JPH0260453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a machining method in wire cut electric discharge machining in which vertical dimensional errors of a workpiece due to wear of the wire electrode are corrected by tilting the wire electrode with respect to the workpiece. It is.

Conventionally, in wire cut electrical discharge machining, when measuring the dimensions of a workpiece after machining, there have often been differences in the upper and lower dimensions. As methods for dealing with this problem, there are generally known methods such as changing the distance between the upper and lower guides of the wire electrode, changing the upper and lower machining fluid pressure, or using a second cut method. However, all of these methods have the drawback that other sacrifices are large in order to eliminate the vertical dimension difference. In other words, the method of changing the distance between the upper and lower guides is that it is known that the smaller the distance between the upper and lower guides, the less vibration the wire electrode has and the higher the rigidity, improving both machining speed and accuracy.
This is not a good idea as conflicting cases may occur. Also, the method of changing the upper and lower machining fluid pressures is not preferred because it prevents effective ejection of machining chips. Furthermore, if the second cut method is used, it is unfavorable from an economical and process standpoint since it naturally requires additional processing time.

As described above, the conventional methods for eliminating the vertical dimension difference of the workpiece have various drawbacks and often impair other characteristics.

Therefore, the inventor of the present invention discovered through various experiments that the above-mentioned vertical dimension difference is caused by wear of the wire electrode, and devised a correction method that does not impair other characteristics.

First, with reference to FIG. 1, the reason why the difference in the vertical dimensions of the workpiece is due to the wear of the wire electrode will be explained.

FIG. 1 is a schematic diagram when the wire electrode 1 is kept perpendicular to the workpiece 2 during processing.
This is usually called straight processing. In this case, the wire electrode 1 is fed from top to bottom as shown by the arrow in the figure.
After going through states a and b, the workpiece 2 on the punch side is machined. At that time, the vertical dimension difference E=
|Lu−Ld| will occur. Furthermore, the range W of the wire electrode 1 indicates the portion that has been consumed due to electrical discharge machining. Here, according to the inventor's experiments, when the dimensions of the workpiece 2 were measured from Lu to Ld, that is, at certain intervals from top to bottom, they almost matched the diameter measurement results at the same position of the wire electrode 1. did. That is, this means that the machined surface of the workpiece 2 is equidistant from the consumable surface of the wire electrode 1, and is machined according to its shape. Therefore, the vertical dimension difference E and the wire electrode diameter difference (the diameter difference in the direction perpendicular to the machined surface before and after processing) almost match.

Next, the characteristics of the vertical dimension difference will be explained with reference to FIGS. 2 and 3.

In Figure 2, a represents the vertical dimension difference E=|Lu−Ld| of the workpiece 2, and b represents the relationship between the two with E on the vertical axis and machining speed FS on the horizontal axis. There is. As can be seen from b, E increases as FS increases, and is almost proportional.
It is generally known that as the machining speed increases, the wear of the wire electrode increases, so it should be seen that the wear greatly dominates the vertical dimensional difference as shown in b.

Next, although FIG. 3 is the same as FIG. 2 regarding the axis, the same figure shows five different feeding speeds of the wire electrode. The results for each feed rate are similar to those shown in Figure 2, but what should be noted is WS ₁
This is the change from to WS ₅ . That is, the figure shows that when compared at the same processing speed, the faster the wire electrode feeding speed is, the smaller the vertical dimensional difference is.
Furthermore, since it is a matter of course that the faster the feed speed is, the less the wear is, it can be seen from the figure that the wear largely dominates the difference in the vertical dimension.

As described above, focusing on the fact that the vertical dimensional difference is largely due to wear of the wire electrode, the present invention provides a method that not only does not impair dimensional accuracy even when processing speed increases, but also improves it. It is.

FIG. 4 shows the principle of the implementation method according to the invention.

First, as shown in a, if the thickness of the workpiece is H, then the vertical dimension difference is E, so a tapered surface with an angle of θ shown in the figure is formed on the machined surface. . In this way, θ is determined in advance by test machining or the like before starting the main machining under the same machining conditions. Next, as shown in b, by inclining the wire electrode 1 by θ with respect to the vertical direction and performing taper processing, the workpiece 2 on the left side of the figure (necessary shape side) is created. This means that the vertical dimension difference E≈0 can be obtained. Further, the taper cut device for carrying out this processing method is the same as a general device and is not a special device. In this way, true straight machining of the workpiece was performed.

Next, a practical example of the method of the present invention is shown in FIG. In the table shown in FIG. 5, the machining speed FSm is listed vertically, the feed speed WSn of the wire electrode is listed horizontally, and all the vertical dimensional differences Emn are listed. The size relationship is shown at the bottom of the table. In this way, if the machining conditions such as the diameter and material of the wire electrode, the pressure and specific resistance of the machining fluid are constant, the difference in the vertical dimension will depend on the thickness of the workpiece and the electrical machining conditions that govern the discharge energy. figure,
It can be said that it is mostly controlled by the processing speed and the feed speed of the wire electrode. This will be explained in more detail. In FIGS. 1, 2, and 3, it was stated that the difference in the upper and lower dimensions is due to the wear of the portion of the wire electrode facing the machined surface. The consumption is originally determined by the number of discharges that a unit length of the wire electrode receives per unit time, that is, the current density per unit length. However, considering that machining speed is said to be approximately proportional to machining current, it is no exaggeration to say that there is a one-to-one relationship between wear and machining speed.

The data obtained for this reason is shown in FIG. 5, and even in various experiments conducted with different plate thicknesses and processing conditions, the data can be summarized in almost one table without much difference.
Although the data in Figure 5 is shown qualitatively, the relationship between magnitudes is clear from the graph in Figure 3, and by conducting an experiment to obtain the graph in Figure 3, the specifics in Figure 5 can be determined. The numerical value can be easily obtained. The specific experimental method was to vary the wire electrode feeding speed and machining speed, select a certain thickness for the workpiece, and keep other machining conditions fixed as shown in the graph in Figure 3. , and create the data shown in Figure 5.

Now, in practice, if we have FIG. 5, the taper angle θ during main processing can be expressed as shown in the figure, with H representing the plate thickness.

As a result of putting this example into practice, the vertical dimensions were kept within approximately several μm. Of course, if you want to perform more precise high-precision machining, it is also possible to perform test machining once under each machining condition and determine the taper angle based on the test machining.

However, if you want to do it simply,
It is better to carry out the example shown in the figure.

That is, before starting the main processing, perform straight line processing (a run-up line is also possible), measure the diameters Du and Dd of the wire electrode 1 as shown in the figure, calculate the taper angle θ using the formula in the figure, and start the main processing. This method is used for In the figure, S indicates the direction facing the processing surface of the workpiece 2, f is the processing progress direction of the wire electrode 1, and b
is the part that corresponds to the back opposite to the direction of machining progress.
It is sufficient to measure Du and Dd in the S direction using a micrometer or the like. Also, Du can be considered to be the same as the diameter of a new wire electrode.

Furthermore, the widths of the machining grooves formed on the upper and lower surfaces of the workpiece 2 may be measured from the same figure, and E' may be determined from the difference.

As mentioned above, various embodiments have been described in which the vertical dimension difference of the workpiece after machining is corrected by the taper angle. It goes without saying that if the main processing is performed using an angle in which the resulting angular error is similarly corrected, a shape with a more accurate desired angle can be obtained. As explained above, in the method of the present invention, a machining power source continuously generates electrical discharge using a machining fluid as a medium in a minute gap between a wire electrode to be fed and a workpiece, and the wire electrode is connected to the workpiece. In a machining method using a wire cut electric discharge machine equipped with a means for inclining the workpiece by a desired angle, the inclination angle of the machined surface of the workpiece due to wear of the wire electrode under desired machining conditions is determined in advance, and the workpiece is When machining an object, the wire electrode is tilted in the vertical direction by the inclination angle to the side opposite to the desired machining surface of the workpiece, and electrical discharge machining is performed. Alternatively, the inclination angle of the wire electrode can be set according to the machining conditions independently of other machining conditions, which has the great effect of maintaining extremely high dimensional accuracy no matter how much the machining speed is increased. Therefore, the effects of its implementation are extremely large.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the vertical dimension difference of the workpiece and wire electrode wear, Figs. 2 and 3 are graphs showing the characteristics of wire electrode wear, Fig. 4 is a diagram of the principle of the method of the present invention, and Fig. 5 The figure is an embodiment diagram showing a practical data table of the present invention, and FIG. 6 is an embodiment diagram showing a simplified method of the present invention. In the figure, 1 is a wire electrode, and 2 is a workpiece.
In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A machining power source continuously generates electrical discharge using a machining fluid as a medium in a minute gap between a wire electrode to be fed and a workpiece, and the wire electrode is moved to a desired position against the workpiece. In the machining method of a wire cut electric discharge machine equipped with means for tilting by an angle, based on a table of the vertical dimension difference E of the workpiece due to wear of the wire electrode determined from the machining speed and wire feed speed prepared in advance, The angle of inclination of the machined surface of the workpiece is determined in advance from the thickness of the workpiece, and when processing the workpiece, the wire electrode is moved by the angle of inclination with respect to the vertical direction to the desired angle of the workpiece. A wire cut electric discharge machining method characterized by performing electric discharge machining on the side opposite to the machined surface. 2 From the table of the vertical dimension difference E of the workpiece, as the plate thickness H of the workpiece, find the inclination angle θ using the formula θ = tan ^-1 E / 2H, and use this as the inclination angle to eliminate the vertical dimension difference. The wire cut electric discharge machining method according to claim 1, wherein the correction value is used as a correction value. 3. Means for inclining the wire electrode at a desired angle with respect to the workpiece by causing a machining power source to continuously generate electric discharge using machining fluid as a medium in a minute gap between the wire electrode being fed and the workpiece. In the machining method of the wire-cut electric discharge machine equipped with the above-mentioned method, the consumption of the wire electrode in the direction perpendicular to the machining progress direction or the vertical dimensional difference or the vertical dimension of the workpiece during pre-machining is determined from the machining speed and wire feed rate prepared in advance. Based on the difference in the width of the machining groove, a correction value for the inclination angle of the wire electrode is determined to correct the vertical dimension difference that occurs in the workpiece when taper machining is performed from the plate thickness of the workpiece, and this correction is performed. A wire cut electrical discharge machining method, characterized in that the wire electrode is tilted based on the value, and taper machining is performed at the machining speed and wire feed rate to obtain a desired inclination angle of the workpiece.