JPH025530B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a wire cut electrical discharge machining method.

In wire cut electric discharge machining, high heat is generated in the wire part of the workpiece and the wire electrode, and in order to prevent the deterioration of the machining speed, machining condition, and machining accuracy of the electric discharge machining or breakage of the wire electrode, high heat is generated in the wire part of the workpiece and the wire electrode. A liquid (usually pure water or water) is sprayed to remove machining debris from the machining part, and new machining fluid is supplied to prevent the generation of high heat. is cooled to some extent, but the cooling effect is not sufficient for wire electrodes with poor heat resistance (usually copper or copper alloy electrode materials, although tungsten etc. are sometimes used), and the processing speed and processing conditions (processing conditions) cannot be said to be sufficient. Not only were the stability (stability) and processing accuracy insufficient, but the wire electrodes were easily broken due to the generation of high heat.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wire cut electric discharge machining method that can sufficiently cool a wire electrode in order to eliminate the above-mentioned conventional drawbacks.

The present invention will be explained below with reference to illustrated embodiments.

The wire cut electrical discharge machining method of the present invention shown in FIG.
Wire-cut electric discharge machining is performed using a wire electrode 2 that is stretched in the vertical direction facing the workpiece 1 and is updated and fed in the axial direction, and a machining start hole is formed at a desired position in the workpiece 1. A wire electrode 2 is extended vertically through 1a, and this wire electrode 2 is guided by boat-shaped, die-shaped, or roller-shaped guides 3 and 4 having a pair of V-grooves arranged vertically opposite each other. The electric discharge machining power source 7 applied between the wire electrode 2 and the workpiece 1 via the brushes 5 and 6 is updated while traveling in the axial direction from the bottom to the top as shown by the arrow. A workpiece is cut into a desired contour shape by electrical discharge machining by repeating pulsed discharge using intermittent voltage pulses.

Above the machining start hole 1a of the workpiece 1, a machining fluid injection nozzle 9 is disposed adjacent to or coaxially with the wire electrode 2 and facing the workpiece 1,
Further, a machining fluid spray nozzle 8 coaxial with the wire electrode 2 is disposed at the bottom of the machining start hole 1a, facing the workpiece 1, and the machining fluid (usually pure water or ) to cool the machining part and remove machining debris from the machining hole 1a, and as will be described later, part of the machining fluid from the nozzle 8 forms an ice film on the surface of the wire electrode 2 fed into the machining part. The ice adheres to the wire electrode and is fed into the processing section.

Further, a container 11 containing a refrigerant 10 such as a cooling liquid such as liquid nitrogen is disposed below as a cooling device for the wire electrode 2 fed from the lower side to the processing section. a guide roller 12 on which a wire electrode 2 is provided as necessary;
13, and after being sufficiently cooled to below the freezing point of water, it reaches the nozzle 8 with an ice layer on its surface, and in some cases may even contain some ice particles. The jet flow of machining fluid coaxially surrounds the bent wire electrode 2 and reaches the machining part to perform electrical discharge machining. Therefore, in the past, overheating of the wire electrode and workpiece in the machining part was prevented by absorbing and consuming the thermal energy generated in the machining part as a temperature increase in the machining fluid (water) present in the machining gap. In contrast, in the present invention, the thermal energy generated in the processing section is consumed as heat of fusion to melt the ice. However, the specific heat of water is about
1cal/℃,g, whereas the heat of melting of ice is approx.
80 cal/℃, g, and the heat of melting of ice is much larger than the specific heat of water. Therefore, according to the present invention, the heat energy generated in the processing section is absorbed extremely efficiently and the processing section, especially the wire electrode, is heated. It can be sufficiently cooled. As a result, the repetition rate of the discharge pulse and 1
The machining current (average current) can be increased by appropriately increasing one or both of the discharge energy of the discharge pulse, which improves the machining speed and machining stability of electric discharge machining, and makes the wire electrode more difficult to break. ing.

In this way, in the present invention, an electric discharge is generated between the wire electrode having an ice coating layer on the surface and the workpiece, but the ratio of the liquid machining fluid to the ice machining fluid is Although the resistance is slightly larger in the ice state, it is approximately the same, so even if ice is present, discharge can be generated as in the conventional case without any problem. Also, the ice coating layer is not necessarily uniformly formed on the wire electrode, and it is possible that ice is partially attached to it, but even though the specific resistance is higher in the icy state, In addition, machining debris is irregularly interposed in the machining gap, and the wire electrode is constantly subject to minute vibrations due to the pressure caused by the intermittent discharge, the flow of machining fluid, or the renewal feed. Therefore, the electric discharge will not concentrate on the areas where no ice has adhered, resulting in unstable machining conditions or breakage of the wire electrode. Furthermore, even if a discharge occurs in a part where no ice is attached, the heat applied to the part where the wire electrode generates the discharge will quickly propagate through the wire electrode due to the high thermal conductivity of the wire electrode, and the ice existing near the part will be absorbed. Therefore, even if ice is only partially attached to the wire electrode, the wire electrode can still be sufficiently cooled more efficiently than in the past.

In the above case, if the machining liquid water sprayed from the nozzle 8 or further from the nozzle 9 has a temperature higher than room temperature,
Even if the wire electrode 2 is cooled to an extremely low temperature,
The specific heat of the wire electrode is small and the wire electrode is usually
Since the wire electrode is as thin as 0.2mmφ and as thin as 0.5mmφ at most, and its heat capacity per unit length is small, there is a possibility that the wire electrode will be heated by the machining fluid and sent into the machining area without ice attached. Therefore, the machining fluid should be cooled to about 5 to 115 degrees Celsius or lower, which is lower than room temperature, and preferably the machining fluid on the nozzle 8 side, which is the feeding side of the cooled wire electrode, should be cooled to about 4 degrees Celsius or lower. Preferably, the workpiece 1
It is desirable that the flow rate or ejection pressure of the machining liquid on the nozzle 8 side be approximately the same or higher than that of the nozzle 9, although this will depend on the machining conditions such as the plate thickness and machining expansion allowance. Various refrigerants and cooling means other than liquid nitrogen can be used for this purpose. For example, the wire electrode and its storage drum are cooled to around 0°C or lower, and the wire electrode 2 pulled out from there is cooled just before the nozzle 8. For example, it may be configured to penetrate a dry ice filling box.

Next, to explain with an example, a plate with a thickness of 25 mm
In machining S55C material, specific resistance of machining fluid water is 5×10 ⁴
Ωcm, the wire electrode 2 is made of brass with a diameter of 0.2 mm, the wire tension between the guides is 0.8 Kgf, the axial renewal feed rate is 3 m/min, the opening of the upper nozzle 9 coaxial with the wire electrode 2 is 3 mm φ, and the machining fluid ejection pressure is 0.3 Kg/cm. As ² ,
It is coaxially inserted into an air suction prevention machining fluid jetting nozzle with an opening diameter of 7 mmφ and placed approximately 3 mm apart from the workpiece 1, and the lower nozzle 8 has an opening diameter of 10 mmφ with an opening of 5 mmφ and a machining fluid jetting pressure of approximately 1 Kg/cm ² . According to the conventional device, which is installed coaxially with the air suction prevention liquid ejecting nozzle and placed within 1 mm from the workpiece 1, the no-load voltage of the voltage pulse is 130V, the duration of the voltage pulse is 7μS, and the voltage Under machining pulse conditions with a pause time between pulses of 7μS, the machining feed speed was adjusted while monitoring the machining state so that machining could be performed stably without breaking the wire electrode, and the temperature of wire electrode 2 When is at room temperature (room temperature: 20℃), the machining speed improved when the temperature of the machining fluid was lowered to 10℃ and even 5℃, but the average machining current was about 6.5A and the machining feed was The speed limit was 2.0 mm/min. In addition, when the average machining current was changed by adjusting the pause time between voltage pulses, the average machining current was as shown above.
When the current exceeded 6.5A, wire electrode breakage accidents occurred and processing became unstable. Next, according to the present invention, the temperature of the machining fluid spouted from the lower nozzle 8 is reduced to 4
℃ and cooled by passing the wire electrode 2 through liquid nitrogen just before the nozzle 8. The surface of the wire electrode 2 leaving the nozzle 8 and entering the processing section of the workpiece 1. An ice layer with a thickness of about 0.045 mm is formed on the wire electrode 2.
The maximum machining speed is
With an average machining current of 8.2 A, it became possible to set the value to 2.5 mm/min or a little higher than this, and machining could be continued without any breakage of the wire electrode 2.

The effect of improving the machining speed in the case of the present invention as described above can be achieved more easily by adjusting the machining feed rate and shortening the voltage pulse pause time, thereby preventing wire electrode breakage accidents. It was also possible to confirm the effects of the present invention under other machining pulse conditions.

Also, the renewal feed rate of the wire electrode is usually 1~
2 m/min, whereas in the above experimental example the update feed rate is set to 3 m/min, by increasing the update feed rate, it compensates for the fact that the heat capacity of the wire electrode per unit length is small. This is to substantially increase heat capacity.

In FIG. 2, the wire electrode 2 is cooled by guiding and holding the wire electrode 2 with ice 22, 23 immediately before the nozzle 8 and, if necessary, immediately after the nozzle 9. The ice 22, 23 is formed by ice forming holders 22A, 23A connected to cooling poles of thermoelements 20, 21 having radiation fins 24, 25 arranged in a cooling duct 26 through which a cooling liquid 27 flows. I try to keep it. Note that 22B and 23B are the holding bodies 22A,
This is a nozzle for replenishing machining liquid water to 23A, and other configurations are the same as those shown in FIG. 1, and the same components are given the same reference numerals and their explanations will be omitted. The thermo elements 20 and 21 are coolant 27
At the same time, as shown in FIG. The endothermic cooling effect of the plates 28, 29, and therefore the holders 22A, 23A is utilized by passing current through them. In this way, the cold ice 2
2, 23. In particular, if the wire electrode 2 is guided by low-temperature ice 22 provided on the feed side of the wire electrode 2 to the processing section, the low temperature of the part in contact with the wire electrode moving during renewal feeding will be reduced. When the ice is processed by the wire electrode, the melting point of the ice in that area is lowered, and the ice in that area melts locally, and the melted liquid machining liquid is transferred to the wire. It adheres to the electrode and leaves the ice 22 area. However, when the ice 22 comes out, the pressurized state is released and the melting point returns to the temperature in the non-pressurized state, so the machining fluid adhering to the wire electrode freezes due to the so-called re-icing phenomenon, and the ice The attached wire electrode is fed into the machining section, and as in the embodiment shown in Figure 1, the wire electrode can be efficiently and sufficiently cooled, making it possible to increase the average machining current and perform high-speed machining. Processing can be carried out under stable processing conditions without causing the wire electrode to break due to overheating. Further, it is preferable that a machining liquid at a low temperature of about 4° C. or less, preferably a machining liquid slightly lower than about 0° C. and containing a large number of microscopic ice pieces or ice particles, is spouted and supplied from the nozzles 8 and 9 under pressure.

As described above, according to the present invention, by feeding the wire electrode with ice attached to it into the processing section, the workpiece and the wire electrode can be efficiently and sufficiently cooled. Even if the average machining current is increased to increase the energy supplied to the machining gap, the machining section will not overheat and the machining condition will become unstable, and the wire electrode will not overheat and break, allowing high-speed machining. can be performed in a stable manner.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a wire cut electric discharge machining apparatus used in one embodiment of the present invention, FIG. 2 is a block diagram of a wire cut electric discharge machining apparatus used in another embodiment of the present invention, and FIG. FIG. 3 is a front view of a thermoelement used in the wire-cut electric discharge machining apparatus shown in FIG. 2. FIG. 1... Workpiece, 2... Wire electrode, 8, 9...
...Machining liquid injection nozzle, 10...Cooling liquid, 20,2
1... Thermoelement, 22, 23... Ice, 2
4, 25...Cooling fan, 26...Cooling duct,
27...Cooling liquid.

Claims (1)

[Scope of Claims] 1. A workpiece is placed opposite to a wire electrode between a pair of guides arranged at a distance from one side through a minute gap between the guides, which are fed from one side and are renewed and moved in the axial direction. Then, while spraying machining fluid from the machining fluid supply nozzle into the gap, intermittent voltage pulses are applied between the workpiece and the wire electrode, and the voltage pulses are perpendicular to the axial direction of the wire electrode between the guides. In wire cut electrical discharge machining, which involves machining by applying a relative machining feed on a flat surface, ice adheres to the wire electrode before it is fed into the machining section facing the workpiece. A wire cut electric discharge machining method characterized in that machining is performed while feeding a wire electrode in a state to the machining section. 2. The wire cut electric discharge machining method according to claim 1, wherein the machining fluid injected and supplied from the machining fluid supply nozzle is a machining fluid at a temperature lower than room temperature.