JP2006130656A - Control device of wire electric discharge machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a wire electric discharge machine that can improve machining speed and machining accuracy and avoid breaking of wire type electrodes. <P>SOLUTION: The number of discharge pulses generated every predetermined time between the wire type electrode 4 and the workpiece 5 is counted by a counting device 7. This counted value Px is compared with the number of reference discharge pulses Ps memorized in a memory device 8 to find out a percentage Px/Ps by a comparison judgment device 9. From this compared result, discharge interruption time controlled by a detection voltage generation device 2 is controlled by a discharge interruption time control device 16. In addition, according to the percentage Px/Ps a cooling liquid amount is controlled by a liquid amount control device 17. According to the percentage, a feed amount acquired by a feed pulse operation device 13 in the predetermined time is also controlled. This prevents surplus energy from being supplied, improves machining speed and machining accuracy, and avoids a wire type electrode wire from breaking. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a wire electric discharge machine, and more particularly to a control device capable of improving a processing speed and processing accuracy.

  FIG. 18 is a diagram showing an outline of a control device of a conventional wire electric discharge machine. The discharge pulse generator 1 applies a voltage to the gap between the wire electrode 4 and the workpiece 5 in order to perform electric discharge machining, and includes a circuit composed of a switching element such as a DC power source and a transistor, a capacitor charging / discharging circuit, etc. It consists of. The detection voltage generator 2 is a device that applies a pulse voltage between the wire electrode 4 and the workpiece 5 in order to detect whether or not the gap between the wire electrode 4 and the workpiece 5 can be discharged. The circuit is composed of an active element, a resistor, a capacitor, etc., a DC power source, and the like.

  The energizing brush 3 is for energizing the wire electrode 4 and is connected to one terminal of each of the discharge pulse generator 1 and the detection voltage generator 2. The workpiece 5 is connected to the other terminals of the discharge pulse generator 1 and the detection voltage generator 2. A pulse voltage generated from the discharge pulse generator 1 and the detection voltage generator 2 is applied between the traveling wire electrode 4 and the workpiece 5.

  The discharge gap detection device 6 is connected to the workpiece 5 and the wire electrode 4 and determines whether the discharge gap is in a dischargeable state based on the transition of the detection pulse voltage from the detection voltage generator 2 and generates a discharge pulse input signal. . Further, for feed control, a feed reference voltage is set through an averaging processing circuit 22 for comparing a pulse-like gap voltage of several μs to several tens of μs or more with a reference voltage to match the processing speed of the feed pulse arithmetic unit. A voltage deviation is obtained by comparison with the output of the device 23. Based on this voltage deviation, the feed pulse calculation device 24 generates a pulse train in which the feed pulse interval is controlled and outputs it to the feed pulse distribution device 12. The feed pulse distributor 12 distributes X-axis and Y-axis drive pulses from this pulse train to the X-axis motor drive apparatus 10 and the Y-axis motor drive apparatus 11 for driving the table on which the workpiece 5 is placed. It is the composition to output.

  First, in order to detect whether or not discharge is possible between the workpiece 5 and the wire electrode 4 as described above, a detection pulse voltage is generated from the detection voltage generator 2 and the workpiece 5 and the wire electrode 4 are detected. Applied to the gap with the electrode 4. When energization occurs between the workpiece 5 and the wire electrode 4 and a voltage drop occurs between the workpiece 5 and the wire electrode 4, the discharge gap detection device 6 detects this voltage drop and discharges. It is determined that it is possible to send a discharge pulse signal to the discharge pulse generator 1, and a discharge pulse is generated from the discharge pulse generator 1, so that a discharge pulse current flows through the gap between the workpiece 5 and the wire electrode 4. . Thereafter, the detection pulse is applied to the gap again after an appropriate pause time for cooling the gap. This operation cycle is repeatedly executed to perform electric discharge machining.

  In this way, machining is performed to remove a part of the workpiece 5 from the workpiece 5 every time an electric discharge pulse is generated. In other words, the detection pulse voltage is used to search for a small conductive path of several tens of μm or less formed in the gap between the opposing wire electrode 4 and the workpiece 5, and immediately a discharge pulse current is applied to heat, evaporate or melt. The electric discharge is started by scattering. The removal amount and processing performance of each discharge pulse are characteristics such as the magnitude of the discharge pulse current, melting heat and thermal conductivity of the material of the wire electrode 4 and the workpiece 5, the viscosity at the time of melting, and the cooling liquid (working liquid). It differs depending on the characteristics related to cooling and sludge discharge. Further, the next discharge following the above-described discharge generation tends to be concentrated mainly in the vicinity of the presence of many small conductive paths through the generated sludge immediately after the end of the discharge. For this reason, accurate servo feed control and pause time control are required so that the discharge generated one after another is not concentrated in one place.

  FIG. 19 is a diagram showing monitoring waveforms of the machining voltage, machining current, and machining speed when the die steel prism shown in FIG. 13 is cut out by a conventional method. The corner where the machining direction changes to a right angle is momentarily fed by the gap. As a result, the machining current decreases and the machining voltage increases. Therefore, the feed speed command becomes large. After the direction is changed, the wire-like electrode and the workpiece are closer than necessary and the gap is narrowed, so that smooth sludge is not discharged. As a result, the sludge density increases, causing discharge concentration and short-circuiting, or the wire electrode is disconnected. Therefore, in the conventional control, the servo feed (relative feed of the wire electrode and workpiece), the discharge pause time, and the fluid pressure of the machining fluid are processed and evaluated in advance for a certain period or distance immediately after the corner. There was a need to add processing. Moreover, the accuracy correction corresponding to the plate thickness change and the corner shape of the workpiece has been very complicated and difficult.

  As described above, the conventional feed control lacks the accuracy of feed because detection is performed with the gap voltage. In particular, when the wire-like electrode is tightly stretched, the wire feed is easily disconnected and the demand for improving the machining speed cannot be met. In addition, it is easy to break at the corner of the machined shape, and it is necessary to add corner control processing such as reducing the feed speed and machining current in advance in order to prevent this. The present invention aims to solve such problems.

  The invention according to claims 1 and 2 of the present application provides wire discharge in which electric discharge machining is performed by supplying a discharge pulse current between the wire electrode and the workpiece while relatively moving the wire electrode and the workpiece. In a control device of a processing machine, a discharge pulse number counting unit that counts the number of discharged pulses every predetermined time, and a moving unit that relatively moves the wire electrode and the workpiece along a processing path based on a movement command A reference discharge pulse number storage unit that stores a preset reference discharge pulse number, a numerical value obtained by the discharge pulse number counting unit every predetermined time, and a numerical value stored in the reference discharge pulse number storage unit The invention according to claim 1 stores the numerical value obtained by the discharge pulse number counting means at predetermined time intervals in the reference discharge pulse number storage means in accordance with the comparison result. Means for controlling the discharge pause time so as to coincide with the numerical value, and the invention according to claim 2 is a pause time control for controlling the discharge pause time so as to suppress excessive input of energy according to the comparison result. By providing the device, disconnection of the wire electrode was prevented, high-precision machining was possible, and high-speed machining was possible.

  According to a third aspect of the present invention, in place of the pause time control device, control is performed such that when the ratio is increased, the coolant amount is increased, and when the ratio is decreased, the coolant amount is decreased. By providing a liquid volume control device, it is possible to prevent wire-like electrodes from being disconnected, enable high-precision machining, and enable high-speed machining. The invention according to claim 4 further includes the distance obtained by multiplying the relative movement distance between the wire-like electrode and the workpiece obtained by the set feed speed and the predetermined time by the ratio as a movement command for each predetermined time. By providing a means for outputting to the moving means and controlling the speed of the relative movement, the wire-like electrode is prevented from being disconnected, high-precision machining is possible, and high-speed machining is possible.

  According to a fifth aspect of the present invention, in the first and second aspects of the present invention, the comparing means further includes a numerical value obtained by the discharge pulse number counting means every predetermined time and a reference discharge pulse number storage means. A liquid amount control device is also provided that calculates a ratio with the stored numerical value, and controls to increase the amount of cooling liquid when the ratio increases and to decrease the amount of cooling liquid when the ratio decreases. This prevents breakage of the wire-like electrode, enables high-precision machining, and enables high-speed machining.

Since the machining feed corresponding to the number of discharge pulses can be realized in the present invention, the following effects are obtained.
a. It becomes possible to maintain the optimum machining current,
b. Wire breakage at the start of cutting with changing machining amount or immediately after passing through a corner can be avoided.
c. The processing speed with high wire tension is greatly improved.
d. The processing accuracy of the corner has been improved.
e. The variation in processing expansion was reduced.

First, the operation principle of the present invention will be described. FIG. 3 is an explanatory diagram of the relationship between the input machining energy and the machining amount in wire electric discharge machining. When the Δ _S portion and the Δ _X portion are processed on the workpiece 5, the following relational expression is established.
P _S * w = Δ _S * t * g
P _X * w = Δ _X * t * g (1)
That is,
Ps / Δs = Px / Δx = t * g / w (2)
It becomes.

Here, t is the plate thickness of the workpiece 5, P _S and P _X are the number of discharge pulses generated at the unit time T in each part, w is the machining amount per discharge pulse, and Δ _S is the number of discharge pulses. The distance that can be moved by P _S , Δ _X is the distance that can be moved by the number of discharge pulses P _X , and g is the machining groove width. Further, if the machining amount w per discharge pulse is constant, the discharge pulse numbers P _S and P _X indicate values proportional to the machining amount generated in the unit time T.

If the machining groove width g is constant on condition that the thickness t does not change, the following equation is obtained.
P _S / P _X = Δ _S / Δ _X (3)
That is, if the change of the number of discharge pulses per unit time T and the change of the feed movement amount by the change can be sent to be equal to each other, it means that the machining groove width g becomes constant.

The reference movement amount Δ _S per unit time T is obtained from the set feed speed SPD as a reference to be set and input by the following equation.
Δ _S = SPD * T (4)
From the equations (3) and (4), the movement amount Δ _X is obtained from the following equation.
Δ _X = SPD * T * (P _X / P _S ) (5)
The above equation (5) means that the set feed speed SPD is changed to a feed speed of SPD * (Px / Ps).
FIG. 4 shows the relationship of equations (3) and (5), where the horizontal axis is the movement amount Δ and the vertical axis is the number P of discharge pulses. If the reference discharge pulse number P _S and the reference set feed speed SPD are set in advance as indicated by the dotted line, the amount of movement Δ _{X is} obtained by counting the number of discharge pulses P _X per unit time T that changes from time to time during machining. Can be generated.
This movement amount Δx is obtained from the equation (1):
Δx = (Px * w) / (t * g)
It can also be expressed as Px * w in this equation is a machining amount when the discharge pulse is generated by Px. Since the movement amount Δx is obtained by dividing the machining amount by the product of the plate thickness of the workpiece and the machining groove width, the movement of the wire electrode by the movement amount Δx is processed by the discharge pulse of Px. The wire electrode is moved by the amount. That is, the equation (5) generates the wire electrode movement amount Δx corresponding to the machining amount by the discharge pulse from the reference discharge pulse number Ps and the count value Px of the number of discharge pulses per unit time T. .

In general, the relationship between the movement amount Δ and the number P of discharge pulses varies depending on the material of the workpiece, the plate thickness t of the workpiece, the machining groove width g, and the like.
For example, when the plate thickness t of the workpiece and the machining groove width g are constant, the relationship between the movement amount Δ and the number of discharge pulses P is as shown in FIG. The slope α of the straight line in FIG. 5A corresponds to (t * g / w) in the formula (2), but since t and g are constant, the slope α is (1 / w in the formula (2). ). In FIG. 5A, the fact that the carbide WC has a larger inclination α than the die steel means that the machining amount w per discharge pulse is smaller in the carbide WC than in the die steel. ing. This is consistent with the fact that carbide WC is less susceptible to electric discharge machining than die steel.

  Further, when the machining groove width g is constant and the plate thickness t is changed with a workpiece made of the same material, the relationship between the movement amount Δ and the number of electric discharge machining pulses P is as shown in FIG. In this case, since g and w in the equation (2) are constant, the slope β of the straight line in FIG. 5B represents the thickness t of the workpiece.

Further, FIG. 5C shows the relationship between the ratio (P / Δ) between the number of discharge pulses P and the movement amount Δ and the plate thickness t of the workpiece, with the machining groove width g being constant (2). From the formula
t = (w / g) * (P / Δ)
Therefore, the slope γ of the straight line in FIG. 5C is (w / g). Here, since the machining groove width g is constant, the slope γ of the straight line represents the machining amount w per discharge pulse. In FIG. 5 (c), the fact that the inclination γ of aluminum is large and the inclination γ of carbide WC is small means that the processing amount w per discharge pulse is large for aluminum and small for carbide WC. ing. This is generally consistent with the fact that aluminum is easy to perform electric discharge machining and that carbide WC is difficult to perform electric discharge machining.

As described above, the relationship between the movement amount Δ and the number P of discharge pulses varies depending on the material of the workpiece, the plate thickness t of the workpiece, the machining groove width g, and the like. In controlling the movement amount Δx of the electrode, a relationship between the reference discharge pulse number Ps and the reference set feed speed SPD (= Δs / T) is obtained in advance. That is, for workpieces of various materials, the plate thickness of the workpiece and the diameter of the wire electrode (machining groove width) are variously changed, and the number of discharge pulses P / T (= Ps) per unit time T and the unit The relationship between the moving speed per time T Δ / T (= Δs) is obtained, and the ratio between the number of discharge pulses P and the moving amount Δ,
κ = P / Δ (6)
Are obtained as shown in Tables 1 to 3. Note that, by multiplying the determined κ by the set feed speed SPD, the reference discharge pulse number Ps (= κ * SPD) can be determined.

  When starting electric discharge machining, κ is read from the above table based on the workpiece material, workpiece thickness, and wire electrode diameter set as machining conditions, and the set feed speed SPD is set to the read κ. To obtain a reference discharge pulse number Ps (= κ * SPD). Then, when performing electric discharge machining, the movement amount (relative movement amount) of the wire electrode with respect to the workpiece is controlled based on the equation (5) while detecting the number P of discharge pulses per unit time.

  Note that the plate thickness set as the processing condition does not necessarily exist in the above table, but in such a case, the κ corresponding to the set plate thickness may be obtained from the known κ existing in the table. For example, when the set plate thickness is between plate thickness 1 and plate thickness 2, it corresponds to the set plate thickness by a method such as proportional distribution from κ1 corresponding to plate thickness 1 and κ2 corresponding to plate thickness 2. Can be determined. Further, an approximate curve of κ with respect to the plate thickness can be obtained from the value of κ corresponding to the plate thickness 1 to plate thickness N, and κ corresponding to the set plate thickness can be obtained. Alternatively, κ can be set manually with reference to the table.

  Further, even when the material of the workpiece to be actually subjected to electric discharge machining does not exist in the above table, κ can be set based on the following concept. As shown in the equation (6), a large κ means that the number of discharge pulses necessary for machining the same distance is large, that is, the machining amount w per discharge pulse is small. . Conversely, the fact that κ is small means that the number of discharge pulses necessary for machining the same distance is small, that is, the machining amount w per discharge pulse is large. For this reason, κ is small for materials that are considered to be easy to perform electric discharge machining, and κ is large for materials that are difficult to perform electric discharge machining. Therefore, even if the material of the workpiece to be actually processed by electric discharge does not exist in the above table, if the degree of machining difficulty of the material is known from past experience, etc., it is the same as the machining difficulty of the material. The material of the processing difficulty level may be searched from the above table and set as the material of the workpiece. Alternatively, when it is understood that the machining difficulty of the workpiece to be actually subjected to electric discharge machining is intermediate between the machining difficulty of the material A and the machining difficulty of the material B, κ of the material A and the material An intermediate value between B and κ may be set manually.

  Next, stop time control will be described.

FIG. 8 is a diagram showing a machining state of the workpiece 5 and states of machining voltage and current between the workpiece 5 and the wire electrode 4 for explaining the downtime.
In FIG. 8, P _X and P _{X + 1} are the number of discharge pulses per unit time T at the positions Δ _X and Δ _{X + 1} , V _X and V _{X + 1} are the respective average machining voltages, and V _P is no load. The voltage, T _ON is the current pulse width, T _OFF is the pause time, and T _{W (X)} and T _{W (X + 1)} are the average no-load time per unit time T, respectively. P _S , V _S , and T _{W (S)} are the number of discharge pulses serving as a reference per unit time T, the average machining voltage, and the average no-load time.
P _X = T / (T _{W (X)} + T _ON + T _OFF )
P _{X + 1} = T / (T _{W (X + 1)} + T _ON + T _OFF )
P _S = T / (T _{W (S)} + T _ON + T _OFF )
V _X = V _P * T _{W (X)} / (T _{W (X)} + T _ON + T _OFF )
V _{X + 1} = V _P * T _{W (X + 1)} / (T _{W (X + 1)} + T _ON + T _OFF )
V _S = V _P * T _{W (S)} / (T _{W (S)} + T _ON + T _OFF )
Furthermore, T _ON << T _W + T _OFF and each T _W + T _ON + T _OFF is replaced with the actual pause time τ, and the above equations are arranged.
T _{W (X)} + T _OFF = τ _X (7)
T _{W (X + 1)} + T _OFF = τ _{X + 1} (8)
T _{W (S)} + T _OFF = τ _S (9)
P _X = T / τ _X (10)
P _{X + 1} = T / τ _{X + 1} (11)
P _S = T / τ _S (12)
V _X = V _P * (τ _X −T _OFF ) / τ _X = V _P * (1−T _OFF / τ _X ) (13)
V _{X + 1} = V _P * (τ _{X + 1} −T _OFF ) / τ _{X + 1}
= V _P * (1−T _OFF / τ _{X + 1} ) …… (14)
V _S = V _P * (τ _S −T _OFF ) / τ _S
= V _P * (1-T _OFF / τ _S ) (15)
Further, the average machining currents I _{m (S)} , I _{m (X)} , I _{m (X + 1)} , and average machining current densities I _{d (S)} , I _{d (X)} , I per unit time T _{d (X + 1)} is obtained by the following equation. Here, t is the plate thickness and g is the processed groove width.
I _{m (S)} = I _p * T _ON * P _S (16)
I _{d (S)} = I _{m (S)} / (t * g) (17)
I _{m (X)} = I _p * T _ON * P _X (18)
I _{d (X)} = I _{m (X)} / (t * g) (19)
I _{m (X + 1)} = I _p * T _ON * P _{X + 1} (20)
I _{d (X + 1)} = I _{m (X + 1)} / (t * g) (21)
The following formula is obtained from the above formula (3) and the above formula.
_{Δ S / Δ X = P S} / P X = I d (S) / I d (X) ...... · (22)
_{Δ S / Δ X + 1 =} P S / P X + 1 = I d (S) / I d (X + 1) ...... · (23)
That is, the expressions (22) and (23) mean that the average machining current density per unit time T increases and decreases when machining is performed based on the above expression (5).

In this regard, FIG. 6 will be described. In FIG. 6A, the horizontal axis represents the sludge concentration S _C in the discharge gap, and the vertical axis represents the average machining voltage Vm. The graph represents the trend of the average machining voltage Vm sludge concentration S _C during discharge machining. When the sludge concentration S _C starts to increase, it is considered that a large number of micro conductive paths through the sludge are detected as a trigger of discharge, and the average machining voltage Vm follows a curve as shown in the graph. FIG. 6B will be described. The horizontal axis represents the sludge concentration S _C in the discharge gap, and the vertical axis represents the number P of discharge pulses generated per unit time and the substantial pause time τ. The graph represents the trend of the discharge pulse number P and substantial downtime per sludge concentration S _C and the unit time changes every moment during discharge machining tau. When the sludge concentration S _C starts to increase, a large number of small conductive paths through the sludge are detected as a trigger for the discharge, the discharge pulse is increased, and a curve like a graph in which the substantial pause time τ is minimized is traced. No-load time T _W becomes shorter, the process proceeds to concentrated discharge from peculiarities of the foregoing discharge products, causing nonuniform deterioration and the groove width of the wire breakage or MenAra is. Conventionally, the worst time is avoided by setting the pause time T _OFF in advance. Furthermore, since the machining area is small when the end face of the workpiece is cut, a large pause time T _OFF is set in advance even when discharge concentrates or the amount of machining fluid to the discharge part escapes and cooling is insufficient.

In the present invention, this problem is solved by automatically changing the pause time (T _OFF ) so that the number of discharge pulses does not increase beyond the limit. FIG. 7A will be described.

The horizontal axis represents the actual pause time τ, the vertical axis represents the number P of discharge pulses per unit time T, and the equations (11) and (12) are illustrated. The (5) to the discharge pulse number P and substantially quiescent time τ per unit time T when processing changes to follow a solid line shown in FIG. 7 (a) according to the processing amount and the sludge concentration S _C on the basis of the equation. The reference discharge pulse number P _{S at} which the optimum discharge pulse density can be obtained and the actual rest time τ _S at that time are set at the point B on the line, and the discharge pulse number P _{X + 1} exceeding the reference discharge pulse number P _S is generated. A description will be given of the pause time control at the time.

In order to make the discharge pulse number P _{X + 1} at point A satisfying P _{X + 1} > P _{S in} FIG. 7A close to the reference discharge pulse number P _S , the substantial pause times τ _{X + 1} and τ _S are set. The set reference pause time T _{OFF (S)} may be extended as shown in FIG. 9 by the difference, that is, by the amount that the no-load pause time _TW is shortened. FIG. 9 is a diagram illustrating a voltage waveform between the wire electrode and the workpiece, and FIG. 9C is a voltage waveform at point B in FIG. 7A, which is a reference voltage waveform. FIG. 9B is a voltage waveform at point A in FIG. 7A, which is a waveform before the present invention is applied. FIG. 9 (a) shows the voltage waveform at point A when the present invention in FIG. 7 (a) is applied. As is clear from FIG. 9, it can be seen that the number of discharges is large in FIG. 9B but decreases in FIG. 9A.

If the control pause time is T _{OFF (X + 1)} , the following equation is obtained.
τ _S −τ _{X + 1} = T _{OFF (X + 1)} −T _{OFF (S)} (24)
Ｔ T _{OFF (X + 1)} = τ _S −τ _{X + 1} + T _{OFF (S)} ...... ・ (25)
The following formula is obtained from formulas (11) and (12).
T _{OFF (X + 1)} = (1 / P _S −1 / P _{X + 1} ) * T + T _{OFF (S)}
...... (26)
That is, in order to control the pause time so as to coincide with the point B that obtains the optimum discharge pulse density, the reciprocal number of the discharge pulse number P _{S serving} as the reference of the point B and the reciprocal number of the discharge pulse number P _{X + 1 at} the point A Is obtained for each unit time T, and the difference is extended from the reference pause time T _{OFF (S)} .

Next, the rest time control when the point C lower than the reference discharge pulse number P _S in FIG. 7B, that is, the discharge pulse number P _X is generated will be described. As in FIG. 7A, the horizontal axis represents the substantial pause time τ, the vertical axis represents the number of discharge pulses P and the average machining voltage Vm, and each of the equations (10), (12), (13), and (15) It changes as you follow the graph. Since the machining amount is usually small at the point C, a discharge pulse having a long substantial rest time having a long no-load time T _{W (X)} is generated as shown in FIG. However, due to the above-mentioned peculiarities of the generation of discharge, the possibility of continuous discharge pulses having a short no-load time T _{W (x)} through sludge is included, causing wire breakage. That is, the phenomenon that the voltage drops instantaneously from the point C ′ to the point B ′ of the average machining voltage and a discharge pulse having a short no-load time T _{W (X)} is injected into the gap is closely observed. Therefore, in order to prevent this short discharge pulse from being injected into the gap, even if the average machining voltage drops below the point B ′ during machining, the substantial pause time τ _X does not exceed τ _S and does not fall below that. If the pause time is extended in advance as shown in FIG.

That is, if the rest time to be controlled is set to T _{OFF (X)} because the average machining voltage at points B ′ and C ′ is equal, the following equation is obtained from equations (13) and (15).
V _P * (τ _X −T _{OFF (X)} ) / τ _X = V _P * (τ _S −T _{OFF (S)} ) / τ _S
...... ・ (27)
Ｔ T _{OFF (X)} = T _{OFF (S)} * τ _X / τ _S ...... ・ (28)
If it arranges from (10) and (12) formula, the following formula will be obtained.
T _{OFF (X)} = T _{OFF (S)} * (P _S / P _X ) (29)
That is, this object is achieved by changing the pause time T _{OFF (X)} to a value obtained by multiplying the reference pause time T _{OFF (S)} by the inverse of the ratio of the reference discharge pulse number P _S and the discharge pulse number P _X. Is done. Thus, based on the evaluation function based on the formulas (26) and (29), the discharge pause time is controlled in advance so as to suppress the excessive input of energy.

  In controlling the discharge pause time based on the equations (26) and (29), as previously described, κ determined in advance for various materials, plate thicknesses, and wire-like electrode diameters is used. be able to. In this case, the determined discharge pulse number Ps (= κ * SPD) is obtained by multiplying the determined κ by the set feed speed SPD, and the calculation of the equations (26) and (29) is performed using this discharge pulse number Ps. Do.

  FIG. 10 is a diagram showing a voltage waveform between the wire electrode and the workpiece, and FIG. 10C is a voltage waveform at point B in FIG. 7B, which is a reference voltage waveform. FIG. 10B is a voltage waveform at point C in FIG. 7B, which is a waveform before the present invention is applied. FIG. 10 (a) shows the voltage waveform at point C when the present invention in FIG. 7 (b) is applied.

In machining at the start of machining or in the part where idle feed occurs at the corner, even if a voltage is applied between the wire electrode and the workpiece, electric discharge hardly occurs (the no-load pause time _TW is large), and the discharge pulse The number Px is smaller than the reference pulse number Ps. For this reason, the pause time T _{OFF (X)} obtained by the equation (29) is larger than the reference pause time T _{OFF (S)} . However, during this time, the wire electrode moves relative to the workpiece and the gap becomes smaller, so that the no-load pause time _TW is reduced and discharge occurs earlier, and the number Ps of discharge pulses within the unit time T is Will increase. When the number of discharge pulses Ps increases, the pause time T _{OFF (X)} obtained by the equation (29) becomes shorter and approaches the reference pause time T _{OFF (S)} .

When the discharge pulse number Px exceeds the reference pulse number Ps, the rest time T _{OFF (X + 1)} is obtained by the calculation of the equation (26), and this rest time T _{OFF (X + 1)} is the reference rest time. It becomes longer than _{TOFF (S)} . The longer the pause time T _{OFF (X + 1)} is, the smaller the number of discharge pulses P _{X + 1} is. (If the no-load pause time T _W is constant, the pause time T _{OFF (X + 1 )} Becomes longer, the number of discharge pulses P _{X + 1} becomes smaller).

In this way, the pause time T _{OFF (X)} is controlled so that the number of discharge pulses Px matches the number of reference pulses Ps.

  On the other hand, if the number of discharge pulses fluctuates, the machining amount processed by the discharge and the temperature rise will fluctuate. Therefore, the present invention controls the temperature rise of the gap accompanying the increase / decrease of the number of discharge pulses per unit time T, and controls the amount (flow rate) of the cooling liquid (working liquid) for discharging sludge generated by the machining. . That is, when the number of discharge pulses per unit time T is increased and the amount of machining is large, the amount of cooling liquid is increased to suppress the rise in the temperature of the gap, and sludge is smoothly removed. When the machining amount is small and the number of discharge pulses per unit time T is small, the amount of coolant is reduced to prevent overcooling, and the wire vibration is suppressed to stabilize the discharge.

11 and 12 are explanatory diagrams for explaining the relationship between the machining state and the coolant amount. The following relationship is obtained from FIG.
P _S ∝Q _S / w ...... ・ (30)
P _X ∝Q _X / w ...... ・ (31)
Q _X / FR _X ∝Q _S / FR _S (32)
Here, w is the amount of sludge per discharge pulse, Q _S and Q _X are the amounts of sludge removed by the number of discharge pulses P _S and P _X , and FR _S and FR _X are the respective liquid amounts.
From the above equations (30), (31), (32), the following equation is obtained.
FR _X ∝ FR _S * (P _X / P _S ) (33)
Evaluation function such that the value obtained by multiplying the ratio of the discharge pulse number P _X during the change the discharge pulse number P _S as a reference to set FR _S as a reference to control the liquid volume according i.e. the amount of sludge Is achieved by changing the liquid amount FR.

  In changing the liquid amount FR based on the equation (33), as described above, κ obtained in advance for various materials, plate thicknesses, and wire-like electrode diameters can be used. That is, by multiplying the obtained κ by the set feed speed SPD, a reference discharge pulse number Ps (= κ * SPD) is obtained, and the calculation of equation (33) is performed using the discharge pulse number Ps.

Based on the principle of the present invention described above, embodiments of the present invention will be described below.
FIG. 1 is a block diagram showing a main part of a control device for a wire electric discharge machine according to an embodiment of the present invention. The same elements as those in the conventional example shown in FIG. In FIG. 1, 1 is a discharge pulse generator comprising a circuit composed of active elements such as transistors for generating a discharge pulse current, a capacitor charge / discharge circuit, a DC power source, etc. One of the outputs is connected to the upper and lower energizing brushes 3. The other is connected to the workpiece 5 and supplies a discharge pulse current between the traveling wire electrode 4 and the workpiece 5. Reference numeral 2 denotes a detection voltage generator comprising an active element such as a transistor for generating a detection voltage for detecting a gap state, a circuit including a resistor and a capacitor, a DC power source, etc. One of the outputs is supplied to the workpiece 5. The other is connected to the upper and lower energizing brushes 3. A table (not shown) on which the workpiece 5 is mounted is driven and controlled by an X-axis motor driving device 10, a Y-axis motor driving device 11 and a feed pulse distribution device 12 that constitute moving means.

  Reference numeral 6 denotes a discharge gap detection device that determines whether or not the gap can be discharged by a detection voltage. One of the inputs is connected to the workpiece 5 and the other is connected to the upper and lower energizing brushes 3. When it is determined that discharge is possible, a discharge pulse injection signal is output to the discharge pulse generator 1. At the same time, it is also output to the discharge pulse number counting device 7.

  The discharge pulse number counting device 7 counts the discharge pulse input signal during the period based on the signal per unit time (predetermined period) T output from the operation clock 14, and is substantially a wire electrode. The discharge pulses generated between 4 and the workpiece 5 are counted.

Reference numeral 8 denotes a reference discharge pulse number storage device that stores a reference discharge pulse number Ps that is input in advance.
The discharge pulse number comparison and determination device 9 counts and stores the number of discharge pulses Px per unit time (predetermined period) T by the discharge pulse number counting device 7 and the reference stored in advance from the reference discharge pulse number storage device 8. The discharge pulse number Ps is compared for each unit time (predetermined period) T, the discharge pulse number Px and the reference discharge pulse number Ps ratio (Px / Ps) are sent, and the pulse calculation device 13, the discharge pause time control device 16, and the liquid amount Output to the controller 17.

  The feed pulse calculation device 13 discharges at a distance (SPD * T) determined from the feed rate SPD sent from the feed rate setting means 15 and the given cycle T for each signal of the given cycle T from the computation clock 14. The movement amount (distance) Δx is obtained by multiplying the ratio (Px / Ps) of the discharge pulse number Px and the reference discharge pulse number Ps sent from the pulse number comparison / determination device 9. That is, the movement amount Δx is obtained by performing the calculation of the above equation (5), and a pulse train corresponding to the movement amount Δx is output to the feed pulse distributor 12. The feed pulse distribution device 12 distributes X-axis and Y-axis drive pulses to the X-axis motor drive device 10 and the Y-axis motor drive device 11 from this pulse train according to the machining program, and drives the table on which the workpiece is mounted. The axis motor and the Y axis motor are each driven.

In response to the ratio (Px / Ps) output from the discharge pulse number comparison / determination device 9, the discharge pause time control device 16 performs the calculation of equation (29) when Px ≦ Ps, and when Px> Ps. The calculation of the equation (26) is performed to obtain the pause time T _OFF and output it to the detection voltage generator 2. The detection voltage generator 2 applies a voltage between the wire electrode 4 and the workpiece 5 after pausing for the rest time T _OFF . In this way, the discharge pause time is controlled based on the evaluation function set in advance so as to suppress excessive input of energy.
Further, the liquid amount control device 17 is based on the discharge pulse number Px and the reference discharge pulse number Ps ratio (Px / Ps) output from the discharge pulse number comparison / judgment device 9 as an evaluation function as shown in the equation (33). The amount of liquid is controlled based on

  As described above, excess energy is supplied by controlling the moving distance, the downtime, and the amount of cooling liquid based on the ratio (Px / Ps) between the number of discharge pulses Px and the number of reference discharge pulses Ps every predetermined time. As a result, the machining speed was improved and the machining accuracy was improved.

  FIG. 2 is a block diagram of a main part of a control device for a wire electric discharge machine according to the second embodiment of the present invention. Only the parts different from the first embodiment shown in FIG. 1 will be described. In this second embodiment, instead of counting and storing the number of discharge pulses, the integrated value of the discharge pulse current is obtained from the current detection circuit 18 and the discharge pulse current integrated value calculation storage device 19, and instead of the reference number of discharge pulses. Is provided with a reference discharge pulse current integral value storage device 20, and a discharge pulse current integral value comparison / determination circuit 21 to be compared calculates and outputs a feed pulse, a discharge pause time, and a ratio for liquid amount control.

  That is, instead of setting the reference number of discharge pulses Ps, instead of setting the reference discharge pulse current integral value and counting the number of discharge pulses Px per unit time T that changes from time to time during processing, What is necessary is just to calculate the discharge pulse current integrated value. Further, as in the case of obtaining κ, reference values for various materials, plate thicknesses, and wire-like electrode diameters can be obtained and used.

  The second embodiment is different in that the integrated value of the discharge pulse current is used instead of the number of discharge pulses, and the rest is the same as the first embodiment, and the operation and effect are also the same.

  FIG. 14 shows a monitor waveform when a workpiece (material SKD11) having a plate thickness of 60 mm is cut from the end face using a wire electrode having a diameter of 0.2 mm (material brass). The horizontal axis is the machining elapsed time (10 seconds / scale), the left vertical axis is the machining voltage (V), the pause time (μsec), the number of discharge pulses per unit time, and the right vertical axis is the machining speed (mm / Min) and machining current (A). Hereinafter, it demonstrates according to processing elapsed time.

  The machining voltage is 70V, the pause time is 12μs, the number of discharge pulses is 0 level, the machining current is 0A, and the machining speed is 3.5mm / min. is doing. By 18 seconds to 20 seconds, the machining voltage decreases to 60 V or less and machining current starts to flow. This time is detected and the feeding of the present invention is started. As the machining amount increases, the number of discharge pulses also increases correspondingly, and at the same time, the pause time gradually approaches the set pause time. The processing speed is gradually increased from about 1 mm / min, and reaches the target processing performance level after about 60 seconds. From this result, it was confirmed that it was possible to avoid the disconnection due to the concentrated discharge and the lack of the liquid amount to the discharge part due to the escape of the machining liquid, which is a problem when cutting the end face.

  FIG. 15 is a monitor waveform when passing through the corner when the punch shape shown in FIG. 13 is cut and processed. The wire electrode has a diameter of 0.2 mm (material brass), and the workpiece has a thickness of 60 mm (material SKD11). The horizontal axis is the machining elapsed time (10 seconds / scale), the left vertical axis is the machining voltage (V), the pause time (μsec), the number of discharge pulses per unit time, and the right vertical axis is the machining speed (mm / Min), read the machining current (A). A description will be given according to the progress of the machining time.

  From the start of monitoring until 26 seconds have passed, it indicates the corner immediately before. The machining voltage is about 42 V, the pause time is about 12 μsec, the number of discharge pulses is about 30 levels, the machining current is about 3.6 A, and the machining speed is about 1.5 mm / min. After entering the right angle corner after 26 seconds, the machining voltage is about 50 V, the pause time is about 20 μs, the number of discharge pulses is about 20 levels, the machining current is about 2 A, and the machining speed until about 32 seconds have passed. Changes to about 1 mm / min, reducing the input energy.

  Thereafter, the speed is gradually increased, and the machining state almost immediately before the corner is restored after about 60 seconds. It can be confirmed that the problem at the corner by the conventional control, that is, concentrated discharge due to excessive feeding and excessive input energy is avoided.

  FIG. 16 shows a workpiece (material: die steel) having a thickness of 60 mm using a wire electrode having a diameter of 0.2 mm (material: brass), and a zigzag shape having a side of 10 mm and a pitch of 1.5 mm shown in FIG. Continuous machining is performed for about 1 hour, and machining voltage, machining current, downtime, and machining speed are monitored. The horizontal axis is the machining elapsed time (2 minutes / scale), the left vertical axis is the machining voltage (V), the downtime (μsec), the right vertical axis is the machining speed (mm / min), and the machining current (A). I Read. A description will be given according to the progress of the machining time. Since the machining start is a cut from the end face, the pause time is extended to about 20 μsec by the control of the present invention, and the machining current and machining speed are also controlled accordingly. The maximum processing speed reaches about 5mm from the corner. At this time, the machining voltage is about 35 V, the pause time is about 10 μsec, the machining current is about 6.7 A, and the machining speed is about 2.6 mm / min. Immediately after passing through the corner, the machining voltage is increased to about 47 V by the control of the present invention, but the machining speed is reduced to about 1.5 mm / min and the machining current is reduced to about 3.6 A.

  As described above, the problem in the conventional control, that is, the avoidance of disconnection immediately after the cutting of the workpiece end face and immediately after passing the corner has been confirmed by the long-time machining according to the present invention.

It is a principal part block diagram of the control apparatus of the wire electric discharge machine which shows the Example of this invention. It is a principal part block diagram of the control apparatus of the wire electric discharge machine which shows the other Example of this invention. It is a figure for demonstrating the production | generation of the movement amount by processing amount change. It is explanatory drawing of the movement amount with respect to process amount change. It is explanatory drawing explaining the characteristic of the electric discharge machining by the material of a workpiece. It is a figure explaining the relationship between sludge density | concentration, an average process voltage, the number of discharge pulses, and substantial rest time. It is a figure for demonstrating the relationship between substantial idle time, the number of discharge pulses, and an average process voltage. It is a figure for demonstrating the relationship between a stop time and a processing amount. It is a figure for demonstrating rest time control in A point in Fig.7 (a). It is a figure for demonstrating rest time control in C point in FIG.7 (b). It is a figure for demonstrating control of the liquid quantity by a processing amount change. It is a figure for demonstrating control of the liquid quantity by the processing amount change. 14 shows the shape of the workpiece when the monitor waveforms in FIGS. 14, 15 and 19 are acquired. 14 is a monitor waveform of a machining voltage, a machining current, a number of discharge pulses, a machining speed, and a downtime immediately after the machining is started when the shape shown in FIG. 13 is machined. 14 is a monitor waveform of machining voltage, machining current, number of discharge pulses, machining speed, and downtime immediately after passing the corner when the shape shown in FIG. 13 is machined. FIG. 18 is a monitor waveform of a machining voltage, a machining current, the number of discharge pulses, a machining speed, and a downtime when the shape of FIG. 17 is machined. It is a figure which shows the example of a process shape. It is a principal part block diagram of the control apparatus of the conventional electric discharge machine. 14 is a monitor waveform of machining voltage, machining current, number of discharge pulses, machining speed, and downtime when machining FIG. 13 with a conventional electric discharge machine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge pulse generator 2 Detection voltage generator 3 Current supply brush 4 Wire-shaped electrode 5 Work piece 6 Discharge gap detection device 7 Discharge pulse number counting device 8 Reference discharge pulse number storage device 9 Discharge pulse number comparison judgment device 10 X-axis motor Drive unit 11 Y-axis motor drive unit 12 Feed pulse distribution unit 13 Feed pulse computation unit 14 Calculation clock 15 Feed rate setting means 16 Discharge pause time control unit 17 Liquid quantity control unit 18 Current detection circuit 19 Discharge pulse current integral value computation storage unit 20 reference discharge pulse current integral value storage device 21 discharge pulse current integral value comparison judgment device

Claims (5)

In a control device for a wire electric discharge machine that performs electric discharge machining by introducing an electric discharge pulse current between the wire electrode and the workpiece while relatively moving the wire electrode and the workpiece,
Discharge pulse number counting means for counting the number of discharged pulses every predetermined time;
A moving means for relatively moving the wire electrode and the workpiece along a machining path based on a movement command;
Reference discharge pulse number storage means for storing a preset reference discharge pulse number;
Comparing means for comparing the numerical value obtained by the discharge pulse number counting means every predetermined time with the numerical value stored in the reference discharge pulse number storage means;
Means for controlling the discharge pause time so that the numerical value obtained by the discharge pulse number counting means every predetermined time in accordance with the comparison result matches the numerical value stored in the reference discharge pulse number storage means. A control device for a wire electric discharge machine. In a control device for a wire electric discharge machine that performs electric discharge machining by introducing an electric discharge pulse current between the wire electrode and the workpiece while relatively moving the wire electrode and the workpiece,
Discharge pulse number counting means for counting the number of discharged pulses every predetermined time;
A moving means for relatively moving the wire electrode and the workpiece along a machining path based on a movement command;
Reference discharge pulse number storage means for storing a preset reference discharge pulse number;
Comparing means for comparing the numerical value obtained by the discharge pulse number counting means every predetermined time with the numerical value stored in the reference discharge pulse number storage means;
A control device for a wire electric discharge machine, comprising: a pause time control device that controls a discharge pause time so as to suppress an excessive input of energy according to the comparison result. In a control device for a wire electric discharge machine that performs electric discharge machining by introducing an electric discharge pulse current between the wire electrode and the workpiece while relatively moving the wire electrode and the workpiece,
Discharge pulse number counting means for counting the number of discharged pulses every predetermined time;
A moving means for relatively moving the wire electrode and the workpiece along a machining path based on a movement command;
Reference discharge pulse number storage means for storing a preset reference discharge pulse number;
Means for determining a ratio between a numerical value obtained by the discharge pulse number counting means every predetermined time and a numerical value stored in the reference discharge pulse number storage means;
A control apparatus for a wire electric discharge machine, comprising: a liquid amount control device that controls to increase a cooling liquid amount when the ratio increases and to decrease a cooling liquid amount when the ratio decreases.   A means for outputting the distance obtained by multiplying the relative movement distance between the wire-like electrode and the workpiece determined by the set feed speed and the predetermined time by the ratio as a movement command to the moving means every predetermined time. 4. A control device for a wire electric discharge machine according to 3.   The comparison means also obtains a ratio between a numerical value obtained by the discharge pulse number counting means every predetermined time and a numerical value stored in the reference discharge pulse number storage means, and when the ratio increases, the amount of the coolant is increased. 3. The wire electric discharge machine control device according to claim 1, further comprising: a liquid amount control device that controls the amount of the cooling liquid to decrease when the ratio decreases.

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