Method for preparing metallographic test sample of axial section of aero-engine gas film hole

Abstract

This invention discloses a method for preparing metallographic specimens for axial section testing of film-forming holes in aero-engines. The invention uses a specially designed clamp to hold and fix the metallographic specimen cut from an aero-engine blade, achieving stable positioning and ensuring that the axial direction of the film-forming holes is parallel to the observation surface. The invention employs a cold-mounting technique to mount the metallographic specimen, ensuring that the mounting solution fills the film-forming holes, and preventing the specimen from being compressed during mounting to avoid tilting. This invention effectively improves the pass rate of metallographic specimens, reduces the number of rework operations during specimen preparation, and thus increases the first-time success rate of metallographic specimen preparation.

Description

Technical Field

[0001] This invention relates to the field of aero-engine manufacturing technology, and in particular to a method for preparing a metallographic test specimen for the axial section of an aero-engine film pore. Background Technology

[0002] After the blades of an aero-engine are processed, the surface condition of the film pores on the blades needs to be inspected. Generally, metallographic specimens along the axial direction of the film pores are prepared for inspection using metallographic methods. When preparing metallographic specimens, thermal mounting is used to protect the metallographic specimens.

[0003] Because the film cooling pores are distributed on the curved surface of the blade, it is impossible to accurately determine the axial direction of the pores after cutting the metallographic specimen. Furthermore, since the specimens cut from aero-engine blades are thin-walled irregular shapes, it is difficult to ensure that the specimen is held firmly during clamping, making it impossible to guarantee a stable observation surface. Therefore, spring coils are typically used to clamp the metallographic specimen before it is placed in a mounting machine for hot mounting. However, this method has the following drawbacks: 1. It is impossible to accurately determine the axial direction of the film cooling pores; relying solely on visual inspection cannot guarantee that the axial direction of the film cooling pores on the metallographic specimen is parallel to the observation surface. 2. Using spring coils to clamp the metallographic specimen during mounting also cannot accurately guarantee that the axial direction of the film cooling pores on the metallographic specimen is parallel to the observation surface, and the metallographic specimen will be under pressure during hot mounting, which can easily cause the metallographic specimen to tilt.

[0004] When the above problems occur during the preparation of metallographic specimens, qualified metallographic specimens cannot be prepared and must be reworked and prepared again. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a metallographic test specimen of the axial section of the air film hole of an aero-engine, which can improve the pass rate of metallographic specimens.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing metallographic specimens for axial section testing of film vents in aero-engines, comprising the following steps:

[0007] Step 1: Cut a metallographic sample with film pores from the blade of the aero-engine.

[0008] Step 2: Make a fixture for auxiliary positioning of metallographic specimens. The fixture is equipped with symmetrically distributed positioning holes. Place the metallographic specimen in the fixture and fix it on the fixture with wire so that the axis of the gas film pores on the metallographic specimen is parallel to the observation surface.

[0009] Step 3: Place the fixture holding the metallographic sample into the vacuum mounting machine and perform pre-vacuuming.

[0010] Step 4: Prepare the cold mounting liquid, use a vacuum mounting machine to draw in the cold mounting liquid and cold mount the metallographic sample onto the fixture.

[0011] Step 5: After the cold mounting liquid has solidified, remove the mounted metallographic sample;

[0012] Step 6: Polish the metallographic sample.

[0013] Furthermore, in step two, the fixture is composed of a base plate and two side plates fixedly connected, and the longitudinal section of the fixture is U-shaped; the positioning holes are arranged in multiple rows on the two side plates of the fixture; the metallographic sample is fixed between the two side plates of the fixture.

[0014] Furthermore, in step three, the vacuum mounting machine is pre-evacuated to a vacuum level of less than 0.3 bar and then maintained for 3 to 10 minutes.

[0015] Furthermore, in step four, the cold mounting liquid is prepared from cold mounting resin and curing agent, with a weight ratio of 1:3; the cold mounting process lasts for 3 to 10 minutes.

[0016] Furthermore, in step six, an automatic grinding and polishing machine is used to grind and polish the metallographic sample. The rotation speed of the automatic grinding and polishing machine's turntable is 220-300 r / min, and the rotation speed of the metallographic sample is 120-200 r / min, with the rotation direction being the same as that of the turntable.

[0017] Furthermore, when grinding and polishing metallographic samples, first use 120# sandpaper for rough grinding; when it is observed that the metallographic sample is almost ground to the air film pores, switch to 500# sandpaper for grinding and polishing; when grinding and polishing to the axial center of the air film pores, switch to 1000# sandpaper for fine polishing for 10 to 30 seconds; finally, switch to polishing cloth for polishing.

[0018] Furthermore, the polishing cloth is an acetate fiber satin woven polishing cloth, and a 3μm diamond suspension is added during the polishing process.

[0019] Furthermore, the fixture is manufactured using 3D printing technology.

[0020] The beneficial effects of this invention are as follows: This invention uses a specially designed clamp to hold and fix the metallographic sample cut from the aero-engine blade, achieving stable positioning of the metallographic sample and ensuring that the axial direction of the film pores of the metallographic sample is parallel to the observation surface; This invention uses a cold mounting technique to mount the metallographic sample, ensuring that the mounting liquid fills the film pores, and the metallographic sample is not subjected to pressure during mounting to avoid tilting; This invention effectively improves the pass rate of metallographic samples, reduces the number of rework operations in the metallographic sample preparation process, thereby improving the first-time success rate of metallographic sample preparation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fixture used in this invention;

[0022] Figure 2 This is a schematic diagram showing the metallographic sample being fixed in a fixture.

[0023] Figure 3 This is an enlarged view of the area to be tested in a metallographic sample prepared using existing methods;

[0024] Figure 4 This is an enlarged view of the test area of ​​the metallographic sample prepared using the present invention.

[0025] The markings in the figure are: 100-metallographic sample, 200-clamp, 210-positioning hole, 220-base plate, 230-side plate, 300-wire. Detailed Implementation

[0026] To facilitate understanding of the present invention, the invention will be further described below with reference to the accompanying drawings.

[0027] In the description of this invention, it should be noted that the terms "front", "rear", "left", "right", "up", "down", "inner", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0028] The method for preparing a metallographic specimen for axial section inspection of film-forming holes in aero-engines disclosed in this invention is used to inspect the surface condition of film-forming holes on aero-engine blades by preparing a metallographic specimen. The preparation is carried out according to the following steps:

[0029] Step 1: Cut a metallographic sample from the blade of the aero-engine. The metallographic sample must have film pores.

[0030] Step 2: Prepare a fixture for assisting in positioning the metallographic specimen.

[0031] The specific structure of the fixture is as follows Figure 1 and Figure 2 As shown, the clamp 100 is composed of a base plate 220 and two side plates 230 connected together. The two side plates 230 are fixed on the two sides of the base plate 220 to form a clamp 100 with a longitudinal section of "U". Multiple positioning holes 210 are provided on both side plates 230 of the clamp 100. The positioning holes 210 are arranged in multiple rows on the side plates 230, and the positioning holes 210 on the two side plates 230 are symmetrically arranged.

[0032] When preparing fixture 100, 3D printing technology can be used. According to the size of the metallographic sample cut out, the external dimensions of fixture 100 are set to 20×20mm.

[0033] After the fixture 100 is prepared, the cut metallographic sample 100 is placed in the groove of the fixture 100, and the metallographic sample 100 is fixed by passing the wire 300 through the positioning holes 210 on the two side plates 230 of the fixture 100 and the air film holes on the metallographic sample 100. After fixing, the axial direction of the air film holes on the metallographic sample 100 is parallel to the observation surface.

[0034] Step 3: Place the fixture and metallographic sample together into the cold mounting mold, then place the cold mounting mold into the vacuum mounting machine, and pre-evacuate the vacuum mounting machine. When the vacuum mounting machine is pre-evacuated to a vacuum degree of less than 0.3 bar, maintain it for 5 minutes.

[0035] Step 4: Prepare the cold mounting liquid. The cold mounting liquid is prepared by cold mounting resin and curing agent. The weight ratio of cold mounting resin and curing agent is 1:3. Mix the cold mounting resin and curing agent and stir for 3 minutes. Use a vacuum mounting machine to draw in the cold mounting liquid and perform cold mounting on the fixture with the metallographic sample. The cold mounting operation lasts for 5 minutes.

[0036] Step 5: After cold mounting is completed, release the vacuum level of the vacuum mounting machine. After the cold mounting liquid has solidified for 8 hours, take out the mounted metallographic sample.

[0037] Step Six: Polishing

[0038] Metallographic samples were polished using an automatic grinding and polishing machine. The turntable speed of the automatic grinding and polishing machine was set to 220 r / min, and the rotation speed of the metallographic sample was 150 r / min, with the rotation direction being the same as that of the turntable. The pressure of each metallographic sample was set to 30 N. The polishing process adopted a grinding and polishing technique. First, 120# sandpaper was used for rough grinding. When it was observed that the metallographic sample was almost ground to the air film pores, 500# sandpaper was used for grinding and polishing. When the axial center of the air film pores was reached, 1000# sandpaper was used for fine polishing for 30 seconds. Finally, polishing cloth was used for polishing. The polishing cloth was a woven cellulose acetate satin polishing cloth, and 3μm diamond suspension was added during the polishing process.

[0039] Examples of metallographic specimens prepared by the above steps of the present invention are compared with comparative examples of metallographic specimens prepared using conventional methods. Figure 3 As shown, the axial section of the film pores in the comparative metallographic specimen cannot be fully observed. Because the metallographic specimen is tilted, the film pores fail to maintain a stable parallel observation plane, appearing as oblique holes; only the orifice portion of the film pore can be observed. Figure 4As shown, the air film pores of the metallographic sample in the embodiment are clearly visible, and the axial cross-section of the air film pores is completely visible in the field of view. Because the metallographic sample in this invention is accurately positioned and stably fixed in the fixture, after the metallographic sample is cold-mounted, the metallographic sample is fixed in the solidified cold mounting liquid, thereby enabling clear observation of the axial direction of the air film pores and meeting the testing requirements.

Claims

1. A method for preparing a metallographic specimen for testing the axial section of a film-forming hole in an aero-engine, characterized in that: Includes the following steps: Step 1: Cut a metallographic sample with film pores from the blade of the aero-engine. Step 2: Fabricate a fixture for auxiliary positioning of the metallographic specimen. The fixture is equipped with symmetrically distributed positioning holes. The fixture consists of a base plate and two side plates that are fixedly connected. The longitudinal section of the fixture is "U" shaped. The positioning holes are arranged in multiple rows on the two side plates of the fixture. The metallographic specimen is fixed between the two side plates of the fixture. The metallographic specimen is placed in the fixture and fixed to the fixture with wire, so that the axial direction of the air film pores on the metallographic specimen is parallel to the observation surface. Step 3: Place the fixture holding the metallographic sample into the vacuum mounting machine and perform pre-vacuuming. Step 4: Prepare the cold mounting liquid. The cold mounting liquid is prepared by cold mounting resin and curing agent. The weight ratio of cold mounting resin and curing agent is 1:

3. The cold mounting liquid is drawn into the vacuum mounting machine and the metallographic sample is fixed in the fixture for cold mounting. The cold mounting work lasts for 3 to 10 minutes. Step 5: After the cold mounting liquid has solidified, remove the mounted metallographic sample; Step 6: Polish the metallographic sample.

2. The method for preparing a metallographic specimen for testing the axial section of an aero-engine film venturi hole as described in claim 1, characterized in that: In step three, the vacuum mounting machine is pre-evacuated to a vacuum level of less than 0.3 bar and then maintained for 3 to 10 minutes.

3. The method for preparing a metallographic specimen for testing the axial section of an aero-engine film venturi hole as described in claim 1, characterized in that: In step six, an automatic grinding and polishing machine is used to grind and polish the metallographic sample. The rotation speed of the automatic grinding and polishing machine is 220-300 r / min, and the rotation speed of the metallographic sample is 120-200 r / min, with the rotation direction being the same as that of the turntable.

4. The method for preparing a metallographic specimen for testing the axial section of an aero-engine film venturi hole as described in claim 3, characterized in that: When grinding and polishing metallographic specimens, first use 120# sandpaper for rough grinding; when it is observed that the metallographic specimen is almost ground to the air film pores, switch to 500# sandpaper for grinding and polishing; when grinding and polishing to the axial center of the air film pores, switch to 1000# sandpaper for fine polishing for 10-30 seconds; finally, switch to polishing cloth for polishing.

5. The method for preparing a metallographic specimen for testing the axial section of an aero-engine film venturi hole as described in claim 4, characterized in that: The polishing cloth is an acetate fiber satin woven polishing cloth, and a 3μm diamond suspension is added during the polishing process.

6. The method for preparing a metallographic specimen for testing the axial section of an aero-engine film venturi hole as described in claim 1, characterized in that: The fixture is manufactured using 3D printing technology.

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