JPS6210780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for correcting runout of a metal bond diamond grindstone (hereinafter referred to as a grindstone). It is generally known that a thin grindstone is used to cut and groove so-called brittle materials that are relatively hard and brittle, such as ferrite and silicon.

FIG. 1 shows a case where a groove having a depth D and a width E is formed in a workpiece 6 using a grindstone 1. The details of the whetstone are shown in Figure 2.
Diamond abrasive grains 7 are mixed into metal bond 8 (bonding material made of iron, copper, nickel, etc.) and bonded together, and are formed into a desired disk shape. 1st
As shown in the figure, the grindstone 1 is fixed from both sides by flanges 2 and 2', is tightened by a threaded portion 4 of a shaft 5 having a rotation C by a nut 3, and is driven by a drive device (not shown). 5 is rotated at high speed, the machining depth D is set in the Z-axis direction, the workpiece is set at a predetermined position by X-axis drive, and the workpiece is fed at a predetermined speed in the Y-axis direction. However, since the above-mentioned grinding wheel usually oscillates as shown by the dotted line, the apparent width of the grinding wheel increases as shown by A, and as a result, not only the width of the machined groove is expanded, but also the machined groove part There was a problem that cracks (chips) and cracks B occurred, resulting in defective processed products.

Conventionally, a normal GC grinding wheel was used to correct such grinding wheel runout, but diamond abrasive grains have high hardness, so it takes a long time to correct it. was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a grindstone runout correcting device that eliminates the drawbacks of the prior art described above and can correct the runout of a grindstone in a short time and with high precision.

In order to achieve the above object, the present invention employs electric discharge machining that does not apply mechanical force, detects the discharge state between the grinding wheel and the electrode, and moves the electrode in the direction of the central axis of the grinding wheel based on the detection signal. Alternatively, machining feed is applied in a direction perpendicular to this, and the run-out of the grinding wheel is automatically corrected.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows the overall configuration of the device based on the present invention. In the figure, 1 is a grindstone, 5 is a shaft, 9 is an electrode,
10 is an insulating plate, 11 is a table, 12 is a pulse power source, and 13 is a control circuit that detects the discharge state and controls the movement of the table 11.

Next, the operation of this device will be explained. The shaft 5 is rotated at low speed by a device not shown, and the groove of the electrode 9 is
The tips of the grindstones 1 are placed opposite each other between F ₀ and an insulating machining fluid is supplied from the machining fluid supply nozzle 100 . Next, electric discharge machining is performed by applying pulse power from a pulse power source 12 between the grinding wheel 1 and the electrode 9, and the electrode 9 is controlled in the X and Y axis directions by the control circuit 13.
At the same time as removing the runout portions G ₁ and G ₂ of the grindstone 1, a desired grindstone width A ₀ is formed. Here, as the electrode 9, it is preferable to use a copper-tungsten alloy or a silver-tungsten alloy, which is relatively less abrasive. Another example of the shape of the electrode is shown as electrode 9' in FIG.
In this case, the method for repairing the grinding wheel is to connect the electrode 9' to the grinding wheel 1.
This method differs from the method shown in FIG. 3 in that it is placed outside of the area.
FIG. 5 is a side view of FIG. 3, showing a state in which the grindstone 1 and the electrode 9 move relative to each other in the Y-axis direction.

Next, the configuration of the control circuit 13 will be explained in detail with reference to FIG. In FIG. 6, 1 is a grindstone, 9 is an electrode, and 12 is a pulse power source. The positive electrode of the pulse power source is connected to the grindstone 1 side, and the negative electrode is connected to the electrode 9 side. 30 and 31 are resistors for dividing the voltage between the grinding wheel 1 and the electrode 9 into voltages of several volts. 32 and 33 constitute an integrating circuit;
is its resistance, and 33 is a capacitor. 34 is a switch, and when connected to the O side, the divided electrode voltage is applied to one input of the comparator amplifier 15, and when connected to the P side, the integrated signal is applied to one input of the comparator amplifier 15. The other input of the comparator amplifier 15 is given a reference value E set for determining the discharge state. Comparison amplifier 1 that discriminated the discharge state
5 is input as an X-axis feed stop signal to the reset (R) of the flip-flop 19, and a start switch 20 for starting the X-axis feed is connected to the set input (S) of the flip-flop 19. The output (Q) of the flip-flop 19 becomes "1" when the set (S) input becomes "0" and becomes "0" when the reset input (R) becomes "0". flip flop 19
The output (Q) is input to an AND gate 22, and another input of the AND gate 22 is a clock pulse generator 21 that generates, for example, one pulse per second for instructing the X-axis feed in units of 1 μm per pulse. A clock pulse is given.
The output of AND gate 22 passes through OR gate 37
This is input to a counter A23 for counting the number of axis feed command pulses, and the contents of the counter A23 are input to a comparator 24. The other input of the comparator 24 is given the contents of a counter B25 for counting the actual feed amount of the X-axis, and the input of the counter B25 is the detection signal of the linear scale 26 for measuring the moving distance of the X-axis. is given. The contents of the counter B25 are displayed by the display circuit 35 as the position on the X axis. The output of the comparator 24 becomes "1" level when the count value of the counter A23 is larger than the count value of the counter B25, and the
It is applied to the shaft feed circuit 27.

Further, the input side of the comparator 29 receives a signal from a presetter 28 for setting the electrode 9 in the X-axis direction by the amount of grinding wheel runout, and the other input receives the contents of the counter B25. The output of the comparator 29 is applied to the input of an AND gate 36 for generating a "0" level when the count value and the preset value become equal.

In addition, the output of the comparison amplifier 15 is sent to a Y-axis feed circuit 17 for feeding the electrode 9 in the Y-axis direction in order to remove and correct the run-out amount of the grinding wheel while performing electrical discharge machining between the electrode 9 and the grinding wheel 1. The other input of the Y-axis feed circuit 17 is connected to the start switch 1.
8 are connected.

Next, the operation of the control circuit 13 will be explained in FIGS. 6 and 7.
This will be explained based on the diagram. Here, to explain about FIG. 7, the waveform a in FIG.
2 shows a pulse voltage waveform generated from 2. Normally, the pulse width is about 0.5 to 2 μs and the period is 1 to 10 μs. Figure b shows the actual voltage waveform between the poles, which is required to charge the stray capacitance that exists between the energizing cable and table for supplying pulse power between the poles from the pulse power source 12 and the ground. Time (0.1μs~1μs)
Therefore, a pulse voltage with a gentle rise is applied. The voltage waveform during actual electrical discharge machining can be classified into four discharge states, as will be explained in detail later. Also, the waveform C
shows the discharge current between the electrodes, which also has a different waveform depending on the discharge state. Also, the waveform a′,
b' and c' correspond to a, b, and c above, and are shown temporally shortened.

Now, before correcting the amount of runout of the grindstone, first, as shown in FIG. 1, it is necessary to measure the width of the grindstone when the whetstone is swinging, that is, the value of the apparent width A of the grindstone. This is done as follows. In FIG. 3, the grindstone 1 is set in the center of the groove of the electrode 9, the grindstone 1 is rotated, the current of the pulse power source 12 is set to a minute value (a current of about several tens of milliamps that does not contribute to electric discharge machining), and the The grinding wheel 1 is moved in the +X direction by the shaft feeding device, and the electrode 9
The display value of the display circuit 35 is reset to 0 using a reset switch (not shown).
Next, the grindstone 1 is moved in the -X direction, brought into contact with the electrode 9 in the same manner, and the X-axis display value of the display circuit 35 is read. The above-mentioned contact can be detected by measuring the voltage between the electrodes when the voltage reaches 0V. The above X-axis display value is X ₀ , and electrode 9
If the groove width F ₀ is measured in advance with a micrometer etc., the value of the apparent grinding wheel width A is
It can be determined by subtracting X ₀ from F ₀ . Now, next, stop the rotation of the grinding wheel 1, measure the width of the grinding wheel in a stationary state with a micrometer, etc., and if this value is set as _A1 , the runout of the grinding wheel is A-
A ₁ , and A-A ₁ /2 on one side. In other words, since the amount to be removed is now determined, this value (indicated by G ₁ and G ₂ in Figure 3) is
Set it in the presetter 28 shown in the figure.

Next, the operation of setting the electrode 9 at a predetermined position in order to eliminate the amount of grindstone runout calculated above will be explained.

The position of the grindstone 1 is set to the position indicated by the solid line as the grindstone 1 in FIG. 5, and at the same time the start switch 20 is turned on, the pulse power source 12 is turned on, and the voltage waveform generated from the pulse power source 12 in FIG. A pulse voltage as shown in a is generated. In reality, between the grinding wheel 1 and the electrode 9, in order to charge the stray capacitance of the cable, a pulse voltage with a gentle rise with a charging time of 0.1 to 1 μs is applied as shown in the voltage waveform b between the electrodes. . When the start switch 20 is turned on, the output Q of the flip-flop 19 becomes "1" level, and this output signal is given to the AND gate 22, so that the clock pulse signal generated from the clock pulse generator 21 is passed through the AND gate 22 and the OR gate 37. It is applied to the counter A23 through . Counter A
The count contents of 23 are compared with the contents of the counter B25 by the comparator 24, and when the contents of the counter A23 are larger than the contents of the counter B25, the output of the comparator 24 becomes "1" level, and the X-axis feed circuit 27 to rotate the X-axis motor forward (+X
direction). The signal input to the counter B25 is such that 1 pulse/1 μm is obtained from a linear scale 26 attached to measure the X-axis feed. That is, pulses are commanded in units of 1 μm, fed back by the linear scale 26, and the X-axis is moved in the + direction at a constant speed. On the other hand, the switch 34 is connected to the O side, and when the grinding wheel 1 and the electrode 9 come close to each other and a discharge occurs, the discharge voltage waveform will be approximately as shown in FIG. 7b.
The voltage suddenly drops to 20V, and at this moment, a discharge current flows as shown in the inter-electrode current waveform c. As a result, the voltage between the poles falls below the set level E of the comparator amplifier 15, so the output (Q) of the flip-flop 19 becomes "0" level, and therefore the clock pulse generated from the clock pulse generator 21 becomes the output of the AND gate 22. Since the command pulse stops, the X-axis feed stops. That is, in FIG. 3, the grindstone 1 approaches the electrode 9,
The feeding in the X-axis direction stops at the position where the discharge starts.

Through the above operations, the starting origin position of the electrode feeding setting for correcting grinding wheel runout is set.

Next, the operation of feeding the electrode 9 in the X-axis direction by the amount of grindstone correction will be explained. Change the position of whetstone 1 to the 5th position.
The grindstone 1' is set at the position shown by the dotted line in the figure, the counter A23 and the counter B25 are reset, and the signal set in the presetter 28 is applied to the comparator 29. The contents of counter B28 and the contents of counter B25 are compared. At this point, the content of the counter B25 is "0", so the output of the comparator 29 is "1".
This signal passes the clock pulse from the clock pulse generator 21 through the AND gate, and the X-axis feed is performed every command pulse by the same operation as described above. preset 2
When the contents of 8 and the contents of counter B25 match,
The output of the comparator 29 becomes "0" level, and the clock pulse is no longer obtained from the AND gate 36, so that the X-axis feed is stopped. In other words, the grinding wheel 1 is sent in the X-axis direction by the amount of deflection (corresponding to _G1 in FIG. 3) described above.

Next, as shown in FIG. 5, the operation of performing electrical discharge machining by feeding the electrode 9 in the X-axis direction will be described.

For feeding in the Y-axis direction, when the start switch 18 is turned on, a feed start signal is given to the Y-axis feed circuit 17, and the grinding wheel runout is corrected by electrical discharge machining. The discharge waveform patterns during electrical discharge machining can be classified into four categories as shown in FIG. 7a, b, and c. In the machining voltage waveform b, K ₁ indicates normal discharge, K ₂ indicates a state where the machining is slightly unstable due to the short machining gap, K ₄ is in a short circuit state, and K ₃ is conversely, the machining is short-circuited. It represents the no-discharge state when it spreads. If the time is short-circuited as shown in a′, b′, and c′, the voltage obtained by integrating the voltage waveform between the poles will be I ₂ of b′.
It can be seen that it fluctuates during one rotation of the grindstone. During electrical discharge machining feed in the Y-axis direction, the switch 34 is connected to the P side, and the discharge waveform is controlled by the comparator amplifier 15.
is compared with _E1 , and if the level of the average value _I2 of the discharge waveform shown by the dotted line in waveform b' in _FIG . The signal provides a stop signal to the Y-axis feed circuit 17 to stop Y-axis feed. Furthermore, if the voltage of the average value I ₂ of the discharge waveform becomes equal to or higher than the E ₁ level, the output of the comparison amplifier 15 will be at the “1” level.
The Y-axis feed returns to the electrical discharge machining operation state. In this way, electrical discharge machining is performed while feeding in the Y-axis direction and detecting the electrical discharge state so that the grindstone 1 and the electrode 9 are not short-circuited. In this case, if the electrode 9 is made of a silver-tungsten alloy or a copper-tungsten alloy that is relatively less abrasive, the feed on the Y axis may be about 20 mm. According to experiments, the amount of deflection of the grindstone is about 10 to 20 .mu.m, so the preset amount of the presetter 28 is about the above value (about 10 to 20 .mu.m). Further, the appropriate rotational speed of the grinding wheel is 100 to 300 rpm; if it is less than this, an abnormal discharge state will occur, and if it is more than this, vibration will occur in the grinding wheel, which is likely to cause a short circuit with the electrode.

As described above, according to the present invention, the runout of a metal bonded diamond grinding wheel can be automatically corrected with high efficiency and precision. An example confirmed by the device of the present invention is as follows: Grinding wheel: Ni-based (or copper-based) metal bonded diamond grinding wheel Abrasive grain size: 3 to 12 μm Grinding wheel width: 0.1 to 0.2 mm Grinding wheel diameter: 40 mm Pulse Conditions: Peak current: 0.2A Pulse width: 1μs Capacitor: 0.68nF Grinding wheel rotation speed: 200 rpm or more When electrical discharge machining was performed, the machining time was 30 minutes and the machining accuracy was ±1 μm.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of processing using a metal bond diamond grinding wheel, Fig. 2 is an explanatory diagram of the configuration of the metal bond diamond grinding wheel, Fig. 3 is an explanatory diagram showing the overall configuration of the device according to the present invention, and Figs. 6 is an explanatory diagram showing a partial configuration of the device, FIG. 6 is a circuit diagram showing an example of a control circuit in the device of FIG. 3, and FIG. 7 is a pulse diagram for explaining the operation of the control circuit of FIG. 6. FIG. 3 is a diagram of a power supply voltage waveform and an inter-electrode voltage waveform and an inter-electrode current waveform representing a discharge state between the electrodes. Explanation of symbols, 1... Metal bond diamond grinding wheel, 9, 9... Electrode, 12... Pulse current, 1
3... Control circuit, 15... Comparison amplifier, 17...
Y-axis feed circuit, 19...Flip-flop, 21
...Clock pulse generator, 23...Counter A, 24...Comparator, 25...Counter B, 26
... Linear scale, 27 ... X-axis feed circuit, 2
8... presetter, 29... comparator, 35... display circuit.

Claims (1)

[Claims] 1. A device for correcting runout of a disk-shaped metal bond diamond grinding wheel, comprising: a support drive member that rotatably supports the metal bond diamond grinding wheel about a central axis and rotates it at a predetermined rotation speed; and a tip of the metal bond diamond grinding wheel. an electrode having a groove facing the center axis and movable in the direction of the central axis and a direction perpendicular thereto; a pulse power source for applying a pulse voltage between the metal bond diamond grinding wheel and the electrode; a detection circuit that detects a discharge state occurring between the metal bond diamond grinding wheel and the electrode by comparing the discharge voltage with a reference voltage using a comparison amplifier; a detection means for detecting contact between the tip and the electrode; a presetter for presetting the amount of runout of the metal bond diamond grinding wheel; and a pulse from a linear scale for detecting the amount of feed of the electrode in the direction of the central axis. a first comparator that compares a first counter that counts the number of pulses; a second comparator that compares the first counter with a second counter that counts the number of pulses from the clock pulse generator;
a first feed circuit that controls the amount of feed of the electrode in the central axis direction based on the output signals of the detection means, the first comparator, and the second comparator; a second feed circuit that controls the amount of feed of the electrode in the direction perpendicular to the central axis; and a second feed circuit that controls the feed amount of the electrode in the direction of the central axis and the direction perpendicular thereto, respectively, based on signals from the first and second feed circuits. and a drive means for moving and positioning a metal bond diamond grinding wheel.