Intelligent electric spark machine tool control method

Abstract

The invention belongs to the technical field of electric spark machine tools, and discloses an intelligent electric spark machine tool control method, which comprises the following steps of: setting an interface module to convert signal line strong current led from an electrode end and a workpiece end of a machine tool into weak current, connecting the weak current to an acquisition card to acquire voltage and current signal data, and performing electromagnetic interference signal isolation processing on the weak current part; the accuracy is ensured; voltage and current thresholds are set at a system end to distinguish various discharge pulses, and a discharge state is used for replacing a harmful discharge rate; 2-3 electrical gauge parameters of the gap voltage, the cutter lifting period and the pulse interval are adjusted in real time, so that the gap spark liquid breakdown strength with the highest machining efficiency is kept, electrode carbon deposition is avoided, and the stable and efficient machining requirements are met. It can be guaranteed that the gap spark liquid breakdown strength between the electrode and the workpiece is suitable for electric spark pulse discharge, carbon deposition is avoided, and the discharge efficiency and the machining efficiency are optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric discharge machining tools, and particularly relates to a control method for an intelligent electric discharge machining tool. Background Art

[0002] Electric discharge machining refers to a method in which pulsed sparks are continuously generated between an electrode and a workpiece through a pulsed power supply, and the workpiece material is locally removed by instantaneous high temperature erosion. This method belongs to non-contact machining, has no macroscopic acting force, and in the machining process, the mechanical properties such as hardness and strength of the machining material can be not considered, and any conductive material can be machined.

[0003] However, due to the high discharge frequency, small machining gap, and complex phenomena such as electricity, heat, liquid, and vaporization during the electric discharge machining process, an unstable machining state is extremely likely to occur. At this time, continuous arc pulses are generated between the electrodes, carbon deposition occurs on the electrodes, and the machining efficiency is greatly reduced. In severe cases, the surface of the workpiece will be burned and the workpiece will be scrapped. Especially for superalloys, due to the high melting point and poor thermal conductivity of some superalloys, the discharge state changes greatly during the machining process, and carbon deposition and arcing are likely to occur, burning the workpiece.

[0004] Experiments show that the parameters that have a greater impact on the stability of electric discharge machining are the gap voltage, the retraction cycle, and the pulse interval. The gap voltage is proportional to the gap distance, and the gap voltage determines the amount of metal chips per unit volume in the gap.

[0005] A large gap voltage indicates a large gap distance, a small content of metal chips per unit volume, and a large breakdown strength of the gap spark liquid; a small gap voltage indicates a small gap distance, a large content of metal chips per unit volume, and a small breakdown strength of the gap spark liquid.

[0006] The breakdown strength of the gap spark liquid determines the types of discharge pulses that appear in the gap. The larger the retraction cycle, the longer the discharge time, the more metal chips are generated, and the more metal chips accumulate in the gap, and vice versa. The deionization after pulsed discharge also determines the strength of the local spark liquid during discharge. When the deionization is sufficient, the breakdown strength of the spark liquid is restored, and the subsequent discharge pulses are effective discharge pulses; when the deionization is insufficient, the breakdown strength of the spark liquid cannot be restored, and the subsequent discharge pulses are harmful discharge pulses. The pulse interval electrical parameter determines whether the deionization is sufficient or not.

[0007] To maintain a stable electric discharge machining condition, an effective method is to establish a closed-loop control system, and change the relevant electrical parameters in real time during the machining process to avoid entering a harmful machining condition.

[0008] One of the invention patents currently disclosed is to construct a control model by coupling the least squares method with the pole configuration method, and adjust the tool lifting cycle in real time to avoid entering the harmful processing stage; the other is a control method based on advance prediction developed on this basis to achieve real-time adjustment of the tool lifting cycle to avoid deterioration of the processing state. Although the tool lifting cycle determines the amount of metal chips generated in the gap, in the middle and late stages of processing, as the metal chips and heat generated by the discharge accumulate in the gap, the processing environment gradually becomes harsh. Even if the tool lifting cycle is reduced to a minimum, metal chips will still be generated in the gap. These metal chips will make the processing process more unstable, resulting in arcing and short circuits. Therefore, the adjustment of the tool lifting cycle is limited to maintaining the stability of the EDM process, especially in harsh processing environments. It is difficult to play a role. Summary of the invention

[0009] In order to overcome the above technical problems, the present invention provides an intelligent EDM machine tool control method.

[0010] The present invention adopts the following technical solutions: Intelligent EDM machine tool control method, The interface module is set to convert the strong current of the signal line from the electrode end and the workpiece end of the machine tool into weak current, and then connect it to the acquisition card to collect voltage and current signal data, and isolate the weak current part from electromagnetic interference signal processing to ensure accuracy; The system side sets voltage and current thresholds to distinguish various discharge pulses and replace harmful discharge rates with discharge states; 2~3 of the three electrical standard parameters, namely gap voltage, tool lifting period and pulse interval, are adjusted in real time to maintain the gap spark liquid breakdown strength with the highest processing efficiency and avoid electrode carbon deposition, so as to achieve stable and efficient processing requirements.

[0011] Preferably, optocoupler isolation is used to completely isolate the analog signal at the input end from the digital signal at the output end.

[0012] Preferably, the actual analog signal is proportionally reduced using the voltage division principle.

[0013] Preferably, three combinations of multiple electrical calibration parameters that change in real time are set, represented by MAD; the first is to change two electrical calibration parameters, gap voltage SV and pulse interval OFF, in real time; the second is to change two electrical calibration parameters, knife lift period DN and pulse interval OFF, in real time; the third is to change three electrical calibration parameters, gap voltage SV, knife lift period DN and pulse interval OFF, in real time.

[0014] Preferably, the process control reference parameters MS and JS are set during the processing preparation stage and displayed on the processing screen.

[0015] Preferably, workpiece material settings, electrode material, and electrode quantity settings are added to the processing settings.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention can adaptively adjust multiple electrical parameter settings of the machine tool in real time according to the processing state of the discharge gap between the electrode and the workpiece and the processing environment state, ensuring that the breakdown strength of the spark fluid in the gap between the electrode and the workpiece is suitable for the electric discharge machining pulse discharge, avoiding carbon deposition, and optimizing the discharge efficiency and processing efficiency; The present invention can process various conductive materials, with a stable processing process, high pulse discharge efficiency, and high processing efficiency; for single-electrode processing, the processing efficiency is more than twice that of ordinary electric discharge machining; for single-electrode processing, the processing capacity is more than five times that of ordinary electric discharge machining; for multi-electrode processing, it is more than ten times that of ordinary electric discharge machining; difficult-to-process materials (conductive materials) that are difficult to process by ordinary electric discharge machining, such as nickel-based superalloy materials, titanium alloy materials, tungsten alloy materials, etc., can be stably and efficiently processed by the present invention; The electrode loss is small. For example, the loss rate of the graphite electrode is less than 1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the principle of the interface module; Figure 2 is a schematic diagram of the voltage and current signals after the actual discharge signal of the discharge gap passes through the interface module; Figure 3 is a schematic diagram of multiple electrical parameter settings that change in real time during the processing Figure 1 ; Figure 4 is a schematic diagram of multiple electrical parameter settings that change in real time during the processing Figure 2 ; Figure 5 is a schematic diagram of multiple electrical parameter settings that change in real time during the processing Figure 3 ; Figure 6 is a schematic diagram of the MAD of the combination form of multiple electrical parameter settings that change in real time; Figure 7 is a schematic diagram of the processing control reference parameters MS and JS; Figure 8 is a schematic diagram of the workpiece material options; Figure 9 is a schematic diagram of the electrode material options; Figure 10 is a schematic diagram of the number of electrodes filled in. DETAILED DESCRIPTION OF THE INVENTION

[0018] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings. Unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments are conventional methods in the art unless otherwise specified. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0019] By monitoring and identifying the current signal and voltage signal generated by the interelectrode discharge pulse, the present invention classifies five types of discharge pulse signals into effective discharge pulses and harmful discharge pulses. The effective discharge pulses play a major role in the erosion of the material, while the harmful discharge pulses indicate the deterioration of the machining process and should be controlled.

[0020] The processing machine can adaptively adjust multiple machine electrical parameter settings in real time according to the machining state and machining environment state of the discharge gap between the electrode and the workpiece, ensuring that the breakdown strength of the spark fluid in the gap between the electrode and the workpiece is suitable for the electrospark pulse discharge, avoiding carbon deposition, and optimizing the discharge efficiency and machining efficiency.

[0021] By monitoring and calculating the machining conditions in real time, the shaping machine can adjust two or three of the electrical parameter settings of the gap voltage, retraction cycle, and pulse interval in real time according to the process requirements, so as to maintain the breakdown strength of the spark fluid in the gap with the highest machining efficiency, while avoiding the occurrence of electrode carbon deposition, in order to meet the requirements of stable and efficient machining.

[0022] The present invention has the following several functions: Function 1: Interface module for strong / weak electricity conversion and isolation of electromagnetic interference signals Generally, electrospark machining uses strong electricity for machining and needs to convert strong electricity into weak electricity. At the same time, during the machining process, electromagnetic interference signals cannot enter the weak electricity system and must be isolated, which is completed by the interface module. The schematic diagram of the interface module is as Figure 1 shown.

[0023] During the actual electrospark discharge machining process, the voltage change range of the signal lines led out from the electrode end and the workpiece end is 0 - 250V, while the maximum input range of the acquisition card is ±3V. To meet the reasonable output relationship, the actual analog signal is scaled down proportionally using the voltage division principle.

[0024] The isolation of electromagnetic interference signals uses optocoupler isolation. Optocoupler isolation can completely isolate the analog signal at the input end and the digital signal at the output end of the detection system through the conversion of optoelectronic signals, reducing environmental interference signals. In addition, since the input impedance of the optoelectronic coupling is less than the internal resistance of the interference source, the interference signal superimposed on the measured signal is greatly attenuated and basically cannot enter the measurement system, thus ensuring the measurement accuracy. Figure 2They are the voltage and current signals after the actual discharge signal between the electrodes passes through the interface module.

[0025] Function 2: Obtain the discharge state between the electrodes during the machining process: Generally, there are five types of discharge pulses in the inter-electrode gap during EDM: spark discharge pulse, transient arcing pulse, steady-state arcing pulse, short-circuit pulse, and open-circuit pulse. According to the collected voltage and current signal data, by setting voltage and current thresholds to distinguish various discharge pulses, and using the discharge state to replace the harmful discharge rate.

[0026] Function 3: Real-time adjustment of multi-electrical parameter (industry development bottleneck), which can be displayed on the display screen during machining, such as Figure 3 、 4 、5: The breakdown strength of the spark liquid determines the type of discharge pulse in the gap.

[0027] When the breakdown strength of the spark liquid is strong, the discharge pulses are mostly spark discharge pulses; When the breakdown strength of the spark liquid is medium, most of them are transient arcing pulses; When the breakdown strength of the spark liquid is weak, most of the discharge pulses are steady-state arcing pulses and short-circuit pulses.

[0028] The breakdown strength of the spark liquid is an important indicator to measure the discharge state in the gap. The breakdown strength of the spark liquid is mainly affected by three factors: gap distance, the amount of metal chips retained in the gap, and the degree of deionization of the spark liquid after discharge.

[0029] (1) The gap distance is the main factor determining the breakdown strength of the spark liquid. The larger the gap distance, the higher the breakdown strength of the spark liquid, and the more difficult it is to break down and form a discharge channel. At this time, the discharge pulses are mainly open-circuit pulses or spark discharge pulses; when the gap distance is appropriately shortened, it means that the breakdown strength of the spark liquid decreases. At this time, the discharge pulses in the gap are mainly transient arcing pulses accompanied by a small amount of spark discharge pulses; when the gap distance is further reduced, the discharge pulses will be dominated by harmful discharge pulses. Therefore, the corresponding discharge pulses can be obtained by adjusting the appropriate gap distance. The gap voltage determines the gap distance. Therefore, the gap voltage is selected as the control variable to adjust the form of the discharge pulse.

[0030] (2) The amount of metal chips in the gap is also an important factor affecting the breakdown strength of the spark fluid. The metal chips generated during machining are mainly removed from the gap through the blasting force of pulsed discharges and the periodic lifting movement of the electrode. As machining progresses, it is difficult to maintain a balance between the generation and discharge of metal chips. Once the discharge of metal chips is slower than the generation, the increasing amount of metal chips in the gap directly reduces the breakdown strength of the spark fluid, leading to the generation of harmful pulses and being unfavorable for machining. The lifting cycle refers to the time period from the previous electrode lift to the next start of electrode lift, which is divided into two parts: discharge time and lift time. The lift time is basically fixed. The longer the discharge time, the more metal chips are generated within one lifting cycle, which is more unfavorable for machining. Therefore, the lifting cycle determines the quality of the discharge state between the electrodes. Thus, the lifting cycle is selected as the key variable for controlling the breakdown strength of the spark fluid.

[0031] (3) The degree of deionization of the spark fluid refers to the degree of recovery from the ionized state to the deionized state during the pulse interval after the end of a discharge pulse. Insufficient deionization will reduce the breakdown strength of the local spark fluid in the gap and increase the probability of steady-state arcing or short-circuit pulses. Therefore, it is necessary to require that the pulse interval time be long enough to ensure sufficient deionization of the spark fluid to provide a good discharge environment.

[0032] To sum up, in order to maintain an appropriate breakdown strength of the spark fluid and reduce the probability of harmful discharge pulses, the gap voltage SV, the lifting cycle DN, and the pulse interval OFF are selected as the control electrical parameter settings for the process control of the intelligent EDM forming machine.

[0033] Function 4: There are three forms of multi-electrical parameter combinations that change in real time, represented by MAD, as Figure 6 shown and displayed on the display screen; 01 represents real-time change of two electrical parameter settings, namely the gap voltage SV and the pulse interval OFF; 02 represents real-time change of two electrical parameter settings, namely the lifting cycle DN and the pulse interval OFF; 03 represents real-time change of three electrical parameter settings, namely the gap voltage SV, the lifting cycle DN, and the pulse interval OFF; Function 5: The process control reference parameters MS and JS are set during the machining preparation stage and displayed on the machining process screen, as Figure 7 shown; Conventional EDM does not have the process control reference parameters MS and JS. MS: 1 - 26 JS: 1 - 26 Function 6: Add options for workpiece material setting and electrode material and quantity setting in the machining settings (1) As Figure 8 shown, the workpiece material options 1 Nickel-based superalloy 2 Titanium alloy 3 Steel 4 Others (2)Electrode material and quantity options, such as Figure 9 、 10 as shown 1 Graphite 2 Red copper 3 Others Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to the above embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. An intelligent EDM machine tool control method, characterized in that: The interface module is set to convert the strong current of the signal line from the electrode end and the workpiece end of the machine tool into weak current, and then connect it to the acquisition card to collect voltage and current signal data, and isolate the weak current part from electromagnetic interference signal processing to ensure accuracy; The system side sets voltage and current thresholds to distinguish various discharge pulses and replace harmful discharge rates with discharge states; 2~3 of the three electrical standard parameters, namely gap voltage, tool lifting period and pulse interval, are adjusted in real time to maintain the gap spark liquid breakdown strength with the highest processing efficiency and avoid electrode carbon deposition, so as to achieve stable and efficient processing requirements.

2. The intelligent electric discharge machining tool control method according to claim 1, characterized in that Optocoupler isolation is used to completely isolate the analog signal at the input end from the digital signal at the output end.

3. The intelligent electric discharge machining tool control method according to claim 1, characterized in that, The actual analog signal is proportionally reduced using the voltage division principle.

4. The intelligent electric discharge machining machine tool control method according to claim 1, characterized in that, Three combinations of multiple electrical calibration parameters that change in real time are set, represented by MAD; the first is to change two electrical calibration parameters, gap voltage SV and pulse interval OFF, in real time; the second is to change two electrical calibration parameters, knife lift period DN and pulse interval OFF, in real time; the third is to change three electrical calibration parameters, gap voltage SV, knife lift period DN and pulse interval OFF, in real time.

5. The intelligent electric discharge machining machine control method according to claim 1, characterized in that, Set the process control reference parameters MS and JS, which are set during the machining preparation stage and displayed on the machining process screen.

6. The intelligent electric discharge machining machine tool control method according to claim 1, characterized in that, Add workpiece material settings and electrode material and electrode quantity settings in the processing settings.

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