JP3548317B2 - Method for manufacturing porous mold - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a porous mold for performing a surface treatment on a sintered body having continuous pores.
[0002]
[Prior art]
In recent years, porous dies have been used as casting dies because of their advantages of excellent gas release and heat retention. When manufacturing a porous mold of this type, first, after forming a sintered body having continuous holes, the sintered body is subjected to cutting or grinding to provide a cavity surface forming portion of a predetermined shape. . Furthermore, in order to prevent the molten metal to be cast, for example, aluminum and the mold material from reacting in a metallurgical manner and causing baking or erosion or the like to reduce the durability of the mold, the cavity surface forming portion includes: A surface treatment such as a nitriding treatment such as a salt bath nitriding method, a gas nitriding method or a fluidized bed nitriding method, and a vapor deposition treatment such as PVD or CVD is performed.
[0003]
[Problems to be solved by the invention]
However, as described above, when grinding or cutting with a grindstone or the like is performed on the shape processing of the sintered body, burrs or the like are generated on the surface of the sintered body. For this reason, it has been pointed out that the pores on the surface side of the sintered body are closed and the air permeability is reduced.
[0004]
Further, when a salt bath nitriding method is used as a surface treatment of the porous mold, the treated salt penetrates into the inside of the sintered body through continuous pores in the sintered body, and is nitrided into the inside of the sintered body to form a porous body. The toughness of the whole quality mold is reduced. In addition, there is a problem that the operation of removing the treatment salt that has entered the inside of the sintered body becomes considerably complicated. In addition, when the gas nitriding method is used, the processing gas enters the inside of the sintered body, and the whole sintered body is nitrided, and the toughness of the entire porous mold may be reduced.
[0005]
Furthermore, when the fluidized-bed nitriding method is used, there is a problem in that sand and gravel of the heating medium enter pores on the surface of the sintered body, and a number of steps are required for the removal operation.
[0006]
On the other hand, when a deposition method such as PVD or CVD is used as the surface treatment, a high degree of vacuum (10 ⁻⁴ to 10 ⁻² torr) is required at the time of the treatment, so that it takes a considerably long time to wash and dry the sintered body. Resulting in. Unless the cutting fluid or grinding fluid that has entered the inside of the sintered body is reliably removed during the processing of the sintered body, the inside of the vapor deposition processing apparatus is contaminated and the desired degree of vacuum cannot be obtained. It is.
[0007]
The present invention solves this kind of problem, and provides a method for producing a porous metal capable of easily and efficiently performing a surface treatment while securing desired air permeability and toughness. Aim.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a method of forming a cavity surface of a sintered body having continuous pores by performing electrical discharge machining to form a predetermined shape. It is possible to prevent the holes provided on the surface of the cavity surface forming portion in the binding from being closed. Further, an ion nitriding treatment is applied to the cavity surface forming portion after the electric discharge machining. This ion nitriding treatment is performed, for example, by glow discharge, and nitriding is performed only on the surface of the cavity surface forming portion. Thereby, the toughness of the entire porous mold can be effectively maintained, and the surface treatment is quickly and easily performed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a vertical sectional view of a low-pressure casting mold 14 incorporating a lower mold 10 and an upper mold 12 which are porous molds manufactured by the manufacturing method according to the present embodiment. The lower die 10 is held by a lower die base 16, and a gate 20 communicates with a cavity surface 18 thereof. The upper mold 12 is supported by an upper mold base 22, and has a cavity surface 24 facing the cavity surface 18 of the lower mold 10.
[0010]
A cavity 26 is formed between the cavity surfaces 18 and 24, and an extrusion pin 28 slidably provided on the upper die base 22 can enter the cavity 26. The lower mold 10 and the upper mold 12 are each provided with a cooling path 30 at a desired position.
[0011]
FIG. 2 shows a schematic configuration diagram of the electric discharge machine 40. The electric discharge machining device 40 includes a tank body 46 in which an insulating electric discharge machining fluid 44 for immersing a sintered body 42 having conductivity is stored, and a discharge electrode 50 that is movable in a predetermined direction via an NC device 48. . The discharge electrode 50 and the sintered body 42 are connected to a pulse power source 52, and the NC device 48 is connected to an NC control unit 54.
[0012]
FIG. 3 shows that the ion-nitriding process is performed on the cavity surface forming portions 56a and 56b of the sintered bodies 42a and 42b after the electric discharge machining in correspondence with the cavity surfaces 18 and 24 of the lower mold 10 and the upper mold 12, respectively. An ion nitriding device 60 is shown.
[0013]
The ion nitriding apparatus 60 includes a vacuum vessel 64 in which a receiving table 62 for placing the sintered bodies 42a and 42b is arranged. A supply pipe 70 connected to a reaction gas flow control valve 68 communicates with a chamber 66 of the vacuum vessel 64, and an exhaust pipe 76 connected to a pressure control valve 72 and a vacuum exhaust device 74. A plasma power supply 78 is connected to the vacuum container 64.
[0014]
Next, the manufacturing method according to the present embodiment will be described below with reference to the flowchart shown in FIG.
[0015]
First, using a powder mainly composed of an iron-based material, the compact is formed by compaction press molding, and then sintered in a vacuum furnace to form a sintered body 42 having continuous pores (step S1). Next, proceeding to step S2, machining is performed on a necessary portion of the sintered body 42, for example, machining corresponding to the cooling path 30 is performed, and then electric discharge machining of the cavity portion is performed by the electric discharge machine 40 ( Step S3).
[0016]
In the electric discharge machining apparatus 40, as shown in FIG. 2, in a state where the sintered body 42 is immersed in the electric discharge machining fluid 44, a current is supplied from the pulse power source 52 to the discharge electrode 50 and the sintered body 42, The NC device 48 is moved in a predetermined direction via the control unit 54. As a result, the sintered body 42 is subjected to electric discharge machining on the side of the cavity and formed into a predetermined shape.
[0017]
As described above, since the electric discharge machining is performed on the cavity portion side of the sintered body 42 through the electric discharge machine 40, the holes provided on the surface of the sintered body 42 are not closed. . Therefore, unlike the conventional processing such as grinding and cutting, there is no problem that burrs and the like are generated on the surface of the sintered body 42 and pores on this surface side are closed, thereby reducing air permeability. Opening processes such as electrolytic polishing and etching are not required.
[0018]
Thereby, an effect is obtained that the sintered body 42 can be efficiently processed while maintaining desired air permeability. Moreover, a deteriorated layer due to electric discharge machining is present on the surface of the sintered body 42, and the deteriorated layer has a function of substantially increasing hardness and improving wear resistance.
[0019]
After cleaning and drying are performed on the sintered bodies 42a and 42b after the electric discharge machining (step S4), an ion nitriding process is performed by the ion nitriding device 60 (step S5).
[0020]
In the ion nitriding apparatus 60, as shown in FIG. 3, after the sintered bodies 42 a and 42 b are arranged on the receiving table 62, the inside of the chamber 66 of the vacuum vessel 64 is evacuated via the vacuum exhaust device 74 and the pressure adjusting valve 72. The pressure is reduced. On the other hand, the reaction gas is supplied into the chamber 66 from the supply pipe 70 via the reaction gas flow control valve 68, and the plasma power supply 78 is driven to perform glow discharge. Note that the ambient temperature is set in the range of 500 ° C to 600 ° C. As a result, the surface portions of the sintered bodies 42a and 42b on the receiving table 62 (cavity surface forming portions 56a and 56b) are subjected to ion nitriding.
[0021]
As described above, in the present embodiment, as the surface treatment of the sintered bodies 42a and 42b, the ion nitriding treatment using glow discharge is performed, so that only the surface portions of the sintered bodies 42a and 42b are nitrided. Therefore, the inside of the sintered bodies 42a and 42b is not nitrided.
[0022]
Therefore, unlike the conventional nitriding treatments such as the salt bath nitriding method and the gas nitriding method, the inside of the material to be treated is not nitrided and the toughness of the entire material to be treated is not reduced. Toughness can be effectively maintained. Further, unlike the salt bath nitriding method, the treatment salt is not impregnated inside the material to be treated, and post-treatment such as removal of the treatment salt after the nitriding treatment becomes unnecessary, so that the nitriding treatment operation is performed efficiently and easily. It has the effect of being performed. Further, the processing atmosphere is also a reduced pressure gas atmosphere, the cleanliness of the sintered bodies 42a and 42b is not required as much as the vapor deposition method such as CVD or PVD, and there is an advantage that the nitriding treatment is simplified.
[0023]
The lower mold 10 and the upper mold 12, which are the sintered bodies 42a and 42b in which the cavity surface forming portions 56a and 56b are ion-nitrided by the ion nitriding treatment, are assembled into the low-pressure casting mold 14 and adjusted as shown in FIG. Is performed (step S6). Next, for example, molten aluminum is poured into the cavity 26 from the gate 20, and an aluminum molded product is formed in the cavity 26.
[0024]
【Example】
Example 1
As a sample, a SUS430-based powder was formed by a compacting press and then sintered in a vacuum furnace to obtain a sintered body having continuous pores having a porosity of 25 vol%. Next, after the electric discharge machining was performed on the surface of the sintered body, an ion nitriding treatment was performed at 580 ° C. for 10 hours at a gas pressure of ₂ torr (N ₂ 50: H ₂ 50).
[0025]
The dimensions of the sample thus obtained were 50 mm × 50 mm × 10 mm, the thickness of the nitride layer was 60 μm, and the hardness was HmV1200. Then, the sample was immersed in a molten aluminum (AC2B) at 710 ° C. for 4 hours.
[0026]
As a comparative example, a sample molded and sintered under the same conditions as above was used, and the sample was immersed in molten aluminum without surface treatment, ie, without surface treatment. After the immersion, as shown in FIG. 5A, the sample without the mechanical processing and the surface treatment has a welded layer 94 with the aluminum alloy 92 as a product on the surface of the porous layer 90, and the porous layer 90 Melting had been induced.
[0027]
On the other hand, in the sample subjected to the electric discharge machining and the ion nitriding treatment, as shown in FIG. 5B, the ion nitride layer 102 is provided on the surface portion of the porous layer 100, and the surface of the ion nitride layer 102 and the aluminum There was a space SP between the product 104. That is, in Example 1, no erosion or welding occurred in the porous layer 100.
Example 2
As a sample, using a SUS434-based porous sintered body (Sintokogio Co. Poserakkusu 2PM35), after discharge machining the cavity section surface, 6 hours at 530 ° C., the gas pressure is 2torr _{(N 2} 50: _H 2 An ion nitriding treatment was performed under the condition of 50). This sample was inserted as a nest near the gate of the casting mold. As a comparative example, a sample was prepared by simply subjecting the surface of the above sintered body to electrical discharge machining, and similarly inserted as a nest near the gate of the casting mold. In this casting mold, an aluminum product was cast by pouring an AC2B material at 700 ° C.
[0028]
As a result, as shown in FIG. 6A, in the nest 110 in which only the surface was subjected to electric discharge machining, the erosion site 112 and welding occurred in 800 shots, but in the nest 120 in which the electric discharge machining surface was subjected to ion nitriding, No erosion or welding occurred after 5000 shot casting.
[0029]
【The invention's effect】
In the method for manufacturing a porous mold according to the present invention, since a cavity surface forming portion of a sintered body having continuous holes is subjected to electric discharge machining to be formed into a predetermined shape, generation of burrs and the like in grinding and cutting work is caused. In addition, the holes provided on the surface of the cavity surface forming portion of the sintered body are not closed. This prevents a decrease in air permeability and eliminates the need for a post-treatment such as a hole opening treatment.
[0030]
Further, since the ion nitriding treatment is performed on the cavity surface forming portion after the electric discharge machining, nitriding is performed only on the surface of the cavity surface forming portion, and the inside thereof can be prevented from being nitrided. Therefore, while maintaining the toughness of the entire porous mold effectively, the post-treatment after the nitriding treatment is not required, and the porous mold can be efficiently and accurately manufactured.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view illustrating a low-pressure casting mold incorporating a porous mold manufactured by a manufacturing method according to an embodiment of the present invention.
FIG. 2 is a schematic explanatory view of an electric discharge machine used in the manufacturing method.
FIG. 3 is a schematic explanatory view of an ion nitriding apparatus used in the manufacturing method.
FIG. 4 is a flowchart illustrating the manufacturing method.
FIG. 5A is an enlarged view showing a welded state after immersing a sample subjected to machining and not subjected to surface treatment in a molten aluminum,
FIG. 5B is an enlarged view after immersing the sample subjected to the electric discharge machining and the ion nitriding treatment in the molten aluminum.
FIG. 6A is a partially enlarged view of a nest subjected to only electric discharge machining after casting.
FIG. 6B is a partially enlarged view of a nest obtained by subjecting an electric discharge machining surface to an ion nitriding treatment after casting.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Lower mold 12 ... Upper mold 14 ... Low pressure casting metal mold 18, 24 ... Cavity surface 26 ... Cavity 40 ... Electric discharge machine 42, 42a, 42b ... Sintered body 44 ... Electric discharge machining liquid 50 ... Discharge electrode 60 ... Ion nitriding Apparatus 64: Vacuum container 68: Reaction gas flow control valve 78: Plasma power supply

Claims (3)

A step of forming a sintered body having continuous pores using a powder mainly composed of an iron-based material,
A step of subjecting the cavity surface molding portion of the sintered body to electrical discharge machining and molding it into a predetermined shape,
Performing an ion nitriding treatment on the cavity surface forming portion after the electric discharge machining,
A method for producing a porous mold, comprising: 2. The method according to claim 1, wherein the iron-based material is a ferrite-based material or a martensite-based material. 3. The method according to claim 1, wherein the ion nitriding is performed by glow discharge.

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