JP2006016672A - Discharge surface treatment method and die subjected to surface treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a discharge surface treatment technique to a component and a die having high thermal conductivity of Cu, Cu alloys or the like, and to improve their durability. <P>SOLUTION: Pulselike discharge is generated between an electrode of a powder compact obtained by compacting metal powder, or the powder of a metallic compound, or the powder of ceramics, or a powder compact obtained by subjecting the above powder compact to heating treatment, and a metal having a thermal conductivity of ≥120 W/mK, and, by energy owing to the discharge, a film composed of the electrode material or a reacted substance from the electrode material by the discharge energy is formed on the surface of the metal having a thermal conductivity of ≥120 W/mK. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a powder molded body obtained by molding a metal powder, a metal compound powder, or a ceramic powder, or a powder molded body obtained by heat-treating the powder molded body as an electrode in a working fluid or in the air. The discharge surface treatment relates to a discharge surface treatment in which a pulsed discharge is generated between the electrodes and an energy is generated to form a film made of an electrode material or a material obtained by reacting the electrode material with the discharge energy.

Conventionally, steel has been used as a casting mold material. However, when conventional hard steel is used as a mold, the thermal conductivity of the mold is as low as about 40 W / mK, so the cooling performance of the casting is inferior. There was a problem of low productivity.
In addition, due to the low thermal conductivity, if the mold requires a long time for preheating, the temperature gradient inside the mold is large, and the plastic strain accumulates due to repeated tensile and compressive stress on the mold surface. This causes problems such as cracks.

  In order to solve this problem, a method of applying a copper alloy having high thermal conductivity to the mold has been studied. However, since the Cu alloy is inferior in strength to steel, the generation of cracks due to the thermal fatigue could not be suppressed. .

Therefore, in order to improve the durability of the mold, a method of applying a cermet film, which is a composite of ceramics and metal, to a portion where damage is likely to occur has been studied and disclosed in Japanese Patent No. 3150291.
However, in the method disclosed in Japanese Patent No. 3150291, the adhesion between the coating film and the mold is poor, so that the coating film peels off and is insufficient to suppress damage.

On the other hand, in order to suppress peeling, a conventional surface treatment method for forming a cermet film on the surface of Cu or Cu alloy is disclosed in JP-A-2002-361394.
According to this, a copper alloy having a thermal conductivity of 120 W / mK or more and a hardness of 180 HV or more, a Ni-based alloy formed by discharge coating as an intermediate layer, and Co, Cu formed by discharge coating thereon. , A technique for forming a cermet layer containing at least one selected from Cr and Ni is disclosed.
A part of the inner surface of a mold made of copper alloy, and the surface of a scalp gate having an opening slightly smaller than the injection port provided to remove the surface oxide film and the inner surface of the injection port. Alternatively, when applied to the entire surface, the durability of the mold can be improved.

Japanese Patent No. 3150291 JP 2002-361394 A

The discharge coating method (electro-spark deposition) disclosed in Japanese Patent Application Laid-Open No. 2002-361394 uses a metal or cermet rod as an electrode, and the electrode uses the energy of discharge generated between the workpiece and the electrode. Is a processing method of melting and depositing on a workpiece.
Because a part of a metal rod having a diameter of 0.1 mm to several mm is melted by a single discharge, the droplet transferred to the workpiece is also 0.1 mm to several mm in diameter, and the droplet volume is large. The film formed by the accumulation of droplets becomes thick.
The use of Cu or Cu alloys for workpieces (parts and molds) often requires high thermal conductivity, and the thermal conductivity decreases when another metal or cermet coating becomes thick. In addition, the strength against thermal fatigue is also reduced, which may impair the desired performance.
In addition, in order to increase the accuracy of the coating formed by electric discharge as a mold, it is necessary to make the coating thin by post-processing such as polishing, and the work efficiency of mold manufacturing is poor.

Furthermore, when a cermet layer containing Co, Cu, Cr or the like is deposited on the melted region formed on the surface of the workpiece, the coating itself becomes diffusion bonding.
The adhesion strength between the coating and the workpiece in this diffusion bonding is higher than that of plating or thermal spraying. However, when a cermet film is formed on Cu or Cu alloy having high thermal conductivity, a cermet layer can be formed directly on the surface of the workpiece due to the thermal diffusion of the workpiece and the compatibility of the cermet and Cu. However, a metal layer such as Ni or Co having a thermal conductivity of about 1/3 of that of Cu is required as an intermediate layer.
Therefore, a separate process step for forming the intermediate layer is required, and the film formation cannot be easily performed.

  The present invention has been made in order to solve the above-mentioned problems, and establishes a discharge surface treatment technique for parts and molds having high thermal conductivity such as Cu and Cu alloy, and improves their durability. For the purpose.

  The discharge surface treatment method according to the present invention includes a metal powder, a metal compound powder, a powder molded body obtained by molding a ceramic powder, or an electrode of a powder molded body obtained by heat-treating the powder molded body, and a thermal conductivity. A film formed of a material in which a pulsed discharge is generated between a metal of 120 W / mK or more and the electrode material or the electrode material reacts with the discharge energy on the metal surface having a thermal conductivity of 120 W / mK or more by energy generated by the discharge. Is formed.

In the discharge surface treatment in which a fine powder is supplied from an electrode and a film is formed by flowing a current value of several tens of A in a few μs, a molten region can be formed on the surface of the workpiece, so that the thermal conductivity is 120 W / mK. A coating film having a thickness of several μm to several tens of μm sufficiently adhered to the coating film can be formed on the surface of the above material, and the surface hardness can be improved while maintaining the property of high thermal conductivity of the workpiece.
In addition, when the coating is formed on the inner surface of the filling port by the discharge surface treatment, the film thickness is very thin, so that the thermal conductivity of 120 W / mK of the mold is hardly reduced, and the productivity of casting is not reduced. The life of the mold can be extended.
It should be noted that post-treatment such as polishing after the discharge surface treatment is not necessary for mold manufacture.

Embodiment 1 FIG.
The principle of forming a cermet film made of WC and Co on the Cu—Cr—Zr alloy in this embodiment by using discharge surface treatment will be described with reference to FIG.
Here, the Cu—Cr—Zr alloy as a base material has a thermal conductivity of 311 W / mK consisting of Cr: 0.2 wt%, Zr: 0.1 wt%, Zn: 0.2 wt%, and the remaining Cu. This alloy is mainly used as a material for molds and printed circuit boards.
The surface treatment electrode for forming a cermet film composed of WC and Co is composed of WC powder having an average particle diameter of about 0.75 μm and Co powder having an average particle diameter of about 1.4 μm, WC: 75 wt%, Co: It is a green compact electrode having conductivity produced by mixing at a weight ratio of 25% by weight, compression molding with a press pressure of about 70 MPa, and then holding it in a vacuum furnace at 740 ° C. for about 2 hours.
In addition to compression molding, the electrode may be molded by slurry, MIM (Metal Injection Molding), thermal spraying, or a method in which nanopowder is entrained in a jet stream.

As shown in FIG. 1, a Cu—Cr—Zr alloy, which is a workpiece, is used as an anode, and a servo is performed on a main shaft so that a green compact electrode (cathode) made of WC and Co does not contact in a machining fluid (oil). It installs in the taken state, and discharge is generated by applying a predetermined voltage to both.
When a discharge occurs after the voltage is applied, a part of the electrode is melted and vaporized by the heat of the discharge, and the powder of the electrode is released by the blast and electrostatic force generated by the discharge, and melted and deposited on the workpiece.

As specific processing conditions, the above-mentioned electrode formed in a rectangular parallelepiped shape of 60 × 16 × 5 (mm) is used, the processing surface is 16 × 5, the current value is 11 A, and the discharge pulse time is 8 μs. It processed for 5 minutes on the Cu-Cr-Zr alloy whose heat conductivity is 120 W / mK or more.
A state after treatment (film surface) is shown in FIG.
The upper part of the workpiece surface is a cermet film made of WC and Co.
Moreover, a film cross-sectional photograph is shown in FIG.
The thickness of the film formed under the above processing conditions is about 15 μm, and does not impair the high thermal conductivity of the Cu—Cr—Zr alloy that is the workpiece.
Note that the film thickness by the discharge surface treatment described in this embodiment can be controlled by changing the processing time.
Moreover, when the Vickers hardness of the film was measured, it was about 1500 HV.
Since the Vickers hardness of the base material Cu—Cr—Zr alloy was about 300 HV, it can be seen that a cermet film made of WC and Co was formed on the surface.
Further, when the surface of the coating was polished with No. 1000 paper and the surface hardness was measured, the coating hardness was almost reduced at about 1450 HV.
This indicates that the film could not be peeled even with paper because of the high adhesion strength of the film.

When the surface roughness of the coating film was measured, the arithmetic average roughness Ra = 4.49, the maximum height Ry = 28.5, and the ten-point average roughness RzDIN = 25.12.
Although the processing conditions in the present embodiment have been described with the above-described current value 11A, discharge time 8 μs, and processing time 5 minutes, a film can be formed even if the current value is 11 A or more.
However, in that case, since the surface roughness becomes large, it is better to make the current value as small as possible when the surface accuracy of a mold or the like is required.

The discharge time must be 8 μs or less.
The state of the film when the discharge time is changed is shown in FIG.
The coating when the discharge time is 4 μs is (a), and the coating when the discharge time is 16 μs is (b). Each right side is polished with paper.
As shown in the figure, the coating (a) with a discharge time of 4 μs hardly peeled off even when rubbed with paper, and the base material is hardly visible, but the coating (b) with a discharge of 16 μs shows a base material.
It is considered that this occurs because only WC having a high melting point is first precipitated before solidification of the Cu alloy in the cooling process, and Cu and WC cannot be combined because Cu and WC are not well-matched.
That is, when the discharge time is short, rapid heating and rapid cooling occur, and Cu and WC can be solidified almost simultaneously, so that a coating with high adhesion strength can be formed.

Since WC powder is a ceramic and requires a large amount of energy to melt, as a result of research by the authors, an average particle size of 0.75 μm is obtained under the conditions of a discharge current value of 8 A or less and a discharge time of 2 μs or less. It was found that the above WC powder could not be melted.
However, when a WC powder having an average particle size of 0.4 μm or less is used, a film can be formed even with a current value of 8 A or less and a discharge time of 2 μs.
That is, when using a green compact electrode mixed with WC powder having an average particle size of about 0.75 μm, a dense and high-hardness film can be formed by processing at a current value of 11 A and a pulse time of about 8 μs. When the diameter is as small as 0.4 μm or less, a film can be formed even with a current value of 8 A or less and a discharge time of 2 μs or less.

Next, FIG. 5 shows a schematic diagram of the dividing surface of the mold for producing an Fe alloy shaft.
Here, the mold material is a Cu—Cr—Zr alloy, and WC and Co are formed on the inner surface (shaded portion) of the mold cavity under the processing conditions of a current value of 11 A and a pulse time of 8 μs using the above electrodes. A cermet film consisting of was formed.
The shape of the hatched portion is a semi-cylindrical surface of 30 mm in width and R15. First, a 60 × 30 × 5 electrode is manufactured, and the electrode is used to face the hatched portion and the surface of the electrode 30 × 5. By processing under the condition of a discharge time of 2 μs, the electrode is broken into a shape following the shaded portion without processing the shaded portion and forming a film on the shaded portion.
Next, the electrode is moved in parallel with the processing portion at a speed of about 10 mm / min, and a cermet film made of WC and Co is formed on the entire shaded portion under the processing conditions of a current value of 11 A and a pulse time of 8 μs.
When a mold manufactured by attaching a cermet film made of WC and Co to a Cu-Cr-Zr alloy in this way is compared with a conventional mold made only of a Cu-Cr-Zr alloy, there is no film. In several tens to 100 shots, a large number of large cracks entered the flow path (shaded area) extending from the mold filling port, and the function as a mold was lost, but a film was formed. The mold did not crack even after 700 shots.
Further, even when a film was formed only on the end surface a of the inner surface (shaded portion) of the filling port that had a particularly large crack, about 300 shots could be used.
In other words, when a WC-Co coating is formed on a Cu alloy mold by discharge surface treatment, the life of the mold can be extended five to seven times, contributing to the cost reduction required for mold manufacture and reducing the manufacturing cost. it can.

In the present embodiment, the case where the workpiece is a Cu-Cr-Zr alloy has been described. However, the workpiece having a thermal conductivity of 120 W / mK or more, in which it was difficult to form a cermet film by a conventional method, Other cermet films can be formed according to this embodiment.
When a material having a thermal conductivity of 120 W / mK or more is used as a work piece, the conventional method cannot form a melting region sufficiently, so a cermet film with high adhesion strength cannot be formed, and a film is formed. Even if it was possible, the thickness was increased, and the property of high thermal conductivity inherent to the workpiece was lost. However, a fine powder was supplied from the electrode, and a current value of several tens A was applied for several μs. In the discharge surface treatment for forming a coating, since it is rapid heating and rapid cooling, a molten region in which WC and Cu are mixed can be formed on the surface of the workpiece, so that the thickness is several μm to several tens of μm sufficiently adhered to the coating. A film can be formed, and surface hardness can be improved while maintaining the property of high thermal conductivity of the workpiece.
In addition, when a film of 120 W / mK or more is used as a mold material and a coating is formed on the inner surface (shaded portion) of the filling port by the above discharge surface treatment, the film thickness is very thin. The lifetime of the mold can be extended without substantially reducing the thermal conductivity of mK and without reducing the productivity of casting.
In this embodiment, a WC-Co film is formed, but cermets such as WC-Ni, TiC-Ni, MoB ₂ -Ni, Cr ₃ C ₂ -Ni, TiC-Co are also Cu or A film can be formed on the Cu alloy. In the case of a mixed film of Ni and ceramics, since the familiarity of the Cu alloy of the base material and Ni is good, the adhesion between the film and the base material becomes higher.

Embodiment 2. FIG.
In the above-described embodiment, the case where the cermet film made of WC and Co is formed using the powder electrode of WC and Co powder has been described. In this embodiment, the WC powder powder compact not containing Co is used. The film formation by the electrode will be described.
The green compact electrode in this embodiment is manufactured by compressing and molding a WC powder having an average particle size of about 1 μm with a press pressure of about 70 MPa and then holding it in a vacuum furnace at 1100 ° C. for about 2 hours. It is a green compact electrode which has.
The shape of the electrode is a rectangular parallelepiped of 50 × 11 × 5 (mm).
As a method for forming the electrode, there is a method in which slurry, MIM, thermal spraying, nanopowder is entrained in a jet stream, and the like in addition to compression molding as described in the first embodiment.

Using the above electrode, the treated surface was 16 × 5, the current value was 15 A, the discharge pulse time was 8 μs, and the Cu—Cr—Zr alloy was treated for 5 minutes to form a coating.
When the Vickers hardness of the film after the treatment is measured, it shows about 2200 HV, which indicates that a WC film is formed.
This confirms that a WC film having a high Vickers hardness is formed on the surface because the Vickers hardness of the Cu—Cr—Zr alloy as the base material is about 300 HV.
The cermet film made of WC and Co in the first embodiment had a hardness of about 1500 HV.
In the present embodiment, since the coating does not contain Co, the hardness can be further increased as compared with the coating according to the first embodiment.

Next, as in the first embodiment, a WC film was formed on the inner surface (shaded portion) of the filling cavity of the mold cavity of the mold for producing an Fe alloy shaft made of a Cu—Cr—Zr alloy.
As described above, as described above, a film was formed using the above electrodes under the processing conditions of a current value of 11 A and a discharge time of 8 μs.
When comparing molds based on the presence or absence of a coating, if there is no coating, a large crack will enter the flow path (shaded area) extending from the filling port of the mold in several tens to 100 shots. However, the mold with the coating film formed no crack even after 700 shots.
Further, even when a film was formed only on the end surface a of the inner surface (shaded portion) of the filling port where particularly large cracks were present, about 500 shots could be used.
In other words, when a WC coating is formed on a Cu alloy mold by discharge surface treatment, the hardness of the mold surface can be increased, the life of the mold can be extended by 5 to 7 times, and the mold can be manufactured. This contributes to cost reduction and manufacturing costs can be reduced.

In the present embodiment, WC has been described as the material of the coating. However, if a ceramic such as TiC or Cr ₃ C ₂ or W or Mo having a Vickers hardness of 1000 HV or more can be formed, a hard coating can be formed similarly. Can extend the life of the mold.

Embodiment 3 FIG.
In the present embodiment, an Al alloy (Al5154) having a thermal conductivity of 127 W / mK and 120 W / mK or more is selected as a base material, and the electrode manufactured in the first embodiment described above is used, and WC- A cermet coating of Co is formed.
As processing conditions, the processing surface was 16 × 5, the current value was 11 A, the discharge pulse time was 8 μs, and the processing time was 5 minutes.
When the Vickers hardness of the film formed on the surface of the Al alloy by the processing of the present embodiment was measured, it was about 1500 HV.
Since the Vickers hardness of the Al alloy as the base material was about 80 HV, it can be seen that a WC-Co film was formed on the surface.
Further, when the surface of the coating was polished with No. 1000 paper and the surface hardness was measured, the coating hardness was almost reduced at about 1450 HV.
Since the adhesion strength of the film is large, it can be seen that the film could not be peeled even with paper.
That is, not only the Cu—Cr—Zr alloy shown in the embodiment but also an Al alloy can be formed with a high-hardness and dense cermet film made of WC and Co by the discharge surface treatment according to this embodiment. it can.

In this embodiment, the cermet made of WC and Co is described as the material of the coating, but ceramics such as WC, TiC, and Cr ₃ C ₂ , MoB ₂ —Ni, Cr ₃ C ₂ —Ni, TiC—Co, etc. If it is a cermet, a hard film can be formed similarly.

When a material having a thermal conductivity of 120 W / mK or less is processed under the above-described processing conditions, a heat spot is formed by the heat of discharge because the thermal conductivity is small, and the removal amount of the workpiece is larger than the supply amount from the electrode. And the workpiece may be removed as a result.
Further, even if a film is formed, the surface roughness becomes Ra = 5 or more, and post-treatment or the like is required.
That is, a dense and high-hardness film can be formed under the above conditions with an Al alloy, Cu alloy, or Ag alloy having a thermal conductivity of 120 W / mK or more.

According to this embodiment, a cermet film or a ceramic film having a thickness of several μm to several tens of μm can be formed on the surface of the Al alloy by the discharge surface treatment, and the heat conduction is hardly changed. The surface can be increased in hardness without reducing the rate.
The coating can suppress the hitting wear of the Al alloy component and improve the durability of the component.

It is a figure which shows the principle of the discharge surface treatment which concerns on this invention. It is the surface figure which formed the WC-Co film in the Cu-Cr-Zr alloy whose thermal conductivity is 120 W / mK or more. It is a film sectional view in which a WC-Co film is formed on a Cu-Cr-Zr alloy. It is a figure which shows the state of the film formed when changing discharge time. It is a schematic diagram of the division surface of the metal mold | die for Fe alloy shaft manufacture.

Claims (12)

Between a metal powder or a powder of a metal compound, or a powder molded body obtained by molding a ceramic powder, or an electrode of a powder molded body obtained by heat-treating the powder molded body, and a metal having a thermal conductivity of 120 W / mK or more A discharge surface characterized by generating a pulsed discharge and forming an electrode material or a film made of a material obtained by reacting the electrode material with discharge energy on a metal surface having a thermal conductivity of 120 W / mK or more by energy generated by the discharge. Processing method. The discharge surface treatment method according to claim 1, wherein the metal having a thermal conductivity of 120 W / mK is Cu, Cu alloy, Al, Al alloy, Ag, or Ag alloy. WC and Co powder mixture, WC and Ni powder mixture, TiC and Ni powder mixture, MoB ₂ and Ni powder mixture, Cr ₃ C ₂ and Ni powder mixture, TiC and Co powder mixture, electrode material _3. The discharge surface treatment method according to claim 1, wherein a cermet film such as WC—Co, MoB ₂ —Ni, Cr ₃ C ₂ —Ni, or TiC—Co is formed. _3. The discharge surface treatment method according to claim 1, wherein a ceramic film such as WC, Cr ₃ C ₂ , or TiC is formed using WC powder, Cr ₃ C ₂ powder, or TiC powder as an electrode material. 4. 3. The discharge surface treatment method according to claim 1, wherein a high-hardness metal film having a Vickers hardness of 1000 HV or more, such as W or Mo, is formed using W powder or Mo powder as an electrode material. The discharge surface treatment method according to claim 1, wherein a current value is 10 A or more and a discharge time is 8 μs or less as conditions for the discharge pulse. Between a metal powder or a powder of a metal compound, or a powder molded body obtained by molding a ceramic powder, or an electrode of a powder molded body obtained by heat-treating the powder molded body, and a metal having a thermal conductivity of 120 W / mK or more A gold characterized in that a pulsed discharge is generated, and an electrode material or a film made of a material obtained by reacting the electrode material with the discharge energy is formed on the metal surface having the thermal conductivity of 120 W / mK or more by the energy of the discharge. Type. The metal mold according to claim 7, wherein the metal having a thermal conductivity of 120 W / mK is Cu, Cu alloy, Al, Al alloy, Ag, or Ag alloy. A mixture of WC and Co, a mixture of MoB ₂ and Ni, a mixture of Cr ₃ C ₂ and Ni, and a mixture of TiC and Co are used as electrode materials, and WC-Co, WC-Ni, TiC-Ni, MoB ₂ -Ni , _Cr 3 _C 2 -Ni, die according to claim 7 or 8, characterized in that to form the cermet coating, such as TiC and -Co. 9. The mold according to claim 7, wherein a ceramic film such as WC, Cr ₃ C ₂ , or TiC is formed using WC powder, Cr ₃ C ₂ powder, or TiC powder as an electrode material. The metal mold according to claim 7 or 8, wherein W powder or Mo powder is used as an electrode material to form a high-hardness metal film having a Vickers hardness of 1000 HV or more, such as W or Mo. The mold according to any one of claims 7 to 11, wherein a coating film is formed in a flow path extending from a filling port in a mold for producing an Fe alloy shaft.

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