JPS6128451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an electric discharge machining apparatus in which machining is performed under control of a numerical control device.

Such electrical discharge machining equipment has recently come into use, and its configuration is almost similar to well-known NC milling cutters and machining centers, and the electrodes can be replaced automatically according to a program programmed into a numerical control device. It consists of multiple steps, such as machining a predetermined machining feed distance using a predetermined electrode attached to the spindle using a device or other device, and when the machining of that step is completed, at least the spindle is pulled up, and then the next step is performed. A series of electrical discharge machining is performed while being controlled by a numerical control device. However, electrical discharge machining equipment is generally a single-item processing machine that does not repeatedly produce large numbers of the same product, and the machining time required to obtain one finished product, that is, the time required for each process, is generally long. differs from general NC cutting machines in that the start and end points to be machined using each electrode are not programmed in advance on the NC tape, but instead the distance between the start and end points is programmed. It is something.

However, the above-mentioned differences are due to the characteristics of electrical discharge machining, and are mutually related.

For this reason, electric discharge machining equipment usually requires information such as the shape and method of use of the electrodes to be used, the parts of the workpiece to be machined using each electrode, and in other words, the parts of the workpiece to be machined when performing electrical discharge machining using each electrode. The position and posture of the body, as well as the position of the main axis or electrode where electrical discharge begins between the two when the electrode is first lowered in the direction of the main axis in the process and brought close to the workpiece (hereinafter referred to as the "discharge starting point"). The direction in which machining feed should be performed and the machining feed distance are programmed.
Further, the machining feed rate is usually controlled by a servo feed device different from the numerical control device, or various pulse motors such as electric or electro-hydraulic that serve both.

Therefore, in electric discharge machining using numerical control, unlike milling and the like, the tool position and machining feed rate are not uniquely determined according to the steps of numerical control.

Furthermore, in electric discharge machining, there is a machining gap between the electrode surface and the workpiece surface, but the value of this machining gap is not strictly constant, so the actual machining surface and control step may differ. The correspondence between the points becomes more uncertain, but as long as the processing is progressing smoothly, the existence of these points of uncertainty does not pose a particular problem.
Also, while processing continues normally in this way,
Although it is possible to check the correspondence between numerical control steps and potential positions at any time, and to check the progress of machining, there is a possibility that some kind of accident may occur during machining, such as a power outage or a short circuit. When machining is interrupted due to a process or when machining is interrupted to check the machining status, if the correspondence between the two immediately before the interruption is unknown, machining cannot be resumed without losing machining accuracy in the process. There was a problem in that it required a complicated procedure to do so.

Generally, when machining is interrupted due to these accidents, the timing and speed at which each part stops differs, so the correspondence between numerical control steps and electrode positions is affected, and the There are many cases where the correspondence between the two parties is inconsistent, and as a result,
If the relationship between the two after the stop was the same as before the stop, an unexpected accident could occur.

Further, when a short circuit accident occurs, the electrode is urgently pulled up, but normally in such a case, the correspondence between the electrode and the control step becomes even more unclear.

In addition, the problem becomes even more troublesome when carbon deposits on the machined surface or other abnormal conditions occur, or when it is necessary to check the electrode and machined surface due to a long power outage. .

Furthermore, even if such an abnormal situation does not occur, for example, in a step that requires particularly high-precision machining, the machining may be interrupted during the process or at the end of the process, and countermeasure inspections, etc., may be performed. Even in this case, unless the operator accurately recognizes the correspondence between the two, it will be impossible to completely restore the numerical control steps and electrode positions after the inspection.

Such problems can be solved by accurately measuring and recording the correspondence between the two at a point in the process when normal machining is being performed. Then, if necessary, you can reverse the numerical control step to the recorded position, place the electrode at the recorded position, and from that state proceed the numerical control in the forward direction to restart machining. , machining can be resumed as an extension of the state before machining was interrupted.

Therefore, it is desirable to perform such recording at the beginning of each process, when the electrode first approaches the workpiece and electrical discharge machining begins. By recording the correspondence between the starting numerical control step and the discharge starting point, it is possible to restart the process after interruption at any point during the process.

The present invention has been made based on the above-mentioned viewpoints, and its purpose is to easily carry out processing without impairing processing accuracy even if processing is interrupted during each process. An object of the present invention is to provide an electrical discharge machining device that can be restarted.

In the present invention, "one step" refers to the period from the end of machining a predetermined machining feed distance using a predetermined electrode attached to the spindle to the time when the spindle is pulled up.

Hereinafter, the present invention will be explained in detail based on the drawings.

The drawing is a circuit diagram showing an embodiment of the electrical discharge machining apparatus according to the present invention, and in the drawing, 1 is a machining head, 2 is a
is the main shaft, 3 is an electrode, 4 is the main shaft, a servo motor that drives 2, 5 is an encoder that detects the main shaft position,
6 is an electrode magazine, 7 is a workpiece, 8 and 9 are X
A pulse motor rotates the axial and Y-axis direction feed screws 10 and 11 to move the workpiece 7 via a cross table (not shown), 12 is a DC power source for machining, 13 is a switching element thereof, and 14 is a machining pulse Control circuit, 15 is an insertion resistor, 16 is a numerical control device, 17 is a servo control device, 18 and 19
is a monostable element, 20 and 21 are bistable elements, 22 is an input negator, 2
3 is a spindle position indicator, 24 and 25 are memories, 2
6 is a stop command device, 27 and 28 are push button switches, and 29 is a power terminal.

In each process, command pulses are sent from the numerical control device 16 according to a predetermined program, and on the other hand, a predetermined amount is transferred from the electrode magazine 6 by an automatic electrode exchange device (not shown). An electrode 3 is attached to the lower end of the selected spindle 2, and on the other hand the pulse motors 8 and 9
The workpiece 7 is moved and placed in a predetermined position by means of a cross table (not shown).

After that, the numerical control device 16 switches to the servo control device 1.
The servo motor 4 is actuated via the servo motor 7, the main shaft 2 is lowered, the electrode 3 is brought close to the workpiece 7, and the switching element 13 is activated via the processing pulse control circuit 14 at a predetermined period and duty factor. It is opened and closed to generate electric discharge between the electrode 3 and the workpiece 7, and electric discharge machining is started and progressed.

The position of the spindle 2 is encoded by the encoder 5, displayed by the spindle position indicator 23, and fed back to the numerical control device 16 and servo control device 17.

On the other hand, the bistable element 20 is reset by a command pulse from the numerical control device 16 at the start of each process in which machining is performed over a predetermined machining feed distance using a selected predetermined electrode, and the bistable element 21 is reset by a command pulse from the numerical control device 16 at the start of machining. It is reset by pressing the button switch 27.

The monostable element 18 has a relatively low triggering level and is triggered by the first electrical discharge that occurs during each step of electrical discharge machining. The trigger output sets the bistable element 20, loads the current display value of the spindle position indicator 23 into the memory 24 by the set output, and
The load value is fed back to the numerical control device 16 and recorded. The numerical control device 16 causes the main shaft to perform machining feed by a predetermined machining feed distance programmed from the recorded value via the servo control device 17 and the servo motor 4.

When the spindle machining feed reaches a predetermined value and the machining of the process is completed due to electrical discharge machining using a predetermined one electrode, the spindle 2 is pulled up in response to a command from the numerical control device 16, and the electrode is replaced and the workpiece is replaced as necessary. , the bistable element 20 is reset, the memory value in the memory 24 is erased, and the recorded value in the numerical control device 16 is cleared to start the next process. Then, a series of electrical discharge machining consisting of a plurality of steps is performed in the same manner.

Note that the monostable element 19 is given a relatively high triggering level that is not triggered by normal electric discharge during machining, and therefore the bistable element 21
Normally, the reset state is maintained unless there is a special accident.

However, in the illustrated embodiment, when, for example, a short-circuit fault occurs and an excessive current flows through the insertion resistor 15 and the monostable element 19 is triggered, when the power supply terminal 29 loses power, or when the pushbutton switch 28 When is pressed, the bistable element 21 is reversed, activates the stop command device 26, stops the progress of machining, and loads the displayed value of the spindle position display device 23 at that time into the memory 25.

Further, it is necessary to configure the system so that the voltage at the power supply terminal 29 is immediately cut off when a power failure occurs in any part of the apparatus.

Furthermore, in the device of the present invention, if the records in the memories 24 and 25 are lost due to a power outage or the like, the purpose of the present invention will not be achieved, so it is necessary to configure the device so that these records are not lost. is necessary. An example of a device for preventing the loss of this record is a local uninterruptible power supply, whereby at least the portion of the circuit including bistable element 21, spindle position indicator 23, and memories 24 and 25 can be backed up by the uninterruptible power supply. It is recommended that you keep it.

Since the present invention is configured as described above, in accordance with the present invention, after the start of machining of each process, the discharge opening point is reliably stored until the start of machining of the next process. , due to some kind of processing accident,
Alternatively, when resuming machining after it has been intentionally interrupted, the electrode is placed at the memorized discharge start point position and the numerical control step is reversed until the machining feed distance is zero, that is, the machining feed start step. If the numerical control proceeds in the forward direction from this state, the servo control device 17 will cause the electrode to be rapidly downwardly fed to the position where electric discharge occurs again between it and the workpiece, and then The machining can be easily restarted without losing machining accuracy by setting the extended state before machining is interrupted, and the machining can be accurately fed by a predetermined programmed machining feed distance.

Numerical control programs are stored in non-volatile memory such as perforated tape, magnetic tape, or floppy disks, and are read by a predetermined reading device to proceed with processing. Since reading is also stopped, even if machining is interrupted due to a power outage, etc., there is no risk of losing track of the process currently in progress, and when machining is resumed, the step of starting machining feed in that process can be easily performed. can be called.

As described above, according to the present invention, the electrode position at the discharge starting point in each process is memorized, and by configuring this memory so that it will not be lost even in the event of a power outage, the electrode can be memorized when machining is resumed after an interruption. Machining can be easily restarted without compromising machining accuracy by simply placing the machine in the position indicated and starting the programming control operation using the numerical control device with the numerical control step set to the machining feed start step. can.

In addition, in the above embodiment, the main axis (electrode) position of the discharge starting point in each process is memorized, but when machining is performed by moving the workpiece together with the electrode or separately from the electrode, In this case, the position of the workpiece may be stored together with or in place of the position of the electrode.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing one embodiment of the electrical discharge machining apparatus according to the present invention. 1... Processing head, 2... Spindle, 3... Electrode,
4... Servo motor, 5... Encoder, 6...
Electrode magazine, 7... Workpiece, 8, 9... Pulse motor, 14... Machining pulse control circuit, 16...
... Numerical control device, 17 ... Servo control device, 23
...Spindle position indicator, 24, 25...Memory, 2
6...Stop command device.

Claims (1)

[Claims] 1. In an electric discharge machining device that performs machining under the control of a numerical control device, each step of machining a predetermined machining feed distance using an electrode attached to the spindle according to a program programmed in the numerical control device. a storage device capable of storing the spindle or electrode position or the workpiece position at the time when the electrode first approaches the workpiece and electrical discharge machining is started; The electric discharge machining apparatus described above is further equipped with a device for preventing storage information stored in the storage device from disappearing until the process is completed and the next process is started.