JP5349391B2 - Fine hole electric discharge machine and fine hole electric discharge machining method - Google Patents

Description

  The present invention relates to a fine hole electric discharge machine and a fine hole electric discharge machining method.

  Conventionally, in the small hole electric discharge machining, there is a problem that the machining becomes unstable when a hole is slightly opened in the workpiece (workpiece) (this state is defined as “at the time of slipping”). Specifically, at the time of removal, the machining fluid ejected from the pipe electrode escapes from the workpiece, so that sludge staying between the electrode and workpiece cannot be discharged, and the sludge causes a short circuit. Frequently occurs. When a short circuit occurs, processing is difficult to proceed because “short circuit back (retraction of electrode)” is performed as a short circuit avoiding operation.

  In addition, in drilling by small hole electric discharge machining, if you want to drill only in the upper layer of a hollow workpiece or if you want to drill a vertical hole in a workpiece that already has a horizontal hole so that it does not pass through the horizontal hole, It is necessary to accurately detect that machining has been completed (penetrated).

  As a technique for detecting penetration of a hole in hole machining in electric discharge machining, there is an invention disclosed in Patent Document 1. The invention disclosed in Patent Document 1 includes means for detecting an update of the lowered position while the electrode is descending, means for sampling and measuring the voltage between the electrode and the workpiece, digitizing to obtain a maximum voltage, sampling and digitizing If the maximum voltage lower than the first maximum voltage value is obtained by the next sampling, the voltage for the first predetermined number of times is set as the first maximum voltage value. Means for comparing the first maximum voltage value with the second maximum voltage value, the electrode is being lowered and its lowest position is updated, and the first maximum voltage value is If an event that is higher than the maximum voltage value by a predetermined voltage value or more occurs continuously for the second predetermined number of times or more, the penetration detection is realized by means for determining that the hole generated by the discharge has penetrated.

JP-A-2005-144651

  However, according to the above-described conventional technique, although penetration of a hole can be detected, it is not possible to detect when the hole is removed. Therefore, it is impossible to solve the problem that the machining becomes unstable when the hole is removed.

  The present invention has been made in view of the above, and a fine hole electric discharge machine and a fine hole electric discharge machine that are capable of detecting a breakage during hole drilling and a penetration of a hole and that can perform stable machining even during the breakage. The purpose is to obtain a processing method.

  In order to solve the above-described problems and achieve the object, the present invention provides a pipe-like electrode for injecting a machining fluid from the tip, and a pulse generating means for applying a pulse voltage including a machining pulse between the electrode and the workpiece. A fine hole electric discharge machine for performing electric discharge machining on a workpiece by intermittently generating electric discharge by a machining pulse in a machining liquid interposed between an electrode and the workpiece with a pause time in between. Based on the detection results of the short-circuit occurrence detecting means for detecting the occurrence of a short-circuit between the electrode and the workpiece, the short-circuit occurrence frequency detecting means for detecting the occurrence frequency of the short-circuit, and the short-circuit occurrence frequency detecting means. And a machining state determining means for judging whether the hole being machined is in a non-penetrating normal state, a partially penetrating state, or a completely penetrating state. .

  According to the present invention, it is possible to detect when a hole is pulled out and through the hole, and it is possible to perform stable machining even when the hole is dropped.

FIG. 1 is a diagram showing a configuration of a first embodiment of a fine hole electric discharge machine according to the present invention. FIG. 2 is a diagram illustrating an operation flow of the fine hole machining of the fine hole electric discharge machine according to the first embodiment. FIG. 3 is a diagram illustrating an example of a waveform of a pulse voltage applied between the electrode and the workpiece. FIG. 4 is a diagram showing the state of the electrode and the workpiece and the flow of the machining liquid during the fine hole electric discharge machining. FIG. 5 is a diagram showing the relationship between the machining time, the short-circuit frequency, and the non-short-circuit frequency when the pause time is extended at the time of disconnection. FIG. 6 is a diagram showing the relationship between the machining time, the short-circuit frequency, and the non-short-circuit frequency when the pause time is not extended at the time of disconnection. FIG. 7 is a diagram showing the relationship between the machining conditions and the machining time at the time of removal. FIG. 8 is a diagram showing a flow of operations of the fine hole machining of the fine hole electric discharge machine according to the second embodiment. FIG. 9 is a diagram illustrating a flow of an operation of fine hole machining of the fine hole electric discharge machine according to the third embodiment.

  Embodiments of a small hole electric discharge machine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a first embodiment of a fine hole electric discharge machine according to the present invention. A thin hole electric discharge machine 1 according to the present embodiment includes an electrode 2, a machining control unit 4, a pulse generation condition setting unit 5, a pulse generator 6, a short circuit detection unit 7, a short circuit frequency detection unit 8, and a machining feed command unit. 9

  The pulse generation condition setting unit 5 sets conditions such as a voltage value of a group pulse (machining pulse) applied between the electrode 2 and the workpiece 3, a voltage value of a check pulse, and a pause time. Note that the voltage value of the group pulse and the voltage value of the check pulse are the same in the normal state and the disconnected state, but the pause time is different. The pulse generator 6 applies a pulse voltage to the electrode 2 and the workpiece 3 under the conditions set by the pulse condition setting unit 5 according to the machining state notified from the machining control unit 4. When the check pulse is applied between the electrode 2 and the work 3, the short-circuit detection unit 7 measures the voltage actually generated between the electrode 2 and the work 3, and compares it with a predetermined threshold value to thereby compare the electrode 2 with the work. It is determined whether the discharge is normally performed between the three or whether the short circuit is short-circuited, and the short-circuit detection result is output to the short-circuit frequency detection unit 8. For example, the short circuit detection unit 7 detects a case where the voltage measured between the electrode 2 and the workpiece 3 when the check pulse is applied is equal to or less than a threshold value as a short circuit, and notifies the short circuit frequency detection unit 8 of the short circuit detection. As a specific example, when a voltage of 50 V is applied as a check pulse, a short circuit is detected when the voltage actually measured between the electrode 2 and the workpiece 3 is 10 V or less. The short-circuit frequency detection unit 8 outputs a short-circuit detection ratio during a predetermined sampling period to the processing control unit 4. For example, if the check pulse is applied 100 times between the electrode 2 and the workpiece 3 during the sampling period and 15 short-circuits are detected, 15% is output to the machining control unit 4 as the short-circuit frequency. The machining control unit 4 is a functional unit that controls the fine hole electric discharge machining by the fine hole electric discharge machine 1, and changes the machining state based on the comparison result between the short circuit frequency and a predetermined threshold value. That is, based on the detection result of the short-circuit frequency detection unit 8, the machining control unit 4 determines whether the hole being machined by electrical discharge machining is in a normal state that is not penetrated, or is in a state of being partially penetrated. It operates as a machining state determining means for determining whether or not the penetrating state has penetrated through. The machining control unit 4 includes a machining state information storage unit 41. The machining state information storage unit 41 stores machining state information indicating whether the machining state is a normal state, a near-run state, or a penetration state. The machining state information is updated based on the short circuit frequency information input from the short circuit frequency detection unit 8 and is output to the pulse generator 6 and the machining feed command unit 9. For example, the machining control unit 4 changes the machining state from the normal state to the exited state when short-circuit frequency information indicating a first threshold value or more is input from the short-circuit frequency detection unit 8 in the normal state. Further, when short-circuit frequency information indicating the second threshold value or less is input in the disconnected state, the machining state is changed to the penetrating state. The machining feed command unit 9 moves the electrode 2 at a speed corresponding to the machining state information notified from the machining control unit 4. Here, the first threshold value is set in advance with a margin (added a predetermined value) having a margin on the upper limit side of the short-circuit occurrence frequency that can be taken in the normal state. As an example, since the occurrence frequency of a short circuit in the normal state is about 30%, “50%” having a margin of about 20% on the upper limit side is set as the first threshold value. The second threshold value is set in advance with a margin (subtracting a predetermined value) having a margin on the lower limit side of the short-circuit occurrence frequency that can be taken in the disconnected state. As an example, since the occurrence frequency of a short circuit in the disconnected state is about 15%, “10%” having a margin of about 5% on the lower limit side is set as the second threshold value.

  The electrode 2 is in the form of a pipe so that the machining liquid can be ejected from the tip during machining.

  FIG. 2 is a diagram illustrating an example of a flow of operations for fine hole machining of the fine hole electric discharge machine 1. When the machining control unit 4 starts the machining operation, the machining control unit 4 notifies the pulse generator 6 and the machining feed command unit 9 of the normal state. The machining feed command unit 9 moves the electrode 2 at the machining feed rate in the normal state, and the pulse generator 6 applies the pulse voltage in the normal state between the electrode 2 and the workpiece 3 (step S101). FIG. 3 is a diagram illustrating an example of a waveform of a pulse voltage applied between the electrode 2 and the workpiece 3. As shown in FIG. 3, the pulse applied between the electrode 2 and the work 3 includes a check pulse for short circuit detection. For this reason, a check pulse is applied between the electrode 2 and the workpiece 3 prior to the group pulse used for actual machining.

  The short circuit detector 7 detects the occurrence of a short circuit based on the voltage actually generated between the electrode 2 and the workpiece 3 when the check pulse is applied. The detection result is output from the short circuit detection unit 7 to the short circuit frequency detection unit 8. The short circuit frequency detection unit 8 detects the short circuit frequency based on the preset total number of check pulses during the sampling period and the number of short circuit detections (step S102). The short circuit frequency detection unit 8 outputs the detected short circuit frequency to the machining control unit 4.

  When the short circuit frequency is input from the short circuit frequency detection unit 8, the processing control unit 4 determines whether or not the short circuit frequency is equal to or higher than a first threshold value (50% in this example) (step S103). . If the short-circuit frequency is 50% or more (step S103 / Yes), the machining control unit 4 changes the machining state from the normal state to the exited state, and sends this to the pulse generator 6 and the machining feed command unit 9. Notice. Further, the machining state information stored in the machining state information storage unit 41 is updated (step S104). Thereafter, the machining feed command unit 9 moves the electrode 2 at the machining feed rate in the disconnected state, and the pulse generator 6 applies the pulse voltage in the disconnected state between the electrode 2 and the workpiece 3 (step S101). Note that the pulse applied between the electrode 2 and the workpiece 3 in the disconnected state has an extended pause time compared to the pulse in the normal state. That is, in the near-run state, processing by a pulse voltage (pause time extension processing) in which the pause time is extended as compared with the normal state is performed.

  FIG. 4 is a diagram showing the state of the electrode 2 and the workpiece 3 during the fine hole electric discharge machining, and the flow of the machining liquid. The arrows in the figure represent the flow of the machining fluid. FIG. 4A shows a normal state, and the sludge 15 is discharged from the hole of the workpiece 3 by the machining liquid sprayed from the tip of the pipe-like electrode 2, so that the occurrence frequency of the short circuit is low. FIG. 4 (b) shows the state when it is pulled out, and the machining fluid sprayed from the tip of the pipe-like electrode 2 flows out from a hole slightly opened in the workpiece 3, and the sludge 15 inside the hole is discharged. It becomes difficult to be done.

  As described above, since the pulse applied by the pulse generator 6 between the electrode 2 and the workpiece 3 in the near-end state has an extended pause time as compared with the normal state, the time for discharging the sludge 15 is increased. In addition to ensuring, the sludge 15 generated per unit time can be reduced. Thereby, the process in the state at the time of removal can be stabilized.

  On the other hand, when the short-circuit frequency input from the short-circuit frequency detection unit 8 is less than the first threshold value (step S103 / No), the processing control unit 4 confirms whether or not the processing state is in a close state (step S103 / No). Step S105).

  If the machining state is a missing state (step S105 / Yes), the machining control unit 4 has the short-circuit frequency input from the short-circuit frequency detecting unit 8 smaller than the first threshold value used for the judgment at the time of missing. It is determined whether or not it is equal to or less than another second threshold value (10% in this example) (step S106). If the short-circuit frequency is less than or equal to the second threshold (step S106 / Yes), the machining control unit 4 changes the machining state from the exited state to the penetrating state and notifies the pulse generator 6 and the machining feed command unit 9. (Step S107). In response to this, the pulse generator 6 and the machining feed command unit 9 stop generating the pulse and feeding the electrode 2 and finish the machining (step S108). On the other hand, when the short circuit frequency exceeds the second threshold value (step S106 / No), the process returns to step S101, and the processing in the disconnected state is continued.

  5 and 6 are diagrams showing the relationship between the machining time, the short circuit frequency, and the non-short circuit frequency. The vertical axis represents frequency (%), and the horizontal axis represents machining time (seconds). FIG. 5 shows the relationship between the machining time and the short-circuit frequency and the non-short-circuit frequency when the pause time is extended at the time of removal, and FIG. 6 shows the machining time and the short-circuit frequency when the pause time is not extended at the time of removal. The relationship with the non-short-circuit frequency is shown. When the resting time is constant regardless of the processing state, short-circuits frequently occur at the time of removal. On the other hand, when the pause time is extended at the time of disconnection, the occurrence of a short circuit at the time of disconnection is reduced, and the machining is stable.

  FIG. 7 is a diagram showing the relationship between the machining conditions and the machining time at the time of removal. If the pause time is not extended at the time of removal, on average, it will be in the state of removal at 45.8 seconds from the start of machining, it will penetrate through 53 seconds from the time of removal, and the overall machining time of 98.8 seconds is required. Yes. On the other hand, if the pause time is extended at the time of removal, on average, it will be in the state of removal at 47 seconds from the start of machining, and will penetrate through 11.2 seconds from the time of removal, requiring a machining time of 58.2 seconds as a whole. doing. Thus, by suppressing the occurrence of a short circuit at the time of disconnection, the number of short-circuit backs can be reduced, and the time required to complete the processing can be shortened. Moreover, the energy consumed by the completion of processing can be reduced.

  As described above, the fine hole electric discharge machine according to the present embodiment can detect the breakage and penetration when drilling, and can shorten the machining time until penetration. In addition, when the short-circuit frequency increases, the pulse pause time is extended, and when the short-circuit frequency decreases in that state, it is determined that the through-hole is detected, so that the penetration can be detected with certainty.

Embodiment 2. FIG.
The configuration of the second embodiment of the fine hole electric discharge machine according to the present invention is the same as that of the first embodiment. FIG. 8 is a diagram showing an example of the flow of operations for fine hole machining of the fine hole electric discharge machine according to the present embodiment. The operation is almost the same as in the first embodiment, but in this embodiment, the short-circuit frequency is equal to or higher than the first threshold value (50% in this example) and the second threshold value (10% in this example). ) When the following state continues for a preset time, it is determined that it has come off or penetrated, and the machining state is switched. For example, if the short-circuit frequency continues for 0.2 seconds or more in the normal state and becomes 50% or more, it is judged that the short-circuit has occurred. If it becomes, it will be judged as penetration. Since the short-circuit frequency is detected every predetermined sampling period, it is detected based on the count value of the counter that the duration of the short-circuit frequency is equal to or greater than the threshold in the example shown in FIG.

  In this embodiment, if the short-circuit frequency is not less than the first threshold value or not more than the second threshold value does not continue for a preset time, it will not be considered as a breakout or penetration, so a false detection of a breakout or penetration will occur. Can be reduced. Since other aspects are the same as those in the first embodiment, a duplicate description is omitted.

Embodiment 3 FIG.
The configuration of the third embodiment of the fine hole electric discharge machine according to the present invention is the same as that of the first embodiment. FIG. 9 is a diagram illustrating an example of a flow of operations for fine hole machining of the fine hole electric discharge machine according to the present embodiment. Although the operation is almost the same as in the first embodiment, in the present embodiment, the machining control unit detects a short-circuit frequency equal to or higher than the first threshold value (50% in this example) in the disconnected state. In this case, the machining state is changed from the close state to the normal state.

  If the pause time of the pulse is extended even though it is not in the state of being pulled out, sufficient pulses are not supplied for processing, so that processing becomes unstable and the short-circuit frequency does not decrease. Therefore, if the frequency of short-circuiting does not decrease in spite of extending the pulse pause time, it is possible to supply sufficient pulses for processing by returning the pulse pause time to the original state, and the time until it becomes in the state of coming off. Can be prevented from prolonging.

  In addition, it is also possible to operate so as to return to the normal state when the state where the short-circuit frequency is equal to or higher than the threshold value continues for a certain period after the transition to the disconnected state. Further, based on a threshold value different from the first threshold value used when determining the transition from the normal state to the exit state, it may be determined whether to return from the exit state to the normal state.

  Since other aspects are the same as those in the first embodiment, a duplicate description is omitted.

  Each of the above embodiments is an example of the present invention, and the present invention is not limited to this. For example, in each of the above embodiments, the case where the first threshold value used for the determination that the processing control unit changes the processing state from the normal state to the exited state is a predetermined value (50%). When the predetermined value becomes larger than the average value of the short-circuit frequency for a certain period (for example, when it becomes larger by 10 or more), the machining state may be changed from the normal state to the close state.

  As described above, the fine hole electric discharge machine according to the present invention is useful in that it can stably perform the processing in the state of being pulled out, and in particular, drilling only the upper layer of a hollow workpiece or an already existing horizontal hole. Suitable for machining vertical holes so as not to pass through.

DESCRIPTION OF SYMBOLS 1 Thin hole electric discharge machine 2 Electrode 3 Workpiece 4 Process control part 5 Pulse generation condition setting part 6 Pulse generator 7 Short circuit detection part 8 Short circuit frequency detection part 9 Process feed command part 41 Process state information storage part

Claims (8)

A pipe-like electrode for injecting a machining fluid from the tip, and pulse generating means for intermittently applying a pulse voltage including a machining pulse between the electrode and the workpiece with a pause time between the electrode and the workpiece A fine hole electric discharge machine that performs electric discharge machining on the workpiece by generating electric discharge due to the machining pulse in the machining liquid interposed between the workpiece,
Short-circuit occurrence detection means for detecting the occurrence of a short-circuit between the electrode and the workpiece;
A short-circuit occurrence frequency detecting means for detecting the occurrence frequency of the short-circuit,
Based on the detection result of the short-circuit occurrence frequency detection means, the hole being machined by the electric discharge machining is in a non-penetrating normal state, in a partially penetrating state, or in a completely penetrating state. A fine hole electric discharge machine comprising machining state determination means for determining whether or not there is. The machining state determination means includes
If the occurrence of short circuit during processing in the normal state is greater than or equal to the first threshold, it is determined that the normal state has transitioned to the exit state,
When the short-circuit occurrence frequency during processing in the disconnected state is equal to or less than a second threshold value that is smaller than the first threshold value, it is determined that the transition from the disconnected state to the penetrating state is made. The fine hole electric discharge machine according to claim 1. The machining state determination means includes
When the state in which the short-circuit occurrence frequency during the processing in the normal state is equal to or higher than the first threshold is continued for a preset time or more, it is determined that the transition from the normal state to the exit state is performed,
When the state in which the frequency of occurrence of the short circuit during the processing in the disconnected state is equal to or less than the second threshold continues for a preset time or more, it is determined that the state has shifted from the disconnected state to the penetrating state. The narrow hole electric discharge machine according to claim 1.   When the machining state determination means determines that the transition from the normal state to the exiting state is made, the machining condition for the electric discharge machining is changed to a pause time extended machining condition in which the pause time is extended from the normal state. 4. The small hole electric discharge machine according to claim 2, further comprising machining condition changing means.   The machining state determination means determines that the normal condition is present when the short-circuit occurrence frequency does not decrease after the machining condition of the electric discharge machining is changed to the downtime extended machining condition, and the machining condition change means 5. The small hole electric discharge machine according to claim 4, wherein the electric discharge machining condition is changed from the machining time extension machining condition to the normal machining machining condition. The pulse generating means applies a pulse voltage including a check pulse for detecting the short circuit prior to the machining pulse between the electrode and the workpiece,
6. The short circuit occurrence detection means detects the occurrence of the short circuit based on a potential difference generated between the electrode and the workpiece when the check pulse is applied. The fine hole electric discharge machine according to claim 1.   7. The narrow hole according to claim 6, wherein the short-circuit frequency detecting means detects the short-circuit occurrence frequency based on a total number of the check pulses during a preset period and the number of occurrences of the short-circuit. Electric discharge machine. The machining fluid interposed between the electrode and the workpiece by intermittently applying a pulse voltage including a machining pulse between the pipe-like electrode for ejecting the machining fluid from the tip and the workpiece with a pause time in between A fine hole electric discharge machining method by a fine hole electric discharge machine that generates electric discharge by the machining pulse in the electric discharge machining to the workpiece,
When the frequency of occurrence of a short circuit between the electrode and the workpiece during normal machining is greater than or equal to a first threshold value, it is determined that a hole has partially penetrated by the electric discharge machining, and the electric discharge machining conditions Changing the downtime to a downtime extended processing condition that is longer than that during the normal processing, and
When the occurrence frequency of the short circuit during the processing under the extended working time is less than or equal to the second threshold value that is smaller than the first threshold value, it is determined that the hole has penetrated by the electric discharge machining. A fine hole electric discharge machining method.

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