group 4A (Ti, Zr, Hf), Group 5A (V, Nb, Ta), Group 6A (Cr, Mo, W) metal on the mold design surface by PVD method Or a carbide, nitride or carbonitride containing two or more, and a group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta), group 6A (Cr, Mo, W) metal or A film forming step for forming a single layer or a multilayer film composed of one kind or two or more kinds selected from the group consisting of nitrides containing two or more kinds and one or two kinds of Si and Al. To do.

In order to solve the above problems, another method for producing a cold forging die according to the present invention is as follows.
Pre-coating irregularity forming process for forming irregularities on the mold design surface by shot peening,
After performing the pre-coating irregularity forming step, the PVD method is used to form a 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal on the mold design surface. Of carbides, nitrides or carbonitrides containing one or more of the above, and group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta), group 6A (Cr, Mo, W) metals A film forming step of forming a single-layer or multi-layer film composed of one kind or two or more kinds selected from the group consisting of nitrides containing one or two kinds and one or two kinds of Si and Al; and
A post-coating concavo-convex forming step of forming concavo-convex so that the surface roughness Ra is measured to be 0.05 μm or more and 0.50 μm or less on the coating by shot peening after performing the coating forming step; The main point is that

  Since the cold forging die according to the present invention is provided with a hard coating having irregularities with a predetermined surface roughness Ra formed on the mold design surface, the convex portion made of the hard coating is hard, and Since it has a predetermined surface roughness Ra, it is difficult to wear. Further, since the unevenness formed on the hard coating film has a predetermined surface roughness Ra, the holding force of the lubricant becomes good and the friction can be reduced. Therefore, the unevenness formed in the hard coating can maintain the retention force of the lubricant over a long period of time, and can prevent wear and peeling of the hard coating. Micro-seizure can be prevented, and thus the galling of the molded product can be suppressed. That is, the cold forging die according to the present invention can prevent wear and peeling of the hard coating and suppress galling of the molded product due to the synergistic effect of the hard coating and the surface roughness Ra (unevenness). Accordingly, the cold forging die according to the present invention can extend the die life, and the cost of the cold forging die and various molded products forged by the cold forging die can be reduced.

Since the method for manufacturing a cold forging die according to the present invention has the above-described configuration, the surface roughness Ra of the die surface is measured from 0.05 μm to 0.50 μm in any direction. It can be. The cold forging die obtained by this method has the same effect as the cold forging die according to the present invention.
In addition, since the method for manufacturing a cold forging die according to the present invention performs shot peening before the formation of the hard coating, the hard coating is cracked compared to the case where shot peening is performed after the hard coating is formed. There is no effect.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
(Cold forging die)
The cold forging die 1 according to an embodiment of the present invention shown in FIG. 1 may be made of cold die steel represented by JIS SKD11 and its improved steel, but the material is particularly limited. It is not something.
The cold forging die 1 has one or two kinds of 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), and 6A group (Cr, Mo, W) metal on the mold design surface 2. Carbides, nitrides or carbonitrides including the above, one or more of 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal And a single-layer or multi-layer hard coating 3 made of one or more selected from the group consisting of nitrides containing Si or Al. The reason why the hard coating 3 is made of such a material is that it is harder than simply nitriding the mold design surface 2 and is therefore less likely to be worn, that is, excellent in wear resistance. In addition, if the hard coating 3 is hard to wear, it will be prevented from peeling off, and the seizure of the molded product (high-tensile steel plate) forged by the cold forging die 1 will be prevented, and galling will be suppressed. is there. However, the mold design surface 2 may be nitrided with a hardened layer depth of 200 μm or less.

  The mold design surface 2 has a surface roughness Ra of 0.05 μm or more and 0.50 μm or less even when measured from any direction. The reason why the surface roughness Ra of the mold design surface 2 is set in this range is to reflect this surface roughness Ra on the “surface roughness Ra of the hard coating 3 formed on the surface of the mold design surface 2”. is there. The reason for this is that when the reflected surface roughness Ra of the hard coating 3 is less than 0.05 μm, sufficient holding power of the lubricant cannot be obtained, and there is not much effect of preventing the hard coating 3 from being worn. This is because if the surface of the mold 4 is too large, the ruggedness of the mold surface 4 is too large to promote galling. Therefore, the surface roughness Ra of the mold design surface 2 is set in this range. The surface roughness Ra of the mold design surface 2 is more preferably 0.05 μm or more and 0.30 μm or less, and further preferably 0.10 μm or more and 0.25 μm or less. However, if the surface roughness Ra of the hard coating 3 can be in these ranges, the surface roughness Ra of the mold design surface 2 is not limited to these ranges.

  The hard coating 3 is in contact with the material to be molded (work) at the time of shot, and the surface roughness Ra is 0.05 μm or more and 0.50 μm or less even when measured from any direction. The reason why the surface roughness Ra of the hard coating 3 is set in this range is that if it is less than 0.05 μm, a sufficient holding force of the lubricant cannot be obtained, and the effect of preventing the hard coating 3 from being worn is not so much. This is because, when the thickness exceeds 50 μm, the unevenness of the mold surface 4 is too large, and the galling is promoted. The surface roughness Ra of the hard coating 3 is more preferably 0.05 μm or more and 0.30 μm or less, and further preferably 0.10 μm or more and 0.25 μm or less.

  The film thickness of the hard coating 3 is preferably 1 μm or more and 20 μm or less as a whole regardless of a single layer multilayer. The reason why the film thickness of the hard coating 3 is set in this range is that if the thickness is less than 1 μm, the effect of preventing the wear and peeling of the hard coating 3 is small, and if it exceeds 20 μm, the coating time becomes long, which is economically disadvantageous. When the hard coating 3 is composed of multiple layers, the stacking order is not particularly limited.

(Cold forging die manufacturing method)
A die 1 for cold forging according to an embodiment of the present invention uses, for example, a die made of cold die steel typified by JIS SKD11 and improved steel, and the following (1) concavo-convex forming step and ( 2) It can manufacture by performing a film formation process in this order. In addition, the following (1) uneven | corrugated formation process is also called a pre-covering uneven | corrugated formation process especially when performing the (3) post-cover uneven | corrugated formation process mentioned later.

(1) Concavity and convexity formation process (pre-coating unevenness formation process)
In the concavo-convex forming step, the surface roughness Ra on the mold design surface 2 by shot peening is 0.05 μm or more and 0.50 μm or less (more preferably 0.05 μm or more and 0.30 μm or less. More preferably, the unevenness is formed to be 0.10 μm or more and 0.25 μm or less. This unevenness is uneven from one direction like a lathe surface, but the effect is not obtained when there is no unevenness from the other direction. Therefore, irregularities are formed so that a predetermined surface roughness Ra can be obtained from any direction. For that purpose, shot peening may be performed by projecting the medium at a projection speed (speed immediately before hitting the surface) of 100 m / sec or less, or a metal medium having a diameter of 100 μm or less is projected (projected). It may be performed by projecting at an initial pressure of 0.1 MPa to 0.6 MPa and a projection distance of 100 mm to 300 mm.

  When the unevenness forming step corresponds to the pre-coating unevenness forming step (when performing the post-coating unevenness forming step described later), the surface roughness Ra is 0.05 μm or more and 0.50 μm or less in the post-coating unevenness forming step. Therefore, the surface roughness Ra when performing the pre-coating irregularity forming step is not particularly limited, but is preferably 0.05 μm or more and 0.50 μm or less. Therefore, shot peening is preferably performed by projecting a metal medium at a projection speed of 100 m / sec. Alternatively, a metal medium having a diameter of 100 μm or less has a projection pressure of 0.1 MPa to 0.6 MPa and a projection distance of 100 mm. It is preferable to carry out by projecting at 300 mm or less.

In any of the above cases, the reason why the projection speed is set to 100 m / second or less is to optimize the surface roughness Ra without excessively roughening and to prevent the galling from becoming worse. Incidentally, even if the condition where the projection speed exceeds 100 m / sec can contribute to the improvement of fatigue strength, the surface roughness Ra becomes excessively rough.
Moreover, before performing shot peening, the mold design surface 2 may be previously nitrided with a hardened layer depth of 200 μm or less. The reason is to cure the mold surface and improve the adhesion of the coating.

(2) Film Forming Process In the next film forming process, a group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta), group 6A (Cr, Mo, W) Carbide, nitride or carbonitride containing one or more metals, 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo) , W) A single-layer or multi-layer hard coating 3 made of one or more kinds selected from the group consisting of nitrides containing one or more kinds of metals and one or two kinds of Si and Al is formed. Since the hard coating 3 is formed on the mold design surface 2 on which irregularities have already been formed by shot peening, the irregular shape of the mold design surface 2 is reflected as the surface shape of the hard coating 3. Accordingly, the hard coating 3 has a surface roughness Ra of 0.05 μm or more and 0.50 μm or less (more preferably 0.05 μm or more and 0.30 μm or less, and even more preferably 0.10 μm or more and 0.25 μm or less). . Alternatively, the hard coating 3 has a surface roughness Ra of 0.05 μm or more and 0.50 μm or less by shot peening in the post-coating irregularity forming step when performing the post-coating irregularity forming step described later. (More preferably, 0.05 μm or more and 0.30 μm or less, and still more preferably 0.10 μm or more and 0.25 μm or less).
Further, the surface roughness Ra of the hard coating 3 is desirably such that the difference is within 50% when measured in any two directions.
The hard coating 3 having the above configuration is hard to be worn because the convex portion is hard and the surface roughness Ra is predetermined. Further, since the unevenness has a predetermined surface roughness Ra, the holding power of the lubricant is good. Therefore, wear and peeling of the hard coating can be prevented, and the unevenness formed on the hard coating can maintain the holding force of the lubricant for a long period of time. Thus, if the hard coating 3 is hard to be worn and the retaining force of the lubricant can be maintained, the friction is reduced, the peeling of the hard coating 3 is prevented, and the molded product forged by the cold forging die 1 ( High seizure steel) is prevented from being seized and galling is suppressed.

  The PVD method performed to form the hard coating 3 may be any of vacuum deposition, ion plating, and sputter deposition, but ion plating is particularly preferable. In the ion plating method, the evaporated metal is ionized, and this metal ion is accelerated by an electric field in a reactive gas atmosphere to adhere to the surface of the processed product (mold design surface 2). As a method of making it, either a method using cathode arc discharge or a holocathode method may be used. The ion plating is preferable because it can be processed at a lower temperature than the CVD method, so that softening due to the heat effect of the cold forging die 1 can be prevented and distortion due to re-quenching can be reduced. Alternatively, resistance heating vapor deposition, electron beam vapor deposition, or molecular beam epitaxy may be used.

When the hard coating 3 is formed by the ion plating method, the electric field voltage for accelerating the ionized metal is preferably 10 to 500V. Moreover, hydrocarbon gas, such as methane, and nitrogen are used as reactive gas, and what is necessary is just to select the pressure from 0.1-10Pa.
At this time, it is preferable that the hard coating 3 is formed so as to have a film thickness of 1 μm or more and 20 μm or less as a whole regardless of a single layer multilayer. In the case of multiple layers, the PVD method may be repeated by changing the type in order from the lower layer side to the upper layer side.

  Prior to the formation of the hard coating 3, the mold design surface 2 may be irradiated with ions. In this case, metal ions such as 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal or Ar ions are used. Sometimes the field voltage for accelerating ions is preferably 500-2000V.

The cold forging die 1 obtained by performing the steps (1) and (2) may be further subjected to the following (3) post-coating irregularity forming step.
(3) Post-coating irregularity forming step In the following post-coating irregularity forming step, the surface roughness Ra of the hard coating 3 is measured from any direction by shot peening even if it is 0.05 μm or more and 0.50 μm or less (more preferably, The unevenness is formed so as to be 0.05 μm or more and 0.30 μm or less, and more preferably 0.10 μm or more and 0.25 μm or less. This unevenness is uneven from one direction like a lathe surface, but the effect is not obtained when there is no unevenness from the other direction. Therefore, irregularities are formed so that a predetermined surface roughness Ra can be obtained from any direction. Therefore, shot peening may be performed by projecting a ceramic or glass medium at a projection speed of 100 m / sec. Alternatively, a medium having a diameter of 100 μm or less made of ceramic or glass may be projected to a pressure of 0.1 MPa or more. The projection may be performed at a projection distance of 6 MPa or less and a projection distance of 100 mm or more and 300 mm or less. Here, the reason why the medium made of ceramic or glass is used instead of the metal medium is that the hard film 3 is hard but brittle, so that the hard film 3 may be broken in the metal medium. . Further, the reason why the medium is projected at a projection speed of 100 m / sec or less is for the same reason as described above.

In the post-coating irregularity forming step, the reason for performing shot peening is that fine irregularities (surface roughness Ra is 0.05 μm or more and 0.50 μm or less, more preferably 0.05 μm or more and 0.30 μm or less, More preferably, it promotes the formation of 0.10 μm or more and 0.25 μm or less) and improves the adhesion of the hard coating 3 by imparting compressive residual stress to the mold design surface 2 and the surface of the hard coating 3, Further, this is to improve the die life of the cold forging die 1.
There are also the following reasons. When ion plating is performed in the film forming process, hemispherical droplets adhere to the surface of the hard film 3 while remaining in a liquid state without evaporating. Since this droplet does not act as an oil reservoir, in order to eliminate this, shot peening is preferably performed after the hard coating 3 is formed.

(Function)
According to the cold forging mold manufacturing method described above, the surface roughness Ra is measured on the mold design surface 2 by shot peening so that the surface roughness Ra is 0.05 μm or more and 0.50 μm or less regardless of the direction. Is formed, and the hard coating 3 is formed thereon by PVD. Accordingly, the uneven shape of the mold design surface 2 is reflected as the surface shape of the hard coating 3, and the surface roughness Ra of the hard coating 3 is 0.05 μm or more and 0.50 μm or less. The cold forging die 1 manufactured in this way is hard to wear because the convex portion formed on the hard coating 3 is hard and has a predetermined surface roughness Ra. Moreover, since the unevenness | corrugation formed in the hard film 3 is the predetermined surface roughness Ra, the retention strength of a lubricant is favorable. Therefore, the holding force of the lubricant is maintained over a long period of time due to the unevenness formed by the hard coating 3.
Thus, when the hard coating 3 is hard to wear and the retention of the lubricant can be maintained, the hard coating 3 is prevented from being peeled off, and the molded product (high-tensile steel plate) forged by the cold forging die 1 is prevented. Micro seizure is prevented and galling is suppressed.
By these synergistic effects, the cold forging die 1 is prevented from being worn, the die life is extended, and the quality of the molded product can be improved.

  If shot peening is further applied to the cold forging die 1 on which the hard coating 3 is formed, the formation of irregularities such that the surface roughness Ra of the hard coating 3 is 0.05 μm or more and 0.50 μm or less is further promoted. In addition to improving adhesion by applying compressive residual stress, droplets are removed. As a result, the cold forging die 1 is further prevented from being worn or peeled off by the hard coating 3, and the seizure of the molded product (high-tensile steel plate) forged by the cold forging die 1 is prevented. The galling is suppressed. By these synergistic effects, the cold forging die 1 is prevented from being worn, the die life is extended, and the quality of the molded product can be improved.

Examples of the present invention and comparative examples will be described below.
(Production of punch and die)
About Examples 1-18 and Comparative Examples 1-5, what processed JIS SKD11 tempered by 59HRC into the punch and die | dye shown in FIG. 2 was prepared.
In addition, on the base surface (portion indicated by the broken line in FIG. 2) of the dies of Examples 1, 4, 6, 9 to 11, 13, 16, and 17 and Comparative Examples 2 to 4, the thickness of the entire hardened layer is set. A 0.05 mm plasma nitriding treatment was performed.

  Next, the media were projected by shot peening on the surfaces of the dies of Examples 1 to 18 and Comparative Examples 2 to 5 (parts indicated by broken lines in FIG. 2) to give minute irregularities. At this time, shot peening was performed at a projection speed of 100 m / sec using Examples 1 to 18 and Comparative Examples 3 to 5 made of steel and having a particle diameter of 100 μm or less. At this time, the projection pressure was 0.1 MPa to 0.6 MPa, and the projection distance was 100 mm to 300 mm. Comparative Example 2 was performed using a medium made of steel and having a particle size of 500 μm at a projection speed of 150 m / sec. At this time, the projection pressure was 0.1 MPa to 0.6 MPa, and the projection distance was 100 mm to 300 mm.

  Next, a hard film was coated on the surfaces of the dies of Examples 1 to 18 and Comparative Examples 1 and 2 (parts indicated by broken lines in FIG. 2) by an ion plating method. At this time, the electric field voltage for carrying out the argon ion bonboard was 500 to 1000 V, the electric field voltage for carrying out the coating was 50 to 300 V, and the pressure of the reactive gas was 1 to 10 Pa. The specific conditions of each example and each comparative example were selected from these according to the type of film shown in Table 1. In the case of multiple layers (Examples 13 to 15), the repeated ion plating method was performed. In the multilayer coatings of Examples 13 to 15, the left side coating in the same table was coated first, and the right side coating was coated later. That is, taking Example 13 as an example, TiN was coated first, and then CrN was coated.

  Next, the surfaces of the dies of Examples 4, 5, 7, 8, 11, 14, 15, 17 and Comparative Examples 2 to 5 (portions indicated by broken lines in FIG. 2) are again applied to the surface by shot peening. Minute irregularities were given. At this time, about each Example and Comparative Examples 3-5, shot peening was performed at the projection speed of 100 m / sec using the medium made from a ceramic or glass and a particle size of 100 micrometers or less. At this time, the projection pressure was 0.1 MPa to 0.6 MPa, and the projection distance was 100 mm to 300 mm. Comparative Example 2 was performed at a projection speed of 150 m / sec using a medium made of glass and having a particle size of 500 μm. At this time, the projection pressure was 0.1 MPa to 0.6 MPa, and the projection distance was 100 mm to 300 mm.

The punch and die of Examples 1-18 and Comparative Examples 1-5 were obtained by the above procedure. The reason why the surface treatment is applied only to the broken line portion in FIG. 2 is that micro-seizure is prevented in other portions and no galling occurs.
And about Examples 1-18 and Comparative Examples 1-5, the film thickness (micrometer) and surface roughness Ra (micrometer) of the surface (part shown with the broken line of FIG. 2) of the die | dye shown in the figure were measured. . The surface roughness Ra is the result of measurement from any two orthogonal directions. The results are summarized in Table 1.

(Hat bending test)
About Examples 1-18 and Comparative Examples 1-5, the hat bending test was done on condition of the following using the punch and die | dye shown in FIG. The hat bending test was repeated while replacing the workpiece every time until galling occurred in the following high-tensile steel plate used as the workpiece.
<Hat bending test conditions>
(1) Stroke 50mm
(2) Workpiece 980 MPa class high strength steel plate, 1.5 mm thickness, no surface treatment (3) Lubricant Antirust oil applied with brush (4) Cold forging die (punch and die) material SKD11
Table 1 also shows the number of workpieces until galling occurs.
FIG. 3 is a graph showing the results of the hat bending test shown in Table 1. The graph of FIG. 3 shows the number of workpieces until galling occurs in relation to the surface roughness Ra.

(Evaluation)
First, according to the comparison between Comparative Examples 1 to 3 and Comparative Examples 4 and 5, when a hard film is formed as in Comparative Examples 1 to 3, the simple nitriding of Comparative Example 4 regardless of the surface roughness Ra. It was found that the number of workpieces until the occurrence of galling significantly increased as compared with the case of only the above and the case of the comparative example 5 with a simple residual compressive stress. Therefore, it was found that the formation of a hard coating is effective in suppressing galling. Further, comparing the comparative examples 4 and 5, the number of processing until the occurrence of galling was significantly increased in the case where the base nitriding was performed, compared to the case where the base nitriding was not performed. I found it effective.

In Examples 1 to 18, the number of processed parts until the occurrence of galling significantly increased compared to Comparative Examples 1 to 3.
First, the reason why Comparative Example 1 had a smaller number of processing until the occurrence of galling was that Comparative Example 1 did not perform either a pre-coating shot or a post-coating shot, and therefore surface roughness Ra compared to Examples 1-18. It can be said that is too fine. In other words, the reason is that in Comparative Example 1, the surface roughness Ra is too fine, so that the holding power of the lubricant is low, or the lubricant is repelled and the hard coating is worn or peeled off. It can be said that the high-strength steel plate) was slightly seized with the die, and galling was likely to occur.

  Next, the reason why the number of processing until the occurrence of galling was small despite the fact that Comparative Example 2 performed both the pre-coating shot and the post-coating shot was that the surface roughness Ra was compared to Examples 1-18. It can be said that is too rough. In other words, the reason is that in Comparative Example 2, since the surface roughness Ra was too rough, the wear of the convex and concave portions was promoted, peeling occurred, and the workpiece (high-tensile steel plate) was slightly seized with the die. It can be said that it became easy to cause galling. Further, the reason for such a result is considered to be that the surface roughness Ra is increased because the projection speed of Comparative Example 2 is set to 150 m / sec.

  Next, Comparative Example 3 performs both pre-coating shots and post-coating shots, and the surface roughness Ra is not significantly different from those of Examples 1 to 18, but the number of processing until galling occurs is small. This is because the surface roughness Ra was different between the X direction and the Y direction (there was roughness anisotropy). In other words, the reason is that in Comparative Example 3, since the surface roughness Ra has roughness anisotropy, the lubricant flows in a certain direction, and as a result, the holding force of the lubricant is weakened. It can be said that wear and peeling of the hard coating occurred, and the high-tensile steel plate caused minute seizure with the die, and galling was likely to occur.

  On the other hand, in Examples 1 to 18, the hard film forms irregularities, the convex portions are hard, and irregularities with a predetermined surface roughness Ra (0.05 μm or more and 0.50 μm or less) are formed. It can be said that since the oil reservoir of the lubricant is formed in the concave portion, the friction is reduced and the hard coating is hardly worn or peeled off. In Examples 1 to 18, since the unevenness was measured within at least a predetermined surface roughness Ra (0.05 μm or more and 0.50 μm or less) when measured from at least two directions, the holding power of the lubricant was good. It can be said that there was. Therefore, Examples 1-18 can suppress wear and exfoliation of a hard film, and maintain the retention of a lubricant rather than comparative examples 1-5 by a synergistic effect of a hard film and surface roughness Ra (unevenness). As a result, it can be said that the work (high-strength steel plate) is prevented from causing micro-seizure with the die, thereby suppressing the occurrence of galling.

  Further, according to the graph of FIG. 3, similarly to the results shown in Table 1, it was confirmed that Examples 1 and 16 were significantly more processed than Comparative Example 2 until galling occurred. Further, when Examples 1 and 18 are compared with each other, it is likely that the shots after coating tend to have a larger number of processing until galling occurs as a whole than those without shots after coating. all right. From the graph of FIG. 3, the surface roughness Ra of the hard coating is preferably 0.05 μm or more and 0.50 μm or less, more preferably 0.05 μm or more and 0.30 μm or less, and even more preferably 0.10 μm or more and 0.25 μm or less. I understood it.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

  The cold forging die and its manufacturing method according to the present invention can improve die life by suppressing die wear and improve the quality of molded products. Industrial use value is extremely high for manufacturers who manufacture products.

It is a figure which shows the cross section of the surface part of the metal mold | die 1 for cold forging. It is a figure which shows the shape of the punch and die used for the hat bending test. It is a graph which shows the result of a hat bending test, and is the graph which showed the number of processing until a galling generate | occur | produces in a workpiece | work in relation with surface roughness Ra.

Explanation of symbols

1 Cold forging die 2 Mold design surface 3 Hard coating 4 Mold surface

Claims (7)

Carbide, nitride, or carbonitriding containing one or more of Group 4A (Ti, Zr, Hf), Group 5A (V, Nb, Ta), Group 6A (Cr, Mo, W) metals on the mold design surface And one or more of 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal and one or two kinds of Si and Al A single-layer or multi-layer coating composed of one or more selected from the group consisting of nitrides containing,
The cold forging die according to claim 1, wherein the coating has a surface roughness Ra of 0.05 μm or more and 0.50 μm or less even when measured from any direction.   The cold forging die according to claim 1, wherein the coating has a thickness of 1 μm to 20 μm.   3. The cold forging die according to claim 1, wherein the die design surface is nitrided with a hardened layer depth of 200 μm or less. 4.   The cold forging die according to any one of claims 1 to 3, wherein the coating is formed after irregularities are formed on the die design surface by shot peening.   5. The cold forging die according to claim 4, wherein the medium at the time of shot peening is projected at a projection speed of 100 m / sec or less. An irregularity forming step of forming irregularities so that the surface roughness Ra is measured from any direction on the mold design surface by shot peening so as to be 0.05 μm or more and 0.50 μm or less,
After performing the unevenness forming step, a kind of 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal on the mold design surface by PVD method Or a carbide, nitride or carbonitride containing two or more, and a group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta), group 6A (Cr, Mo, W) metal or A film forming step of forming a single-layer or multi-layer film composed of one kind or two or more kinds selected from the group consisting of nitrides containing two or more kinds and one or two kinds of Si and Al. A method for manufacturing a cold forging die. Pre-coating irregularity forming process for forming irregularities on the mold design surface by shot peening,
After performing the pre-coating irregularity forming step, the PVD method is used to form a 4A group (Ti, Zr, Hf), 5A group (V, Nb, Ta), 6A group (Cr, Mo, W) metal on the mold design surface. Of carbides, nitrides or carbonitrides containing one or more of the above, and group 4A (Ti, Zr, Hf), group 5A (V, Nb, Ta), group 6A (Cr, Mo, W) metals A film forming step of forming a single-layer or multi-layer film composed of one kind or two or more kinds selected from the group consisting of nitrides containing one or two kinds and one or two kinds of Si and Al; and
A post-coating concavo-convex forming step of forming concavo-convex so that the surface roughness Ra is measured to be 0.05 μm or more and 0.50 μm or less on the coating by shot peening after performing the coating forming step; A method for producing a cold forging die, comprising:

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