JP2510240B2 - EDM liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) The electric discharge machining method includes a wire electric discharge machining method and a die-sinking electric discharge machining method. All of these are processing methods in which the gap between the electrode and the workpiece is filled with a machining liquid having a high insulating property, and machining is performed by spark discharge generated in the gap. In the wire electrical discharge machining method, since the facing area between the workpiece and the wire electrode is small, a stable electrical discharge state can be maintained even if the insulation of the machining fluid deteriorates a little, and new wire electrodes are sequentially supplied to the machining area. Therefore, it is not necessary to suppress the electrode wear rate so low that the water-based flame-retardant working fluid is widely used. On the other hand, in the die-sinking electric discharge machining method, since the facing area between the electrode and the workpiece is large, it is necessary to pay close attention to the insulation of the machining liquid in order to maintain a stable electric discharge machining state. If the consumption is large, the electrode shape changes and the edge portion sags, which leads to deterioration of the finish accuracy of the workpiece. Therefore, it is necessary to keep the electrode consumption rate as low as possible. In addition, the amount of machining itself is orders of magnitude larger than that of wire electric discharge machining, so a sufficient machining speed is required, and the finish of the machined surface is also an important factor.

Many studies have been conducted on water-based flame-retardant electrical discharge machining fluids for die-sinking electrical discharge machining and patent applications have been filed. For example, JP-A-58-181900 and JP-A-56-4533.
No. 1 publication discloses a W / O emulsion type electric discharge machining liquid in which water and a nonionic surfactant are added to kerosene,
Further, JP-A-61-2623 discloses a mixture of an ethylene oxide propylene oxide copolymer (hereinafter abbreviated as EOPO) and water, having a specific gravity of more than 1.0 and a copolymer ratio of 22 to 30. A weight percent EDM fluid is disclosed. It is stated that with this processing liquid, the electrode consumption rate is about the same as when mineral oil is used alone, and the processing speed is equal to or higher than that when using a 30% polyethylene glycol solution. In addition, JP-A Nos. 62-236623, 62-236624 and 62-
Each of the publications of 236625 discloses a working fluid in which 0.5 to 85% of an alkoxyoxyethylene derivative is contained in water.

(Problems to be solved by the invention) However, when comprehensively evaluating the electrode wear rate, machining speed, machined surface finish, and electrical discharge stability over the entire range from rough machining to finish machining, mineral oils that have been widely used in the past have been used. At present, the water-based machining fluid superior to the electric discharge machining fluid has not yet been put into practical use.

Mineral oil-based electric discharge machining fluid has a characteristic that it has a certain level of machining speed due to its excellent insulating properties and appropriate cooling properties, and the electrode consumption rate is low, but it is a flammable substance, so there is a constant risk of fire. It has the big drawback of being sexual. Therefore, it is the biggest obstacle to the demand for the improvement of the electric discharge machining technology from the aspect of the equipment due to the increase in the size of the electric discharge machine, the increase of the machining current, etc., and the improvement of the productivity by the implementation of the night unmanned operation.

In order to overcome the drawbacks of this mineral oil-based machining fluid, many water-based flame-retardant machining fluids have been prototyped and patent applications have been filed as described above. As described above, it has not been put to practical use because of serious drawbacks such as poor performance.

Therefore, an object of the present invention is to overcome the drawbacks of conventional water-based flame-retardant electric discharge machining fluids and provide a water-based electric discharge machining fluid having properties as close as possible to mineral oil-based fluids.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a mixed electric discharge machining fluid of polyether and water, wherein the polyether is the following general formula: R-OC ₂ H ₄ O _n H ( R in the formula is a C _{5 to} C ₁₁ alkyl group, which may be linear or branched, and n represents an integer of 1 to 4),
The weight ratio of the polyether to water satisfies the following formula: polyether: water = 30: 70 to 70:30.

In the polyether used in the present invention, R in the above formula is C _5-
C ₁₁ and n is required to be an integer of 1 to 4 for the following reason.

That is, a polyether having a chain length of R ≦ 4, such as ethylene glycol monobutyl ether or diethylene glycol monobutyl ether, is miscible with water at an arbitrary ratio, but easily evaporates, and in particular, the electric discharge machining performance is poor under intermediate to finishing machining conditions. There is.

On the other hand, a polyether having a chain length of R ≧ 12, for example, one in which R is a lauryl group, is not suitable as an electric discharge machining fluid because of remarkable foaming and gelation in some cases.

Particularly preferred polyethers are those in which R is C _{6 to} C ₈ and n is 1 or 2, such as ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol mono-octyl ether or diethylene glycol mono-hexyl ether, Alternatively, those in which R is C _{8 to} C ₁₀ and n is 3, such as triethylene glycol mono-2-ethylhexyl ether,
Mention may be made of triethylene glycol monononyl ether, triethylene glycol monoundecyl ether or monoisooctyl ether.

The present invention has been made based on the finding that when the above-mentioned polyether and water are blended in the above weight ratio, it exhibits a performance close to that of a mineral oil-based working liquid in the entire range from roughing to finishing. It was also clarified that the longer the alkyl chain and the shorter the ethylene oxide chain of the alkylene glycol ether, the closer to the performance of the mineral oil-based electric discharge machining liquid, as long as the gelation and foaming problems do not occur.

The electric discharge machining liquid of the polyether of the present invention and water forms a uniform solution phase at room temperature. However, during electrical discharge machining, the electrical discharge between the electrode and the surface of the workpiece exposes the machining fluid in contact with the part to a high temperature locally, and this local temperature rise causes the local machining fluid to quickly form a W / O emulsion locally. Form. FIG. 1 shows the state of the liquid in a local area, and as shown in (a), the polyether 1 forms a continuous phase. By having the ability to form a W / O emulsion in this way, the electrodes and the surface of the processed material are made hydrophobic,
In terms of electrode wear rate, processing speed, and finish of the processed surface, it has the epoch-making effect of showing performance almost equal to that of 100% polyether. This emulsion formation temperature is called the cloud point. In addition, if the temperature is further increased, two phases are separated. Therefore, the electric discharge machining liquid present in the electric discharge portion forms a W / O type emulsion by electric discharge and further causes two-phase separation. Since the bulk working fluid is maintained at about 30 to 50 ° C., heat exchange with the local working fluid or liquid movement is repeated.

On the other hand, when the concentration of the polyether becomes lower than the range of the present invention, as shown in (b) of FIG.
Although a W-type emulsion is formed and water 2 forms a continuous phase, the above effect cannot be obtained with the liquid having the O / W-type emulsion forming ability. Therefore, in the present invention, the polyether is required to have a concentration of 30% or more. However, 30 or more water is generally required for flame retardancy.

The clouding point of the working fluid of the present invention is preferably about 40 ° C or higher. More preferably, the temperature is set to 60 ° C or higher. That is, if the temperature is lower than 40 ° C., the liquid immediately undergoes two-phase separation in the bulk portion before the liquid locally exists in the electric discharge machining, and the intended effect cannot be exhibited. Therefore, the temperature is preferably 40 ° C or higher, more preferably 60 ° C or higher. The cloud point is a pressure glass container,
For example, a test tube or the like may be placed in a glass autoclave, filled with a sample solution, heated, and observed from the outside for measurement. Usually, it can be measured up to about 180 ° C, but when measured with the working fluid of the present invention, those having a cloud point up to 180 ° C exhibited sufficient effects, but those having a cloud point at temperatures higher than this are also effective. Met. That is, a cloud point up to 180 ° C. or higher under a pressure of 6 to 7 kg / cm ² or higher is also effective, and in general, the upper limit in terms of atmospheric pressure is about 210 ° C.

However, the polyether used in the present invention also includes those sparingly soluble in water, and these compounds are polyethers which exhibit high performances close to those of the mineral oil-based working fluid as described above, Since the cloud point is lower than room temperature and it is poorly soluble in water,
It is difficult to use as it is. Therefore, when a compatibilizer for dissolving these into the concentration range of the present invention at room temperature was examined, polyhydric alcohols such as propylene glycol, dipropylene glycol, 1,3-butanediol, and 2,3-butanediol were effective. Therefore, in order to sufficiently raise the cloud point, it is necessary to add these within the range of 0 to 30% by weight. The fact that these polyhydric alcohols do not have any adverse effect on the electric discharge machining performance can be understood by comparing the case where the polyhydric alcohol is added at a constant concentration of water-soluble polyglycol solution at room temperature and the case where no polyhydric alcohol is added. I'm confirming.

Incidentally, in the electric discharge machining fluid of the present invention, previously known components such as a rust inhibitor, a metal deactivator, a corrosion inhibitor, an antioxidant, and a corrosion inhibitor are added to the composition in advance, if necessary. However, the respective performances can be imparted by these additives.

(Examples) The contents of the present invention will be specifically described below based on Examples and Comparative Examples.

 The test method used is as follows.

〔Test method〕

(1) Electric Discharge Machining Co., Ltd. Electric discharge machine EDNC-22 manufactured by Makino Milling Machinery Co., Ltd. was used as a graphite electrode ED-3 as an electrode and as a work material.
It was carried out using SK-5 steel. Table 1 shows the main electrical discharge machining conditions.

(2) Electric discharge machining fluid performance test After the set depth machining, the electric discharge machining performance of the test machining fluid was evaluated by the following items.

Machining speed: Machining amount (g) / Machining time (min) Electrode wear rate: [Electrode wear length (mm) / Machining depth (m
m)] × 100 (%) Processed surface roughness: maximum surface roughness R _max (μm) Further, cloud point measurement and observation of two-phase separation state of the test processing liquid were performed as follows.

(3) Cloud point measurement The prepared electric discharge machining fluid was sealed in a test tube and then immersed in a water bath. The temperature at which the machining fluid began to turn cloudy was gradually set as the cloud point. The higher cloud point was measured in a glass autoclave.

(4) Observation of Two-Phase Separation State Since all the base materials used in the present invention are colorless and transparent, which of the polyether phase and the aqueous phase is the continuous phase in the two-phase separation process in the temperature range above the cloud point? Is difficult to identify. Therefore, a very small amount of water-insoluble dye Sudan III
Visual observation was performed using (trade name). That is, at a temperature below the cloud point, the electric discharge machining liquid is uniformly colored by Sudan III, but when separated into two phases, only the polyether phase is colored.

Examples 1 to 3 and Comparative Examples 1 to 5 The electric discharge machining fluids (Examples 1 to 3) of the present invention and the comparative machining fluids (Comparative Examples 1 to 5) were compounded at the blending ratios (volume%) shown in Table 2 below. ) Were prepared respectively. In addition, Table 2 also shows the observation results of the cloud point and the continuous phase at the time of two-phase separation.

Specifically, Example 1 is a binary liquid mixture of hexyl diglycol and water. In Example 2, propylene glycol was uniformly dissolved in water to dissolve hexyl diglycol in a higher concentration. Example 3 is a uniform aqueous solution of 2-ethylhexyldiglycol, which is almost insoluble in water, and a small amount of hexyldiglycol, using dipropylene glycol. on the other hand,
In Comparative Examples 1 to 3, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and triethylene glycol monobutyl ether aqueous solutions were taken up as typical examples of short-chain alkylene glycol ethers. In addition, Comparative Example 4 is a low concentration aqueous solution of hexyldiglycol as an example in which even the compound according to the present invention does not satisfy the concentration range and the predetermined performance is not obtained, and Comparative Example 5 is a mineral oil-based electric discharge machining liquid. C ₁₃ normal paraffin was used as each. FIG. 2 and FIG. 3 show the results of the electric discharge machining test under the rough machining conditions of the machining fluids of Examples and Comparative Examples, respectively.

As is clear from FIG. 2 and FIG.
In all of the machining fluids of No. 3 and Comparative Examples 1 to 3 and 5, the electrode consumption rate continuously decreased as the pulse width increased, and the electrode consumption rate became zero at a certain pulse width. When the machining speeds are compared at the point where the electrode wear rate becomes zero, the working fluids of Examples 1 to 3 all show 2.2 to 2.3 g / min. The amounts were 1.6, 1.7 and 2.3 g / min, and the mineral oil-based working fluid of Comparative Example 5 had 1.6 g / min. Therefore, except that Comparative Example 3 is equivalent to Examples 1 to 3,
It was confirmed that the working liquids of Comparative Examples 1 to 3 and 5 had a lower working speed than those of Examples 1 to 3. In Comparative Example 4, not only the electrode consumption rate does not fall below zero, but also the processing speed is low.

Further, since the surface roughness is almost determined by the pulse width regardless of the type of the electric discharge machining liquid, the smaller the pulse width τ at which the electrode wear rate becomes zero in practice, the better the finished surface finish. It will be. Comparing the values of τ, all of Examples 1 to 3 are 200 to 300 μs, which is close to 200 μs of the mineral oil-based working liquid of Comparative Example 5, but Comparative Examples 1 to 3
Since it shows a large value of 300 to 500 to μs, Example 1 to
It can be seen that the machining liquid of No. 3 is superior to the comparative examples 1 to 3 in terms of finishedness of the machined surface. In Comparative Example 4, not only there is no point where the electrode wear rate falls below zero, but the processed surface roughness is clearly larger than in the other Examples and Comparative Examples.

Next, Table 3 below shows the results of the electrode wear rate, the machining speed, and the finish of the machined surface in the electric discharge machining test under the intermediate finishing and finishing machining conditions of Example 3 and Comparative Examples 2 and 5.

Under the conditions of medium finishing and finishing for which the electric current value is small, the performance difference between the working fluids of Example and Comparative Example becomes more remarkable in the case of the water-based working fluid. From the test results of Table 3, Comparative Example 2 is under such working conditions. However, it can be seen that the working fluid of Example 3 exhibits a performance close to that of the mineral oil-based working fluid of Comparative Example 5.

(Effects of the Invention) As described above, the electric discharge machining fluid of the present invention overcomes the drawbacks of the conventional water-based flame-retardant electric discharge machining fluid and exhibits properties close to those of mineral oil.

Further, the polyether used in the present invention has various advantages as compared with the polyether used in the above-mentioned comparative examples, that is, the evaporation loss is small, the odor is small, and the influence on the sealing material, the resin and the paint is small.

[Brief description of drawings]

1 (a) and 1 (b) are explanatory views showing a two-phase separated state of the polyglycol aqueous solution, and FIG. 2 is a pulse width and machining speed in the electric discharge machining liquids of Examples 1 to 3, and electrode consumption. FIG. 3 is a graph showing the relationship between the pulse width and the machining speed, the electrode consumption rate, and the machined surface roughness of the electric discharge machining liquids of Comparative Examples 1 to 5, and FIG. 1 ... polyether, 2 ... water

Claims (4)

(57) [Claims] 1. A mixture discharge machining fluid of polyether and water, polyether follows the general _{formula, R-OC 2 H 4 O} n H (R in the formula is a straight alkyl group of C ₅ -C ₁₁ May be chain-like or branched, and n represents an integer of 1 to 4),
A discharge machining fluid characterized in that the weight ratio of the polyether to water satisfies the following formula: polyether: water = 30: 70 to 70:30. 2. The electric discharge machining fluid according to claim 1, which contains a polyhydric alcohol in a range of up to 30% by weight. 3. The electric discharge machining liquid according to claim 1, which has a cloud point of 40 ° C. or higher and forms a W / O type emulsion. 4. The electric discharge machining fluid according to claim 1, which has a cloud point in the range of 60 ° C. to 210 ° C.