JP2004001086A - Surface treatment method for metal mold by electronic beam irradiation and treated metal mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To finish a metal mold with low surface roughness in a short time by overcoming a fault in hand polishing the mold which is applied to electrical discharge machining. <P>SOLUTION: In a surface treatment method for a metal mold, a mold material made of carbon steel is smoothed, improved in corrosion resistance, polished, and improved in surface hardness by using a low energy pulse electronic beam apparatus capable of forming a large area without causing electronic beam scattering due to the existence of anode plasma. The electronic beam irradiation method is performed under a condition that energy density ≥1 J/cm<SP>2</SP>, the number of pulse irradiations ≥5 times, and a pulse width ≥1 μs. The metal mold is applied with surface treatment by the method. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mold member and a method of manufacturing the same, and particularly to a method of surface treatment of a mold in a mold manufacturing process.
[0002]
[Prior art]
In the molding die industry, it is required that the die materials have high hardness that can be used as a product such as a die, high hardness that can secure abrasion resistance, and excellent machinability. As a mold material, application of pre-hardened steel is known. Pre-hardened steel is a quenching process in which a steel material that has been adjusted to a predetermined hardness is machined without taking the steps of increasing the strength (hardness) by annealing, machining, and quenching applied to ordinary steel. Used as a mold without performing Ni, Al, Cu etc. are added to increase the hardness by utilizing the precipitation effect, and the pre-hardened steel material adjusted to the high machinability bainite structure realizes high hardness and relatively good machinability. It is an effective steel material. No quenching after processing is required, making it extremely easy for mold makers to use.
[0003]
However, even if a material that can be easily processed is formed, for example, in order to process a mold having a complicated shape, electric discharge machining in addition to laser processing is indispensable. In particular, a special ultra-precision mold used for manufacturing semiconductor parts has been using electric discharge machining.
[0004]
Further, in the electric discharge machining, it is possible to mold a mold made of a cemented carbide having difficulty in workability, such as WC-Co, SK3, and SKD61, regardless of the workability of the material.
[0005]
[Problems to be solved by the invention]
However, electrical discharge machining is widely used for machining precision dies because it is effective for processing hard-to-hard materials, but in practice, it is rare to use the electrical discharge machined surface as it is. In order to reduce surface layer defects such as micro cracks and improve shape accuracy, polishing by hand polishing is finally performed. However, this process often depends on the skill of a skilled person and requires a long time, so that high efficiency has been a conventional problem.
[0006]
An object of the present invention is to overcome the drawbacks of hand polishing of a metal mold subjected to electric discharge machining and to finish the surface with a low surface roughness in a short time.
[0007]
[Means for Solving the Problems]
According to the present invention, it is possible to overcome the drawbacks of hand polishing of the electric discharge machined mold by using electron beam irradiation, and to finish the surface with low surface roughness in a short time.
The device used in the present invention is also applied to surface corrosion resistance, gloss, improvement of fatigue characteristics, adjustment of hardness, etc. of various metals such as molds and denture bases. The presence of the anode plasma eliminates electron beam scattering that often occurs in a vacuum, and can provide a large-area metal surface modification as compared with surface processing by a laser.
[0008]
The surface treatment method for a mold according to the present invention includes the steps of: generating an anode plasma in a container; and forming a low energy pulsed electron beam capable of surface modification in a large area by the presence of the anode plasma in the container. Disposing the mold on the trajectory of the electron beam so that the electron beam smoothes the surface of the mold material, improves corrosion resistance, enhances gloss, and improves surface hardness.
The anode plasma is formed to prevent electron beam scattering.
[0009]
The parameters of the action of the electron beam preferably vary within the following ranges:
The energy density is about 1 J / cm ² or more, preferably, about ² J / cm ² or more and 10 J / cm ² or less. More preferably, it is in the range of about 4 J / cm ² or more and 8 J / cm ² or less. Most preferably, the range is about 5 J / cm ^{2 to} 7 J / cm ² .
The pulse width is 1 μs or more.
As for the number of irradiations, a considerable effect can be obtained even with one irradiation, but the minimum number is preferably at least about 5 or more. The maximum number is appropriately determined in consideration of production costs and the like. Preferably, the range is about 20 to 40 times around about 30 times.
[0010]
The surface hardening mold according to the present invention is a mold that has been surface-treated by the surface treatment method of the present invention.
Examples of the mold material include carbon steel. For example, a pre-hardened steel such as a steel called NAK80, a steel called SK3, a steel called SKD61, and a cemented carbide called WC-Co by Daido Special Steel may be used.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The low-energy, high-current-density electron beam apparatus used in the present invention will be described below with reference to FIG. 1 (reference patent: US 2003/0019850 A1, published on January 30, 2003, Kensuke Uemura, etc.).
[0012]
The mold 12 was placed in the vacuum vessel 1, and the vessel was evacuated from atmospheric pressure to 3 × 10 ⁻² Pa or less by the scroll pump 2 and the turbo molecular pump 3. Inert gas is introduced from the flow control valve 4. When the pressure in the container is stabilized to a certain constant ^{value of} 0.5 to 3 × 10 ⁻¹ Pa, a current is instantaneously passed to the solenoid 5 provided outside the electron gun, and a strong Generate a pulsed magnetic field. At the same time as the generation of the magnetic field, a positive pulse voltage (about 5 kV) is applied to the ring-shaped anode 6 to accelerate natural electrons in the chamber.
[0013]
The Penning effect occurs because the electrons are present in the electric and magnetic fields. The electrons undergo a spiral motion under Lorentz force, so that the electron travel can be lengthened. The electrons are finally collected by the anode, but before that they collide with gas molecules many times to ionize the gas molecules and generate anode plasma 7 in the space near the anode ring. Since the ionization of the gas is excited as described above, high-density plasma can be obtained.
[0014]
When the anode plasma is generated and the amount of the anode plasma becomes maximum (about 20 to 30 μs after the voltage is applied to the anode), a negative pulse acceleration voltage (20 kV to 40 kV, pulse width) is applied to the cathode of the electron gun. 2-4 μs). The rising time of the pulse voltage applied by the spark trigger switch is 5 to 10 ns. Further, since the anode plasma plays the role of a virtual anode and the apparent distance between the anode and the cathode is shorter than in the case without plasma, an extremely strong electric field is concentrated on the tip of the sharp needle-like cathode surface 8. A high electric field is created on the surface of the cathode, whereby electrons are explosively emitted from the cathode, producing a high density cathode plasma 9 of the cathode.
[0015]
Since a cathodic plasma has been generated near the cathode and an anodic plasma around the anode, a double layer 10 is formed between the two plasmas. As a characteristic of the plasma, it has high conductivity, and both plasmas act like a negative electrode and a positive electrode, respectively. Since the space between the two virtual electrodes is a narrow double layer, a high electric field is concentrated between them, and the electrons jumping out of the cathode plasma are accelerated by the high electric field of the layer. Thus, a high-density electron beam 11 is formed. The high-density electron beam irradiated the mold 12.
[0016]
【Example】
Example 1
Pre-hardened steel (Daido Special Steel NAK80) was subjected to electric discharge machining using a copper electrode (φ10 mm) under the conditions (discharge current: 3 A, pulse width: 2 μs, duty factor: 10%) (machining liquid: kerosene). The sample was irradiated with an electron beam (electron density: 7.3 J / cm ² , pulse width: ² to 3 μs, pulse frequency: 0.2 Hz, pulse number: 30 times, beam diameter: about 80 mm). In the steel material, two directions were prepared because the carbide was elongated in the rolling direction and the properties were different depending on the direction.
As shown in FIG. 2, before irradiation, a surface on which discharge traces having a diameter of several tens of μm were accumulated was formed. However, on the surface after irradiation, no discharge trace was observed and the roughness was considerably improved.
[0017]
Example 2
Next, the electron beam was irradiated onto the electric discharge machining surface while changing the energy density. FIG. 3 shows changes in surface roughness and glossiness with respect to energy density. The energy density was changed in a range of more than 0 and about 15 J / cm ² or less.
The surface roughness sharply decreases at an energy density of 1 to 4 J / cm ² , and becomes a minimum at an energy density of 6 to 7 J / cm ² , but increases slightly at higher values. Glossiness (Glossiness, JISZ8741 compliant) showed a change corresponding to the surface roughness, and the maximum glossiness was obtained when the surface roughness was minimum. From this result, the effect of smoothing is higher as the energy density increases to some extent.
[0018]
FIG. 3 shows that the effect appears when the energy density is in the range of about 1 J / cm ² or more. Preferably, it is in the range of about ² J / cm ² or more and 10 J / cm ² or less. More preferably, it is in the range of about 4 J / cm ² or more and 8 J / cm ² or less. A range of about 5 J / cm ^{2 to} 7 J / cm ² is most preferred.
[0019]
Example 3
Next, changes in surface roughness when the number of times of electron beam irradiation is changed at an energy density of 7.3 J / cm ² are shown (FIG. 4). In this case, irradiation was performed in a range of 1 to 50 times. The surface roughness sharply decreases after several irradiations, and does not change much after the fifth irradiation. From this fact, it can be understood that a considerable effect can be obtained by one irradiation, but it is preferable that the minimum number of times is at least about 5 times or more. Then, the maximum number of times may be appropriately determined in consideration of production costs and the like. Preferably, the range is about 20 to 40 times around about 30 times.
Almost the same tendency was shown at an energy density of 4.2 J / cm ² .
[0020]
Example 4
Carbon steel undergoes martensitic transformation and can be applied to surface hardening. When a mold of SK3 steel (1 to 1.1% C) was subjected to a pulse electron beam (6 J / cm ² ) 20 times, the surface hardness was increased. FIG. 5 shows the surface hardness after and before electron beam processing using a microhardness tester. In the Vickers hardness test, a load is applied to the diamond indenter, and the hardness is calculated from the depression on the surface of the sample. Therefore, where the load is low, the influence of the hardness of the substrate is small and the actual surface hardness is approximated. In measurement, a load as low as possible is desirable. As shown in FIG. 6, it can be seen that the Vickers hardness after the treatment increases when the load is low, and in this case, the surface is about 1.5 times as hard.
[0021]
Similarly, when a mold of SKD 61 (0.32 to 0.42% C) was irradiated with an electron beam, the surface hardness was increased. FIG. 6 shows the surface hardness of SKD61.
[0022]
Example 5
A superalloy WC-Co (G5) mold was subjected to electric discharge machining using a copper electrode (φ10 mm) under the conditions of a discharge current of 3 A, a pulse width of 2 μs, and a duty factor of 10% (working fluid: kerosene). The surface was irradiated with an electron beam. In order to examine the effect of smoothing by the irradiation beam, the pulse energy density of the beam was set to 7.3 J / cm ² , the pulse width: ² to 3 μs, the pulse frequency: 0.2 Hz, the number of pulses: 30, The mold was irradiated with a beam diameter of about 80 mm.
[0023]
As shown in FIG. 7, when the energy density of the beam pulse is 2 to 8 J / cm ² , the effects of smoothing and glossing can be obtained.
FIG. 7 shows that the effect appears when the energy density is in the range of about 1 J / cm ² or more. Preferably, it is in the range of about ² J / cm ² or more and 10 J / cm ² or less. More preferably, it is in the range of about 4 J / cm ² or more and 8 J / cm ² or less. A range of about 5 J / cm ^{2 to} 7 J / cm ² is most preferred.
[Brief description of the drawings]
FIG.
1 schematically shows a low-energy pulsed electron beam device capable of emitting a large area used in an embodiment of the present invention.
FIG. 2
In the present invention, a change in surface roughness of a pre-hardened steel mold irradiated with an electron beam is shown.
FIG. 3
In the present invention, changes in surface roughness and gloss of an irradiated prehardened steel mold with respect to electron beam energy density are shown.
FIG. 4 shows a change in surface roughness of an irradiated prehardened steel mold with respect to the number of electron beam pulses in the present invention.
FIG. 5 shows a change in surface hardness of an SK3 steel mold irradiated with an electron beam in the present invention.
FIG. 6 shows a change in surface hardness of an SKD61 steel mold irradiated with an electron beam in the present invention.
FIG. 7 shows changes in surface hardness and gloss of a WC-Co superalloy mold irradiated with an electron beam in the present invention.
[Explanation of symbols]
Reference Signs List 1 vacuum vessel 2 scroll pump 3 turbo molecular pump 4 flow control valve 5 solenoid 6 anode 7 anode plasma 8 cathode 9 cathode plasma 10 electric double layer 11 electron beam 12 processed mold 13 sample holder

Claims (8)

Generating an anode plasma in the vessel;
Forming a low-energy pulsed electron beam capable of surface modification of a large area by the presence of the anode plasma in the container;
Disposing the mold on the trajectory of the electron beam so that the electron beam smoothes the surface of the mold material, improves corrosion resistance, enhances gloss, and improves surface hardness. Surface treatment method. The method of claim 1, wherein the anode plasma is formed to prevent scattering of the electron beam. The method according to claim 1, wherein the mold material is carbon steel. 4. The method according to claim 1, wherein the electron beam irradiation has an energy density of 1 J / cm ² or more. The method according to any one of claims 1 to 4, wherein the number of times of the electron beam irradiation is 5 or more. 6. The method according to claim 1, wherein the pulse width of the electron beam irradiation is 1 μs or more. 4. The method according to claim 1, wherein the electron beam irradiation has an energy density of 1 J / cm ² or more, an irradiation frequency of 5 times or more, and a pulse width of 1 μs or more. A mold surface-treated by the surface treatment method according to any one of claims 1 to 7.

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