JPS5949854B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention moves an electrode and a workpiece relatively, and performs electrical discharge machining on the surface of the workpiece by repeating it multiple times (for example, creating a matte finish on the surface of a roll-shaped workpiece). Regarding electrical discharge machining equipment (which forms uneven surfaces), the relative movement speed is not constant, but is set within a range that does not affect machining, especially in response to periodic changes in machining speed that adversely affect the surface roughness of the machined surface. The present invention relates to a device that can eliminate non-uniformity on a machined surface, where the machining state of a specific part of the machined surface changes from that of other parts, which is caused by periodic changes in the machining speed, by making a minute change.

Conventionally, when finishing the surface of a workpiece, such as a copper strip rolling roll, especially a cold rolling roll (hereinafter, a rolling roll will be explained as an example, and the workpiece will be simply referred to as a roll), shot has been used. , hard metal grains such as grids,
Previously, a method was adopted in which a beam was projected onto a polished roll surface to form an indentation on the roll surface, but in recent years attempts have been made to perform this type of machining by electrical discharge machining. As is well known, electrical discharge machining involves interposing an insulating liquid, such as kerosene, in a narrow machining gap between an electrode and a workpiece, and periodically applying a pulse voltage between the electrode and the workpiece to generate an electrical discharge. This is a method of processing the surface of a workpiece by By repeating such electrical discharge machining on the roll surface, rotating the roll in the circumferential direction, and at the same time gradually moving the electrode in the direction of the rotation axis of the roll, the roll surface will undergo a continuous spiral satin finish. The roll surface can be covered with discharge marks. This is a method of uniformly applying a satin finish to the surface of a roll using electrical discharge machining. The resulting satin surface not only has a larger difference in unevenness and a much more regular shape than mechanical impressions made by metal particle projection, but the shape also depends on the roll manufacturing method and hardness. figure,
It also has many advantages, such as the metal structure on the roll surface being hardened by electrical discharge, making it ideal for use as a rolling roll. By the way, the conditions that should be met by the electrical discharge machining equipment that processes this roll are 1. The device must be capable of electric discharge machining of rolls in a short time; 2. 3. The equipment can process the roll surface uniformly over the entire surface (for example, a satin surface with a uniform desired surface roughness); 3.
For equipment that moves the roll and electrode relative to each other in a spiral orbit, the equipment must not leave spiral machining streaks on the roll surface, that is, the equipment must not cause uneven machining due to relative movement. Among the conditions for satisfying the above two items, the present invention solves periodic fluctuations in the machining voltage due to instability of the machining pulse power source, and discharge gap caused by periodic mechanical vibration between the poles. When a regularity occurs in which the period of fluctuation is an integer multiple of the roll's outer circumference, that is, the distance of repeated relative movement, a horizontal striped pattern of intensity appears in a specific part, as shown in Figure 1. The purpose of this is to suppress the phenomenon that occurs as much as possible.

By the way, when the machining voltage fluctuates as described above during electrical discharge machining, the input to the electrical discharge part (and therefore the machining amount)
p=V-I-T P: Input V: Machining voltage I: Machining current t: Machining current energization time It varies depending on the value of v, so the amount of machining per unit time (i.e. machining speed) will fluctuate.

In addition, when the gap between the machining electrodes (discharge gap) varies due to mechanical causes, the input to the discharge part (machining amount) is P=V-I-t ・η P: Input V: Machining voltage E: Machining current η: Efficiency (treated as a function of the discharge gap) t: Machining current The efficiency η, which is treated as a function of the discharge gap, fluctuates as shown by the energization time, and the amount of machining per unit time (machining speed ) will change.

As mentioned above, if the fluctuation period of the machining voltage or the discharge gap becomes regular with respect to the relative movement distance as described above, the uneven surface of the discharge machining will overlap in a specific circumferential portion.
This phenomenon will be exacerbated as the number of machining increases.

Therefore, the uniformity of the entire circumferential surface of the roll is impaired, making it impossible to satisfy the above two conditions. Therefore, in order to reduce this phenomenon as much as possible, the roll rotation speed should be adjusted in processing so that the above-mentioned fluctuation period does not have the regularity that it matches an integral J number multiple of the roll outer circumference length (relative movement distance). It suffices to change it by a minute amount within a range that does not have any effect.

The method of changing the roll rotation speed is as shown in FIGS. 2A and 2B.

In other words, the roll rotation speed may be slightly varied continuously (Fig. a) or in steps (Fig. B) relative to the reference rotation speed Rs. By doing this, the unevenly machined surface is dispersed and normal electric discharge machining is superimposed on the machined surface, so that a uniform machined surface can be obtained over the entire surface. As explained above, in order to obtain a desirable roll with a uniform machined surface over the entire surface, conditions such as the electric processing conditions of the pulse power supply device and the moving speed of the electrode in the roll rotational axis direction, which affect the surface roughness of the machined surface, are necessary. It is necessary to select and set each to an optimum value, and to set the roll rotation speed optimally against disturbances (variations in machining voltage and variations in machining gap due to mechanical causes). In this invention, attention is paid to the roll rotation speed among these items, and in order to prevent uneven surface roughness from occurring due to disturbances, the roll rotation speed is not constant but is varied by a minute amount.

An embodiment of the present invention will be described below with reference to FIG.

That is, in FIG. 3, 1 is a bed, 2 and 2' are bearings installed on the bed 1, 3 is a roll of the workpiece supported horizontally by the bearings 2 and 2', and 4 is a roll of the roll 3. The part 1 and 5 which chittle one end are a roll rotation drive device installed on the bed 1, and the part 4 shown in FIG.
The roll 3 is rotated by rotating the roll 3.

Reference numeral 6 denotes a base, which is configured to be slidable on the bed 1 from side to side in the figure by the action of a column lateral feed drive device (T) feed screw 8. 9, 9' are head columns fixed on the base 6; 10, 10' are electrode holders mounted on the head column 9; 11, 11' are the holders 10, A plurality of electrodes are installed at equal pitches on 10', and these electrodes 1
1 and 11' are opposed to the roll 3 through a machining gap, and are made of copper plates having the shape shown in a perspective view in FIG. 4, and are also formed in the same shape.

13 is a machining tank held on the roll 3; 14 is a machining fluid supplied into the machining tank 13 by a pump not shown; the machining fluid 1 overflowing from the machining tank 13;
4 is finished and is supplied to the processing tank 13 again.

Further, 15, 15/ is a pulse power supply device, and each of the above electrodes 11
and the roll 3 so as to form an electric discharge. In the figure, the positive electrode is connected to the electrode 11, and the negative electrode is connected to the roll 3, but processing can also be performed in the reverse direction. Further, the spindle feeding of the electrode 11 in a direction perpendicular to the processed surface of the roll 3 is carried out independently by each head column 9, 9'. Furthermore, 1
6 is a roll rotation speed control device which forms the core of this invention;
The roll rotation drive device 5, which affects the roughness of the satin surface of the roll 3, is controlled to set the rotational speed of the roll 3 to an optimum value. The apparatus of the present invention is configured to vary the relative movement speed of the electrode and the workpiece by a minute amount in order to obtain a desired processed surface, as described above, so that an extremely homogeneous processed surface can be obtained.

[Brief explanation of the drawing]

Fig. 1 shows a conventional example, and shows a horizontal striped pattern appearing on the entire circumferential surface of the roll, Fig. 2A and b are explanatory diagrams showing a state in which the roll rotation speed is varied by a minute amount with respect to the reference rotation speed, FIG. 3 is an overall schematic diagram showing an embodiment of the present invention, and FIG. 4 is a perspective view showing an example of the electrode shape used in the device shown in FIG.

Claims (1)

[Claims] 1. In an apparatus that repeatedly performs electric discharge machining on the surface of a workpiece by placing the workpiece and an electrode facing each other and moving them relatively, a drive source that moves the electrode and the workpiece relative to each other is used. An electrical discharge machining device characterized by comprising a control device that temporally varies a relative movement speed by a minute amount with respect to a reference value.