JPS6128452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a roll-shaped workpiece that uses electric discharge to finish the outer circumferential surface of a roll-length workpiece with a satin finish with a constant surface roughness (forms a satin-like uneven surface on the surface of the roll-shaped workpiece). The present invention relates to an electrical discharge machining apparatus for processing a workpiece (hereinafter simply referred to as a roll), and in particular controls the moving speed of an electrode in the direction of the rotational axis of the roll in proportion to the average machining current between the electrode and the roll.

Conventionally, when finishing the surface of a steel strip rolling roll, especially a cold rolling roll, to a matte finish, a method has been used to create impressions on the roll surface by projecting hard metal particles such as shot or grit onto the polished roll surface. However, 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 also has a shape that is independent of the manufacturing method and hardness of the roll. 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.

However, when manufacturing this roll electrical discharge machining device, one obstacle is that it is extremely difficult to uniformly satin finish the entire surface of the roll, and the accuracy of this roll surface depends on the speed at which the electrode moves in the direction of the roll rotation axis. ,
changes slightly.

By the way, in this roll electric discharge machining apparatus, the electrode is controlled to move at a constant speed in the direction of the rotation axis of the roll, but the roll surface accuracy when the electrode is moved at a constant speed in the direction of the rotation axis of the roll will be described.

In Figures 1 and 2, 3 is a roll, 11, 1
Reference numeral 1' denotes two electrodes that face the roll 3 across a machining gap, and the roll 3 is driven to rotate in its circumferential direction, and the electrodes 11 and 11' are driven at a constant speed in the direction of the rotational axis of the roll 3. When being moved, the following phenomena occur.

That is, in electric discharge machining, the machining speed is generally not constant, but changes from time to time depending on the state of the machining gap, and the purpose of this invention is to finish the entire roll surface with a matte finish. In this case, after the start of machining, the machining speed gradually increases and the average machining current tends to increase until the entire surface of the machined part is satin-finished.

Generally speaking, it is well known in electric discharge machining that the average machining current is proportional to the machining speed, as described below.In other words, as a satin surface is formed, electric discharges are more likely to be formed and the machining speed increases. The average machining current increases in proportion to the machining speed, and eventually the machining speed and average machining current become approximately constant values.

For this reason, as illustrated in Figures 1 and 2, the amount of machining removed at the beginning of machining is small and increases as machining progresses.
It has been revealed that if the electrode 11 is moved at a constant speed in the direction of the rotational axis of the roll 3, a uniform satin-finished surface cannot be obtained over the entire surface. To explain this in more detail, the part indicated by A in FIG. The part indicated by B in the figure is the machined part where the electrode 11' is processed by moving the distance β in the right direction from the position shown in the figure as a starting point, and the part C in FIG.
1 and 11', and as illustrated below the electrodes 11 and 11' in FIGS. There is a fact that part R is formed.

This is the same even when the roll 3 is processed by one electrode 11, and FIG. 3 shows this state. This FIG. 3 is a drawing corresponding to FIGS. 1 and 2, and the explanation thereof will be omitted by giving the same reference numerals, but in this case, an unprocessed portion remains at the processing start portion of the roll 3. Furthermore, when machining becomes unstable at a portion other than the machining start portion, the machining speed decreases, leaving an unmachined portion indicated by R' in the figure.

Next, the average machining current and machining speed will be explained. It is known that the following equation holds true when the amount of machining per time is calculated from the number of times electric discharges occur after performing electric discharge machining many times. That is, m=A・I _p ^B・τp where m is the machining weight per discharge (g) and I _p is the discharge current peak value (A).

τ _p is the discharge current pulse width (μs).

A and B are constants determined by the polarity of the electrode and the combination of the materials of the electrode and the workpiece, respectively. When processing a workpiece made of steel using a copper electrode as the positive electrode, A
=1.5×10 ² , B=1.5.

From the above, the processing speed per minute W (g/min) is calculated as follows: W = 60m x f = 60m・1/T = 60・m/(τ _p +τ _r +τ _o ) = 60・A・I _p ^B・τ _p / (τ _p + τ _r + τ _o ) = 60・A・I _p ⁰ . ⁵・I _p・τ _p / (τ _p + τ _r + τ
_o ) = ⁶⁰・A・I _p ^0.5・I (g/min), and it can be seen that the machining speed per minute is proportional to the average machining current. In the above formula, I is the average machining current.

f is the number of discharge occurrences per unit time.

T is the time of one cycle.

τ _r is the discharge current pulse pause width (μs).

τ _o is τ _p + τ _r (μs).

It is.

As described above, when the electrode is controlled to be fed at a constant speed in the direction of the rotational axis of the roll as in the conventional method, there is a problem that uniform processing cannot be performed over the entire surface of the roll.

In view of this point, the present invention controls so that the electrode is moved in the direction of the roll rotation axis in proportion to the average machining current in order to obtain a uniform satin-finished surface over the entire surface of the roll.

An embodiment of the present invention will be described below with reference to FIG. This figure shows a device equipped with two head columns, which will be described later.

That is, in Figure 4, 1 is bet, 2, 2'
3 is a roll of the workpiece that is supported horizontally by bearings 2 and 2'; 4 is a roll that chucks one end of the roll 3; and 5 is a roll that is installed on the bed 1. It is a rotation drive device that rotates the celery 4 and rotates the roll 3. Reference numerals 6 and 6' designate bases which are configured to be able to slide left and right on the bed 1 by the actions of column traverse drive devices 7 and 7' and feed screws 8 and 8'. 9, 9' are head columns fixed on the bases 6, 6' (the head columns are considered to be integrated and are referred to as such); 10;
10' is an electrode holder attached to the head columns 9, 9'; 11, 11' are a plurality of electrodes attached at equal pitches to the holders 10, 10' via insulating plates 12, 12'; ,11′
are opposed to the roll 3 with a predetermined gap therebetween, and are made of a steel plate having the shape shown in a perspective view in FIG. 5, and are formed in the same shape. 13 is a processing tank held on the roll 3, 14 is a processing tank 1
The machining fluid 1 is supplied by a pump (not shown) into the machining tank 13 and overflows from the machining tank 13.
4 is filtered and supplied to the processing tank 13 again. Further, reference numerals 15 and 15' denote pulse power supply devices, which are connected to each electrode 11 and 11' and the roll 3 so as to generate an electric discharge. In the diagram,
Although the positive electrode is connected to the electrodes 11 and 11', and the negative electrode is connected to the roll 3, processing can also be performed in the opposite manner. Further, main axis feeding of the electrodes 11, 11' in a direction perpendicular to the machined surface of the roll 3 is carried out independently by each head column 9, 9'. Further, 16 and 16' are detection devices for detecting the average machining current, and 17 and 17' are column traversal drive devices 7 and 7' at a speed proportional to the average machining current detected by the detection devices 16 and 16'. It is a movement speed control device that limits.

The embodiment according to the present invention is constructed as described above, and the processing method thereof will be explained next.

First, the electrodes 11, 11' are mounted on the electrode holders 10, 10' with high accuracy at electrode mounting pitches corresponding to the processing width of the roll 3.

Next, a machining fluid 14 is put into the machining tank 13, and the roll 3 is rotated at a constant speed by the roll rotation drive device 5. Then, the electrodes 11 and 11' of each head column 9 and 9' start machining at the same time (the spindle feed is controlled so that the electrodes 11 and 11' of the head columns 9 and 9' start machining at the same time). The detection signals from the machining current detectors 16, 16' control the column transverse feed drive devices 7, 7' via the movement speed controllers 17, 17', and each head column 9, 9' is controlled at a speed proportional to the average machining current. Machining of roll 3 is carried out while horizontally feeding the roll. In this way, the entire surface of the roll 3 can be uniformly processed from the start of processing to the end of processing without being affected by changes in processing speed.

To explain in more detail, the machining speed in electric discharge machining, that is, the amount of metal removed from the roll 3 per unit time is proportional to the average machining current and is uniquely determined. For example, when the average machining current is kept constant, the machining speed, that is, the amount of metal removed, becomes a predetermined value, so if the moving speed of the head columns 9, 9' in the direction of the roll rotation axis is increased, the machining depth on the surface of the roll 3 can be increased. The depth of machining becomes shallower in inverse proportion, and if the speed is made slower, the depth of machining becomes deeper in inverse proportion.

However, in reality, the average machining current, that is, the machining speed, varies depending on the state of the machining gap.

Therefore, in order to keep the machining depth constant and obtain a uniform machined surface over the entire surface, first, the roll 3 is rotated at a constant speed using the embodiment shown in FIG. 4, and the power supply is turned off. A predetermined voltage is applied from electrodes 15 and 15' to start discharge between the electrodes 11 and 11' and the roll 3.

Next, the average machining current of each electrode 11, 11' is detected by the average machining current detectors 16, 16', and the moving speed controllers 17, 17' adjust the head columns 9, 9' in the direction of the roll rotation axis. The moving speed is proportional to the average machining current, i.e.
When there is an unstable machining area and the average machining current decreases, the moving speed of the electrodes 11, 11' in the direction of the roll rotation axis is reduced, and when the average machining current increases, the electrodes 11, 11' By controlling the movement speed of ' in the direction of the roll rotation axis to increase, the machining depth of the surface of the roll 3 becomes constant.

In the above description, a device comprising a plurality of head columns having a plurality of electrodes has been described, but there is no difference in the technique even if the number of electrodes is one.

FIG. 6 shows an example device in which the number of electrodes 11 is one. The same or corresponding parts as in FIG.
In the case of 1 piece, the processing time becomes very long, so it may not be put to practical use.

As explained above, according to the present invention, the average machining current is detected and the detection signal is used to control the moving speed of the electrode in the direction of the roll rotation axis so as to be proportional to the average machining current. As illustrated in FIG. 3, it is possible to provide an electric discharge machining apparatus that does not leave any unprocessed portions on the roll surface and can produce rolls with a uniform machined surface.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams for explaining the moving speed and machining accuracy of two electrodes and the rotational axis of a roll-shaped workpiece, and Figure 3 is a diagram of one electrode and the rotational axis of a roll-shaped workpiece. 1 and 2 for explaining the moving speed and machining accuracy in the direction, FIG. 4 is a diagram for explaining one embodiment of the device of the present invention, and FIG. FIG. 6 is a perspective view of an electrode used in the device shown, and is a diagram for explaining another embodiment of the device of the present invention. Note that the same reference numerals in the figures indicate the same or corresponding parts. 3 is a roll-shaped workpiece, 5 is a roll rotation drive device, 7, 7' is a column transverse feed drive device, 9,
9' is a head column, 11, 11' are electrodes, 15,
15' is a power supply device, 16 and 16' are detection devices, 1
7 and 17' are movement speed control devices.

Claims (1)

[Claims] 1. While rotating the roll-shaped workpiece, an electrode is moved in the direction of the rotation axis of the roll-shaped workpiece, and an electric discharge is formed between the electrode and the roll-shaped workpiece, so that the surface of the roll-shaped workpiece is In an electric discharge machining device for machining a material into a matte finish, a detection device detects an average machining current between the electrode and the roll-shaped workpiece, and a detection signal controls the rotation of the roll-shaped workpiece by the detection device. An electric discharge machining apparatus for a roll-shaped workpiece, comprising a movement speed control device that makes the movement speed in the axial direction proportional to the average machining current.