A machining method of a backflow device for an aero-engine

Abstract

The application belongs to the field of aero-engines, and particularly relates to a machining method of a backflow device for an aero-engine. Since the backflow device cover plate and the backflow device body are both thin-walled disc parts, clamping and machining deformation are difficult to control. The application provides a machining method of the backflow device, rough machining of the shape contour of the backflow device cover plate, drilling and tapping, and heat treatment; semi-finish turning of the profile contour of the backflow device cover plate and heat treatment; finish positioning of the reference on the backflow device cover plate; clamping of the backflow device cover plate by using a special fixture and finish turning of the profile contour; rough machining of the shape contour of the backflow device body, drilling and tapping, rough milling of the blade profile, and heat treatment; semi-finish turning of the shape contour of the backflow device body, semi-finish milling of the blade profile, and heat treatment; finish positioning of the reference of the backflow device body; finish milling of the blade profile of the backflow device body and finish turning of the shape contour of the backflow device body; assembly of the backflow device assembly; semi-finish machining of the backflow device assembly; and finish machining of the backflow device assembly. The application has the characteristics of high machining efficiency, high qualified rate and high machining quality.

Description

Technical Field

[0001] This invention belongs to the field of aero-engines, and specifically relates to a processing method for a return flow device for aero-engines. Background Technology

[0002] The return valve is a typical disc-shaped component in aero engines. For example... Figure 1 As shown, the reflux device consists of a reflux device cover plate 4 and a reflux device body 1 connected by screws. The reflux device body 1 includes a circumferential boss 2 on the outer periphery and a back flow channel starting point 3 on the inner periphery at the bottom.

[0003] Since both the reflux cover plate 4 and the reflux body 1 are thin-walled disc-type parts made of titanium alloy, it is difficult to control the deformation during clamping and machining. Currently, the machining method of repeated turning is used to gradually reduce the deformation of the parts. However, since the clamping deformation of the parts cannot be completely eliminated and there is a lack of effective measures to control the machining deformation, the pass rate of the parts is very low and the machining efficiency is also very low. Summary of the Invention

[0004] The purpose of this invention is to provide a processing method for a reflux device, which reduces clamping deformation and processing deformation of parts, and improves processing efficiency and yield.

[0005] The technical solution of the present invention is: a processing method for a return flow device for an aero-engine, the method comprising the following steps:

[0006] S1. Rough machining of the outer contour of the reflux cover plate, drilling and tapping, and heat treatment;

[0007] S2. Semi-finish machining of the reflux cover plate and heat treatment;

[0008] S3. Refine the positioning reference on the reflux cover plate;

[0009] S4. Use a special fixture to clamp the return valve cover and precisely model the surface contour.

[0010] The main body of this special clamp is the support structure for the return valve cover plate, including several tension screws arranged circumferentially that can connect to the back of the return valve cover plate and a central clamping mechanism. The main body of the central clamping mechanism is a positioning cylinder, which includes an inner annular cavity and several through holes surrounding the inner annular cavity. Several radially arranged through holes are provided on the annular wall between the inner annular cavity and the through holes, in which ball bearings are installed. A cone is pressed into the inner annular cavity by a screw, and the conical surface of the cone abuts against the inner profile of the ball bearing. A tapered pin is installed in the through holes, and the conical surface of the tapered pin abuts against the outer profile of the ball bearing. By tightening the screw, the cone is pressed downward, thereby pushing the tapered pins out of the positioning cylinder and thus clamping the return valve cover plate in the middle. An integral support ring is installed on the outer end face of all the tapered pins by a screw.

[0011] S5. Rough machining of the outer contour of the reflux condenser body, drilling and tapping, rough milling of the blades and heat treatment;

[0012] S6. Semi-finish turning of the outer contour of the reflux body, semi-finish milling of the blade profile and heat treatment;

[0013] S7. Refine the positioning reference of the reflux condenser body;

[0014] S8. Mill the blade shape of the reflux body and finish the outer contour of the reflux body.

[0015] S9. Assemble the reflux assembly;

[0016] S10, Semi-finished reflux assemblies;

[0017] S11, Finished reflux assembly.

[0018] Advantageously, a spring is connected to the bottom surface of the tapered pin to pull the tapered pin back into the through hole after the force is released.

[0019] Advantageously, the inner end face of the cone has a stepped hole in which a second spring is installed to apply outward pressure to the cone.

[0020] Advantageously, the positioning cylinder is connected to the body on the bottom surface by a number of screws.

[0021] Advantageously, the S3 and S7 use a three-point positioning method for clamping, which avoids clamping deformation.

[0022] Advantageously, when finishing the profile of the return valve cover in S4, a reverse compensation method is used for turning to offset machining deformation.

[0023] Advantageously, in S8, before the precision milling of the blade profile of the returner body, a 2mm machining allowance is uniformly left along the flow channel profile from the inner diameter position of the circumferential boss to the starting point of the back flow channel.

[0024] Advantageously, the return flow body adopts an over-positioning method, adjusting the positioning gap by the filling method and positioning by the main positioning surface of the outer ring.

[0025] Advantageously, the finishing process in S8 uses paraffin filling to increase the rigidity of the parts and employs sharp cutting tools with R0.4 tool tips and V-shaped inserts.

[0026] The advantages of this invention are: high processing efficiency, high pass rate, and high processing quality. Attached Figure Description

[0027] Figure 1 A schematic diagram of the structure of a return flow device for an aircraft engine;

[0028] Figure 2This is a schematic diagram of the structure for clamping on a special fixture. Detailed Implementation

[0029] The general process flow of the present invention is as follows: rough machining of the return valve cover plate—stress relief—semi-finishing—stress relief—datum repair—finish turning—rough machining of the return valve body—stress relief—semi-finishing—datum repair—finish milling of the blade profile—finish machining of the surface—assembly—component finish machining. Specifically, it includes the following steps:

[0030] Step 1: Rough machining of the reflux condenser cover plate

[0031] Roughly machine the outline of the return valve cover, and drill and tap holes;

[0032] Step 2: Heat treat the reflux condenser cover to relieve stress;

[0033] Step 3: Semi-finish machining the profile of the return valve cover.

[0034] This step uses the threads machined in step 1 for clamping and fixing;

[0035] Step 4: Heat treat the reflux condenser cover to relieve stress;

[0036] Step 5: Fine-tune the positioning reference on the return valve cover plate.

[0037] A three-point positioning method is used for clamping to avoid clamping deformation;

[0038] Step 6: Finish machining the profile of the return valve cover.

[0039] Specialized fixtures were used to add auxiliary support, increasing the rigidity of the part while ensuring no clamping deformation. The positioning datum used in step 5 was employed for positioning, and a reverse compensation method was used for turning to offset machining deformation.

[0040] like Figure 2 As shown, the special fixture includes a main body 13, a tensioning screw 14, and a clamping structure (composed of a tapered pin 5, a second screw 6, a support ring 7, a first screw 8, a cone 9, a ball bearing 10, a second spring 11, a positioning cylinder 15, and a first spring 16), which is connected to the fixture main body by a third screw 12. The return valve cover is tightened onto the fixture by the tensioning screw 14. Tightening the first screw 8 pushes the cone 9 to the left, causing the cone surface to push the ball bearing 10 outwards. The tapered pin 5 drives the support ring 7 to the right until it presses against the end face of the part, providing support.

[0041] Step 7: Rough machining of the reflux unit body

[0042] Rough machining of the outer contour of the return unit body, and drilling, tapping and rough milling of the blade profile;

[0043] Step 8: Perform heat treatment on the reflux condenser body to relieve stress;

[0044] Step 9: Semi-finishing of the reflux unit body

[0045] Use the threads processed in step 7 to clamp and fix the device, semi-finish turn the outer contour of the reflux body and semi-finish mill the blade shape;

[0046] Step 10: Perform heat treatment on the reflux condenser body to relieve stress;

[0047] Step 11: Fine-tune the positioning reference of the reflux unit body.

[0048] A three-point positioning method is used for clamping to avoid clamping deformation;

[0049] Step 12, finish milling the blade profile

[0050] Positioning is performed using the positioning datum processed in step 11, and clamping is performed using over-positioning and filling methods to avoid clamping deformation and increase the rigidity of the part. At this time, it is specially designed that before the precision milling of the blade shape of the return body, a 2mm machining allowance is evenly left along the flow channel surface in the area from the inner diameter of the circumferential boss 2 to the starting point 3 of the back flow channel to increase the rigidity of the part. Combined with the precision turning in the next step, the technical effect of avoiding machining deformation is achieved.

[0051] The thinnest part of the blade of the reflux vane disk is 0.5mm, and the wall thickness of the part in the flow channel is 2mm. Therefore, the deformation and vibration of the part are relatively large during the blade milling process. In order to enhance the rigidity of the part during processing, an over-positioning method is adopted, and the positioning gap is adjusted by the filling method. The main positioning surface of the outer ring is used for positioning, and it is tightened with 10 screws. The middle positioning surface and pressure plate are increased, which improves the rigidity of the part.

[0052] In this embodiment, a 2mm allowance is left on the back side of the precision milled blade front flow channel, resulting in a part thickness of 4mm. This increases the overall rigidity of the part and solves the problem of blade deformation during precision milling. After testing, the deformation of the part after finally removing the remaining 2mm allowance is between 0.05mm and 0.08mm, meeting the part's precision requirements. Milling the blade is a chip-breaking process, resulting in higher stress and greater deformation after machining. In contrast, turning the back side of the flow channel is a continuous turning process, resulting in relatively lower stress and less deformation after machining.

[0053] Step 13: Fine-machine the outer contour of the reflux unit body.

[0054] The finishing process uses paraffin filling to increase the rigidity of the parts and employs sharp tools to ensure minimal residual cutting stress and prevent deformation. In this embodiment, an R0.4 tool tip and V-shaped inserts are used for turning to reduce cutting forces.

[0055] Step 14: Assembly of the reflux assembly

[0056] Assembly is carried out using a symmetrical tightening method, and is divided into two steps: pre-tightening and tightening. The reflux body and reflux cover are connected together with screws. Measurement is performed after constraining the parts with measuring fixtures to simulate the working state of the parts and ensure the accuracy of the parts in the working state.

[0057] Based on the actual assembly requirements of the return flow unit, a simulated assembly measuring fixture was designed and manufactured to simulate the actual assembly state in the engine. The return flow unit reference A is fixed to the fixture reference surface using the measuring fixture, with one plane supporting the assembly at a distance of 0.6 mm from A and another plane supporting the assembly at a distance of 9.17 mm from A. Under simulated assembly conditions, this ensures that there are no gaps between the tips of all blades on the return flow unit's blade disk and the return flow unit cover plate.

[0058] Step 15: Semi-finishing of the reflux assembly

[0059] Turning profile dimensions;

[0060] Step 16: Finishing of the reflux assembly

[0061] The assembly stop is precision machined, and the locating holes are precision bored to complete the overall machining of the part. Measurements are taken using a measuring fixture to constrain the part, simulating its working state and ensuring its accuracy under operating conditions.

[0062] In this design, the reflux cover plate undergoes low-temperature stress relief processes after rough machining and semi-finish turning. To ensure final accuracy, a datum turning process is added before finish machining to guarantee positioning accuracy. During turning, a fixture with axial positioning bolts and auxiliary support is used. A perforated plane is selected for positioning, and threads are machined at the hole locations. The fixture only requires one plane, with smooth holes machined at corresponding positions. Screws are then passed through the smooth holes in the fixture and tightened onto the threaded holes on the part. The fixture structure is simple, allowing machining of the entire end face of the part without considering the position of the pressure plate. During clamping, a dial indicator is used to check for changes in the clamping position, controlling clamping deformation to within 0.02mm to minimize part clamping deformation. A new auxiliary support structure is designed, which is simple to operate, highly accurate, and ensures part rigidity during turning. The finish turning process uses a machining deformation compensation method. The CNC program for the finish turning of the large flat surface is adjusted to compensate for part deformation by 0.05mm, ensuring dimensional accuracy after deformation.

Claims

1. A method for processing a return flow device for an aero-engine, characterized in that, The method includes the following steps: S1. Roughly machine the outline of the reflux cover plate (4), drill and tap holes and heat treat it; S2, semi-finish machining of the reflux cover plate (4) and heat treatment; S3. Refine the positioning reference on the return valve cover plate (4); S4. Use a special fixture to clamp the return valve cover plate (4) and precisely model the surface contour. The main body (13) of the special clamp is a support structure for the return valve cover (4), including several tension screws (14) arranged circumferentially that can be connected to the back of the return valve cover (4) and a central clamping mechanism. The main body of the central clamping mechanism is a positioning cylinder (15), which includes an inner annular cavity and several through holes surrounding the inner annular cavity. Several radial through holes are arranged circumferentially on the annular wall between the inner annular cavity and the through holes, in which ball bearings (10) are installed. The screws pass through the inner annular cavity. 8) A cone (9) is press-fitted, with the conical surface of the cone (9) pressing against the inner profile of the ball (10); a tapered pin (5) is installed in the through hole, with the conical surface of the tapered pin (5) pressing against the outer profile of the ball (10); by tightening the first screw (8) downwards, the cone (9) is pressed down, thereby pushing several tapered pins (5) out of the positioning cylinder (15) and thus pressing the return cover plate (4) in the middle; an integral support ring (7) is installed on the outer end face of all the tapered pins (5) by the second screw (6); S5. Rough machining of the outer contour of the reflux body (1), drilling and tapping, rough milling of the blade shape and heat treatment; S6. Semi-finish machining of the outer contour of the reflux body (1), semi-finish milling of the blade shape and heat treatment; S7. Refine the positioning reference of the reflux condenser body; S8. Mill the blade shape of the reflux body and finish the outer contour of the reflux body. S9. Assemble the reflux assembly; S10, Semi-finished reflux assemblies; S11, Finished reflux assembly.

2. The processing method of the aero-engine return flow device according to claim 1, characterized in that: A spring (16) is connected to the bottom surface of the tapered pin (5), which pulls the tapered pin (5) back into the through hole after the force is released.

3. The processing method for the aero-engine return valve according to claim 2, characterized in that: The inner end face of the cone (9) has a stepped hole in which a spring (11) is installed to apply outward pressure to the cone (9).

4. The processing method of the aero-engine return flow device according to claim 3, characterized in that: The positioning cylinder (15) is connected to the main body (13) on the bottom surface by a number of screws (12).

5. The method for processing a return flow device for an aircraft engine according to any one of claims 1-4, characterized in that: The S3 and S7 use a three-point positioning method for clamping to avoid clamping deformation.

6. The method for processing a return flow device for an aircraft engine according to any one of claims 1-4, characterized in that: When precision turning the profile of the return valve cover in S4, a reverse compensation method is used to offset the machining deformation.

7. The method for processing a return flow device for an aircraft engine according to any one of claims 1-4, characterized in that: Before milling the blade shape of the return flow body in S8, a 2mm machining allowance is uniformly left along the flow channel surface from the inner diameter position of the circumferential boss (2) to the starting point (3) of the back flow channel.

8. The processing method of the aero-engine return flow device according to claim 7, characterized in that: The reflux rectifier body adopts an over-positioning method, using a stuffing method to adjust the positioning gap, and using the main positioning surface of the outer ring for positioning.

9. The processing method of the aero-engine return flow device according to claim 8, characterized in that: The finishing process in S8 uses paraffin filling to increase the rigidity of the parts and employs sharp cutting tools with R0.4 tool tips and V-shaped inserts.

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