CN110856880B - Mould-carving electric discharge machine - Google Patents
Mould-carving electric discharge machine Download PDFInfo
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- CN110856880B CN110856880B CN201910644615.0A CN201910644615A CN110856880B CN 110856880 B CN110856880 B CN 110856880B CN 201910644615 A CN201910644615 A CN 201910644615A CN 110856880 B CN110856880 B CN 110856880B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
- B23H1/00—Electrical discharge machining, i.e. removing metal with a series of rapidly recurring electrical discharges between an electrode and a workpiece in the presence of a fluid dielectric
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
- B23H1/00—Electrical discharge machining, i.e. removing metal with a series of rapidly recurring electrical discharges between an electrode and a workpiece in the presence of a fluid dielectric
- B23H1/02—Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges
- B23H1/022—Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges for shaping the discharge pulse train
Abstract
The invention provides a die-cut electric discharge machine capable of continuously providing a current pulse with a pulse width of each discharge current pulse accurately set to a constant value in an ultra-fine machining region where the pulse width of the current pulse is less than 1 mu sec. The die-cutting electric discharge machine is provided with: a first switching element (32) disposed in series between the positive electrode of the DC power supply (5) and the machining gap in the ultra-fine machining circuit (23); a second switching element (33) which is arranged in series with the first switching element (32) between the negative electrode of the DC power supply (5) and the machining gap in the ultra-fine machining circuit (23); a detection resistor (35) disposed in series between the first switching element (32) and the machining gap in the ultra-fine machining circuit (23); and a control device (22) which turns on both or one of the switching elements (32, 33) after a preset rest time, and turns off both or one of the switching elements (32, 33) after a predetermined time after the discharge generation detection device (24) detects the discharge generation of the machining gap.
Description
Technical Field
The present invention relates to a die sinking electric discharge machine (die sinking electric discharge machine), and more particularly, to a die sinking electric discharge machine including a machining power supply device that repeatedly supplies a current having the same discharge energy to a machining gap while matching waveforms of current pulses having a very short pulse width.
Background
As shown in patent document 1 or patent document 2, for example, the die-sinking electric discharge machine is configured to: the tool electrode formed into a desired machining shape is arranged to face the workpiece with a predetermined machining gap therebetween, a voltage is applied to the machining gap to generate an electric discharge, the material of the workpiece is removed by the electric discharge energy at that time, and the above operation is repeated to transfer the shape of the tool electrode to the workpiece, thereby machining the workpiece into the desired shape.
In electric discharge machining, machining is performed by using, among electric discharge phenomena, spark discharge and subsequent discharge in the transient arc region, and therefore there is a limit to the length of time that a current suitable for electric discharge machining can be supplied. If the current is continuously supplied beyond the limit time, the arc discharge state is entered, and the heat generated by the current flow causes the tool electrode or the workpiece to melt, resulting in failure of machining.
Therefore, the electric discharge machining circuit that generates electric discharge generates spark discharge that contributes to machining by applying a predetermined voltage to the machining gap, temporarily stops supplying current after a predetermined time from the generation of electric discharge, and generates spark discharge by applying a predetermined voltage again to the machining gap after a predetermined time of stopping for deionizing the machining gap to recover the degree of insulation.
Since electric discharge machining is a machining method for removing a material of a workpiece by using electric discharge energy, theoretically, the amount of material that can be removed by one-shot electric discharge is approximately proportional to the magnitude of the electric discharge energy per one-shot electric discharge. The magnitude of the discharge energy depends on the magnitude of the current flowing through the machining gap when the discharge occurs, in other words, the magnitude of the current density.
In the electric discharge machining, when a material is removed by electric discharge, a hole called a crater (discharge mark) is formed in a work. The larger the dent, the more material is removed, but the machined surface roughness becomes rougher. Therefore, the required fine machined surface is usually obtained efficiently by performing at least one of the following steps: a rough machining step of machining the material substantially without removing the material with as large a discharge energy as possible; and a subsequent finishing step of performing machining by reducing the discharge energy in stages until the required fine machined surface roughness is achieved.
The smaller the deviation of the size of the dent, the finer the machined surface. Therefore, it is important that the measured value of the surface roughness represented by the average of the sizes of the plurality of dimples is small, and it is also important that the variation in the sizes of the dimples is small, from the viewpoint of obtaining a good-quality machined surface. If the magnitude of the discharge energy is constant, in other words, if the waveform of the repeated current pulse is constant, the sizes of the pits are almost the same, that is, almost no variation occurs. Therefore, in order to obtain a high-quality machined surface, it is desirable that the waveforms of the current pulses per one-shot discharge be uniform and constant.
In order to control the supply of current so that the waveform of the current pulse per one striking discharge is constant, it is sufficient to turn off the switching element (switching device) after a predetermined time after applying a voltage to the machining gap. However, in practice, after a voltage is applied to the machining gap, discharge occurs in the machining gap and a current starts to flow after an unpredictable unspecified time called a no-load time or a discharge standby time, and therefore, even if the switching element is turned off after a predetermined time, the pulse width (time width) of the current pulse per one striking discharge is different, and the waveforms of the current pulses that are continuous cannot be made identical and identical.
Therefore, the following techniques are being implemented: the pulse width of the current pulse for each striking discharge is made uniform and constant by detecting the occurrence of discharge in the machining gap and controlling the switching element to be turned off after a predetermined time from the occurrence of discharge. Hereinafter, a method of turning off the switching element after a predetermined time after detecting the discharge generation is referred to as an on clamp (on clamp) method. An example thereof is disclosed in patent document 1. In more detail, since the rising and falling characteristics of the waveform of the current pulse and the peak current value are determined substantially uniformly by the circuit element, the same waveform of current pulse can be continuously supplied as long as the pulse width of the current pulse per one striking discharge can be made uniform and constant by appropriately setting the predetermined time.
However, in principle, it is impossible to turn on and off the current pulse in a repetitive cycle shorter than the control time that elapses until the switching element is turned off after the occurrence of the discharge is detected. In other words, it is impossible to provide a current pulse having a shorter pulse width than a delay time (time-lag) required until the switching element is turned off after the discharge generation is detected. In particular, the waveform of the rise and fall of the voltage pulse is smoothed by the capacitance and resistance components existing in the electric discharge machining circuit, and thus the delay time becomes longer. Therefore, the lower limit of the pulse width of the current pulse that can be supplied by the configuration of the truing circuit in the current die electric discharge machine is approximately 1 μ sec (second). Therefore, the clamping method cannot be applied to the so-called "micromachining" in which a current pulse having an extremely short pulse width of nanosecond is supplied to form a particularly fine dimple.
Therefore, in the micromachining, a current pulse is supplied by a so-called multi-oscillation method. The multi-oscillation system is a system in which a switching element is turned on and off at a high-frequency switching frequency of 1MHz or more to supply a current pulse based on an on time and an off time set in advance as an electric machining condition, regardless of the generation of electric discharge. According to the multi-oscillation system, the pulse width of the current pulse can be set to nanosecond level, and thus the roughness of the machined surface can be further reduced. However, in the multi-oscillation method, since the pulse width of the current pulse is not constant without specifying the no-load time, the size of the dimple varies, and the quality of the machined surface is not very good. In addition, in the multi-oscillation method, in many cases, electric discharge is not generated or electric discharge that substantially contributes to machining is generated during a period in which electric discharge is necessary, and as a result, machining efficiency is rather low and machining speed tends to decrease compared to the clamping method.
Further, as shown in patent document 2, for example, the following techniques are also known: after the first non-conductive element makes the direct current power supply and the tool electrode non-conductive, the second non-conductive element makes the direct current power supply and the tool electrode non-conductive, and a differential voltage is applied between the electrodes. According to such a technique of supplying a current pulse using a high-speed switching element, a current pulse having a pulse width of nanosecond can be formed.
[ Prior art documents ]
[ patent document ]
[ patent document 1] Japanese patent Japanese Kokoku publication Sho 44-13195
[ patent document 2] Japanese patent laid-open No. 2003-127028
Disclosure of Invention
[ problems to be solved by the invention ]
However, in any of the techniques that can continuously supply current pulses having nanosecond-level pulse widths, the occurrence of discharge cannot be detected to control the turn-off of the switching element, and thus the pulse width of the current pulse for each discharge stroke cannot be accurately set to be constant and continuously supplied. Therefore, in the ultra-fine machining region of the electric discharge machining, there is room for improvement in the quality of the machined surface.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a die-cut electric discharge machine capable of improving the quality of a machined surface by accurately and continuously providing a constant pulse width of a current pulse per one shot in an ultra-fine machining region where the pulse width of the current pulse is less than 1 μ sec.
[ means for solving problems ]
The die electric discharge machine of the present invention can provide current pulses having an extremely short pulse width of less than 1 μ sec by eliminating the hindrance to the reduction in the pulse width of the current pulses, by basically applying the clamping manner described above. That is, the die-sinking electric discharge machine of the present invention includes: a main electric discharge machining circuit including a direct-current power supply connected in series to a machining gap formed by a tool electrode and a workpiece; a micromachining circuit that is disconnected from the main electric discharge machining circuit, removes electrostatic capacitance and resistance components as much as possible, and applies a current from the dc power supply to the machining gap as a current pulse having a pulse width of less than 1 μ sec; a first switching element disposed in series between a positive electrode of the dc power supply and a machining gap in the micromachining circuit; a second switching element connected in series between a negative electrode of the dc power supply and the machining gap in the ultra-fine machining circuit and arranged in series with the first switching element; an electric discharge generation detection device that detects generation of an electric discharge in the machining gap; a detection resistor which is arranged in series between the first switching element and the machining gap in the ultra-fine machining circuit, and which has a resistance value for supplying a voltage pulse to the machining gap, the voltage pulse requiring a shorter rise time and a shorter fall time than a pulse width of the current pulse of 100nsec or more and less than 1 μ sec of the machining gap, and a voltage drop immediately after discharge in a waveform of the voltage pulse being stable and regular; and a control device which is provided as close as possible to the discharge occurrence detection device, turns on one or both of the first switching element and the second switching element after a predetermined rest time, and turns off one or both of the first switching element and the second switching element after a predetermined time after the discharge occurrence detection device detects the occurrence of the discharge.
Preferably, the discharge occurrence detection device is provided on the machine side apart from the electrical side including the main electric discharge machining circuit.
Further, the discharge occurrence detection device preferably includes a voltage divider circuit.
Further, it is desirable to further have: and a relay switch which is a path connecting the machining gap and the dc power supply, is inserted in the main electric discharge machining circuit and the ultra-fine machining circuit, respectively, and is configured to be in a non-conductive state when one of the main electric discharge machining circuit and the ultra-fine machining circuit is in a conductive state.
[ Effect of the invention ]
Hereinafter, the effects of the present invention will be described with reference to fig. 4. Fig. 4 (a) shows an ideal voltage pulse waveform, which instantaneously rises to a predetermined voltage at time t11, and when electric discharge occurs in the machining gap at time t12, the voltage instantaneously falls to a discharge voltage. Therefore, a detection threshold value Th shown in the figure is theoretically set, and when the voltage of the machining gap drops to a predetermined voltage shown by the detection threshold value Th, it is determined that discharge is generated in the machining gap, and the generation of discharge is detected, and for example, by turning on the switching element or the like as described above for a predetermined time between time t12 and time t13, a current pulse having a constant pulse width (equal to the time length of a predetermined period from time t12 to time t 13) can be supplied to the machining gap.
However, actually, a detection delay ds as shown in fig. 4 (b) occurs due to the influence of the capacitance or resistance component in the electric discharge machining circuit, and therefore, considering the control time required until the switching element is turned off after the discharge is detected, it is difficult to control the current pulse to a constant pulse width when the pulse width of the current pulse is an extremely short time less than 1 μ sec. Here, by reducing the capacitance or resistance component in the electric discharge machining circuit as much as possible, the rise and fall of the voltage waveform in the machining gap can be made more rapid as shown in fig. 4 (c). As a result, the voltage drop to the detection threshold Th and the discharge can be detected more quickly, and thus the detection delay ds can be improved.
However, when the capacitance or the resistance component in the electric discharge machining circuit is reduced as much as possible, the resistance component in the machining circuit becomes substantially the resistance component of the machining gap, and therefore the voltage change pattern immediately after the voltage drop after the electric discharge is generated is more strongly affected by the state of the machining gap which is constantly changing, and becomes unstable. Therefore, as shown in fig. 4 (c), the voltage change immediately after the discharge in the machining gap is directly reflected on the detection voltage, and the timing at which the discharge is detected varies depending on, for example, ts1, ts2, and ts3, so that the discharge in the machining gap cannot be reliably detected, and as a result, it is difficult to control the current pulse to a constant pulse width. However, since the clamping method cannot be practically performed in the ultra-fine machining region, it is hardly known that the discharge generation cannot be stably detected due to unstable timing (timing) of detecting the discharge generation.
The mold cutting electric discharge machine of the present invention is finally obtained by finding out the interference factors which interfere with the reliable detection of the discharge, and the electric discharge machine can make the voltage rise and drop rapidly, and the electric discharge machine is provided with a detection resistor in the ultra-fine machining circuit which can provide the current pulse with the pulse width less than 1 musec, and the resistance value of the detection resistor is necessary to be sufficiently small in the aspect of preventing the unstable voltage drop mode immediately after the discharge of the machining gap. By providing such a detection resistor, the voltage waveform of the machining gap is slightly delayed from the voltage waveform of fig. 4 (c) in time until the voltage rises as shown in fig. 4 (d), but the irregular voltage drop pattern immediately after the discharge is generated per voltage pulse is suppressed. Thus, the mold-sinking electric discharge machine of the present invention can supply a current pulse having an extremely short pulse width of nanosecond order, for example, about 100nsec, a constant pulse width, and a uniform waveform to the machining gap.
Further, since the die-cut electric discharge machine according to the embodiment shown in fig. 1 is configured such that the discharge occurrence detection device includes a voltage divider circuit having a high impedance, even when the detection voltage is small, a reliable detection voltage with almost no detection delay can be obtained, and the discharge occurrence can be detected more reliably.
As described above, according to the present invention, dimples having a uniform size can be formed in an ultra-fine machining region using an extremely small current pulse having a pulse width of less than 1 μ sec, and a machined surface having a small roughness of the machined surface and a uniform surface quality can be obtained. In particular, a voltage pulse having a sharp rise and fall can be supplied at each striking discharge, so that the formed dimples of uniform size become relatively large-area and shallow-depth dimples with smooth edges, and smooth machined surfaces with gentle undulations, such as improvement in mold releasability, can be obtained. Further, the effect of improving the machining efficiency is exhibited as compared with the multi-oscillation system.
Drawings
Fig. 1 is a block diagram showing a die-sinking electric discharge machine according to an embodiment of the present invention.
Fig. 2 is a front view showing an external appearance of the die electric discharge machine.
Fig. 3 is a schematic diagram of waveforms of voltage and current and a control signal in the machining gap to explain the effect of the die-cut electric discharge machine.
Fig. 4 is a schematic diagram of voltage waveforms of a machining gap, which explains operations of a conventional die electric discharge machine and the die electric discharge machine of the present invention.
[ description of symbols ]
1: tool electrode
2: workpiece to be processed
5: direct current power supply
10: machine tool machine
20: numerical control power supply device
21: main discharge machining circuit
22: main processing control device
23: ultra-fine processing circuit
24: discharge generation detection device
25: controller
30: relay switch
32: first switching element
33: second switching element
34: change-over switch
35: detection resistor
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a circuit block diagram showing a machining power supply device including an electric discharge machining circuit of an engraving electric discharge machine according to an embodiment of the present invention, and fig. 2 is a front view showing an external appearance of the engraving electric discharge machine. First, the overall structure of the die-cut electric discharge machine will be described with reference to fig. 2. The engraving electric discharge machine is, for example, a engraving electric discharge machine, and basically includes a machine main body 10 and a numerical control power supply device 20.
The machine tool 10 is configured to reciprocate a head (head)11 in a depth direction (Z-axis direction) by a servo motor (servo motor) such as a linear motor, reciprocate a ram (ram)12 in a front-rear direction (Y-axis direction), and reciprocate a table 13 in a lateral direction (X-axis direction), respectively, so that a tool electrode EL and a workpiece WP can be relatively moved in three axial directions at least in a vertical one-axis direction and a horizontal two-axis direction. As to a more specific mechanism for achieving such relative movement, various well-known mechanisms can be applied.
The tool electrode EL is fixed to an attachment plate provided at the lower end of the head 11, and the workpiece WP is attached to a surface plate provided on the table 13 surrounded by the processing tank 14. The numerical control power supply device 20 is installed at a distance of, for example, about several meters (m) from the machine tool 10, and supplies power and control signals to the machine tool 10 via a coaxial cable CB.
Next, the structure of the machining power supply device of the die-cut electric discharge machine according to the present embodiment will be described. The electric discharge machining circuit of the machining power supply device shown in fig. 1 includes at least a main electric discharge machining circuit 21 and an ultra-fine machining circuit 23. The main electric discharge machining circuit 21 includes a rough machining circuit to a finishing circuit that share the variable dc power supply 5, but detailed description thereof is omitted. The electric discharge machining circuit includes a machining gap formed by the tool electrode 1 and the workpiece 2. The tool electrode 1 corresponds to the tool electrode EL shown in fig. 2, and the workpiece 2 corresponds to the workpiece WP similarly shown in fig. 2. The electric discharge machining circuit shown in fig. 1 includes a capacitance (capacitor component) 3 for machining a gap and an inductance component 4 including line-to-line inductance.
The machining power supply device is provided in a numerical control power supply device 20 shown in fig. 2, and includes a main electric discharge machining circuit 21, a main machining control device 22, and an ultra-fine machining circuit 23. In fig. 1, the main electric discharge machining circuit 21 is shown separately from the variable dc power supply 5 for easy understanding, but the main electric discharge machining circuit 21 of the present invention also includes the dc power supply 5. The micromachining circuit 23 includes a discharge generation detection device 24 dedicated to the micromachining circuit 23 and a controller 25 serving as a control device dedicated to the micromachining circuit 23. The main circuit including the switching circuit of the micromachining circuit 23, the discharge generation detection device 24, and the controller 25 are electrically insulated from each other, thereby preventing the influence of induced current.
The ultra-fine machining circuit 23 including the discharge occurrence detection device 24 and the controller 25 is preferably provided as close as possible to the machining gap on the machine side in order to shorten the circuit, reduce the resistance value, and further improve the response. Wherein, can constitute: the controller 25 is included in the main machining control device 22 provided on the power supply side, for example, in a range capable of supplying a current pulse controlled to a constant pulse width of less than 1 μ sec. Alternatively, the main process control device 22 including the controller 25 may be provided on the machine side within a range where the control device can be sufficiently protected from damage.
The electric discharge machining circuit shown in fig. 1 includes a relay switch (relay switch)30 inserted in a path connecting the machining gap and the variable dc power supply 5. The relay switch 30 is operated by, for example, the main machining control device 22 such that a pair of relay switches 30A on the main electric discharge machining circuit 21 side and a pair of relay switches 30B on the ultra-fine machining circuit 23 side are arranged to be mutually exclusive, that is, such that one of them is brought into a conductive state and the other is brought into a non-conductive state.
The discharge occurrence detector 24 is provided in the micromachining circuit 23, and is configured to accurately detect a voltage applied to the machining gap at a higher speed. A detection signal indicating the generation of the discharge, which is output from the discharge generation detection device 24, is input to the controller 25 in a very short time. The controller 25 is a Field Programmable Gate Array (FPGA) and receives setting data of the machining conditions output from the main machining control device 22 and setting signals of Gate signals for controlling the first switching element 32 and the second switching element 33 of the micromachining circuit 23 to be turned on and off, and outputs the Gate signals to the pair of switching elements 32 and 33. The switching elements 32 and 33 are set to an on state, that is, a state in which a voltage from the variable dc power supply 5 is applied to the machining gap, respectively, upon receiving the gate signal.
In addition, in the present embodiment, the following processing can be selectively performed: as described above, the current pulse having a very short pulse width in the order of nanoseconds is supplied to the ultra-fine machining in the machining gap, and the current pulse having a longer pulse width is supplied to the rough machining to the finish machining in the machining gap. That is, in the micromachining, as shown in fig. 1, one set of relay switches 30A on the main electric discharge machining circuit 21 side among the relay switches 30 for switching the main electric discharge machining circuit 21 and the micromachining circuit 23 is set to a non-conductive state, and one set of relay switches 30B on the micromachining circuit 23 side is set to a conductive state. Thus, a voltage pulse having an extremely short pulse width, which is controlled to be turned on and off by the switching elements 32 and 33, is applied to the machining gap. In contrast, in rough machining, the relay switch 30A is turned on, and the relay switch 30B is turned off. Thus, a voltage pulse having a relatively long pulse width, which is controlled to be turned on and off by a plurality of switching elements, not shown, connected in parallel with each other in the main electric discharge machining circuit 21 is applied to the machining gap.
Here, a detection resistor 35 is disposed in series between the switching element 32 and the machining gap.
In the micromachining circuit 23 of the machining power supply apparatus according to the embodiment shown in fig. 1, the switch 34 is provided so that the plurality of detection resistors 35 connected in parallel can be selectively turned on, and the on/off of the switch 34 can be switched in accordance with the size of the tool electrode 1 or the machining condition including the pulse width of the current pulse required, and the resistance value of the detection resistor 35 is adjusted so that a sufficiently fast voltage rise that can supply the current pulse by the clamping method is obtained, and a sufficiently small resistance value is required in order to prevent an unstable and irregular change pattern at the time of voltage drop immediately after discharge, which causes a timing deviation of detection.
Further, the micro-machining circuit 23 including the discharge occurrence detection device 24 and the controller 25 exclusively for the micro-machining circuit 23 has as small electrostatic capacitance and resistance elements as possible as a whole. The discharge occurrence detector 24 is provided as close to the machining gap as possible, and includes a high-impedance voltage divider circuit 24A.
The operation of the engraved electric discharge machine of the present embodiment having the above-described configuration will be described below. First, the rough machining step will be explained. In this case, the relay switch 30 is set to the state in the rough machining. The main machining controller 22 outputs a gate signal according to machining conditions for rough machining to a switching element, not shown, of the main electric discharge machining circuit 21.
The plurality of switching elements of the main electric discharge machining circuit 21 are repeatedly turned on and off based on machining conditions of rough machining, and apply voltage pulses to a machining gap between the tool electrode 1 and the workpiece 2. The shape of the tool electrode 1 is transferred to the workpiece 2 by the rough machining step, and the workpiece 2 is machined into a substantially desired shape. In the rough machining step, the main machining control device 22 receives a detection voltage based on the machining gap voltage Vg as shown in fig. 1, and thus can selectively supply the current pulse in a clamping manner. In the main electric discharge machining circuit 21, the pulse width of the current pulse supplied to the machining gap is, for example, about 1 μ sec to 100 μ sec. When the finishing process is performed more than once, the finishing process is switched to the processing condition of the finishing process, and a gate signal according to the processing condition of the finishing process is output from the main process control device 22 to a switching element, not shown, of the main electric discharge processing circuit 21. In the finishing step, a machining hole having a shape close to a desired machining shape is formed in the workpiece 2, and the electric discharge machining is performed to finish the machining shape and reduce the roughness of the machined surface by one or more finishing steps.
Next, an ultra-fine machining process performed after performing a rough machining process to at least one finishing machining process performed by the main electric discharge machining circuit 21 will be described. First, the relay switch 30 is operated to physically completely cut off the main electric discharge machining circuit 21 from the electric discharge machining circuit, and the ultra-fine machining circuit 23 is connected to the electric discharge machining circuit. As shown in fig. 1, the main machining controller 22 sends data CN indicating parameters of machining conditions for the ultra-fine machining, and a reference gate signal AGate and a gate signal BGate to the controller 25. The controller 25 outputs gate signals to the switching elements 32 and 33 at the same time or with a time shift in accordance with the on-time and off-time set in accordance with the machining conditions.
The gate signals output from the controller 25 are input to the gates of the first switching element 32 and the second switching element 33, and the switching element 32 and the switching element 33 are repeatedly turned on and off, thereby applying a voltage pulse to the machining gap between the tool electrode 1 and the workpiece 2. After the voltage pulse is applied, discharge is generated in the machining gap after an unspecified no-load time, and the material of the workpiece 2 is removed by the discharge energy at that time. By repeating the above-described discharge and material removal, the shape of the tool electrode 1 is transferred to the workpiece 2, and the workpiece 2 is machined into a desired shape. In the ultrafine machining, in order to make the pits particularly fine, it is desirable that the pulse width of the current pulse supplied to the machining gap be small and constant, less than 1 μ sec.
The switching elements 32 and 33 according to the embodiment are, for example, Field Effect transistors (MOS-FETs), and the response speed of the switching elements 32 and 33 provided so far has a capability of providing current pulses having a pulse width of 1 μ sec or less. However, as described above with reference to fig. 4, it is difficult in the conventional apparatus to actually detect the discharge occurrence and to set the pulse width of the current pulse to be constant based on the detection. Therefore, in the present embodiment, in the ultra-fine machining circuit 23 in which the time required for the voltage to rise and fall is made shorter by removing the capacitance and the resistance component as much as possible, and the occurrence of discharge can be detected in a very short time, the detection resistor 35 is set to a resistance value in which a sufficiently small resistance value is required in a manner that the unstable and irregular variation of the voltage at the time of the voltage fall immediately after the occurrence of discharge in the machining gap can be prevented in a range in which the time required for the voltage to rise and fall is fatally long, unlike a case in which a current pulse having a constant pulse width of 100nsec or more and 1 μ sec or less cannot be supplied.
By providing the detection resistor 35, the waveform of the machining gap voltage is roughly as shown in fig. 4 (d). That is, the detection voltage is input to the discharge generation circuit 24 at a sufficiently fast timing immediately after the discharge is generated, and the manner of voltage drop can be suppressed from becoming unstable and irregular, and the discharge generation can be detected at substantially the same timing from the generation of the discharge, so that the discharge generation can be detected more quickly and reliably. Thus, the die-cut electric discharge machine of the present embodiment can apply the current pulse of the clamping method to the machining gap by supplying the current pulse of an extremely short constant pulse width of nanosecond order, for example, about 100nsec, in the machining region of the ultra-fine machining. Therefore, not only can the surface roughness Rz specified by Japanese Industrial Standards (JIS) be made extremely small, but also a machined surface with high surface quality having uniform and fine dents can be obtained, and the surface roughness Rsm can be remarkably improved to obtain a smooth machined surface with shallow and wide dents, so that the mold release property of the machined product can be improved.
Here, the aspect of supplying a current pulse of a constant pulse width to the machining gap after the discharge generation of the machining gap is accurately detected will be described with reference to fig. 3. Fig. 3 (a) to 3 (e) schematically show changes in the detection voltage and the like with time t. Fig. 3 (a) shows a waveform of a voltage Vg in the standard machining gap of the micromachining circuit 23. As shown in the figure, at time t1 substantially equal to when the controller 25 turns on the first switching element 32 and the second switching element 33 simultaneously in accordance with the gate signal AGate and the gate signal BGate, the voltage Vg of the machining gap rises sharply, and when the discharge occurs at time t2 after the unspecified no-load time, the voltage Vg starts to fall. At this time, by providing the detection resistor 35 as described above, the manner of decreasing the voltage Vg does not vary for each shot.
The discharge occurrence detection device 24 can obtain an accurate detection voltage more stably at high speed even if the detection voltage input to the high-impedance voltage divider circuit 24A is extremely small. The voltage signal output from the voltage divider 24A is compared with a detection threshold Th in a comparator 24D via an operational amplifier (operational amplifier)24B and a level shifter 24C. As shown in fig. 3 c, when the voltage signal based on the machining gap voltage Vg exceeds the detection threshold Th, the comparator 24D outputs a signal (hereinafter referred to as a clamp signal) OC indicating the discharge generation to the controller 25 to start detecting the discharge generation. Then, when the voltage signal is lower than the detection threshold Th, the output of the clamp signal OC is stopped. In the discharge occurrence detection device 24 of the present embodiment, each of the operation amplifier 24B, the level conversion Circuit 24C, and the comparator 24D includes an Integrated Circuit (IC) that operates at high speed, and transmits a detection signal in a very short time of several tens nsec.
When the electric discharge is generated, the current I in the machining gap formed by the tool electrode 1 and the workpiece 2 flows in a waveform as shown in fig. 3 (b) during a time period t2 to t3 until the switching element is turned off, in accordance with the clamp signal OC. More specifically, the micromachining circuit 23 operates as follows. The discharge occurrence detection means 24 stops the output of the clamp signal OC immediately after the occurrence of the discharge. Immediately after the discharge generation detection device 24 stops clamping the signal OC, the controller 25 stops the output of the gate signals AGate and BGate to turn off the first switching element 32 and the second switching element 33 simultaneously. At this time, as shown in fig. 3 (c) and 3 (d), after the occurrence of the discharge is detected, until the pair of switching elements 32 and 33 are turned off, as shown in fig. 3 (b), a slight period td of at least about 50nsec is required, and the current I flows through the machining gap to reach the peak current value in the slight period td. When the pair of switching elements 32 and 33 is turned off, the current I drops sharply. As described above, for example, by adjusting the time until the pair of switching elements 32 and 33 are turned off after the discharge is detected based on the voltage Vg of the machining gap, a current pulse having an extremely short constant pulse width of about 100nsec to 1 μ sec is supplied to the machining gap.
Further, if there is only one switching element between the dc power supply 5 and the machining gap, the positive side or the negative side of the dc power supply 5 is kept connected to the machining gap when the switching element is turned off, and the discharge circuit cannot be completely turned off, so that the current drop in the machining gap is delayed and a short current pulse due to a sharp drop as shown in fig. 3 (b) cannot be obtained. In the present invention, since the time delay may be a problem, in the micromachining circuit 23, the two pair of switching elements 32 and 33 are turned off at the same time, and the dc power supply 5 and the machining gap are completely turned off.
The first switching element 32 and the second switching element 33 are also separately operable. Since the MOS-FET is turned on and off in a saturation region, it is turned on and off with a time shift when a long pulse is to be supplied to a small peak current. When these switching elements are operated individually, they are turned off simultaneously at the time of turning off in order to obtain a current waveform with a stable pulse width.
The micromachining circuit 23 of the present embodiment can be completely disconnected from the main electric discharge machining circuit 21, and the electric discharge generation detection device 24 and the controller 25 are disposed in the main circuit including the pair of switching elements 32 and 33 closest to the micromachining circuit 23, thereby shortening the time from when a detection signal based on the machining gap voltage Vg is obtained to when the gate signals AGate and BGate are output as much as possible. By providing the micro-machining circuit 23 including the discharge occurrence detection device 24 and the controller 25 in the machine tool 10, in other words, in a position closer to the machining gap, the capacitance, resistance component, and inductance component included in the electric wire are reduced, the rise and fall of each of the voltage pulse and the current pulse are made steeper, and the time for supplying the voltage pulse and the current pulse is shortened. As a result, not only the current pulse having the pulse width of less than 1 μ sec can be supplied, but also the current pulse can be supplied with a constant current pulse width and the waveform of the current pulse can be made uniform. Further, the controller 25 of the microfabrication circuit 23 of the present embodiment can provide a pulse width of 100nsec to 1 μ sec by finely controlling the microfabrication circuit in units of 10 nsec.
Claims (4)
1. A die-sinking electric discharge machine comprising:
a main electric discharge machining circuit including a direct-current power supply connected in series to a machining gap formed by a tool electrode and a workpiece;
a micro machining circuit which is disconnected from the main electric discharge machining circuit and applies a current from the dc power supply to the machining gap as a current pulse having a pulse width of less than 1 μ sec;
a first switching element disposed in series between a positive electrode of the dc power supply and a machining gap in the micromachining circuit;
a second switching element connected in series between a negative electrode of the dc power supply and the machining gap in the ultra-fine machining circuit and arranged in series with the first switching element;
an electric discharge generation detection device that detects generation of electric discharge in the machining gap;
a detection resistor which is arranged in series between the first switching element and the machining gap in the ultra-fine machining circuit and has a resistance value for supplying a voltage pulse to the machining gap, the voltage pulse requiring a shorter rise time and a shorter fall time than a pulse width of the current pulse of 100nsec or more and less than 1 μ sec of the machining gap, and a voltage drop of a waveform of the voltage pulse immediately after discharge is stable and regular; and
and a control device which is provided as close as possible to the discharge occurrence detection device, turns on one or both of the first switching element and the second switching element after a predetermined rest time, and turns off one or both of the first switching element and the second switching element after a predetermined time after the discharge occurrence detection device detects the occurrence of the discharge.
2. The die-sinking electric discharge machine of claim 1, wherein the discharge generation detecting device is disposed on a machine side away from an electrical side including the main electric discharge machining circuit.
3. The die-sinking electric discharge machine according to claim 1 or 2, wherein the discharge generation detecting means includes a voltage dividing circuit.
4. The die-sinking electric discharge machine according to claim 1 or 2, further comprising: and a relay switch which is a path connecting the machining gap and the dc power supply, is inserted in the main electric discharge machining circuit and the ultra-fine machining circuit, respectively, and is configured to be in a non-conductive state when one of the main electric discharge machining circuit and the ultra-fine machining circuit is in a conductive state.
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| JP2018-155918 | 2018-08-23 | ||
| JP2018155918A JP6541287B1 (en) | 2018-08-23 | 2018-08-23 | Electric discharge machine |
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| JP2020028948A (en) | 2020-02-27 |
| CN110856880A (en) | 2020-03-03 |
| JP6541287B1 (en) | 2019-07-10 |
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