JPS599294B2 - What's going on? - Google Patents

Description

[Detailed description of the invention] Conventionally, electrical discharge machining using a dielectric liquid such as kerosene as a medium is well known, but machining using this method has many effects such as control of machining gap, removal effect of machining debris, and arc switching speed. Although it is not impossible to obtain a finished surface roughness of 10 μRmax or less, it is extremely difficult.

Therefore, in the past, methods such as mechanical lapping or chemical or electrochemical polishing have been used after this electrical discharge machining, but these methods have the drawback of being inefficient due to slow machining speeds. From this point of view, the present invention is particularly designed for finishing electric discharge machining, in which the electrode and the workpiece are placed opposite each other in a reduced pressure atmosphere, which allows for easy finishing to about 0.5μRmax, and the machining is performed by applying electric discharge to the opposing gap. By changing the product p-d value of the atmospheric pressure p and the discharge gap length d and controlling the ratio of the ion machining action and the electronic machining action, it is possible to perform any processing from rough machining to super finishing. It is characterized by the following. In a reduced pressure atmosphere below atmospheric pressure, if discharge is repeated between electrodes facing each other in the discharge gap, one of the electrodes will be extremely worn out, but this wear will occur on the Θ pole side and the + pole will not wear out. Utilizing this phenomenon, the electrode is set to 100%, and the workpiece is set to the H pole for electrical discharge machining.

This discharge phenomenon in a reduced pressure gaseous medium follows Passien's law Vs-f (p-d) in which the dielectric breakdown voltage Vs is uniquely determined by the product of the atmospheric pressure p and the gap length d.

This relationship is as shown in FIG. 1 if the electrode materials and areas are kept constant and areas other than the opposing areas are strictly insulated. p-d on the horizontal axis is shown in units of Torr*my, p
"d21~2Torr-C7rL shows the lowest value with the lowest discharge starting voltage, and around this value ×102~×10T
orr. In the lowest value range of the acclimatization level, the curve is relatively flat and the discharge starting voltage is low (IKV or less), but beyond this range, the discharge starting voltage suddenly decreases regardless of whether the p-d value increases or decreases. increases and becomes difficult to discharge. This is because when the p-d value increases beyond the above-mentioned minimum range, the discharge gap widens and the mean free path becomes shorter as the pressure approaches atmospheric pressure, causing acceleration of electrons due to the electric field and impact ionization. Even if the p-d value is too low, that is, assuming the d value is constant, if the atmospheric pressure p drops too much, the mean free path is too long, so the number of collisions between the electrons will increase. It is said that this is because impact ionization becomes inactive again as the amount decreases. Another feature is that under a constant pressure, the smaller the gap length d, the less likely the discharge occurs, a phenomenon that is not seen in liquids or in the atmosphere. Therefore, in the present invention, preferably this p-d value is ×10-2 to ×10Torr-
By setting and controlling the atmospheric pressure and the discharge gap d so as to be in the CTrL range, the discharge pressure is lowered to perform electric discharge machining in an easy discharge state.

Note that this d value and p value are as follows: In actual processing machines, d is several 10C.
rfL or less is used, and when the p value approaches the atmospheric pressure of 100T0rr or more, there is oxidation of the anode and coating of the anode metal on the cloud electrode, and in this temperature and pressure range, one of them is N2 etc. on the machined surface. p is preferably 100T0 to prevent abnormal temperature rise and white nitriding phenomenon.
rr or less is practical. And like this p−d=×
By setting and controlling the discharge conditions to 10-2~×10T0rr-I, I can not only lower the discharge starting voltage, but also improve the discharge cut-off and the 0N. 0FF occurs instantaneously.

For example, when the vacuum gap was kept constant at 1.40]11 and the pressure was changed from 750 to 10@-5 T0rr, the discharge formation time was experimented, and the results shown in FIG. 2 were obtained.
The horizontal axis shows the discharge formation time when the voltage is applied and the discharge starts, and the vertical axis shows the load voltage. According to this relationship, 1T0rr (
1.4×10] TOrr-? ), it takes only a very short time of 2 to 3 μS for discharge to form, but at
rr (1.4×10-3T0rr・Cm) is 10
It can be seen that a long time of up to 0 μS is required.

Therefore, from this point of view as well, it is necessary to control the settings of the atmospheric pressure p and gap d, and it is important to set p and d to the conditions where the discharge starting voltage is the lowest. As a result, high-speed machining with a high discharge repetition frequency becomes possible. The present invention is based on such a practical p-d value range (x101 to x10T0rr-CTn), and performs any process from rough machining to finishing machining by changing this p-d value. It is something.

That is, the minimum value of the p-d value curve is 1 to 2T0rr-Cm, and if it is larger than this (1 to 10T0rr-Cm),
Machining is performed on the discharge surface consisting of a collection of craters, accompanied by discharge craters, and this machining is mainly based on the ion effect, and as the p-d value increases, the size of the craters also increases proportionally. Processing is performed. And the p
-When the d value is at its lowest value of 1 to 2T0rr-I, a pulse discharge is formed and the discharge point is dispersed and moves over a wide range, but the spark is small and the crater is also small. Small value (10-2~1T0rr-C
m), a dilute and extremely dispersed discharge (close to a glow discharge) can be seen. According to this electric discharge, the machining surface of the (d) side workpiece is machined with minute craters of atomic size, and in this range, the electronic machining effect mainly due to the action of electrons is 0.1 to 1
Super finishing processing of approximately μRmax is performed.

Therefore, the present invention changes the ratio of the ion processing action and the electronic processing action by controlling one or both of the air pressure p and the gap length d to change the product p-d value and perform any desired processing. The purpose is to perform machining based on surface roughness.

The present invention will be described below with reference to an embodiment of the drawings. In Fig. 3, 1 is a processing tank whose interior is kept airtight, 2 is a workpiece inserted into this tank, 3 is an electrode, and the workpiece is 2 is attached to the processing table 4, and the electrode 3 is attached to a support spindle 5 inserted into the tank 1 from the outside via a vacuum bellows or the like.
Fixedly supported.

6 is an NC control device that feeds the electrode and the workpiece, and 1i. X and Y axis feed motors 7 and 8 are provided and are controlled by an NC device 6.

Reference numeral 10 denotes a machining pulse power source that generates a pulse discharge between the electrode 3 and the workpiece 2, which is configured by charging and discharging a pulse capacitor, and is also configured by on/off switching control of a semiconductor switch such as a transistor. Any suitable circuit arrangement may be used, such as one adapted to generate pulses.

11 is a vacuum pump that evacuates the processing tank 1 under reduced pressure.

The inside of the machining tank 1 is evacuated by a vacuum pump 1, and an electrode 3 is placed in this reduced pressure gas medium, facing the workpiece 2, and a pulse voltage supplied from a power source 10 is applied to this gap to repeatedly generate electric discharge for machining. is similar to conventional submerged electrical discharge machining.

While the atmospheric pressure d in the processing tank 1 is controlled by the vacuum pump 11, the Z-axis feed control of the electrode 3 is performed by the motor 9, and the p-d value is from x10-2 to x10T0rr-
? Ion bombardment processing is performed by controlling the p-d value to a large extent by adjusting either or both of the air pressure p and the gap length d within this range. By controlling the p-d value to a small value, it is possible to perform high-speed machining with large craters, and by controlling the p-d value to a small value, it is possible to perform super-finishing machining with fine craters caused by electronic machining.
The p-d value can be easily finely adjusted by controlling and feeding the electrode 3 using the motor 9 while keeping the atmospheric pressure constant, and machining can be easily performed under any conditions depending on the purpose of machining. can. Further, the workpiece 2 is moved through the opposing part of the electrode 3 under NC control of the processing table 4, but since the opposing gap d changes depending on the machining shape of the workpiece 2, the spindle 5 is controlled at the same time. also do
It is possible to control the p-d value set at constant intervals so that it does not change, and to machine the entire machined surface of the workpiece with a constant surface roughness. Although not shown, when changing the machining conditions (changing the p-d value) by finely adjusting the atmospheric pressure p, a gas nozzle is opened in the gap, and the inside of the machining tank 1 is brought to a high vacuum by the pump 11. After exhausting the air, the air pressure can be controlled by supplying gas through the nozzle.
This allows the p-d value to be controlled to change.

Further, processing can be performed with any gas present in the discharge atmosphere. As described above, the present invention controls the ratio of the ion machining action and the electronic machining action by changing the p-d value by controlling the change in the discharge gap d, making it easy to perform everything from rough machining to finishing machining. Yes, 0.5~1μR
Super-finishing to the maximum level can be easily achieved.

Also, the p-d value is 10-2 to 10T0rr-? By machining within the range of 350 to 1000, it is possible to process the discharge voltage at a low voltage of about 350 to 1000, and by using a pulse for the power supply, it is easy to control the discharge position, and the movement and dispersion of the discharge point is easy. It also has unique effects such as the ability to change and control discharge energy and discharge large amounts of power. Pulse width is 0
．． It can be used from about 1 to 10 μS to a maximum of about 10 mS. The electric discharge machining of the present invention can perform high-speed rough machining by increasing the discharge energy, but it can also easily process finishing and super-finishing by changing the p-d value. This occurred due to shape machining by machining the part, mold machining using a full mold shape electrode, finishing of the liquid discharge machining surface, and machining. Deburring, finishing of machined surfaces, ultra-fine satin finishing of surfaces, rust removal, oil removal,
Surface treatment for painting, vapor deposition, plasma coating, surface roughening, surface area expansion of metal powder, activation treatment of powder and spherical surfaces, processing of insulation parts, etc., as well as sandblasting, liquid honing, etc. A wide range of applications can be considered, such as ultra-blasting instead. Also p-
By controlling the d value, p-d2101 to 1T0rrCTn
If the processing is controlled to a certain degree, the surface of the workpiece will be processed into a single atomic-sized crater, and the dirt that was on the surface before processing will be sparked and removed, which will be used as a base preparation for chemical plating and electroplating. It is used for surface etching, surface etching of vapor deposition base materials, base treatment and cleaning of other metal surfaces, and p-d-1 to 10T0rr.
−? Super-finishing of the machined surface (0.1 μR
(approximately max).

In addition, if the discharge atmosphere is nitrogen gas, nitriding processing can be performed, and depending on the type of gas supplied, diffusion processing such as carburizing, nitriding, and sulfurizing can be performed. It can also be used as In addition, since the processing of the present invention is carried out in a reduced pressure gas that is exhausted from the processing section, there is no phenomenon such as gas generation and fire, unlike in conventional submerged processing of kerosene, etc., and the process is completely safe. We can provide pollution-free processing machines.

Unfortunately, the workpiece heats up during long-term machining, but by incorporating a cooling device with cooling pipes into the processing table to which it is attached, it is possible to reduce the amount of time the electrical discharge is interrupted. By using a slow pulsed discharge, sufficient cooling can be achieved during the pulse pause and by controlling the pause width, and processing can be performed without heat deterioration or the like.

In addition, pay attention to insulating the parts of the workpiece other than the machined part, for example, by applying oil-viscous Vaseline grease, etc., you can machine only the target part, and narrow the discharge gap between the electrode and the workpiece. For example, when machining with a minute gap of about 0.05 to 10 nm, it is possible to stabilize the workpiece by coating an extremely thin layer of insulating material on the surface of the workpiece and placing the electrodes facing each other with a gas gap between them. Pulse discharge occurs, allowing machining without short circuits or arcs.

[Brief explanation of the drawing]

1 and 2 are characteristic diagrams for explanation, and FIG. 3 is a configuration diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. Even in an atmosphere reduced to atmospheric pressure or lower, when machining is performed by applying a pulse voltage to the gap between the electrode and the workpiece facing each other to generate electric discharge, the length of the facing gap between the electrode and the workpiece is changed. An aerial electrical discharge machining method characterized in that the ratio of ion machining action and electronic machining action is changed and controlled.