High-precision numerical control machining method for large-size large-curvature TiAl alloy turbine blade

Abstract

The invention discloses a large-size large-curvature TiAl alloy turbine blade high-precision numerical control machining method which comprises the following steps that TiAl alloy is poured into a metal mold, and a blade ingot is manufactured; the blade ingot is subjected to hot isostatic pressing and heat treatment; firstly, a blade profile and runner surfaces of upper and lower margin plates are machined according to a blade model, the upper margin plate, sealing teeth and the lower margin plate of the blade are continuously machined, and a root extending part is machined to a tolerance zone on a three-dimensional model to serve as a reference surface; a three-coordinate measuring machine is adopted to carry out blade profile and full-size measurement on a machined blade, and the size is manually assisted to be ground to a blade product tolerance zone. According to the method, the advantages of five-axis machine tool machining are utilized, the problems that the metallurgical quality of the large-size blade is difficult to control and manual grinding is difficult to control are solved, the consistency of products machined through the method is good, the quality is guaranteed, the efficiency and the percent of pass can be greatly improved, and the productivity is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aeroengines, and in particular relates to a high-precision numerical control machining method for a large-size and large-curvature TiAl alloy turbine blade. Background Art

[0002] TiAl alloy is a new type of high temperature resistant structural material with a density of only half that of nickel-based high temperature alloys and excellent high temperature performance. Recently, the demand for weight reduction in aircraft engines has become increasingly urgent. TiAl alloy low-pressure turbine blades can partially replace nickel-based high temperature alloy blades, promote the design optimization and lightweight development of aircraft engine blade disk components, and have great application potential. With the explosive growth in demand for domestic engines such as Changjiang 1000 and Changjiang 2000, how to meet the production capacity demand for large-size TiAl alloy low-pressure turbine blades has become a very important issue.

[0003] Traditional investment casting can produce TiAl alloy blades. Using the lost wax method and oxide mold shells, castings with excess are obtained, and then samples that meet the size requirements are obtained through post-processing and polishing. However, the investment casting process has many steps and a long cycle, with more than 50 steps, and the post-processing and non-destructive testing are complicated and alternating; metallurgical problems such as looseness and inclusions restrict the product qualification rate. Because titanium alloys are active and react with almost all oxide mold shells, it is very easy to cause inclusions, and the product qualification rate is difficult to meet the needs of batch shipments; the blade body and upper and lower edge plates of smaller investment casting products have small excess sizes, which is convenient for grinding small-sized blade products, while large-sized and large-curvature blades pose huge challenges to casting and post-processing grinding and polishing. In order to fully form and avoid metallurgical defects, the blade body and upper and lower edge plates will have a large excess during the casting process, and it is extremely difficult to adjust the size by manual grinding. First, large-sized casting blades have a large processing allowance to solve metallurgical defects; second, large-sized blades are more likely to deform during casting, hot pressing and heat treatment, and their sizes are more likely to deviate from the three-dimensional model; third, large-sized investment casting blade products are affected by multiple coupled dimensions of size and torsion, and the qualified quality of products becomes increasingly uncertain. In addition, there are large differences in the accuracy and consistency of the reference points and reference planes of manually polished large-sized investment casting blade products, resulting in deviations from the reference coordinate system and difficulties in final size processing. This is because it depends on the experience and technical level of the processing personnel, which can easily cause inaccurate measurement problems, causing trouble for subsequent processing and assembly; because the castings have a large allowance, there is a large demand for skilled polishing personnel, and the personnel are highly dependent, which is very unfavorable for improving production capacity. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to provide a method for processing large-size and large-curvature TiAl alloy turbine blades by metal mold casting blocks + CNC machining + manual assisted grinding to prepare qualified products, breaking through the problems of difficult to solve metallurgical defects such as inclusions and looseness and low pass rate in traditional investment casting processes, reducing dependence on manual grinding, improving product quality and consistency, and greatly improving delivery capabilities.

[0005] In order to solve the above technical problems, the present invention is implemented by the following technical solutions: A high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades, comprising the following steps: Step 1: pouring TiAl alloy into a metal mold to obtain a blade ingot; Step 2: Process the top countersunk holes at the symmetrical positions on both ends of the blade ingot, and use the top countersunk holes to clamp and position the blade ingot on the five-axis machine tool; Step 3: First, process the blade profile and the flow path surfaces of the upper and lower edge plates according to the blade model, and reserve allowances based on the three-dimensional model tolerances of the blade profile; continue to process the blade upper edge plate and sealing teeth, lower edge plate and extended root parts, and reserve allowances based on the three-dimensional model tolerances of the blade upper edge plate, sealing teeth and lower edge plate; the extended root parts are processed to the upper tolerance zone of the three-dimensional model as the reference surface; Step 4: Cut off the top countersunk clamping parts at both ends and the parts connected to the blades, leaving a cutting margin; Step 5: Use a three-dimensional coordinate measuring machine to measure the blade profile and full size of the machined blade to obtain the measurement results; Step 6: According to the dimension results of three-coordinate measurement, manually assist in grinding the dimensions to the tolerance zone of the blade product; Step 7: Polish the blade surface by manual or mechanical polishing, with the blade body and flow channel surface roughness Ra0.3-Ra1.0, and the rest of the roughness Ra1.5-Ra4.0; Step 8: The blades are tested for average grain size using the line-intercepting method.

[0006] Preferably, in step three, firstly, the blade profile and the flow path surfaces of the upper and lower edge plates are processed according to the blade model, and a margin of 0.03-0.08 mm is reserved on the basis of the three-dimensional model tolerance of the blade profile; the upper edge plate and sealing teeth, lower edge plate and root extension of the blade are continued to be processed, and a margin of 0.03-0.08 mm is reserved on the basis of the three-dimensional model tolerance of the upper edge plate, sealing teeth and lower edge plate of the blade.

[0007] Preferably, the metal mold in step one uses three-dimensional software to process the blades with symmetrical or asymmetrical inclusions, and then obtains the inner cavity size of the metal mold based on the offset inclusion size of the blades.

[0008] Preferably, when the blade is processed into a symmetrical or asymmetrical enclosure using three-dimensional software, the symmetrical offset dimensions along the highest point in the width and height directions are 8-16 mm in total, and the symmetrical offset dimensions in the length direction are 30-50 mm in total based on the enclosure.

[0009] Preferably, in step one, the material of the metal mold is hot working die steel, the metal mold is preheated to 350℃-500℃, and after the insulation time is 2-4h, the TiAl alloy is poured into the metal mold, the centrifugal speed is 180-450r / min, the furnace cooling time is more than 10min, and the blade ingot is obtained.

[0010] Preferably, the blade ingot obtained in step one is subjected to hot isostatic pressing and heat treatment to improve defects such as porosity.

[0011] Preferably, the hot isostatic pressing process is: temperature 1200℃-1310℃, pressure 120MPa-160MPa, holding time 200min-260min, Ar gas protection; the heat treatment process is: 950℃-1100℃, time 450min-500min, furnace cooling.

[0012] Preferably, in step 4, the processing method of cutting off the top countersunk clamping parts at both ends and the parts connected to the blades is wire cutting, and the cutting allowance is 0.3-1.0 mm; Preferably, in step six, the manual assisted polishing method uses a combination of machine automated polishing and manual polishing operations.

[0013] Preferably, the length dimension of the large-sized and large-curvature TiAl alloy turbine blade product obtained in step eight is greater than 150 mm.

[0014] Compared with the prior art, the present invention is beneficial in that: This processing method solves the problems of difficult quality control of large-sized blades in the field of investment casting and difficult control of manual grinding. It can avoid the problems of long TiAl alloy casting process, long production time, and large disadvantages of large number of personnel. It can effectively improve production capacity. Under the premise of ensuring efficiency, it adopts the method of machining + manual assisted grinding to ensure the size accuracy and surface quality of the product blades.

[0015] By using a metal mold to cast TiAl alloy blocks, the probability of high-density and low-density inclusion defects produced in the process of preparing titanium alloys with conventional oxide shells is reduced, which is of great benefit to improving the pass rate.

[0016] In particular, for large-sized and large-curvature blades, in order to compensate for the large deformation and metallurgical defects in the casting process, which make manual grinding and polishing extremely difficult, this method makes it easier to ensure the size and greatly improves production efficiency. Through the optimal hot isostatic pressing and heat treatment process, the pores and loose defects inside the material are further reduced to ensure the qualified rate of the product.

[0017] This method takes advantage of the five-axis machine tool processing. After the blade is machined, the grinding allowance size is 0.03-0.08mm. The grinding allowance of the product after high-precision CNC machining is small, which is convenient for manual assisted machining and grinding. The extended root part of the planar structure is directly machined to the tolerance zone by machining. Compared with the method of leaving an allowance at the extended root position and then manually grinding to the tolerance zone, the extended root part is directly machined to obtain the consistency of the two positioning points A1 and A2 by machining. It is better than leaving an allowance at the extended root position and then manually grinding the blade product to the tolerance zone to obtain the consistency of the two positioning points A1 and A2 of the product, thereby improving the quality and consistency of large-size blade products, giving full play to the flexibility of manual labor, and processing products with good consistency, quality assurance, greatly improved efficiency and qualified rate, and a significant leap in production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described below in conjunction with the accompanying drawings.

[0019] Figure 1 It is a schematic diagram of the structure of the blade undergoing inclusion body processing in three-dimensional software.

[0020] Figure 2 It is a metallographic diagram of the leaf body cross-section.

[0021] Figure 3 It is a schematic diagram of the positioning points A1 and A2 at the root of the blade. DETAILED DESCRIPTION

[0022] The present invention is described in detail below in conjunction with specific embodiments: Embodiment (I): A high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades comprises the following steps: Step 1: If Figure 1 As shown, the blade is processed with a symmetrical or asymmetrical inclusion body using three-dimensional software, and the width and height directions are symmetrically offset outward along the highest point, with a total of 10 mm, and the length direction is symmetrically offset on the basis of the inclusion body, with a total of 40 mm, to obtain the offset inclusion body size of a single blade, and the inner cavity size of the metal mold is the size of 1-4 of the above-mentioned rectangular parallelepipeds, and the material of the metal mold is hot working die steel; Step 2: preheat the metal mold to 400°C, keep it warm for 2.5 hours, pour the TiAl alloy into the metal mold, centrifuge at 260r / min, cool it in the furnace for 15 minutes, and then get out of the furnace to obtain a blade ingot; Step 3: The TiAl alloy ingot is subjected to hot isostatic pressing and heat treatment to improve defects such as porosity. The hot isostatic pressing process is: temperature 1230℃, pressure 130MPa, holding time 220min, Ar gas protection; the heat treatment process is: 1000℃, time 460min, furnace cooling; Step 4: Process the top countersinks at the symmetrical positions on both ends of the ingot for the top positioning and clamping of the five-axis machine tool. The center line of the top countersink coincides with the center axis of the blade; Step 5: First, process the blade profile and the flow path surface of the upper and lower edge plates according to the blade model. On the basis of the 3D model tolerance of the blade profile, reserve a 0.04mm margin; continue to process the blade upper edge plate, sealing teeth and lower edge plate. On the basis of the 3D model tolerance of the blade upper edge plate, sealing teeth and lower edge plate, reserve a 0.04mm margin; process the root extension part to the 3D model tolerance zone as the reference surface; Figure 3 As shown in the figure, the two reference points A1 and A2 in the six-point positioning of the blade product are on the reference plane of the extended root part; the non-extended root part of the blade has elastic deformation during machining, and a grinding allowance of 0.04mm is reserved; Step 6: Use wire cutting to cut off the top countersunk clamping parts at both ends and the parts connected to the blades, with a cutting margin range of 0.5mm; Step 7: Use a three-dimensional coordinate measuring machine to measure the blade profile and full size of the machined blade to obtain the measurement results; Step 8: When three-coordinate measuring large-size and large-curvature blades, the six-point positioning principle is adopted (reference: Paper Literature April 2020, Issue 4, Application of Six-Point Positioning Principle in Engine Blade Fixture Design, Wang Shan, (School of Energy and Power Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100191)), two of which are located at the root of the plane structure, three points are located at the blade body of the curved surface structure, and one point is located at the tenon of the blade. According to the size results of three-coordinate measurement, after a certain margin is manually assisted in grinding, three-coordinate measurement correction is performed, and then grinding is continued until the size of the manual assisted grinding reaches the tolerance band of the blade product; Step 9: Polish the blade surface by manual or mechanical polishing, with the blade body and flow channel surface roughness Ra0.5 and the rest of the roughness Ra2.0; Step 10: Figure 2As shown, the blade was tested for average grain size by the line section method. The blade was mainly composed of full-layered layers, with an average grain size of 72.1 μm and a grain size grade of 4.5. The length of the large-sized and large-curvature TiAl alloy turbine blade product processed by this method is greater than 210 mm.

[0023] Embodiment (two): A high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades comprises the following steps: Step 1: If Figure 1 As shown, the blade is processed with a symmetrical or asymmetrical inclusion body using three-dimensional software, and the width and height directions are symmetrically offset outward along the highest point, with a total of 13 mm, and the length direction is symmetrically offset on the basis of the inclusion body, with a total of 45 mm, to obtain the offset inclusion body size of a single blade, and the inner cavity size of the metal mold is the size of 1-4 of the above-mentioned rectangular parallelepipeds, and the material of the metal mold is hot working die steel; Step 2: preheat the metal mold to 460°C, keep it warm for 3.3 hours, pour the TiAl alloy into the metal mold, centrifuge at 250r / min, cool it in the furnace for 20 minutes, and then get out of the furnace to obtain a blade ingot; Step 3: The TiAl alloy ingot is subjected to hot isostatic pressing and heat treatment to improve defects such as porosity. The hot isostatic pressing process is: temperature 1260℃, pressure 150MPa, holding time 240min, Ar gas protection; the heat treatment process is: 1050℃, time 480min, furnace cooling; Step 4: Process the top countersinks at the symmetrical positions on both ends of the ingot for the top positioning and clamping of the five-axis machine tool. The center line of the top countersink coincides with the center axis of the blade; Step 5: First, process the blade profile and the flow path surface of the upper and lower edge plates according to the blade model. On the basis of the 3D model tolerance of the blade profile, reserve a 0.06mm margin; continue to process the blade upper edge plate, sealing teeth and lower edge plate. On the basis of the 3D model tolerance of the blade upper edge plate, sealing teeth and lower edge plate, reserve a 0.06mm margin; process the root extension part to the 3D model tolerance zone as the reference surface; Figure 3 As shown in the figure, the two reference points A1 and A2 in the six-point positioning of the blade product are on the reference surface of the root extension; therefore, a grinding allowance of 0.06mm is reserved; Step 6: Use wire cutting to cut off the top countersunk clamping parts at both ends and the parts connected to the blades, with a cutting margin range of 0.8mm; Step 7: Use a three-dimensional coordinate measuring machine to measure the blade profile and full size of the machined blade to obtain the measurement results; Step 8: When three-coordinate measuring large-size and large-curvature blades, the six-point positioning principle is adopted (reference: Paper Literature April 2020, Issue 4, Application of Six-Point Positioning Principle in Engine Blade Fixture Design, Wang Shan, (School of Energy and Power Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100191)), two of which are located at the root of the plane structure, three points are located at the blade body of the curved surface structure, and one point is located at the tenon of the blade. According to the size results of three-coordinate measurement, after a certain margin is manually assisted in grinding, three-coordinate measurement correction is performed, and then grinding is continued until the size of the manual assisted grinding reaches the tolerance band of the blade product; Step 9: Polish the blade surface by manual or mechanical polishing, with the blade body and flow channel surface roughness Ra0.8 and the rest of the roughness Ra3.0; Step 10: The blade is tested for average grain size by the line section method. The blade is mainly composed of full-layer, with an average grain size of 78.9 μm and a grain size grade of 4.0. The length of the large-size and large-curvature TiAl alloy turbine blade product processed by this method is 360 mm.

Claims

1. A high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades, characterized in that: The following steps are included: Step 1: pouring TiAl alloy into a metal mold to obtain a blade ingot; Step 2: Process the top countersunk holes at the symmetrical positions on both ends of the blade ingot, and use the top countersunk holes to clamp and position the blade ingot on the five-axis machine tool; Step 3: First, process the blade profile and the flow path surfaces of the upper and lower edge plates according to the blade model, and reserve allowances based on the three-dimensional model tolerances of the blade profile; continue to process the blade upper edge plate and sealing teeth, lower edge plate and extended root parts, and reserve allowances based on the three-dimensional model tolerances of the blade upper edge plate, sealing teeth and lower edge plate; the extended root parts are processed to the upper tolerance zone of the three-dimensional model as the reference surface; Step 4: Cut off the top countersunk clamping parts at both ends and the parts connected to the blades, leaving a cutting margin; Step 5: Use a three-dimensional coordinate measuring machine to measure the blade profile and full size of the machined blade to obtain the measurement results; Step 6: According to the dimension results of three-coordinate measurement, manually assist in grinding the dimensions to the tolerance zone of the blade product; Step 7: Polish the blade surface by manual or mechanical polishing, with the blade body and flow channel surface roughness Ra0.3-Ra1.0, and the rest of the roughness Ra1.5-Ra4.0; Step 8: The blades are tested for average grain size using the line-intercepting method.

2. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1 is characterized in that: In step three, firstly, the blade profile and the flow path surfaces of the upper and lower edge plates are processed according to the blade model, and a margin of 0.03-0.08mm is reserved on the basis of the three-dimensional model tolerance of the blade profile; the upper edge plate and sealing teeth, lower edge plate and root extension of the blade are continued to be processed, and a margin of 0.03-0.08mm is reserved on the basis of the three-dimensional model tolerance of the upper edge plate, sealing teeth and lower edge plate of the blade.

3. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1 is characterized in that: The metal mold in step one uses three-dimensional software to process the blade into a symmetrical or asymmetrical enclosure, and then obtains the inner cavity size of the metal mold based on the blade offset enclosure size.

4. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 3 is characterized in that: When using three-dimensional software to process the blade into a symmetrical or asymmetrical enclosure, the symmetrical offset dimensions along the highest point in the width and height directions are 8-16 mm in total, and the symmetrical offset dimensions in the length direction are 30-50 mm in total based on the enclosure.

5. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1 is characterized in that: In step 1, the material of the metal mold is hot working die steel. The metal mold is preheated to 350°C-500°C and kept warm for 2-4 hours. Then, the TiAl alloy is poured into the metal mold at a centrifugal speed of 180-450r / min. The furnace cooling time is more than 10 minutes and the blade ingot is obtained.

6. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 5 is characterized in that: The obtained blade ingot is subjected to hot isostatic pressing and heat treatment to improve defects such as porosity and looseness.

7. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 6 is characterized in that: The hot isostatic pressing process is: temperature 1200℃-1310℃, pressure 120MPa-160MPa, holding time 200min-260min, Ar gas protection; the heat treatment process is: 950℃-1100℃, time 450min-500min, furnace cooling.

8. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1 is characterized in that: In step 4, the processing method for cutting off the top countersunk clamping parts at both ends and the parts connected to the blades is wire cutting, and the cutting allowance is 0.3-1.0mm.

9. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1 is characterized in that: In step six, the manual assisted grinding method uses machine automated grinding combined with manual grinding processing operations.

10. The high-precision CNC machining method for large-size and large-curvature TiAl alloy turbine blades according to claim 1, characterized in that: The length of the large-size and large-curvature TiAl alloy turbine blade product is greater than 150 mm.

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