Adaptive Shaking Feed Method and System for High-Speed Electro-Discharge Machining of Small Holes

Abstract

The present invention discloses an adaptive rocking feed method and system applicable to high-speed small-hole electric discharge machining, belonging to the technical field of electro-machining control. The method includes: collecting in real time the short-circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the electric discharge machining process; the control terminal converts the servo feed and rocking machining of the machining system according to the preset thresholds of the effective feed amount and the short-circuit pulse ratio; the control terminal adaptively adjusts the rocking time and rocking frequency of the rocking machining system according to the circuit pulse duty ratio and the effective feed amount collected in real time during the electric discharge machining process. Starting from the rocking machining of high-speed small-hole electric discharge machining and combining it with the adaptive control algorithm, the present invention proposes an adaptive rocking feed algorithm for high-speed small-hole electric discharge machining, and takes the recast layer, which is the key quality index of air film cooling hole machining, as the core to explore a control scheme with high efficiency and the lowest recast layer.

Description

Technical Field

[0001] The present invention relates to the technical field of electric machining, and more particularly to an adaptive rocking feed method and system suitable for high-speed electric discharge machining of small holes. Background Art

[0002] With the development of electric machining technology, electric discharge machining has been widely applied in production due to its outstanding advantages such as high machining accuracy and low manufacturing cost. The electric discharge machining process is a weakly steady-state process. If the flushing or chip evacuation condition is poor during the machining process, the system will enter an unstable state and the discharge state fluctuation will increase, resulting in surface burning of the workpiece and affecting the machining efficiency. Therefore, how to control electric discharge machining is a key issue.

[0003] Traditional electric discharge rocking machining is to perform regular and periodic interpolation movements by the movement axis other than the main servo machining axis, which can effectively reduce the accumulation of machining chips in the discharge gap. Many scholars have carried out relevant research on this. Staelens et al. optimized the electric discharge rocking machining strategy. In the optimization scheme, the method of continuously measuring the eccentricity was used to calculate and adjust the pulse current and discharge time online, so that the discharge process always maintained the state of maximum energy input. Sanchez et al. studied the optimization method of multi-axis linkage electric discharge rocking machining. The calculation method of the rocking radius of each rocking axis was proposed, and the accuracy of the optimization strategy was analyzed. Experiments showed that multi-axis linkage rocking electric discharge machining can reduce the machining time and electrode wear. Sanchez et al. also carried out research on the rocking gap at the same time, providing a certain basis for adjusting and meeting the machining needs. Bamberg studied the micro-hole electric discharge rocking machining of micro electro-discharge machining. The results showed that flushing can improve the surface finish and significantly reduce the electrode wear; Yu Zuyuan et al. used the rocking method to improve the depth-to-diameter ratio of small hole machining, and at the same time used ultrasonic vibration-assisted rocking machining to reduce the viscous resistance in the discharge gap.

[0004] As an advanced control method, adaptive machining has also been widely applied in electric discharge machining in recent years. However, adaptive control is mainly applied to traditional electric discharge machining and wire electrical discharge machining, and there are relatively few adaptive control schemes for high-speed electric discharge machining of small holes.

[0005] It can be found through previous research that rocking machining and adaptive control mainly aim at traditional electric discharge and wire cutting machining, and there are very few applications for high-speed electric discharge machining of small holes; at the same time, these two are studied separately and independently by researchers, and the exploration of the combined effect has not been carried out; moreover, in the application of electric discharge of these three machining methods, it is mainly reflected in the machining efficiency and stability, and there is a great blank in the exploration of the influence on the recast layer.

[0006] Therefore, how to provide an adaptive rocking feed method and system for high-speed small-hole electric discharge machining, reduce the recast layer, and ensure the machining efficiency is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides an adaptive rocking feed method and system for high-speed small-hole electric discharge machining. Starting from the rocking machining of high-speed small-hole electric discharge machining and combining it with an adaptive control algorithm, an adaptive rocking feed algorithm for high-speed small-hole electric discharge machining is proposed. Taking the recast layer, which is a key quality index for air film cooling hole machining, as the core, a control method and system with high efficiency and the lowest recast layer are explored.

[0008] To achieve the above object, on the one hand, the present invention provides an adaptive rocking feed method for high-speed small-hole electric discharge machining, including the following steps:

[0009] Preset the effective feed amount of the feed axis and the threshold of the short-circuit pulse ratio of the pulse power supply at the control terminal;

[0010] Real-time collect the short-circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the electric discharge machining process;

[0011] The control terminal converts the servo feed and rocking machining of the machining system according to the preset threshold of the effective feed amount and the short-circuit pulse ratio;

[0012] The control terminal adaptively adjusts the rocking time and rocking frequency of the rocking machining system according to the circuit pulse duty ratio and the effective feed amount collected in real time during the electric discharge machining process.

[0013] Further, the process of determining the threshold of the effective feed amount includes:

[0014] Determine the threshold of the effective feed amount according to the recast layer influence formula, and the recast layer influence formula is:

[0015] RL = T on ·V·R normal ·δ

[0016] Wherein, RL is the generation amount of the recast layer; Ton is the pulse duration; V is the servo feed rate; Rnormal is the ratio of normal discharge; δ is an empirical coefficient, which is a fixed constant value.

[0017] Further, the specific process by which the control terminal converts the servo feed and rocking machining of the machining system according to the preset thresholds of the effective feed rate and the short-circuit pulse ratio is as follows: When the short-circuit pulse ratio of the pulse power supply and the effective feed rate of the feed axis during the electric discharge machining process collected in real time reach the preset thresholds of the effective feed rate and the short-circuit pulse ratio of the control terminal, the control terminal controls the system to stop the servo feed, and controls the system to perform rocking machining according to the preset rocking frequency and rocking time.

[0018] Further, the specific process by which the control terminal adaptively adjusts the rocking time and rocking frequency of the rocking machining system according to the circuit pulse duty ratio and the effective feed rate during the electric discharge machining process collected in real time is as follows: After the control terminal controls the system to complete the machining according to the preset rocking time and rocking frequency, the control terminal adjusts the next rocking time according to the short-circuit pulse ratio of the pulse power supply during the electric discharge machining process collected in real time.

[0019] Further, the control terminal adjusts the next rocking time according to the short-circuit pulse ratio of the pulse power supply during the electric discharge machining process collected in real time, including: If the short-circuit pulse ratio collected in real time after the rocking machining is completed according to the preset rocking time and rocking frequency is still greater than the threshold of the preset short-circuit pulse duty ratio, the rocking time of the next rocking machining will be increased to 1.3 times that of the previous rocking time; If the short-circuit pulse ratio collected in real time after the rocking machining is completed according to the preset rocking time and rocking frequency is equal to the threshold of the preset short-circuit pulse duty ratio, the rocking duration will remain unchanged.

[0020] On the other hand, the present invention provides an adaptive rocking and feeding system applicable to high-speed electric discharge machining of small holes, including a control terminal, a collection unit, a servo feed subsystem, and a rocking machining subsystem; the collection unit is connected to the control terminal, and the servo feed subsystem and the rocking machining subsystem are respectively connected to the control terminal;

[0021] The collection unit is used to collect the short-circuit pulse ratio of the pulse power supply and the effective feed rate of the feed axis during the electric discharge machining process in real time, and send them to the control terminal;

[0022] The control terminal is used to receive the short-circuit pulse ratio and the effective feed rate collected in real time by the collection unit, and send control signals to the servo feed subsystem and the rocking machining subsystem according to the preset thresholds of the short-circuit pulse ratio and the effective feed rate;

[0023] The servo feed subsystem is used to control the start and stop of the servo feed according to the control signal sent by the control terminal;

[0024] The rocking machining subsystem is used to control the start and stop of the rocking machining according to the control signal sent by the control terminal, as well as the rocking frequency and rocking time during the rocking machining.

[0025] Further, after the control terminal completes the shaking process according to the preset shaking time and shaking frequency, it adaptively adjusts the shaking time and the shaking frequency according to the short-circuit pulse ratio collected in real time by the acquisition unit.

[0026] Further, the specific process of the control terminal adaptively adjusting the shaking time and the shaking frequency according to the short-circuit pulse ratio collected in real time by the acquisition unit includes: if the short-circuit pulse ratio collected in real time is still greater than the threshold of the preset short-circuit pulse duty cycle, the shaking time of the next shaking process will be increased to 1.3 times that of the previous shaking time; if the short-circuit pulse ratio collected in real time by the acquisition unit is less than or equal to the threshold of the preset short-circuit pulse duty cycle after the shaking process is completed according to the preset shaking time and shaking frequency, the shaking duration will remain unchanged.

[0027] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses an adaptive shaking feed method and system applicable to high-speed small-hole electric discharge machining. Starting from the shaking process of high-speed small-hole electric discharge machining and combining it with an adaptive control algorithm, the present invention proposes an adaptive shaking feed algorithm for high-speed small-hole electric discharge machining. Taking the key quality index of gas film cooling hole machining - the recast layer as the core, an efficient control scheme with the lowest recast layer is explored. Using the method of the present invention, the reduction rate of the recast layer is 73.47%, and the machining efficiency is increased by 18.52%. Therefore, the adaptive shaking feed method of the present invention is an effective way applicable to high-speed small-hole electric discharge machining, which can significantly reduce the recast layer and ensure the improvement of machining efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0029] Figure 1 It is a flowchart of the adaptive shaking feed method applicable to high-speed small-hole electric discharge machining of the present invention.

[0030] Figure 2 It is a logic control diagram of the control terminal of the present invention for adaptively adjusting shaking parameters.

[0031] Figure 3 It is a schematic structural diagram of the adaptive shaking feed system applicable to high-speed small-hole electric discharge machining of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] The embodiments of the present invention disclose an adaptive rocking feed method applicable to high-speed electrical discharge machining of small holes. In the present invention, a high-speed electrical discharge small hole machine tool of Suzhou Zhonggu is selected. This machine tool has 7 axes and is dedicated to the machining of air film cooling holes of turbine blades. Among them, XYBC is used for hole position positioning before machining, W is responsible for the secondary stroke, the Z-axis is the main servo machining axis for machining small holes after positioning, and S is used for the rotation of the servo machining axis. The rocking machining mode is selected as the step rocking mode, that is, after the Z-axis feeds a certain distance, the XY-axis performs a rocking motion.

[0034] The control terminal selects a numerical control system independently developed by Suzhou Maikequan Co., Ltd. This system is divided into a control end and an execution end. The adaptive control algorithm is embedded into the execution end through self-written C language, periodically obtains the discharge state statistical data, and directly connects to the motors of each axis of the machine tool to perform real-time control of servo feed and rocking control during machining. As Figure 1 shown, it includes the following steps:

[0035] As the basis for switching between rocking machining and servo feed, the effective feed amount D feed and the short-circuit pulse ratio R short The determination of specific values is the most crucial. Therefore, the present invention pre-sets the threshold values of the effective feed amount of the feed axis and the short-circuit pulse ratio of the pulse power supply in the control terminal.

[0036] Furthermore, regarding the determination of the threshold value of the effective feed amount, through processing experience and multiple experiments, it is found that when rocking is adopted after feeding a long distance, the reduction effect on the recast layer is extremely small; if rocking machining is adopted when the feed distance is short, it will greatly affect the machining efficiency. Therefore, the present invention determines the threshold value of the effective feed amount according to the recast layer influence formula. The recast layer influence formula is:

[0037] RL = T on ·V·R normal ·δ

[0038] where RL is the generation amount of the recast layer; T on is the pulse duration; V is the servo feed rate; R normal is the ratio of normal discharge; δ is an empirical coefficient, which is a fixed constant value.

[0039] Initially select a compromise effective feed amount D feedThreshold value. Preferably, the initial effective feed amount can be selected as 3 mm for each servo feed, and rapid shaking is adopted. The duration of each shaking is 500 ms.

[0040] Furthermore, according to the machining experience of electric discharge machining, the threshold value of the short-circuit pulse ratio Rshort is determined to be 60%. This threshold value can reflect whether the actual machining process is in an obvious short-circuit state. When the short-circuit pulse ratio Rshort exceeds 60%, the shaking machining starts with a very short duration to promptly eliminate the short-circuit state during the machining process.

[0041] The short-circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the electric discharge machining process are collected in real time; among them, the effective feed amount D feed is determined by the downward feed distance of the feed axis of the numerical control system, and the short-circuit pulse ratio R short is obtained through the single-pulse detection circuit of high-speed small-hole electric discharge machining. The ratio of the short-circuit pulses to all pulses within a unit time is the short-circuit pulse ratio. The control terminal converts the servo feed and the shaking machining of the machining system according to the preset threshold values of the effective feed amount and the short-circuit pulse ratio.

[0042] The control terminal adaptively adjusts the shaking time and shaking frequency of the shaking machining system according to the circuit pulse duty ratio and the effective feed amount during the electric discharge machining process collected in real time. Since the size of the gas film cooling hole is determined, the shaking radius is not considered as a shaking parameter, and the shaking parameters are selected as the shaking frequency and the shaking duration. In terms of the shaking frequency, the shaking machining is triggered by the effective feed amount and the short-circuit pulse ratio threshold value. When the discharge statistical parameters reach the two threshold values, the servo feed is stopped, and the shaking machining mode is entered. At the same time, the effective feed amount and the short-circuit pulse ratio are cleared. Since the molten metal generated during the effective feed amount period is much higher than the remaining molten metal during the short-circuit pulse ratio period, the former has a more obvious impact on the shaking parameters.

[0043] Furthermore, the specific process of the control terminal converting the servo feed and the shaking machining of the machining system according to the preset threshold values of the effective feed amount and the short-circuit pulse ratio is as follows: when the short-circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the electric discharge machining process collected in real time reach the preset threshold values of the effective feed amount and the short-circuit pulse ratio of the control terminal, the control terminal controls the system to stop the servo feed and controls the system to perform shaking machining according to the preset shaking frequency and shaking time.

[0044] Further, the specific process of the control terminal adaptively adjusting the shaking time and shaking frequency of the shaking machining system according to the circuit pulse duty ratio and effective feed amount in the EDM process collected in real time is as follows: After the control terminal control system completes machining according to the preset shaking time and shaking frequency, the control terminal adjusts the next shaking time according to the short-circuit pulse ratio of the pulse power supply in the EDM process collected in real time.

[0045] Further, as Figure 2 shown, the control terminal adjusts the next shaking time according to the short-circuit pulse ratio of the pulse power supply in the EDM process collected in real time, including: If the short-circuit pulse ratio collected in real time after shaking machining is completed according to the preset shaking time and shaking frequency is still greater than the threshold of the preset short-circuit pulse duty ratio, the shaking time of the next shaking machining will be increased to 1.3 times that of the previous shaking time; If the short-circuit pulse ratio collected in real time after shaking machining is completed according to the preset shaking time and shaking frequency is equal to the threshold of the preset short-circuit pulse duty ratio, the shaking duration remains unchanged.

[0046] It is not difficult to see from the results of the comprehensive comparison experiment in Table 1 that the adaptive shaking feed method is the best method for reducing the thickness of the recast layer and improving the machining efficiency compared with the traditional machining method. The reduction rate of the recast layer under this method is 73.47%, and the machining efficiency is increased by 18.52%. Therefore, it can be concluded that the adaptive shaking feed method is an effective way applicable to high-speed EDM of small holes, which can significantly reduce the recast layer and ensure the improvement of machining efficiency.

[0047] Table 1 Comprehensive machining experiment design scheme

[0048]

[0049] On the other hand, the present invention provides an adaptive shaking and feeding system applicable to high-speed EDM of small holes, as Figure 3 shown, including a control terminal, a collection unit, a servo feeding subsystem, and a shaking machining subsystem; the collection unit is connected to the control terminal, and the servo feeding subsystem and the shaking machining subsystem are respectively connected to the control terminal;

[0050] The collection unit is used to collect the short-circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis in the EDM process in real time and send them to the control terminal;

[0051] The control terminal is used to receive the short-circuit pulse ratio and effective feed amount collected in real time by the collection unit, and send control signals to the servo feeding subsystem and the shaking machining subsystem according to the preset thresholds of the short-circuit pulse ratio and the effective feed amount;

[0052] The servo feeding subsystem is used to control the start and stop of the servo feeding according to the control signal sent by the control terminal;

[0053] The shaking processing subsystem is used to control the start and stop of shaking processing according to the control signal sent by the control terminal, as well as the shaking frequency and shaking time during shaking processing.

[0054] Furthermore, after the control terminal completes the shaking processing according to the preset shaking time and shaking frequency, it adaptively adjusts the shaking time and shaking frequency according to the short-circuit pulse ratio collected in real time by the acquisition unit.

[0055] Furthermore, the specific process of the control terminal adaptively adjusting the shaking time and shaking frequency according to the short-circuit pulse ratio collected in real time by the acquisition unit includes: if the short-circuit pulse ratio collected in real time is still greater than the threshold of the preset short-circuit pulse duty cycle, the shaking time of the next shaking processing will be increased to 1.3 times the previous shaking time; if the short-circuit pulse ratio collected in real time by the acquisition unit after the shaking processing is completed according to the preset shaking time and shaking frequency is less than or equal to the threshold of the preset short-circuit pulse duty cycle, the shaking duration remains unchanged.

[0056] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, refer to the description of the method part.

[0057] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An adaptive rocking feed method applicable to high-speed electrical discharge machining of small holes, characterized in that, It includes the following steps: Preset the threshold of the effective feed amount of the feed axis and the short - circuit pulse ratio of the pulse power supply at the control terminal in advance; Real - time collect the short - circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the EDM process; The control terminal converts the servo feed and the rocking machining of the machining system according to the preset threshold of the effective feed amount and the short - circuit pulse ratio. The specific process is as follows: When the short - circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the real - time collected EDM process reach the preset threshold of the effective feed amount and the short - circuit pulse ratio of the control terminal, the control terminal controls the system to stop the servo feed, and the control system performs rocking machining according to the preset rocking frequency and rocking time; The control terminal adaptively adjusts the rocking time and rocking frequency of the rocking machining system according to the circuit pulse duty ratio and the effective feed amount during the real - time collected EDM process.

2. An adaptive rocking feed method applicable to high-speed small-hole electrical discharge machining according to claim 1, characterized in that The process of determining the threshold of the effective feed amount includes: Determine the threshold of the effective feed amount according to the recast layer influence formula, and the recast layer influence formula is: ； Among them, RL is the generation amount of the recast layer; T on is the pulse duration; V is the servo feed rate; R normal is the ratio of normal discharges; δ is an empirical coefficient and is a fixed constant value.

3. An adaptive rocking feed method applicable to high-speed small-hole electric discharge machining according to claim 1, characterized in that, The specific process of the control terminal adaptively adjusting the rocking time and rocking frequency of the rocking machining system according to the circuit pulse duty ratio and the effective feed amount during the real - time collected EDM process is as follows: After the control terminal controls the system to complete the machining according to the preset rocking time and rocking frequency, the control terminal adjusts the next rocking time according to the short - circuit pulse ratio of the pulse power supply during the real - time collected EDM process.

4. An adaptive rocking feed method applicable to high-speed electro-discharge machining of small holes according to claim 3, characterized in that, The control terminal adjusts the next rocking time according to the short - circuit pulse ratio of the pulse power supply during the real - time collected EDM process, including: If the short - circuit pulse ratio collected in real - time after the rocking machining is completed according to the preset rocking time and rocking frequency is still greater than the preset short - circuit pulse duty threshold, the rocking time of the next rocking machining will be increased to 1.3 times that of the previous rocking time; If the short - circuit pulse ratio collected in real - time after the rocking machining is completed according to the preset rocking time and rocking frequency is less than or equal to the preset short - circuit pulse duty threshold, the rocking duration remains unchanged.

5. An adaptive shaking and feeding system applicable to high-speed small-hole electrical discharge machining, characterized in that, It includes a control terminal, a collection unit, a servo feed subsystem, and a rocking machining subsystem; the collection unit is connected to the control terminal, and the servo feed subsystem and the rocking machining subsystem are respectively connected to the control terminal; The collection unit is used to collect the short - circuit pulse ratio of the pulse power supply and the effective feed amount of the feed axis during the EDM process in real - time and send them to the control terminal; The control terminal is used to receive the short - circuit pulse ratio and the effective feed amount collected in real - time by the collection unit, and send control signals to the servo feed subsystem and the rocking machining subsystem according to the preset threshold of the short - circuit pulse ratio and the threshold of the effective feed amount; After the control terminal completes the rocking machining according to the preset rocking time and rocking frequency, it adaptively adjusts the rocking time and the rocking frequency according to the short - circuit pulse ratio collected in real - time by the collection unit; The specific process of the control terminal adaptively adjusting the shaking time and the shaking frequency according to the short - circuit pulse ratio collected in real time by the collection unit is as follows: If the short - circuit pulse ratio collected in real time by the collection unit is still greater than the threshold of the preset short - circuit pulse duty cycle, the shaking time of the next shaking machining will be increased to 1.3 times that of the previous shaking time; If the short - circuit pulse ratio collected in real time by the collection unit is less than or equal to the threshold of the preset short - circuit pulse duty cycle after the shaking machining is completed according to the preset shaking time and shaking frequency, the shaking duration remains unchanged; The servo feed subsystem is used to control the start and stop of the servo feed according to the control signal sent by the control terminal; The shaking machining subsystem is used to control the start and stop of the shaking machining according to the control signal sent by the control terminal, as well as the shaking frequency and shaking time during the shaking machining.

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