JPS5918178B2 - Electric discharge machining method - Google Patents

Description

[Detailed Description of the Invention] 10 The present invention provides an electric discharge machining method for finishing the surface of a roll-shaped or plate-shaped workpiece with a constant surface roughness by electric discharge (making the surface of the workpiece a satin-like uneven surface). The present invention relates in particular to electrode feeding control.

15 Below, a case will be described in which the method of the present invention is applied to satin finishing of the surface of a roll-shaped workpiece.

Conventionally, for example, when finishing the surface of a steel strip rolling roll, especially a cold rolling roll, with a satin finish, hard metal particles such as shot or grid are projected onto the polished 20-roll surface to create impressions on the roll surface. However, in recent years, attempts have been made to perform this type of machining by electrical discharge machining.

As is well known, electric discharge machining involves inserting an insulating liquid, such as kerosene, into the narrow machining gap between the electrode and the workpiece.
This is a method of machining the surface of a workpiece by periodically applying a pulse waveform voltage between the electrode and the workpiece to cause discharge. By repeating such electrical discharge machining on the roll surface, rotating the roll in the circumferential direction, and at the same time moving the electrode gradually 30 degrees in the direction of the rotation axis of the roll, the roll surface will continuously form a spiral-shaped satin finish. After being processed, 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 not only has a much more regular surface roughness that can be adjusted more freely by changing processing conditions than mechanical indentations made by metal particle projection, but also has a much more regular shape. It has many advantages, such as being independent of the manufacturing method and hardness, and the metal structure on the roll surface being hardened by electrical discharge, making it ideal for rolling rolls. By the way, in normal machining methods such as drilling, the electrode feed control is performed by comparing the voltage of the machining gap with a preset reference voltage so that the average voltage value of the machining gap is always constant. A method is used to control a drive device consisting of a motor, hydraulic pressure, etc. based on this difference, and for this reason, the machining gap repeatedly oscillates around a certain standard depending on the frequency response of the drive device. It is something.

When this control method is applied to machining of a rotary roll, etc., which is the object of the present invention, a temporal change in the machining amount due to vibration of the machining gap appears as a striped pattern on the surface of the roll. Of course, this change in the amount of machining is minute and cannot be determined just by looking at the machined surface with the naked eye, but can only be barely discerned by a Chiyoke test in which Chiyoke powder is applied to the roll surface or a test using an oil stone. However, even this degree of striped pattern will have an adverse effect on the steel strip if it is used as a steel strip rolling roll for final rolling, and the steel strip will be rejected as a product. This invention provides an electric discharge machining method that does not cause striped patterns on the roll surface as described above, and uses a mixture of low-voltage pulses and high-voltage pulses in the machining pulse, and discharges the machining gap by applying the low-voltage pulses. This method is characterized by forming a matte surface on the surface of the roll by continuously applying high voltage pulses for a predetermined period of time after the length is set to a possible length.

An embodiment of the method of this invention will be described below with reference to the drawings.

Referring to FIG. 1, 1 is an electrode for machining, 2 is a main shaft that holds the electrode 1, 3 is a pulse motor that feeds the electrode 1, 4 is opposed to the electrode 1 through a machining gap, and has a satin finish. The roll to be processed, 5 is a low voltage pulse DC power supply,
6 is a current limiting resistor for low voltage pulses, 7 is a switching element for low voltage pulses, 8 is a DC power supply for high voltage pulses, 9 is a current limiting resistor for high voltage pulses, 10 is a switching element for high voltage pulses, 11 is a high voltage pulse A unidirectional rectifying element such as a diode that prevents the current of the high voltage power supply 8 from flowing back into the low voltage power supply 5 when the voltage pulse switching element 10 is operated;
12 is an amplifier circuit for driving the switching element 7 for low voltage pulses, 13 is an amplifier circuit for driving the switching element 10 for high voltage pulses, 14 is an oscillation circuit for generating a rectangular waveform, and 15 is a processing current. 16 is a determination circuit that determines the presence or absence of machining current when only low voltage pulses are applied; 17 is a drive circuit that receives the signal from the determination circuit 16 and drives the pulse motor 3.

Note that the transmitting circuit 14 is configured to thin out high voltage pulses at certain regular intervals and send the signal to the amplifier circuit 13.

In the above apparatus, a high voltage pulse and a low voltage pulse are simultaneously applied to the machining gap between the electrode 1 and the roll 4, but the second
As shown in the figure, since the oscillation circuit 14 sends a signal to the amplifier circuit 13 to thin out high voltage pulses at a certain period, only low voltage pulses are sometimes applied to the machining gap.

The presence or absence of the machining current at that time is detected by the detection circuit 15, and the pulse motor 3 is driven to narrow the machining gap until the occurrence of electric discharge is recognized in the detection signal, and the electrode feed is stopped at the same time as the electric discharge starts, and then after a certain period of time. A high voltage pulse is continuously applied for a period of time. In this way, the machining gap is fixed at a length that allows discharge by low voltage pulses, so that discharge can be efficiently performed with subsequent continuous application of high voltage pulses. In addition, in the method of this invention, since the roll, which is the workpiece, is rotating, a new machined surface is constantly created, so there is no accumulation of machining debris in the machining gap, and changes in the machining gap are prevented. It will depend almost entirely on the electrode wear rate.

According to the results of actual processing experiments, the surface roughness is 18 μB.
nle, the electrode is a copper plate with a width of 501n and a thickness of 21m, a circumferential speed of the roll surface of 6m/Min, and a diameter of 620mm. When processing a roll, the electrode wear rate was 92 μ per roll rotation under conditions that caused the greatest electrode wear (pulse peak value 30 A, pulse width 8 μs, pause time 2 μs).
That is, the roll diameter is 620? Therefore, the wear rate with respect to the relative movement distance between the electrode and the roll is 92μ/6207cm
=0.047μ/I. Assuming that the low voltage pulse is 80V and the high voltage pulse is 300V, it is thought that there is a difference of 10μ or more in the discharge start gap, so even if there is a change of about 5μ in the machining gap, the difference between the discharge pulse and the applied pulse is It is thought that there is almost no difference in the proportions. In order to produce this 5 μ machining gap change due to electrode wear, it is necessary to calculate 5/0.047 from the electrode wear rate.
This is because a relative movement distance between the electrode and the roll of 106[0 tn] is required, that is, the above-mentioned transfer distance is 1060n, and it is considered that there will be no change in processing even if the electrode feeding mechanism is fixed. Although the method of the present invention has been illustrated and explained above with reference to the case of forming a matte surface on the surface of a roll, the present invention is not limited thereto. Of course, this method can also be applied to the case where the processed part is moved and a matte surface is formed on the surface of the workpiece, and the same effect can be obtained even if the electrode is moved relative to the workpiece. It is something to play.

As explained above, according to the method of the present invention, when the surface of the workpiece is satin-finished, the machining gap is fixed as much as possible without causing unnecessary vibration of the machining gap. Moreover, since the amount of machining is kept constant, a good machined surface can be obtained without forming stripes on the machined surface.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining the method of the present invention, and FIG. 2 is a diagram showing a machining gap voltage waveform during machining. In the figure, 1 is a processing electrode, 3 is a pulse motor, 4 is a roll-shaped workpiece, 5 is a DC power source for low voltage pulses, 7 is a switching element for low voltage pulses, 8 is a DC power source for high voltage pulses, 10 is a high voltage pulse switching element, 1
2 and 13 are amplifier circuits, 14 is an oscillation circuit, 15 is a machining current detection circuit, 16 is a discrimination circuit, and 17 is a drive circuit.

Claims (1)

[Claims] 1. A machining gap is formed between the electrode and the workpiece, and the feed of the electrode is controlled to control the machining gap, and the machining part of the workpiece to be machined by the electrode is relative to the electrode. In an apparatus that processes the surface of the workpiece into a matte finish by moving the workpiece, a high-low voltage pulse containing a mixture of high-voltage pulses and low-voltage pulses is applied to the processing gap, and only the low-voltage pulse is discharged into the processing gap. The feed of the electrode is controlled so as to narrow the machining gap while the low voltage pulse is applied until the pulse is applied, and when electric discharge occurs in the machining gap while only the low voltage pulse is applied, the feed of the electrode is stopped and An electrical discharge machining method in which application of the low voltage pulse is cut off, and then the high voltage pulse is applied for a predetermined period of time to form a discharge to machine the workpiece.