JP3668519B2 - Processed liquid for powder mixed electric discharge machining and electric discharge machining method using powder mixed processed liquid - Google Patents

Description

[0001]
[Industrial application fields]
In the present invention, a machining electrode is opposed to a workpiece through a minute gap, and a discharge is performed by applying an intermittent voltage pulse with a working liquid interposed in the gap with a pause time between them. And an electric discharge machining method for machining by applying a machining feed relative to the opposite direction, and the electric discharge machining method includes: In the machining fluid of the above, facing each other through a minute gap, applying an intermittent voltage pulse between them to generate a discharge, along with the relative machining feed in the facing direction, if necessary, the facing direction Drilling or die-sinking electric discharge machining while giving a translational motion feed in a direction perpendicular to the axis, and wire electrodes stretched between a pair of spaced-apart positioning guides using wire electrodes as the machining electrodes. While sending updates to Discharge by applying an intermittent voltage pulse between the two in a state where a discharge gap is formed in the machining liquid in the machining tank with the work piece facing each other at a slight interval from the direction perpendicular to the axis. In particular, a hydrocarbon-based mineral oil is used as a machining fluid that is supplied to the discharge gap, for example, through a wire electric discharge machining that cuts by giving a relative machining feed having a desired contour shape in the perpendicular direction. A so-called oil-based electrical discharge machining fluid containing a conductive or semi-conductive solid powder mixed in a so-called oil-based electrical discharge machining fluid, and a powder mixture containing a new and useful powder as the solid powder The present invention relates to a machining fluid for electric discharge machining.
[0002]
[Prior art]
The powder-mixed electric discharge machining using the above-mentioned machining liquid mixed with a solid powder is basically well known, for example, Japanese Patent Publication Nos. 55-43, 849, 52-26, 357, and Japanese Patent Laid-Open No. 54-159, No. 798 and the like, and it is also possible to use the powder-mixed electric discharge machining as a surface layer treatment or a kind of surface coating on a processed surface of a workpiece, for example, Japanese Patent Publication No. 59-2,746, This is well known as described in Japanese Patent Laid-Open No. 2-83,119 and Japanese Patent Laid-Open No. 3-277,421.
[0003]
Then, the latter powder-mixed electric discharge machining is performed at a high speed in a small area to a large area in the field of the above-described drilling or die-sinking electric discharge machining, and a mirror finishing technique for machining a workpiece surface (JP-A-3-277,421). As well as in the field of wire electric discharge machining (for example, JP-A-6-206,121, 6-320,342). No. publication etc.).
[0004]
And according to the various prior arts described above, various types of powders for the powder-mixed electric discharge machining, for example, according to the above-mentioned JP-A-3-277,421, Silicon, germanium, aluminum or the like, or further, a metal such as tungsten or molybdenum or a compound such as tungsten carbide or zirconium boride, or various semiconductor powders, the average particle size distribution is 5 to 5 The amount added to the kerosene oil-based or water-soluble processing fluid is 10 g / l, and the concentration is 20 g / l. For example, according to JP-A-6-320,342 related to wire electric discharge machining Powder, silicon, carbon, iron, aluminum, copper, silicon carbide, titanium carbide, titanium nitride, silicon oxide powder, etc. 0.1～5Myuemufai, also those which are described as 0.5% to 5% such as the addition mixing amount.
[0005]
However, in any of the above documents, the specific experimental examples and results are mainly carbon (graphite, graphite, C) and silicon (silicon, Si) as powder types. There is a lack of specific verification for various powders, and there is an experimental example that can perform mirror finishing in the above powder. The latter silicon powder was added to and mixed with a hydrocarbon-based oil-based electric discharge machining liquid. In some cases, there is a real upper limit. The amount of silicon powder to be added and mixed is about 0.5 to 3% (about 5 to 30 g / l) in weight ratio and is almost common. In addition to the above, there was considerable variation such as 3 to 30 μm, 10 to 40 μm, and 20 to 40 μm.
[0006]
[Problems to be solved by the invention]
And according to the powder-mixed electric discharge machining using the silicon (Si) powder-mixed machining fluid, the processed surface of SUS304, 13Cr steel, or high-speed steel has no gaps due to a dense silicon thin film or metal alloy film. A highly wear-resistant mirror surface coating having high corrosion resistance and high-temperature oxidation resistance that can withstand the covered aqua regia is formed (Japanese Patent Laid-Open Nos. 62-24,916 and JP No. 2-83,119)), the surface properties or surface characteristics of the surface to be processed are not clear yet, and the development of usage is delayed.
[0007]
For example, a steel material for molds such as SKD61 is processed as a workpiece by electrical discharge machining using Si powder mixed machining fluid, and is processed in order from rough machining conditions to intermediate machining and intermediate finish machining as necessary. After surface imposition to a surface roughness of about 6 μm Rmax and desired shape accuracy, when the powder-mixed electric discharge machining process is performed, the coated surface has a thickness of about 5 to 6 μm and the surface has been finished to a surface roughness of about 0.5 μm Rmax. It is well known that a layer is formed. When the cross section of the processed surface of the workpiece is examined from the surface side for properties, particularly hardness (average of two degrees measurement), as shown in Table 1 below. The surface portion of the coated altered layer is significantly harder and decreases to a value close to the base material hardness as it approaches the base material, and after the base material hardness has once decreased significantly below the base material hardness, especially in the shallow part of the base material A kind of recovery Weak portion is formed from the coating at the thickness of the affected layer is thin in some applications, the mold surface to be polished in some cases, further is that there is a problem in terms of its strength and the like.
[0008]
[Table 1]
[0009]
In Table 1, no. 9 is the hardness of the workpiece base material. 4 is the weak point portion of the base material immediately below the affected layer.
[0010]
For this reason, the present inventors have conducted various experiments and researches on electric discharge machining using a powder-mixed machining fluid, and as a result, the work surface of the work piece has a dense, hard and wear-resistant mirror surface. Is thicker than in the case of electric discharge machining using the silicon powder-mixed machining fluid, and the above-mentioned no. The present invention is proposed by finding a powder-mixed electric discharge machining fluid that does not form a weakened portion having a greatly reduced hardness such as 4 and an electric discharge machining method using the powder-mixed machining fluid. .
[0011]
[Means for Solving the Problems]
The above-mentioned problems are as follows: (1) A processing electrode is opposed to a workpiece through a minute gap, and a pause is placed between the two with a machining fluid mixed with solid powder interposed in the gap. In an electrical discharge machining fluid that is processed by applying an electrical voltage pulse to generate an electrical discharge and relatively machining in the opposite direction, the machining fluid is composed of a hydrocarbon-based mineral oil, By making the mixed solid powder into a powder mixed electric discharge machining fluid comprising a silicide, (2) the above-mentioned problem is that when M is a metal element and Si is a silicon element, the silicide is MSi.₂(3) Further, the above-described problem is that the metal element M constituting the silicide is a chromium element (Cr). By using the powder mixed electric discharge machining fluid as described in (1) or (2) above (4), the above-mentioned problem is that the size of the silicide powder is 0.5 to 15 μmφ, preferably 1 to 10 μmφ. More preferably, by using the powder mixed electric discharge machining fluid according to (1), (2), or (3) of 1.5 to 8 μmφ, (5) In the above (1), (2), (3) or (4), the amount of the compound added to the processing fluid is 3 to 50 g / l, preferably 4 to 35 g / l, more preferably 5 to 25 g / l. Achieved better by using the powder mixed EDM machining fluid It is intended to be.
[0012]
(6) Further, the above-mentioned problem is that a machining electrode is opposed to a workpiece through a minute gap, and a rest time is set between the two in a state where a machining liquid mixed with solid powder is interposed in the gap. In an electric discharge machining method in which electric discharge is generated by applying intermittent voltage pulses and machining is relatively applied in the facing direction, the machining liquid is obtained from a hydrocarbon-based mineral oil-based electric discharge machining liquid. And the mixed solid powder has an average particle diameter of 0.5 to 15 μmφ, preferably 1 to 10 μmφ, and M is a metal element Ti, V, Cr, Zr, Nb, Mn, Mo, Fe, Co, W, or MSi composed of Ni₂This type of silicide powder is added to and mixed with the mineral at a rate of 3 to 50 g / l, preferably 4 to 35 g / l. Electrical machining conditions such as voltage pulse that finishes machining surface roughness and dimensional / shape accuracy as desired using electrical discharge machining fluid. Electrical discharge machining in two or more steps that can be switched sequentially such as rough machining, medium machining, and finishing machining. A powder-mixed working fluid comprising: a step of electric discharge machining using a powder-mixed processing fluid having a glossy surface finish on a processing surface whose electrical processing conditions are finished to the desired processing surface roughness and dimensional shape accuracy. By adopting the electric discharge machining method to be used, (7) the above-mentioned problem is that the electric discharge machining causes the rod-like / general die-shaped machining electrode to be processed in the machining liquid in the machining tank. Opposing each other through a minute gap, both Electric discharge is generated by applying intermittent voltage pulses to the surface, and drilling or die-sinking electric discharge machining is performed while providing a relative machining feed in the opposite direction and a translational movement feed in a direction perpendicular to the opposite direction as necessary. By adopting the electric discharge machining method using the powder-mixed machining fluid as described in (6) above, (8) and the above-mentioned problem is the voltage for finishing the workpiece to a desired machining surface roughness and dimensional / shape accuracy. The electrical machining conditions such as pulses are set to the condition that the machining electrode is low consumption, preferably no consumption, in the electric discharge machining stage of two or more steps that are sequentially switched such as rough machining, medium machining, and finishing machining. By using the electric discharge machining method using the powder-mixed machining liquid according to (6) or (7), (9) or the above-mentioned problem is that the workpiece has a desired machining surface roughness and Finish with dimensional and shape accuracy Gloss is applied to the machined surface where the voltage applied polarity is reversed in two or more electrical discharge machining stages where electrical machining conditions such as voltage pulses are switched sequentially, and the surface roughness and dimensional / shape accuracy are finished as desired. By adopting the electric discharge machining method using the powder mixed machining liquid according to (6), (7), or (8), wherein the voltage application polarity at the stage of powder mixed electric discharge machining for surface finishing is positive. (10) The above-described problem is that the electrical machining conditions at the stage of powder-mixed electrical discharge machining of the glossy surface finish on the workpiece processed surface finished with the desired processed surface roughness and dimensional / shape accuracy are The power supply line between the voltage pulse source and the discharge gap is selected as a low-capacitance power supply line, and a parallel circuit of an inductance ring and a resistor is inserted in series, and a discharge having an amplitude of 2 to 8 A with a pulse width of 2 to 5 μs. pulse Set the as supplied (6), (7), by a discharge machining method using a powder mixing process solution according to (8) or (9), is better achieved.
[0013]
(11) Further, the above-described problem is that the electric discharge machining uses a wire electrode as the machining electrode, while the wire electrode stretched between a pair of spaced positioning guides is updated and fed in the axial direction. In a state where a discharge gap is formed in the machining liquid in the machining tank with the workpieces facing each other at a slight interval from the direction substantially perpendicular to the axial direction, an intermittent voltage pulse is applied between the two to cause discharge. It is also achieved in the electric discharge machining method using the powder mixed machining liquid according to (6), which is wire electric discharge machining that is generated and cut by applying a relative machining feed of a desired contour shape in the perpendicular direction. Is.
[0014]
[Action]
The powder-mixed electrical discharge machining fluid of the present invention has the above-described configuration, so that it has a glossy mirror-like coated alteration layer with a fine surface roughness of 1 μmRmax or less from a narrow machining area to a wide machining area. Is sufficiently thick compared to the case of electrical discharge machining using a conventional silicon powder-mixed machining fluid, and the altered coating layer is formed in a state where no weak point portion such as a decrease in the hardness of the base material is generated in the base material portion immediately below. In addition, it is useful as a powder mixed electric discharge machining fluid for electric discharge machining finishing of various molds and parts because the above-mentioned thick coated alteration layer has high hardness, abrasion resistance and corrosion resistance.
[0015]
Moreover, according to the electric discharge machining method using the powder-mixed machining fluid of the present invention, in the electric discharge machining using the powder-mixed electric discharge machining fluid, a desired high hardness on the workpiece surface of the workpiece. A thick, glossy, mirror-like coated alteration layer can be reliably and desirably formed.
[0016]
【Example】
FIG. 1 is an explanatory diagram of an embodiment of a power supply circuit for machining mainly for finishing for drilling or die-sinking electric discharge machining when the electric discharge machining method of the present invention is carried out in the drilling or die-sinking electric discharge machining method. 1 is a mold electrode for drilling or engraving such as copper or graphite, 3 is a workpiece attached to a work stand 4 placed in a machining liquid in a machining tank 20, and 21 is the machining liquid. The processing tank 20 and the processing liquid are supplied so that a powder mixed processing liquid, which will be described later, is circulated and supplied between the processing tank 20 and the processing liquid circulation supply device 22 so that the mixed powder does not precipitate and accumulate and the mixed powder concentration does not change. The supply device 22 is provided with stirrers 23 and 22A, respectively, and the filter for separating and removing the processing waste in the processing liquid is an appropriate circulatory path, or the processing waste of the workpiece 3 and is usually a ferromagnetic material. Processing scrap Magnetic adsorber 22B of the magnetic adsorptive separation are those provided at an appropriate position in 択的.
[0017]
Thus, the electrode 1 is opposed to the workpiece 3 in the powder-mixed electric discharge machining liquid in the machining tank 20 through a minute gap, and an intermittent voltage pulse with a pause time therebetween is provided. Is applied to generate a discharge and a machining feed by relative normal servo control in the opposite direction is given, and if necessary, a relative feed different from the servo-controlled machining feed is applied to the electrode or workpiece during machining. Drilling or die-sinking electric discharge machining is performed while intermittent reciprocating motions such as close separation are intermittently performed and / or further, translational motion in a direction substantially perpendicular to the facing direction is applied.
[0018]
Reference numeral 5 denotes the intermittent voltage pulse supply circuit, which is an intermittent second voltage pulse supply circuit 6 that supplies a voltage pulse with a small current capacity at a voltage higher than the normal processing voltage pulse. The voltage pulse supply circuit 8 is provided in parallel, and the processing current increasing circuit used in the above-described processing under the so-called rough machining conditions, the middle machining step, etc. is not shown.
[0019]
Thus, the normal processing voltage pulse supply circuit 6 is variable from about 60 to 260 V. For example, the DC voltage source 6 A normally used as a substantially constant voltage of about 80 V and the current capacity are used. Conventionally the most conventional circuit comprising a series circuit of a plurality of electronic switching elements 6B such as MOS-FET transistors connected in parallel, a switchable current limiting resistor 6C such as about 100Ω, and a reverse voltage preventing rectifier 6D. An intermittent voltage pulse generation and supply circuit 6, which is preferably a low-capacitance power supply line such as a single wire or a fuel wire by the changeover switch 9 and its contacts 9A and 9B in the roughing process and the intermediate processing process. The low-inductance feed line 10A such as a coaxial cable is selectively switched from 10B to the discharge gap between the electrode 1 and the workpiece 3, and the intermittent voltage pulse is It generated desired control of the switching element 6B by pulse controller 7.
[0020]
That is, the control device portion of the switch device 6B of the control device 7 includes a constant ON time signal τON and an OFF time that are selected and set in advance, except when the switch device 6B is controlled to be changed by the discharge state detection signal of the discharge gap. When a voltage pulse is generated and supplied by repeating the signal τOFF alternately and regularly, and the discharge start delay until the discharge starts after the voltage pulse is applied to the discharge gap after the voltage pulse is applied to the discharge gap. Increases as a function of period, that is, starts measurement of the on-time signal from the start of discharge in the discharge gap after the start of voltage pulse application, so that the discharge duration of each discharge pulse is set to a constant value, and switches on when measurement is completed. There is one that controls the element 6B to be turned off and shifts to the off time. In the following description, the latter case will be mainly described. In addition, the present invention is not limited to this. Further, the contacts 9A and 9B of the changeover switch 9 for switching between the feeding lines 10A and 10B are provided only on one side of both the positive and negative feeding circuits, and the other side feeding line 10B is always used as one of the low inductance feeding lines 10A. It is also possible to have a connected configuration.
[0021]
The second voltage pulse supply circuit 8 is another voltage pulse supply circuit comprising a series circuit of a variable DC voltage source 8A, a switch element 8B, a current limiting resistor 8C, and a reverse voltage prevention rectifier 8D. The second voltage pulse supply circuit 8 is used as desired by the open / close switch 8E. For example, the DC voltage source 8A is about 80 to 260 V of the DC voltage source 6A having a constant normal output voltage. On the other hand, it is variable and has a voltage value of about 100 to 350 V, for example, about 150 V or 280 to 300 V, which is equal to or greater than that. The current limiting resistance 8C is a large setting for the resistance 6C, for example, about 1 kΩ, and the current capacity of the circuit 8 And the switch element 8B is applied by the pulse control device 7 prior to the voltage pulse application, for example, as the switch element 6B is turned on / off synchronously or cut off. Thus, the average machining voltage of the gap is controlled by, for example, controlling the voltage application to be cut off by detecting the start of discharge in the discharge gap and the on-off of the switch element 6B by turning off the switch element 8B. This is a secondary power supply that promotes the start of discharge by increasing the voltage and facilitates the servo control operation by detecting the gap voltage to maintain stable machining, and is not essential for the implementation of the present invention.
[0022]
The intermittent voltage pulse supply circuit 5 as described above is preferably a twisted wire or a single wire from the low-inductance feeder 10A by the changeover switches 9, 9A, 9B when finishing the glossy surface formation of the present invention. The low-capacitance power supply lines 10B and 10B are switched to be connected to the discharge gap. The present invention further includes an inductance for shaping the waveform of the supply discharge pulse discharge current from the voltage pulse supply circuit 5 in the connection discharge circuit. A parallel circuit of the wire ring 11 and the resistor 12 is inserted in series by opening the contact 13 </ b> A of the open / close switch 13. A reflux circuit 14 is connected in parallel to the output terminal of the voltage pulse supply circuit 5 by closing the contact 13B of the opening / closing switch 13. The reflux circuit 14 is composed of a series circuit of a rectifier 14A and a resistor 14B, and finishes the glossy surface. Therefore, the processing conditions of the discharge current pulse set in the voltage pulse supply circuit 5, for example, the ON time during which the current flows through the switches 6B and 8B for supplying the discharge current pulse is 1 to 5 μs, and the set current amplitude is The pulse current of 2 to 8 A is reduced by the resistor 12 and is smoothed by suppressing the rise of current by the inductance wire ring 11, and at that time, part of the energy of the discharge current is transferred to the wire ring 11 as electromagnetic energy. After the switches 6B and 8B are turned off and the supply of the discharge power is stopped, the discharge is stopped without stopping the discharge. The accumulated energy of the wire 11 is discharged to the discharge circuit through the machining gap and the reflux circuit 14 to extend the discharge pulse, and the discharge circuit, in response to the set discharge current pulse condition in the voltage pulse supply circuit 5, That is, the pulse width of the discharge current pulse that actually flows through the machining gap is as long as twice or more of the setting condition 1 to 5 μs, and the discharge current amplitude is as low as 1/2 or less of the setting condition 2 to 8 A except for the rising portion. The discharge current pulse is used (note that the processing conditions and the like are detailed in, for example, Japanese Patent Publication No. 60-3932).
[0023]
The finishing process for forming the glossy surface by using the powder-mixed processing liquid, which is the final finishing process described above, is performed by so-called positive processing using the workpiece 3 as the positive electrode and the electrode 1 as the negative electrode. In processing steps such as roughing, intermediate processing, and intermediate finishing prior to the processing step, the powder-mixed processing fluid in the final finishing processing step may be used as it is as the processing fluid, but drilling, die-sculpting, etc. In the machining using the mold electrode 1, the polarity switch 24 required for setting the machining conditions for low or no wear of the electrode is connected to the output of the voltage pulse supply circuit 5 in order to avoid wear deformation of the mold electrode 1. It is provided between the partial discharge gaps, and in the machining step such as rough machining, the polarity switch 24 is used to switch the reverse polarity with the electrode 1 as the positive electrode and the workpiece 3 as the negative electrode.
[0024]
The present invention has an important point in the kind of the powder mixed in the powder-mixed processing liquid 21, and the present invention uses a silicide powder as the powder, and The silicide powder is preferably MSi in which M is composed of the metal element Ti, V, Cr, Zr, Nb, Mn, Fe, Mo, Co, W, Ni, or the like.₂So-called oil-based electric discharge machining of a hydrocarbon type at a rate of 3 to 50 g / l, preferably 4 to 35 g / l with an average particle size of 0.5 to 15 μmφ, preferably 1 to 10 μmφ. It is added to the liquid and mixed.
[0025]
Thus, the silicide is a compound of silicon and an element that is more electrically positive than that, and usually refers to a binary compound with a metal. M, which has properties and does not necessarily satisfy the valence, and is a compound with Li, Cu, Cr, Ni or the like₃M which is a compound with Si type, Ca, Fe, Co, Ni or the like₃Si₂M which is a compound with a mold, Cr, Mo, W, Ni or the like₂Si₃MSi which is a type or a compound such as Co₃There are types, but usually the above-mentioned MiSi₂Mold and this MSi₂MSi type and M to make the same metal and compound as the type₂Si type is easily available. And these silicides are generally hard and brittle and can be easily crushed. Lithium and alkaline earth metal silicides interact with water and hydrolyze with dilute acid to give silane, In addition to generating hydrogen, etc., it has strong resistance to chemicals, and calcium silicide is converted to siloxane (Si by the action of hydrochloric acid.₆O₃H₃) Is difficult to oxidize, and the low silicide has high heat resistance.
[0026]
For this reason, some metal silicide powders are used as heat- and oxidation-resistant ceramic materials, and MoSi has high oxidation resistance.₂Is used as a high-temperature heater in the atmosphere, and the MSi has a relatively low melting point.₂The type is not the length used for oxidation-resistant surface coating or the like by low-pressure plasma spraying or the like, but is also used for sintering or particle-dispersed composite materials.
[0027]
Among these silicides, as additive powder useful as a working fluid composition for powder-mixed electrical discharge machining of the present invention, MSi is relatively easily available.₂Mold silicides, especially TiSi₂, ZrSi₂, NbSi₂, TaSi₂, CrSi₂, MoSi₂Or WSi₂Table 2 below shows approximate values of some of the physical constants of the silicides.
[0028]
These silicides can be obtained by direct combination of the constituent elements, by reducing silicon dioxide with excess metal, or by reducing silicon dioxide and each metal oxide with carbon at high temperature. In addition, a product obtained by sieving coarse particles having a particle size of approximately 6 to 12 μmφ and fine particles having a particle size of approximately 2 to 5 μmφ is commercially available.
[0029]
[Table 2]
[0030]
Next, the present invention will be described with specific experimental examples.
Workpiece Material SKD61
Electrode Material Copper
Dimension 40mmφ
Machining fluid
Type Hydrocarbon oil (3rd class 4th class petroleum)
Viscosity 1.885 cSt / 40 ° C
Flash point 100 ° C
Total oxidation 0.01
Specific gravity 0.7629g / cm³
Processing liquid mixed powder
Particle size and impurity composition
[0031]
[Table 3]
[0032]
In Table 3 above, TiSi₂, CrSi₂, MoSi₂And WSi₂Each of about 5 μmφ powder was added and mixed at various ratios in the above-mentioned machining liquid and processed under various electric discharge machining conditions, and the above-mentioned CrSi which seems to be a combination consistent with the selected machining conditions₂The best processing results are obtained when using the powder, then the WSi₂Powder and MoSi₂The order was powder. Table 4 below shows the CrSi as a powder.₂These are various processing conditions and data other than those described above when processing using a combination of the electrode and the workpiece using powder.
[0033]
[Table 4]
[0034]
In Table 4, the voltage pulse source (6) corresponds to the voltage pulse supply circuit 6 shown in FIG. 1, and the voltage pulse source (8) corresponds to the voltage pulse supply circuit 8, respectively. Electrode reduction value is -0.4 (one side), electrode jumping and translational motion (orbit type) are used in combination. Processing time is 150 minutes. ) And (2), after the rough machining (2) is completed, the electrode is replaced with an electrode with an electrode reduction value of −0.15 (one side). Consuming, electrode jumping and translational movement are used together, and the machining feed length for each machining process is the intermediate machining (3) and finishing machining (4) and (5) up to the fifth machining process. Therefore, the processed surface of the work piece can be mirror-finished or can be subjected to imposition for realizing it. A processing step, the processing surface are those which are finished to a surface roughness of about 10MyumRmax. Then, normally, the processing up to the fifth processing step is finished with the above-described surface roughness, the target shape and dimensional accuracy, and the next glossing processing is started. Moreover, since the discharge energy and density of each discharge pulse is large until this machining step, the process of excavating proceeds without causing the adhesion residual phenomenon to the processed surface of the mixed powder material etc. In order to avoid the problem, the powder mixed machining fluid may be used from the rough machining (1), but the machining may be performed with a normal oil-based electrical discharge machining fluid until the finishing machining (5).
[0035]
And the post-processing liquid of the said process process (5) is silicate silicide (CrSi).₂) And an oil-based electric discharge machining fluid mixed with 6 g / l of about 5 μmφ size powder, the polarity of the machining voltage is switched to the positive polarity by the polarity switch 24, and the power supply line from the voltage pulse supply circuit 5 is switched to the switches 9, 9 A, 9B switches the low-inductance power supply line 10A to the low-capacitance power supply line 10B, sets the energy of the supply discharge pulse to a pulse width of about 2 to 5 μs and a current amplitude of about 2 to 8 A, and opens and closes the contacts 13A and 13B of the switch 13 respectively. Then, the finishing operations (6) and (7) for glossing are performed for 15 minutes each under the conditions described in Table 4 so that the waveform shaping circuits 11 and 12 and the reflux circuit 14 function. Therefore, the finished surface has a mirror surface with a surface roughness of about 0.7 μm Rmax, and the processed surface has a thickness of about 6-8 μm. An overlying alteration layer was formed.
[0036]
Table 5 shows the silicified chrome (CrSi₂) As a result of the above-mentioned silicon powder mixing processing, the properties, particularly hardness, of the coating altered layer formed on the processed surface of the workpiece and the workpiece base material in the vicinity of the formed portion by electric discharge machining using the powder mixed machining fluid No. 1 shown in the same manner as in Table 1 of No. 1 on the inner side of the base material further than the joint portion between the coated altered layer and the base material. 6 and no. 7 has a portion whose hardness is slightly lower than that of the base material itself, but is not so weak as to be a weak point portion, and is high over the entire coated altered layer portion formed as described above. The hardness is maintained and it is promising as an electric discharge machining die and parts.
[0037]
That is, the electric discharge machining surface as in the present invention, and the mirror-like surface formed on the machining surface by electric discharge machining using such a powder-mixed machining fluid are resistant to the machining surface due to the presence of the altered layer. Although it is superior to corrosivity, according to the salt water injection test, the red rust on the processed surface using the powder-mixed processing liquid was removed by light friction with a cotton swab to restore the original gloss, but chromium silicide (CrSi₂) No particular superiority was observed in the above-mentioned test example of contamination.
[0038]
However, in small-area machining with electrode copper 20 mmφ, the processed surface of the workpiece is finished to a certain processed surface roughness, for example, about 7 μm Rmax, and then polished for about 10 to 15 minutes with the powder-mixed processing liquid. The wear length in the processing feed direction at the tip of the electrode is about 10 μm in the case of silicon powder, and about 3 μm in accordance with the above experimental example, and titanium carbide is (TiC) and chromium carbide (Cr₂C₃) It tends to be less than about 4 μm when using powder, and is equivalent to about 3 μm when using tungsten carbide (WC) powder. Further, since the electrode consumption is small, the dimensional accuracy can be accurately processed, and the processed surface can be subsequently applied, so that there is an advantage that good shape accuracy can be easily obtained.
[0039]
In addition, regarding the roughness of the machined surface, there is still a problem of insufficient search for suitable machining conditions, but chromium silicide (CrSi₂) Is silicon (Si) and chromium carbide (CrC)₃), But tend to be superior to titanium carbide (TiC) and tungsten carbide (WC). Also, the hardness of Table 5 shows the maximum value of the surface. Liquid: 824HV, silicon (Si): 885HV, titanium carbide (TiC): 914HV, tungsten carbide (WC): 946HV, chromium carbide (Cr₂C₃): 982HV, and chromium silicide (CrSi)₂): A value of 1018 HV is also obtained, which is promising.
[0040]
[Table 5]
[0041]
Silicided chrome (CrSi) to be mixed with machining fluid₂)), It is necessary to select a certain level of change depending on the magnitude of the discharge energy per discharge pulse in the machining process and its waveform characteristics. As long as it is performed by setting the processing conditions as described, it is preferably 0.5 μmφ or more at which the coated altered layer can be formed as desired, and 15 μmφ or less that does not give an obstacle such as a pseudo short circuit to the processing state. Is preferably selected from 1 to 10 μmφ, more preferably from 1.5 to 8 μmφ, and the amount of added mixture to the oil-based electric discharge machining fluid is slightly affected by the size of the powder particles, but the coated altered layer is formed as desired. It is necessary to be at least 3 g / l or more, and on the other hand, the maximum addition amount needs to be 50 g / l or less, in which a defective discharge state starts to appear in the processed state, preferably 4 to 35 g. / L, more preferably 5 to 25 g / l is added and mixed and processed while stirring. Depending on the type of powder to be added and mixed, for example, tantalum silicide (TaSi)₂) Or tungsten silicide (Wolfram, WSi)₂In the case of a high specific gravity powder such as), it seems that at least the powder must be refined or added in a larger amount than described above.
[0042]
Table 6 shows the detailed processing conditions and processing data when processing a SKD61 workpiece using a 100 mm × 100 mm large surface copper electrode as the processing electrode. The processing conditions according to Table 4 are the same.
[0043]
In Table 6, machining steps (1) and (2) are rough machining for about 150 minutes, and machining steps (3), (4) and (5) are intermediate finishing to finishing machining for a total of about 240 minutes. Then, the processed surface is finished and roughened to a processed surface roughness of about 15 μm Rmax. In the processing step (6), in the same manner as in the processing steps (5) and (6) of Table 4 above, The voltage polarity, waveform shaping circuit, etc. can be switched and selected, the processing conditions can be switched, the glossing processing can be performed for about 60 minutes by timer processing, and the processing surface can be made into a mirror surface with a roughness of about 0.9 μm Rmax. The deteriorated coating layer was formed in substantially the same manner as in the experiment of Table 4 above, and the surface properties and the like thereof were substantially the same as in Table 5 above.
[0044]
[Table 6]
[0045]
In addition, although the present inventors have proposed to use carbide powder, particularly fine powder of titanium carbide (TiC), in the case of wire electric discharge machining, as powder particles for electric discharge machining using a powder-mixed machining fluid. In the case of the titanium carbide powder, the hardness of the outermost layer portion of the coated altered layer is much higher and the electric conductivity is higher, or the coated altered layer formed is generally thinner than in the case of Si powder. The hardness characteristics from the surface layer to the inner base material tend to be almost the same as those in the case of the Si powder-mixed working fluid shown in Table 1 above. The 4-5 portion has a low-hardness portion of about 1/2 of the base material hardness, and there are limitations on applications, etc., but the present invention overcomes the above-mentioned drawbacks.
[0046]
Further, the above-described machining fluid for electric discharge machining of the present invention of the present invention can be applied also to so-called wire electric discharge machining using a wire electrode that is renewed and guided in the axial direction as a machining electrode. The following patent application previously proposed by the present inventors as a machining liquid in which titanium carbide (TiC) fine powder is added and mixed as the powder and a wire electric discharge machining method using the machining liquid.
Reference number P95-004
Application date February 2, 1995
Application No. 1995 Patent Application No. 51673
Title of Invention Electric discharge machining method using powder mixed working fluid and powder mixed electric discharge machining fluid
It is recommended to use the power supply circuit for electric discharge machining similar to FIG. 1 of the present invention shown in FIG. 1 and the circuits shown in FIG. 2 and FIG. May be controlled so as to maintain a smooth discharge with a rise of 2 to 4 μs and an amplitude of 2 to 4 A.₂As a powder of chrome silicide (CrSi)₂) Is not required to be as fine as the previously proposed titanium carbide (TiC), and it can be polished with a powder mixed working fluid having an average particle size of about 1 μmφ.
[0047]
【The invention's effect】
The powder-mixed electrical discharge machining fluid of the present invention has the above-described configuration, so that it has a glossy mirror-like coated alteration layer with a fine surface roughness of 1 μmRmax or less from a narrow machining area to a wide machining area. Is sufficiently thick compared to the case of electrical discharge machining using a conventional silicon powder-mixed machining fluid, and the altered coating layer is formed in a state where no weak point portion such as a decrease in the hardness of the base material is generated in the base material portion immediately below. In addition, since the thick coating-modified layer has high hardness and abrasion resistance, it is useful as a powder mixed electric discharge machining fluid for electric discharge machining forming finishing of various molds and parts.
[0048]
Moreover, according to the electric discharge machining method using the powder-mixed machining fluid of the present invention, in the electric discharge machining using the powder-mixed electric discharge machining fluid, a desired high hardness on the workpiece surface of the workpiece. A thick, glossy, mirror-like coated alteration layer can be reliably and desirably formed.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of an embodiment of a power supply circuit mainly for finishing, which performs an electric discharge machining method of the present invention.
[Explanation of symbols]
Type 1 electrode
3 Workpiece
4 Workstand
5 Voltage pulse supply circuit
6, 8 First and second voltage pulse supply circuits
6A, 8A DC voltage source
6B, 8B Electronic switch element
6C, 8C current limiting resistor
6D, 8D Reverse voltage prevention rectifier
7 Control device
8E Open / close switch
9, 9A, 9B selector switch and switching contact
10A low inductance feeder
10B low capacitance feeder
11 Inductance wire ring (waveform shaping circuit)
12 resistors
13, 13A, 13B Open / close switch and open / close contact
14 Reflux circuit
14A rectifier
14B resistor
20 Processing tank
21 Powder mixed processing fluid
22 Processing fluid circulation supply device
22A, 23 Stirrer
22B Magnetic adsorption body
24 polarity switcher

Claims (3)

Applying an intermittent voltage pulse with a processing time in which the processing electrodes are opposed to each other through a minute gap and a working liquid mixed with solid powder is interposed in the gap, with a pause between them. In the machining fluid for electric discharge machining that generates electric discharge and performs machining by applying a machining feed in the opposite direction, the machining fluid is made of hydrocarbon mineral oil, and the mixed solid powder is made of silicide. A powder mixed electric discharge machining fluid characterized by comprising: The powder mixed electric discharge machining fluid according to claim 1, wherein when M is a metal element and Si is a silicon element, the silicide is a MSi ₂ type compound. Apply an intermittent voltage pulse with a pause between the workpiece electrodes facing each other through a minute gap with a machining fluid mixed with solid powder in the gap. In the electric discharge machining method of generating electric discharge and machining by giving a machining feed relatively in the facing direction,
Together with the working fluid consists of mineral oil-based EDM fluid of hydrocarbon, the mixed solid powder average particle size of 0.5 to 15 m phi, M is a metal element Ti, V, Cr, Zr, Nb, Mn MSi ₂ type silicide powder consisting of Mo, Fe, Co, W, or Ni, added to and mixed with the mineral oil at a rate of 3 to 50 g / l. The electrical processing conditions such as the above-mentioned voltage pulse that finish the desired surface roughness and dimensional / shape accuracy using a liquid or non-powdered oil-based electrical discharge machining fluid are sequentially applied, such as rough machining, medium machining, and finishing machining. Stages of electric discharge machining with two or more processes to be switched, and stages of electric discharge machining using powder-mixed machining liquid for glossy surface finishing on the machining surface whose electrical machining conditions are finished to the desired machining surface roughness and dimensional shape accuracy It is characterized by consisting of An electrical discharge machining method that uses powder mixed machining fluid.

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