A current generation method to improve EDM efficiency and reduce surface defects

Abstract

The present invention discloses a current generation method for improving the efficiency of electric spark machining and reducing surface defects. The method comprises: applying voltage between a workpiece and an electrode, and when inter-electrode discharge is detected, obtaining superimposed pulse current waveforms of different pulse parameters by controlling the resistance and resistance action time in the access circuit; comparing the first performance values ​​corresponding to the superimposed pulse current waveforms of different superimposed positions, and determining the optimal superimposed pulse current waveform according to the first performance comparison result; comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of different pulse parameters, and determining the optimal superimposed pulse current parameters of the optimal superimposed pulse current waveform according to the second performance comparison result; and comparing the third performance values ​​corresponding to the superimposed pulse energy of different proportions, and determining the energy proportion of the optimal superimposed pulse current according to the third performance comparison result. This method can not only improve the efficiency of electric spark machining, but also reduce crack defects on the surface of electric spark machining.

Description

Technical Field

[0001] The invention relates to the technical field of electric spark machining, and in particular to a current generating method for improving the efficiency of electric spark machining and reducing surface defects. Background Art

[0002] Electrospark machining is an indispensable special machining technology in modern manufacturing technology. It processes materials by utilizing the electro-corrosion phenomenon generated by pulsed spark discharge between the tool electrode and the workpiece electrode in the dielectric. Because of its advantages of "softness over hardness, precision and micro-fineness, and realistic profiling", it plays an important role in the machining of parts with special requirements such as difficult-to-cut materials, special complex surfaces, fine surfaces, and low stiffness. It is currently widely used in aerospace, automobile, electronics and other fields. In electrospark machining, part of the molten material that is not removed will form a recast layer under the cooling effect of the medium. There will be some crack defects in the recast layer, which greatly reduces the fatigue life of the electrospark machined sample. This is because the presence of cracks reduces the two stages of fatigue failure - crack formation and crack propagation - to one crack propagation stage. In addition, the crack tip will also cause stress concentration, thereby reducing the service life of the sample. Compared with mechanical machining, the efficiency of electrospark machining is relatively low, which leads to a longer product production cycle. Therefore, improving the efficiency of EDM and reducing surface crack defects are of great significance to improving the economic benefits of enterprises.

[0003] There are many factors that affect the characteristics of EDM, such as machining polarity, discharge area, pulse parameters, material properties, etc. Among these factors, the pulse parameters have the greatest impact on the machining characteristics. At present, the discharge current waveform used in EDM is usually a rectangular current waveform. In EDM, the discharge maintenance voltage remains basically unchanged, so the pulse current and pulse width determine the size of the pulse energy. Increasing the pulse current or pulse width will lead to an increase in discharge energy, which usually leads to an increase in machining efficiency. However, surface defects will also usually increase. Correspondingly, although the cracks on the machined surface can be reduced by reducing the discharge energy of EDM, the machining efficiency is also greatly reduced. Therefore, it is difficult to reduce the defects on the machined surface while improving the machining efficiency by adjusting the discharge energy. In addition to the pulse energy having an important influence on EDM, the energy input method also has an important influence. For example, under the same pulse discharge energy, when the discharge energy is less than 0.2mJ, the material cannot be removed under the energy input method of long pulse width and low current, while the material can still be removed under the energy input method of high current and short pulse width. Since the voltage remains basically unchanged during EDM, the pulse current waveform determines the input process of pulse energy. Therefore, new discharge current waveforms can be developed to improve machining efficiency and reduce machining surface defects.

[0004] In summary, the currently used rectangular current waveform is difficult to improve machining efficiency while reducing surface defects. Therefore, it is necessary to develop a new discharge current waveform to improve EDM efficiency and reduce surface defects. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] To this end, an object of the present invention is to provide a current generation method for improving the efficiency of electrospark machining and reducing surface defects, so as to achieve the purpose of improving the efficiency of electrospark machining and reducing surface defects of electrospark machining.

[0007] Another object of the present invention is to provide a current generating device for improving the efficiency of electrospark machining and reducing surface defects.

[0008] To achieve the above object, an embodiment of the present invention provides a current generation method for improving the efficiency of electrospark machining and reducing surface defects, comprising:

[0009] A voltage is applied between the workpiece and the electrode. When inter-electrode discharge is detected, the superimposed pulse current waveform with different pulse parameters is obtained by controlling the resistance in the circuit and the resistance action time.

[0010] Comparing the first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions, and determining the optimal superimposed pulse current waveform according to the first performance comparison result;

[0011] Comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of the different pulse parameters, and determining the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; and,

[0012] The third performance values ​​corresponding to the superimposed pulse energies of different proportions are compared, and the energy proportion of the optimal superimposed pulse current is determined according to the third performance comparison result.

[0013] The current generation method for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention may also have the following additional technical features:

[0014] Furthermore, the superimposed pulse current waveform with different pulse parameters is obtained by controlling the resistance in the access circuit and the resistance action time, including: controlling the switch state of the transistor in the access circuit to determine the state parameters of the superimposed pulse current; and controlling the timing of the transistor switch and the number of access resistors to obtain the superimposed pulse current waveform with different pulse parameters.

[0015] Furthermore, the comparing the first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions and determining the optimal superimposed pulse current waveform according to the first performance comparison result also includes: obtaining the electric spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms; comparing the electric spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms, and determining the optimal superimposed pulse current waveform based on the electric spark performance value of the front superimposed pulse current waveform.

[0016] Furthermore, the pulse width in the optimal superimposed pulse current parameter is less than half of the overall pulse width.

[0017] Furthermore, the ratio of the superimposed pulse energy to the total pulse energy is 0%, 9%, 20% and 40%.

[0018] To achieve the above object, another embodiment of the present invention provides a current generating device for improving the efficiency of electrospark machining and reducing surface defects, comprising:

[0019] The superposition current acquisition module is used to apply voltage between the workpiece and the electrode. When the inter-electrode discharge is detected, the superposition pulse current waveform with different pulse parameters is obtained by controlling the resistance in the access circuit and the resistance action time.

[0020] An optimal current waveform determination module, used to compare first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions, and determine an optimal superimposed pulse current waveform according to the first performance comparison result;

[0021] A superimposed pulse current parameter determination module, used for comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of the different pulse parameters, and determining the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; and

[0022] The energy ratio determination module is used to compare the third performance values ​​corresponding to the superimposed pulse energies of different ratios, and determine the energy ratio of the optimal superimposed pulse current according to the third performance comparison result.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0025] Figure 1 A flow chart of a current generation method for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of a superimposed pulse current waveform according to an embodiment of the present invention;

[0027] Figure 3 is a schematic diagram of a current waveform control circuit according to an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of switching timing of a transistor according to an embodiment of the present invention;

[0029] Figure 5 Schematic diagram of different superimposed pulse current waveforms according to an embodiment of the present invention;

[0030] Figure 6 A comparison diagram of the surface morphology and processing efficiency of samples processed by a rectangular current waveform and a front superimposed pulse current waveform according to an embodiment of the present invention;

[0031] Figure 7 A schematic diagram of the structure of a current generating device for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0033] The following describes a current generation method and device for improving EDM efficiency and reducing surface defects according to an embodiment of the present invention with reference to the accompanying drawings.

[0034] First, a current generating method for improving the efficiency of electrical discharge machining and reducing surface defects according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0035] Figure 1 The present invention is a flow chart of a current generation method for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention.

[0036] like Figure 1 As shown, the current generation method for improving the efficiency of electrospark machining and reducing surface defects includes the following steps:

[0037] S1, applying voltage between the workpiece and the electrode. When the inter-electrode discharge is detected, the superimposed pulse current waveform with different pulse parameters is obtained by controlling the resistance in the circuit and the resistance action time.

[0038] S2, comparing first performance values ​​corresponding to superimposed pulse current waveforms at different superimposed positions, and determining an optimal superimposed pulse current waveform according to the first performance comparison result;

[0039] S3, comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of different pulse parameters, and determining the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; and

[0040] S4, comparing third performance values ​​corresponding to superimposed pulse energies of different proportions, and determining an optimal superimposed pulse current energy proportion according to the third performance comparison result.

[0041] As an example, generating Figure 2 The method of superimposing the pulse discharge current waveform shown is as follows:

[0042] like Figure 3 As shown in the figure, a certain voltage is applied between the workpiece and the electrode. When the inter-electrode discharge is detected, the control circuit is activated to generate a superimposed wave pulse current waveform by controlling the resistance size and action time in the circuit. In the superimposed pulse current waveform, the current size, rise or fall is controlled by controlling the transistor T r1 、T r2 ,…,T rn The t d , t p and t on This is achieved by controlling the timing of transistor switches ( Figure 3 ). Figure 4 An example of transistor switching timing for generating a superimposed wave pulse current waveform is shown, where the time between 5 and 6 (the apex of the current waveform) (i.e., the pulse width t of the superimposed pulse) p ) can be set to multiples of 1 microsecond. The time points at which each transistor turns on and off can be set at Figure 3 The pin positions on the program board shown in the figure can be set arbitrarily, and by changing the resistors R1, R2, ..., R n By changing the size of , the size of ΔI can be changed. By controlling the switching timing and the amount of resistance connected, the superimposed pulse current waveform with different pulse parameters can be obtained.

[0043] Furthermore, after obtaining the superimposed pulse current waveform by the above method, the waveform parameters for improving the EDM efficiency and surface defects were determined by EDM machining experiments, and the steps are as follows:

[0044] Firstly, the influence of pulse superposition position on processing efficiency and surface defects was clarified, and three typical superposition positions were selected ( Figure 5 ), that is, the front superimposed pulse current waveform ( Figure 5a), superimposed pulse current waveform ( Figure 5 b) and the post-superimposed pulse current waveform ( Figure 5 c). The experiment found that the front superimposed pulse current waveform has the highest processing efficiency and the least surface defects. As the superimposed pulse moves backward, the processing efficiency decreases and the surface defects increase. Compared with the rectangular current waveform with the same pulse discharge energy and pulse width, the front superimposed pulse current waveform has a higher processing efficiency and fewer surface defects. Since the front superimposed pulse current waveform has a better processing effect, this waveform can be used instead of the rectangular current waveform for processing. In order to determine the appropriate parameters of the front superimposed pulse current waveform, the following experiment was carried out.

[0045] Next, the effects of the parameters of the front superimposed pulse current (current size and pulse width) on machining efficiency and surface defects were studied. Here, other pulse parameters remain unchanged. The results show that with the increase of pulse current or pulse width, machining efficiency increases and surface defects also tend to increase. When the superimposed pulse energy is the same, different combinations of pulse current and pulse width will lead to differences in material removal rate and surface defects. Therefore, the combination of current and pulse width of the superimposed pulse has an important influence on EDM.

[0046] Then, based on the above, the superimposed pulse energy is kept constant, and the effects of different combinations of superimposed pulse current and pulse width parameters on processing efficiency and surface defects are experimentally studied. The results show that with the increase of pulse width (the decrease of superimposed pulse current), the processing efficiency shows a trend of first increasing and then decreasing, and the surface cracks gradually increase. It is particularly important that when the width of the superimposed pulse exceeds 1 / 2 of the overall pulse width, the surface cracks increase sharply, so it is best not to set the superimposed pulse width to more than half of the overall pulse width.

[0047] Finally, determine the proportion of superimposed pulse discharge energy. When the superimposed pulse energy is large, the material removal rate is also large, and the surface defects are reduced. However, the surface roughness will also be too large. Therefore, it is necessary to determine a suitable superimposed pulse energy ratio. Previous experiments have found that when the superimposed pulse width is about 1 / 2 of the total pulse width, the processing efficiency is high, the surface defects are relatively small, and the surface roughness is not too large. On the basis of setting the superimposed pulse width to 1 / 2 of the total pulse width, determine the appropriate proportion of superimposed pulse energy. Here, the proportion of superimposed pulse energy to total energy is taken as 0, 9%, 20%, and 40%. The results show that when the superimposed pulse discharge energy accounts for 20% of the total energy, the comprehensive processing effect is the best, that is, it has a higher material removal rate, fewer surface cracks, and appropriate roughness.

[0048] In summary, in order to improve the efficiency of EDM and reduce the crack defects on the surface of EDM, the front superimposed pulse current waveform can be used to replace the rectangular current waveform commonly used in current EDM for processing. When the energy of the superimposed pulse accounts for 20% of the total pulse energy and the superimposed pulse width is 1 / 2 of the total pulse width, a better processing effect can be obtained.

[0049] In order to further prove the effectiveness of the front superposition pulse current waveform and corresponding parameters in improving the EDM characteristics, an EDM experiment was carried out. The method for calculating the EDM efficiency is as follows: an electronic balance is used to measure the mass of the sample before and after EDM, and a stopwatch is used to record the processing time. The mass of material removed is divided by the processing time to obtain the processing efficiency. The surface defects are tested using a field emission electron scanning microscope. The parameters of the rectangular wave current waveform used are: pulse width of 19 microseconds, current of 2.2A, and pulse interval of 20 microseconds. According to the above-mentioned method for setting the parameters of the front superposition pulse discharge current waveform, the parameters of the front superposition pulse current waveform are set as follows: basic current I1 is 1.7A, superposition pulse current I2 is 1.1A, and superposition pulse width t p The pulse interval is 9 microseconds and the pulse interval is 20 microseconds. The experimental results show that the efficiency of EDM is increased by 59.6%, and the surface cracks are greatly reduced. Therefore, a front superimposed pulse current waveform is used instead of a rectangular current waveform for processing, and the current waveform parameters are set according to the above method. While improving the processing efficiency, the crack defects on the processing surface can be reduced. The embodiment of the present invention uses a front superimposed pulse current waveform instead of a traditional rectangular current waveform for processing. By adjusting the parameters of the pulse current waveform, high-efficiency and low-surface-defect EDM (such as Figure 6 The superimposed pulse current waveform includes two parts, namely a basic current part similar to a rectangular current waveform and a superimposed pulse current part.

[0050] The current generation method for improving the efficiency of electric spark machining and reducing surface defects proposed in the embodiment of the present invention can not only improve the efficiency of electric spark machining, but also reduce crack defects on the surface of electric spark machining.

[0051] Next, a current generating device for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0052] Figure 7 A schematic diagram of the structure of a current generating device for improving the efficiency of electrospark machining and reducing surface defects according to an embodiment of the present invention.

[0053] like Figure 7As shown, the current generating device 10 for improving the efficiency of electrospark machining and reducing surface defects includes: a superimposed current acquisition module 100, an optimal current waveform determination module 200, a superimposed pulse current parameter determination module 300 and an energy ratio determination module 400.

[0054] The superposition current acquisition module 100 is used to apply voltage between the workpiece and the electrode. When the inter-electrode discharge is detected, the superposition pulse current waveform with different pulse parameters is obtained by controlling the resistance in the access circuit and the resistance action time.

[0055] The optimal current waveform determination module 200 is used to compare the first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions, and determine the optimal superimposed pulse current waveform according to the first performance comparison result;

[0056] A superimposed pulse current parameter determination module 300, used to compare the second performance values ​​corresponding to the superimposed pulse current waveforms of the different pulse parameters, and determine the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; and

[0057] The energy ratio determination module 400 is used to compare the third performance values ​​corresponding to the superimposed pulse energies of different ratios, and determine the optimal superimposed pulse current energy ratio according to the third performance comparison result.

[0058] Furthermore, in one embodiment of the present invention, the superposition current acquisition module 100 is further used for:

[0059] Controlling the switch state of the transistor in the access circuit to determine the state parameters of the superimposed pulse current; and,

[0060] By controlling the timing of transistor switches and the number of connected resistors, superimposed pulse current waveforms with different pulse parameters are obtained.

[0061] Furthermore, in one embodiment of the present invention, the above-mentioned optimal current determination module 200 is also used for:

[0062] Obtain the spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms;

[0063] The spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms are compared, and the optimal superimposed pulse current waveform is determined based on the spark performance value of the front superimposed pulse current waveform.

[0064] Further, in one embodiment of the present invention, the pulse width in the optimal superimposed pulse current parameter is less than half of the overall pulse width.

[0065] Further, in one embodiment of the present invention, the ratio of the superimposed pulse energy to the total pulse energy is 0%, 9%, 20% and 40%.

[0066] It should be noted that the above explanation of the method embodiment is also applicable to the device of this embodiment, and will not be repeated here.

[0067] The current generating device for improving the efficiency of electric spark machining and reducing surface defects proposed in the embodiment of the present invention can not only improve the efficiency of electric spark machining, but also reduce crack defects on the surface of electric spark machining.

[0068] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0069] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0070] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for generating electric current to improve the efficiency of electrospark machining and reduce surface defects, characterized in that: The following steps are involved: A voltage is applied between the workpiece and the electrode. When inter-electrode discharge is detected, the superimposed pulse current waveform with different pulse parameters is obtained by controlling the resistance in the circuit and the resistance action time. Comparing the first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions, and determining the optimal superimposed pulse current waveform according to the first performance comparison result; Comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of the different pulse parameters, and determining the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; as well as, The third performance values ​​corresponding to the superimposed pulse energies of different proportions are compared, and the energy proportion of the optimal superimposed pulse current is determined according to the third performance comparison result.

2. The method according to claim 1, characterized in that The method of obtaining superimposed pulse current waveforms with different pulse parameters by controlling the resistance in the access circuit and the resistance action time includes: Controlling the switch state of the transistor in the access circuit to determine the state parameter of the superimposed pulse current; and, The timing of transistor switches and the number of connected resistors are controlled to obtain superimposed pulse current waveforms with different pulse parameters.

3. The method according to claim 1, characterized in that The comparing the first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions and determining the optimal superimposed pulse current waveform according to the first performance comparison result also includes: Obtain the spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms; The spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms are compared, and the optimal superimposed pulse current waveform is determined based on the spark performance value of the front superimposed pulse current waveform.

4. The method according to claim 1, characterized in that: The pulse width in the optimal superimposed pulse current parameter is less than half of the overall pulse width.

5. The method according to claim 1, characterized in that The ratio of the superimposed pulse energy to the total pulse energy is 0%, 9%, 20% and 40%.

6. A current generating device for improving the efficiency of electrospark machining and reducing surface defects, characterized in that: include: The superposition current acquisition module is used to apply voltage between the workpiece and the electrode. When the inter-electrode discharge is detected, the superposition pulse current waveform with different pulse parameters is obtained by controlling the resistance in the access circuit and the resistance action time. An optimal current waveform determination module, used to compare first performance values ​​corresponding to the superimposed pulse current waveforms at different superimposed positions, and determine an optimal superimposed pulse current waveform according to the first performance comparison result; A superimposed pulse current parameter determination module, used for comparing the second performance values ​​corresponding to the superimposed pulse current waveforms of the different pulse parameters, and determining the parameters of the optimal superimposed pulse current of the optimal superimposed pulse current waveform according to the second performance comparison result; as well as, The energy ratio determination module is used to compare the third performance values ​​corresponding to the superimposed pulse energies of different ratios, and determine the energy ratio of the optimal superimposed pulse current according to the third performance comparison result.

7. The device according to claim 6, characterized in that The superposition current acquisition module is also used for: Controlling the switch state of the transistor in the access circuit to determine the state parameter of the superimposed pulse current; and, The timing of transistor switches and the number of connected resistors are controlled to obtain superimposed pulse current waveforms with different pulse parameters.

8. The device according to claim 6, characterized in that The optimal current waveform determination module is further used for: Obtain the spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms; The spark performance values ​​corresponding to the front, middle and rear superimposed pulse current waveforms are compared, and the optimal superimposed pulse current waveform is determined based on the spark performance value of the front superimposed pulse current waveform.

9. The device according to claim 6, characterized in that The pulse width in the optimal superimposed pulse current parameter is less than half of the overall pulse width.

10. The device according to claim 6, characterized in that The ratio of the superimposed pulse energy to the total pulse energy is 0%, 9%, 20% and 40%.

Images