JPH11309625A - Method of measuring working clearance length of powder contamination type discharge working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the working clearance length independently of the specific gravity of the powder and change of the specific gravity of the working liquid by computing the working clearance length on the basis of the relation between the discharge possible range obtained on the basis of the axis position at the time of starting discharge and the axis position when the discharge is stabilized and the previously measured discharge possible range and the working clearance length. SOLUTION: A clearance control 9 section is a controller for driving a position control motor 12 on the basis of the mean voltage 13 constantly holds the discharge pulse density and the working clearance length. The clearance control section 9 monitors the electrode position so as to always output the signal for showing the axis position to a gap computing section 10. The gap computing section 10 computes a difference between the axis position at the time of starting the discharge just after jumping and the axis position when the discharge is stabilized so as to measure the discharge possible range, and obtains the working clearance length 14 of a clearance with a reference of a data memory section 11 for storing the relation between the discharge possible range previously obtained by experiments and the working clearance length 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder-mixed electric discharge machine using a machining fluid mixed with a conductive powder, and to a method for measuring a machining gap length in a powder-mixed electric discharge machine.

[0002]

2. Description of the Related Art Conventionally, in a powder-mixed electric discharge machine, the machining gap length is an important factor for determining the machining time and the surface roughness of a workpiece, but it has been found that the machining gap length is significantly affected by the powder concentration. . This is disclosed in Japanese Unexamined Patent Publication No. Hei 8-252725, and as shown in FIG. 3, by changing the concentration of the conductive powder, the working gap length is changed by more than twice. In addition, in order to reduce the machining time in EDM, machining is performed while automatically switching the machining conditions from rough machining conditions to finishing machining conditions. It is necessary to finish the processing within the precision dimensions. In this case, the processing gap length is an important value when the processing conditions are automatically switched, and is used during the processing conditions.

[0003] The machining gap length measured when determining the machining conditions is required to obtain the same machining gap length in the subsequent machining. If the same value is not obtained, the machining gap length is processed to the finishing machining conditions. However, the set surface roughness and precision dimensions cannot be obtained. For this reason, even in a powder-mixed electric discharge machine, it is necessary to ensure that the same value as the machining gap length measured when determining machining conditions is obtained in subsequent machining, and for this reason, the powder concentration is kept constant. Need to keep.

In order to keep the powder concentration constant, it is necessary to measure the powder concentration. Conventional methods for measuring the powder concentration include a method based on specific gravity measurement, a method using surface tension, and a method based on transmitted light intensity. And so on. Further, a method of directly measuring a machining gap length by bringing a reference sphere into contact between electrode workpieces has been devised.

However, the measurement of the powder concentration by the conventional method involves the following problems and is not always a sufficient method.

In the conventional method based on specific gravity measurement, a liquid after powder mixing is sampled in a specified volume, and the weight of the sample is measured to determine the concentration of the mixed powder. However, this method can be used when the specific gravity of the powder particles to be mixed is large to some extent and the mixing amount is large, but when the specific gravity of the powder particles is light and the mixing amount is small, for example, when carbon powder is mixed at 2 g / L. The measurement of the powder concentration is almost impossible due to variations in specific gravity depending on the production lot of the electric discharge machining fluid and changes in specific gravity due to the temperature of the machining fluid.

[0006] Even when the specific gravity of the powder is high to some extent,
Automatic measurement of the powder concentration is difficult because the powder component is adsorbed on the container or pipe for sampling the processing fluid, which makes it difficult to measure the powder concentration automatically, and the operator manually measures the powder concentration. The situation.

In the conventional method for measuring the concentration based on surface tension, the change in tension due to carbon sludge generated in the machining fluid due to electric discharge is large, and in the case of a powder-mixed machining fluid in which the discharge time has continued for a certain degree or more, the surface tension and the machining gap length are reduced. Since the relationship changes, there are still many practical problems. The conventional method of measuring the density based on the transmitted light intensity has a problem that the output value changes due to contamination of the light input / output unit, and it is necessary to periodically clean the light input / output unit. Further, in this measuring method, there is a problem that the output value largely fluctuates due to carbon sludge generated in the machining fluid by electric discharge.

In the above concentration measurement method, if the particle size distribution of the powder to be mixed is in a constant state, the relationship between the machining gap length and the powder concentration is reproduced relatively well. There is also a problem that the particle size distribution is reduced and the result of the concentration measurement differs from the machining gap length with the discharge time.

Further, the machining is interrupted, and a hard sphere having a known diameter is brought into contact between the electrode and the workpiece, and a further known hard sphere diameter is obtained from the difference between the Z-axis position before the machining interruption and the Z-axis position at the time of the hard sphere contact. A method of calculating the processing gap length by subtraction was also devised, but it was necessary to interrupt the processing on the way, and when contacting the hard sphere between the electrode and the workpiece, powder with a diameter of 1 to 20 μm was mixed Accurate measurement was not possible because the working fluid remained between the electrode and the workpiece. The present invention has been made in order to solve the above-described problems, and an object of the present invention is to eliminate the need for measuring the powder concentration, and to reduce the machining gap length in a powder-mixed electric discharge machine that is not affected by carbon sludge. It is to provide a measuring method.

[0010]

According to the present invention, there is provided a drive control means for controlling at least one of a discharge electrode and a workpiece, a gap control means for controlling an operation of the drive control means, After separating the discharge electrode from the workpiece by a predetermined distance, the gap control unit controls the jump operation, which is an operation of moving the discharge electrode again to a position just before the dischargeable position, and the discharge electrode, A discharge power source serving as a power source when a discharge pulse is applied to the workpiece, a discharge pulse control unit for controlling a state of the discharge pulse, and an axis representing a positional relationship between the discharge electrode and the workpiece. Axis position measuring means for measuring the position,
With respect to a method of measuring a machining gap length in a powder-mixed electric discharge machine having the above, the object of the present invention is to determine a difference between the axis position at the start of discharge immediately after the end of the jump operation and the axis position at the time of stable discharge, This is achieved by obtaining the dischargeable range from the difference and calculating and calculating the working gap length based on the correspondence between the dischargeable range and the working gap length measured in advance and the dischargeable range obtained from the difference. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is an overall configuration diagram showing a powder-mixed electric discharge machine according to an embodiment of the present invention, and the configuration will be described with reference to the drawings. In FIG. 1, a stirrer for the powder-mixed working fluid, an NC controller, and the like are omitted because they are not directly related to the present embodiment. In this powder-mixed electric discharge machine, the electric power output from the electric discharge power supply 1 is pulse-controlled in accordance with electric conditions given by a control device (not shown) to generate a discharge pulse in the gap between the electrode 5 and the workpiece 4. The machining fluid tank 2 is a tank for storing the electro-discharge machining fluid 3 mixed with the conductive powder, and immerses the electrode 5 and the workpiece 4 therein. The position control motor 12 is a motor that drives and controls the position of the electrode 5 based on a command from the gap control unit 9.

The average voltage measuring section 8 measures the voltage in the gap between the electrode 5 and the workpiece 4 and outputs it as an average voltage 13. The average voltage 13 is obtained by smoothing the discharge voltage waveform with a low-pass filter or the like. The average voltage decreases when the discharge pulse density is high, and the average voltage tends to increase when the discharge pulse density is low. The gap control unit 9 controls the position control motor according to the average voltage 13.
This is a control device that drives 12 and keeps the discharge pulse density and the machining gap length constant. The gap controller 9 constantly outputs a signal indicating the axis position to the gap calculator 10 by monitoring the electrode position.

The gap calculation unit 10 measures the dischargeable range by calculating the difference between the axis position at the start of discharge immediately after the jump and the axis position at the time of stable discharge, and determines the dischargeable range and the machining gap length obtained in advance by experiments. The working gap length 14 of the gap is obtained by referring to the data storage unit 11 which stores the correspondence relation of The machining gap length 14 obtained by the gap calculation unit 10 is notified to the machine operator via the control device,
Provides information on the current machining gap length.

The operation of the embodiment of the present invention will be described with reference to FIG. FIG. 2A shows the passage of time and the change of the average voltage, and FIG. 2B shows the shaft position as a result of the control by the position control motor 12. In FIG. 2, the jump operation is performed immediately before time T1. The jump operation is an operation of moving the electrode 5 to a position just before the dischargeable position again after the electrode 5 is separated from the workpiece 4 by a predetermined distance. At this time, since the electrode 5 is separated from the workpiece 4 by more than the dischargeable distance, no discharge occurs, and the average voltage 13 also indicates V0 which is the maximum output voltage of the discharge power supply.

Immediately before time T1, the jump operation is completed and the state shifts to the gap control state. The gap control unit 9 has a target average voltage V1 therein, and generates and outputs a speed command signal to the position control motor 12 by multiplying the difference voltage between the target average voltage V1 and the average voltage 13 by a speed coefficient. Thereby, the gap control unit 9 controls the length of the working gap between the electrode 5 and the workpiece 4.

By this gap control, the electrode 5 further gradually approaches the workpiece 4, and reaches the dischargeable position Z1 at time T1. At the dischargeable position Z1, discharge starts, but since the distance of the gap is not yet sufficiently short, the discharge pulse density is low, and the average voltage 13 does not reach the target average voltage V1.

For this reason, the position of the electrode 5 is further controlled in the direction in which the machining gap length becomes narrower, and the Z position advances from Z1 to Z2. The average voltage 13 decreases from V0 to V1 by increasing the discharge pulse density according to the electrode position. At this time, since the upper limit value is set for the speed command signal generated from the gap control unit 9, the actual operation of the electrode position moves gently as shown from Z1 to Z2 in FIG. The decrease in the voltage 13 also shows a substantially similar tendency. After the average voltage 13 reaches the target voltage V1, the gap control unit 9 drives and controls the position control motor 12 until time T3 so that the average voltage 13 becomes an approximate value of V1. At time T3, a preset discharge time (T3-T
In order to reach 1), a jump operation for separating the electrode 5 from the workpiece 4 by a predetermined distance is started.

In FIG. 2, the dischargeable range Zpos is defined as shown in the following equation 1.

## EQU1 ## Zpos = Z1-Z2 The dischargeable range Zpos represents the difference between the maximum machining gap length at which discharge can be performed and the machining gap length at which the optimum discharge pulse density defined by the target average voltage V1 is obtained. It has been newly found by experiments that the dischargeable range Zpos has a correspondence shown in FIG. 4 with the working gap length 14 of the gap.
That is, based on the relationship between the relationship shown in FIG. 4 and the dischargeable range Zpos calculated from Equation 1, it is possible to measure the machining gap length 14 without finding the powder concentration.

The relationship between the dischargeable range and the machining gap length depends on the discharge area of the electrode, the material of the electrode, the shape of the electrode,
It depends on discharge electric conditions (peak current, on-time, off-time, feed speed of gap control, cycle or amount of jump control), and the like. For this reason, the dischargeable range must be measured under the same conditions as when the relationship between the reference dischargeable range Zpos and the machining gap length 14 was measured.
In addition, it is necessary to use electrical conditions in which the working gap length is increased by mixing the powder, that is, finishing working conditions.

The embodiment shown in FIG. 1 is a method for measuring the machining gap length using the entire electric discharge machine. The machining gap length during machining can also be reduced by preparing a dedicated measuring instrument having the above-mentioned components. It is possible to perform online measurement, and it becomes possible to take measures to suppress fluctuations in the machining gap length during machining even for a workpiece that requires machining for a long time.

[0021]

As described above, according to the present invention, the dischargeable range is determined from the axial position at the start of discharge and the axial position at the time of stable discharge, and the determined dischargeable range and the dischargeable range measured in advance are determined. The machining gap length is calculated and derived based on the correspondence between the range and the machining gap length. Therefore, according to the present invention, the working gap length can be measured without being affected by the change in the specific gravity of the powder or the specific gravity of the working fluid, and there is no measurement error that occurs when contact detection is used. Further, according to the present invention, the machining gap length can be measured without any problem even if the powder concentration in the machining fluid changes due to carbon sludge generated by electric discharge. When a dedicated measuring unit is manufactured, online measurement of the processing gap length is possible during processing. In addition, by notifying the machine operator of the current machining gap length value, the machine operator can take appropriate measures, for example, adding a conductive powder or changing the machining fluid. For example, it is possible to prevent the processing time from being abnormally prolonged or the processed surface quality not becoming glossy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a powder-mixed electric discharge machine using a machining gap length measuring method of the present invention.

FIG. 2 is a graph showing a relationship between a discharge voltage average value and a dischargeable range.

FIG. 3 is a graph showing a relationship between a powder mixing concentration and a processing gap length.

FIG. 4 is a graph showing a relationship between a dischargeable range and a machining gap length.

[Explanation of symbols]

 1 Discharge power supply 2 Machining tank 3 Powder mixed working fluid 4 Workpiece 5 Electrode 8 Average voltage measuring unit 9 Gap control unit 10 Gap calculation unit 11 Data storage unit 12 Z-axis position control motor 13 Average voltage 14 Processing gap length

Claims (1)

[Claims] 1. A drive control means for driving and controlling at least one of a discharge electrode and a workpiece; a gap control means for controlling an operation of the drive control means; A jump control means for causing the gap control means to control a jump operation, which is an operation of moving the discharge electrode again to a position just before a dischargeable position, after a predetermined distance, and discharging the discharge electrode and the workpiece. A discharge power supply serving as a power supply when applying a pulse, a discharge pulse control means for controlling a state of the discharge pulse, and an axial position measuring means for measuring an axial position which is a positional relationship between the discharge electrode and the workpiece. In the method for measuring the machining gap length in a powder-mixed electric discharge machine, comprising: a difference between the axis position at the start of discharge immediately after the end of the jump operation and the axis position at the time of stable discharge. Calculating the discharge gap range from the difference, calculating the gap length based on the correspondence between the discharge gap range and the machining gap length measured in advance and the discharge gap range obtained from the difference. A method for measuring a machining gap length in a powder-mixed electric discharge machine characterized by the above-mentioned.