Electric spark and electrolysis combined machining method

Abstract

The invention relates to the technical field of non-traditional machining, in particular to an electric spark and electrolysis combined machining method. Compared with a traditional electric spark and electrolysis combined machining hole making method, the electric spark and electrolysis combined machining method has the advantages that ultra-narrow pulse width electrolytic machining with machining gap selectivity is achieved by means of the coupling characteristic between a power capacitor and an electrolytic tank interface double-electric-layer capacitor; when the machining gap between the machined workpiece and the tool electrode exceeds a certain value, workpiece metal is not dissolved any more during electrolytic machining, and therefore the problem that the machining size and shape are uncontrollable due to the fact that the electrolytic effect is accumulated along with time in electric spark electrolytic combined machining is solved.

Description

Technical Field

[0001] The invention relates to the technical field of special machining, in particular to an electric spark electrolysis composite machining method. Background Art

[0002] Turbine blades are important hot-end components of aircraft engines. They have been in service for a long time under extremely high ambient temperatures and complex alternating load conditions. Their working stability and reliability are the basis for the safety of the entire aircraft engine. With the increase in the demand for aircraft engine performance, the temperature of the gas before the turbine continues to rise, which greatly tests the temperature-bearing capacity of core hot-end components such as turbine blades. In order to ensure the service safety and life of turbine blades in high-temperature environments and improve the high-temperature resistance of turbine blades, in addition to improving the performance of high-temperature alloy materials and adopting thermal barrier coating technology, most of the advanced aircraft engine turbine blades at home and abroad currently adopt a film cooling design scheme. The cooling airflow is introduced into the inner cavity of the hollow turbine blade, so that it flows through the cooling channel and is ejected through the film holes distributed on the blade body to form a cooling air film covering the blade, isolating the blade surface from the high-temperature gas, and taking away part of the radiant heat of the high-temperature gas or bright flame on the wall, thereby playing a good protective role on the blade surface. Therefore, the film hole is one of the key structures to improve the temperature-bearing capacity of aircraft engine turbine blades. Especially with the development of a new generation of aircraft engines, in order to ensure the cooling effect and fatigue life of turbine blades, higher requirements are put forward for the quality and efficiency of film hole processing.

[0003] Since blade materials are often high-temperature alloys, which are typical difficult-to-process materials, coupled with the high-quality processing requirements and tiny structural dimensions of air film holes, the processing of air film holes mainly adopts special processing methods, including electric spark, electro-hydraulic beam and femtosecond laser. Among them, the hole wall of the electro-hydraulic beam hole has no remelting layer, but the processing localization is poor, resulting in poor hole shape, large inner hole mouth, and easy damage to the blade wall, and low processing qualification rate. There is no remelting layer on the hole wall of the femtosecond laser hole, but due to the characteristics of pulsed laser energy release, femtosecond laser processing always has the limitations of difficulty in protecting the wall from damage and inability to process interference holes, and the processing efficiency is low and the processing cost is high. In contrast, electro-spark processing is based on spark discharge to melt and etch materials, and has the advantages of high processing efficiency, processing interference holes and special-shaped holes, and low equipment and processing costs. However, due to the instantaneous high temperature generated during the spark discharge process, a remelting layer exists on the surface of the electro-spark processing. The remelting layer contains a large number of defects such as pores and microcracks, which can easily lead to the generation and expansion of cracks and reduce fatigue life.

[0004] In order to control the remelting layer produced by EDM, the current method mainly relies on process optimization thinning or combined process removal. For example, Zhang Zhen et al. from Huazhong University of Science and Technology and HT Lee et al. from National Cheng Kung University in Taiwan achieved control of the remelting layer <12 μm through process parameter optimization, but the process parameter optimization method can only reduce the thickness of the remelting layer to a limited extent, and the current optimization results are not ideal. For thicker remelting layers and obvious microcracks, they can only be removed through secondary processes, such as using abrasive flow and chemical grinding methods to remove the remelting layer after processing.

[0005] In order to effectively reduce or even completely remove the remelting layer, research institutions at home and abroad are trying to explore new processes and technologies. Among them, the EDM electrolytic composite machining method uses EDM to quickly form air film holes, and uses the electrolytic machining action in an open circuit state to remove the remelting layer on the EDM surface. It is an efficient and convenient zero-remelting layer hole making method. However, existing research generally uses a chopping pulse power supply, and in order to pursue high-efficiency EDM, a higher voltage is generally used for EDM. Due to the fast electrochemical dissolution rate under a large machining voltage and low selectivity for the machining surface, the hole machining size is seriously expanded, and because the electrolytic action time accumulates continuously with the machining feed process, the controllability of the machining shape accuracy is poor.

[0006] Therefore, it is an urgent problem to be solved in the field of special processing of turbine blades to study a method for making holes with zero remelting layer by high-precision electrospark electrolysis composite machining of turbine blades and to achieve high-efficiency, high-quality, and zero remelting layer machining of air film holes. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide an electric spark electrolytic composite machining method. The electric spark electrolytic composite machining method provided by the present invention has machining gap selectivity. When the machining gap between the workpiece being machined and the tool electrode exceeds a certain value, the electrolytic machining no longer dissolves the workpiece metal, thereby solving the problem of uncontrollable machining size and shape caused by the cumulative effect of electrolysis over time in electric spark electrolytic composite machining.

[0008] The present invention provides an electrospark electrolytic composite machining method, comprising:

[0009] In the electrolyte, the workpiece is subjected to high-localized electrolytic composite machining by using a tool electrode;

[0010] A pulse voltage is applied between the tool electrode and the workpiece to be processed through a capacitive pulse power supply;

[0011] The capacitance of the capacitive pulse power supply is 10 nF~200 nF.

[0012] The method provided by the present invention is to perform electric spark electrolytic composite machining on a workpiece to be machined in an electrolyte using a tool electrode; wherein the electric spark electrolytic composite machining is specifically to perform electric spark electrolytic composite machining to form holes. In certain embodiments of the present invention, the workpiece to be machined is a turbine blade. In an electrolyte, the turbine blade is subjected to electric spark machining to form holes using a tool electrode, and an air film hole is formed on the turbine blade. The machining speed of the tool electrode of the present invention is 50 r / min~200 r / min.

[0013] The electric spark electrolysis composite machining method provided by the present invention is a composite machining method that combines an electric spark machining process with a high-localized electrolysis machining process. The tool electrode of the present invention applies a pulse voltage to the workpiece to be machined through a capacitive pulse power supply. Due to the limited energy storage and discharge characteristics of the capacitor, a transient ultra-narrow pulse width pulse current is generated to complete pulse electrolysis. Specifically, the present invention utilizes the coupling characteristics between the discharge of the capacitive power supply and the double electric layer at the interface of the electrolytic cell, and matches the power supply capacitor according to the properties of the double electric layer at the interface of the electrolytic cell and the electrolyte, to provide an ultra-narrow pulse width pulse power supply for electrolytic machining, and the amplitude is sensitive to the machining gap, to constrain the scope of electrolysis, and when the machining gap between the workpiece to be machined and the tool electrode exceeds a certain value (this value is the cut-off machining gap d max ), electrolytic machining no longer dissolves the workpiece metal, thus solving the problem of uncontrollable machining size and shape caused by the cumulative effect of electrolysis over time in electric spark electrolytic composite machining.

[0014] The pulse voltage of the present invention is applied by a capacitive pulse power supply with a capacitance of 10 nF to 200 nF. The peak voltage of the pulse voltage is 60 V to 140 V; the pulse width of the pulse voltage is 1 μs to 20 μs; and the pulse interval of the pulse voltage is 1 μs to 20 μs. The capacitive pulse power supply of the present invention is used in electrolytic machining. According to the electrochemical principle, the equivalent circuit diagram of the capacitive pulse power supply electrolytic machining during the pulse width period and the pulse interval period is as follows: Figure 1~Figure 2 As shown, Figure 1 For capacitive pulse power electrochemical machining during the pulse width (T on ), Figure 2 The period between pulses (T off ) is an equivalent circuit diagram; the power storage capacitor is used to supply power to the double electric layer between the workpiece and the electrolyte, so that the double electric layer voltage between the workpiece and the electrolyte increases first, and then decreases due to the exhaustion of the charge of the power storage capacitor. By matching the pulse power capacitor with the double electric layer interface characteristics, ultra-narrow pulse width electrolytic machining can be achieved.

[0015] The electrolyte of the present invention is selected from NaNO 3 、NaClO 3,NaCl or Na 3 At least one of Cit, preferably Na 3 Cit; the conductivity of the electrolyte is 1 mS / cm~10 mS / cm. The present invention matches the capacitance of the capacitive pulse power supply according to the double electric layer of the electrolytic cell interface and the electrolyte properties. The matching method includes: according to Figure 1 The gap between the workpiece to be machined and the tool electrode is shown in the cut-off machining gap d. max The equivalent circuit calculation of the working process of the electrolytic cell composed of the workpiece to be processed, the electrolyte and the tool electrode is different from the capacitance size C of the capacitive pulse power supply. power The peak voltage V of the double electric layer at the interface between the workpiece to be processed and the electrolyte p =f(C power ), let the double layer voltage peak value V p Less than or equal to the electrolytic machining threshold voltage V of the workpiece to be machined th , that is, let V p ≤V th , then the calculated capacitance C power，max In order to meet the maximum critical value of the above-mentioned EDM high-localized electrochemical machining (at this time, the cut-off machining gap is d max ), and then according to the efficiency of high-localized electrolytic composite machining of electric sparks and the thickness of the machining remelting layer under different capacitance sizes of the capacitive pulse power supply, the capacitance size of the capacitive pulse power supply is preferably selected. In certain embodiments of the present invention, the conductivity of the electrolyte is 1 mS / cm~3 mS / cm, the peak voltage of the pulse voltage is 90 V~110 V, and the capacitance size of the capacitive pulse power supply obtained by matching according to the above matching method is 50 nF~70 nF.

[0016] The formation mechanism of the ultra-narrow pulse width electrolytic machining described in the present invention is explained as follows: During electrolytic machining, the capacitive pulse power supply utilizes the power storage capacitor to supply power to the double electric layer between the workpiece being machined and the electrolyte, so that the double electric layer voltage between the workpiece being machined and the electrolyte first increases, and then decreases due to the exhaustion of the charge of the power storage capacitor. By matching the pulse power supply capacitor with the double electric layer interface characteristics, ultra-narrow pulse width electrolytic machining can be achieved. The ultra-narrow pulse width electrolytic machining can reduce the duration of a single pulse electrolysis action and reduce the average electrolysis action time, thereby avoiding excessive machining entrance diameter caused by over-machining. In contrast, in general electrolytic machining or electric spark electrolytic machining, in order to ensure that the electrolytic machining can act on the workpiece being machined, a chopper pulse power supply is generally used. At this time, the power supply can continuously provide charge to the double electric layer at the interface of the electrolytic cell, and the electrolysis occurs during the entire pulse width, such as Figure 3 As shown, Figure 3This is a schematic diagram comparing the change process of the double electric layer potential at the workpiece-electrolyte interface during electrolytic machining between a capacitive pulse power supply and a general electrolytic machining power supply. The electrolytic action time of ultra-narrow pulse width electrolytic machining under a capacitive pulse power supply is significantly shorter than that of general electrolytic machining. The reduced electrolytic action time can avoid excessive machining entrance diameter caused by over-machining.

[0017] The capacitive pulse power supply described in the present invention is used in electrolytic machining, and the mechanism by which the electrolytic voltage amplitude is sensitive to the machining gap is explained as follows: the charging time of the double layer at the workpiece-electrolyte interface is determined by the machining gap. The larger the machining gap, the longer the charging time, the later the threshold potential required for electrolytic machining is reached, or even the threshold potential required for electrolytic machining is not reached, and the charge of the power supply energy storage capacitor is exhausted. In electrolytic machining, only when the potential difference across the double layer capacitor is higher than the machining threshold voltage will the workpiece material undergo an electrochemical dissolution reaction. Therefore, the double layer charging delay characteristics of the electrolytic cell interface under different machining gaps are utilized to make the electrolytic voltage amplitude sensitive to the machining gap, thereby realizing the selection of the machining range in the electrolytic machining process.

[0018] The present invention also includes auxiliary processing by using high-pressure internal flushing liquid during the process of electric spark electrolysis combined machining. The high-pressure internal flushing liquid is used to achieve rapid renewal of the working medium, thereby avoiding the problem of difficulty in updating the electrolysis products in the machining gap due to failure of the internal flushing liquid during the electrolysis machining stage in the electric spark electrolysis combined machining, and no additional electrolysis machining time is required, thereby improving the machining efficiency.

[0019] The present invention provides an electrospark electrolytic composite machining method. Compared with the traditional electrospark electrolytic composite machining hole making method, the electrospark electrolytic composite machining method provided by the present invention utilizes the coupling characteristics between the power supply capacitor and the double electric layer capacitor at the interface of the electrolytic cell to realize ultra-narrow pulse width electrolytic machining with machining gap selectivity. When the machining gap between the machined workpiece and the tool electrode exceeds a certain value, the electrolytic machining no longer dissolves the workpiece metal, thereby solving the problem of uncontrollable machining size and shape caused by the cumulative effect of electrolysis over time in the electrospark electrolytic composite machining. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 For capacitive pulse power electrochemical machining during the pulse width (T on ) is an equivalent circuit diagram;

[0021] Figure 2 The period between pulses (T off ) is an equivalent circuit diagram;

[0022] Figure 3 It is a schematic diagram comparing the change process of the double electric layer potential at the workpiece-electrolyte interface during electrolytic machining between a capacitive pulse power supply and a general electrolytic machining power supply;

[0023] Figure 4 This is a schematic diagram of the processing results of the capacitive pulse power supply;

[0024] Figure 5 This is a graph showing the change of the double electric layer potential at the workpiece-electrolyte interface under different machining gaps of the capacitive pulse power supply;

[0025] Figure 6 This is a scanning electron microscope image of Example 1 of the present invention after a capacitive pulse power supply is used to make holes on the test piece;

[0026] Figure 7 This is a schematic diagram of the processing results of the chopping pulse power supply;

[0027] Figure 8 This is a diagram showing the change of the double-layer voltage at the workpiece-electrolyte interface at different machining gaps of the chopper pulse power supply;

[0028] Fig. 9 This is an optical microscope image of the test piece after holes were made using a chopper pulse power supply in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention discloses a method for electrospark electrolytic composite machining. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0030] The present invention will be further described below in conjunction with embodiments:

[0031] Example 1

[0032] The present invention will be further described below by taking a circular hole with a diameter of 0.5 mm as an example in conjunction with the accompanying drawings.

[0033] Through the workpiece to be processed, the hollow electrode wire with an outer diameter of 0.38 mm is clamped by the EDM composite function spindle head, the hole to be processed is adjusted to the work position, and the air film hole processing control program is started, including motion unit control, EDM power supply control, flushing system control, processing process detection and recognition and feedback control, etc. Weak electrolytes are used as internal and external flushing liquids, and hollow electrode wire with an outer diameter of 0.38 mm is used to realize air film hole processing. Among them:

[0034] In this example, the workpiece material is a single crystal high-temperature alloy DD9 specimen with a thickness of 1.5 mm. The weak electrolyte is a low-concentration NaCl solution with a conductivity of 3 mS / cm. The designed power supply is a capacitive pulse power supply with an adjustable peak voltage of 0~200 V. The peak voltage of the power supply is set to 100 V in the experiment. According to the above-mentioned EDM composite machining process conditions, the matching capacitance value is 60 nF, the power pulse width is set to 5 μs, the pulse interval is 5 μs, and the electrode rotation speed is 200 r / min.

[0035] like Figure 4 and Figure 5 As shown, Figure 4 This is a schematic diagram of the processing results of the capacitive pulse power supply. Figure 5 The double electric layer potential variation diagram of the workpiece-electrolyte interface under different machining gaps of the capacitive pulse power supply is shown in Figure 2. a <Processing clearance d b <Processing clearance d c , A represents the machining gap d a Case A and B represent the machining gap d b Case B and C represent the machining gap d c Situation C. The holes of the machined turbine blades were tested by scanning electron microscope. The results are as follows Figure 6 As shown, Figure 6 This is a scanning electron microscope image of Example 1 of the present invention after the test piece is pierced with a capacitive pulse power supply.

[0036] It can be seen that since the impedance distribution between the workpiece surface and the tool electrode is determined by the distance d between the two and the conductivity of the electrolyte between the two, assuming that the electrolyte is evenly distributed, the greater the distance d between the two, the greater the impedance Re. The greater the impedance Re, the slower the double-layer capacitance between the workpiece and the electrolyte is charged, and the threshold voltage V is reached. th Time requiredT th The longer it is, the harder it is to reach the processing threshold voltage V th (like Figure 4 and Figure 5 Case C) so that no material is removed, thereby increasing the sensitivity of the electrolytic machining process to the machining gap. When the machining gap exceeds the cut-off machining gap, no metal dissolution reaction occurs, realizing the selection of the machining range during the electrolytic machining process and improving the machining accuracy. The capacitive pulse power supply is used in electrolytic machining to make the electrolytic voltage amplitude sensitive to the machining gap and form a cut-off machining gap to ensure the shape accuracy of the machining result.

[0037] Comparative Example 1

[0038] A conventional chopper-type pulse power supply was selected for comparative experiments, and the peak voltage of the pulse power supply was set to 100 V, the pulse width to 5 μs, and the pulse interval to 5 μs. Other experimental conditions were the same as those in Example 1.

[0039] like Figure 7 and Figure 8 As shown, Figure 7 This is a schematic diagram of the processing results of the chopper pulse power supply. Figure 8 The double-layer voltage variation diagram of the workpiece-electrolyte interface at different machining gaps of the chopper pulse power supply is shown in Figure 2. d <Processing clearance d e <Processing clearance d f , D represents the processing gap d d When D, E represents the processing gap d e When E and F represent the machining gap d f The hole of the machined turbine blade was observed under an optical microscope. The results are as follows: Fig. 9 As shown, Fig. 9 This is an optical microscope image of comparative example 1 of the present invention after the test piece is made with a chopper-type pulse power supply, and the cross-sectional dimensions and morphology of the processed holes in the comparative example.

[0040] It can be seen that as the processing gap increases (processing gap d d <Processing clearance d e <Processing clearance d f ), the interface double layer voltage can always reach the processing threshold voltage V th As a result, electrolytic machining is constantly removing material, and the cumulative effect of electrolysis over time makes the processing size and shape uncontrollable. Figure 4 The capacitive pulse power supply shown is applied in electrolytic machining, so that the electrolytic voltage amplitude is sensitive to the machining gap and forms a cut-off machining gap, thereby ensuring the shape accuracy of the machining result.

[0041] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for electrospark electrolytic machining, characterized in that: include: In the electrolyte, the workpiece is subjected to high-localized electrolytic composite machining by using a tool electrode; A pulse voltage is applied between the tool electrode and the workpiece to be processed by a capacitive pulse power supply; The capacitance of the capacitive pulse power supply is 10 nF~200 nF.

2. The electric spark electrolytic composite machining process according to claim 1, characterized in that: The peak voltage of the pulse voltage is 60 V to 140 V; the pulse width of the pulse voltage is 1 μs to 20 μs, and the pulse interval of the pulse voltage is 1 μs to 20 μs.

3. The electric spark electrolytic composite machining process according to claim 1 or 2, characterized in that: The capacitance of the capacitive pulse power supply is matched by the following method: According to the gap between the workpiece to be processed and the tool electrode, the gap between the workpiece to be processed and the tool electrode is cut off. max The equivalent circuit of the electrolytic cell composed of the workpiece to be processed, the electrolyte and the tool electrode during the working process is used to calculate the capacitance C of different capacitive pulse power supplies. power The peak voltage V of the double electric layer at the interface between the workpiece to be processed and the electrolyte p , let the double layer voltage peak value V p Less than or equal to the electrolytic machining threshold voltage V of the workpiece to be processed th , then the calculated capacitance C power，max In order to meet the maximum critical value of the above-mentioned high-localized electrolytic composite machining of electric sparks, the capacitance size of the capacitive pulse power supply is matched according to the efficiency of high-localized electrolytic composite machining of electric sparks and the thickness of the machining remelting layer under different capacitance sizes of the capacitive pulse power supply.

4. The electric spark electrolytic machining method according to claim 3, characterized in that: The electrolyte is selected from at least one of NaNO3, NaClO3, NaCl or Na3Cit.

5. The electric spark electrolytic machining method according to claim 4, characterized in that: The conductivity of the electrolyte is 1 mS / cm~3 mS / cm.

6. The electric spark electrolytic machining method according to claim 1, characterized in that: The machining speed of the tool electrode is 50 r / min~200 r / min.

7. The electric spark electrolytic machining method according to claim 1, characterized in that: The method comprises the following steps: performing electrospark electrolytic composite machining, specifically performing electrospark electrolytic composite machining to make holes.

8. The electric spark electrolytic machining method according to claim 7, characterized in that: In an electrolyte, a tool electrode is used to perform electric spark machining on a turbine blade to form a hole, thereby forming an air film hole on the turbine blade.

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