A machining method of an aero-engine head casing and a floating counter-pressure clamping fixture

Abstract

The application discloses a processing method of an aero-engine head casing and a floating counter-pressure clamp, and belongs to the technical field of aero-engine casing processing. The method is as follows: a main gear shaft hole and a positioning end face are coarsely milled; after stress release through secondary clamping, the main gear shaft hole and the positioning end face are semi-finely milled; surface defects are checked; corrosion protection is carried out; a small-end main gear shaft hole is fine-bored, and the positioning end face thereof is fine-milled; a positioning end face of a large-end main gear shaft hole is super-finely milled by a single-blade diamond face milling cutter; the positioning end face of the large-end main gear shaft hole is coated with rust-proof oil; the floating counter-pressure clamp clamps the head casing; a first auxiliary gear shaft hole and an end face are processed; and a second auxiliary gear shaft hole and an end face are processed. The application avoids resource waste caused by full-process processing of a defective blank, improves the processing precision of the positioning end face, reduces the risk of part compression deformation, and solves the problem of cumulative errors caused by the dependence of traditional tooling on theoretical models.

Description

Technical Field

[0001] This invention relates to a machining method for the head casing of an aero-engine and a floating counter-clamping fixture, belonging to the field of aero-engine casing machining technology. Background Technology

[0002] As the core load-bearing component of the transmission system, the nose cone of an aero-engine serves to support internal rotating parts such as gears and bearings, and withstand complex alternating loads from the rotor system and tail rotor assembly. These parts are typically manufactured using lightweight materials such as magnesium alloys, and are characterized by thin walls and high-precision spatial hole structures. Their machining quality directly affects the transmission accuracy and operational reliability of the engine.

[0003] Existing processing technologies typically employ a multi-step, step-by-step processing strategy:

[0004] Rough machining stage: The end face and the mounting hole of the main gear shaft are rough machined by milling.

[0005] Semi-finishing stage: Semi-finish milling of the mounting hole for the main gear shaft;

[0006] Precision machining stage: Carbide cutting tools are used to precision machine the positioning end face and mounting holes of the main gear shaft;

[0007] Auxiliary hole system machining: Using the main gear shaft hole as the positioning reference, the positioning end face and mounting hole of the auxiliary gear shaft are machined by a special fixed angle fixture.

[0008] The above process route has the following technical defects:

[0009] 1. Insufficient adaptability to material processing:

[0010] Magnesium alloys have high thermal conductivity and low melting point. Traditional multi-edged carbide tools are prone to local overheating due to concentrated cutting heat during the cutting process, which can lead to material oxidation or even combustion, severely restricting the surface quality of the machined parts and the tool's service life.

[0011] 2. Low positioning accuracy of spatial hole system:

[0012] Existing fixed-angle fixtures use a rigid positioning method, which makes it difficult to compensate for the cumulative errors in the spatial angle and intersection points of the main and auxiliary gear shaft mounting hole axes, resulting in a large deviation rate in the positional accuracy of the hole system.

[0013] 3. Deformation control is difficult for thin-walled structures:

[0014] The positioning reference conversion error caused by multiple clamping and the cutting force of the carbide tool work together to induce plastic deformation in the thin-walled area, resulting in a high product qualification rate. Summary of the Invention

[0015] To address the problems existing in the background art, the present invention provides a processing method for the head casing of an aero-engine and a floating counter-clamping fixture.

[0016] To achieve the above objectives, the present invention adopts the following technical solution: a method for processing the nose casing of an aero-engine, the method comprising the following steps:

[0017] S1: Rough milling the large end main gear shaft hole, the small end main gear shaft hole, and the two positioning end faces of the head casing;

[0018] S2: After the stress is released by the second clamping, the large end main gear shaft hole, the small end main gear shaft hole, and the two positioning end faces of the head housing are semi-finished milled.

[0019] S3: Inspect the surface defects of the head casing;

[0020] S4: Provide corrosion protection for the head casing;

[0021] S5: Precision boring of the small end main gear shaft hole of the head housing and precision milling of its positioning end face;

[0022] S6: Use a single-edged diamond face milling cutter to ultra-precise mill the positioning end face of the large end main gear shaft hole of the head housing;

[0023] S7: Apply anti-rust oil to the positioning end face of the main gear shaft hole at the large end of the head housing, then use a floating counter-clamping fixture to clamp the head housing, finish mill the positioning end face of the first auxiliary gear shaft hole with a single-edged diamond face milling cutter, and finish bore the first auxiliary gear shaft hole with a diamond boring cutter.

[0024] S8: Use a single-edged diamond face milling cutter to ultra-precise mill the positioning end face of the second auxiliary gear shaft hole and the small end main gear shaft hole of the head housing, and use a diamond boring cutter to precision bore the second auxiliary gear shaft hole.

[0025] Furthermore, the floating anti-clamping fixture S7 includes a base, a positioning plate, a large-end positioning pin, an angular pin, a fixed-point clamping mechanism, and a balanced clamping mechanism; the upper end of the base is detachably and fixedly connected to both ends of the horizontally arranged positioning plate, and the large-end positioning pin and the angular pin are inserted into the positioning plate; two parallel fixed-point clamping mechanisms are installed on one side of the base, and a balanced clamping mechanism is installed on the other side of the base.

[0026] Furthermore, the base includes a base plate, upright plates, and reinforcing ribs; the upper end of the base plate is fixedly connected to two parallel upright plates, and each upright plate has a reinforcing rib between its outer side and the base plate, and the upper ends of the two upright plates are fixedly connected to the two ends of the positioning plate.

[0027] Furthermore, the positioning plate has a circular hole at its center and a semi-open window with a trapezoidal cross-section on one side. The circular hole has two main positioning holes and two auxiliary positioning holes along its circumference. Both ends of the positioning plate have countersunk holes, pin holes, and threaded holes.

[0028] Furthermore, a lifting ring is installed at the upper end of the positioning plate.

[0029] Furthermore, the balancing clamping mechanism includes a clamping screw, a nut, a push rod, a guide sleeve, a support rod, a top pin, a compression spring, and a top shaft; an L-shaped hole is provided on one side of the base plate, the end face of the horizontal hole of the L-shaped hole is fixedly connected to the nut, the top face of the vertical hole of the L-shaped hole is fixedly connected to the guide sleeve, and a horizontally arranged clamping screw is screwed into the nut, the inner end of the clamping screw extending into the L-shaped hole and being connected to the horizontally arranged guide sleeve. The outer end of the push rod is inserted into the hole, and the inner end of the push rod is a wedge-shaped block. The wedge-shaped block is inserted into the lower end of the top shaft, which is vertically set in the guide sleeve. The upper end of the top shaft is hinged to the middle of the support rod. The two sides of the upper end of the support rod are respectively inserted into the corresponding top pins. The top surface of each top pin is a spherical surface. A compression spring is fitted on the outer side of the top shaft. The lower end of the compression spring abuts against the middle boss of the top shaft, and the upper end of the compression spring abuts against the guide sleeve.

[0030] Furthermore, each of the aforementioned fixed-point clamping mechanisms has the same structure, including a second guide sleeve, a second clamping screw, a second nut, a second push rod, a second compression spring, and a support shaft. An L-shaped hole is provided on the other side of the base plate. The end face of the horizontal hole of the L-shaped hole is fixedly connected to the second nut, and the top face of the vertical hole of the L-shaped hole is fixedly connected to the second guide sleeve. A horizontally arranged clamping screw is screwed into the second nut. The inner end of the clamping screw extends into the L-shaped hole and is inserted into the outer end of the push rod, which is horizontally arranged in the L-shaped hole. The inner end of the push rod is a wedge-shaped block, which is inserted into the lower end of the support shaft, which is vertically arranged in the second guide sleeve. The top surface of the support shaft is a spherical surface. A second compression spring is fitted on the outer side of the support shaft. The lower end of the second compression spring abuts against the central boss of the support shaft, and the upper end of the second compression spring abuts against the second guide sleeve.

[0031] Furthermore, step S7 includes the following steps:

[0032] S701: Before machining, align the small end main gear shaft hole to determine the center, and align the main positioning hole of the head casing to determine the angular direction;

[0033] S702: Using a coordinate measuring machine on a flexible production line, with the small end main gear shaft hole as the reference, measure whether the deviation value of the AZ axis meets the requirements of intersecting the FY axis at point P1 and the intersection angle error of ±1°.

[0034] S703: Correct the tool entry position and direction for machining the first auxiliary gear shaft hole based on the actual measured deviation value;

[0035] S704: Use a diamond boring tool to precision bore the large end main gear shaft hole and the inner hole of the main gear shaft to determine the axis of the main gear shaft mounting hole, i.e., the FY axis;

[0036] S705: Move the head housing with the large end facing up into the fixture, so that the positioning surface of the small end main gear shaft hole contacts the upper end of the top pin on the support rod and the upper end of the support shaft.

[0037] S706: Adjust the angular orientation of the large end of the head casing so that the two main positioning holes at the large end of the head casing are aligned with the corresponding positioning holes on the positioning plate, and then insert the corresponding large end positioning pin and angular pin respectively.

[0038] S707: Adjust the clamping screw two to clamp the push rod two. Through the wedge block at the inner end of the push rod two and the support shaft, the lateral displacement of the push rod two is converted into the longitudinal displacement of the support shaft, so that the support shaft fits against the small end positioning surface of the head casing.

[0039] S708: Adjust the clamping screw to clamp the top rod. The wedge block at the inner end of the top rod cooperates with the top shaft to convert the lateral displacement of the top rod into the longitudinal displacement of the top shaft, so that the top pin fits against the small end positioning surface of the head housing.

[0040] S709: Alternately adjust the three clamping bolts to achieve four-point support for the small end face of the head casing until the large end positioning surface of the head casing is tightly fitted with the positioning end face of the positioning plate.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. This invention avoids resource waste caused by processing defective blanks throughout the entire process by adding fluorescence inspection and chromic acid test after rough machining, and checking for blank defects and adding surface protection treatment before fine machining.

[0043] 2. This invention uses a face milling cutter with only a single diamond insert to mill the positioning end face of the main and auxiliary gear shaft holes of the head casing. This avoids the deformation of the parts caused by excessive cutting force, and improves the machining accuracy of the positioning end face due to the ultra-long machining life of the diamond cutter.

[0044] 3. The present invention adopts a multi-point support and counter-pressing method, which allows the main and auxiliary gear mounting holes to be processed in the same process, improving the spatial position accuracy of the straight lines of the mounting holes of each shaft; at the same time, the support and pressing structure of the balance arm, with four-point support and pressing, makes the support force more uniform and reduces the risk of deformation of the parts under pressure.

[0045] 4. This invention uses a flexible production line coordinate measuring machine to correct the processing path based on actual contour data, thus solving the problem of cumulative error caused by traditional tooling relying on theoretical models. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of the aircraft engine head casing of the present invention;

[0047] Figure 2 yes Figure 1 Top view;

[0048] Figure 3 This is a schematic diagram of the floating counter-clamping fixture;

[0049] Figure 4 yes Figure 3 AA section view;

[0050] Figure 5 yes Figure 4 BB cross-sectional view;

[0051] Figure 6 yes Figure 5 It is a CC sectional view;

[0052] Figure 7 This is a structural diagram of the base;

[0053] Figure 8 yes Figure 7 Side view;

[0054] Figure 9 yes Figure 7 A sectional view;

[0055] Figure 10 This is a structural diagram of the positioning plate;

[0056] Figure 11 yes Figure 10 A sectional view;

[0057] Figure 12 This is a structural schematic diagram of the push rod one;

[0058] Figure 13 yes Figure 12 Top view;

[0059] Figure 14 This is a schematic diagram of the support shaft structure;

[0060] Figure 15 This is a structural diagram of the support rod;

[0061] Figure 16 yes Figure 10 A sectional view;

[0062] Figure 17 This is a schematic diagram of the angular pin structure. Detailed Implementation

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0064] A method for machining the nose cone casing of an aircraft engine, the method comprising the following steps:

[0065] S1: Using the scribing lines of the blank as a reference, rough mill the large end main gear shaft hole 25, the small end main gear shaft hole 26, and the two positioning end faces of the head casing.

[0066] S2: After the stress is released by the second clamping, the large end main gear shaft hole 25, the small end main gear shaft hole 26, and the two positioning end faces of the head housing are semi-finished milled.

[0067] S3: Inspect the surface defects of the head casing using fluorescence;

[0068] S4: Chromate treatment is used for corrosion protection of the head casing;

[0069] S5: Precision boring of the small end main gear shaft hole 26 of the head casing and precision milling of its positioning end face;

[0070] S6: Use a single-edged diamond face milling cutter to ultra-precision mill the positioning end face of the large end main gear shaft hole 25 of the head housing;

[0071] S7: Apply No. 5 anti-rust oil to the positioning end face of the main gear shaft hole 25 at the large end of the head housing to protect the reference surface. Then, use a floating counter-clamping fixture to clamp the head housing. Use a single-edged diamond face milling cutter to finish mill the positioning end face of the first auxiliary gear shaft hole 28, and use a diamond boring cutter to finish bore the first auxiliary gear shaft hole 28.

[0072] S8: Use a single-edged diamond face milling cutter to ultra-precision mill the positioning end face of the second auxiliary gear shaft hole 27 and the small end main gear shaft hole 26 of the head housing, and use a diamond boring cutter to precision bore the second auxiliary gear shaft hole 27.

[0073] Furthermore, the floating anti-clamping fixture mentioned in S7 includes a base 1, a positioning plate 2, a large-end positioning pin 5, an angular pin 6, a fixed-point clamping mechanism, and a balanced clamping mechanism; the upper end of the base 1 is detachably and fixedly connected to both ends of the horizontally arranged positioning plate 2 by corresponding screws and positioning plate limiting pins, and the large-end positioning pin 5 and the angular pin 6 are inserted into the positioning plate 2; two parallel fixed-point clamping mechanisms are installed on one side of the base 1, and a balanced clamping mechanism is installed on the other side of the base 1.

[0074] Furthermore, the base 1 includes a base plate 3, upright plates 7, and reinforcing ribs 29; the base plate 3 has a rectangular structure, and the upper end of the base plate 3 is integrally formed and fixedly connected to two parallel upright plates 7. Each upright plate 7 has an integrally formed reinforcing rib 29 between its outer side and the base plate 3. In order to adapt to the gripping of the robotic arm in the automated flexible production line and to reduce weight, the material of the base 3 is aluminum; the upper ends of the two upright plates 7 are correspondingly fixedly connected to the two ends of the positioning plate 2.

[0075] Furthermore, the positioning plate 2 is a square steel plate. The center of the positioning plate 2 has a circular hole with a diameter slightly larger than the main gear shaft hole 25 at the large end of the head casing. One side of the positioning plate 2 has a semi-open window with a trapezoidal cross-section to avoid the component base. The circular hole has two main positioning holes and two auxiliary positioning holes along its circumference. The two ends of the positioning plate 2 perpendicular to the line connecting the centers of the two main positioning holes are provided with countersunk holes, pin holes and threaded holes for connecting the base 3 and the lifting ring 4.

[0076] Furthermore, the balancing clamping mechanism includes a clamping screw 10, a nut 12, a push rod 13, a guide sleeve 14, a support rod 19, a top pin 20, a compression spring 23, and a top shaft 24; one side of the base plate 3 has an L-shaped hole penetrating its top surface and the corresponding side surface. The end face of the horizontal hole of the L-shaped hole is fixedly connected to the nut 12, and the top face of the vertical hole of the L-shaped hole is fixedly connected to the guide sleeve 14. A horizontally arranged clamping screw 10 is screwed into the nut 12, and the inner end of the clamping screw 10 extends into the L-shaped hole and is connected to the horizontally arranged... The outer end of the top rod 13, which is placed in the L-shaped hole, is inserted. The inner end of the top rod 13 is a wedge-shaped block. The wedge-shaped block is inserted into the lower end of the top shaft 24, which is vertically set in the guide sleeve 14. The upper end of the top shaft 24 is hinged to the middle part of the support rod 19 by a pin. The two sides of the upper end of the support rod 19 are respectively inserted into the corresponding top pins 20. The top surface of each top pin 20 is a spherical surface. A compression spring 23 is fitted on the outer side of the top shaft 24. The lower end of the compression spring 23 abuts against the middle boss of the top shaft 24, and the upper end of the compression spring 23 abuts against the guide sleeve 14.

[0077] Furthermore, each of the aforementioned fixed-point clamping mechanisms has the same structure, including a guide sleeve 16, a clamping screw 17, a nut 21, a push rod 22, a compression spring 15, and a support shaft 18; the other side of the base plate 3 has an L-shaped hole 2 penetrating its top surface and the corresponding side surface, the end face of the horizontal hole of the L-shaped hole 2 is fixedly connected to the nut 21, the top face of the vertical hole of the L-shaped hole 2 is fixedly connected to the guide sleeve 16, and the nut 21 is screwed with a horizontally arranged clamping screw 17. The inner end of the clamping screw 17 extends into the L-shaped hole and is inserted into the outer end of the push rod 22, which is horizontally set in the L-shaped hole. The inner end of the push rod 22 is a wedge-shaped block. The wedge-shaped block is engaged with the lower end of the support shaft 18, which is vertically set in the guide sleeve 16. The top surface of the support shaft 18 is a spherical surface. A compression spring 15 is fitted on the outer side of the support shaft 18. The lower end of the compression spring 15 abuts against the central boss of the support shaft 18, and the upper end of the compression spring 15 abuts against the guide sleeve 16.

[0078] The positioning pin 5 and the angular pin 6 have the same structure, differing only in size. Both are three-stage stepped structures. The first stage cooperates with the head housing, the second stage cooperates with the positioning plate 2, and there is a hollow slot structure between the first and second stages. The third stage is a tail shank for hand gripping. In addition, the first stage of the angular pin 6 is a diamond-shaped structure used to fix the angular part of the head housing.

[0079] The top rod 13 and the top rod 22 have the same structure. The inner end is a wedge block with a flat strip trapezoidal structure, and the tail end is a cylindrical structure. The tail end is provided with a threaded hole with a T-slot.

[0080] The guide sleeve 14 and guide sleeve 2 16 have the same structure, which is a typical bushing structure, only the inner diameter is different. Both types of guide sleeves have three stepped holes on the outer flange edge and a part of the semicircle is cut off.

[0081] The main bodies of the support shaft 18 and the top shaft 24 are both three-stage stepped cylindrical structures, and the inner part of the tail cylinder is provided with a long trapezoidal through hole; the supporting end of the support shaft 18 is spherical.

[0082] The support rod 19 is a long strip-shaped balance arm structure with top pin mounting holes at both ends;

[0083] The top pin 20 has a stepped shaft structure, with the large end being a convex spherical surface.

[0084] Furthermore, step S7 includes the following steps:

[0085] S701: Before machining, align the small end main gear shaft hole 26 within 0.01 to determine the center, and align the main positioning hole 11 of the head casing within 0.01 to determine the angular direction;

[0086] When machining the main positioning hole 11, first insert the two auxiliary positioning pins through the positioning plate and then into the two auxiliary positioning holes 8. The auxiliary positioning pins have a stepped four-level structure, and the outer diameter of the tail shank of the fourth level is textured.

[0087] S702: Using a coordinate measuring machine for flexible production lines, with the small end main gear shaft hole 26 as the reference, measure whether the deviation value of the AZ axis 31 meets the requirement of intersecting with the FY axis 32 at point P1 and the intersection angle error of ±1°.

[0088] S703: Correct the tool entry position and direction for machining the first auxiliary gear shaft hole 28 based on the actual measured deviation value;

[0089] S704: Use a diamond boring tool to precision bore the large end main gear shaft hole 25 and the main gear shaft inner hole 33 to determine the main gear shaft mounting hole axis, i.e., FY axis 32;

[0090] S705: Move the head housing with the large end facing up into the fixture, so that the positioning surface of the small end main gear shaft hole 26 contacts the upper end of the top pin 20 on the support rod 19 and the upper end of the support shaft 18.

[0091] S706: Adjust the angular direction of the large end of the head casing so that the two main positioning holes 11 at the large end of the head casing are aligned with the corresponding positioning holes of the positioning plate 2. Then, insert the corresponding large end positioning pin 5 and angular pin 6 respectively. The long axis of the angular pin 6 should be placed tangentially to the gear shaft hole.

[0092] S707: Adjust the clamping screw 217 to clamp the push rod 22. The wedge block at the inner end of the push rod 22 cooperates with the trapezoidal hole at the tail end of the support shaft 18 to convert the lateral displacement of the push rod 22 into the longitudinal displacement of the support shaft 18, so that the support shaft 18 fits against the small end positioning surface of the head casing.

[0093] S708: Adjust the clamping screw 10 to clamp the push rod 13. The wedge block at the inner end of the push rod 13 cooperates with the trapezoidal hole at the tail end of the top shaft 24 to convert the lateral displacement of the push rod 13 into the longitudinal displacement of the top shaft 24, so that the top pin 20 fits against the small end positioning surface of the head housing.

[0094] S709: Alternately adjust the three clamping bolts to achieve four-point support for the small end face of the head casing until the large end positioning surface of the head casing is tightly fitted with the positioning end face of the positioning plate 2.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0096] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for machining the nose casing of an aircraft engine, characterized in that: The method includes the following steps: S1: Rough mill the large end main gear shaft hole (25), the small end main gear shaft hole (26), and the two positioning end faces of the head housing; S2: After the stress is released by the second clamping, the large end main gear shaft hole (25), the small end main gear shaft hole (26), and the two positioning end faces of the head housing are semi-finished. S3: Inspect the surface defects of the head casing; S4: Provide corrosion protection for the head casing; S5: Precision boring of the small end main gear shaft hole (26) of the head housing and precision milling of its positioning end face; S6: Use a single-edged diamond face milling cutter to ultra-precision mill the positioning end face of the large end main gear shaft hole (25) of the head housing; S7: Apply anti-rust oil to the positioning end face of the main gear shaft hole (25) of the head housing, and then use a floating counter-clamping fixture to clamp the head housing. Use a single-edged diamond face milling cutter to finish mill the positioning end face of the first auxiliary gear shaft hole (28), and use a diamond boring cutter to finish boring the first auxiliary gear shaft hole (28). The floating anti-clamping fixture S7 includes a base (1), a positioning plate (2), a large-end positioning pin (5), an angular pin (6), a fixed-point clamping mechanism, and a balanced clamping mechanism; the upper end of the base (1) is detachably and fixedly connected to both ends of the horizontally arranged positioning plate (2), and the large-end positioning pin (5) and the angular pin (6) are inserted into the positioning plate (2); two parallel fixed-point clamping mechanisms are installed on one side of the base (1), and a balanced clamping mechanism is installed on the other side of the base (1); The base (1) includes a base plate (3), a vertical plate (7) and a reinforcing rib plate (29); the upper end of the base plate (3) is fixedly connected to two parallel vertical plates (7), and a reinforcing rib plate (29) is provided between the outer side of each vertical plate (7) and the base plate (3), and the upper ends of the two vertical plates (7) are fixedly connected to the two ends of the positioning plate (2). The balancing clamping mechanism includes a clamping screw (10), a nut (12), a push rod (13), a guide sleeve (14), a support rod (19), a top pin (20), a compression spring (23), and a top shaft (24). An L-shaped hole is provided on one side of the base plate (3). The end face of the horizontal hole of the L-shaped hole is fixedly connected to the nut (12), and the top face of the vertical hole of the L-shaped hole is fixedly connected to the guide sleeve (14). A horizontally arranged clamping screw (10) is screwed into the nut (12). The inner end of the clamping screw (10) extends into the L-shaped hole and is horizontally arranged in the L-shaped hole. The outer end of the top rod (13) is inserted, and the inner end of the top rod (13) is a wedge-shaped block. The wedge-shaped block is inserted into the lower end of the top shaft (24) which is vertically set in the guide sleeve (14). The upper end of the top shaft (24) is hinged to the middle of the support rod (19). The two sides of the upper end of the support rod (19) are respectively inserted into the corresponding top pins (20). The top surface of each top pin (20) is a spherical surface. The outer side of the top shaft (24) is fitted with a compression spring (23). The lower end of the compression spring (23) abuts against the middle boss of the top shaft (24), and the upper end of the compression spring (23) abuts against the guide sleeve (14). Each of the fixed-point clamping mechanisms has the same structure, including a guide sleeve (16), a clamping screw (17), a nut (21), a push rod (22), a compression spring (15), and a support shaft (18); an L-shaped hole (2) is provided on the other side of the base plate (3), the end face of the horizontal hole of the L-shaped hole (21) is fixedly connected to the nut (21), the top face of the vertical hole of the L-shaped hole (22) is fixedly connected to the guide sleeve (16), and a horizontally arranged clamping screw (17) is screwed into the nut (21). 7) The inner end extends into the L-shaped hole II and is inserted into the outer end of the top rod II (22) which is horizontally set in the L-shaped hole II. The inner end of the top rod II (22) is a wedge-shaped block. The wedge-shaped block is engaged with the lower end of the support shaft (18) which is vertically set in the guide sleeve II (16). The top surface of the support shaft (18) is a spherical surface. The outer side of the support shaft (18) is fitted with a compression spring II (15). The lower end of the compression spring II (15) abuts against the middle boss of the support shaft (18), and the upper end of the compression spring II (15) abuts against the guide sleeve II (16). S7 includes the following steps: S701: Before machining, align the small end main gear shaft hole (26) to determine the center, and align the head housing main positioning hole (11) to determine the angle. S702: Using a flexible production line coordinate measuring machine with the small end main gear shaft hole (26) as the reference, measure whether the deviation value of the AZ axis (31) meets the requirements of intersecting with the FY axis (32) at point P1 and the intersection angle error ±1°; S703: Correct the entry position and direction of the first auxiliary gear shaft hole (28) based on the actual measured deviation value; S704: Use a diamond boring tool to precision bore the large end main gear shaft hole (25) and the main gear shaft inner hole (33) to determine the main gear shaft mounting hole axis, namely: FY axis (32). S705: Move the head housing with the large end facing up into the fixture, so that the positioning surface of the small end main gear shaft hole (26) contacts the upper end of the top pin (20) on the support rod (19) and the upper end of the support shaft (18). S706: Adjust the angle of the large end of the head casing so that the two main positioning holes (11) at the large end of the head casing are aligned with the corresponding positioning holes of the positioning plate (2), and then insert the corresponding large end positioning pin (5) and angle pin (6). S707: Adjust the clamping screw two (17) to clamp the top rod two (22). Through the wedge block at the inner end of the top rod two (22) and the support shaft (18), the lateral displacement of the top rod two (22) is converted into the longitudinal displacement of the support shaft (18), so that the support shaft (18) fits against the small end positioning surface of the head casing. S708: Adjust the clamping screw (10) to clamp the top rod (13). Through the wedge block at the inner end of the top rod (13) and the top shaft (24), the lateral displacement of the top rod (13) is converted into the longitudinal displacement of the top shaft (24), so that the top pin (20) fits against the small end positioning surface of the head casing. S709: Alternately adjust the three clamping bolts to achieve four-point support for the small end face of the head casing until the large end positioning surface of the head casing is tightly fitted with the positioning end face of the positioning plate (2); S8: Use a single-edged diamond face milling cutter to super-precision mill the positioning end face of the second auxiliary gear shaft hole (27) of the head housing and the small end main gear shaft hole (26), and use a diamond boring cutter to precision bore the second auxiliary gear shaft hole (27).

2. The method for processing the nose casing of an aero-engine according to claim 1, characterized in that: The positioning plate (2) has a circular hole at its center and a semi-open window with a trapezoidal cross-section on one side. The circular hole has two main positioning holes and two auxiliary positioning holes along its circumference. Both ends of the positioning plate (2) are provided with countersunk holes, pin holes and threaded holes.

3. The method for processing the nose casing of an aero-engine according to claim 2, characterized in that: A lifting ring (4) is installed on the upper end of the positioning plate (2).

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