JPS6137050B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrical discharge machining method, in particular, to feed a tool electrode relative to a workpiece in the main machining direction (hereinafter referred to as the Z-axis), and to feed an auxiliary tool along a plane perpendicular to the Z-axis (hereinafter referred to as the XY plane). The present invention relates to an improved method for performing electric discharge machining between a tool electrode and a workpiece while performing machining feed. Electrical discharge machining that provides a main machining feed in the Z-axis direction and an auxiliary machining feed along the XY plane between the tool electrode and the workpiece is well known, and an example of this is shown in Japanese Patent Publication No. 3594/1983. . According to this conventional method,
It has the advantage that multiple stages of machining such as rough machining, semi-machining, semi-finishing machining, finishing machining, and fine finishing machining can be performed continuously using a single tool electrode. In other words, generally in rough machining, only the main machining feed in the Z-axis direction is given, and at this time electrical discharge machining is performed using a large current, and as a result, it is known that the machining gap is relatively large. On the other hand, the discharge current is controlled to gradually decrease at each machining stage proceeding to the subsequent fine finishing machining, and the machining gap decreases accordingly, but by applying the auxiliary machining feed along the XY plane as described above A single tool electrode can smooth the machined surface while compensating for the reduction in the machining gap. In addition, according to the conventional equipment provided with auxiliary machining feed, the auxiliary machining feed removes cutting powder from the workpiece that stays in the discharge gap or denatured substances in the insulation working fluid that are thermally decomposed by the high-temperature arc during the discharge. can be removed by the pumping action of the machining fluid, resulting in good surface roughening. Figure 1 shows a general machining situation in a conventional method in which a workpiece 2 is machined by an electrode 1 consisting of a scalene triangle. A machining feed is given and the radius of its circular motion is denoted by R. According to this conventional method, it is possible to obtain the same effect as using an electrode larger than electrode 1 by an arbitrarily set radius R, but as is clear from FIG. A machining action is obtained by the arc-shaped electrode, and as a result, the shape of the workpiece becomes significantly different from the shape of the electrode, resulting in a disadvantage that highly accurate electrical discharge machining cannot be achieved. In order to eliminate the drawbacks of the auxiliary machining feed using the revolving circular motion shown in Figure 1, several auxiliary machining feed methods have been considered. A method in which the object 2 is displaced relative to the object 2 is shown. In FIG. 2, the radial displacement of each angle is indicated by vectors a, b, and c, the magnitude of which is set to R. However, as is clear from the shape of the workpiece in FIG. 2, even with such radial relative displacement, a shape of the workpiece that is significantly different from the shape of the electrode 1 is obtained due to the difference in the tip angle of each angle, resulting in a high It was not possible to obtain accurate electrical discharge machining. FIG. 3 shows another improved conventional method, in which auxiliary machining feed is shown in which each side A, B, and C are relatively displaced at a ratio of similarity magnification K. However, even in this conventional method, except in the case of an equilateral triangle, the machining gaps α, β, and γ between the electrode 1 and the workpiece 2 have different values, making it difficult to obtain a workpiece shape corresponding to the shape of the electrode 1. The drawback was that it was not possible. That is, according to the conventional method shown in FIG. 3, the expansion widths α, β, and γ that are expanded by the auxiliary machining feed from the actual shape of the electrode 1 are different for each side, and for this reason, the process from rough machining to fine machining is repeated multiple times. In electrical discharge machining, it is not possible to obtain a uniform machined surface, resulting in the disadvantage that highly accurate electrical discharge machining with good surface roughness cannot be obtained. In view of the above problems, the present inventors proposed the following improved electric discharge machining method. FIG. 4 shows the auxiliary machining feed action of the electrode 1 according to this improved method. In FIG. 4, the shape of the workpiece to be machined by the electrode 1 is shown by straight lines A', B', and C' that are parallel to each side and spaced apart by a distance R from each side of the electrode 1. The intersection points of each straight line A′, B′ and C′ are P ₁ , P ₂ , P ₃
And, the vertices of each corner of electrode 1 are q ₁ , q ₂ , q ₃ ,
Further, the angles are indicated by θ ₁ , θ ₂ , and θ ₃ , respectively. In FIG. 4, since a uniform enlarged width R is obtained from each side A, B, and C of the electrode 1, the supplementary processing feed vectors a, b, and c will be explained using vector a as an example.
Now, if a perpendicular line is drawn from the vertex q ₁ to straight lines A' and B' and their intersection points are r ₂ and r ₁ , the length will be equal to the enlarged width R. Here triangle p ₁ r ₂ q ₁ and triangle
p ₁ r ₁ q ₁ shares one side p ₁ q ₁ and the other side r ₂ q ₁ and
Since r ₁ q ₁ is a right triangle with the same length, the two are congruent, and the straight line p ₁ q ₁ , that is, the vector a, is an angle
It becomes the bisector of r ₁ p ₁ r ₂ . Therefore, when the vector a is displaced, the trajectory of the vertex q ₂ also moves in parallel to q ₂ ', and the angle at the apex angle q ₂ of the parallelogram P ₁ q ₁ q ₂ q ₂ ' is θ ₁ /2. From this, vector a has an azimuth of θ ₂ +θ ₁ /2 and a magnitude of

It can be obtained using [Formula]. Similarly, the other displacement vectors b, c can be determined by simple calculations, and each vector a, b, c will have the azimuth and magnitude shown in FIG. Therefore, if the relative displacement between electrode 1 and workpiece 2 is auxiliary machining fed along the XY plane according to vectors a, b, and c, it follows the shape of electrode 1 and the shape of the corner also corresponds to the electrode shape. It becomes possible to obtain a good workpiece shape. FIG. 6 shows an auxiliary machining feed vector obtained by converting the vectors a, b, and c in FIG. 5 into continuous vectors.
By applying a relative displacement according to the vector shown in the figure, it is possible to obtain a desired shape of the workpiece. By the way, the machined surface of the workpiece after electrical discharge machining as described above has a satin-like appearance due to the accumulation of electrical discharge marks, and this surface is usually polished using a tool such as a file. I am finishing it. However, if the machining shape is complex or if the workpiece is an internal corner, tools such as the file mentioned above often cannot enter the workpiece, making it difficult to perform high-precision electrical discharge machining using the above-mentioned relative motion. Even with age, there were practical drawbacks due to the problem of polishing the machined surface. The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a method for polishing the machined surface of a target workpiece after electrical discharge machining with high precision and efficiency. The principle of the present invention will be explained using FIG. 7. After machining the workpiece 2 using the electrode 1 by well-known electric discharge machining, the electrode 1 and the workpiece 2 after the electric discharge machining are left as they are, and grease mixed with abrasive particles for polishing is used instead of the electric discharge machining fluid. A viscous fluid 3 or the like is injected into the gap between the electrode 1 and the workpiece 2. Then, the main trajectory vector K as shown in Fig. 7
While performing the same relative motion as during electrical discharge machining, the main trajectory is multiplied by the rotation vector ω. The rotation vector ω rotates at a fast cycle of about 60 to 300 times per minute. The radius of this vector is about 1 to 30 .mu.m, and the contact surface between the electrode 1 and the workpiece 2 changes constantly in the gap, so that the electrode is not locally burdened. Also, electrode 1
The gap between the electrode 1 and the workpiece 2 is determined by detecting the presence or absence of contact by applying a voltage to the gap that is sufficient to prevent machining due to electrical discharge.When contact occurs, the radius of the rotation vector is minimized to prevent contact, and Direct contact can be prevented. Next, one embodiment of the present invention will be described in detail using FIG. That is, the workpiece 2 is placed on the XY drive table 4, and the numerical control device 5 drives and controls the motors 4X and 4Y to cause the electrode 1 to move along the main trajectory as shown in FIG. 7, which is programmed in advance. This can be done for
During electric discharge machining, the relative movement is performed along this main trajectory, and the workpiece 2 is subjected to electric discharge machining using a well-known method. After electrical discharge machining, the electrical discharge machining fluid (not shown) is transferred to the electrical discharge machining fluid tank 6, and then to the abrasive tank 7.
A pump 8 injects a viscous fluid 3 containing abrasive particles into the gap through a nozzle 9. The electrode 1 is attached to a crosshead 10, which is driven by motors 11 and 12.
It can move parallel to the table 4 within the XY plane. Furthermore, detectors 13 and 14 are attached to detect the displacement position of the crosshead 10, and the crosshead 1 is detected via detectors 15 and 16.
A voltage corresponding to a displacement of 0 is input to adders 17 and 18. The two-phase oscillators 19 are in phase with each other.
A sinusoidal signal shifted by 90°, i.e. φ ₁ = sinω
t, φ ₂ = cosωt, and these signals φ ₁ and φ ₂ are input to the adders 17 and 18, so the error voltage with the outputs of the detectors 15 and 16 is zero volts. The motor 11,
12 are driven by amplifiers 19 and 20. When the motors 11 and 12 move in response to the output of the two-phase oscillator 19, the crosshead 10
Eccentric movement is performed at the period ωt of the signals φ ₁ and φ ₂ from the phase oscillator 19, and the electrode 1 does not rotate, but performs a relative displacement movement that is a multiplication of the main locus movement by the numerical control device 5 and the eccentric rotation movement. , workpiece 2
is ground more than the machining allowance for electrical discharge machining by the radius of eccentric rotation. If the electrode 1 and the workpiece 2 are too close together, the voltage Vg at the output end of the pulse power source 21 for electrical discharge machining will decrease, so this voltage should be adjusted to a predetermined voltage level.
Vr and the comparator 22 detect the output voltage of the two-phase oscillator 19, which is detected by the transistors 23 and 24.
to zero volts and return the position of the crosshead 10 to the point where the radius of eccentric rotation is zero, at the same time inputting a stop signal S to the numerical control device 5, and then gradually increasing the input voltage of the transistors 23 and 24. By gradually expanding the eccentric rotation radius,
After reaching a predetermined radius, the stop signal S output to the numerical control device 5 is released. Regarding the above method of once zeroing and gradually increasing the output, the output of the comparator 22 is
5, the voltage of the capacitor 27 is set to -Vcc by the NPN transistor 26, and then the voltage of the capacitor 27 is set to -Vcc by the NPN transistor 26.
The voltage of capacitor 27 gradually increases through
Increase the bias voltage of transistors 23 and 24 2
This is done by increasing the output voltage of the phase oscillator 19. In the above embodiment, the eccentric movement is superimposed on the displacement during electrical discharge machining, but substantially the same effect can be obtained by increasing the displacement amount during electrical discharge machining by a small amount. In this case, the offset correction function of the numerical control device is used to move the same trajectory many times to polish the electrical discharge machined surface. Furthermore, it is also possible to perform polishing by electrolytic action without using an abrasive by interposing an electrolyte solution in the gap. Electric discharge machining equipment that uses water as a machining fluid has a rust-proof structure, and can be more easily processed than using an abrasive. As explained above, according to the present invention, the surface of the workpiece after electrical discharge machining is polished by an amount of eccentricity from the surface of the electrical discharge machining, and the steps from electrical discharge machining to polishing work can be performed with the same device. Moreover, it has the excellent advantage of not impairing accuracy during polishing work, and its implementation effects are remarkable.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams for machining by applying relative displacement between a conventionally known electrode and a workpiece, and FIG. 3 is an explanatory diagram for machining a workpiece similar to the electrode. FIG. 4 is a diagram illustrating ideal relative displacement;
5 and 6 are relative displacement vector diagrams in FIG. 4, FIG. 7 is a principle diagram explaining the method of the present invention, and FIG. 8 is a diagram showing an apparatus for implementing the method of the present invention. be. In the figure, 1 is an electrode, 2 is a workpiece, 3 is a viscous fluid,
4 is an XY drive table, 5 is a numerical control device, 6 is an electric discharge machining liquid tank, 7 is an abrasive tank, 10 is a crosshead, 15 and 16 are detectors, 19 is a two-phase oscillator, and 21 is a pulse power source for electric discharge machining. be.
Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. An electrode and a workpiece are opposed to each other with a desired gap therebetween, and the workpiece is machined by causing electric discharge to occur in the gap, and after the electric discharge machining of the workpiece is completed, the workpiece is machined. An abrasive or an agent having an equivalent function is injected into the workpiece, and a relative displacement is applied between the electrode and the workpiece by multiplying a trajectory uniformly larger than the electrode shape by a slight eccentric rotational motion. An electrical discharge machining method characterized by polishing the electrical discharge machined surface of the workpiece. 2. The electrical discharge machining method according to claim 1, wherein the relative displacement between the electrode and the workpiece is controlled so that the electrode and the workpiece do not come into direct contact. 3. The electric discharge machining method according to claim 1, wherein the relative displacement between the electrode and the workpiece is controlled to be slightly larger than the relative displacement during electric discharge machining.