JPS5949853B2 - Electric discharge machining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention processes the outer surface of a workpiece (for example, a roll-shaped workpiece) by electrical discharge machining.

For example, the present invention relates to an electric discharge machining method for finishing a roll-shaped workpiece with a satin finish with a constant surface roughness. Conventionally, workpieces such as steel strip rolling rolls, especially cold rolling rolls (hereinafter, rolling rolls will be explained as examples,
When finishing the surface of a workpiece (the workpiece is simply referred to as a roll) with a satin finish, a method is adopted in which hard metal particles such as shot or grid are polished and projected onto the roll surface to create impressions on the roll surface. However, in recent years, attempts have been made to perform this type of machining by electric discharge machining.

As is well known, electric discharge machining involves interposing an insulating liquid such as kerosene in a narrow discharge gap between an electrode and a workpiece, and periodically applying a pulse voltage between the electrode and the workpiece to generate an electric 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 continuous spiral-like satin finishing. , 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 matte surface has a larger difference in unevenness and a much more regular shape than mechanical impressions made by metal particle projection, but the shape depends on the manufacturing method and hardness of the roll. Furthermore, it 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. Next, we will explain the satin finishing of rolls using electric discharge based on an actual mechanical device.

In FIG. 1, 1 is a processing pulse power supply, 2 is an electrode made of, for example, a copper plate, 3 is a roll to be satin finished, 4 is a mounting base for the electrode 2, and 5 is a connection between the electrode 2 and the roll 3. This is a head column for controlling the machining gap.

The head column 5 is moved in the direction of the arrow during processing by a drive device (not shown). 6 is the above roll 3
T is a speed reducer, 8 is a roll rotation motor, and 10 is a power supply brush for supplying power to the roll 3.

In machining, first, machining conditions for the machining pulse power supply device 1 are set.

These processing conditions determine the surface roughness of the satin finish on the surface of the roll 3. The machining gap between the electrode 2 and the roll 3 is placed in an insulating liquid such as kerosene, and a pulse voltage is applied to the machining gap by the power source 1 to generate an electric discharge, thereby performing electrical discharge machining. At this time, the roll 3 is simultaneously rotated and the electrode 2 is moved in the direction of the rotation axis of the roll 3. In Fig. 1, the head (hereinafter referred to as the main head HM) on which five electrodes 2 are attached is moved from left to right in the figure by the distance of the electrode mounting pitch, and is the part of the roll 3 through which the copper plate passes when it is rolled. The surface is processed, and the left and right heads (hereinafter referred to as auxiliary heads Hs) each having one electrode 2 attached thereto are moved in the direction away from the roll to process the ends of the roll.
In Fig. 1, when machining is performed only with the main head 5,
As shown in FIG. 2, the shape of the roll after processing is such that the end portions of the roll remain unprocessed and are higher than the processed portion in the center. When actually machined with a machined surface roughness of 18 μRz, this machining step L
, is approximately 20μ. The thickness of the copper plate to be rolled is sufficiently large compared to the processing step, and the board width is smaller than the effective processing width Le processed by the main head (the length in the direction of the roll rotation axis of the uniformly satined portion), so this step is This is not a problem during rolling, but for example, when idling the upper and lower rolls by directly pressing the pear-finished surfaces of the upper roll and lower roll to extend the life of the rolls, the ends contact each other and the center does not contact, which defeats the purpose. I can't fulfill it. Therefore, in the past, in order to make the roll ends flush with the center part, left and right auxiliary joints were provided as shown in Figure 1, and during processing, each was fed out in the direction away from the roll ends. are being processed.

However, with such processing, when the electrode comes to a position where it is off the roll end, as shown in Figure 5, it is difficult for the current i to flow through the part of the electrode that is off the roll surface, and therefore the wear rate of the electrode decreases. Therefore, at the end of machining, the electrode of the auxiliary head Hs has an electrode consumption level L2 as shown in Fig. 3.
occurs. Therefore, when machining the next roll, the electric discharge concentrates on this electrode tip 21 and creates an arc state, making machining impossible. Therefore, it was necessary to replace the electrode of the auxiliary head with a new electrode every time one roll was processed.

Therefore, this invention focused on the above-mentioned drawbacks, and when processing the roll end, reciprocates the auxiliary head Hs so that the electrode moves in and out of the roll end by a small amount, thereby keeping the electrode tip flat even at the end of processing. It is meant to be.

This invention will be explained below. That is, as shown in Fig. 4, processing using the main head HM is carried out in the same manner as before, and the left and right auxiliary heads Hs are first fed horizontally in the direction away from the end of the roll.
At a position where the electrode 2 protrudes from the substantial end 31 of the roll by a small amount S (approximately 1/10 of the electrode width), the feeding direction is reversed and the electrode 2 is fed to a position where it is retracted by a small amount S from the roll end. Reverse the feed direction again.

Repeat this operation and perform reciprocating cross-feeding until the machining depth at the end of the roll is slightly larger than the machining depth at the center.
Processing is completed at the position where the electrode 2 is retracted from the end of the roll. In this way, the electrode 2 of the auxiliary head is so-called shaped to have a flat tip, and can be used as is when processing the next roll, and the processed roll will not cause any problems in use.

As a device for reciprocating the electrode 2 in this way, the electrode 2 is
The column is transversely fed by a screw shaft driven by a motor, and a limit switch is provided corresponding to the minute amount s, and the limit switch reverses the direction of rotation of the motor, thereby making it possible to drive the column back and forth.

Then, when the electrical discharge machining is finished, the drive is controlled so that the entire width of the electrode is always facing the roll surface. Note that the reciprocating drive mechanism is not limited to these, and may be driven by a hydraulic cylinder or the like, as long as it drives the electrodes back and forth. As explained above, the present invention enables the roll end to be machined without any hindrance by reciprocating and cross-feeding the electrode so as to move in and out of the roll end by a small amount during roll end processing. This makes it possible to significantly reduce the frequency of electrode replacement.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram explaining the electric discharge machining method for a roll-shaped workpiece, Figure 2 is an explanatory diagram showing the roll shape when machining is performed only with the main head, and Figure 3 is a schematic diagram showing the conventional machining method. FIG. 4 is a schematic diagram showing the method of the present invention, and FIG. 5 is an explanatory diagram of the operation of the present invention. Note that the same reference numerals in the figures indicate the same or equivalent parts. 2... Electrode, 3... Roll shaped workpiece, 4... Electrode mounting base, 5... Head column.

Claims (1)

[Claims] 1. In electric discharge machining, in which the surface of the workpiece is processed by moving the workpiece and the electrode, the electrode that is placed opposite to the end of the workpiece and processes this end is placed on the workpiece. An electric discharge machining method characterized in that the electrode is moved back and forth at a predetermined amplitude with the end as a reference, and when machining is completed, the electrode is in a position facing the workpiece over the entire width of the tip.