Electrolytic machining method for titanium-aluminum single crystal blade

Abstract

The invention discloses an electrolytic machining method for a titanium-aluminum single crystal blade. The method comprises the steps that firstly, a technological reference block is machined on a blade blank, and a workpiece is clamped on an electrolytic machining machine tool through a special arc-shaped flow guide tool; then preparing a composite electrolyte which takes sodium chloride as a main material and is added with citric acid and boric acid so as to ensure the processing quality and inhibit stray corrosion; the machining process is divided into a rapid material removing stage and a precision machining stage, the mode of constant-speed feeding of a conventional pulse power source and the mode of coupling of an intermittent bipolar high-frequency group pulse power source and same-frequency vibration feeding are sequentially adopted, products are effectively discharged, and locality is improved; and after the electrolytic machining is finished, the profile tolerance and the surface roughness of the molded surface of the blade are detected, and if the blade is detected to be unqualified, the blade is repaired or scrapped according to unqualified items. By means of the method, high-precision machining with the blade profile tolerance and the surface roughness meeting the machining requirements of the titanium-aluminum single crystal blade can be finally achieved, cutting stress and tool loss are avoided, and the method is suitable for precise and efficient manufacturing of aero-engine blades.

Description

Technical Field

[0001] This invention relates to the field of aero-engine blade manufacturing technology, specifically to an electrolytic processing method for titanium-aluminum single-crystal blades. Background Technology

[0002] Blades are critical components in aero engines, characterized by their large quantity and high unit value. They have complex shapes and high twist, and must operate reliably for extended periods under high temperature and high pressure conditions. To meet these requirements, blades must not only possess precise dimensions and excellent surface quality, but also be made of high-temperature resistant and deformation-resistant materials.

[0003] Titanium-aluminum single crystal is a new generation of high-performance alloy material developed both domestically and internationally. It combines low density with excellent high-temperature performance, creep resistance, flame retardancy, and high elastic modulus, making it promising for applications in advanced aero-engine turbine blades and compressor blades. This material possesses a face-centered cubic ordered superlattice structure, exhibiting significant anisotropy and room-temperature brittleness. Its microstructure is extremely sensitive to processing methods. In traditional machining processes, the high hardness, poor thermal conductivity, and strong chemical reactivity of titanium-aluminum single crystal easily lead to rapid tool wear, microcracks on the machined surface, work hardening, and residual stress concentration, severely impacting the fatigue life and reliability of the blades.

[0004] Titanium-aluminum single-crystal blade blanks are mostly formed using directional solidification or single-crystal casting processes, and are generally in bar form with a large machining allowance. Existing machining methods are not only prone to surface defects such as tearing and chipping when dealing with this type of material, making it difficult to meet aerospace-grade requirements, but also have low machining efficiency and extremely high tooling costs.

[0005] Electrochemical machining, as a non-contact manufacturing process, removes materials through electrochemical dissolution. It is not limited by the hardness or strength of the workpiece, and it involves no cutting force, no tool wear, and can process complex three-dimensional surfaces, making it particularly suitable for difficult-to-machine materials such as titanium alloys and nickel-based superalloys. However, titanium-aluminum single crystals are prone to stray corrosion, uneven passivation, and poor processing stability in conventional electrolytes, leading to difficulties in controlling forming accuracy and surface integrity. Currently, the electrochemical machining process for titanium-aluminum single crystal blades is still immature, particularly lacking systematic optimization in electrolyte formulation, pulse power supply mode, and flow field design, which limits the application of this technology in high-performance blade manufacturing. Summary of the Invention

[0006] The purpose of this invention is to provide an electrolytic machining method for titanium-aluminum single crystal blades to solve the problems of poor surface quality, high processing cost, and low efficiency in the machining of titanium-aluminum single crystal blades.

[0007] To achieve the above objectives, the technical solution provided by this invention is: an electrolytic processing method for titanium-aluminum single crystal blades, comprising the following steps: S1: A process reference block is machined on the blade bar blank by CNC milling. The blade is positioned by the reference block and clamped in a special tooling fixture with an arc-shaped flow guide structure inlet and outlet. The assembled tooling is then fixed on the electrolytic machining tool. S2: Prepare the electrolyte, connect the inlet and outlet pipes of the electrolyte circulation system to the inlet and outlet ports on the tooling; start the electrolyte circulation and verify the sealing performance. S3: Perform electrolytic machining, including two stages: rapid material removal and precision electrolytic machining. The first stage is rapid material removal processing, using a pulse power supply with a frequency of 1kHz to 2kHz and a duty cycle of 60% to 80%, and the cathode is fed at a constant speed of 1 to 3mm / min. The second stage is precision electrolytic machining, which uses an intermittent bipolar high-frequency group pulse power supply. The forward pulse voltage is 5 to 10 times that of the reverse pulse voltage, the frequency of a single high-frequency pulse is 50kHz to 100kHz, and the frequency of the pulse group is 50Hz to 100Hz. The cathode adopts a vibration feed mode, and its vibration frequency is equal to the frequency of the pulse group, forming a coupled vibration feed. S4: After electrolytic machining, the profile and surface roughness of the blades are inspected.

[0008] To optimize the above technical solution, the specific measures also include: In step S1, the minimum machining allowance of the area to be machined in the blade bar blank is 0.5mm to 1mm.

[0009] The reference block is a rectangular block, which is machined on the upper and lower edge plates of the blade, and has cooling holes for heat dissipation.

[0010] The side of the reference block located near the upper edge plate of the blade is used as the conductive surface for electrolytic machining, and the inlet and outlet of the cooling hole are opened on two opposite non-conductive surfaces of the reference block.

[0011] Furthermore, step S1 also includes: installing a tool cathode on the spindle of the electrolytic machining tool, adjusting the relative position of the cathode and the workpiece; connecting the positive terminal of the power supply to a reference block located near the upper edge plate of the blade to make the blade positively charged, and connecting the negative terminal of the power supply to the tool cathode.

[0012] In step S2, the electrolyte contains 15%~25% sodium chloride, 3%~6% citric acid and 1.5%~3% boric acid by mass; the pH value of the electrolyte is 5.5~6.5, and the temperature of the electrolyte during processing is controlled at 25℃~40℃.

[0013] Further, in step S2, the step of starting the electrolyte circulation and verifying the sealing is specifically as follows: with the power off, start the electrolyte circulation system and circulate the electrolyte at a test pressure lower than the processing pressure for a period of time; simultaneously monitor whether the flow rates of the inlet and outlet match. If there is a continuous abnormal deviation, it is determined that there is a leak, and the tooling seal needs to be checked and adjusted. After confirming there is no leakage, maintain electrolyte circulation and test pressure, and observe whether the system pressure remains stable without significant drop to determine if the sealing is qualified.

[0014] Furthermore, in step S4, the detection of the blade profile and surface roughness specifically includes: the blade profile is not greater than 0.1 mm, the blade surface roughness is less than Ra 0.4 μm, and there are no short-circuit burns on the blade processing surface.

[0015] If the inspection fails, the blades will be repaired or scrapped based on the specific defects: If the profile of the blade is not up to standard, the blade is re-clamped into the special tooling fixture, and the same power parameters and feed mode as the precision electrolytic machining stage are used to perform local electrolytic repair on the out-of-tolerance area. If the surface roughness of the blade is not up to standard, the blade shall be mechanically or chemically polished. If short-circuit burns occur on the machined surface of the blade and cannot be eliminated through local repair, it should be scrapped.

[0016] Furthermore, in step S1, the radius of curvature of the arc-shaped flow guiding structure of the special tooling fixture is 50mm to 200mm, guiding the electrolyte to flow uniformly along the blade profile.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention removes material through electrolytic machining, which has a much higher processing speed than traditional CNC milling. It is especially suitable for high-hardness, high-brittleness, and difficult-to-machine materials such as titanium-aluminum single crystals. The machining process has no mechanical cutting force and will not introduce residual stress, microcracks, or structural damage on the blade surface, which is beneficial to maintaining the original mechanical properties and fatigue strength of titanium-aluminum single crystal materials.

[0018] This invention combines rapid material removal and precision electrolytic machining in two stages, achieving high-precision forming of the blade profile while ensuring material removal efficiency. It also eliminates defects such as tool marks and vibration lines commonly found in machining, resulting in good surface integrity and meeting the stringent requirements of aero-engine blades for aerodynamic performance and fatigue life.

[0019] This invention utilizes an intermittent bipolar high-frequency group pulse power supply, combined with a cathode vibration feed mode, to achieve frequency coupling between the pulse group and mechanical vibration. Modulating the high-frequency main pulse into a group pulse output not only suppresses stray corrosion in non-processed areas but also ensures effective discharge of electrolytic products during pulse intervals. Simultaneously, when the power supply is in negative polarity, it can remove trace impurities adhering to the cathode surface, improving the precision of electrolytic machining.

[0020] This invention adds citric acid and boric acid to the sodium chloride electrolyte solution. The citric acid and boric acid form a passivation layer on the surface of the titanium-aluminum single crystal material, thereby inhibiting corrosion in low current density areas, improving the stray corrosion phenomenon of titanium-aluminum single crystal materials in sodium chloride electrolyte, and achieving higher processing accuracy, better surface quality, and a more stable processing process.

[0021] The rework strategy for non-compliant contours and roughness in this invention allows for repair through localized electrolysis if the contour is out of tolerance, and subsequent polishing to address insufficient surface roughness. This design enhances the process's tolerance and adaptability, improving product yield and reducing scrap losses. Attached Figure Description

[0022] Figure 1 This is a blank image of a certain type of titanium-aluminum single crystal blade.

[0023] Figure 2 This is a three-dimensional model of the blade in the example of this invention.

[0024] Figure 3 This refers to the blade blank before electrolytic processing in this embodiment of the invention.

[0025] Figure 4 This is a schematic diagram of the coupling method between the intermittent bipolar high-frequency group pulse power supply and the vibration feed in an embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0027] This invention provides an electrolytic processing method for titanium-aluminum single crystal blades, comprising the following steps: S1: A process reference block is machined on the blade bar blank by CNC milling. The blade is positioned by the reference block and clamped in a special tooling fixture with an arc-shaped flow guide structure inlet and outlet. The assembled tooling is then fixed on the electrolytic machining tool. In some embodiments, in step S1, the minimum machining allowance of the area to be machined in the blade bar blank is 0.5mm to 1mm.

[0028] The reference block is a rectangular block, which is machined on the upper and lower edge plates of the blade, and has cooling holes for heat dissipation.

[0029] Preferably, the side of the reference block located near the upper edge plate of the blade is used as the conductive surface for electrolytic machining, and the inlet and outlet of the cooling hole are opened on two opposite non-conductive surfaces of the reference block.

[0030] Step S1 also includes: installing a tool cathode on the spindle of the electrolytic machining machine tool, adjusting the relative position of the cathode and the workpiece; connecting the positive terminal of the power supply to the reference block located near the upper edge plate of the blade to make the blade positively charged, and connecting the negative terminal of the power supply to the tool cathode.

[0031] In some embodiments, in step S1, the radius of curvature of the arc-shaped flow guiding structure of the special tooling fixture is 50mm to 200mm, guiding the electrolyte to flow uniformly along the blade profile.

[0032] S2: Prepare the electrolyte, connect the inlet and outlet pipes of the electrolyte circulation system to the inlet and outlet ports on the tooling; start the electrolyte circulation and verify the sealing performance. In some embodiments, in step S2, the electrolyte contains 15%~25% sodium chloride, 3%~6% citric acid and 1.5%~3% boric acid by mass; the pH value of the electrolyte is 5.5~6.5, and the temperature of the electrolyte during processing is controlled at 25℃~40℃.

[0033] Sodium chloride electrolyte is a non-passivating electrolyte with high current density, making it highly efficient for the electrolytic processing of titanium-aluminum single crystal materials. Adding citric acid and boric acid creates a weakly acidic environment, increasing the solubility of the titanium-aluminum single crystal material in the electrolyte. Simultaneously, citric acid reacts with the hydroxides generated during processing, reducing the adhesion of electrolytic products to the processed surface, thereby improving processing efficiency and precision.

[0034] Preferably, the electrolyte temperature is controlled at 25℃~40℃ during the processing, which is beneficial to improve the reaction rate and suppress pitting corrosion on the anode surface.

[0035] In some implementations, in step S2, the electrolyte circulation is started. To prevent electrolyte leakage from affecting the flow field stability in the processing area, the sealing performance needs to be verified: with the power off, the electrolyte circulation system is started and the electrolyte is circulated at a test pressure lower than the processing pressure for a period of time; the flow rates of the inlet and outlet are monitored simultaneously to see if they match. If there is a continuous abnormal deviation, it is determined that there is a leak, and the tooling seal needs to be checked and adjusted. After confirming there is no leakage, maintain electrolyte circulation and test pressure, and observe whether the system pressure remains stable without significant drop to determine if the sealing is qualified.

[0036] In some implementations, S3: Electrolytic machining is performed, including two stages: rapid material removal and precision electrolytic machining. The first stage is rapid material removal processing, using a pulse power supply with a frequency of 1kHz to 2kHz and a duty cycle of 60% to 80%, and the cathode is fed at a constant speed of 1 to 3mm / min. The second stage is precision electrolytic machining, employing an intermittent bipolar high-frequency pulse power supply. The forward pulse voltage is 5 to 10 times the reverse pulse voltage, the frequency of a single high-frequency pulse is 50kHz to 100kHz, and the pulse group frequency is 50Hz to 100Hz. The cathode uses a vibration feed mode, with its vibration frequency equal to the pulse group frequency, forming a coupled vibration feed. Preferably, high-frequency pulses can suppress stray corrosion in non-processed areas, improve the localization of electrolytic processing and the final forming accuracy, while low-frequency pulse groups facilitate coupling with cathode vibration.

[0037] The main purpose of the rapid material removal stage is to remove material, so a uniform feed processing method is adopted. In the precision electrolytic machining stage, the machining gap is relatively small, and it is difficult to remove the electrolytic products. The vibration feed processing method is beneficial to improve the flow field and the removal of products.

[0038] S4: After electrolytic machining, the profile and surface roughness of the blades are inspected.

[0039] In some embodiments, step S4, which involves detecting the blade profile and surface roughness, specifically includes: the blade profile is no greater than 0.1 mm, the blade surface roughness is less than Ra 0.4 μm, and there are no short-circuit burns on the blade processing surface.

[0040] If the inspection fails, the blades will be repaired or scrapped based on the specific defects: If the profile of the blade is not up to standard, the blade is re-clamped into the special tooling fixture, and the same power parameters and feed mode as the precision electrolytic machining stage are used to perform local electrolytic repair on the out-of-tolerance area. If the surface roughness of the blade is not up to standard, the blade shall be mechanically or chemically polished. If short-circuit burns occur on the machined surface of the blade and cannot be eliminated through local repair, it should be scrapped.

[0041] Preferably, since stray corrosion occurs during electrolytic machining, which corrodes the tooling fixture and affects the clamping accuracy, the entire tooling fixture needs to be made of non-metallic materials. The workpiece is connected to the power line through a metal conductive block. At the same time, since the current is large, the metal conductive block needs to be provided with liquid passage holes for heat dissipation and cooling to prevent burns and adhesion at the conductive contact points.

[0042] In this embodiment, the turbine blade blank of a certain type of aero-engine is a titanium-aluminum single-crystal cast bar, such as... Figure 1 As shown, the 3D model is... Figure 2 .

[0043] According to the processing method provided by the present invention, firstly, a V-block is used to clamp the outer circle of the blade blank, and CNC milling is used to machine the electrolytic machining process reference block and cooling holes, such as... Figure 3 As shown.

[0044] In some implementations, after CNC milling, the blade is precisely formed using an electrolytic machining process, with the reference block as the process reference. The surface roughness of the electrolytic machined surface is lower than Ra 0.4 μm, and the blade profile profile is 0.1 mm. The specific operation is as follows: The blade is assembled with a specialized tooling fixture, and the assembled fixture is fixed on the electrochemical machining tool platform. A special tool cathode is installed on the machine tool spindle, and the relative position of the cathode and the workpiece is adjusted using a specialized calibration device. The positive terminal of the power supply is connected to one of the reference blocks on the workpiece to make the blade positively charged, and the negative terminal of the power supply is connected to the tool cathode to make the tool cathode negatively charged.

[0045] Prepare an electrolyte solution composed of sodium chloride, citric acid, and boric acid, with the following mass fractions: sodium chloride 21.5%, citric acid 4.3%, and boric acid 2.15%, respectively, and ensure that the pH of the electrolyte solution is between 5.5 and 5.8.

[0046] Connect the inlet and outlet pipes of the electrolyte system to the corresponding interfaces on the tooling, and verify the sealing performance of the tooling by starting the electrolyte circulation system. Simultaneously, set the corresponding power supply and cathode processing modes, performing processing in two stages: a rapid material removal stage, using pulsed current combined with uniform cathode feed; and a precision electrolytic machining stage, using an intermittent bipolar high-frequency group pulse power supply and coupled vibration feed. The coupling relationship between this power supply and cathode is described in [reference needed]. Figure 4 After verifying that the test parameters are correct and that there is no short circuit in the tooling, the electrolyte is turned on and the power is switched on for processing.

[0047] After machining, the blade profile was evaluated using a coordinate measuring machine. The blade profile accuracy was 0.1 mm, meeting the drawing requirements. The surface roughness of the blade was evaluated using a surface roughness comparison sample, which also met the drawing requirements. Under a microscope, the machined surface showed no short-circuit burns, and the surface quality met the drawing requirements.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. An electrolytic processing method for titanium-aluminum single crystal blades, characterized in that, Includes the following steps: S1: A process reference block is machined on the blade bar blank by CNC milling. The blade is positioned by the reference block and clamped in a special tooling fixture with an arc-shaped flow guide structure inlet and outlet. The assembled tooling is then fixed on the electrolytic machining tool. S2: Prepare an electrolyte solution using 15%~25% sodium chloride, 3%~6% citric acid and 1.5%~3% boric acid by mass fraction. Connect the inlet and outlet pipes of the electrolyte circulation system to the inlet and outlet ports on the tooling. Start the electrolyte circulation and verify the sealing performance. S3: Perform electrolytic machining, including two stages: rapid material removal and precision electrolytic machining. The first stage is rapid material removal processing, using a pulse power supply with a frequency of 1kHz to 2kHz and a duty cycle of 60% to 80%, and the cathode is fed at a constant speed of 1 to 3mm / min. The second stage is precision electrolytic machining, which uses an intermittent bipolar high-frequency group pulse power supply. The forward pulse voltage is 5 to 10 times that of the reverse pulse voltage, the frequency of a single high-frequency pulse is 50kHz to 100kHz, and the frequency of the pulse group is 50Hz to 100Hz. The cathode adopts a vibration feed mode, and its vibration frequency is equal to the frequency of the pulse group, forming a coupled vibration feed. S4: After electrolytic machining, the profile and surface roughness of the blades are inspected.

2. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: In step S1, the minimum machining allowance of the area to be machined in the blade bar blank is 0.5mm to 1mm.

3. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: The reference block is a rectangular block, which is machined on the upper and lower edge plates of the blade, and has cooling holes for heat dissipation.

4. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 3, characterized in that: The side of the reference block located near the upper edge plate of the blade is used as the conductive surface for electrolytic machining, and the inlet and outlet of the cooling hole are opened on two opposite non-conductive surfaces of the reference block.

5. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: Step S1 also includes: installing a tool cathode on the spindle of the electrolytic machining machine tool, adjusting the relative position of the cathode and the workpiece; connecting the positive terminal of the power supply to the reference block located near the upper edge plate of the blade to make the blade positively charged, and connecting the negative terminal of the power supply to the tool cathode.

6. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: In step S2, the pH value of the electrolyte is 5.5~6.5, and the temperature of the electrolyte during processing is controlled at 25℃~40℃.

7. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: In step S4, the detection of the blade profile and surface roughness specifically includes: the blade profile is no greater than 0.1 mm, the blade surface roughness is less than Ra 0.4 μm, and there are no short-circuit burns on the blade processing surface.

8. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 7, characterized in that: If the inspection fails, the blades will be repaired or scrapped based on the specific defects: If the profile of the blade is not up to standard, the blade is re-clamped into the special tooling fixture, and the same power parameters and feed mode as the precision electrolytic machining stage are used to perform local electrolytic repair on the out-of-tolerance area. If the surface roughness of the blade is not up to standard, the blade shall be mechanically or chemically polished. If short-circuit burns occur on the machined surface of the blade and cannot be eliminated through local repair, it should be scrapped.

9. The electrolytic processing method for titanium-aluminum single crystal blades according to claim 1, characterized in that: In step S2, the step of starting the electrolyte circulation and verifying the sealing performance specifically involves starting the electrolyte circulation system with the power off and circulating the electrolyte at a test pressure lower than the processing pressure for a period of time. Simultaneously monitor whether the flow rates at the inlet and outlet match. If there is a continuous abnormal deviation, it is determined that there is a leak, and the tooling seal needs to be checked and adjusted. After confirming there is no leakage, maintain electrolyte circulation and test pressure, and observe whether the system pressure remains stable without significant drop to determine if the sealing is qualified.

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