JP2006257556A - Electrical-discharge surface-treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrical-discharge surface-treatment method of forming a dense thick coat on a workpiece without using techniques such as welding and thermal spraying. <P>SOLUTION: In an electrical-discharge surface-treatment method where a pulse-like electrical discharge is caused between an electrode and a workpiece in a working fluid or in an air, and with the energy of the pulse-like electrical discharge, a coat being formed with a material constituting the electrode or a substance that is generated by a reaction of the material due to the energy of the pulse-like electrical discharge is formed on a surface of the workpiece, using an electrode obtained by mixing and compression-molding a metallic powder or a metallic compound having an average grain diameter of 6μm to 10μm, and the metallic powder of a material, which is less likely to form carbide, electrical-discharge is performed under working conditions that a pulse width is 50μs to 500μs and a peak current value is 2A to 30A, thus a coat essentially consisting of the metal or metallic compound constituting the electrode is formed on a workpiece. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge surface treatment technique, and more specifically, an electrode formed from a metal powder or a metal compound powder is used, and a pulsed discharge is generated between the electrode and a workpiece. The present invention relates to a technique for forming a dense thick film by a discharge surface treatment in which a film made of an electrode material or a film made of a material in which an electrode material reacts with discharge energy is formed on a work surface.

  As a surface treatment technology for forming a film on a workpiece by pulsed discharge using a green compact obtained by compressing a powder material as an electrode, for example, the main focus is on a hard film near normal temperature. A technique for forming a thin hard film has been established (for example, see Patent Document 1).

  In the technique disclosed in Patent Document 1 described above, the electrode material is suppressed to a certain level while suppressing the supply of the electrode material by discharging, and the supplied material is sufficiently melted to form a hard ceramic film on the workpiece surface. is doing. However, in this method, the film that can be formed is limited to a thin film having a thickness of up to about 10 μm.

  In addition, as a technique for forming a thick film by discharge surface treatment, a technique for forming a film containing carbide as a main component on the surface of aluminum (see, for example, Patent Document 2), a technique for forming a film containing carbide as a main component. (For example, refer to Patent Document 3), and a technique for forming a thick film of about 100 μm by increasing the discharge pulse width to about 32 μs (for example, refer to Patent Document 4).

International Publication No. 99/58744 Pamphlet JP-A-7-70761 Japanese Patent Laid-Open No. 7-197275 Japanese Patent Laid-Open No. 11-827

  However, in any of the techniques disclosed in the above patent documents, a thick film is mainly composed of carbide, and a dense thick film cannot be formed. For this reason, in Patent Document 2 and Patent Document 3 described above, after forming a porous thick film, a remelting process is required with an electrode with little wear.

  For example, in the technique of Patent Document 3, even when a seemingly dense film can be formed, it is a porous film when examined in detail. In the technique of Patent Document 4, when a film is formed using a hydride as an electrode, a thick film can surely be formed. However, the coating is dense only in the vicinity of the workpiece surface where the workpiece material and the coating material are melted, and as shown in FIG. 13, the thickly raised portion A is a porous coating.

  In recent years, there has been a demand for the formation of a dense and relatively thick film (thick film of about 100 μm or more) in applications that require strength and lubricity in a high temperature environment. As a technology for thickening the coating, welding is performed by welding the material of the welding rod to the workpiece by means of electric discharge between the workpiece and the welding rod (overlay welding), and spraying the workpiece in a sprayed state after melting the metal material. There is thermal spraying to form a coating.

  However, since any method requires skilled work by hand, there is a problem that the work is difficult to line and the cost is increased. In particular, welding is a method in which heat concentrates and enters the workpiece. Therefore, when processing thin materials, or materials that are easily broken such as directional control alloys such as single crystal alloys and unidirectionally solidified alloys. When used, there is a problem that weld cracking is likely to occur and the yield is low.

  Therefore, it is possible to create a line that eliminates manual work as much as possible, and forms a thick film that has strength and lubricity in a high temperature environment using discharge surface treatment technology that prevents intensive heat input to the workpiece. It was anxious to establish technology to do.

  The present invention has been made in view of the above, and an object thereof is to provide a discharge surface treatment method for forming a dense thick film on a workpiece without using a technique such as welding or thermal spraying.

  In order to solve the above-described problems and achieve the object, a discharge surface treatment method according to the present invention generates a pulsed discharge between an electrode and a workpiece in a machining fluid or in the air, and uses the discharge energy. In a discharge surface treatment method for forming a film made of an electrode material or a film made of a material obtained by reacting an electrode material with discharge energy on a work surface, a metal powder or a metal compound powder having an average particle size of 6 μm to 10 μm; A metal or metal compound constituting an electrode by using an electrode formed of a metal powder made of a material difficult to form carbides, and discharging the discharge pulse under a processing condition of 50 μs to 500 μs and a peak current value of 2 A to 30 A. It is characterized in that a film mainly composed of is formed on a workpiece.

  In the present invention, there is a strong correlation between the particle size of the electrode material powder constituting the electrode, the peak current value, and the pulse width when forming a dense thick film by the discharge surface treatment. Found by the inventors' research.

  That is, according to the present invention, a dense thick film can be formed by performing discharge surface treatment under appropriate discharge surface treatment conditions corresponding to the average particle diameter of the electrode material constituting the electrode for discharge surface treatment. , Has the effect.

  Embodiments of a discharge surface treatment method according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the accompanying drawings, the scale of each member may be different for easy understanding.

Embodiment 1 FIG.
First, the concept for forming a dense thick film by discharge surface treatment in the present embodiment will be described. In the conventional discharge surface treatment, an electrode material such as titanium (Ti) is chemically reacted by discharge in oil to form a hard carbide film such as titanium carbide (TiC). For this reason, the ratio of the material which is easy to shape | mold a carbide | carbonized_material was contained in the electrode used for discharge surface treatment.

  As a result, as the discharge surface treatment progresses, for example, when performing a discharge surface treatment on steel, the material of the workpiece (work) surface changes from steel to TiC, which is a ceramic, and accordingly, characteristics such as heat conduction and melting point Was changing.

  In the process of forming such a film, the inventor is able to make the formed film a metal-based film and to increase the film thickness by adding a material that is not easily carbonized to the component of the electrode material. It was found by the experiment. This is because by adding a material that is difficult to carbonize to the electrode, the material that remains in the metal state without becoming a carbide is increased. This is important for thickening the coating.

Next, the process for manufacturing the electrode for discharge surface treatment will be described with reference to FIG. FIG. 1 is a cross-sectional view showing a concept of a method for manufacturing a discharge surface treatment electrode (hereinafter, simply referred to as an electrode) in the first embodiment. First, Cr (chromium) powder 1 which is a material that easily forms carbides and Co (cobalt) powder 2 that is a material that hardly forms carbides are in a predetermined ratio (for example, Cr: 25 wt%, Co: 75 wt%). Mix with.

  In FIG. 1, the mixed powders 1 and 2 fill a space surrounded by the upper punch 3 of the mold, the lower punch 4 of the mold, and the die 5 of the mold. Then, the mixed powders 1 and 2 are compressed by the upper punch 3 and the lower punch 4 to form a green compact having a predetermined shape. In the discharge surface treatment, the green compact is used as a discharge electrode. In the present embodiment, Cr powder 1 and Co powder 2 having an average particle diameter of about 6 μm to 10 μm are used.

  In order to improve the transmission of pressure to the inside of the mixed powders 1 and 2 at the time of compression molding, mixing of waxes such as paraffin into the mixed powders 1 and 2 can improve the moldability of the mixed powders 1 and 2. . However, since wax is an insulating substance, if it remains in a large amount in the electrode, the electrical resistance of the electrode increases and the discharge performance deteriorates.

  Therefore, when the mixed powders 1 and 2 are mixed with wax, it is preferable to remove the wax. Wax can be removed by placing the green compact electrode in a vacuum furnace and heating it. In addition, by heating the green compact electrode, other effects such as lowering the electrical resistance of the green compact electrode and increasing the strength of the green compact electrode can be obtained. Heating later makes sense.

  Now, using the green compact electrode produced as described above as a discharge surface treatment electrode, discharge surface treatment was performed to form a coating film. The discharge pulse conditions were a peak current value ie = 10 A, a discharge duration (discharge pulse width) te = 64 μs, and a rest time to = 128 μs. In forming a dense thick film by discharge surface treatment, the relationship between the particle size of the powder constituting the electrode, the peak current value, and the pulse width is strongly related, and is found to be as follows. It was done.

  When the discharge surface treatment is performed using an electrode composed of a powder having a certain average particle diameter, a dense thick film can be formed when the discharge surface treatment is performed under electrical conditions within an appropriate pulse width range. . However, in any case where the pulse width is shorter than the appropriate range or the pulse width is longer than the appropriate range, the formed film becomes porous. Further, when the pulse width is short, the electrode material adheres to the workpiece, but the attached electrode material has no strength at all, and the film becomes tattered.

  This is because the pulse width during discharge surface treatment deviates from the appropriate pulse width, and if the pulse width is shortened, the discharge energy is insufficient and the powder of that particle size cannot be melted, and the coating becomes porous. Is done. Also, if the pulse width at the time of discharge surface treatment deviates from the appropriate pulse width and the pulse width becomes longer, the discharge energy becomes excessive, so that the electrode is greatly collapsed, and the gap between the electrodes, i.e., between the electrode and the workpiece. It is considered that it is difficult to melt all of them with a discharge pulse because a large amount of powder is supplied.

  In addition, although the range of the appropriate pulse width changes to some extent depending on the peak current value, it has also been found by the inventors' experiment that it increases as the particle size of the electrode material powder increases.

  In addition, when a pulse width condition is used as a discharge pulse condition, a dense film is obtained when discharge surface treatment is performed using an electrode composed of powder having an appropriate particle size range corresponding to the pulse width. Can be formed. However, even when a certain pulse width condition is used, when a discharge surface treatment is performed using an electrode composed of a powder having a particle size larger than the appropriate range, the powder having a particle size smaller than the appropriate range is used. In any case where the discharge surface treatment is performed using the constituted electrode, the formed film is porous. When the discharge surface treatment is performed using an electrode composed of a powder having a larger particle size, the electrode material adheres to the workpiece, but there is no strength and the coating is in a tattered state.

  The relationship between the particle shape of the powder constituting the electrode and the pulse width is influenced by the electrode hardness determined by the heating temperature of the electrode. That is, when the electrode hardness is hard, the pulse width suitable for the discharge surface treatment is shifted in the longer direction. When the electrode hardness is soft, the pulse width suitable for the discharge surface treatment is shifted in the short direction. The correlation between the hardness of the electrode and the film formation has been found by the inventors' experiments.

  Further, regarding the peak current value of the discharge pulse conditions, if the peak current value is extremely small, problems such as causing pulse cracking of the discharge and inability to melt the powder of the electrode material occur. However, if the peak current value is 30 A or less, an appropriate film can be formed by selecting an appropriate pulse width.

  Further, according to the inventors' experiment, a peak current value of 2 A or more is necessary to prevent pulse cracking. On the other hand, when the peak current value exceeds 30 A, the electrode is damaged by the shock wave generated by the energy of the discharge pulse and locally collapses, and the powder material is excessively supplied to the workpiece side, so that the coating film becomes porous.

  According to the present embodiment, the discharge surface treatment electrode composed of Cr powder 1 and Co powder 2 having a particle size of about 6 μm to 10 μm is used, and the pulse width of the discharge pulse is in the range of 50 μs to 500 μs. By using it, a dense thick film could be formed. In other words, by carrying out processing (discharge surface treatment) under processing conditions (discharge pulse conditions) optimal for the particle size of the powder constituting the electrode for discharge surface treatment, it is possible to carry out a dense thick build-up, and in a high temperature environment It can be said that a dense thick film having sufficient strength can be formed even under.

  Among metal elements, Cr is a material that forms an oxide at high temperature and exhibits lubricity. Therefore, by performing discharge surface treatment using the discharge surface treatment electrode containing Cr as described above, a thick film having lubricity in a high temperature environment can be formed.

  Therefore, according to the present embodiment, it is possible to form a line with minimal manual work, and use a discharge surface treatment technology that prevents intensive heat input to the workpiece. It is possible to form a thick film having properties.

  The definition of “dense thick film” described here is not easy to remove even if the film is rubbed with a file (of course, removal will proceed if it is cut off), but polishing will give a metallic luster. It means a state that can be obtained.

  In the present invention, the environment in which the discharge surface treatment is performed may be in the working fluid or in the air.

Embodiment 2. FIG.
Next, Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 2 shows a compression of a mixed powder in which a powder of carbide Cr ₃ C ₂ (chromium carbide: particle size 3 μm) and a powder of Co (cobalt: particle size 2 μm), which is a material difficult to form carbide, are mixed. When discharge surface treatment is performed using a discharge surface treatment electrode manufactured by heating after molding, the ease of forming a thick film changes by changing the Co content in the discharge surface treatment electrode. It shows a state.

The material used as the base of the discharge surface treatment electrode was Cr ₃ C ₂ . Further, the content of Co, which is a material that hardly forms carbides, was set to 40% by volume or more, and the heating temperature after compression forming of the mixed powder was set to about 900 ° C.

  Using a green compact electrode (area 15 mm × 15 mm) produced under such conditions, discharge surface treatment was performed to form a coating. An example of the discharge pulse condition when the discharge surface treatment is performed is shown in FIGS. 3A and 3B. 3A and 3B are diagrams showing an example of pulse conditions of discharge during discharge surface treatment, FIG. 3A shows a voltage waveform applied between an electrode and a workpiece during discharge, and FIG. 3B shows during discharge The current waveform of the flowing current is shown. As shown in FIG. 3A, a no-load voltage ui is applied between the two electrodes at time t0, but current starts to flow between the two electrodes at time t1 after the discharge delay time td has elapsed, and discharge starts. The voltage at this time is the discharge voltage ue, and the current flowing at this time is the peak current value ie. When the supply of voltage between the two electrodes is stopped at time t2, no current flows.

  Time t2-t1 is the pulse width te. The voltage waveform at time t0 to t2 is repeatedly applied between both electrodes with a rest time to. That is, as shown in FIG. 3A, a pulsed voltage is applied between the discharge surface treatment electrode and the workpiece.

  In the present embodiment, the discharge pulse conditions during the discharge surface treatment are the peak current value ie = 10 A, the discharge duration (discharge pulse width) te = 64 μs, and the rest time to = 128 μs. The processing time is 15 minutes.

As shown in FIG. 2, when the content of Co in the electrode is 0%, that is, when the content of Cr ₃ C ₂ in the electrode is 100%, the thickness of the film that can be formed is limited to about 10 μm. Yes, the thickness of the film cannot be increased any further. The coating is made of a material containing Cr ₃ C ₂ as a main component and mixed with base material components.

In addition, when the material which is hard to form a carbide | carbonized_material does not exist in an electrode, the mode of formation of the film with respect to processing time becomes like FIG. As shown in FIG. 4, at the initial stage of the discharge surface treatment, the film grows and becomes thicker with time, and the thickness of the film is saturated at a certain time (about 5 minutes / cm ² ).

Although the film thickness does not grow for a while after that, if the discharge surface treatment is continued for a certain time (about 20 minutes / cm ² ) or more, the film thickness starts to decrease, and finally the film thickness is negative, that is, the workpiece is dug. It will be changed to be included. However, the film is present even in the dug state, and the thickness itself is about 10 μm, which is almost the same as the state processed in an appropriate time.

  Returning to FIG. 2, the coating can be formed thicker as the content of Co, which is a material that is difficult to carbonize, is increased, and the thickness of the coating that is formed when the Co content in the electrode exceeds 20% by volume. It has been found that when the thickness exceeds 40% by volume, it becomes easy to form a thick film stably. By increasing the amount of the material remaining as a metal in the coating in this way, a coating containing a metal component that is not carbide can be formed, and a thick film can be easily formed stably. Co is considered to play the role of a binder in the coating.

  In addition, the volume% here is a ratio of a value obtained by dividing the weight of each powder to be mixed by the density of each material, and is a ratio of the volume occupied by the material in the volume of the material of the whole powder.

For example, in the case of the volume percentage of Co powder, “volume percentage of Co powder = volume of Co powder / (volume of Cr ₃ C ₂ powder + volume of Co powder) × 100”.

  The volume of the powder is not an apparent volume (volume as a powder) but a substantial volume of the powder material. For example, “volume of Co powder = weight of Co powder / density of Co powder”.

  From the above points, it is preferable that the ratio of the material that is hardly carbonized contained in the electrode is 40% by volume or more. As shown in FIG. 2, in the case of the aforementioned discharge pulse conditions, the peak current value ie = 10 A, the discharge duration (discharge pulse width) te = 64 μs, and the rest time to = 128 μs, it is difficult to carbonize the electrodes. Even when the proportion of the material is 40% by volume or less, a film of about 10 μm can be formed. However, in order to form a dense thick film, the pulse conditions must be set appropriately. For example, even if the proportion of the material that is hard to be carbonized contained in the electrode is about 30% by volume, a dense thickness can be achieved, but the range of the conditions is extremely narrow.

  When there is too much material to form carbide in the electrode, electrical conditions are not appropriate, or the electrode is in poor condition, a swell is formed, but it can be easily removed or polished A film in such a state that gloss cannot be obtained is formed. However, in the present embodiment, by performing processing (discharge surface treatment) under processing conditions (discharge pulse conditions) optimum for the particle size of the powder constituting the electrode, the metal in the formed film is contained in the film. By being connected, it is possible to perform a dense thick build-up and to form a film having sufficient strength.

  For reference, a photograph of a coating formed when the Co content in the electrode is 70% by volume is shown in FIG. This photograph illustrates the formation of a thick film. In the photograph shown in FIG. 5, a thick film having a thickness of about 2 mm is formed. This film is formed in a processing time of 15 minutes under the above-mentioned conditions. However, if the processing time is increased, a thicker film can be formed.

  In this way, an electrode containing 40% by volume or more of a material that is difficult to carbonize such as Co is used in the electrode, and the processing (discharge pulse condition) is optimized for the particle size of the powder constituting the electrode. By performing the (surface treatment), a stable and dense film can be formed on the workpiece surface by the discharge surface treatment.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to the drawings. FIG. 6 is a cross-sectional view showing the concept of the method for manufacturing the electrode for discharge surface treatment in the third embodiment.

  In FIG. 6, the space surrounded by the upper punch 12 of the mold, the lower punch 13 of the mold, and the die 14 of the mold is filled with Co powder 11 having a particle size of about 1 μm. It compresses and forms with the lower punch 13, and forms the green compact of a predetermined shape. In the discharge surface treatment, the green compact is used as a discharge electrode.

  By applying a predetermined pressing pressure to the powder in this way, the powder hardens and becomes a green compact. However, in this state, the green compact has a high electric resistance, and there is a problem in using it as it is as an electrode for discharge surface treatment. In order to measure the electric resistance of the electrode, for example, as shown in FIG. 7A, the electrode 21 is sandwiched between the metal plates 22, and the electrode terminal 24 of the tester 23 is brought into contact with the metal plate 22 to measure the resistance value. The approximate electric resistance value can be measured by a general method.

  Further, as shown in FIG. 7B, an approximate determination can be made by a simpler method of measuring the resistance value by bringing the electrode terminal 34 of the tester 33 into contact with both ends of the electrode 31.

  Co used as an electrode material in the present embodiment is a material having a melting point exceeding 1000 ° C. However, when the electrode is observed in detail, it has been clarified by the inventor's research that a part of the material (Co) melts even at a temperature of about 200 ° C. to lower the electric resistance of the electrode.

  When the Co powder having a particle diameter of about 1 μm shown in FIG. 6 is formed into a green compact having a diameter of about 18 mm and a length of about 30 mm, the measurement method shown in FIG. The measured electrical resistance showed a value of several Ω to several tens of Ω. FIG. 8 shows the relationship between the electrical resistance value and the heating temperature after the green compact has been heated in a vacuum furnace for a predetermined time and then held at a predetermined heating temperature for 1 to 2 hours.

  When the heating temperature of the green compact is low (100 ° C. or lower), the electrical resistance of the green compact after heating hardly decreases. However, when the green compact was heated in the temperature range T of about 200 ° C. shown in FIG. 8, the electrical resistance value of the green compact was almost 0Ω. In the case of a green compact formed from the above material, a temperature of about 200 ° C. to 250 ° C. was an optimum value as a heating temperature for forming an electrode for discharge surface treatment. Further, when the heating temperature exceeds 300 ° C., the hardness of the electrode becomes too hard, and as a result, the supply amount of the electrode material between the electrode materials due to the discharge during the discharge surface treatment decreases. Therefore, it has become difficult to form a thick film.

  FIG. 9 shows a state in which the discharge surface treatment is performed by the discharge surface treatment apparatus using the electrodes manufactured by the above steps. FIG. 9 shows a state in which a pulsed discharge is generated. Moreover, the photograph of the film formed by this discharge surface treatment is shown in FIG. In the photograph shown in FIG. 10, a thick film having a thickness of about 1 mm is formed.

  The discharge surface treatment apparatus shown in FIG. 9 is the above-described discharge surface treatment electrode, and is a discharge surface treatment electrode comprising a green compact obtained by heat-treating a green compact obtained by compression-molding Co powder 11 having a particle size of about 1 μm. 41 (hereinafter may be simply referred to as an electrode 41), a discharge surface treatment that generates a pulsed discharge (arc column) 44 by applying a voltage between the machining liquid 43 and the electrode 41 and the workpiece 42. Power supply device 45. In FIG. 9, the servo mechanism for controlling the distance between the electrodes, that is, the distance between the electrode 41 and the workpiece 42, the storage tank for storing the processing liquid 43, and the like are omitted because they are not directly related to the present invention.

  In order to form a coating film on the workpiece surface by this discharge surface treatment apparatus, the electrode 41 and the workpiece 42 are arranged opposite to each other in the machining liquid 43. In the machining liquid 43, a pulsed discharge is generated between the electrode 41 and the work 42 using the power supply device 45 for discharge surface treatment. Specifically, a voltage is applied between the electrode 41 and the workpiece 42 to generate a discharge. A discharge arc column 44 is generated between the electrode 41 and the workpiece 42 as shown in FIG.

  Then, a coating film of the electrode material is formed on the workpiece surface by the discharge energy of the discharge generated between the electrode 41 and the workpiece 42, or a coating film of a substance reacted with the electrode material is formed on the workpiece surface by the discharge energy. The polarity is used as negative polarity on the electrode 41 side and positive polarity on the work 42 side. In this configuration, the current I during discharge flows in a direction from the electrode 41 toward the discharge surface treatment power supply device 45.

  The conditions of the discharge pulse in the discharge surface treatment are the peak current value = 10 A, the discharge duration (discharge pulse width) = 8 μs, and the rest time = 16 μs. In the present embodiment, a film having a thickness of about 1 mm is formed by the treatment for 5 minutes.

  In the first embodiment described above, an electrode made of a mixed powder of Cr powder 1 and Co powder 2 having a particle size of about 6 μm to 10 μm is used, so that the formed thick film varies in irregularity. In the first embodiment, a dense film is formed using a pulse width of 50 μs to 500 μs in the discharge pulse. However, by reducing the particle size of the powder, the pulse width is reduced to form a dense film. be able to.

  This is because if the particle size of the electrode material powder constituting the electrode is reduced, the electrode material powder can be sufficiently melted even under conditions of low pulse width and low energy, and a film is formed by stacking small discharge craters. This is because a dense film can be formed.

  In the case of the Co powder having a particle diameter of about 1 μm used in this example, a dense film could be formed with a pulse width of 50 μs or less. If a discharge pulse having a pulse width extended to 50 μs is used, the electrode is greatly collapsed due to the discharge, and the coating becomes porous.

  The hardness of the electrode will be described. The hardness of the electrode was measured using a pencil scratch test for coating film in JIS K 5600-5-4 when the particle diameter of the powder constituting the electrode was large and the hardness of the electrode was soft. Moreover, when the particle diameter of the powder constituting the electrode was small and the hardness of the electrode was hard, the measurement was performed using Rockwell hardness or the like. The standard of JIS K 5600-5-4 is originally used for the evaluation of a paint film, but it has been found that it is suitable for the evaluation of a material with low hardness. Of course, the results of other hardness evaluation methods and the results of the pencil scratch test for coating film can be converted to each other, and other methods may be used as an index.

  When the particle diameter of the powder constituting the electrode is about 5 to 6 μm, the electrode is in the best condition when the hardness of the electrode is about 4B to 7B, and a dense thick film can be formed. However, there is a range in which a thick film can be formed even if this range is slightly deviated, and in the direction of increasing hardness, a thick film can be formed with a hardness of about B. Further, in the direction in which the hardness becomes softer, a thick film can be formed up to about 8B.

  However, as the hardness of the electrode becomes harder, the film formation rate tends to be slower. With a hardness of about B, the formation of a thick film becomes quite difficult. When the hardness of the electrode is further increased, a thick film cannot be formed, and the workpiece (workpiece) side is removed as the hardness of the electrode increases.

  In the direction where the hardness of the electrode becomes softer, it is possible to form a thick film up to a hardness of about 8B. However, when the structure of the formed thick film is analyzed, the number of pores tends to increase gradually. When it becomes softer than about 9B, a phenomenon that the electrode component adheres to the workpiece (work) side without being sufficiently melted is observed. Note that the relationship between the hardness of the electrode and the state of the coating changes somewhat depending on the discharge pulse conditions to be used. When appropriate discharge pulse conditions are used, the electrode hardness range within which a somewhat good coating can be formed. It is also possible to enlarge.

  In the above embodiment, since the powder having a particle size of about 5 μm was used, the electrode hardness as described above was an optimum value. However, this optimum value greatly depends on the particle size of the powder constituting the electrode. This is due to the following reason. That is, whether or not the electrode material is discharged from the electrode by discharge depends on the bond strength of the powder constituting the electrode. When the bond strength is strong, the powder is not easily released by the energy of the discharge. On the other hand, when the bond strength is weak, the powder is easily released by the energy of discharge.

  Moreover, when the particle size of the powder constituting the electrode is large, the number of points where the powder in the electrode is bonded to each other is reduced, and the electrode strength is weakened. On the other hand, when the particle diameter of the powder constituting the electrode is small, the number of points where the powder in the electrode is bonded to each other increases, and the electrode strength increases.

  As described above, in the present embodiment, a dense thick buildup is performed by processing under the optimum processing conditions for the particle diameter of the electrode material powder constituting the electrode and the hardness of the electrode. And a film having sufficient strength can be formed.

  As described above, when Co powder, which is a material that does not easily form carbides, is used as an electrode material, the discharge pulse width should be 50 μm or less and the peak current value should be about 10 A. Thus, a dense and thick film can be formed. However, it has been found through experiments by the inventors that a dense thick film (only Mo) can be formed even with an electrode using Mo (molybdenum, particle size 0.7 μm), which is a material that easily forms carbides, as an electrode material.

  Since Mo is a material that easily forms carbides, it is possible to use a relatively long condition with a discharge pulse width of 60 μs or more and 70 μs or less to supply an electrode material that cannot be melted by the discharge pulse to the workpiece. Was effective to form. In the case of a material that easily forms carbides such as Mo, when the electrode material is supplied to the workpiece side in a completely melted state by a discharge pulse, the electrode material supplied to the workpiece side is carbonized to molybdenum carbide. As a result, it becomes difficult to form a thick film. However, it is possible to form a dense coating by adjusting the discharge pulse width as described above and supplying an electrode material that cannot be melted by the discharge pulse to the workpiece.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a cross-sectional view showing the concept of the method for manufacturing the electrode for discharge surface treatment in the fourth embodiment. In FIG. 11, a space surrounded by the upper punch 52 of the mold, the lower punch 53 of the mold, and the die 54 of the mold is filled with Co alloy powder 51 having a particle size of about 1 μm. 52 and the lower punch 53 are compressed to form a green compact having a predetermined shape. In the discharge surface treatment, the green compact is used as a discharge electrode.

  In the present embodiment, a Co-based alloy containing Cr (chromium), Ni (nickel), W (tungsten) or the like as the Co alloy powder 51 (Cr: 20 wt%, Ni: 10 wt%, W: 15% by weight, Co: balance) is used, and the average particle size is about 1 μm.

  In this state, the green compact has a high electric resistance, and as such, there is a problem in using it as an electrode for discharge surface treatment.

  Further, since the Co alloy powder 51 is a hard alloy, it is difficult to harden the powder with a press, and it is necessary to add wax such as paraffin to the Co alloy powder 51 in order to improve formability. However, the greater the residual amount of wax in the electrode, the worse the electrical conductivity during the discharge surface treatment. For this reason, it is preferable to remove the wax in a later step.

  Therefore, in order to remove the wax and lower the electrical resistance of the electrode, the green compact electrode is put in a vacuum furnace and kept at a predetermined heating temperature for 1 to 2 hours after a predetermined temperature rising time.

  In the third embodiment, when the electrode forming is performed with Co powder having a particle diameter of 1 μm, the heating temperature is optimally 200 ° C. to 250 ° C., whereas when the electrode forming is performed with Co alloy powder 51 The optimum heating temperature for reducing the electric resistance was as high as 800 ° C to 900 ° C. Here, when the electrode is heated to 800 ° C. at once, the wax is carbonized and remains as an impurity in the electrode. Therefore, it is necessary to remove the wax at a low temperature once.

  The electrode of this structure was in a tattered state when the heating temperature was 200 ° C. and 300 ° C., and no film could be formed. In addition, when the heating temperature was 1000 ° C., the hardness of the electrode was so high that no film could be formed.

  Next, the conditions under which a dense film can be formed were examined using the average particle diameter of the Co alloy powder 51 as a parameter. The peak current value was 10 A, and the pulse width was changed variously. Each electrode was formed to have an appropriate hardness when performing the discharge surface treatment. Here, “appropriate hardness” means having a condition capable of forming a dense film.

  If the hardness of the electrode is not appropriate, it is difficult to form a dense thick film. If the electrode is too hard, a thick film cannot be formed. In addition, when the hardness of the electrode is too soft, a raised film can be formed, but the film becomes porous and not dense.

  FIG. 12 shows the results of examining the conditions under which a dense coating can be formed using the average particle diameter of the Co alloy powder as a parameter. There is a part that overlaps the range in which the formed film becomes dense and the range in which the formed film cannot be made dense, such as porous. This is because the range is somewhat different depending on the hardness of the electrode etc. It is.

  In FIG. 12, since the optimum hardness of the electrode varies depending on the particle size of the electrode material powder, comparison is made with respect to the hardness at which a dense coating can be formed with a powder having a certain particle size. For example, when the electrode material has an average particle diameter of 2 μm to 6 μm, a dense coating can be formed even with a pulse width of about 10 μs if the hardness of the electrode is high. On the other hand, when the hardness of the electrode is soft, a porous film is formed even with a pulse width of about 40 μs.

  As described above, there are differences in the condition of the pulse width to be dense depending on conditions such as the hardness of the electrode, but there are generally conditions under which a dense thick film can be formed within the range shown in FIG.

  In the above, the material which pulverized the alloy whose alloy ratio is "Cr (chromium): 20 weight%, Ni (nickel): 10 weight%, W (tungsten): 15 weight%, Co (cobalt): remainder" However, the alloy to be powdered may of course be an alloy of other composition. For example, an alloy having an alloy ratio of “Cr (chromium): 25 wt%, Ni (nickel): 10 wt%, W (tungsten): 7 wt%, Co (cobalt): balance” can be used. An alloy having an alloy ratio of “Mo (molybdenum): 28 wt%, Cr (chromium): 17 wt%, Si (silicon): 3 wt%, Co (cobalt): balance”, “Cr (chromium)” : 15% by weight, Fe (iron): 8% by weight, Ni (nickel): remaining alloy, “Cr (chromium): 21% by weight, Mo (molybdenum): 9% by weight, Ta (tantalum) 4% by weight %, Ni (nickel): balance ", alloy ratio is" Cr (chromium): 19 wt%, Ni (nickel): 53 wt%, Mo (molybdenum) 3 wt%, Cd (cadmium) + Ta ( Alloys such as “tantalum): 5 wt%, Ti (titanium): 0.8 wt%, Al (aluminum): 0.6 wt%, Fe (iron): balance” can also be used. However, when the alloy ratio of the alloys is different, properties such as the hardness of the material are different, so that there are some differences in the formability of the electrode and the state of the coating.

  In the present embodiment, the Co alloy powder containing Co as a main component is used as the electrode component, which is effective for increasing the thickness of the coating as described above. In the discharge surface treatment using an electrode made only of a material that easily forms carbide, the formed coating is in a carbide ceramic state, so that the thermal conductivity of the coating is deteriorated, and the removal of the coating is facilitated by discharge.

  Therefore, by mixing Co, which is a material difficult to form carbides, as a component, the thermal conductivity of the coating is not deteriorated, and the coating can be made thicker. Materials having the same effect as Co include Ni and Fe.

  Although the peak current value of the discharge condition is 10 A in this example, a dense thick film can be obtained in approximately the same range as long as it is about 30 A or less. When the peak current value is 30 A or more, problems such as the electrode being unnecessarily collapsed due to the impact of discharge or the hardness of the electrode becoming harder due to an increase in heat input are caused.

  According to this embodiment, by carrying out processing (discharge surface treatment) under the optimum processing conditions (discharge pulse conditions) for the particle size of the powder constituting the electrode and the hardness of the electrode, a dense thick overlay And a film having sufficient strength can be formed.

  As described above, the discharge surface treatment method according to the present invention is useful for industries that require a dense and relatively thick film, and particularly requires strength and lubricity in a high temperature environment. Suitable for applications.

It is sectional drawing which shows the concept of the manufacturing method of the electrode for discharge surface treatment. It is a characteristic view which shows a mode that the ease of forming a thick film changes by changing Co content in an electrode. It is a characteristic view which shows a voltage waveform when the discharge surface treatment is performed. It is a characteristic view which shows the current waveform corresponding to the voltage waveform of FIG. 3A. It is a characteristic view which shows the mode of the formation of the film with respect to processing time when the material which cannot form a carbide | carbonized_material is not in an electrode. It is a figure which shows the image which shows the film formed when Co is 70 volume%. It is sectional drawing which shows the concept of the manufacturing method of the electrode for discharge surface treatment. It is a figure which shows the method of measuring the electrical resistance value of an electrode simply. It is a figure which shows the method of measuring the electrical resistance value of an electrode more simply. It is a characteristic view which shows the relationship between heating temperature and the electrical resistance of an electrode. It is a figure which shows a mode that discharge surface treatment is performed in a process liquid. It is a figure which shows the image of the formed film. It is sectional drawing which shows the concept of the manufacturing method of the electrode for discharge surface treatment. It is a figure which shows the result of having performed the film formation by changing the average particle diameter and pulse width of an electrode material. It is a figure which shows the electron microscope image at the time of forming the film by the conventional electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mixed powder 2 Powder 3 Upper punch 4 Lower punch 5 Die 11 Powder 12 Upper punch 13 Lower punch 14 Die 21 Electrode 22 Metal plate 23 Tester 24 Electrode terminal 31 Electrode 33 Tester 34 Electrode terminal 41 Discharge surface treatment electrode 42 Work 43 Processing Liquid 44 Arc column 45 Power supply device for discharge surface treatment 51 Alloy powder 52 Upper punch 53 Lower punch 54 Die

Claims (11)

A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
Using an electrode formed from a metal powder or metal compound powder having an average particle diameter of 6 to 10 μm and a metal powder made of a material difficult to form carbides, the pulse width of the discharge pulse is 50 μs to 500 μs, and the peak current value is 2A. A discharge surface treatment method characterized by forming a film mainly comprising a metal or a metal compound constituting the electrode on the workpiece by discharging under a processing condition of 30A. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
Using an electrode formed from a metal powder or metal compound powder having an average particle diameter of 3 μm or less and a metal powder made of a material that is difficult to form carbides, a processing condition with a pulse width of 70 μs or less and a peak current value of 30 A or less A discharge surface treatment method comprising: forming a film mainly comprising a metal or a metal compound constituting the electrode on the workpiece. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
It is a material that is difficult to form carbides, and uses an electrode formed from a metal powder or metal compound powder with an average particle diameter of 1 μm, and discharges under a processing condition of a discharge pulse width of 8 μs to 50 μs and a peak current value of 30 A or less. Then, a discharge surface treatment method characterized in that a film mainly composed of a metal or a metal compound constituting the electrode is formed on the workpiece. The discharge surface treatment method according to any one of claims 1 to 3, wherein an electrode mixed with 40% by volume or more of metal powder made of a material that hardly forms carbide is used as the electrode. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
Using a molded electrode containing Mo powder and discharging the pulse width of the discharge pulse under a processing condition of 60 μs or more to form a film composed mainly of a metal or a metal compound constituting the electrode on the workpiece. Discharge surface treatment method. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
A metal powder or metal compound powder having an average particle diameter of 6 to 10 μm containing a metal component that is difficult to be carbonized is used as the electrode, and the discharge pulse is discharged under processing conditions of a pulse width of 50 to 500 μs and a peak current value of 30 A or less. And forming a coating mainly comprising a metal or a metal compound constituting the electrode on the workpiece. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
Using a metal powder or metal compound powder having an average particle size of 3 μm or less containing a metal component that is difficult to be carbonized as the electrode, discharging under a processing condition of a pulse width of a discharge pulse of 70 μs or less and a peak current value of 30 A or less, A discharge surface treatment method, comprising: forming a film mainly comprising a metal or a metal compound constituting the electrode on the workpiece. A pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the discharge energy causes the coating film made of the electrode material or the electrode material to react with the discharge energy on the workpiece surface. In the discharge surface treatment method for forming the coating film,
A metal powder or metal compound powder having an average particle diameter of 2 to 6 μm containing a metal component that is difficult to carbonize is used as the electrode, and the discharge pulse is discharged under processing conditions of a pulse width of 5 to 100 μs and a peak current value of 30 A or less. And forming a coating mainly comprising a metal or a metal compound constituting the electrode on the workpiece. The discharge surface treatment method according to any one of claims 6 to 8, wherein the metal component that is not easily carbonized is at least one of Co, Ni, and Fe. As the electrodes, “Cr (chromium), Ni (nickel), W (tungsten), Co (cobalt)”, “Mo (molybdenum), Cr (chromium), Si (silicon), Co (cobalt)”, “Cr (Chromium), Fe (iron), Ni (nickel) "," Cr (chromium), Mo (molybdenum), Ta (tantalum), Ni (nickel) ", or" Cr (chromium), Ni (nickel), Mo 9. A powder of a metal compound containing a metal component of (molybdenum), Cd (cadmium) + Ta (tantalum), Ti (titanium), Al (aluminum), Fe (iron) ”is used. The discharge surface treatment method according to any one of the above. As the electrode, “Cr (chromium): 20 wt%, Ni (nickel): 10 wt%, W (tungsten): 15 wt%, Co (cobalt): remaining”, “Cr (chromium): 25 wt%, Ni (nickel): 10 wt%, W (tungsten): 7 wt%, Co (cobalt): remaining "," Mo (molybdenum): 28 wt%, Cr (chromium): 17 wt%, Si (silicon): 3% by weight, Co (cobalt): remaining "," Cr (chromium): 15% by weight, Fe (iron): 8% by weight, Ni (nickel): remaining "," Cr (chromium): 21% by weight, Mo (Molybdenum): 9% by weight, Ta (tantalum): 4% by weight, Ni (nickel): remaining ”, or“ Cr (chromium): 19% by weight, Ni (nickel): 53% by weight, Mo (molybdenum): 3% by weight, Cd (cadmium) + T (Tantalum): 5% by weight, Ti (titanium): 0.8% by weight, Al (aluminum): 0.6% by weight, Fe (iron): the balance ” The discharge surface treatment method according to claim 10, wherein a powder of the metal compound blended at a ratio is used.