Five-axis linkage high-speed electric discharge milling method for special-shaped gas film hole

Abstract

A kind of special-shaped gas film hole five-axis linkage high-speed electric discharge milling processing method, first with the starting point of whole tool path inserts milling to preset depth, then in side milling stage, adopt the mode of side wall discharge along the side profile of diffusion port to generate tool path, while corresponding electrode compensation is carried out to electrode loss, then carry out geometric precision control to five-axis linkage electric discharge machining machine tool, so that electrode moves along predetermined feed track, to realize the accurate processing of diffusion port.The electrode is milled along the profile side of diffusion port during processing, side wall discharge is used instead of end face discharge, which greatly expands the discharge area, thereby improving the processing efficiency, and the whole block of material remaining in the center is excavated, further reducing the time and energy consumption of discharging removal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical processing, and particularly relates to a five-axis linkage high-speed electric spark milling method for processing a special-shaped gas film hole. BACKGROUND

[0002] The existing processing of diffusion-type gas film cooling holes is generally composed of a cylindrical hole and a diffusion port, and is realized by using high-speed electric spark small hole processing and electric spark forming processing respectively. However, this processing scheme inevitably involves two clamping of the workpiece and frequent electrode correction, which causes the centering error between the cylindrical part and the diffusion port, greatly reduces the processing efficiency and the yield. In addition, in the same blade, there may be several different diffusion ports, and the use of different forming electrodes for different diffusion ports greatly increases the pressure of electrode preparation and further increases the position error between different diffusion ports.

[0003] To solve this problem, the academic and industrial circles currently propose a combined electrode processing method for the diffusion-type gas film cooling hole, but this technology still cannot avoid the centering error between the gas film hole and the diffusion port; a layer-by-layer high-speed electric spark milling processing method, but this method still needs to be improved in terms of processing efficiency, surface integrity and automation degree. In addition to the electric processing scheme, laser processing is also applied to the processing of the diffusion port, but its processing capacity for large depth-diameter ratio holes is poor and the processing cost is high. SUMMARY

[0004] The present application proposes a five-axis linkage high-speed electric spark milling method for processing a special-shaped gas film hole to solve the problems existing in the prior art. During processing, the electrode mills along the profile side of the diffusion port, adopts side wall discharge instead of end face discharge, greatly expands the discharge area, thereby improving the processing efficiency, and further reduces the time and energy consumption for discharging and removing the remaining large block of material in the center.

[0005] The present application is realized by the following technical scheme:

[0006] The present application relates to a five-axis linkage high-speed electric spark milling method for processing a special-shaped gas film hole. The starting point of the entire tool path is inserted to a preset depth, then in the side milling stage, the side wall discharge is used to generate the tool path along the side profile of the diffusion port, and the electrode loss is compensated, and the geometric precision of the five-axis linkage electric spark processing machine tool is controlled, so that the electrode moves along the predetermined feed path, thereby realizing accurate processing of the diffusion port.

[0007] The electrode wear refers to that due to the serious side wall discharge and the existence of internal hollow flow channel, the part of the electrode sinking into the workpiece to participate in the side wall discharge will be broken after a certain milling distance. After the breakage, the processing depth sharply decreases, the discharge position gradually changes from the side discharge as the main part in the side milling stage to the bottom discharge as the main part, and the inter-electrode signal also sharply fluctuates.

[0008] The electrode compensation refers to that after collecting the original signal in the processing, the characteristic signal representing the current processing state is extracted after the smoothing processing, the quantization result is obtained after the stability quantization, and the real-time monitoring of the electrode breakage is realized according to the quantization result and the stability characteristics of each processing stage. When the electrode breakage is detected, the current processing is paused, the electrode is compensated and fed along the axial direction to the required depth, and after the compensation is completed, the side milling along the tool path is continued. The compensation action is continuously performed until the side milling is completed.

[0009] The original signal in the processing includes the directly collected signal or the characteristic signal obtained after processing, wherein the directly collected signal includes the inter-electrode current, voltage, feed depth and feed speed, and the characteristic signal obtained after processing includes the kurtosis signal, normalized kurtosis signal and peakness signal.

[0010] The smoothing processing is preferably a single-sided sliding average smoothing method.

[0011] The stability quantization refers to that each characteristic signal in a preset window is selected, the normalized kurtosis in the window is calculated after the smoothing processing, and the quantization value of the processing stability in the time period is taken as the normalized kurtosis. , wherein: X is the sampling point of the characteristic signal of the window, is the i th sampling point, n is the number of sampling points, is the mean value of the sampling points of the characteristic signal in the window, is the kurtosis value of the characteristic signal in the window, is the root mean square of the sampling points in the window, is the normalized kurtosis.

[0012] The real-time monitoring of the electrode breakage according to the quantization result and the stability characteristics of each processing stage refers to that the stability of each processing node is quantized by using the normalized kurtosis. When the stability of the processing sharply fluctuates, it indicates that the electrode is broken, so that the real-time monitoring of the electrode breakage is realized.

[0013] The geometric accuracy control method is that the side wall gap is measured by using a small hole machining experiment and the bottom gap is measured by using a single discharge experiment, and the milling track is generated by taking the above into account.

[0014] The small hole machining experiment is that a single hole is machined by using the same electrode, the same workpiece and the same electrical parameters, the side wall gap is measured, the side wall discharge gap under the condition is obtained, and the milling track is compensated.

[0015] The single discharge experiment is that a single discharge is carried out by using the same electrode, the same workpiece and the same electrical parameters, the bottom discharge gap is measured, the bottom discharge gap under the condition is obtained, and the milling track is compensated.

[0016] Technical effects

[0017] The hollow cylindrical electrode is used to mill along the profile side of the diffusion port, and the normalized kurtosis and other machining signals are used to judge the stability of the current machining, so that the electrode fracture detection and electrode compensation are realized. Compared with the prior art, the gas film hole and the diffusion port can be machined on the same machine tool, the repeated clamping of the electrode and the secondary positioning of the workpiece are avoided, and the centering error is eliminated. And by using the unique tool path planning, the workpiece removal volume is reduced, and the machining efficiency is greatly improved. The machining efficiency is greatly improved while the machining quality is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a tool path diagram of the application;

[0019] Figure 2 It is a five-axis linkage EDM milling machining platform schematic diagram;

[0020] Figure 3 It is a normalized kurtosis data diagram of the gap voltage signal in the whole process of five-axis linkage EDM milling machining;

[0021] Figure 4 It is the effect of different diffusion type gas film cooling holes in the embodiment;

[0022] In the figure: (a) is the five-axis linkage EDM milling machining consistency; (b) is the pyramid gas film hole; (c) is the nozzle-shaped gas film hole; (d) is the funnel-shaped gas film hole;

[0023] Figure 5 It is the maximum profile error of different diffusion type gas film cooling holes in the embodiment;

[0024] Fig. (a) is a pyramid profile measurement error; (b) is a nozzle profile measurement error; (c) is a funnel profile measurement error;

[0025] Figure 6 The surface quality of different diffusion type gas film cooling holes processed by the method of the present application is shown. DETAILED DESCRIPTION

[0026] As shown in Figure 2 , a five-axis linkage high-speed electric discharge milling processing platform involved in the present embodiment comprises a rotating worktable 3, a workpiece to be processed 1 arranged thereon, a hollow tubular electrode 2 arranged opposite to the workpiece to be processed 1, and an electrode fracture online discrimination system 7, wherein: a high-frequency voltage is arranged between the hollow tubular electrode 2 and the workpiece to be processed 1, so as to generate a discharge phenomenon, and realize workpiece material removal, i.e. gas film cooling holes on the workpiece; the electrode fracture online discrimination system 7 collects discharge information on the workpiece to be processed 1 and the hollow tubular electrode 2 through a voltage differential probe 4, a current probe and an amplifier 5, and a data acquisition and processing unit 6, realizes real-time monitoring of electrode fracture, and thus performs electrode compensation.

[0027] The hollow tubular electrode 2 is internally provided with high-pressure high-speed water-based working fluid, which plays a role of chip removal and cooling during the processing, and realizes continuous and stable processing.

[0028] The electrode fracture online discrimination system 7 comprises: the voltage differential probe 4, the current probe and the amplifier 5, and the data acquisition and processing unit 6, wherein: the voltage differential probe 4 and the current probe and the amplifier 5 collect discharge information between the workpiece to be processed 1 and the hollow tubular electrode 2, such as inter-electrode voltage and current. Then the data is transmitted to the data acquisition and processing unit 6, through processing of the original data, information such as normalized kurtosis is extracted. When the normalized kurtosis calculation results in 100 continuous sampling periods are all greater than 1, it is considered that the current processing state is unstable. Otherwise, it is considered to be in a stable state. Combined with the change of the processing state since the start of the side milling processing, it can be judged whether the electrode is fractured.

[0029] As shown in Figure 2 , the present embodiment relates to a special-shaped gas film hole five-axis linkage high-speed electric discharge milling processing method based on the above platform, according to a three-dimensional model of a blade, a CAM module in an existing commercial software is used to generate a side wall milling track; while the side wall milling processing is performed by the five-axis linkage high-speed electric discharge milling processing platform, the electrode fracture online discrimination system 7 is used to monitor whether the electrode is fractured online, when the electrode is fractured, the processing is immediately paused and electrode loss compensation is performed.

[0030] The electrode wear compensation refers to: when the electrode fracture is detected, the current side milling processing is paused, the electrode is compensated to the required depth along the axial direction, after the compensation is completed, the side milling along the tool path is continued, and the electrode wear compensation is iteratively performed until the side milling is completed.

[0031] The sampling period in the embodiment is 1 ms, the signal window width is pre-set to 10 sampling periods, and the original signal sampling rate is 50 MHz. The single-side sliding average filtering order is 10. In each sampling period, the signal processing unit first obtains the original data from the signal acquisition unit, and then sends the original data to the online discrimination system. The online discrimination system updates the last element of the window according to the pre-set window width, and then calculates the normalized kurtosis after sliding average filtering.

[0032] As shown in Figure 3 , the discharge is relatively stable in the initial milling stage, and the normalized kurtosis factor of the gap voltage signal maintains at a low level. After the end of the plunge milling, the five-axis linkage side milling stage is entered, due to the sudden changes of the discharge area, the flushing condition and the discharge gap, the gap voltage signal will appear unstable for a short time, which is characterized by a large peak value, but the duration is short. With the gradual stability of the processing, the stability is restored again, until the electrode is broken. At the moment of the electrode fracture, , the gap voltage signal will suddenly increase and fluctuate sharply for a long time. Therefore, it can be seen that the normalized kurtosis can well capture the mutation of the discharge state, so as to accurately judge whether the electrode is broken or not.

[0033] Three different diffusion type gas film cooling holes are processed by using the method, an electric spark perforation machine tool provided by Suzhou Zhonggu Machinery and Electronics Technology Co., Ltd. is used, the model is ZGDC506, and the electric parameters used in the experiment are shown in Table 1. As shown in the processing result Figure 4 , the feasibility and processing consistency of the process are verified. In addition, in order to measure the processing precision, the diffusion port profile after processing is measured and compared with the ideal diffusion port profile, as shown in Figure 5 , the results show that the maximum deviation between the processing profile and the ideal profile can be well controlled within 19 microns, which can meet the precision requirements of the turbine blade.

[0034] The existing high-speed electric discharge milling method in the industry and academia all adopts the layered milling method to realize the processing of the diffusion port of the special-shaped gas film hole. The single-layer processing depth is usually set to half of the discharge gap. Since the conductivity of the deionized water used is very low, the discharge gap is only about 50 μm, so the actual processing usually sets the single-layer depth to 20 μm. When the processing depth is large or the processing efficiency is required to be high, this method becomes less applicable.

[0035] To measure the efficiency advantage of the present invention, three different diffusion-type film cooling holes were processed using this process and a high-speed EDM layer-by-layer milling process under the same machining conditions. The machining time for each method is shown in Table 2.

[0036] Table 1 Discharge parameters used in the experiment

[0037]

[0038] Table 2

[0039]

[0040] Results show that this method reduces machining time by 15.5% to 46.8% compared to high-speed EDM layer-by-layer milling, significantly improving machining efficiency. Furthermore, the degree of machining time reduction varies for different diffusers, due to the varying proportion of excavated material in the total machining volume. Therefore, the efficiency advantage of this method increases for diffusers with a higher proportion of excavated material.

[0041] Under the same processing conditions, the surface roughness and recast layer thickness of the two process methods were compared and measured. Figure 6 As shown, the results show that compared with the high-speed electric spark layer-by-layer milling process, the surface roughness and average surface roughness of this invention are reduced from Ra 2.65μm and Sa 2.25μm to Ra 1.36μm and Sa 1.51μm respectively, and the average thickness of the recast layer is increased from 2.6μm to 3.5μm. For turbine blades, their surface roughness and recast layer thickness meet the technical requirements.

[0042] It can be seen from the description of the embodiments that the present invention has significant advantages in processing accuracy and processing efficiency compared to the traditional diffusion-type film cooling hole processing technology.

[0043] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A five-axis linkage high-speed electric spark milling method for special-shaped air film holes, characterized in that: The tool path is first plunge milled to a preset depth from the starting point of the entire tool path. Then, in the side milling stage, sidewall discharge is used to generate the tool path along the side profile of the diffuser. At the same time, electrode loss is compensated accordingly. Then, the five-axis linkage EDM machine is subjected to geometric accuracy control to ensure that the electrode moves along the predetermined feed trajectory, thereby achieving precise processing of the diffuser. The electrode compensation method involves collecting raw signals during machining, smoothing them, extracting characteristic signals representing the current machining state, and then performing stability quantification to obtain quantitative results. Based on the quantitative results and the stability characteristics of each machining stage, real-time monitoring of electrode fracture is then achieved. When electrode fracture is detected, the current machining process is paused, and the electrode is fed axially for compensation to the required depth. After compensation is completed, side milling continues along the tool path, and the compensation action is continued until side milling is complete. The original signals during the machining process include: inter-electrode current, voltage, feed depth, and feed speed; The characteristic signals representing the current processing state include: kurtosis signal, normalized kurtosis signal, and peak value signal; The stability quantification mentioned above refers to selecting each characteristic signal within a preset window, smoothing it, and calculating the normalized kurtosis within this window as the quantitative value of the processing stability within this time period. Specifically, it is: ,in: , X is the characteristic signal sampling point of the window, is the i-th sampling point, n is the number of sampling points, is the mean value of the characteristic signal sampling points in the window, is the kurtosis value of the characteristic signal in the window, is the root mean square of the sampling points in the window, is the normalized kurtosis.

2. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 1 is characterized in that: The geometric accuracy control refers to: using a small hole machining experiment to measure the side wall clearance and a single discharge experiment to measure the bottom clearance, and taking these into account when generating the milling trajectory; For problems with large errors in machining width and depth, after machining is completed, the same electrode is used to perform trimming along the original path.

3. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 2 is characterized in that: The small hole machining experiment is to use the same electrode, the same workpiece and the same electrical parameters to machine a single hole, measure the sidewall gap and obtain the sidewall discharge gap under these conditions, thereby achieving compensation for the milling trajectory.

4. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 2 is characterized in that: The single discharge experiment refers to: using the same electrode, the same workpiece and the same electrical parameters to perform a single discharge, measuring the bottom discharge gap, and obtaining the bottom discharge gap under the condition, thereby achieving compensation for the milling trajectory.

5. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 2 is characterized in that: The method is implemented on a five-axis linkage high-speed electric spark milling processing platform, which includes: a rotating worktable, a workpiece to be processed arranged on the platform, a hollow tubular electrode arranged relative to the workpiece to be processed, and an electrode fracture online discrimination system, wherein: a high-frequency voltage is set between the hollow tubular electrode and the workpiece to be processed, thereby generating a discharge phenomenon and realizing workpiece material removal; the electrode fracture online discrimination system collects discharge information on the workpiece to be processed and the hollow tubular electrode through a voltage differential probe, a current probe and an amplifier and a data acquisition and processing unit, thereby realizing real-time online monitoring of electrode fracture. When the electrode breaks, the processing is immediately suspended and electrode loss compensation is performed.

6. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 5 is characterized in that: The online electrode fracture detection system includes: a voltage differential probe, a current probe and an amplifier, and a data acquisition and processing unit, wherein: the voltage differential probe, the current probe and the amplifier collect discharge information between the workpiece and the hollow tubular electrode, and then transmit the data to the data acquisition and processing unit. By processing the original data, the normalized kurtosis is extracted. When the normalized kurtosis calculation results are greater than 1 in multiple consecutive sampling cycles, the current machining state is considered to be unstable; otherwise, it is considered to be in a stable state. Combined with the changes in the machining state since the start of the side milling process, it can be determined whether the electrode is broken.

7. The five-axis linkage high-speed EDM milling method for special-shaped air film holes according to claim 5 is characterized in that: The electrode loss compensation means that when an electrode break is detected, the current side milling process is paused, the electrode is fed axially to the required depth for compensation, and after the compensation is completed, the side milling is continued along the tool trajectory, and the electrode loss compensation is iterated until the side milling is completed.

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