JPS6333969B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wire cut discharge device for machining a workpiece using a wire electrode. Conventionally, a workpiece is placed on a processing table that can perform two-dimensional plane movement within the XY-axis plane, a wire electrode is provided passing through the workpiece, and a wire electrode is placed between the wire electrode and the workpiece. A predetermined voltage is applied to generate electrical discharge, an insulating machining fluid is supplied to this machining section, and the machining table is controlled and driven by a control device consisting of an NC and copying mechanism to machine the workpiece. A wire cut electric discharge machining apparatus is known. This type of wire-cut electric discharge machining equipment is mainly used for machining molds with penetrating holes, such as press molds and extrusion dies for aluminum sash. This makes it possible to manufacture molds with extremely high precision compared to conventional processing methods. Furthermore, the overall mold manufacturing time using a wire-cut electric discharge machining device can be said to be the same or slightly faster than when conventional mechanical cutting or normal electric discharge machining is used because the manufacturing process is simple. However, regarding the machining speed itself, the current wire cut machining speed is 0.1 g/min, and even with normal electrical discharge machining equipment, which is said to be slower than mechanical cutting, the practical machining speed is several g/min. Considering this, there is a problem that the processing speed is extremely slow. The reason why the machining speed is so slow even though it is the same electric discharge machining is that there is a problem unique to wire-cut electric discharge machining equipment, such as wire electrode breakage.
The limit of machining energy input is determined by the limit of occurrence of wire breakage. On the other hand, the difference from wire-cut electrical discharge machining is that the practical machining speed limit of normal electrical discharge machining is limited by machining accuracy and machined surface roughness rather than the limit of energy input. It is. By the way, machining accuracy and surface roughness are not ignored in wire cut electrical discharge machining, and generally even at the maximum speed (approximately 0.1 g/min) as mentioned above,
A fine machined surface roughness of about 15μRmax can be obtained, so
It's just not that much of a problem. On the other hand, if we consider the case where the surface roughness is finished to several μRmax, the machining speed under such surface roughness conditions is:
It is only a few mg/min, which is a few tenths of the maximum machining speed, which is not practical, so after machining at the maximum machining speed, set the machining conditions to the desired surface roughness and trace the machined surface again. There is a method of processing, which is called second cut processing. However, as mentioned above, when machining at the maximum machining speed,
There is a surface roughness of 10 to 15μRmax, and the maximum machining speed itself is extremely slow, so if the cutting length is several hundred mm, the machining time itself will be several hours to several tens of hours. Due to changes in temperature and deformation of the workpiece, the shape accuracy is 10 to 20 μm.
There are also some parts that are off-kilter. Conventionally, in order to finish the surface of such a workpiece to about several μRmax, the processing conditions were changed all at once, and second cut processing was performed at a processing speed of about several mg/min. FIGS. 1A to 1E show changes in the machined surface due to conventional second cut processing. In this figure, the machined surface 12 with respect to the drawing dimension surface 10 is a surface with large unevenness immediately after the rough finishing of A, and when the first second cutting process is performed, the top of the unevenness is partially cut off, resulting in B. becomes the state of
In the second second cut process, the top part is further cut off as shown in C, and after several second cuts are made at the same time, almost no large peaks are left in the state shown in D, and finally the top part is cut off as shown in E. The surface 12 is machined to match the drawing dimension surface 10. However, with this method, the amount of machining stock that can be machined in one second cut process is very small, and there are also areas where electrical discharge occurs and areas where it does not occur, resulting in the inconvenience that the electrical discharge becomes extremely unstable. . Furthermore, in order to completely finish the surface, it is necessary to perform the finishing process by repeating trial and error many times, which has the drawback of being very inefficient in terms of time. An object of the present invention is to provide a wire-cut electrical discharge machining device with good machining accuracy and machining efficiency. The present invention provides a wire-cut electrical discharge machining apparatus that applies a predetermined voltage between a workpiece and a traveling wire electrode to cause discharge, and uses this discharge energy to cut the workpiece. A power source for second cutting that can change the applied voltage that applies a predetermined voltage between the wire electrode and the workpiece during the second cut in which the cut portion is subjected to electric discharge machining multiple times, and electrical conditions and the workpiece. A storage means stores a plurality of sets of the relationship between the thickness of the object and the machining width as one data group, and stores the machining width in sequence for each second cutting process from among the plurality of data groups stored in the storage means. A small data group is selected, and the electrical conditions and the offset value of the wire electrode are changed to become smaller according to the selected data group, and the wire electrode and workpiece are changed as the electrical conditions are changed. The present invention is characterized by a configuration including a control means for increasing the voltage of the second cut power supply in order to prevent a drop in the discharge generation voltage between the two. In addition, in the present invention, "electrical conditions" includes "current" but does not include "voltage", and therefore, in the present invention, "change in electrical conditions" does not include "change in current". There is, but "voltage change"
First of all, it is defined that "change of electrical energy" as used in the present invention means such "change of electrical conditions". Embodiments of the present invention will be described below based on the drawings. FIG. 2 shows a schematic configuration of an embodiment of the device of the present invention. In the figure, the processing table 20 includes an upper table 22 and a lower table 24. The upper table 22 is driven by an X-axis drive motor 26 in the X-axis direction, that is, the direction of arrow P, and the lower table 24 is driven by a Y-axis drive motor 28. It is possible to drive in the Y-axis direction, that is, in the arrow Q direction. A workpiece 30 is placed on the upper table 22 of the processing table 20, a wire electrode 32 is provided passing through the workpiece 30, and a wire electrode 32 is provided between the wire electrode 32 and the workpiece 30. An insulating working fluid 34 is interposed. This machining fluid 34 is sprayed from a tank 36 by a pump 38 into the gap between the workpiece 30 and the wire electrode 32 through a nozzle 40 . The wire electrode 32 is connected to a wire supply reel 42
The wire passes through the lower wire guide 44 and the workpiece 30, reaches the upper wire guide 46, and is wound up by the wire take-up reel 50, which also serves as a tension roller, via the electrical energy feeder 48. ing. One end of a processing power supply 52 for supplying electrical energy is connected to the electrical energy power supply section 48 .
The other end is connected to the workpiece 30. Also,
The processing power source 52 includes an electric circuit 54 that serves as a power source for second cutting, which is finishing processing.
This electric circuit 54 is capable of changing the applied voltage for reasons to be described later, and is connected to a control means 58 of a computer 56, so that the applied voltage is controlled by a signal from a storage means 60 during second cut processing. ing. This control means 5
8 has an X-axis drive motor 26 and a Y-axis drive motor 2.
8 is also connected and similarly driven and controlled by signals from the storage means 60. Note that in FIG. 2, reference numeral 62 indicates a machining start hole provided in the workpiece 30, and reference numeral 64 indicates a machining trajectory. In such a configuration, in order to process the workpiece 30, the wire electrode 32 supplied from the wire supply reel 42 via the lower wire guide 44 is passed through the machining start hole 62 of the workpiece 30, and then the upper A predetermined winding tension is applied to the wire take-up reel 50 via the wire guide 46 and the electric energy feeder 48. In this state, a predetermined voltage is supplied from the machining power source 52 to the workpiece 30 and the electrical energy supply unit 48, and the pump 38 is driven to supply the machining liquid 34 in the tank 36 from the nozzle 40 to the wire electrode 32 and the workpiece. 30. Next, the control means 58 of the computer 56 drives the X-axis drive motor 26 and the Y-axis drive motor 28 to cause the workpiece 30 and the wire electrode 32 to move relative to each other within a two-dimensional plane within the XY-axis plane, thereby performing the desired processing. A trajectory 64 is obtained. By the way, after the first cut processing, which is rough processing, is performed, during the second cut processing of the workpiece 30 as shown in FIGS. 3 and 4,
Letting E be the electrical energy, F be the relative machining speed between the workpiece 30 and the wire electrode 32, t be the thickness of the workpiece 30, and ε be the machining width, the following relational expression holds between these. E∝K×F×t×ε (1) ∴ε∝E/k×F×t (2) Here, k is a relationship in which the thickness t of the workpiece 30 is used as a parameter. Therefore, the machining width ε is determined by the machining speed F, the electrical energy E, and the thickness t of the workpiece 30. Table 1 below shows the machining speed F in equation (2) above.
The figure shows the machining width ε(I, J) when the electric energies E, I and the thicknesses t, J of the workpiece 30 are used as parameters. Such an associated data group is also prepared for the case where the machining speed F is changed, and is stored in the storage means 60 of the computer 56. In the first cut machining, the offset amount is increased by _N 〓 ^J=1 ε(I, J) and the machining is performed.
In other words, the drawing size is gradually made closer to the drawing size of 10 by performing a second cut process to make the drawing size smaller by _N 〓 ^J=1 ε (I, J) than the drawing size of 10. 5A to 5J show the process of the processing method according to the present invention, where A is the state after rough machining, B is the first second cut, and C is the second second cut. The state in which machining is being performed, hereafter, passes through states D, E, and F, and reaches the final machining state J, where the machining is completed. That is, in FIG. 5A, when the rough machining that is first cut machining is completed, the machined surface 12 of the workpiece 30 is separated from the drawing dimension surface 10 by a distance of _N 〓 ^J=1 ε (I, J). There is. Then, the electric energy E
(1) Workpiece

[Table] The processing width ε (1, J) for the thickness t, J of 30 mm is set by the computer 56, the offset amount that allows processing by that processing width is determined, and under that condition, the first second Perform cut processing. FIG. 5B shows this state. When the first second cut machining is completed, the computer 56 determines the machining width ε with electrical energy E(2).
(2, J) is selected, the offset amount is determined so that the cutting width can be processed, and the second second cutting process is performed under these conditions. FIG. 5C shows this state. In this way, according to the table stored in the storage means 60 of the computer 56, the second cut process is continued until the process width ε(N, J) is reached, and the process is completed. At this time, although FIGS. 5D to 5F are shown in three stages for drawing purposes, in reality, processing is performed in several stages according to the table stored in the storage means 60. Further, the wire electrode 32 is processed while relatively moving in the direction of the arrow in FIG. According to this embodiment as described above, the processing width is sequentially reduced compared to the processing width of the first second cut processing, and the processing width is reduced in the final second cut processing in units of one step of the second cut processing performed two or more times. Since machining is performed in an almost zero state, the machining speed is faster than the conventional second-cut machining method, and the machined surface can be machined with fine precision. In addition, in the above example, if the remaining machining width is larger than _N 〓 ^J=1 ε (I, J) as a result of rough machining, machining must be performed several times with electric energy E(1). Machining is carried out until a predetermined remaining machining width is reached, and thereafter, the electric energy E is successively lowered and the machining is carried out in the same way as in the previous embodiment. Also, the remaining machining width is
If it is less than _N 〓 ^J=1 ε(I, J), machining is started from electric energies E and I that match the remaining machining width at that time, and thereafter machining is continued by lowering the electric energy E sequentially. In this way, it is possible to carry out machining without loss of efficiency, regardless of the result of rough machining. FIG. 6 shows a machining path when wire cut electric discharge machining is performed, and machining is performed from a machining start hole 62 in the order of a → b → c → d → e → f → g. At this time, the rough machining may be performed according to the above-mentioned path, returning from point g to the machining start hole 62, and the second cut machining may be performed in the same manner, but the machining may proceed to point g in the rough machining. In this case, it is also possible to automatically change the electric energy and offset amount using the computer 56, and continue in the direction b to proceed to the second cut process. According to the method of not returning to the machining start hole 62 in this way, it is possible to eliminate the back and forth between the machining start hole 62 and the point g, which is a wasteful movement of the wire electrode 32, and it is possible to further improve the machining efficiency. . Next, the reason why the voltage applied to the electric circuit 54 serving as the power source during the second cutting process is changed by the command signal from the computer 56 will be explained based on the power supply diagram of FIG. 7. In FIG. 7, reference numeral 54 is an electric circuit that serves as the power source for the second cut described above, and the applied voltage E1 can be changed, and the other circuits are conventionally known circuits. Thing 3
0 is the gap between the opposing electrodes, R1 is the power supply resistance, R2 is the resistance between the electrodes, E2 is the voltage between the electrodes, and S is the switching means. With the above configuration, changing the electrical conditions to be smaller for each second cut process as described above means reducing the current flowing through the gap G between the electrodes, which means that the power supply resistance R1 is reduced. It means making it bigger. However, when the resistor R1 is increased in this way, the interelectrode voltage E2 inevitably becomes smaller, and the voltage sufficient to generate a discharge, in other words, the so-called no-load voltage does not reach a sufficient value, and the discharge becomes stable. This will no longer occur, and as a result, machining will become unstable. Therefore, in the present invention, in order to prevent such problems, an electric circuit 54 serving as a power source for the second cut is provided.
The applied voltage E1 is increased to prevent the discharge generation voltage from decreasing. Note that even if the applied voltage E1 is increased, the electrode gap G
Since R1 of the current I (=E/R ₁ +R ₂ ) flowing through is extremely large, its change can actually be ignored. As described above, the present invention has the effect of speeding up, increasing precision, and automating the second cut machining, and also maintains a predetermined discharge generation voltage during the second cut machining, stably. This has the effect that electrical discharge machining can be performed.

[Brief explanation of the drawing]

1A to 1E are explanatory diagrams showing changes in the drawing dimension surface and the machined surface due to conventional second cut machining, and FIG. 2 is a schematic configuration diagram showing an embodiment of the wire cut electric discharge machining apparatus according to the present invention. 3 and 4 are a front view and a plan view showing the size and speed relationship between the workpiece and the wire electrode during the second cut process, and FIGS. 5A to 5J are explanatory views showing the second cut process according to the present invention. FIG. 6 is an explanatory diagram showing the machining path in the present invention, and FIG. 7 is an explanatory diagram of the power source of the present invention. In each figure, the same members are given the same reference numerals, 20 is a processing table, 26 is an X-axis drive motor, 28 is a Y-axis drive motor, 30 is a workpiece, 32 is a wire electrode, 48 is an electrical energy feeder, 52 is a processing power source; 54 is an electric circuit constituting a second cutting power source; 58 is a control means; 60
is the storage means, E is the electric energy, F is the machining speed, t is the thickness of the workpiece, and ε is the machining width.

Claims (1)

[Claims] 1. In a wire cut electrical discharge machining device that applies a predetermined voltage between a workpiece and a traveling wire electrode to cause discharge, and cuts the workpiece with this discharge energy, after cutting the workpiece, the cut portion is In addition, a second cut power supply that applies a predetermined voltage between the wire electrode and the workpiece during the second cut that is performed multiple times by electrical discharge machining, and a variable applied voltage power supply, as well as electrical conditions and the thickness of the workpiece, are provided. A storage means that stores a plurality of data groups containing relationships between the cutting width and the machining width, and one set with a smaller machining width for each second cutting process from among the plurality of data groups stored in the storage means. The electrical conditions and the offset value of the wire electrode are changed to be smaller in accordance with the selected data group, and the electric discharge between the wire electrode and the workpiece is reduced due to the change in the electrical conditions. A wire cut electrical discharge machining apparatus comprising: control means for increasing the voltage of the second cut power supply in order to prevent a drop in the generated voltage.