JPS599299B2 - Wire cut electrical discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire-cut electrical discharge machining device that can machine corner portions with high precision.

For example, as shown in FIG. 1, a workpiece 1 is machined using a wire-cut electric discharge machining device that moves a wire and a wire electrode relatively to process a workpiece into an arbitrary shape by electric discharge.
When the wire electrode 2 and the wire electrode 2 are relatively moved along the path 3 shown by the dotted line, the shape of the corner portion 4 may be distorted.

This is generally called corner droop, and the cause is that the wire electrode 2 is bent in the opposite direction to the machining direction when machining is performed by bending the corner. Therefore, in order to reduce the corner droop, it is sufficient to increase the tension of the wire electrode 2. However, simply increasing the tension of the wire electrode 2 increases the risk of the wire electrode 2 breaking. There are drawbacks to doing so.

The present invention has been made to improve the above-mentioned drawbacks, and its purpose is to improve the machining accuracy at corner portions without the risk of wire electrode breakage.

Examples will be described in detail below. The present invention is applied to a wire-cut electrical discharge machining device in which a workpiece and a wire electrode are moved relative to each other at a substantially constant speed. It is known that the amount of machining per hit is less than the amount of machining on a straight section. Figure 2 is a diagram for explaining this. As can be seen from the figure, the amount of machining 52 at the corner section is smaller by the amount of machining 53 than the amount of machining 51 at the straight section. . In the figure, 5 is a workpiece, and 6 is a wire electrode. By the way, the fact that the amount of machining per unit time is small means that the number of discharges per unit time is small. By increasing the tension, corner droop can be prevented without the risk of breaking the wire electrode.

Also, as the number of discharges decreases, the average machining voltage between the workpiece and the wire electrode increases and the average machining current decreases, so the average machining voltage, average machining current, or per unit time Detects the machining amount per unit time from the number of discharges,
If the tension of the wire electrode is controlled based on this detection result, the tension of the wire can be increased only at the corner portions. FIG. 3 is a block diagram of an embodiment of the present invention, where w is a workpiece, P is a wire electrode, and IN
T is an integrator, COM is a comparator, PG is a pulse generator that generates a single pulse at the falling edge of the output of the comparator COM, HL
D is a hold circuit, RYl, RY2 are relays Ryl, r
y2 is the relay connection AMPl, AMP2 is the summing amplifier,
NC is a numerical control device, B is a brake for controlling the tension of the wire electrode P, R1 to R are resistors, ZD is a Zener diode, and Tr is a transistor.

The integrator 1NT integrates and smoothes the difference between the voltage between the work w and the wire electrode P divided by the resistors R, , R2 and the reference voltage V.

Therefore, the output of the integrator 1NT corresponds to the average machining voltage. The comparator COM compares the output of the integrator 1NT with the reference voltage V, and while the output of the integrator 1NT is larger, current flows through the relay RYl, turning on the contact Ryl and turning on the integrator 1NT. When the output becomes lower than the reference voltage V2, the pulse generator PG, which generates a single pulse at the falling edge of the output of the comparator COM, is activated to reset the hold circuit HLD. Furthermore, before machining a corner, the numerical control device NC determines whether the corner angle of the corner is within a predetermined range, and when it determines that the corner angle is within a predetermined range. Immediately before the corner portion is strengthened, a set signal SET is applied to the hold circuit HLD to set the hold circuit HLD. Note that the numerical control device NC determines, for example, whether the corner angle is within a predetermined range or not, based on command data that commands relative movement between the workpiece w and the wire electrode P, as described below. This is to determine the timing to output the set signal SET.

The command data of the numerical control device NC basically commands a straight line or circular arc, and when commanding a straight line as shown in Fig. 4A, the movement amount ΔX with respect to the starting point vector X (XO, yO) (ΔX, Δy) is given using the code GOl,
When commanding the clockwise arc shown in Figure B, the arc center position (1, J) and movement amount Δma (ΔX, Δy) for the starting point vector or (XOl.yO) are specified using the code GO.
2 and when commanding the counterclockwise arc shown in Figure C, the arc center position (1, J) and movement amount ΔX (ΔX, Δy
) is given using code GO3.

Therefore, the unit vectors Ul and U2 in the direction perpendicular to the direction of travel at the starting point and the ending point of the straight line are as shown in the following equation (1).

Also, the direction of movement at the start and end points of the clockwise arc →
The unit vectors Ul and U2 in the direction perpendicular to the right of → are shown in the following equations (2) and (3), respectively.

In addition, the unit vectors Ul, U, in the direction perpendicular to the direction of movement at the starting point and ending point of the counterclockwise arc are expressed by the following equations (4) and (5
).

Therefore, if the corner is formed by a straight line and a counterclockwise arc, as shown in Figure 5A, for example, the unit vector U2 at the end point of the straight line can be found using equation (1). , the unit vector U at the starting point of the counterclockwise arc →
1 using equation (4) and further taking the inner product of both, we get
The value corresponds to the corner angle, and if the corner is formed from a counterclockwise arc and a clockwise arc, as shown in Figure B, the end point of the counterclockwise arc is → Find the unit vector U2 from equation (5),
The unit vector U1 at the starting point of the clockwise → circular arc is expressed by the formula (
3) and then take the inner product of both, the value corresponds to the corner angle.

Note that if the smaller angle of the angles formed by the two line segments is the corner angle, then the corner angle and the unit vectors Il, ij. The inner product of is the relationship shown in Figure 6→
Therefore, it can be determined whether the corner angle is within a predetermined range based on the inner product of the unit vectors Ul.

The operation will be explained below with reference to the flowchart of FIG.

When the numerical controller NC starts the operation of the nth block,
The corresponding equation (1), (
3) or (5) is used to find the unit vector U2 at the end point of the n-th → block, and store it in an internal memory (not shown).

Next, the numerical controller NC controls the (n+
1) Preread the block and determine whether the code of the (n+1)th block is GO1, GO2, or GO3.
Based on this judgment result, the above equation (1), (
2) or (4) to find the unit vector U at the starting point of the (n+1)th block, and then calculate the inner product with the unit vector U2 stored in the memory. demand.

Next, the numerical controller NC controls the inner product of unit vectors Ul and U2, 100.・Determine whether or not the size satisfies the condition of the following equation (6). Ili2≦1−δ1 ・・・・・・
(6) However, δ is a preset value in order to determine the range of corner angles for outputting the set signal SET. For example, if the corner angle is 135
If the set signal SET is to be output only when the value is less than or equal to the value, it is sufficient to set δ1 to 1-=, as can be seen from FIG. 72 = When the numerical value stabilization device NC determines that the condition of equation (6) is satisfied, it calculates the following equations (7) and (8), and calculates the X coordinate Xn+1 and Y coordinate Yn+1 of the end point of the nth block. demand.

Xn+1=Xn+ΔXn・・・・・・・・・・・・・・・
・(7) Yn+1=Yn+ΔYn・・・・・・・・・
(8) However, Xn, yn are the X, Y coordinates of the starting point of the n-th block, and ΔXn, ΔYn are the command data of the n-th block given to indicate the amount of movement relative to the starting point.

Next, the numerical controller NC performs the calculation shown in the following equation (9) to obtain the square value L of the distance between the current position of the wire electrode P and the end point of the n-th block.

L=(XO+1-x)2+(Yn+1-y)2...
...(9) Then, when it is detected that the square value L of the distance has become smaller than the reference value δ, the numerical control device NC
outputs a set signal SET.

Note that the reference value δ2 is set in advance in order to determine the timing of outputting the set signal SET, and it is necessary to keep it at an extremely small value. As described above, when the set signal SET is output from the numerical controller NC, the hold circuit HLD is set and the relay RY is set.
2 to turn on the contact Ry2.

Then, when the contacts Ryl and ry2 are both turned on, the output signal of the integrator INT is applied to the summing amplifier AMPl. In this case, the contact Ry
Even during machining of straight parts, the average machining voltage fluctuates to some extent.
This is because if the tension of the wire electrode P is changed in response to this variation, not only will the accuracy of the machined surface deteriorate, but there is also a risk that the wire electrode will break.

Also, only when the corner angle is within a predetermined range, the contact point Ry
The reason why I turned on 2 is because the corner angle is 180
If the tension is close to 0, corner sag will not be much of a problem even if the tension is the same as for the straight section, and the accuracy of the machined surface will be better if the tension of the wire electrode P is not changed. This is because it can be done. Contact point Ryl,r
When y2 are both turned on, the output of the integrator 1NT is added to the summing amplifier AMPl, and the multiplier MUL's multiplier 1...
is added and amplified with the reference voltage V, corresponding to the multiplier MU.
Added to L.

The multiplier MUL multiplies the output of the summing amplifier AMP1 by a reference voltage V4 corresponding to the initial setting value of the tension of the wire electrode P, and adds the result of the operation to the summing amplifier AMP2.
The Zener diode ZD is connected between the summing amplifier AMPl and the multiplier MUL because the signal applied from the summing amplifier AMPl as a multiplier to the multiplier MUL is changed from the reference voltage V5 to V, +VzO (however, V2O is the zener voltage). ) to prevent the tension of the wire electrode P from becoming too weak or too strong. Furthermore, the reference voltage V
, corresponds to the multiplier Tq'' of the multiplier MUL.
The summing amplifier AMP2 adds and amplifies the output signal of the multiplier MUL and the voltage appearing across the resistor Rs, and adds the result to the base of the transistor Tr.
Since the output signal of No. 2 becomes larger as the output of the integrator INT becomes larger, the current flowing from the power source E through the transistor Tr and the brake B1 resistor Rs increases during machining of the corner portion.

By the way, as shown in FIG. 8, the brake B is attached to the brake shaft BS around which the wire electrode P is wound, and the torque increases as the current flows. The tension of the wire electrode P can be increased only at the corner portions, and therefore the machining accuracy at the corner portions can be improved. In addition, in the same figure, 7
8 is a wire take-up reel, 8 is a wire feed reel, 9 is an upper guide, 10 is a lower guide, and 11 is a wire feed reel, and the same reference numerals as in other FIG. 3 represent the same parts. In addition, in the example, based on the average machining voltage,
Although the amount of machining per unit time is detected, it is of course possible to detect the amount of force per unit time based on the average machining current or the number of discharges.

Further, in the embodiment, relays RYl, RY2 and contacts Ryl, ry2 are used, but it goes without saying that switching elements such as transistors may also be used. As explained above, the present invention provides a detection means such as an integrator 1NT that detects the amount of machining per unit time only when the amount of machining per unit time is less than a predetermined value and the corner angle is within a predetermined range. Since it is equipped with a control means for controlling the tension of the wire electrode based on the detection result, it is possible to cut the corner part without the risk of breaking the wire electrode and without deteriorating the machining accuracy of the straight part. This has the advantage of improving machining accuracy.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the drawbacks of the conventional method, Fig. 2 is a diagram for explaining the difference in machining amount between a corner part and a straight part, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 C, Figure 5 A, B
, FIG. 6 is a diagram for explaining a method for determining whether a corner angle is within a predetermined range, and FIG. 7 is a diagram showing the operation when determining whether a corner angle is within a predetermined range. The flowchart shown in FIG. 8 is a block diagram of the wire cut electrical discharge machining apparatus. 1, 5, W are workpieces, 2, 6, P are wire electrodes, INT
is an integrator, COM is a comparator, HLD is a hold circuit, N
C is a numerical control device, RYl, RY2 are relays, Ryl,
ry2 is the relay contact, PG is the pulse generator, AMPL
, AMP2 is a summing amplifier, MUL is a multiplier, B is a brake, BS is a brake switch, ZD is a Zener diode, Tr is a transistor, E is a power supply, and R1 to R are resistors.

Claims (1)

[Claims] 1. Detection means for detecting the amount of machining per unit time in a wire-cut electrical discharge machining device that processes a workpiece by moving the workpiece and a wire electrode relatively at a substantially constant speed based on numerical information; Comparison means for comparing the machining amount per unit time detected by the detection means with a reference value, and a judgment result of whether or not the angle of the corner is within a predetermined range immediately before machining the corner based on the numerical information. and after the judgment means outputs a judgment result indicating that the corner angle is within a predetermined range, the comparison means detects that the amount of machining per unit time has fallen below the reference value. A wire-cut electrical discharge machining apparatus characterized by comprising a control means for controlling the tension of the wire electrode based on the detection result of the detection means.