JPH02106272A - Method for discharge dressing grinding wheel - Google Patents

Abstract

PURPOSE:To quantitatively grasp a dressing condition and surely carry out the optimum dressing by stopping dressing when a statistic value becomes below a defined value for each defined period of a detected discharging current value. CONSTITUTION:A switch 56 is closed by a switch control circuit 58 for a short time for each defined period T at the end of grinding of a grinding wheel 1, and the maximum value of the voltage V1 which is inputted during this defined period T is held by a peak hold circuit 5 and outputted. The output voltage V2 therefrom is inputted into a low-pass filter circuit 6 and smoothed. The smoothed voltage 3 is inputted into a comparing circuit 7, where it is compared with a constant voltage VA and, when the smoothed voltage V3 becomes lower than the constant voltage VA, a comparing output of level '1' is generated, thereby exciting a relay 82 and opening a normally closed contact to stop the feed of power to a motor 8. Thereby, the feed of the grinding wheel 1 is stopped at the point of time of the optimum dressing condition, to complete dressing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for discharging a grindstone, and more particularly to a method for quantitatively understanding the dressing state in contact discharge dressing using twin electrodes.

[Prior art] Metal-bonded diamond grinding wheels and the like are used for grinding ceramics, but it is difficult to perform mechanical dressing, and electric discharge dressing, which melts and removes the metal bonds using electric discharge, is used. Attention has been paid.

Conventional discharge dressings have had the disadvantage of high equipment costs due to the provision of a slip ring-brush mechanism or the need to take measures to prevent electric shock due to the relatively high voltage. In so-called twin-electrode dressing, in which a discharge electrode is provided and the slip ring-brush mechanism is abolished, a method of contact dressing that generates discharge at an even lower voltage has been proposed (Hitachi Regional Conference Proceedings, pp. 139-141). 1988
)).

In this method, a pair of electrode plates to which a voltage is applied are provided at intervals in the circumferential direction of the grinding wheel, and these electrode plates are ground by the grinding wheel to produce flow-shaped chips along the circumference of the grinding wheel. Intermittent electrical discharge is generated between the surfaces to melt and remove the binding material (bond) of the grinding wheel, and new abrasive grains are made to protrude.

[Problems to be Solved by the Invention] According to the dressing device proposed above, low voltage (110
Since it is possible to reliably generate a discharge at
There is no need to take precautions to prevent electric shock, and the slip ring
The fact that a brush mechanism is not required makes it possible to easily and inexpensively dress diamond grindstones, etc. However, there is currently no way to quantitatively grasp the dressing status, and the end of dressing cannot be determined by visual inspection. Therefore, it has been difficult to always perform optimal dressing such that the protrusion amount of the abrasive grains is 20 to 30% of the average abrasive grain diameter.

The present invention has been made in view of this background, and an object of the present invention is to provide a method for electrical discharge dressing of a grindstone, which can quantitatively grasp the dressing state and always obtain optimal dressing.

[Means for Solving the Problems] The method of the present invention provides a grinding wheel having a grinding surface in which a large number of abrasive grains are buried and held by a conductive binder, and a pair of electrode plates spaced apart along the grinding surface. is provided, each of the electrode plates is ground with the abrasive grains to produce a flow-shaped chip along the ground surface, and a voltage is applied between these electrode plates,
In a grindstone discharge dressing method that generates an intermittent discharge between the tip and the grinding surface and melts and removes the conductive binder, the current value of the discharge is detected, and the statistical value of the detected discharge current value at a certain period. The device is characterized in that the dressing is stopped when the discharge frequency becomes less than a predetermined value, and the frequency of the above-mentioned discharge is detected for each fixed period, and the dressing is stopped when the detected discharge frequency is less than a predetermined value. It is characterized by this.

[Effect] The current value and frequency of discharge during dressing change depending on the state of the chip generated from the picture electrode, but if the rotation speed of the grindstone is constant, the dressing progresses from the initial stage of discharge and as the abrasive grains are exposed. The current value tends to gradually decrease, and the discharge frequency also decreases.

Therefore, if the dressing is finished when the statistical value of the discharge current value becomes less than a predetermined value or the discharge frequency becomes less than a predetermined value, an appropriate abrasive grain protrusion amount will be obtained.

[First Embodiment] In FIG. 1, a rotating grindstone 1 (arrow in the figure) has a grinding surface on its outer periphery in which abrasive grains such as diamond are embedded and held by a conductive bonding material such as bronze. A pair of electrode plates 2A and 2B are provided below the grinding wheel and spaced apart from each other in the circumferential direction of the grindstone. Each electrode plate 2A, 2B is provided with a constant length in the direction perpendicular to the plane of the paper, and is made of a highly plastic material such as aluminum.

A DC voltage of about 40 V is applied from a power source 3 to the electrode plates 2A and 2B, and the grinding wheel 1 causes the electrode plates 2A and 2B to
When 2B is cut a certain amount and ground at a constant speed in the longitudinal direction, flow-shaped chips are generated from each electrode plate 2A and 2B along the circumferential surface of the grinding wheel, and intermittent discharge occurs between the chips and the grinding surface, resulting in bonding. The material is gradually melted away, and the abrasive grains are gradually exposed and dressed.

The relationship between the dressing time and the discharge current at this time is schematically shown in FIG. When the binding material on the ground surface is removed by dressing and the protrusion amount of the abrasive grains gradually increases, the magnitude of the discharge current changes microscopically, but overall the current value increases as the dressing progresses as shown in the figure. is clearly declining. Therefore, if the dressing is stopped when this current value reaches a predetermined value, an optimal dressing state can be obtained.

Hereinafter, an example of a circuit for realizing this method will be explained with reference to FIG. 1 above.

A resistor 4 with a small resistance value is provided in the power supply line to the electrode plates 2A and 2B, and a voltage proportional to the discharge current is applied to both ends of the resistor 4.
1 is obtained. This both-end voltage V1 is input to the peak bold circuit 5. The peak hold circuit 5 has front-stage and rear-stage OP amplifiers 51 and 52.
constitutes a half-wave rectifier circuit together with the diode 53, and the subsequent OP amplifier 52 constitutes a voltage buffer circuit with large input impedance, and a feedback resistor 57 connects them. And the above OP amplifier 51.5
A diode 54 and a hold capacitor 55 having one end grounded are provided between the capacitor 2 and the capacitor 55, and a reset transistor switch 56 is connected in parallel to the capacitor 55.

The transistor switch 56 is a switch control circuit 58
The switch control circuit 58 causes the switch 56 to be closed for a short time every fixed period T when the grindstone 1 finishes grinding the electrode plates 2A, 2B from one longitudinal end to the other. Thus, the peak bold circuit 5 holds the maximum value of the voltage 1 input during the constant period T and outputs it (voltage V2). This is shown in FIG.

The output voltage (2) of the peak hold circuit 5 is reset at a constant period T as described above and becomes 0 (2) for a short time. Therefore, in order to smoothly connect the maximum voltage values of each period T,
The above output voltage (2) is input to a low-pass filter circuit 6 composed of a resistor 61 and a capacitor 62, and is smoothed. This smoothed voltage (3) is shown in FIG. In this case, the time constant of the low-pass filter circuit 6 needs to be optimally selected in consideration of the reset time.

The smoothed voltage V3 is input to the comparator circuit 7, where the constant voltage V3
It is compared with A. This constant voltage VA is set by determining in advance the maximum voltage value when the protrusion amount of the abrasive grains becomes optimum through an experiment.

Reference numeral 8 denotes a grindstone feeding motor, and a normally closed contact of a relay 82 is provided in its power supply line, and the relay 82 is forcibly stopped by the output of the comparator circuit 7 via a transistor 81. That is, when the smoothed voltage (3) becomes lower than the constant voltage VA, a comparison output of "1" level is generated,
As a result, the relay 82 is energized, the normally closed contact is opened, and the power supply to the motor 8 is stopped.

In this way, when the optimal dressing state is reached (
At Ta) in FIG. 4, the feeding of the grindstone 1 is stopped and the dressing is completed.

In the above embodiment, the method of the present invention was realized using a simple circuit that stops the feed motor by detecting the maximum value of the discharge current (that is, the voltage vi) that changes within a fixed period T for each rotation of the grindstone. , if a microcomputer or the like is available, there is a method of reading the voltage V1 within the constant period T at sufficiently short regular intervals, obtaining an average value or other statistical value, and comparing this with the predetermined value. can be adopted.

[Second Example] As is clear from FIG. 2, as the dressing progresses, the discharge current gradually becomes smaller and the discharge period becomes longer (although there are microscopic variations, this is the overall trend). Therefore, by detecting the discharge frequency at regular intervals and stopping the dressing when the frequency becomes equal to or less than a predetermined value, an optimal dressing state can be obtained.

To achieve this, for example, take in the voltage (1) above the noise level, input it into a one-shot circuit after shaping the waveform, and count this one-shot output with a counter that is reset at regular intervals. , the feed motor 8 is stopped when the count value becomes less than a predetermined value.

In this embodiment, it is also possible to detect the maximum value, average value, or other statistical value of the discharge cycle at regular intervals, and to stop dressing when these values exceed a predetermined value.

In each of the above embodiments, the feed motor was automatically stopped, but a meter was provided that had dual scales for the voltage value or frequency value and the corresponding grinding wheel protrusion amount, and the above-mentioned motor was started after checking the meter indication. You can also stop it. in this case,
Of course, instead of stopping the motor, the discharge power source may be cut off.

Furthermore, it is also possible to adopt a method of detecting the discharge power l at regular intervals and stopping the dressing when the discharge power l becomes equal to or less than a predetermined value.

In addition, the method of the present invention uses, in addition to the metal bond grindstone,
It goes without saying that it can also be applied to resin bonded grindstones mixed with metal powder, and is not affected by the shape of the grindstone or the structure for holding the abrasive grains.

[Effects of the Invention] As described above, according to the dressing method of the present invention, in contact discharge dressing of twin electrodes.

Since the dressing state can be grasped quantitatively, unlike the conventional visual observation, it is possible to reliably obtain the optimum dressing, and it is possible to suitably dress metal bonded diamond grindstones and the like.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a circuit that implements the method of the present invention, Figure 2 is a graph schematically showing changes in discharge current as dressing progresses, and Figures 3 and 4 are peak hold, respectively. It is a graph showing the time change of voltage and 1L sliding voltage. 1... Grinding wheels 2A, 2B... Electrode plate 3... Power supply 4... Resistor 5... Peak hold circuit 6... Low pass filter circuit 7... Comparison circuit 8... Grinding wheel feed motor Figure 2 Figure 3

Claims (2)

[Claims] (1) A pair of electrode plates are provided at intervals along the grinding surface of a grinding wheel having a grinding surface in which a large number of abrasive grains are buried and held by a conductive binder, and each of the electrode plates is is ground to produce a flow-shaped chip along the ground surface, and a voltage is applied between these electrode plates to generate intermittent discharge between the chip and the ground surface to melt and remove the conductive bonding material. A grindstone discharge dressing method, characterized in that the discharge current value of the discharge is detected, and the dressing is stopped when the statistical value of the detected discharge current value for each fixed period becomes equal to or less than a predetermined value. Method. (2) A pair of electrode plates are provided at intervals along the grinding surface of a grinding wheel having a grinding surface in which a large number of abrasive grains are buried and held by a conductive binder, and each of the electrode plates is is ground to produce a flow-shaped chip along the ground surface, and a voltage is applied between these electrode plates to generate intermittent discharge between the chip and the ground surface to melt and remove the conductive bonding material. A grindstone discharge dressing method, characterized in that the frequency of the discharge is detected at regular intervals, and the dressing is stopped when the detected discharge frequency is equal to or less than a predetermined value.