JP2730307B2 - Electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge wire machining apparatus using a wire cutting method, and more particularly to a traveling wire electric discharge machine capable of performing precise three-dimensional electric discharge machining.

[0002]

2. Description of the Related Art An electric discharge machining method is known as a method for processing an electric conductor material. In this method, a fine crater is formed on the surface of the work piece by causing discharge between the work piece and the cathode using the work piece as an anode, and processing is performed by accumulating craters. The electric discharge machining method is roughly classified into a die engraving method and a wire cutting method, and the wire cutting method is to cause electric discharge using a wire as a machining electrode. In the conventional wire cutting method, the wire is caused to travel between the two-point indicating members to discharge between the workpiece and the workpiece. The wire is vibrated and is not suitable for accurate machining. A wire electric discharge grinding method is known as a method that solves this drawback and is suitable for fine processing. In this method, a wire having a diameter of usually 30 to 300 μm supplied from a supply bobbin is caused to travel to a winding bobbin via a wire guide provided in the vicinity of a work piece, and discharge is performed by a wire at a tip portion of the wire guide close to the work piece. As a result, the position of the wire discharge is determined, so that very accurate machining can be performed. JP-A-1-23
No. 4122 discloses a method of processing a fine shaft or a fine electrode using a wire electric discharge grinding method. The micro-shaft or electrode having a diameter of, for example, 13 microns produced in this manner can be used as an electrode for drilling discharge such as an ink-jet injection hole, a diesel engine injection hole, an air damper air hole, etc., having a diameter of 15 microns.

[0003]

However, the diameter of the traveling wire usually varies by about 0.1 to several microns due to the fluctuation of the jig in the wire manufacturing process and the fluctuation of the tension during traveling. For this reason, even when the wire guide position is constant, the discharge point at which the wire side discharge occurs (hereinafter, referred to as a wire discharge point) varies, and the discharge machining point of the workpiece (hereinafter, referred to as the workpiece discharge point) varies accordingly. , Gives processing errors. Therefore, such a variation in wire diameter becomes a problem particularly when an attempt is made to perform electric discharge machining with higher accuracy.

[0004] Further, for such high-precision machining, precise position control of the wire and the workpiece is required, but no such conventional position control is performed in a conventional electric discharge machining apparatus.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a discharge point position control device for precisely determining the relative position between a discharge point of a traveling wire and a discharge point of a workpiece. This discharge point position control device three-dimensionally controls the relative position of the wire discharge point with respect to the workpiece discharge point.

The present invention also provides a means for maintaining the tension of the traveling wire constant, a wire diameter sensor for monitoring the wire diameter, and when a change in the diameter is detected by the wire diameter sensor, the change in the diameter is detected at the discharge point position. A wire discharge point position compensator is provided for precisely compensating the relative position by feeding back to the controller.

In order to carry out precise micromachining, it is necessary to further reduce the discharge power corresponding to the amount of machining per discharge (ie, the size of one crater). In order to perform machining as quickly as possible, the amount of electric discharge machining per unit time must be large. Therefore, in order to satisfy these two contradictory requirements, the present invention provides a discharge circuit that discharges at a very low frequency but discharges at a very high frequency.

[0008]

As described above, according to the present invention, the wire discharge point with respect to the predetermined workpiece discharge point can be controlled three-dimensionally in order to make it possible to machine a microscopic object to a macroscopic object.

In this case, the tension of the traveling wire is kept constant in order to prevent the fluctuation of the wire discharge point due to the tension of the traveling wire diameter.

In addition, the diameter of the wire is monitored to compensate for the variation in diameter inherent to the wire.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention having the above configuration will be described with reference to the drawings. Here, FIG. 1 is a plan view showing the arrangement of a system (hereinafter, referred to as a wire traveling system) 100 for traveling a wire 104 of the electric discharge machining apparatus of the present invention, a discharge circuit 600, and a work piece 800, and FIG. FIG. FIG.
Is an enlarged plan view of an electric discharge region of the electric discharge machine, and shows a detailed positional relationship among the wire guide 114, the traveling wire 104, and the work piece 800.

First, the basic configuration of the electric discharge machine will be described. The electric discharge generally involves the traveling wire 104 and the workpiece 80.
Occurs between the closest points of 0 (wire discharge point A and workpiece discharge point B in FIG. 3). From the workpiece discharge point B, a very small amount of material is scraped from the workpiece by sparking, resulting in a very fine crater on the workpiece surface. The size of each crater depends on the power of one discharge. The next discharge point on the workpiece side moves to the point closest to the wire discharge point A at this time. Discharge usually occurs only when the distance between both discharge points is smaller than a certain threshold value (critical discharge distance) L. The discharge critical distance L is governed by the electric field formed between the wire discharge point A and the workpiece discharge point B. This electric field is determined by various parameters such as the diameter of the wire 104, the material, and the dielectric constant of the working fluid, and L is usually several microns or less.

[0013] Since the wire 104 is running, even if it receives a change due to the discharge, it has not passed through the wire guide and has no effect on the next discharge.

When the discharge is performed in the air, since the workpiece material removed by the spark remains in the vicinity of the crater and the discharge does not continue, the discharge surface of the workpiece 800 is required to perform the discharge continuously. Is supplied with a liquid such as insulating oil or water. In this case, the work piece material in the crater portion is scattered by the spark together with the insulating liquid, and the next discharge can be performed. Insulating working fluid for this purpose is injected from the working fluid supply pipe 310 of FIG. 1 to the discharge region. The container 320 stores the used working fluid.

Next, the details of the present apparatus will be described. First, a work piece position control device will be described. Workpiece 800
Is mounted on a rotating device 820 such as a mandrel, and the rotation angle and the movement in the direction of the axis J are controlled by a work piece controller 810 linked to the rotating device. The position of an arbitrary point on the planned contour of the work piece 800 (hereinafter, this point is referred to as a planned processing point b in FIGS. 1 and 3) is defined by the axis J as the z-axis of the cylindrical coordinates and the point b to the axis. Assuming that the distance is r, the rotation angle about the z-axis measured from an arbitrary reference line (FIG. 3JK) is θ, and the distance from the perpendicular foot H descending from the point b to the axis J to the coordinate origin O is z, the cylinder is Coordinates b (r,
θ, z). In this embodiment, the computer
Is stored as a function r = r (θ, z) of (θ, z), and is interlocked with the rotating device 820 so that the wire discharge point A is located at a distance L from the point b in the r direction. The position of the XY table 200 is computer-controlled. During EDM, this position control is performed while continuously changing θ and z.

Next, the wire traveling system 100 for traveling the wire 104 serving as the cathode of the discharge will be described. The wire 104 supplied from the wire supply bobbin 102 is sent out at a very accurate constant speed by a brake roller 106 and a counter roller 108, and the first traveling roller 11 is maintained while the wire tension is maintained constant by a tension buffer roller 110.
2. After passing through the wire guide 114, it is guided by the second and third traveling rollers 116 and 118, is wound up by the winding roller 120, and is wound on the winding bobbin 124. The wire traveling speed is determined by the rotation speed of the winding roller 120. The running speed of the wire is determined according to the amount of electric discharge machining, but is usually about several centimeters / minute. Hoisting bobbin 124 from wire supply bobbin 102
Above constitutes the wire traveling system 100. The wire traveling system is mounted on an XY table 200 that can move on rails 210 on a base 400. The XY table 200 is controlled by an XY controller 133 (not shown) so that the wire discharge point A is at a predetermined position on an XY plane (FIG. 1) described below.

As shown in FIG. 1, the wire traveling system 100 has an X
-The center of the disc-shaped wire guide 114 and the tip a on the processed piece side with respect to the base 400 via the Y table 200
It can move in the X direction passing through (FIG. 3) and in the Y direction parallel to the running surface of the wire and perpendicular to the X direction (XY).
The origin of the coordinate system is appropriately selected), and the r direction (direction from point H to point b) from the z-axis (that is, the axis J of the mandrel) to the discharge point b to be machined matches the X direction. ing. Therefore, the wire discharge point A, which is the point on the wire guide closest to the work piece, is on this X axis, and the XY coordinate of the wire discharge point A in the XY coordinate system is (d, 0). The scheduled discharge point b is at (d + L, 0) in the XY coordinate system.
In the cylindrical coordinate system, the wire discharge point A
Is (r + L, θ, z).

X-Y scheduled for this wire discharge point A
The position is the work piece shape memory of the computer 132 (FIG. 4).
The computer 132 controls the work piece controller 810 based on the r, θ, and z of the work piece stored in the XY table 133 and controls the inchworm (not shown) of the XY controller 133 to thereby control the XY table 200. Is controlled to realize the predetermined wire discharge point b. Since this position control is performed by continuously changing θ and z during the electric discharge machining, the workpiece is machined into a desired shape. As described above, the discharge point position control device includes the traveling wire system 100, the XY table 200, and the workpiece rotating device 82.
0, work piece controller 810, computer 132,
And an XY table controller 133 (FIG. 4).

In this case, compensation for the fluctuation of the wire diameter described below is further performed. Since the wire discharge point A is located closest to the work piece of the wire on the outer periphery of the wire guide, when the wire diameter changes, the discharge point A actually deviates from the expected position by that much. Therefore, the electric discharge machine of the present invention compensates for this positional deviation of the point A due to the change in the diameter of the traveling wire, and performs more precise electric discharge machining that is not affected by the change in the wire diameter. Therefore, the following mechanism is provided. That is, a wire diameter sensor 130 is provided at an appropriate position after the passage of the tension buffer roller 110 and before the wire guide 114 arrives, for example, between the tension buffer roller 110 and the first traveling roller 112 to monitor the wire diameter. As this sensor, for example, a laser diameter measuring instrument of type M550A commercially available from Anritsu Electric can be used. This sensor measures 1000 times per second, measures the wire diameter with an accuracy of ± 0.3 μm, encodes the result, and sends it to the wire diameter compensator of the computer 132 (FIG. 4). The computer 132 sends a table position signal to the XY table controller 133 for compensating the predetermined discharge point position by the variation of the wire diameter based on the variation of the wire diameter. This compensation signal is sent when the wire variation portion should reach the processing point A, and based on this signal, the XY controller 133 drives the inchworm and drives the XY table 200 in the X direction. In addition, a predetermined position of the wire discharge point is secured. The XY table controller is, for example, Burleigh Instrument, Burleigh Park, NY, USA.
s, Inc.). This inchworm has a step of 0.00
It has a stride of 4 microns. Therefore, the controllable accuracy of the X table controller 133 is 0.004 microns. Thus, the wire diameter discharge point compensator includes the wire diameter sensor 130, the computer 132, the XY table controller 133, and the XY table 200.

FIG. 5 is a circuit diagram of a so-called accumulation type discharge circuit 600 (FIG. 3) used in the present machining discharge device. In this circuit, a discharging unit SP is connected in parallel to a capacitor C in a closed circuit including a DC power supply E, a switch S, a resistor r, and a capacitor C. The switch S is an electronic switch that can be turned on / off by the computer. The discharge part SP uses a wire as a cathode and a work piece as an anode, and the insulating liquid is interposed between both electrodes. When the switch S is closed, the capacitor is charged. When the discharge threshold voltage V is reached, dielectric breakdown occurs between the wire and the workpiece, and the charge Q = cV stored in the capacitor flows through the discharge unit. The energy consumed for discharging (one discharge power) is the energy (1/2) c stored in the capacitor C.
A V ^2. The size of the crater of the work piece is determined by this energy. The discharge threshold V is the shape of the workpiece,
It depends on the type of insulating material between the wire and the workpiece, the distance between the two, and the like.

When the accumulated charge is lost by discharging, charging starts again. The time constant is 1 / rc determined by the resistance r and the capacitance c of the capacitor, and therefore, the discharge cycle is also determined by the product rc.

In order to realize precise electric discharge machining, the smaller the crater formed by one electric discharge, the better. On the other hand, in order to perform machining quickly, the amount of crater generated per unit time must be large. Thus, in the present discharge circuit, two independent parameters, voltage V and capacitance c, are selected. It should be noted that the desired optimum discharge amount and discharge cycle can be realized by this.

In this embodiment, the wire was a brass wire having a diameter of 100 microns, the capacitance c was 10 pF, the voltage V was 60 volts, and the number of pulses was 10 ⁸ to 10 ⁹ / sec. This frequency is much higher than that of a conventional transistor type pulse generator (frequency of about 1 MHz). The critical distance L was approximately 1 micron, and the size of the crater was about 0.1 micron in diameter. Therefore, the accuracy of the surface shape is about 0.1.
Processing of 1 micron was completed.

Here, the relationship between the above-mentioned scheduled discharge point b and the workpiece discharge point B where the discharge actually occurs will be described. As shown by the solid line BMN in FIG. 3, the outer shape of the work piece before the processing is generally closer to the wire discharge point than the above-mentioned predetermined contour (the shape of the dotted line bmN in FIG. 3). Therefore, when that part enters the discharge area, it is processed by electric discharge. However, if the adjacent part comes into contact with the wire, the discharge circuit 600 is short-circuited and the discharge is stopped. The sensor Vm detects this and transmits it to the discharge section short-circuit processing section of the computer. The discharge section short-circuit processing section instructs the XY controller 133 to slightly retreat the wire discharge point A with the work piece stopped, to continue discharging again from the retracted position, and to remove the adjacent portion by electric discharge machining. You. Thereafter, this process is repeated until the discharge point A returns to the predetermined discharge point. Thereafter, the electric discharge machining is continued while securing the relative position between the traveling wire discharge point and the work piece discharge point according to the work piece shape stored in the work piece shape memory of the computer again, and the work piece is machined into a desired shape. . The control mechanism for moving the XY table 200 forward and backward may be a known servo mechanism, and details thereof will be omitted.

When machining a gear or the like, as shown in FIG. 6, the axis J may be rotated 90 degrees around the X axis from the position in FIG. 3 so as to come to a position J 'in the same plane as the drawing. . The control mechanism required for this is a mandrel position control mechanism by a computer, which is well-known and will not be described further.

In the above description, in determining the relative position between the wire running system and the work piece, the z position of the work piece is controlled with respect to the relative z direction position, and the wire running system is controlled with respect to the XY direction position. However, this is a matter of convenience, and it will be apparent that it is possible to control the X, Y and z positions of both the wire running system and the work piece.

[0027]

According to the machining apparatus of the present invention, the three-dimensional relative position between the discharge point of the traveling wire and the discharge point of the workpiece is computer-controlled. 3D shape processing of macroscopic objects that are considered to be objects of

Since the electric discharge machining apparatus of the present invention uses a discharge circuit for generating a high-frequency electric discharge in units of very small electric discharges, electric discharge machining and machining on the order of submicrons can be performed accurately and quickly.

In this precision machining, the machining apparatus measures the variation of the traveling wire diameter with a sensor for measuring the traveling wire diameter and compensates for the traveling wire discharge point position corresponding to the variation. Extremely precise electrical discharge machining can be maintained, since point variations can be compensated and, as a result, independent of wire diameter variations.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing an electric discharge machine according to an embodiment of the present invention.

FIG. 2 is a side view of the embodiment shown in FIG. 1;

FIG. 3 is an explanatory diagram showing a discharge region of the device shown in FIG.

FIG. 4 is a block diagram showing a configuration of the device shown in FIG.

FIG. 5 is a circuit diagram of a discharge circuit of the device shown in FIG.

FIG. 6 is a diagram showing the arrangement of a work piece and a wire when processing a gear or the like by the present apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 wire traveling system 130 wire diameter sensor 132 computer 200 XY table equipped with wire traveling system 310 working fluid supply pipe 400 base 600 discharge circuit 800 work piece 810 work piece controller 820 mandrel

Claims (1)

(57) [Claims] 1. An electric discharge machining apparatus for machining a work piece by causing an electric discharge between a travel wire and a conductive work piece that travels via a wire guide under a constant tension. A discharge point position control device for positioning the discharge point of the workpiece and the discharge point of the workpiece at a predetermined relative position, a wire diameter sensor for measuring the diameter of the running wire, and a wire diameter sensor based on the wire diameter measured by the sensor. A wire discharge point compensator for compensating for a displacement of the traveling wire discharge point with respect to a predetermined relative position due to a change in wire diameter.