SU1756048A1 - Method of spark erosion machining - Google Patents

Abstract

Usage: in electroerosive treatment of electrically conductive materials and concerns methods of coating, surface strengthening of tools and machine parts. SUMMARY OF THE INVENTION: The alloying electrode 1 is placed with a spacing of 3 between the surface of the workpiece 2. In the gap 3, pulses are supplied in pairs in a cycle, causing discharges between electrode 1 and the workpiece 2. The first pulse in gap 3 is supplied from a capacitive storage 4 along the circuit 4 , 5,1,3, 2. The second pulse is supplied from the power source 14 of the direct current voltage along the circuit of elements 14,15, 16,17,1,3,2. Cyclic repetition with the scanning movement of the electrode 1, the workpiece 2 is processed. The temperature of the electrode 1 is measured and the heat input to the electrode 1 in each pair of pulses is changed by changing the duration of each second pulse inversely proportional to the temperature of the electrode. Maintaining the temperature of the electrode is ensured only by adjusting the duration of the second pulse of the process current, as a result, the quality and performance of the treatment are increased. 2 Il. sl C

Description

The invention relates to electrophysical and electrochemical methods for the treatment of electrically conductive materials, relates to surface alloying methods and may find application in the machine-building industry for coating, surface strengthening of tools and machine parts.

There is a known electrotreatment method implemented in a device for electroerosive processing (1), according to which an electrode state sensor receives radiant energy emitted by an electrode during heating during processing. When the electrode temperature reaches a predetermined limit value, the threshold circuit turns off the process current source at

a long time sufficient to cool the electrode, then, according to a controlled degree of radiation, the generator of the technological current source is turned on, resuming the treatment of the part with an electrode. A disadvantage of the known method is the complete disconnection of the supply of technological current to the erosion gap during the time of decreasing the electrode temperature, causing forced thermal cycling in the treatment area with a lower frequency than the pulse frequency. This leads to uneven thickness of the doped layer due to the unevenness of the erosive effect and a corresponding decrease in the quality of processing. Processing performance

VI

so about

&

for a given non-uniformity, the erosion effect is also reduced.

The aim of the invention is to increase the productivity and quality of processing during EDM doping.

Fig. 1 shows a block diagram of an apparatus for carrying out the proposed method; figure 2 - timing charts of the device. :

The method is carried out as follows.

The alloying electrode is driven into oscillatory oscillating and scanning movement relative to the workpiece surface. As the working surface of the electrode tip approaches during the oscillating movement, the impulse of technological current is applied to the erosion gap in the area of the breakdown distance. The gap breaks through and a pulsed current flows through it, ensuring the transfer of the material of the alloying electrode to the surface of the part and its doping. During the subsequent approaching, the electrode and the workpiece are mechanically contacted, at which time the technological currents do not flow through the treatment area, the treatment area deionizes, the electrode material crystallizes, perforates and cools. Due to the oscillating movement, the electrode moves from the surface of the workpiece. After the contact of the electrode with the workpiece is broken, while the electrode is still in the area of the breakdown distance, a pulse of technological current is applied to the erosion gap. A repeated breakdown of the erosion gap occurs in the processing cycle and a second pulse of technological current flows through it. The second pulse ensures the melting of the crystallized microroughnesses, arising from the impact of the first pulse of the technological cycle current. The alignment of the alloyed surface and the intensive mixing of the ligature ensures an increase in the quality of the alloying. During subsequent oscillatory movements of the electrode, the processes described are cyclically repeated with the frequency of the initiation factors. During processing, the temperature of the working end of the alloying electrode is monitored by the intensity of its thermal radiation. With increasing under the influence of external factors, the temperature of the second pulse decreases inversely proportional to the signal of temperature over several treatment cycles of the electrode. As a result, the heat input into the treatment zone from the second pulses decreases, the total heat input of both pulses during the processing cycle also decreases, the electrode temperature decreases. to the original, given

prior to processing and optimal for this alloying process. In the case of a decrease under the influence of external factors of the average temperature of the electrode, the described processes proceed in the opposite

0 order, the heat input from the second pulse and the total per cycle increase, which ensures the restoration of the desired temperature and a stable course of the doping process.

5 Thus, the temperature of the electrode and the working area is controlled by changing the energy of the second pulse, while the parameters of the first pulse, ensuring the transfer of electrode material to the part, do not

0 is changed during processing and is optimally selected for these processing conditions, which ensures an equal thickness of the doped layer. Stabilizing the temperature of the working end of the electrode additionally

5 stabilizes the doping process by keeping the erosion resistance of the electrode material constant at a given optimal temperature.

0 The supply of the second impulse, leveling the traces of the impact of the first impulse, after mechanical contact of the surfaces of the electrode and the part, ensures effective melting and mixing

5 since during the contact the fluidized ligature layer is squeezed by the surface of the alloying electrode and when the electrode moves away from the part, an imprint of the electrode remains on its surface, a part of the surface of which is equidistant to the surface of the second discharge and smoothing out the uneven surface of the ligature. This improves the quality of processing.

The proposed method is carried out using the device shown in Fig. 1.

The device contains an electrode 1, which can make oscillatory oscillating and scanning line-frame movements relative to the workpiece 2. The average value of the erosion gap 3 during the oscillation period

5 is maintained unchanged during the scanning movement over the complex-shaped surface of the workpiece 2 by an electrode supply system (not shown). The capacitive storage device 4 is connected by one lining.

through the power diode 5 to the electrode 1 and the other lining to the workpiece 2 along the discharge circuit. The drive 4 is connected via a series transistor power switch 6 and the current limiter 7 to the pole of the power source 8 of the DC voltage, its second pole is connected to the workpiece 2 via a charge circuit.

The first pole of source 8 is connected via serial measuring voltage source 9, connected according to power source 8, gap 3 conduction sensor 10, current limiter 11, diode 12 to electrode 1. These elements form a measuring circuit together with comparator f3. The workpiece 2 is connected via a series of direct current power source 14, a power switch 15, a current limiter 16 and a power diode 17 to the electrode t. The workpiece 2 is also connected via successive low voltage DC measuring voltage source 18, a gap 3 conductance sensor 19, an inductive element 20 and a decoupling diode 21 to electrode 1. Sources 14 and 18 are connected to the workpiece 2 with poles of the same polarity the polarity of the source pole 8. The common point of the diode 21 and element 20 is connected via a series of reverse diode 22 and voltage sensor 23 to the common point of element 20 and sensor 19. Diodes 5 and 12 are connected according to the polarity of sources 8 and 9, diodes 17 and 21 according to The polarity of sources 14 and 18. Diode 22 is turned on according to the direction of the emf of self-induction of element 20 at the moment of interruption a point through it. ,

In the exemplary embodiment of the device for implementing the method, the negative poles of the sources 8, 14 and 18 are connected to the workpiece 2 and the processing is carried out with positive polarity on the doping electrode 1. The signal output of the sensor 23 is connected via a hysteresis comparator 24 to the trigger input of the controlled single vibrator 25. An infrared radiation sensor 26 is connected via a serial switch 27, a filter 28. a signal voltage storage unit 29, an integrator 30 and a comparison unit 31 to a voltage control input of a duration and pulses. The duration of the output pulse is inversely proportional to the magnitude of the signal voltage at this input. The second input of unit 31 is connected to the reference level setter 32. The output of the sensor 19 is also connected via the comparator 33 and the single-oscillator 34 to the reset input (gating) of the voltage storage unit 29.

The outputs of the comparator 13 and the one-shot 25 are also connected to the inputs of the adder 35, the output of which is connected via the delays for turning off the switch 36 to the control input 5 of the key 27. Through the optical filter 37 with a passband in the wavelength range of the electrode the end of the electrode 1 is focused by the lens 38 on

10 of the sensor element 26. The lens 38 is configured so that with oscillating movements of the electrode 1, its working end is in the field of view of the lens 38. The sensor output 19 is also connected via serial comparator 39 and amplifier 40 to the second control input of the key 15.

Before processing the adjustment of the source 8 set the necessary for

0 transferring the electrode material to a part, the amplitude of the pulse from the accumulator 4 by adjusting the capacitance of the accumulator 4 taking into account the voltage of the source 8 - the duration of this pulse, adjusting the voltage of the 5 source 14 - the necessary voltage to ignite the discharge at a given speed of oscillatory movement of the electrode and electrode materials 1 and blanks 2. By adjusting the value of the resistance of the current limiter 16, the current amplitude of the second pulse is set, and by adjusting the gauge 32, its average duration.

Approaching the electrode 1 to the surface of the workpiece 2 during an oscillating motion reduces the erosion gap 3. When the working end of the electrode 1 enters the breakdown distance for the sum of the potentials of sources 8 and 9, a gap 3 of the gas medium occurs, a measuring current along the circuit arises: positive source pole 8, source 9, sensor 10, current limiter 11, diode 12, electrode 1, gap 3, workpiece 2, negative pole of source 8. At the output of comparator 13 a discrete signal appears that closes key 6 (A1 diagram on 2). There is also a power current in the circuit: the first lining of the drive 4, diode 5.

0 electrode 1, gap 3, workpiece 2, second plate of accumulator 4 (diagram A2). In this case, the current from the source 8 into the gap 3 is absent, since the key 6 is closed and the discharge in the gap 3 has a purely pulsed

5 character. The small internal resistance of the accumulator 4 ensures a rapid increase of the current in the gap 3, which ensures the intensification of the transfer of the alloying electrode 1 to the surface of the workpiece 2 for

the time of the first pulse of the cycle, since the destruction of the surface of the electrode 1 in the spots of local contacts with the surface of the workpiece 2 is ensured. As a result, a specified amount of the material of electrode 1, electrode 1 and the working area are heated by the energy of the first pulse.

Further reduction of the gap 3 leads to the mechanical contact of the electrode 1 with the workpiece 2, the alloying material on the surface of the workpiece is forged by the body of the electrode 1. This results in a measuring current through the circuit: the positive pole of source 18, sensor 19, element 20, diode 21. electrode 1, workpiece 2, the negative pole of source 18 (diagram A3). Next, the electrode 1 moves the surface of the workpiece 2, the contact of the electrode 1 with the surface of the workpiece 2 is interrupted, a gap 3 is formed. Due to the low voltage and the insignificant current of the source 18 when the contact is broken, the measuring current is interrupted and the EMF from the energy stored in the element 20 is applied through diode 22 to sensor 23, from the output of which the signal goes through comparator 24 to the trigger input of a controlled one-shot 25 (graph A4). From the output of the one-shot 25, a pulse of a predetermined duration opens the key 15 (diagram A5). Thus, the duration of the generated pulse is inversely proportional to the magnitude of the signal about the heating temperature of the electrode.

With an increase in heat removal due to a change in the processing conditions during doping (a signal proportional to the heat removal from the treatment area to the environment is shown in diagram A6), the signal duration increases proportionally (A5) and the electrode temperature is restored to a predetermined level. After opening the key 15, the voltage of the source 14 is applied to the gap 3 and due to the working end of the electrode in the area of the breakdown distance, the gap 3 breaks, the pulse current flows through the circuit: the positive pole of the source 14, the key 15, the current limiter 16, the diode 17, electrode 1, gap 3, workpiece 2, negative pole of source 14, Due to the presence of a current limiter 1 b in this power circuit, the current of the second pulse is limited in amplitude, as a result, it has a predominantly smoothing and mixing action on the material transferred to the surface of the part during the first pulse of the cycle, since the short-term discharge is connected in the interval 3 by anodic and cathodic spots to the microprotrusions of the surface of the alloying electrode 1 and the surface of the ligature on the workpiece 2. This increases

continuity and adhesion of the ligature, which provides an increase in the quality of doping. During the second pulse, the working zone of the gap 3 and the working end of the electrode 1 are heated. So the second impulse

0 performs a combination of functions: mixing the doped layer on the surface of the workpiece 2 and heating the working end of the electrode 1 until the optimum temperature of the doping process set before the treatment begins. Further, the pulse from the output of the one-shot 25 stops, the key 15 is closed, the pulse of the arc discharge is interrupted. On this single cycle impact on the workpiece 2

0 is ending.

With further oscillating movement of the electrode 1 from the workpiece 2, the measuring current through the diode 12 is interrupted (A1), the signal from the output of the sensor 10 disappears,

5, key 6 is opened and drive 4 is charged along the circuit: the positive pole of source 8, current limiter 7, key 6, drive 4, negative pole of source 8, ensuring that the first impulse circuit is ready for the next initiation of the erosion gap 3, a sequence is formed during the oscillation process operating cycles with the frequency of the mechanical vibration of the electrode 1

5 (diagram AT), which ensures, by the scanning movement of the electrode 1, the processing of a given area of the workpiece 2. The thermal radiation of the working end of the electrode 1 and the doping zone enters the filter 37, which passes the thermal radiation of the heated end of the electrode 1, significantly weakened UV and visible radiation of Gap 3 with the passage of current pulses. This radiation is focused

5 by a lens 38 on the sensing element of the radiation sensor 26. The electrical signal from the sensor 26 through the low-pass filter 28, which protects against interference, goes to the memory unit 29 and, from its output, to

0 integrator 30. An analog signal from the output of integrator 30, proportional to the temperature of the working end of the electrode t, is compared in block 31 with the signal from the setter 32. The differential analog signal corresponding to the polarity and the error value specified before the start of processing and the actual temperature of electrode 1 is supplied to the control input of the one-shot 25 and sets the duration of the generated pulse.

When conduction of the erosion gap 3 occurs, the signal from the output of the comparator 13 or / and the signal from the output of the one-oscillator 25 when forming the second pulse goes through the adder 35 and the switch-off delay element 36 to the control input of the switch 27, which is inertia-free closes. As a result, during the passage of power pulses of the technological current through the gap 3 and the existence of intense pulsed radiation accompanying the erosion doping process, the key 27 is closed and the interference signal from the spark gap 3 does not pass to the output of the switch 27 and to the optical-electronic feedback circuit . On the one hand, this makes it possible to increase the sensitivity of the feedback circuit, i.e., the accuracy and reliability of maintaining the electrode temperature set before the treatment, on the other hand, to use the optical type sensor, i.e., contactless, to measure the temperature of the working end of the electrode. Such a solution allows any restrictions on the nature and parameters of the oscillating mechanical oscillating movement of the alloying electrode to be removed, since, regardless of the stability of the initiation, the protection circuit of the treatment area interferes.

During mechanical contact of the gap electrodes, the signal from the output of the sensor 19 through the comparator 33 and the triggering one-oscillator 34 resets the previous value stored by the voltage block 29 proportional to the heating temperature of the electrode 1. After the end of the second discharge cycle and delay from block 36, the disappearance time plasma in the erosion gap 3 includes key 27, block 29 stores the next current voltage value, which is proportional to the temperature of the electrode 1 in the current period. Starting the reset circuit (gating) of unit 29 from sensor 19 of contact electrode 1 with workpiece 2 ensures the reset of unit 29 during the period of the closed state of key 27, which makes it possible to automatically use a forced pause in receiving information to prepare this circuit for measurement following - the temperature value. As a result, the change in the duration of the second pulse and the adjustment of the pulses before the treatment starts does not affect the accuracy of measurement and maintenance of temperature. Enhanced technological capabilities are provided, since the implementation of the method is possible with the supply of additional alloying material to the doping zone in the form of dispersed particles. The contact signal in the doping zone and the open gap 3 can be used to maintain an average gap (not shown) from the output of sensor 19, since the circuit of sensor 19 determines the ratio of the mechanical contact time of the electrode with the workpiece to the pause time. The signal is removed from output A (in Fig. 1). In the event of an unstable oscillation mode that causes contact bounce and re-closure of gap 3 during the arc pulse, the signal from the sensor output 19 through the comparator 39 and the amplifier 40 turns off the switch 15 without inertia, and the arc pulse interrupts, eliminating the welding of electrode 1 to the alloyed surface and its damage, which further improves the quality of processing.

The first impulse in this device arises when the breakdown distance of the gap is reached during oscillation, the second impulse - at the moment of separation of the electrode surface from the ligature on the part, regardless of the duration of the contact. This ensures that the supply of the first and second pulses is synchronized with the periods of oscillating movement of the alloying electrode, which additionally stabilizes the thickness and continuity of the doped layer, improving the quality of processing.

The method in this specific embodiment is carried out in the following modes:

The amplitude of the first pulse. current, A885

The duration of the first

current pulse, с5,2-10

The rate of increase of the front

v5

5.4-10

34

impulse, A / s

Amplitude of the second current pulse, A Range of pulse durations during regulation, c4 10 5-75 10 5 Following frequency of initiation factor, Hz150 Average temperature of the working end of the electrode. ° C440 Relative error of temperature stabilization, ° C ± 3.7 The second pulse acts on the diverging surface of the electrodes of the erosion gap, as a result the pulse duration when regulating the temperature during the cycle time is not limited in principle, the increased second-degree pulse provides for the adjustment heat input to the treatment area. The increased duration is provided by the ignition of the second pulse in the breakdown distance zone, and is maintained by the current source of the second pulse and outside the breakdown distance zone due to the ionization of the gap from the second pulse.

The second pulse acts on the cooling surfaces of the gap electrodes, the current amplitude is limited, and the electrodes diverge, as a result, the transfer of the alloying electrode material to the workpiece from the second pulse is small and does not cause uneven thickness of the doped layer during adjustment of the duration of the second pulse. temperature of the working end of the electrode. At the same time, a treatment zone that is colder during adjustment is affected by a longer pulse with a large heat input, which compensates for the increase in erosion resistance with decreasing temperature of the doping zone. As a result, a shorter pulse with a lower heat input acts on the zone which is warmer during the process. In both

In these cases, the temperature of the zone and the average temperature of the alloying electrode are kept constant and equal to the value specified by the technology.

The method allows to maintain the temperature of the electrode only by adjusting the duration of the second pulse of the process current, as a result, the quality and performance of the treatment are increased. Compared to the prototype, the productivity is increased 2.4 times, the quality due to the increase in the continuity of the doped layer - 1.3 times.

Claims (1)

Claims Electro-processing method, which includes periodic excitation of the discharge between the electrode and the workpiece, at which the electrode temperature is controlled, characterized in that, in order to improve the performance and quality of treatment with electro-erosion doping, the pulses are fed in pairs in a cycle and change the duration of each second pulse back proportional to the temperature of the electrode. A2 BUT ft II A3 L7 l 1 P P TO;  th "; /