JPS6052890B2 - Wire cut electrical discharge machining control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for optimally controlling machining electrical conditions according to changes in the thickness and material quality of a workpiece material in a wire-cut electrical discharge machining device that performs electrical discharge machining using a wire electrode. be.

This type of wire cut electrical discharge machining equipment is 0.05~0.
A metal wire of about 3mφ is used as an electrode to connect the workpiece to the XY
This is a device that performs processing such as cutting and extracting a desired ring shape by applying relative feed in the direction.

In this case, the controlled feed is usually performed by giving a constant speed feed in steps of 1 μm per pulse to cause discharge, and the discharge energy etc. are caused to be discharged at a constant voltage in the machining gap to be controlled. When the thickness of the workpiece is constant, machining can be performed successfully even with the constant speed feed described above, but for example, when the thickness of the workpiece is not constant, the initial feed speed is Since machining is performed by setting the machining feed rate at the maximum plate thickness (maximum machining area), even if the plate thickness becomes thinner during machining, the feed rate remains at the slow speed set at the beginning, making it extremely efficient. bad. In addition, even when the thickness of the workpiece is constant, when machining into a shape with corners, it is better to increase the machining feed rate or weaken the 1 discharge energy so that the corners will not be rounded and can be machined sharply. Yes, constant speed feeding is not convenient. Additionally, a conventional method to compensate for the drawbacks of constant-speed feed machining described above is to detect the voltage in the machining gap, that is, the machining voltage, and control the machining feed rate so that this remains constant. . FIG. 1 shows the configuration and operation of this conventional device. A machining current is supplied between the wire electrode 1 and the workpiece 2 by a machining power source 3. Average value Eg of machining voltage and reference voltage E. are input to the error amplifier 4, and the average value Eg of the machining voltage and the reference voltage E. A machining feed rate F proportional to the error voltage that is the difference between the
Drives shaft motor My7. Here, Fx20Fy2=F
It is 2. The conventional device is configured as above, but
In such a configuration, the machining gap between the wire electrode 1 and the workpiece 2 becomes small, and the machining electric current FEE,g becomes the reference voltage E.

When it becomes smaller, the machining feed rate F becomes smaller, the machining gap is widened, and the machining voltage Eg becomes the reference voltage E. It works to bring it closer to. Conversely, when the machining voltage Eg becomes larger than the reference voltage EO, the machining feed rate F increases and eventually the machining voltage E
g is the reference voltage E. will come close to. In this way, with a device that feeds back the machining voltage to change the machining feed rate, the machining feed rate becomes faster when machining a thinner plate, and conversely, the machining feed rate becomes slower when the plate is thicker, resulting in an increase in the unit machining area. The machining speed per hit is almost constant. By controlling the machining feed rate to keep the machining voltage constant as described above, the loss in machining feed rate that occurs during steady feed can be avoided to some extent. Here, Fig. 2 shows the current waveform for charging the charge/discharge condenser, and its setting elements are charging and discharging. Peak current 1p of pulse current, pulse width Tp
, pause width Tr, etc. Further, FIG. 3 shows the inside of the machining power supply 3 of FIG. 1, where 9 is a capacitor whose capacity affects the roughness of the machined surface, and 10 is a current limiting resistor R that determines the charging peak current 1p. 11 is a switch, a switching transistor, and 12 is an oscillator, which controls the pulse width γP of the machining current.
, the pause width γr is determined.

13 is an internal DC power supply.

The energy for electrical discharge machining is determined by setting these electrical conditions.
Even if the average machining electric power FEEg is the same, the width is different,
Generally, when processing thin objects, concentrated discharge tends to occur, and unless the processing energy is lowered by changing the electrical conditions described above, the wire electrode will break.

When machining objects with varying plate thickness using a device that controls the machining feed rate so as to keep the machining electric power constant, the electrical conditions are set so that the wire electrode does not break at the thinnest part of the plate. , where the plate is thick, the electrical conditions are too weak and the machining speed decreases.

It has also been found that increasing the electrical conditions is better for machining accuracy in areas where the plate thickness is thicker. Further, the processed shape becomes substantially equivalent to a thinner plate at the corners, and in this case, sharper edges can be obtained by lowering the electrical conditions.

In this way, conventional constant-speed feed and machining speed control that maintains a constant machining voltage do not provide sufficient machining speed and accuracy, and the electrical conditions are manually set, which requires empirical elements and is difficult to set. It was difficult and there was a possibility of cutting the wire electrode, resulting in low reliability. This invention was made in view of these points, and the workpiece is machined by generating an electrical discharge in the machining gap where the wire electrode and the workpiece face each other, and the machining is performed using the voltage or machining current of the machining gap. In a wire-cut electric discharge machining control method that controls the feed rate, a plurality of sets of data are stored in memory, each pairing the electrical conditions of the machining power source that are optimal for each thickness of the workpiece and the corresponding machining feed rate. The electrical conditions are changed by shifting the data stored in the memory in accordance with the machining feed rate during machining, so that the machining feed rate during machining and the machining feed rate stored in the memory are roughly matched. This is what I did.

FIG. 4 is a block diagram of an embodiment of the present invention, in which a computer 8 or an equivalent device (hereinafter referred to as a computer) 8 is added to FIG. The computer 8 inputs the machining feed rate F, and changes the electrical conditions of the machining power source 3, that is, the peak power source 1p, pulse width γP, rest width γR, and capacitor capacity C, by interpreting changes in this as changes in plate thickness.
A detailed explanation of the invention will be given below.

In Fig. 4, the machining voltage E? Reference voltage E. is compared, the machining voltage Eg is always equal to the reference voltage E
The machining feed rate F changes so as to approach the value of EEO. Let us consider a case where the plate thickness becomes thicker after finishing processing with a constant plate thickness in such a configuration. The machining feed rate F is controlled to keep the machining gap voltage constant even when the plate thickness increases, and if the electrical conditions are also the same, the machining energy is considered to be almost constant, so the machining speed per machining area also increases. The processing feed rate becomes almost constant and decreases in inverse proportion to the plate thickness. The machining feed rate F is input to the calculator 8, and the decrease in the machining feed rate F is regarded as an increase in the thickness of the workpiece 2, and the machining feed rate is determined based on the electrical condition setting table stored in the memory inside the calculator 8. F1, that is, the optimum electrical conditions for the thickness of the workpiece 2 is selected and commanded to the machining power source 3. When the electric conditions for machining are strengthened, the machining energy increases and the machining feed rate F increases slightly, so the calculator 8 uses the increased machining feed rate F as a new input and further increases the electric conditions by taking into account the current output electric conditions. If a change is necessary, a new setting command is issued to the machining power source 3. In this way, the workpiece 2 can finally be processed under the optimal electrical conditions for its thickness. Figure 5 shows the plate thickness t and machining feed of the workpiece 2 when machining is performed using the conventional method by setting the electrical condition (machining energy) EC to the thinnest point of the plate thickness so that the wire electrode 1 is not cut. This shows the relationship with the speed F, and it can be seen that since the electrical conditions are constant, the machining feed speed F decreases in almost inverse proportion to the plate thickness t.

Figure 6 shows the relationship between the plate thickness t of the workpiece 2 and the machining feed rate F when the electrical conditions are experimentally set to obtain the maximum machining feed rate F. Even as the temperature increases, the electrical conditions become stronger, so the machining feed rate F does not decrease that much. FIG. 7 shows the automatic electrical condition setting method according to the present invention, and the experimentally determined graph of FIG. 6 is approximated by a line. Here, the electrical condition is approximated as ECO when the thickness t of the workpiece 2 is between 0 and 1, and the electrical condition ECl is approximated between the thickness t and t1, and the machining feed rate F at that time is FO- It is between F″0, F4 and F″4. FIG. 8 shows data stored in the internal memory of the computer 8, showing specific parameters of the electrical conditions EC for each plate thickness t, namely machining peak current 1p, pulse width γP, rest width γR, capacitor capacity C, and the The upper and lower limits of the machining feed rate F are listed. A more detailed explanation of the operation of the present invention will be given with reference to FIGS. 7 and 8.

Assume that a workpiece 2 whose thickness t satisfies T3 x t<T4 is being machined under electrical conditions EC4. This electrical condition, that is, the charging peak current is IP4 pulse width γP4, pause width γ
When machining with R4 and capacitor capacity C4, the machining feed rate F is between F4 and F''4. Now suppose that the thickness t of the workpiece 2 becomes t1 < t < T2. The electrical conditions are EC4. Therefore, the machining feed rate F increases to F>F4, which exceeds the upper limit of the machining feed rate F of the electrical condition EC4, so the computer 8 lowers the electric condition by one level and commands EC3 to the machining power source 3.Electrical condition EC3. So IP3-γP3-γR3-
Machining is performed under conditions C3, and the upper limit machining feed speed F at this time is F3, but since the actual plate thickness is thinner than the electrical condition EC3, the machining feed rate F exceeds F3. Calculator 8 is the 8th
While referring to the table shown in the figure, the electrical condition is further lowered from the electrical condition EC3 to output the electrical condition EC2. Since the plate thickness t of the workpiece 2 is between t1 and T2, the machining feed rate F is between F2 and F''2, and the calculator 8 continues to output this condition, that is, IP2-γP2-γR2-C2. Similarly, when the thickness t of the workpiece 2 increases, electrical conditions such that the current machining feed rate falls between the F upper limit and the F lower limit are automatically selected and output.In the above explanation, the calculator 8 Only the electrical condition parameters Ip-γp-γr-C were recorded in the internal memory of the machine, but if you add the open voltage of the power supply, the machining voltage, etc. that affect the machining speed, you can get more detailed information. In addition, by changing the electrical condition parameters, it is easy to obtain the maximum machining speed and keep the groove width constant.
Differences in processing electrical conditions depending on the material of the workpiece can also be accommodated by providing a separate table. In addition, these parameters can be easily controlled by storing wire feed speed, wire tension, machining fluid pressure, machining fluid conductivity, etc. as a table in the memory. As described above, according to the present invention, there is no need to set electrical conditions according to the workpiece as in the past, and operability is improved. There is no risk of damage etc.

Furthermore, since the electrical condition settings become more reproducible, machining accuracy also improves.

In particular, when machining workpieces with varying thicknesses, conventional methods extremely slow down the machining speed and degrade accuracy, but with this invention, the processing speed is automatically adjusted according to the thickness of the workpiece. Since the optimal electrical conditions are set, machining speed and machining accuracy are greatly improved, there is no chance of incorrect electrical condition settings, wire breaks are eliminated, and reliability is greatly improved. In addition, when the thickness of the workpiece varies widely, unmanned operation is practically impossible with conventional machines, but according to the present invention, highly advanced machining can be achieved completely unmanned. In the explanation of this invention, the electrical conditions were optimally set according to the plate thickness, but the plate thickness is not particularly necessary to output the electrical conditions from the memory, and it is sufficient to input the machining feed rate during machining. It's self-evident.

[Brief explanation of the drawing]

Figure 1 shows a device that controls the machining feed rate F to keep the machining voltage constant during machining in a conventional wire-cut electrical discharge machine, and Figure 2 shows the current pulse waveform of the machining power source shown in Figure 1. 3 is a detailed internal view of the machining power source, FIG. 4 is a diagram showing an embodiment of the present invention, and FIG. 5 is a conventional machining method in which machining is carried out at a constant voltage and electrical conditions. Figure 6 shows the relationship between the machining feed rate and the thickness of the workpiece when the electrical conditions are changed in response to changes in the machining feed rate according to the present invention. A diagram showing the conditions and machining feed speed. Figure 7 is a graph when Figure 6 is approximated by a polygonal line and stored in the computer's memory. Figure 8 is a graph for storing Figure 7 in the computer's memory. It is a figure showing a format. In the figure, 1 is a wire electrode, 2 is a workpiece, 3 is a processing power source, and 8 is a computer.

Claims (1)

[Claims] 1. Wire-cut electrical discharge machining in which the workpiece is machined by generating electrical discharge in the opposing machining gap between a wire electrode and the workpiece, and the machining feed rate is controlled by the voltage or machining current in the machining gap. In the control method, multiple sets of data are stored in memory, each pairing the electrical conditions of the machining power supply that are optimal for each thickness of the workpiece and the corresponding machining feed rate, and the data is set in memory to correspond to the machining feed rate during machining. wire cut electric discharge machining control characterized in that the data stored in the memory is shifted to change the electrical conditions, and the machining feed rate during machining and the machining feed rate stored in the memory are approximately matched. Method. 2. The wire-cut electric discharge machining control method according to claim 1, wherein the contents stored in the memory can be set from the outside. 3. The first claim characterized in that the conditions related to the processing speed can be selected for each material of the workpiece.
The wire cut electric discharge machining control method according to item 1 or 2.