JPS637894B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to electrical discharge machining equipment, and in particular, in electrical discharge machining methods and equipment that use simple shaped electrodes such as rod-shaped or wire-shaped electrodes and perform electrical discharge machining while numerically controlling electrode feed, abnormal electrical discharges and short circuits can be avoided. etc. are likely to occur, or if they occur and such conditions persist, how to avoid the continuation of abnormal machining gap conditions that cause such abnormal discharges, short circuits, etc. and devices. Using a simple rod-shaped or wire-shaped electrode, the tip of the electrode faces the workpiece with a small machining gap in between, and voltage pulses are applied between the electrode and the workpiece while supplying machining liquid to the machining gap. Electrical discharge machining methods and devices using a so-called creative machining method are well known, in which the workpiece is machined into a desired shape by supplying an electric discharge to generate an electric discharge within the machining gap, and numerically controlling the relative position between the electrode and the workpiece to form a desired shape. , is becoming widely used. Therefore, when using such a processing method, not only can complicated shapes be processed without manufacturing a full-form electrode, but also high processing accuracy can be obtained even when processing under electrode consumption conditions. This method has the advantage that it is easy to remove machining debris in the machining gap, which was an extremely serious problem when using a full-type electrode, and machining efficiency is high. However, even with this machining method, it is inevitable that abnormal discharges or short circuits accompanied by excessive currents such as arc discharges, which are harmful to machining, or short circuits, or conditions similar to these, will occur, and in such cases, prevent excessive discharges as soon as possible. In order to extinguish the resulting arc and avoid damage due to a complete short circuit between the electrode and the workpiece, it is necessary to quickly separate the electrode and workpiece. Conventionally, when an abnormal discharge or short circuit is about to occur or actually occurs, the electrode is pulled upward along the column main axis direction (z-axis direction), or the workpiece is constantly Alternatively, record the machining feed path of the electrode and immediately reverse it, or furthermore, expand the machining gap by performing a combined movement of these, extinguishing the arc caused by abnormal discharge, and removing the electrode and the target. Machining debris accumulated in the machining gap due to the pumping action caused by the relative movement between the workpieces,
Gas etc. were removed and insulation was restored. This method of pulling the electrode upward is an effective method in electrical discharge machining using a full-type electrode, and reversing the feed is an effective method in wire cut electrical discharge machining. However, it has been found that these methods are not necessarily optimal for the creation process using rod-shaped electrodes and the like. The present invention has been made based on the above-mentioned viewpoints, and its purpose is to provide an electrode separation method or an abnormal machining gap state avoidance method suitable for this generating electric discharge machining. The method is to retract the electrode in the normal direction of its tip movement locus, or to combine the retraction movement in the normal direction and the electrode retraction movement in the direction perpendicular to the tangential line and the normal line of the electrode tip locus. The purpose is to avoid short circuits between the electrode and the workpiece. Hereinafter, details of the configuration of the present invention will be explained with reference to the drawings. FIG. 1 is an explanatory diagram of generating electric discharge machining, FIGS. 2 to 4 are explanatory diagrams of an electrode retraction method in the short circuit avoidance method according to the present invention, and FIG. 5 is an illustration of an implementation of the short circuit avoidance device according to the present invention. FIG. 3 is a circuit diagram showing an example. In FIG. 1, 1 is an electrode having a simple shape such as a rod shape, 2 is a workpiece, 3 is a power source for processing, 4 is a switching element for processing, and 5 is a processing pulse for controlling the switching element 4. An oscillator, 6 an inserted resistor for detecting overcurrent, short circuit, etc., and 7 a circuit for detecting abnormal machining gap conditions such as abnormal discharge or short circuit. The electrode 1 is attached to a processing head of a known processing machine (not shown), and is
Positioned and processed in the axial direction, the workpiece 2
is mounted on a cross table provided in a known processing tank (not shown), and is positioned and processed in the xy plane by a motor or the like provided on the cross table. The operations of these motors and the like are controlled by a known numerical control device, so that the electrode 1 is positioned and processed in three dimensions in xyz relative to the workpiece 2. Of course, depending on the machine, either the electrode 1 or the workpiece 2 may be configured to move in three axes, or one may move in two axes, zx or yz, and the other may move in two axes, zx or yz. It may be configured for uniaxial movement in the y-axis or the x-axis, and further,
Although machining feed using a polar coordinate system or a cylindrical coordinate system may be adopted, or a greater degree of freedom may be provided, the present invention is applicable to either case. However, in the following description, in order to simplify the explanation, it is assumed that the workpiece 2 is stationary and the electrode 1 moves three-dimensionally in xyz along the workpiece surface of the workpiece 2. There are various methods for machining and feeding the electrode 1, but here, the electrode machining and feeding is performed within the xy plane, and the electrode tip is placed along a predetermined contour line 2 on the workpiece surface.
When the electrode 1 is moved to form contour lines a and 2a and the scheduled machining for one contour line is completed, the electrode 1 is fed a minute distance machining in the z-axis direction, and the next stage of contour line machining is performed. The height and shape of these contour lines are determined in advance in detail by a numerical control program step by step from the beginning of processing through intermediate stages to the final target shape. In addition, the machining feed for each stage is based on the xy plane as described above,
In other words, it is not necessarily performed for each contour line; for example,
Although it may be performed on the yz plane (equal longitude plane) or the zy plane (equal latitude plane), the principle is the same, so here we will explain the machining feed as normally performed along contour lines. The basic principle of the present invention is that when an abnormal discharge or a short circuit is about to occur or its occurrence is detected, and when the electrode 1 is separated from the workpiece 2, the tangent line T of the movement trajectory of the tip of the electrode 1 The purpose is to move the electrode 1 in a plane perpendicular to the . Therefore, many methods can be considered for this movement. Theoretically, what is most desirable is to move the electrode 1 in the normal direction of the surface to be processed. However, this method requires a complicated calculation circuit, so the easiest and recommended method is to move the electrode 1 away from the workpiece 2 in the normal direction of the electrode tip movement trajectory, as shown in Figure 2. As shown in FIGS. 3 and 4, an even more efficient method is to move the electrode 1 in a direction perpendicular to the tangent and normal line of the electrode tip movement trajectory in synchronization with the tangential retraction movement. , i.e. in the direction perpendicular to the principal plane,
A method of retracting the workpiece 2 also in a direction away from the workpiece 2 is recommended. In Figures 3 and 4, T is the tangent to the recording tip movement trajectory, ΔN is the retraction motion vector in the normal direction, Δz is the retraction motion vector in the direction perpendicular to the principal plane, and Δ is ΔN and Δz. is the sum vector of Therefore, if a method for retracting movement along the vector ΔN is shown, it is obvious that the electrode 1 can be retracted along the vector Δz in synchronization with the method, and by this, the tip of the electrode 1 can eventually be It is also obvious that the retracting motion can be made in the direction of the resultant vector Δ. For example, N ₁ in the normal direction perpendicular to the tangent T of the electrode tip movement locus in the xy plane in Figure 2.
Alternatively, if the electrode 1 can be moved by ΔN in either direction of N ₂ , then if the electrode 1 is also moved in the z-axis direction by numerical control in synchronization with this, the retraction movement can be performed along the resultant vector Δ. This is something that can be achieved. Therefore, here, the electrode retraction movement in the normal direction will be mainly explained. FIG. 5 is a block diagram of a device that performs the electrode retraction movement in the ΔN direction. In the figure, 8 is a central controller including a numerical controller, 9 and 10 are registers for the integrable variables x and y, and 11 and 10 are registers for the integrable variables x and y. 12 is an adder; 13 and 14 are accumulators for integral variables X and Y; 15 and 16 are flip-flops for recording the code of the machining feed pulse; and 17 is for retracting the electrode in either the left or right direction of the machining progress direction. 18 and 19 are registers for recording overflow pulses of accumulators 13 and 14; 20 and 21 are registers for recording polarity; 22, 22', 23, 23', 24,
24', 25, and 25' are parallel-to-serial converters, 26 to 37 are AND circuits, 38 to 46 are OR circuits, and 47 is an electrode retraction that operates according to the output of the abnormal gap state detection circuit 7 such as abnormal discharge or short circuit. A pulse oscillator for motion control, 48 and 49 are motors for machining feed in the x-axis direction and y-axis direction, respectively; 5
0 and 51 are terminals for connecting the motors 48 and 49 to the operating power source; 52, 52, 53, and 53 are forward rotation switching elements; 52', 52', and 53';
53' is a switching element for reverse rotation. Although the figure shows an example of linear interpolation processing using a digital differential analyzer, the gist of the present invention has nothing to do with numerical control methods or interpolation methods, and is applicable to any other pulse distribution method. It will be readily understood from the following description that it can also be combined with the interpolation method. First, the normal machining state will be explained. The motor 48 that feeds machining in the x-axis direction rotates one step in either the forward or reverse direction each time the accumulator 13 oscillates an overflow pulse, drives a machining feed device (not shown), and rotates the machining feed device (not shown) in units of setting. When the overflow pulses are oscillated one step at a time, with the length or angle corresponding to each step being one step, and the overflow pulses are oscillated one after another at high speed, processing is carried out smoothly as if it were continuous. That is, when the flip-flop 15 is in the set state, the overflow pulse is output to the AND circuit 2.
The forward rotation switching elements 52 and 52 are made conductive through the AND circuit 26 and the OR circuit 42, causing the motor 48 to rotate in the forward direction. The reverse rotation switching elements 52', 52' are made conductive through the reverse rotation switching elements 52', thereby causing the motor 48 to rotate in the reverse direction. Similarly, a motor 49 that feeds machining in the y-axis direction
is operated one step at a time in either the forward or reverse direction each time the accumulator 14 oscillates an overflow pulse. Since the machining feed amount corresponding to one rotation angle of one step is an extremely small distance, and the overflow pulses are generated continuously and at high speed, substantially smooth continuous machining feed is performed. When the flip-flop 16 is in the set state, the overflow pulse conducts the switching elements 53, 53 for forward rotation through the AND circuit 27 and the OR circuit 43, causing the motor 49 to rotate in the forward direction. In the reset state, this overflow pulse conducts the reverse rotation switching elements 53', 53' via the AND circuit 29 and the OR circuit 45, causing the motor 49 to rotate in the reverse direction. When the motors 48 and 49 rotate one step forward, the tip of the electrode 1 is moved in the positive direction of the x-axis and y-axis by ε (where ε> 0), and when the motors 48 and 49 rotate in reverse, they are moved by ε in the negative direction of the x-axis and the y-axis, respectively. Since these processes are rotary processing using linear interpolation using the well-known DDA method, further explanation will be omitted. Next, the retraction motion control device will be explained. This device consists of an x-axis retraction motion control device and a y-axis retraction motion control device that are configured symmetrically to each other.
In addition, since the operations of these control devices are symmetrical and substantially the same, the y-axis retraction motion control device will mainly be explained here. The y-axis retraction motion control device includes registers 18 and 2.
0, parallel serial converter 22, 22', 24,
24', AND circuits 30, 32, 34, 36, and OR circuits 38, 40, 42, and 44. The output of the OR circuit 46 which receives the outputs of the accumulators 13 and 14 is output from the registers 18 and 20.
It is used as a shift pulse. That is, when the accumulator 13 or 14 generates an overflow pulse, the output state of the accumulator 13 is newly recorded in the register 18, and at the same time, the previously recorded data is shifted lower by 1 bit. The state of the flip-flop 15 is recorded in 20, and at the same time, the previously recorded data is shifted downward by one bit. Therefore, the registers 18 and 19 have an OR circuit 46.
The output state of the accumulator 13 and the state of the flip-flop 15 during the recent period in which the output of 8 pulses was generated are respectively recorded, and at the same time, the output state of the accumulator 14 during the same period is recorded in the registers 19 and 21. and the state of the flip-flop 16 are recorded. These data indicate past machining feeds in the x-axis direction and y-axis direction and their directions. That is, when the data in the registers 18 and 20 is 1, it indicates that the electrode machining feed was actually performed in the x-axis direction and the y-axis direction, respectively, and when the data is 0, it indicates that the electrode machining feed was actually performed in the corresponding direction. indicates that processing feed was not performed, and register 2
For data 1 of 0,21, the corresponding machining feed is x
This indicates that the machining feed was performed in the positive direction of the axis and the y-axis, and data 0 indicates that the machining feed was performed in the negative direction. It will be readily understood that the data shown corresponds to the electrode tip movement trajectory shown in FIG. Each time the records in registers 18 and 20 are updated,
The data is transferred to the parallel-to-serial converters 22, 22' and 24, 24', respectively, but while the electrical discharge machining is progressing normally, the pulse oscillator 47 does not operate, and therefore the parallel-to-serial converter does not operate. None of the converters 22, 22', 24, 24' produce an output. Therefore, when the abnormal gap state detection circuit 7 detects abnormal discharge, short circuit, etc., for example, abnormal excessive current,
The numerical control operation of the central controller 8 is temporarily interrupted by a circuit not shown, and at the same time the pulse oscillator 47 is activated. The pulse oscillator 47 first outputs one output terminal 47.
-1 to 8 pulses are oscillated to activate the parallel-serial converters 22 and 24, and then 8 pulses are oscillated from the other output terminal 47-2 to activate the parallel-serial converters 22' and 24. ’ is activated. Parallel serial converter 22 and 24: 22'
The outputs from and 24' control the motor 49 during the electrode retraction movement, the outputs 22 and 24 control the retraction process, and the outputs 22' and 24' control the return process. That is, the parallel-serial converters 22 and 24 serially output data sequentially from the latest data to the past over time using the output pulses from the output terminal 47-1. These data are passed through OR circuits 38 and 40 to AND circuits 30 to 36, respectively.
input into a selection circuit consisting of. The inputs of this selection circuit are these OR circuits 38,
40 and the set output of flip-flop 17, this selection circuit responds to the combination of these inputs and performs the input/output conversion necessary for electrode retraction movement. This conversion is performed as shown in the feed conversion table on the next page. In this table, x=+1 is a machining feed pulse that makes a machining feed of ε in the positive direction of the x-axis, and x=-1
is a machining feed pulse that makes a machining feed of ε in the negative direction of the x-axis. As shown in this conversion table, when retracting to the right in the direction of electrode movement, x=+1, -
1 is converted to y=-1, +1 in the evacuation process, and y=+1, -1 in the return process, respectively.
Conversely, when performing a retreat movement to the left, x = +1,
-1 means that y=+ in the evacuation process, contrary to the above
In the return process, Y=-1 and +1 are respectively converted.

[Table] The same is true for the y-axis machining feed pulse, and when performing a retraction movement to the right, y=+1,
-1 is converted to x = +1, -1 in the retraction process, and x = -1, +1 in the return process, and when performing a retraction movement to the left, in the retraction process. becomes x=-1, +1, and in the return process x=
These are converted to +1 and -1, respectively. When the retraction movement to the right is to be performed, the flip-flop 17 is in the set state, and the outputs of the OR circuits 38 and 40 cannot pass through the AND circuits 34 and 36, but instead pass through either 30 or 32. . When the output of the OR circuit 38 is in the state 0, that is, when no machining feed is performed in the x-axis direction, the outputs of the AND circuits 30 and 32 are also in the state 0, and the motor 49 is not driven, but the OR circuit 38
When the output is in state 1, the motor 49 is driven one step in either the forward or reverse direction depending on the output state of the OR circuit 40. When the output of the OR circuit 40 is in state 1, that is, when x=+1, the AND circuit 30
The output becomes state 1, and the output pulse conducts the switching elements 53' and 53' via the OR circuit 45, causing the motor 49 to rotate in the reverse direction. In other words, the selection circuit changes x=+1 to y=-1
It would have been converted to . In the illustrated state, all data in the parallel-to-serial converter 24 is 0, so x=-1
In this case, it is clear that the conversion to y=+1 is performed. In synchronization with the control of the motor 49 described above, the parallel-to-serial converters 23 and 25 also oscillate serial outputs, and these outputs are passed through OR circuits 39 and 41 to select signals from AND circuits 31, 33, 35, and 37. The signal is input to the circuit, the signal is converted in the same manner as described above, and the motor 48 is driven, resulting in an electrode retraction movement along N ₁ or N ₂ shown in FIG. When this evacuation step is completed, and after a certain pause time has elapsed, the pulse oscillator 47 switches to its output terminal 47-2.
8 pulses are oscillated as before. So, this time, parallel serial converter 2
Data 2', 24', 21' and 23' are output, but contrary to the above, these data are output serially in the order of occurrence starting from the oldest data, and are parallel-to-serial converter. Vessel 2
The outputs of 4' and 25' are configured to be input to OR circuits 40 and 41 via input negators. Therefore, in this return process, the signal conversion of the return process in the above conversion table is performed, so that the electrode reverses the path traveled in the retreat process and returns to its original position. This reciprocation is performed a predetermined number of times, usually one to several times, and when the reciprocation is completed, the central controller 8 restarts the electrical discharge machining. In the above explanation, the electrode retraction movement in the z-axis direction was not explained, but the z-axis direction (not shown) is generated by the logical sum of the output pulses of the output terminals 47-1 and 47-2 of the pulse oscillator 47. If the electrode machining feed motor is driven and the electrode is raised and lowered in synchronization with the above-mentioned retraction movement, the direction of the electrode retraction movement will be the theoretically most desirable direction, that is, closer to the normal to the surface to be machined, and the electrode retraction movement It will be immediately understood that the effects of this will be further enhanced. At this time, the output terminal 47- of the pulse oscillator 47
1 and 47-2 output pulse;
The pulse rate of the motor drive pulse for feeding the electrode machining in the z-axis direction is normally 1:1, but depending on the inclination of the surface to be machined, this ratio may be 2:1 or 1:2. Furthermore, if the electrode machining feed is performed not on the xy plane but, for example, on the yz plane, the x-axis machining feed motor 48 and the z-axis machining feed motor 48 may be replaced. This will be understood immediately. Since the present invention is configured as described above, it is possible to reliably and efficiently avoid short circuits between the electrode and the workpiece. Note that the configuration of the present invention is not limited to the above-mentioned embodiments; for example, the present invention can be applied not only to rectangular coordinate systems, but also to processing apparatuses using polar coordinate systems, cylindrical coordinate systems, etc. Regarding the configuration of the control circuit, the route to be evacuated may be stored instead of storing the machining feed route, and among these storage devices, parallel-to-serial converters 22, 22', etc. may be used. First, the data in the register 18 may be read and used, and various registers, RAM, and other memories can be used as these circuit elements, and the selection circuit or signal conversion method is also covered by the present invention. The design can be freely modified using widely known materials within the scope of the purpose, and the present invention encompasses all of them.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of generating electric discharge machining, FIGS. 2 to 4 are explanatory diagrams of an electrode retraction method in the short circuit avoidance method according to the present invention, and FIG. 5 is an illustration of an implementation of the short circuit avoidance device according to the present invention. FIG. 3 is a circuit diagram showing an example. DESCRIPTION OF SYMBOLS 1... Electrode, 2... Workpiece, 3... Power source for processing, 4... Switching element for processing, 5... Pulse oscillator for processing, 6... Insertion resistor, 7... Abnormal gap state detection circuit, 8... Numerical control device, 9,10
... Register, 11, 12 ... Adder, 13, 1
4... Accumulator, 15, 16, 17...
Flip-flop, 18, 19, 20, 21...
Register, 22, 23, 24, 25, 22', 2
4', 24', 25'...parallel serial converter,
26, 27, ~ 37...AND circuit, 38, 3
9, ~ 46...OR circuit, 47...Pulse oscillator, 48, 49...Motor, 50, 51...Power terminal, 52, 53...Switching element for forward rotation, 52', 53'...Reverse rotation switching element.

Claims (1)

[Scope of Claims] 1. Avoidance of abnormal machining gap conditions such as abnormal discharge and short circuits employed in electrical discharge machining in which machining is performed by numerically controlling the electrode feed using simple shaped electrodes such as rod-like or linear electrodes. A method for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit in electrical discharge machining as described above, characterized in that the method comprises the steps described in the following items (a) to (e). (a) A process of predetermining and recording the direction in which the electrode is to be retracted. (b) The process of recording the data necessary to determine the normal direction of the movement trajectory of the electrode tip. (c) A process to detect the occurrence of abnormal machining gap conditions exceeding a certain limit, such as abnormal discharge or short circuit. (d) When the occurrence of an abnormal machining gap condition exceeding a certain limit is detected in the process described in the previous section, the electrode tip is moved in the normal direction indicated based on the data recorded in the process described in (b), and (a A step of moving a minute distance in the direction recorded by the step described in item ). (e) A step of returning the electrode tip, which has been moved a small distance by the step described in the previous section, to its original position. 2. The following methods are used to avoid abnormal machining gap conditions such as abnormal discharge and short circuits that are adopted in electrical discharge machining that uses simple shaped electrodes such as rods or wires and performs machining by numerically controlling the electrode feed. A method for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit in the above electric discharge machining, characterized by comprising the steps described in items (f) to (j). (f) A process of predetermining and recording the direction in which the electrode is to be retracted. (g) A process of recording the data necessary to determine the normal direction of the movement trajectory of the electrode tip. (h) A process to detect the occurrence of abnormal machining gap conditions exceeding a certain limit, such as abnormal discharge or short circuit. (i) When the occurrence of an abnormal machining gap condition exceeding a certain limit is detected by the process described in the previous section, the electrode tip should be aligned in the normal direction indicated based on the data recorded in the process described in (g) and (f The direction and direction of the sum vector of the vector in the direction recorded by the process described in item ) and the vector in the direction that makes a certain angle to the main plane on which the electrode processing feed is performed and in which the electrode tip moves away from the workpiece. The process of moving a small distance. (j) A step of returning the tip of the electrode, which has been moved a small distance by the step described in the previous section, to its original position. 3. The method according to claim 2, wherein the angle between the main plane and the vector in which the electrode tip is directed away from the workpiece is a right angle in a direction that makes a certain angle to the main plane on which the electrode processing feed is carried out. How to avoid abnormal machining gap conditions such as abnormal discharge and short circuit in electrical discharge machining. 4. A device for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit, which is adopted in electric discharge machining equipment that uses simple shaped electrodes such as rods or wires and performs machining while controlling the electrode feed with a numerical control device. In the following
A device for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit in electrical discharge machining as described above, characterized by comprising the components described in items (k) to (n). (k) A memory for predetermining and recording the direction in which the electrode should be retracted. (l) A memory in which data that can determine the normal direction of the movement trajectory of the electrode tip is recorded. (m) A device that can detect the occurrence of abnormal machining gap conditions exceeding a certain limit, such as abnormal discharge or short circuit. (n) When an abnormal machining gap condition exceeding a certain limit is detected by the detection device described in the previous paragraph, the electrode feeding control by the numerical control device is stopped, and the electrode tip is changed to the data recorded in the memory described in paragraph (l). A device that operates an electrode feeding device so as to move the electrode a small distance in the normal direction indicated by and in the direction recorded in the memory described in item (k), and then return it to the original position. 5. A device for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit, which is adopted in electrical discharge machining equipment that uses simple shaped electrodes such as rod or wire shapes and performs machining while controlling electrode feed with a numerical control device. An apparatus for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit in electric discharge machining as described above, characterized by comprising the components described in the following items (o) to (r). (o) A memory for predetermining and recording the direction in which the electrode should be evacuated. (p) A memory in which data that can determine the normal direction of the movement trajectory of the electrode tip is recorded. (q) A device that can detect the occurrence of abnormal machining gap conditions exceeding a certain limit, such as abnormal discharge or short circuit. (r) When an abnormal machining gap condition exceeding a certain limit is detected by the detection device described in the previous paragraph, the electrode feeding control by the numerical control device is stopped, and the electrode tip is changed to the data recorded in the memory described in paragraph (p). The normal direction indicated by and the direction vector recorded in the memory described in (o), and the direction that makes a certain angle to the main plane where the electrode machining feed is performed and the direction in which the electrode tip leaves the workpiece. A device that operates the electrode feeding device to move the electrode a small distance in the direction and direction of the sum vector of the vector, and then return it to the original position. 6. The method according to claim 5, wherein a vector in a direction forming a certain angle to the main plane on which the electrode processing feed is performed and in which the electrode tip is directed away from the workpiece is at a right angle with the main plane. A device for avoiding abnormal machining gap conditions such as abnormal discharge and short circuit during electric discharge machining.