Precise and efficient machining method for molded surface of blade body of blade

Abstract

The invention discloses a precise and efficient machining method of a blade body molded surface, which comprises ultrasonic numerical control milling and blade body selective strengthening which are carried out in sequence, on one hand, ultrasonic waves are applied to a blade body in the direction of a cutter shaft or the cutting direction by the ultrasonic numerical control milling, and on the other hand, the blade body is milled in a surrounding milling or reciprocating milling mode; the surface roughness of the milled blade body meets the final surface roughness requirement of the blade body; a blade body is divided into a plurality of different areas including the front edge, the rear edge, the blade root, the blade middle and the blade tip through blade body selective area strengthening, strengthening is conducted on the different areas through a strengthening method capable of reducing the surface roughness, and different residual compressive stress and distribution depth are obtained in each area. And the surface roughness of all the areas meets the final surface roughness requirement of the blade body of the blade. Existing machining procedures are reduced, the production efficiency and the product surface consistency are improved, selective strengthening is carried out while the blade body is strengthened, the size consistency of the blade is further improved, and the anti-fatigue life of the blade is further prolonged.

Description

Technical Field

[0001] This invention belongs to the field of machining technology for aero-engine blade forgings, and in particular, relates to a precision and efficient machining method for the blade profile. Background Technology

[0002] The current processing technology for compressor blades (fan blades) in the industry is as follows: CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing. This process is lengthy and inefficient, and the multiple steps can affect the dimensional stability of the product. Among these processes, mechanical shot peening of compressor blades is a disordered process, and the inconsistent compressive stress state of the blade body can lead to poor fatigue resistance and manufacturing stability. Furthermore, shot peening reduces the surface finish of the blade body, requiring an additional vibration finishing process. During the subsequent vibration finishing process, some compressive stress is released, which weakens the shot peening strengthening effect and reduces the fatigue life of the blade. At the same time, the conventional CNC milling process suffers from problems such as tool chatter, uneven tool wear, and excessive cutting stress, which can result in poor blade body waviness and even obvious tool marks at the transition radius, blade tip, and leading and trailing edges, severely restricting the improvement of blade efficiency and product quality.

[0003] Currently, some domestic blade manufacturers have replaced manual labor with automation in the machining process of blade profiles. This has reduced quality fluctuations caused by human factors to some extent, and improved production efficiency to a certain extent by reducing waiting waste through lean unit layout. However, the fundamental process still uses the machining process of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing", and there is still considerable room for improvement in production efficiency and product quality. For example, Chinese invention patent 201611019692.X discloses a CNC machining method and device for complex compressor rotor blade profiles. The blade profile is machined by "edge milling → spiral milling of the blade body from tip to root → edge milling → root cleaning". Although this solves the problem of precision CNC machining of complex compressor rotor blade profiles to some extent, subsequent grinding and polishing processes are still needed to remove tool marks, mechanical shot peening is used for strengthening, and surface vibration finishing is used to improve the surface finish. The problems of long process flow and low efficiency remain unsolved. Summary of the Invention

[0004] The present invention aims to provide a precision and efficient machining method for blade profiles, which reduces existing machining steps, improves production efficiency, enhances product surface consistency, and performs selective reinforcement while strengthening the blade body, thereby further improving the dimensional consistency and fatigue life of the blade.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A precision and efficient machining method for blade profiles includes: Step 1, ultrasonic CNC milling, involves applying ultrasonic waves to the blade body along the tool axis or cutting direction, and milling the blade body using a circular milling or reciprocating milling method. After milling, the surface roughness of the blade body meets the final surface roughness requirements of the blade body. Step 2: Selective reinforcement of the leaf blade. The leaf blade is divided into several different regions, including the leading and trailing edges, leaf root, leaf middle, and leaf tip. Reinforcement methods that can reduce surface roughness are used to reinforce different regions separately. Different residual compressive stresses and distribution depths are obtained in each region, and the surface roughness of all regions meets the final surface roughness requirements of the leaf blade.

[0006] As one approach, in step one, when milling the blade using a milling or reciprocating milling method, the cutting speed is 100 m / min to 300 m / min, the feed rate is 0.1 mm / rev to 0.5 mm / rev, the cutting depth is 0.1 mm to 0.5 mm, and the spindle speed is 1000 r / min to 3000 r / min.

[0007] As one approach, in step one, the amplitude of the ultrasonic wave along the tool axis or cutting direction is 10μm to 50μm, and the frequency is 20kHz to 40kHz.

[0008] As one approach, in step one, the surface roughness of the blade after milling is ≤ Ra0.4μm.

[0009] As one approach, the strengthening method for reducing surface roughness in step two includes ultrasonic rolling, high-frequency electrical pulse-assisted micro-forging, axial ultrasonic-assisted micro-forging, or electromagnetically driven micro-forging.

[0010] As one approach, in step two, the residual compressive stress values ​​in the leading and trailing edge regions of the reinforced regions are less than those in the leaf root region, leaf middle region, and leaf tip region.

[0011] As an option, The residual compressive stress values ​​in the leading and trailing edge regions are 300 MPa to 400 MPa; The residual compressive stress in the leaf root region is 500 MPa to 900 MPa. The residual compressive stress values ​​in the leaf mid-region and leaf tip region are 500MPa to 800MPa.

[0012] As one approach, in step two, the minimum residual compressive stress distribution depth in the leading and trailing edge regions after reinforcement is less than that in the middle and tip regions of the blade, while the minimum residual compressive stress distribution depth in the middle and tip regions of the blade is less than that in the root region of the blade.

[0013] Alternatively, the residual compressive stress distribution depth in the leading and trailing edge regions is 50 μm to 400 μm; The residual compressive stress distribution depth in the leaf root region is 300 μm to 800 μm; The residual compressive stress distribution depth in the leaf mid-region and leaf tip region is 150μm to 700μm.

[0014] As one approach, after selective reinforcement of the blade area, the surface roughness of all regions is ≤Ra0.4μm.

[0015] Compared with existing processing methods, this invention introduces ultrasonic-assisted milling technology to replace the original CNC milling technology. This significantly reduces cutting force and heat generation through mechanisms such as intermittent cutting with high-frequency micro-amplitude vibration, improved chip formation and removal, reduced tool-workpiece contact time, and enhanced cooling and lubrication. Therefore, the blade milling path can employ either circular milling or reciprocating milling, thereby improving blade machining efficiency and surface quality. Furthermore, it introduces a selective blade strengthening process to reduce surface roughness, replacing the original mechanical shot peening and vibration finishing processes. Finally, it considers the service characteristics of different parts of the blade, such as the leading and trailing edges, root, middle, and tip. By reserving residual compressive stress of different values ​​and depths according to the properties and thickness of the blade, the advantages of integrated processing, efficient surface treatment, reduced process chain length, automated integration, and process flexibility can be achieved. This effectively shortens the process flow of blade surface strengthening and further improves the fatigue life of the blade. By effectively combining the characteristics of ultrasonic assisted milling and blade selective strengthening processes, the existing processing process of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing" can be reduced to "ultrasonic CNC milling → blade selective strengthening". This can significantly reduce the number of processes, improve production efficiency, and improve the consistency of product quality through the reduction of processes. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of ultrasonic vibration-assisted milling. Figure 2 A schematic diagram showing the effect of ultrasonic vibration-assisted circumferential milling on the blade body; Figure 3 A schematic diagram showing the effect of ultrasonic vibration-assisted reciprocating milling on the blade body; Figure 4 This is a schematic diagram of an electromagnetic micro-forging structure. Figure 5 This is a schematic diagram of selected areas for strengthening the blade. Detailed Implementation

[0017] The present invention will be further described below with reference to 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 modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0018] For the existing process flow of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing", the solution of this invention is: to introduce ultrasonic-assisted milling process to replace the original CNC milling process, to introduce selective area strengthening process to replace the original mechanical shot peening strengthening process and vibration finishing process, and to optimize the process flow to "ultrasonic CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing" and the characteristics of the newly introduced process, in combination with the characteristics of the original process flow of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing" and the newly introduced process flow.

[0019] In the ultrasonic CNC milling process, the blade milling path can adopt a circular milling or reciprocating milling machining scheme. The cutting speed is (100~300) m / min, the feed rate is (0.1~0.5) mm / rev, the cutting depth is (0.1~0.5) mm, and the spindle speed is (1000~3000) r / min. Its auxiliary ultrasonic parameters are: amplitude (10~50) μm and frequency (20~40) kHz along the tool axis or cutting direction. After ultrasonic CNC milling, the surface roughness requirement of the blade is the final product requirement, which is generally ≤Ra0.4μm.

[0020] In the selective strengthening process of the blade, strengthening processes such as ultrasonic rolling, high-frequency electric pulse assisted micro forging, axial ultrasonic assisted micro forging, and electromagnetic drive micro forging can be used to reduce the surface roughness of the workpiece. The blade is divided into parts such as the leading and trailing edges, blade root, blade middle, and blade tip. After selective strengthening, the roughness of each part of the blade must meet the requirements of the finished product (generally, the roughness requirement of the final finished blade is ≤Ra0.4μm). For thin-walled structures at the leading and trailing edges, the residual compressive stress and depth after strengthening should be appropriately reduced (generally, the residual compressive stress is 300MPa–400MPa, and the depth is 50μm–400μm). For structures in areas where fatigue preferentially occurs at the blade root, the residual compressive stress and depth after strengthening should be appropriately increased (generally, the residual compressive stress is 500MPa–900MPa, and the depth is 300μm–800μm). For structures in non-sensitive fatigue-initiating areas such as the blade middle and tip, the residual compressive stress and depth after strengthening should be maintained at an appropriate level (generally, the residual compressive stress is 500MPa–800MPa, and the depth is 150μm–700μm). Factors affecting the effectiveness of selective strengthening in the blade area include the specific strengthening process and its parameters. When necessary, orthogonal experiments (including fatigue tests) or finite element simulation analysis should be conducted to determine the optimal process parameters, taking into account the specific blade material properties and structural design.

[0021] The precision and efficient machining method for the blade profile of this invention reduces the existing machining process of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing" to "ultrasonic CNC milling → selective blade strengthening". The implementation process of this invention is as follows: 1. Material preparation. The blades are machined up to the precision milling stage according to the existing processing technology.

[0022] 2. Ultrasonic CNC precision milling of the blade. During the ultrasonic CNC milling process, the blade milling path can employ either winding milling or reciprocating milling. The cutting speed is 200 m / min, the feed rate is 0.3 mm / rev, the depth of cut is 0.4 mm, and the spindle speed is 2000 r / min. Figure 1 As shown, its auxiliary ultrasonic parameters are: amplitude 50 μm and frequency 40 kHz along the blade axis. Figure 1 The upper right image shows a magnified view of a portion of the milling process. The motion trajectory shown is the magnified actual toolpath trajectory formed after axial ultrasonic vibration, indicating that the magnified toolpath is not flat but has a certain amplitude. The surface roughness requirement after ultrasonic CNC milling of the blade is the same as the final product requirement, generally ≤Ra0.4μm (when the final product requirement is ≤Ra0.4μm). Figure 2 , Figure 3 As shown, after ultrasonic-assisted milling, whether the blade body is milled around or reciprocated, the surface roughness of the blade body can meet the requirement of ≤Ra0.4μm. Figure 2 , Figure 3 In the diagram, the three rectangular areas corresponding to the arrows represent the leaf crown (or leaf tip), leaf middle, and leaf root from left to right. Below the arrows are the measurement results of the white light interferometer for the leaf crown (or leaf tip), leaf middle, and leaf root, respectively, and the values ​​at the bottom represent the surface roughness.

[0023] 3. Selective strengthening of the blade body. The selective strengthening process of the blade body employs electromagnetically driven micro-forging as a strengthening process to reduce the surface roughness of the workpiece. The electromagnetically driven micro-forging device is as follows: Figure 4 As shown, to reduce workpiece transfer and frequent workpiece loading and unloading, it is recommended to integrate the electromagnetic drive micro-forging device with the ultrasonic CNC milling machine; in the blade selective strengthening process, the blade is divided into leading and trailing edges, blade root, blade middle, and blade tip, etc. Figure 5As shown, the roughness of each part of the blade after selective reinforcement meets the requirements of the finished product (generally, the roughness requirement of the final finished blade is ≤Ra0.4μm). For the thin-walled structures at the leading and trailing edges, the residual compressive stress value and depth formed after reinforcement are appropriately reduced (generally, the residual compressive stress is 300MPa~400MPa and the depth is 50μm~400μm). For the structures in the fatigue preferential initiation area at the blade root, the residual compressive stress value and depth formed after reinforcement are appropriately increased (generally, the residual compressive stress is 500MPa~900MPa and the depth is 300μm~800μm). For the structures in the non-fatigue initiation areas such as the middle and tip of the blade, the residual compressive stress value and depth formed after reinforcement are maintained appropriately (generally, the residual compressive stress is 500MPa~800MPa and the depth is 150μm~700μm). Factors affecting the effectiveness of blade selective reinforcement include the specific reinforcement process and its parameters. When necessary, orthogonal tests (including fatigue tests) or finite element simulation analysis should be conducted in conjunction with the specific blade material properties and structural design to determine the optimal process parameters.

[0024] Compared with existing processing methods, this invention reduces the original processing technology of "CNC milling → (CNC) grinding and polishing → (mechanical shot peening) → surface finishing" to "ultrasonic CNC milling → selective blade strengthening", thereby achieving the purpose of reducing processes, improving production efficiency, and improving product surface consistency. Furthermore, selective strengthening is performed while strengthening the blade, which can further improve the dimensional consistency and fatigue life of the blade.

[0025] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A precision and efficient machining method for the blade profile, characterized in that, include: Step 1, ultrasonic CNC milling, involves applying ultrasonic waves to the blade body along the tool axis or cutting direction, and milling the blade body using a circular milling or reciprocating milling method. After milling, the surface roughness of the blade body meets the final surface roughness requirements of the blade body. Step 2: Selective reinforcement of the leaf blade. The leaf blade is divided into several different regions, including the leading and trailing edges, leaf root, leaf middle, and leaf tip. Reinforcement methods that can reduce surface roughness are used to reinforce different regions separately. Different residual compressive stresses and distribution depths are obtained in each region, and the surface roughness of all regions meets the final surface roughness requirements of the leaf blade.

2. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step one, when milling the blade using milling or reciprocating milling, the cutting speed is 100 m / min to 300 m / min, the feed rate is 0.1 mm / rev to 0.5 mm / rev, the cutting depth is 0.1 mm to 0.5 mm, and the spindle speed is 1000 r / min to 3000 r / min.

3. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step one, the amplitude of the ultrasonic wave along the tool axis or cutting direction is 10μm to 50μm, and the frequency is 20kHz to 40kHz.

4. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step one, the surface roughness of the blade after milling is ≤ Ra0.4μm.

5. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step two, the strengthening methods that can reduce surface roughness include ultrasonic rolling, high-frequency electrical pulse assisted micro forging, axial ultrasonic assisted micro forging, or electromagnetically driven micro forging.

6. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step two, the residual compressive stress values ​​in the leading and trailing edge regions of the strengthened regions are less than those in the leaf root region, leaf middle region, and leaf tip region.

7. The precision and efficient machining method for the blade profile according to claim 6, characterized in that: The residual compressive stress values ​​in the leading and trailing edge regions are 300 MPa to 400 MPa; The residual compressive stress in the leaf root region is 500 MPa to 900 MPa. The residual compressive stress values ​​in the leaf mid-region and leaf tip region are 500MPa to 800MPa.

8. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: In step two, after strengthening, the minimum residual compressive stress distribution depth in the leading and trailing edge regions is less than that in the middle and tip regions of the leaf, while the minimum residual compressive stress distribution depth in the middle and tip regions of the leaf is less than that in the root region of the leaf.

9. A precision and efficient machining method for the blade profile according to claim 8, characterized in that: The residual compressive stress distribution depth in the front and rear edge regions is 50 μm to 400 μm; The residual compressive stress distribution depth in the leaf root region is 300 μm to 800 μm; The residual compressive stress distribution depth in the leaf mid-region and leaf tip region is 150μm to 700μm.

10. The precision and efficient machining method for the blade profile according to claim 1, characterized in that: After selective reinforcement of the blade, the surface roughness of all areas is ≤Ra0.4μm.

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