Electric spark multivariable self-adaptive efficient machining control system and method

Abstract

The invention belongs to a non-traditional machining electric spark machining technology in the field of manufacturing, and discloses an electric spark multivariable self-adaptive efficient machining control system. The control system comprises an interelectrode discharge pulse distinguishing module, a gap machining state detection module, a gap environment machining state detection module, a gap voltage control module, a cutter lifting period control module and a pulse interval duration control module. By means of the method, the breakdown strength of spark liquid can be effectively maintained under various machining conditions, the probability of abnormal discharge is reduced, the machining process is stable, the discharge efficiency and the machining efficiency are high, and by establishing a corresponding machining process mathematical model and a control strategy, according to the machining condition of the discharge gap, the machining efficiency is improved. The optimal electric gauge calibration parameter configuration under the current machining condition is obtained, the electric gauge calibration parameters are adaptively changed and controlled in real time, and therefore the stable and efficient machining purpose is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of special machining electric spark machining in the manufacturing field, and specifically relates to an electric spark multivariable adaptive high-efficiency machining control system and method. Background Art

[0002] Electrospark machining refers to a method of using a pulse power supply to continuously generate pulsed spark discharge between the electrode and the workpiece, locally generating instantaneous high temperature to erode the workpiece material;

[0003] The EDM process is a nonlinear weak steady-state process. Fixed electrical alignment parameters cannot suppress the occurrence of harmful pulses between electrodes under harsh processing conditions, resulting in carbon deposits and burns to the workpiece. Due to the high discharge frequency and small machining gap in the EDM process, accompanied by complex electrical, thermal, liquid, vaporization and other phenomena, unstable machining states are very likely to occur. At this time, continuous arc pulses are generated between the electrodes, carbon deposits form on the electrodes, and the machining efficiency is greatly reduced. In severe cases, the workpiece surface will be burned and the workpiece will be scrapped.

[0004] One of the invention patents disclosed so far is to construct a control model by coupling the least square method with the pole configuration method, and to adjust the tool lifting cycle according to the control signal calculated by the control model to avoid entering the harmful processing stage; the other is an adaptive control method for EDM based on 2-step-ahead prediction, which realizes real-time adjustment of the tool lifting cycle by online identification of process parameters and using the online identified process parameters to obtain the control signal according to the control model and the current discharge state to avoid deterioration of the processing state;

[0005] Although the above two methods can simply adjust the tool lifting cycle, 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 circuiting. Therefore, the adjustment of the tool lifting cycle has limited effect on maintaining the stability of the EDM process, especially in harsh processing environments. Therefore, the present application designs a new EDM multivariable adaptive and efficient processing control system and method. Summary of the invention

[0006] The purpose of the present invention is to provide an EDM multivariable adaptive high-efficiency machining control system and method to solve the problems raised in the above background technology.

[0007] In order to achieve the above-mentioned object, the present invention provides the following technical solutions: an electrospark multivariable adaptive high-efficiency machining control system, the control system comprising: an inter-electrode discharge pulse identification module, a gap machining state detection module, a gap voltage control module, a gap machining environment state detection module, a tool lifting cycle control module, and a pulse interval duration control module;

[0008] The inter-electrode discharge state identification module: according to the characteristics of various discharge pulses, different discharge states are identified by setting voltage and current thresholds; the discharge state includes discharge pulses and pulse intervals;

[0009] The gap voltage control module controls the gap voltage and thus controls the appropriate gap distance to obtain the corresponding discharge pulse;

[0010] The gap processing state detection module detects the processing state in real time and feeds back to the gap voltage control module, thereby controlling the gap processing state by controlling the gap distance;

[0011] The in-gap machining environment state detection module detects the quality of the inter-electrode machining environment state to avoid excessive metal chips directly reducing the breakdown strength of the spark liquid;

[0012] The tool lifting cycle control module: detects the time from the last tool lifting to the next tool lifting. The tool lifting cycle determines the quality of the inter-electrode machining environment state;

[0013] The pulse interval duration control module controls the pulse interval duration to ensure sufficient deionization time for the spark liquid and provide a good discharge environment.

[0014] Preferably, the discharge pulse includes five forms: spark discharge pulse τ spark 、Transient arc pulse τ tran，arc 、Steady-state arc pulse τ stab，arc 、Short circuit pulse τ short and open circuit pulse τ open ;

[0015] Among them, the spark discharge pulse and the transient arc pulse are effective processing pulses τ effec ; Steady-state arc pulse and short-circuit pulse are harmful processing pulses τ del .

[0016] Preferably, the spark liquid breakdown strength is affected by three factors: the gap distance, the amount of metal chips retained in the gap, and the degree of deionization of the spark liquid after discharge;

[0017] The corresponding discharge pulse is obtained by adjusting the appropriate gap distance. The gap voltage determines the gap distance, and the gap voltage is selected as the control variable for adjusting the form of the discharge pulse.

[0018] Preferably, the knife lifting cycle is divided into two parts: discharge time and knife lifting time, and the knife lifting cycle determines the quality of the inter-electrode discharge condition.

[0019] Preferably, the control variable of the EDM high-efficiency adaptive control system is the gap voltage X sv (t), knife lifting cycle X DN (t) and pulse interval time X OFF (t).

[0020] Preferably, the control method comprises the following steps:

[0021] Step 1: Sampling and threshold comparison: Collect the voltage and current data in the gap, compare the collected voltage and current data with the preset threshold, and identify the various pulses in the gap through comparison;

[0022] Step 2: Count pulse ratio: Count the number of harmful discharge pulses, count the total number of the entire discharge pulses, calculate the ratio of the harmful discharge pulses to the entire discharge pulses, and thus obtain the current processing state;

[0023] Step 3: Calculate the control variable: According to the adaptive control rate, determine the calculation method of the control variable, and use the adaptive control rate and the current processing state to calculate the control variable;

[0024] Step 4: Transmitting control variables: Transmitting the calculated control variable data to the mainframe of the EDM control cabinet;

[0025] Step 5: Change the electrical standard parameters: The EDM control cabinet host adjusts the corresponding electrical standard parameters according to the received control variable data to achieve precise control of the EDM process.

[0026] Preferably, the step 3 further comprises inputting the expected value of the processing state σ before determining the calculation method of the control variable. me (t) and the expected value of the gap environment state σ enve (t).

[0027] Preferably, the control variables of step three include gap voltage, electrode discharge time and pulse interval electrical standard parameter values.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention can effectively maintain the breakdown strength of the spark liquid under various processing conditions through this method, reduce the probability of abnormal discharge, stabilize the processing process, and have high discharge efficiency and processing efficiency; because of the adaptive control of deionization, the loss of the electrode is greatly reduced. It is actually verified that the electrode loss rate of the nickel-based high-temperature alloy GH4169 is sharply reduced compared with conventional EDM, between 0.6% and 0.7%. At the same time, in response to the requirements of different workpiece materials and different processing difficulties, the multivariable adaptive control system can more flexibly adapt to changes in processing conditions, and the control system greatly improves the processing capability of EDM.

[0030] 2. The present invention realizes stable and efficient EDM in a harsh machining environment. By controlling the breakdown strength of the spark fluid in the EDM gap (the gap between the machining electrode and the workpiece, referred to as the inter-electrode gap), the effective discharge pulse is maximized, especially the transient arc pulse (a type of effective discharge pulse) with the highest machining efficiency is increased, the probability of harmful discharge pulses is reduced, and the stability of the machining process is ensured, thereby achieving a stable and efficient machining method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of five different forms of discharge pulse voltage and current of the present invention;

[0032] Figure 2 This is a schematic diagram of the principle of the multivariable adaptive control system for electric sparks of the present invention;

[0033] Figure 3 A schematic diagram of the EDM machining assisted by the EDM multivariable adaptive control system of the present invention;

[0034] Figure 4 It is a comparison diagram of the open-loop machining and multivariable adaptive machining GH4169 of the present invention;

[0035] Figure 5 This is a state diagram of conventional electrospark machining of the present invention;

[0036] Figure 6 It is a processing state diagram under the multivariable adaptive control system of the present invention;

[0037] Figure 7 This is a diagram of the digital processing process of area A in the initial stage of the present invention;

[0038] Figure 8 This is a diagram of the digital processing process of area B in the conventional stage of the present invention;

[0039] Fig. 9 This is a diagram of the digital processing process of area C in the conventional stage of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figures 1 to 9 As shown, the embodiment of the present invention provides an EDM multivariable adaptive high-efficiency machining control system, which includes: an inter-electrode discharge pulse identification module, a gap voltage control module, a gap machining state detection module, a gap machining environment state detection module, a tool lifting cycle control module, and a pulse interval duration control module;

[0042] The inter-electrode discharge state identification module: according to the characteristics of various discharge pulses, different discharge states are identified by setting voltage and current thresholds; the discharge state includes discharge pulses and pulse intervals;

[0043] The gap voltage control module controls the gap voltage and thus controls the appropriate gap distance to obtain the corresponding discharge pulse;

[0044] Gap processing state detection module: by detecting the pulses appearing in the gap, counting the processing state, and feeding back to the gap voltage control module, the gap processing state is regulated by controlling the gap distance;

[0045] The in-gap machining environment state detection module detects the quality of the inter-electrode machining environment state to avoid excessive metal chips directly reducing the breakdown strength of the spark liquid;

[0046] The knife lifting cycle control module: detects the time from the last knife lifting to the next knife lifting. The knife lifting cycle determines the quality of the inter-electrode discharge condition.

[0047] The pulse interval duration control module controls the pulse interval duration to ensure sufficient deionization time for the spark liquid and provide a good discharge environment.

[0048] Among them, the discharge pulse includes five forms: spark discharge pulse τ spark 、Transient arc pulse τ tran，arc 、Steady-state arc pulse τ stab,arc 、Short circuit pulse τ short and open circuit pulse τ open ;

[0049] Among them, the spark discharge pulse and the transient arc pulse are effective processing pulses τ effec , the erosion of workpiece material is mainly due to the effective processing pulse; the steady-state arc pulse and short-circuit pulse are harmful processing pulses τdel , the burns on the workpiece surface are caused by these two pulses; while the open circuit pulse does not discharge and is an invalid processing pulse.

[0050] Processing status m (t) is the ratio of the number of harmful discharge pulses to the total number of pulses per unit time; the gap environment state σ env (t) is defined as a quantitative gap environment index (also called inter-electrode discharge condition), which has a functional relationship with the current and previous processing states and has a certain correlation.

[0051] The spark liquid breakdown strength is affected by three factors: the gap distance, the amount of metal chips retained in the gap, and the degree of deionization of the spark liquid after discharge;

[0052] The corresponding discharge pulse is obtained by adjusting the appropriate gap distance. The gap voltage determines the gap distance, and the gap voltage is selected as the control variable for adjusting the form of the discharge pulse.

[0053] During the EDM process, the breakdown strength of the spark fluid determines the type of discharge pulse in the gap. When the breakdown strength of the spark fluid is strong, the discharge pulse is mostly a spark discharge pulse; when the breakdown strength of the spark fluid is medium, most of the discharge pulses are transient arc pulses; if the breakdown strength of the spark fluid is weak, most of the discharge pulses are steady-state arc pulses and short-circuit pulses. Therefore, the breakdown strength of the spark fluid is an important indicator for measuring the gap discharge condition. The breakdown strength of the spark fluid is mainly affected by three factors: the gap distance, the amount of metal chips retained in the gap, and the degree of deionization of the spark fluid after discharge.

[0054] The amount of metal chips in the gap is also an important factor affecting the breakdown strength of the spark liquid. The metal chips generated by processing are mainly moved out of the gap through the explosive force of pulse discharge and the periodic lifting movement of the electrode. As the processing proceeds, 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 liquid, which in turn leads to the generation of harmful pulses, which is not conducive to processing.

[0055] The degree of spark liquid deionization refers to the degree of recovery from the ionized state to the deionized state during the pulse interval after a discharge pulse ends. Insufficient deionization will reduce the breakdown strength of the local spark liquid in the gap and increase the probability of steady-state arcing or short-circuit pulses. Therefore, the pulse interval must be long enough to allow the spark liquid to be fully deionized to provide a good discharge environment.

[0056] The knife lifting cycle is divided into two parts: discharge time and knife lifting time. The knife lifting cycle determines the quality of the inter-electrode discharge condition.

[0057] The knife lifting cycle refers to the time from the last knife lifting to the next knife lifting, which is divided into two parts: discharge time and knife lifting time. The knife lifting time is basically fixed. The longer the discharge time, the more metal chips are generated in a knife lifting cycle. Therefore, the knife lifting cycle determines the quality of the inter-electrode discharge condition. Therefore, the knife lifting cycle is selected as the key variable to control the breakdown strength of the spark liquid.

[0058] Among them, the control variable of the EDM high-efficiency adaptive control system is the gap voltage X sv (t), knife lifting cycle X DN (t) and pulse interval time X OFF (t).

[0059] The control method includes the following steps:

[0060] Step 1: Sampling and threshold comparison: Collect the voltage and current data in the gap, compare the collected voltage and current data with the preset threshold, and identify the various pulses in the gap through comparison;

[0061] Step 2: Count pulse ratio: Count the number of harmful discharge pulses, count the total number of the entire discharge pulses, calculate the ratio of the harmful discharge pulses to the entire discharge pulses, and thus obtain the current processing state;

[0062] Step 3: Calculate the control variable: According to the adaptive control rate, determine the calculation method of the control variable, and use the adaptive control rate and the current processing state to calculate the control variable;

[0063] Step 4: Transmitting control variables: Transmitting the calculated control variable data to the mainframe of the EDM control cabinet;

[0064] Step 5: Change the electrical standard parameters: The EDM control cabinet host adjusts the corresponding electrical standard parameters according to the received control variable data to achieve precise control of the EDM process.

[0065] Wherein, the step 3 also includes inputting the expected value of the processing state σ before determining the calculation method of the control variable me (t) and the expected value of the gap environment state σ enve (t).

[0066] The control variables of step three include gap voltage, pulse closing time, electrode discharge time and pulse interval electrical standard parameter value.

[0067] Experimental verification of system processing capability:

[0068] Processing blind holes, a closed surface, can verify the control system's ability to perform stable processing when chip evacuation is poor.

[0069] In order to verify whether the system is executed according to the designed control strategy and to check whether the EDM performance under this system is improved, a set of comparative verification experiments were carried out. In experiment 1, the discharge state detection system was used to observe the different stages of the entire open-loop machining process without an adaptive control system. In experiment 2, the adaptive control strategy was tested under multivariable adaptive control to verify its ability to adjust when the working conditions change.

[0070] The experiment used a graphite electrode with a diameter of 16 mm and the workpiece was a nickel-based high-temperature alloy GH4169. The two experiments were consistent except for the control variables, and the selected parameters were the medium-energy electrical parameters commonly used in actual processing.

[0071] Processing actual picture Figure 4 As shown, the left side is the cross section of the conventional EDM hole, the processing depth is only 20.3mm, and arcing occurs, and processing cannot continue; the right side is the cross section of the multivariable adaptive processing hole, the processing depth reaches the set 70mm and no arcing occurs.

[0072] The processing state of the traditional open-loop experiment is as follows Figure 5 As shown in the figure. The figure shows the change curve of the machining state during the machining process, and the horizontal axis is the number of tool lifts, which is used to characterize the machining process. In order to more clearly analyze the changes in the open-loop machining process, the entire machining process is divided into the initial stage, the conventional stage, and the arc drawing stage. Among them, the average value of the machining state in the initial stage is 0.0152. It can also be seen from the figure that the machining state is stable in this stage, the breakdown strength of the spark liquid in the gap is high, and the discharge is mainly effective discharge pulses. In the conventional stage, the average value of the machining state is 0.144. This is due to the increase in machining depth and time, the gradual accumulation of metal chips and heat in the gap, the decrease in the breakdown strength of the spark liquid in the gap, resulting in an increase in harmful discharge pulses and an increase in the frequency of their occurrence. In the final arc drawing stage, the average value of the machining state is 0.547. The discharge pulse is mainly harmful discharge pulses, the breakdown strength of the spark liquid in the gap is too low, and the machining can no longer proceed. The electrode carbon deposits arc and burns the workpiece surface. The final machining depth stays at 20.3mm.

[0073] The machining process under multivariable adaptive control is as follows Figure 6 As shown, under the multivariable adaptive control, during the processing with a set processing depth of 70 mm, there was no burning of the electrode and the workpiece due to arcing.

[0074] In the initial stage, the average value of the processing state is 0.017, and the average value of the gap environment state is 0.0165, which is the expected value. The processing state is stable, such as Figure 7As shown in the figure. In the conventional stage, the machining state value and the gap environment state value gradually increase with the machining depth and machining time, the proportion of harmful discharge pulses increases, and the breakdown strength in the gap gradually decreases. However, compared with the traditional open-loop machining, the average machining state value under the multivariable adaptive control system is 0.065, and the average gap state value is 0.052, which are lower than the traditional open-loop. Figure 8 shown.

[0075] From the above description, it can be concluded that the multivariable adaptive control system established by the present invention can adjust the control variables in real time during the processing at different stages according to the formulated adaptive control strategy to balance the stability and efficiency of the processing.

[0076] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0077] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. EDM multivariable adaptive high-efficiency machining control system, characterized by: The control system includes: an inter-electrode discharge pulse identification module, a gap processing state detection module, a gap processing environment state detection module, a gap voltage control module, a tool lifting cycle control module, and a pulse interval duration control module; The inter-electrode discharge pulse identification module: according to the characteristics of various discharge pulses, different discharge states are identified by setting voltage and current thresholds; the discharge state includes discharge pulses and pulse intervals; Gap processing state detection module: It detects the processing state in real time during the processing and feeds it back to the gap voltage control module, and regulates the processing state by controlling the gap distance; The processing environment state detection module: detects the balance between the generation and discharge of metal chips to judge the quality of the processing environment, and avoids excessive metal chips directly reducing the breakdown strength of the spark liquid; The gap voltage control module controls the gap voltage and thus controls the appropriate gap distance to obtain the corresponding discharge pulse; The knife lifting cycle control module: detects the time from the last knife lifting to the next knife lifting. The knife lifting cycle determines the quality of the inter-electrode discharge environment. The pulse interval duration control module controls the pulse interval duration to ensure sufficient deionization time for the spark liquid and provide a good discharge environment.

2. The multivariable adaptive high-efficiency EDM machining control system according to claim 1 is characterized in that: The discharge pulse includes five forms: spark discharge pulse τ spark 、Transient arc pulse τ tran,arc 、Steady-state arc pulse τ stab,arc 、Short circuit pulse τ short and open circuit pulse τ open ; Among them, the spark discharge pulse and the transient arc pulse are effective processing pulses τ effec ; Steady-state arc pulse and short-circuit pulse are harmful processing pulses τ del .

3. The multivariable adaptive high-efficiency EDM machining control system and method according to claim 1, characterized in that: The spark liquid breakdown strength is affected by three factors: the gap distance, the amount of metal chips retained in the gap, and the degree of deionization of the spark liquid after discharge; The corresponding discharge pulse is obtained by adjusting the appropriate gap distance. The gap voltage determines the gap distance, and the gap voltage is selected as the control variable for adjusting the form of the discharge pulse.

4. The multivariable adaptive high-efficiency EDM machining control system and method according to claim 1, characterized in that: The tool lifting cycle is divided into two parts: discharge time and tool lifting time. The tool lifting cycle determines the quality of the inter-electrode machining environment state.

5. The multivariable adaptive high-efficiency EDM machining control system and method according to claim 1, characterized in that: The control variable of the EDM high-efficiency adaptive control system is the gap voltage X sv (t), knife lifting cycle X DN (t) and pulse interval time X OFF (t).

6. The multivariable adaptive high-efficiency EDM machining control method according to claims 1-5, characterized in that: The control method comprises the following steps: Step 1: Sampling and threshold comparison: Collect the voltage and current data in the gap, compare the collected voltage and current data with the preset threshold, and identify the various pulses in the gap; Step 2: Count pulse ratio: Count the number of harmful discharge pulses, count the total number of the entire discharge pulses, calculate the ratio of the harmful discharge pulses to the entire discharge pulses, and thus obtain the current processing state; Step 3: Calculate the control variable: According to the adaptive control rate, determine the calculation method of the control variable, and use the adaptive control rate and the current processing state to calculate the control variable; Step 4: Transmitting control variables: Transmitting the calculated control variable data to the mainframe of the EDM control cabinet; Step 5: Change the electrical standard parameters: The EDM control cabinet host adjusts the corresponding electrical standard parameters according to the received control variable data to achieve precise control of the EDM process.

7. The multivariable adaptive high-efficiency EDM machining control method according to claim 6, characterized in that: The step 3 also includes inputting the expected value of the processing state σ before determining the calculation method of the control variable me (t) and the expected value of the gap environment state σ enve (t).

8. The multivariable adaptive high-efficiency EDM machining control method according to claim 6, characterized in that: The control variables of step three include gap voltage, electrode discharge time and pulse interval electrical standard parameter value.

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