JPS6211969B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention efficiently processes workpieces with changes in thickness.
Furthermore, the present invention provides a wire cut electric discharge machining apparatus that performs machining with high precision.

Fig. 1 shows a schematic configuration diagram of a conventional wire-cut electric discharge machining device. 1 is a running wire electrode, which is usually made of copper, tungsten, or brass wire with a diameter of about 0.04 to 0.2φ, and is connected to the workpiece 2. A high-frequency pulse voltage is applied to form an electric discharge, and a relative shape feed is applied between the wire electrode 1 and the workpiece 2 to process the desired shape.

3 is a processing power supply device, which includes a DC power supply E that determines the open voltage internally, and a switching transistor.
Oscillator that determines the Tr pulse width τ _p and pause width τ _r
OSC, a resistor R that determines the charging peak current _Ip , a capacitor C, etc. are built-in.

However, in the above-mentioned conventional wire-cut electric discharge machining apparatus, the machining electrical conditions (hereinafter simply referred to as electrical conditions) of the machining power supply device 3, which have a large influence on the machining speed and the machining groove width, that is, the charging peak current I
_p , pulse width τ _p , pause width τ _r , capacitor value C,
Open voltage V etc. were all manually set externally.

Electrical conditions I _p , τ _p , τ of the processing power supply device 3
It is known that _r , C, V, etc. need to be set to have optimal values for the thickness of the workpiece 2, and when machining is performed under such optimal conditions, the machining speed The width of the machining groove is also large, and the width of the machining groove is constant, making it possible to perform high-precision machining. On the contrary, when processing a thin plate under the optimal electrical conditions for thick plates, the processing energy increases compared to the optimal electrical conditions for thin plates, and the excess energy is concentrated in one location of the wire electrode 1. Causes wire breakage.

In other words, when machining a workpiece 2 with a change in thickness as shown in Fig. 1 using conventional equipment, weak electrical conditions for the minimum thickness must be set in advance to ensure machining without wire breakage. , the entire part must be machined under these electrical conditions, and the machining feed rate (hereinafter simply referred to as feed rate) in this case is said to be slow enough to prevent short circuits at the maximum plate thickness. Machining speed is extremely reduced.

In other words, the electrical conditions must be set based on the minimum plate thickness, and the feed speed must be set based on the maximum plate thickness, resulting in an extremely low processing speed.

Furthermore, since thin plates are machined at a feed rate much lower than the appropriate feed rate, surplus discharge occurs, the groove width widens greatly, and the machining accuracy is significantly reduced.

Conventionally, as a method of compensating for these drawbacks, a voltage servo system has been used in which the feed rate is determined so that the machining gap voltage during machining is constant, as shown in FIG.

The average value Eg of the machining voltage in the machining gap and the reference voltage Eo are input to the error amplifier 4, and a machining feed rate F proportional to the error voltage, which is the difference between the machining average voltage Eg and the reference voltage Eo, is determined. This feed rate F is divided into X-axis component Fx and Y-axis component by speed distributor 5.
Fy and drive the X-axis motor 6 and Y-axis motor 7, respectively. Here, Fx ² +Fy ² =F ² .

In the conventional device shown in FIG. 2, when the gap between the wire electrode 1 and the workpiece 2 becomes smaller and the average machining voltage Eg becomes smaller than the reference voltage Eo, the feed rate F decreases, widening the gap and increasing the average machining voltage.
It works to bring Eg closer to the reference voltage Eo.

Conversely, when the machining average voltage Eg becomes larger than the reference voltage Eo, the feed rate F increases in exactly the same way, and the machining average voltage Eg approaches the reference voltage Eo.

In this method of changing the feed rate by feeding back the machining average voltage, the feed rate becomes faster when processing a thinner plate, and conversely, the feed rate becomes slower in a thicker plate, resulting in an increase in machining area rate. remains almost constant.

As described above, by controlling the feed rate to keep the machining voltage constant, it is possible to avoid the loss of feed rate and the decrease in accuracy that occur during constant-speed feed to some extent.

However, even with the apparatus shown in FIG. 2, the electrical conditions for machining are always fixed, so the feed rate and machining accuracy are considerably lower than when machining is performed under the optimal electrical conditions for each plate thickness. Accordingly, there is an apparatus shown in FIG. 3 that has been proposed for processing workpieces 2 whose thicknesses vary under electrical conditions optimal for each thickness. In the apparatus shown in FIG. 3, the feed rate F output from the error amplifier 4 is input to the control device 8, which instructs the machining power supply device 3 to set electrical conditions in accordance with the value of the feed rate F. in this case,
As shown in FIG. 4, the material of the workpiece 2 is determined, and the material and diameter of the wire electrode 1, as well as the reference voltage
Once Eo, the specific resistance of the machining fluid, the surface roughness, etc. are determined, the optimum electrical condition Ec for the thickness t of the workpiece 2 and the feed rate F at that time are uniquely determined.

FIG. 5 is a table in which the relationship shown in FIG. 4 is stored as a data table, in which the feed rate F corresponds to the electrical condition Ec.

The feed rate F output from the error amplification device 4 in FIG. 3 is input to the control device 8, and this control device 8 corresponds to the input feed rate F by referring to the data table shown in FIG. Outputs electrical condition Ec. Since the optimum electrical conditions obtained through experiments are registered in the data table, even if the thickness of the workpiece 2 changes, the optimum processing conditions are automatically output to the processing power supply device 3. In this case, only the relationship between the feed rate F and the electrical condition Ec is required as a data table, and the plate thickness t is not particularly required.

In this way, the apparatus shown in FIG. 3 is operated under various conditions, namely, the material of the workpiece, the material and diameter of the wire electrode, the reference voltage Eo during machining, the specific resistance of the machining fluid,
Once the surface roughness etc. are determined, the optimum electrical conditions are determined experimentally based on these conditions and stored in the controller 8 in the form of a data table shown in FIG. It was possible to perform optimal machining that corresponds to the change in plate thickness.

However, the disadvantage of the apparatus shown in Figure 3 is that it is necessary to find the optimal electrical conditions for each plate thickness before processing, which is difficult and time consuming to create a data table. That's what it takes. In addition, the data table once created is unique to various machining conditions, such as the workpiece material, wire electrode material and diameter, reference voltage Ec during machining, machining liquefaction resistance, surface roughness, etc. It cannot be used if the materials of the objects are different.

In general, wire-cut electric discharge machining equipment processes various materials, and the machining conditions at that time are also different. If the equipment shown in Figure 3 is used in such a case, the number of data tables created will be extremely large. , and it becomes impractical. That is, the third
The device shown in the figure is suitable for use as a dedicated machine that processes workpieces 2 made of the same material under the same conditions, and has the disadvantage that it cannot be used with general wire-cut electric discharge machining devices that require machining under various conditions. have.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that can perform machining at high machining speeds and high precision, which was impossible with conventional wire-cut electric discharge machining apparatuses, with very easy operation.

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

FIG. 6 is a block diagram of an apparatus according to the present invention for processing workpieces with varying thicknesses under optimal electrical conditions for each thickness.

When the wire electrode 1 comes to the thickness changing part of the workpiece 2 in FIG. 6, the new thickness after the thickness change is input to the thickness/speed converter 10 by the NC tape 9.

Since the NC tape 9 is used to command the shape and dimensions of machining to the NC device, the dimensions of the part where the thickness of the workpiece 2 changes are known in advance, and the thickness and speed are converted at the time of the thickness change. It is very easy to inform the device 10 of the new thickness.

In this way, as the machining progresses, when the wire electrode 1 reaches the thickness changing part of the workpiece 2, the NC tape 9 sends a new plate thickness signal after the plate thickness change to the plate thickness/speed converter 10. is input.

The plate thickness/speed conversion device 10 outputs the feed rate for the input plate thickness of the workpiece 2, and pairs the plate thickness for the material of the workpiece 2 with the optimum feed rate determined by experiment. read-only as a data table as shown in Figure 7.
It is stored in a storage element such as a memory. In this way, when the plate thickness of the plate thickness changing part is inputted using the NC tape 9, the optimum feed rate Fs for the plate thickness is determined by the plate thickness/speed converter 10, and outputted to the electrical condition setting device 11. be done. In addition to the optimum feed rate Fs, the current feed rate F is input to the electrical condition setting device 11 from the error amplifier 4.

The electrical condition setting device 11 has a built-in comparator, and the feed rate F during processing is the optimum feed rate.
The electrical conditions for the machining power supply device 3, that is, the machining energy, are increased or decreased so as to be equal to Fs.

To increase or decrease the electrical conditions, that is, the machining energy, it is possible to use a data table such as the one shown in Fig. 8 in which the electrical conditions (charging peak current I _p , pulse width τ _p , pause width τ _r ) are arranged in order of strength. Good and
Further, the open circuit voltage and capacitor value inside the processing power supply device 3 may be increased or decreased.

In the above explanation, the plate thickness/speed conversion device 10 has a built-in plate thickness/speed table for machining the material of the workpiece 2 under certain conditions; If the machining conditions are different from the conditions at the time of creating the data table, calculate the feed rate at the thickness of workpiece 2 before the thickness change and the feed rate at the thickness after the thickness change from the data table. By multiplying the optimum feed rate of the workpiece 2 before the thickness change by the ratio of the two values, the optimum feed rate for the new plate thickness after the thickness change can be calculated.
The basis for this is explained below.

FIG. 9 is a graph of the ratio of plate thickness t to feed rate, and is created by setting the maximum feed rate at 100% when the plate thickness is 10 mm as an example. In this case, the ninth
It has been experimentally confirmed that the graph in the figure has a substantially constant shape regardless of the material of the workpiece 2 or various processing conditions. In other words, the optimal feed rate ratio when the plate thickness changes, even if the material of the workpiece, wire electrode material, electrode wire diameter, reference voltage Eo during machining, machining fluid specific resistance, surface roughness, etc. change. The value remains almost constant. In other words, if the various conditions associated with these processes are determined and the optimum feed rate for a certain plate thickness is determined, the optimum feed rate for other plate thicknesses can be easily determined.

To give a specific example, let us assume that there is a workpiece whose optimum feed rate under processing conditions is F=800 μm/min when the plate thickness is 20 mm. Plate thickness and thickness under the same processing conditions
The optimal feed rate when machining 100 mm is F = 800 since the speed ratio is 20/80 = 1/4 from Figure 9.
The optimum machining feed rate is F = 200 μm/min, which is obtained by multiplying μm/min by 1/4.

In addition, in Figure 9, the ratio of feed speed to each plate thickness was graphed and used as a data table, but the data table was created by plotting the plate thickness change ratio on the horizontal axis and the speed change ratio on the vertical axis. It is obvious that the same effect can be achieved even if used.

In the explanation of the operation so far, all plate thickness command values read from the NC tape are converted into feed speeds, and optimal machining is achieved by changing the electrical conditions to obtain that feed speed. 10
A similar effect can be obtained by using a table of board thickness and electrical conditions as shown in the figure as a data table.

In addition, in the present invention, hardware is used for control, and the data table uses read-only memory. However, when a computer is used for control, all data tables are stored in the computer's internal memory. All functions can be performed by computer software.

As described in detail above, the wire cut electric discharge machining apparatus according to the present invention includes a storage medium that stores shape and size information of machining including information regarding changes in thickness of a workpiece to be machined into a desired shape, and a machining power supply device that supplies machining energy between a wire electrode and a workpiece that move relative to each other according to the information provided by the machining power supply device; an error amplification device that compares the machining voltage between the workpieces with a reference voltage and outputs a signal that causes the electrode and the workpiece to move relative to each other at a machining feed rate proportional to the difference voltage; and a plate thickness of the storage medium. A plate thickness/velocity converter receives information regarding the change as input and outputs a relative velocity signal between the wire electrode and the workpiece according to this information;
an electrical condition setting device that receives the output signal of the speed conversion device as an input and controls the electrical conditions of the processing power supply device so that the output signal of the error amplification device matches the output signal of the plate thickness/speed conversion device; The plate thickness/speed conversion device stores the relationship between the plate thickness and the optimum machining feed rate for a predetermined material of the workpiece, and the machining feed rate at the plate thickness before the change in the thickness of the workpiece; The machining feed rate for the plate thickness after the plate thickness change is determined by referring to the above memory contents, and the new plate thickness after the plate thickness change is calculated by multiplying the ratio of the two by the machining feed rate before the plate thickness change of the workpiece. Since it has a function to calculate the feed rate for the workpiece, just by commanding the thickness of the workpiece to be machined, the material of the workpiece, wire electrode material, wire electrode diameter, reference voltage during machining, and machining fluid ratio can be calculated. Due to differences in machining conditions such as resistance and surface roughness, it is not necessary to create memory contents each time, and optimal machining can be performed very easily, machining speed and machining accuracy are dramatically improved, and wire breakage is also avoided. The reliability of the device is also greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional wire-cut electric discharge machining device, Fig. 2 is a block diagram of another conventional device, Fig. 3 is a block diagram of yet another conventional device, and Fig. 4 is a block diagram of a workpiece. Figure 5 is a diagram showing the relationship between plate thickness, machining electrical conditions, and machining feed rate; Figure 5 is a data table based on Figure 4; Figure 6 is a configuration diagram of an apparatus according to an embodiment of the present invention; Figure 7 is a table showing plate thickness and feed speed, Figure 8 is a diagram showing machining electrical conditions arranged in order of strength, Figure 9 is a diagram showing feed rate ratio to plate thickness, and Figure 10 is a diagram showing the feed rate ratio to plate thickness. The figure is a table showing the optimum processing electrical conditions for each plate thickness. In the drawing, 1 is a wire electrode, 2 is a workpiece, 3 is a processing power supply device, 4 is an error amplifier, 5 is a speed distributor, 8 is a control device, 9 is an NC tape, and 10 is a plate thickness speed conversion The device 11 is an electrical condition setting device. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A storage medium that stores processing shape and dimension information including information regarding changes in the thickness of the workpiece to be processed into a desired shape, and a wire electrode and the workpiece that move relative to each other according to the information stored in this storage medium. Compare the machining voltage between the wire electrode and the workpiece when machining the workpiece with the machining power supply device that supplies machining energy between the machining power supply device and the machining energy of the machining power supply device with a reference voltage. an error amplification device that outputs a signal to relatively move the electrode and the workpiece at a machining feed rate proportional to the differential voltage; and an error amplification device that inputs information regarding changes in the thickness of the storage medium, and controls the wire electrode according to this information. and a plate thickness/velocity converter that outputs a relative speed signal between the workpiece and the workpiece, and receives the output signal of the error amplification device and the output signal of the plate thickness/velocity converter as input, and outputs the output of the error amplification device. An electrical condition setting device is provided for controlling the electrical conditions of the machining power supply device so that the signal matches the output signal of the plate thickness/speed converting device, and the plate thickness/speed converting device The relationship between the plate thickness and the optimum machining feed rate for the material of is memorized, and the machining feed rate for the plate thickness before the thickness change of the workpiece and the machining feed rate for the plate thickness after the plate thickness change are determined by referring to the above stored contents. A wire cut electric discharge machining apparatus is a device that calculates the feed rate for the new plate thickness after the thickness change of the workpiece by multiplying the ratio of the two by the machining feed rate before the thickness change of the workpiece.