JP4842704B2 - Mold repair method - Google Patents

Description

  The present invention relates to a mold repair method for repairing various molds including a forging mold.

  In general, in a die such as a forging die, a pressing die, and a casting die, stress acts on a contact portion between the dies and a portion where molten metal hot water collides at high speed, and cracks, wear, etc. Arise.

  Damaged parts such as cracks and wear in the mold cause burrs and distortions in the product, increasing the deburring and shaping operations of the product in the subsequent process. Therefore, in order to prevent such product defects from occurring, repair is performed on the damaged mold.

  As such a repair method, it is conceived that a mold reinforcing method for building up a portion where the mold is easily damaged is applied. That is, overlaying is performed on the damaged part by electric discharge machining. In this build-up method, electrode materials such as metals, carbide ceramics, and cermets are deposited on the surface of the mold where damage is likely to occur using the high temperature associated with spark discharge, and surface treatment is performed to obtain hardness and corrosion resistance. In addition, a discharge coating process that improves durability and the like is performed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 1-210133

  However, if repair is performed by building up, the bonding strength between the building up part and the mold is fragile and its durability is limited. Therefore, it is necessary to perform repair frequently, resulting in a decrease in product productivity. There is a difficulty.

  In particular, forging dies have high stress during use, are subject to thermal fatigue, and the built-up portion is easy to peel off, making repair by building up difficult. Therefore, if the forging die is damaged, it is forced to be disposed of, which is uneconomical.

  The present invention has been made to solve the above-described problems, and makes it possible to restore the durability of the mold by a strong and reliable repair, and contribute to the improvement of product productivity and economy. It aims to provide a mold repair method that can be used.

In order to achieve the above object, a mold repair method according to the present invention includes a first element powder having a property of increasing the hardness of a mold made of an Fe-based alloy by being carbideized, and the first element powder. Coating a mixed powder having a second element powder having a low melting point on at least a region to be repaired of the mold; and
Heating at least a region to be repaired of the mold coated with the mixed powder to carbonize and diffuse the first element powder in the mixed powder into the mold;
A mold repair method is provided.

  That is, this repair method is carried out in order to recover the damaged portion after the damaged portion is generated in the mold. According to the repair method, the hardness and strength of the mold can be recovered, so that a highly durable mold that does not easily re-wear even when the forging process is repeatedly performed and hardly re-defects is obtained. be able to. Eventually, product productivity is improved again. Of course, the same applies to dies such as press dies and casting dies.

  Suitable examples of the Fe-based alloy include tool steel, high-speed tool steel, die steel, powder steel alloy steel, SCM, SNC, SNCM, SCr structural alloy steel, or carbon steel, low carbon steel structure. For example.

  In addition, it is preferable that the first element powder is at least one of a group of Fe, Ni, and Co. This is because the hardness of the mold made of the Fe-based alloy is improved satisfactorily by being carbideized.

  Further, as the second element powder, Al or an Al—Mn eutectic alloy is preferable. Al has a lower melting point than the first element powder, and the eutectic point of the Al—Mn eutectic alloy is lower than the melting point of Al. Such Al and Al-Mn eutectic alloys act as attractants for the first element powder.

  Furthermore, it is preferable to add a reducing agent for reducing the oxide film present on the surface of the Fe-based alloy to the mixed powder. In this case, since the oxide film is removed when the atoms of the first element powder diffuse, atomic diffusion occurs with low energy.

  In addition, when Al is used as the second element powder, the reducing agent captures oxygen to prevent oxidation of Al. Therefore, the characteristic deterioration of Al is prevented and the adhesion of the first element powder to the Fe-based alloy is improved.

  Preferable examples of the reducing agent include carbon powder, resin or Si.

  Moreover, it is more preferable to add W, Ti, V, Mo, or Nb to the mixed powder. This is because the strength of the mold is further improved in this case.

  According to the mold repair method according to the present invention, the hardness and strength of the mold can be reliably improved again, so that it is difficult to wear even if the forging process is repeated, and it is difficult to cause defects. A mold is obtained. Eventually, product productivity and economy can be improved again.

  Preferred embodiments of the mold repair method according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic overall perspective view of a forging die 10 in which the die repairing method according to the present embodiment is implemented. This forging die 10 is a die for forging a spider that constitutes a constant velocity joint for smoothly and uniformly transmitting the engine power of an automobile to a wheel. An Fe-based alloy, for example, tool steel, It consists of alloy steels such as high speed tool steel, die steel and powdered high speed steel.

  The forging die 10 includes a lower die 11 and an upper die 12 that can be displaced relative to the lower die 11. The lower die 11 and the upper die 12 are matched to the shape of a constant velocity joint. Then, cavities 11a and 12a into which materials (workpieces) such as heat-softened steel materials are press-fitted are formed.

  The forging die 10 is repaired when the forging process is repeatedly performed and a damaged portion such as a crack C as shown in FIG. 2 is generated. That is, first, a first element powder having a property of increasing the hardness by carbideizing a forging die 10 made of an alloy steel which is an Fe-based alloy, and a lower melting point than the first element powder, for example, a melting point of 600 ° C. A mixed powder with the second element powder at 750 ° C. is prepared.

  Preferable examples of the first element powder include at least one selected from the group consisting of Fe, Ni, and Co. In the subsequent step, if the metal species of the carbide to be diffused is Fe, a mixed powder containing Fe powder may be prepared. If the metal species to be diffused is Ni, a mixed powder containing Ni powder is prepared, and if it is Co, a mixed powder containing Co powder may be prepared. Of course, for example, when both Fe and Co are diffused, a mixed powder containing both Fe powder and Co powder may be prepared.

  On the other hand, a suitable example of the second element powder is Al or an Al—Mn eutectic alloy.

  Here, a spontaneously formed oxide film usually exists on the surface of the forging die 10 (alloy steel) to be repaired. In order to diffuse the metal atoms contained in the first element powder in this state, a large amount of heat energy must be supplied so that the metal atoms can pass through the oxide film. In order to avoid this, the mixed powder is preferably mixed with a reducing agent capable of reducing the oxide film, for example, carbon.

  Alternatively, a mixed powder of the first element powder and the second element powder is added to a solvent, and a substance that acts as a reducing agent on the oxide film and does not react with the alloy steel is dispersed or dissolved in the solvent. An agent may be prepared. Preferable examples of such a reducing agent include nitrocellulose, polyvinyl, acrylic, melamine, styrene, and epoxy resins, but are not particularly limited thereto. Note that the concentration of the reducing agent may be about 5%.

  Furthermore, you may make it add the substance which has the property to raise the intensity | strength after repair of the metal mold | die 10 for forging to mixed powder. As a suitable example of such a substance, at least one member of the group of W, Ti, V, Mo, and Nb can be mentioned.

  As shown in FIG. 3A, the mixed powder prepared in this way is applied to the area where the crack C is generated on the surface of the cavity 11a (12a) in the forging die 10, that is, the repair planned area, and the crack C is applied. Fill. Thereby, the mixed powder layer 14 is formed on the crack C.

  The mixed powder may be applied by applying a coating agent prepared by dispersing the mixed powder in a solvent as described above. As the solvent, it is preferable to select an organic solvent that easily evaporates, such as acetone or alcohol. When the coating agent is prepared, powders such as Ni and Co may be dispersed in a solvent, and powders such as C and Si as a reducing agent may be dispersed.

  Moreover, as a coating method, a brush coating method using the brush 13 may be employed. Of course, a known coating technique other than the brush coating method, for example, spray coating may be employed.

  Next, as shown in FIG. 3B, heat treatment is performed on the cavity 11 a (12 a) of the forging die 10. In this case, the heat treatment is performed by the burner flame 15.

  During the heat treatment, the mixed powder layer 14 is reflowed, and the inner surface of the cavity 11a (12a) of the forging die 10 is uniformly coated with the mixed powder. At this time, the second element powder having a melting point lower than that of the first element powder is first melted so that the second element powder is attracted to the first element powder, and further, W, Ti, V, Mo , At least one of the Nb groups is evenly coated.

  This phenomenon is more likely to occur as the melting point of the second element powder is lower. Therefore, as described above, among metals, it is preferable to use Al having a relatively low melting point or an Al—Mn eutectic alloy whose eutectic point is lower than the melting point of Al. Al moves to the surface layer while being replaced by the first element powder, and finally combines with oxygen such as a solvent to be sludged on the surface layer. For this reason, it is avoided that the forging die 10 is embrittled or broken due to the presence of Al inside.

  By this phenomenon, the first element powder uniformly enters the forging die 10 from the crack C so as to be attracted to the previously melted low melting point second element powder.

In addition, when reducing agents, such as carbon powder and resin, exist in mixed powder, this reducing agent captures O. For example, carbon powder or C generated by decomposition of resin combines with O to become CO and CO ₂ . For this reason, it can prevent that various metals including Al are oxidized.

  Furthermore, in the cavity 11a (12a) of the forging die 10, C, which is a constituent element of alloy steel, C generated by decomposition of the reducing agent, and the first element powder react to generate carbide. The When at least one member selected from the group consisting of W, Ti, V, Mo, and Nb is added, these also form carbides.

  The generated carbide diffuses deep inside the cavity 11a (12a) of the forging die 10 while repeating decomposition and generation. That is, the generated carbide is immediately decomposed and returned to the first element powder, and in this state, the carbide moves relatively to the surface layer side.

  In this way, carbide diffuses in the vicinity of the crack C in the cavity 11a (12a) of the forging die 10, and as a result, as shown in FIG. It will be recovered. The thickness of the diffusion layer, i.e., the diffusion distance of carbides, extends to a depth of about 15 mm from the surface.

  Note that the carbide concentration gradually decreases, and a clear interface does not occur between the carbide diffusion reaching end portion and the forging die 10. Accordingly, it is possible to avoid the occurrence of brittle fracture due to stress concentration at this portion, and thus the toughness of the cavity 11a (12a) of the forging die 10 in which the diffusion layer 17 is formed is ensured.

  In other words, in this case, it is possible to avoid an increase in brittleness due to the diffusion of the metal element. Therefore, even if the forging process is repeatedly performed, the forging die 10 is hardly damaged such as a crack. That is, the life of the forging die 10 can be extended.

  In addition, the hardness of the forging die 10 is improved in the region where carbide is present. As described above, according to the mold repair method according to the present embodiment, since carbides exist deep inside the forging mold 10, the hardness and strength of the forging mold 10 increase to the inside, As a result, the internal wear resistance is improved and deformation is difficult.

  Furthermore, when TiC, TiN, or the like is generated, the heat resistance of the metal is improved by a so-called carbide effect, and the strength of the metal is improved by a so-called carbide dispersion effect.

  In short, the hardness of the forging die 10 is improved again to the depth at which the carbides are diffused. In other words, the damaged portion of the forging die 10 is filled with the coating agent, and in the damaged portion, the presence of the diffusion layer 17 increases the hardness and strength to the inside again, improving the wear resistance, and deforming. It becomes difficult to do. As a result, the forging die 10 can be recovered to a state having characteristics that are desired when it is put to practical use.

  As mentioned above, although the metal mold repair method concerning this embodiment was explained in full detail, this invention is not specifically limited to this embodiment, The spirit of the invention described in the claim of this invention Various modifications can be made without departing from the scope.

  For example, the Fe-based alloy may be a structural alloy steel of SCM, SNC, SNCM, or SCr, or a structural steel of carbon steel or low carbon steel, in addition to the alloy steel.

  The die is not limited to the forging die 10 and may be a die provided for other than forging, such as a pressing die and a casting die.

It is a schematic perspective view of the metal mold | die for forging in which the metal mold | die repair method which concerns on this Embodiment is implemented. It is a principal part schematic longitudinal cross-sectional view which shows the state with which the coating agent was filled in the crack (damage part) of the forging metal mold | die shown in FIG. 3A to 3C are process explanatory views showing a repair process of the forging die shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Forging die 11 ... Lower die 11a, 12a ... Cavity 12 ... Upper die 13 ... Brush 14 ... Mixed powder layer 15 ... Burner flame 17 ... Diffusion layer C ... Crack

Claims (7)

At least repair of the mold with a mixed powder having a first element powder having the property of increasing the hardness of a mold made of an Fe-based alloy by being carbideized and a second element powder having a melting point lower than that of the first element powder. Covering the planned area;
Heating at least a repair planned region of the mold coated with the mixed powder to carbonize and diffuse the first element powder in the mixed powder into the mold;
A mold repairing method characterized by comprising:   2. The mold repair method according to claim 1, wherein the Fe-based alloy is tool steel, high-speed tool steel, die steel, powder steel alloy steel, SCM, SNC, SNCM, SCr structural alloy steel, or carbon steel. A mold repair method characterized by being structural steel of low carbon steel.   3. The mold repair method according to claim 1, wherein the first element powder is at least one of a group of Fe, Ni, and Co. 4.   4. The mold repair method according to claim 1, wherein the second element powder is Al or an Al—Mn eutectic alloy. 5.   5. The mold repair method according to claim 1, wherein a reducing agent for reducing an oxide film present on the surface of the Fe-based alloy is blended in the mixed powder. Mold repair method.   6. The mold repair method according to claim 5, wherein the reducing agent is carbon powder, resin, or Si.   The mold repair method according to any one of claims 1 to 6, wherein at least one member selected from the group consisting of W, Ti, V, Mo, and Nb is added to the mixed powder. Repair method.

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