A method of manufacturing a "t" section variable thickness stringer part

Abstract

The present application belongs to the technical field of aircraft sheet metal part processing, and relates to a manufacturing method of a "T" section variable-thickness longeron part. The present application changes the material to a "T" section profile material, uses a "numerical control milling-cutting-stamping forming-manual forming" process flow to replace a "numerical control milling-cutting-manual finishing" process flow, and cooperates with three newly designed tool sets for milling and sheet metal forming, thereby simplifying the milling clamp structure, reducing the part milling difficulty, manufacturing cost, and profile distortion, residual stress and the like in the machining process, improving the material utilization and product quality, and realizing the precise manufacturing and lean manufacturing of the "T" section variable-thickness longeron part through a simple numerical control milling-cutting and sheet metal forming combined process flow. The present application has generalizability and can be widely used in the machining and manufacturing of complex longeron parts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aircraft sheet metal part processing, and relates to a manufacturing method of a long stringer part with a T-shaped section and variable thickness. BACKGROUND

[0002] As a longitudinal component of the fuselage structure, the long stringer is mainly used to bear the axial force caused by the bending of the fuselage, support the skin, improve the critical stress of the skin in compression and shear instability, bear part of the aerodynamic force acting on the skin of the fuselage and transfer it to the bulkhead. Since the long stringer has a very important influence on the strength of the aircraft, the processing quality directly affects the overall quality of the aircraft, especially in the key parts such as the fuselage and the wing, the long stringer with variable thickness and complex shape is often used, and the manufacturability and economy of the long stringer have great challenges. The current bottleneck is that during the milling process, the material removal rate is high, the milling time is long, the error accumulation is large, the residual stress is concentrated, and the profile distortion is difficult to repair, which finally leads to low raw material utilization, low production efficiency, poor manufacturing precision and surface quality, etc. of the processed parts, which not only increases the manufacturing cost, but also affects the assembly and use performance of the aircraft. In addition, the milling process of complex parts has a complex fixture structure, a long manufacturing cycle and high cost. In view of the above reasons, the variable cross-section complex long stringer part has increased difficulty in processing. SUMMARY

[0003] The purpose of the application is to invent a manufacturing method of a long stringer part with a T-shaped section and variable thickness. The manufacturing method uses a new set of fixed clamps for milling and cutting, a set of knock-modifying dies and a set of bending dies for sheet metal forming, and changes the process flow of "numerical control milling - manual finishing" to "numerical control milling - stamping forming - manual forming". The T-shaped section raw material used in the application is close to the final size of the part, has a low material removal rate and a high utilization rate. The milling clamp used in the application only processes the straightened state of the part, has a simple tool structure and a small part processing difficulty, and has a high processing efficiency. The knock-modifying die and the bending die can process the straightened state blank after milling to the final state of the part. Although the number of tooling increases and the sheet metal forming link is added, the cost of raw materials for part processing is reduced, the processing difficulty is reduced, the processing precision and surface quality are improved, so the precise manufacturing of the long stringer part with a T-shaped section and variable thickness can be realized.

[0004] In order to achieve the above purpose, the technical scheme of the application is as follows:

[0005] A manufacturing method of a long stringer part with a T-shaped section and variable thickness, comprising three processes of numerical control milling, stamping forming and manual forming.

[0006] The first process is numerical control milling.

[0007] The part raw material used in the numerical control milling process is a T-shaped cross-section aluminum alloy profile.

[0008] The aluminum alloy profile can realize the processing of all edges and thickness of the part in the straightened state, and the vertical rib and the web are 90°, which is convenient for subsequent sheet metal forming. During milling, the profile raw material is first milled according to the thickness of the web inside, the thickness of the vertical rib and the edge in the straightened state of the part. Since the thickness of the raw material is large at this time, the deformation is small during milling, and it can be completed by using a milling clamp. After the above milling is completed, the thickness of the web outside and the edge is milled. At this time, the material removal rate of the milling area is high, and the remaining thickness is only 2mm-8mm, which is easy to deform, so a special milling clamp is used for clamping.

[0009] The "fixed clamp" includes a base, a baffle, a positioning plate, a cylindrical pin, a bolt, a hex head pressing screw and a positioning pin.

[0010] The tooling "fixed clamp" can realize the milling of the aluminum alloy profile with the vertical rib and the web inside thickness to the edge and thickness of the part in the straightened state, the vertical rib and the web are 90°, and the deformation amount is minimized during milling. The working surface of the base is designed as a "T" shape, which is used to embed the processed vertical rib of the profile, and the upper surface is tightly attached to the processed surface of the web inside the profile. Considering the slender structure characteristics of the tooling, the bottom of the base is widened to increase the stiffness and stability and facilitate clamping, and the whole is a "convex" structure. The baffle is arranged at one end of the base and is fixed by tightening the bolt, which is used to limit the position of the part during milling. The positioning plate is arranged at the other end of the base and is connected with the base by the cylindrical pin and is fixed by tightening the bolt, which is used for positioning the part in the length direction. The hex head pressing screw is arranged on the side surface of the positioning plate and the base, and the depth can be adjusted to fix the part in the base from the end and the side to prevent the part from moving horizontally and vertically during milling. The positioning pin is arranged at the bottom end of the base for quick positioning and installation of the milling clamp on the milling platform. The above structure is manufactured according to the data set, the profile manufacturing tolerance is ±0.1mm, and the surface roughness of the working profile surface is not higher than Ra1.6.

[0011] The second stamping forming.

[0012] The tooling used in the stamping forming process is a bending die, and the bending die tooling includes a lower die, a cylindrical pin, a die locking pin, an upper die, a die handle and a screw.

[0013] The bending die can realize bending of the part in the straight state after all edges and thicknesses are milled by the numerical control to the final angle of the part, and the angle of the part is 63°-66°. Considering the length of the part and the close bending angle, the bending forming can be carried out by segmented feeding and pressing, so that the length of about 300 mm of the part is intercepted as the basis for the bending die design. The lower die adopts a left and right split structure, and the working surface thereof is designed according to the inner surface of the intercepted part web, the gap between the two lower dies is determined according to the maximum thickness of the vertical rib of the part, and the lower die is connected by a cylindrical pin. The rectangular clamping groove is arranged at the bottom of the lower die to facilitate the installation of the lower die on the press. The die pin is used for the quick alignment of the upper die and the lower die, and prevents the position of the upper die and the lower die from moving to cause the error of the surface during forming or even damage the die. The working surface of the upper die is designed according to the bottom surface of the intercepted part web, and the bending forming of the part is completed by the lower die under the impact of the stamping equipment. The die handle is used for connecting the bending die and the stamping equipment, and transmits the stamping force during the up and down movement of the equipment. The die handle and the upper die are connected by a screw. The above structure has a manufacturing tolerance of ±0.1 mm for the surface, and the roughness of the working surface is not higher than Ra1.6.

[0014] The third process is formed by hand.

[0015] The tool used for hand forming is a "knocking and repairing die", and the "knocking and repairing die" tool includes a tire body, a stop block, a cylindrical pin, a screw and a lifting ring screw.

[0016] The tool "knocking and repairing die" can realize the forming of the part to the final shape, and can be used for repairing the deformation after heat treatment and quenching. The structure of the tire body is designed according to the bottom surface of the part web and the edge line of the part is drawn on the tire body, which is used for positioning during part forming, and the transition area of thickness change is appropriately increased to avoid. The stop block adopts a detachable split structure, which is arranged at the two end heads and 1 / 4, 1 / 2 and 3 / 4 positions of the tool, and the working surface is designed according to the corresponding position of the part. The vertical rib surface is designed, and the appropriate gap is left at the lower end to embed the part web. The stop block and the tire body are connected by a cylindrical pin and fixed by a screw. During the forming and repairing process, the stop block can be disassembled according to the use requirement, and the part web and the vertical rib surface are formed and repaired when the stop block is installed. When the stop block is disassembled, the web forming and repairing are carried out alone. The lifting ring screw is installed on the tire body and is used for lifting and carrying the tool. The above is designed and manufactured according to the part engineering data set, the manufacturing tolerance of the surface is ±0.1 mm, and the roughness of the working surface is not higher than Ra1.6.

[0017] The implementation effect of the present application

[0018] By changing the material to "T" section profile material, using the process flow of "numerical control milling-cutting-punching forming-manual forming" instead of the process flow of "numerical control milling-cutting-manual finishing", cooperating with three new designed toolings for milling and sheet metal forming, the milling clamp structure is simplified, the part milling difficulty, manufacturing cost and profile distortion, residual stress in the machining process are reduced, the material utilization and product quality are improved, and the precise manufacturing and lean manufacturing of the long string part with "T" section variable thickness are realized through the simple process flow of numerical control milling and sheet metal forming. The invention has popularization, and can be widely used in complex long string part machining and manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a part drawing;

[0020] Figure 2 is a milling part cross-sectional view;

[0021] Figure 3 is a fixed clamp overall structure view;

[0022] Figure 4 is a fixed clamp detailed structure top view;

[0023] Figure 5 is a fixed clamp detailed structure left view;

[0024] Figure 6 is a fixed clamp detailed structure right view;

[0025] Figure 7 is a bending die structure top view;

[0026] Figure 8 is a bending die structure front view;

[0027] Figure 9 is a bending die structure AA cross-sectional view;

[0028] Figure 10 is a knock repair die structure front view;

[0029] Figure 11 is a knock repair die structure AA cross-sectional view.

[0030] In the figure: 1, base; 2, baffle; 3, positioning plate; 4, cylindrical pin; 5, bolt; 6, hex head pressing screw; 7, positioning pin; 8, lower die; 9, cylindrical pin; 10, die pin; 11, upper die; 12, die handle; 13, screw; 14, carcass; 15, stop block; 16, cylindrical pin; 17, screw; 18, lifting ring screw. DETAILED DESCRIPTION

[0031] The manufacturing method of the long string part with "T" section variable thickness includes the following steps:

[0032] Step one: numerical control milling

[0033] The aluminum alloy profile with the material brand 7B04 T74 and the specification XC212-87 is used for milling, the section of the material is a "T" shape, the web width is 100mm, the thickness is 12.5mm, the stud height is 100mm, and the thickness is 8mm.

[0034] The length of the raw material used for milling is 1550mm, first, the raw material is fixed horizontally on the milling platform, the stud is upward, after being fixed by the pressing plate, the Φ30R3 milling cutter is used to mill the web inside thickness, the stud thickness and the stud edge according to the numerical control program prepared in advance, rough milling is firstly performed and then finish milling is performed, after the above milling is completed, the pressing plate is disassembled, and the blank is taken out. The "fixed clamp" is hoisted to the milling platform, the positioning pin 7 of the base is aligned with the positioning hole on the milling platform to complete the rapid positioning and is fixed by the pressing plate. The hexagonal head pressing screw 6 on the side of the positioning plate 3 and the base 1 is loosened, the blank that has been milled on the stud and the web is put in, the blank is ensured to be tightly attached to the baffle 2 on one side, and then the hexagonal head pressing screw 6 on the side of the positioning plate 3 and the base 1 is tightened, so that the blank is completely fixed in the length direction and tightly attached to one side of the base in the width direction, thereby the clamping of the part is completed. The coordinate system is aligned, so that the coordinate system of the machine tool coincides with the programming coordinate system, the numerical control milling program is run, and the web bottom thickness and the edge contour milling of the part are completed according to the numerical control program prepared in advance. After the milling is completed, the machine tool button is closed, the aluminum chips on the surface of the part are cleaned, and whether the edge size and the surface of the part are pressed and other mechanical damages are checked. After the above operations are completed, the hexagonal head pressing screw 6 on the side of the positioning plate 3 and the base 1 is loosened, and the part is taken out. Compared with directly milling the whole contour and profile of the part by using the 7B04 T74, δ80mm forged piece, the material removal rate of the milling process of the present application is low, the milling profile is simple, the milling difficulty is low, the residual stress is small, and the deformation after milling is small.

[0035] Step two: stamping forming

[0036] The "bending die" is centrally placed in the general die holder of the press, the deflection wheel handle of the general die holder is pulled, the inclined angle die lower die 8 is clamped and fixed by the jaws of the general die holder, the upper and lower dies are aligned by the cylindrical pin 9, the die handle 12 is aligned with the die handle hole of the slide, the equipment is started, the slide is slid downward, the "bending die" die handle 12 enters the die handle hole of the slide, the die handle hole is manually locked, and the "bending die" upper die 11 is clamped and fixed on the slide. The press is operated to slide the slide upward, the upper and lower dies of the "bending die" are separated, the milled "T" shaped section blank stand is placed downward into the gap between the two lower dies, it is ensured that the blank is placed in the die on one side, the press is controlled to move the slide downward, the upper die of the "bending die" moves toward the lower die, the blank is deformed under pressure, the web gradually adheres to the working surface of the lower die, the angle between the stand and the web gradually decreases from 90°, when the upper and lower dies of the "bending die" are completely closed, the pressure is maintained for more than 5 seconds, the hydraulic press switch is released, and the slide is slid upward to the initial position. The above operation is repeated to gradually press the 90° stand to 63°-66° by segmental and gradual inclined angle forming;

[0037] Step three: manual forming

[0038] The "knocking die" is placed on the horizontal workbench, the screws 17, cylindrical pins 16 and all blocks 15 are removed, the punched blank is placed on the tire body 14 and fixed with the general clamp, the blank is manually formed by using a hammer and an aluminum hammer, and it is ensured that the part is tightly attached to the tire body when the edge line of the web of the blank coincides with the edge of the tool. Then, the cylindrical pin 16, the block 15 are installed and fixed with the cylindrical pin 16, the stand is formed by using a hammer and an aluminum hammer, so that the stand is tightly attached to the block; the above is completed to obtain the part shape; the blank is less deformed during numerical control milling, and the stand angle is pressed during stamping forming, so that the difficulty of manual forming is smaller;

[0039] Step four: quenching

[0040] The part is quenched to improve the strength and hardness of the part. The part is quenched to improve the strength and hardness of the part. The specific operation is as follows: the part is cleaned and loaded into a nitrate heat treatment equipment, the heating temperature range is 465-475℃, and the holding time is 20min. After quenching, the part is completely cooled in flowing cold water at 10-40℃ for not less than 2min;

[0041] Step five: finishing

[0042] Due to the deformation caused by quenching, the part is placed on the knocking die and fixed by using the general quick clamp, it is ensured that the edge of the part is aligned with the edge line of the part on the knocking die, then the quenching deformation is finished by using a manual method and tools such as a hammer and an aluminum hammer, and it is ensured that the gap between the part and the tool is not greater than 0.5mm;

[0043] Step six: artificial aging

[0044] The purpose of artificial aging is to eliminate internal stress, stabilize the organization and size; first clean the parts, ensure the surface is dry, no dirt, oil and grease, etc., the equipment all temperature sensors to the process requirements of the temperature range, the parts into the furnace. First aging: heating temperature range: 115±5℃, aging holding time: 7h-8h; after the first aging, the parts do not come out of the furnace directly into the second aging, heating temperature range: 165±5℃, holding time: 15h-16h. After completing the aging, the parts are cooled by air cooling;

[0045] Step seven: physical and chemical performance testing

[0046] It includes fluorescent penetrant inspection and conductivity or hardness inspection. The purpose of fluorescent penetrant inspection is to check whether the parts have crack defects, and the purpose of hardness and conductivity inspection is to measure whether the performance of the parts such as hardness and strength is qualified. First, clean the parts, and then perform fluorescent penetrant crack inspection. If there is no crack, conduct conductivity or hardness testing. If there is a crack, the parts are scrapped. If the conductivity and hardness testing are both unqualified, repeat the heat treatment and finishing, and then perform the step testing until the physical and chemical performance is qualified and can enter the subsequent process;

[0047] Step eight: surface treatment

[0048] Anodizing and paint spraying are performed on the parts to improve the corrosion resistance of the parts.

[0049] (1) Anodizing: under the conditions of temperature 13℃-25℃ and voltage 13V-24V, the parts are oxidized in a sulfuric acid anodizing tank for 15min-40min, and then cleaned in a cold water tank for 1min-2min;

[0050] (2) Potassium dichromate sealing: under the condition of temperature 90℃-100℃, the parts are treated in a potassium dichromate sealing tank for 15min-20min, and then cleaned in a warm water tank at 40℃-60℃ for 1min-2min, and dried with compressed air;

[0051] (3) Paint spraying: use the prepared paint within the effective period, and the thickness of the paint should be controlled within 25μm-35μm. Dry the painted parts at temperature 100℃-110℃ for 1h-3h.

[0052] After completing the above steps, the final state parts are obtained.

Claims

1. A method for manufacturing a T-shaped cross-section variable thickness stringer part, characterized in that, It includes three processes: CNC milling, stamping, and manual forming; The first process is CNC milling; The raw material used for the parts is a T-shaped aluminum alloy profile; The aluminum alloy profile is processed to ensure all edges and thicknesses are processed in the straightened state of the part, with the vertical ribs and web forming a 90° angle, which facilitates subsequent sheet metal forming. During milling, the profile raw material is first milled to complete the inner thickness of the web, the thickness of the vertical ribs, and the edges in the straightened state of the part. After the above milling is completed, the outer thickness of the web and the edges are milled. At this time, the material removal rate in the milling area is high, and the remaining thickness is only 2mm to 8mm, which is prone to deformation. Therefore, a milling fixture is used for clamping. The milling fixture includes: a base (1), a baffle (2), a positioning plate (3), a cylindrical pin (4), a bolt (5), a hexagonal head clamping screw (6), and a positioning pin (7); The milling fixture described above can mill aluminum alloy profiles with completed vertical rib and web inner thickness processing to the edge and thickness of the part in a straight state, with the vertical rib and web at 90°, and ensure minimal deformation during the milling process; The second stamping process forms the shape. The tooling used in the stamping forming process is a "bending die". The "bending die" tooling includes: lower die (8), cylindrical pin (9), die closing pin (10), upper die (11), die handle (12) and screw (13). The lower die (8) adopts a split structure, and its working surface is designed according to the inner surface of the web of the part to be cut. The gap between the two lower dies is determined according to the maximum thickness of the vertical rib of the part of 4mm, and they are connected by cylindrical pins (9). A rectangular slot is set at the bottom of the lower die to facilitate installation on the press. The mold closing pin (10) is used to quickly align the upper die (11) and the lower die (8) to prevent the upper and lower dies from shifting positions, which may cause errors in the forming surface or even damage the mold. The working surface of the upper die (11) is designed according to the bottom surface of the web of the part to be cut. Under the impact force of the stamping equipment, it cooperates with the lower die to complete the bending and forming of the part. The third step is hand-forming; The tooling used for manual forming is a "knock-down mold". The "knock-down mold" tooling includes: a jig (14), a stop (15), a cylindrical pin (16), a screw (17), and a lifting eye screw (18). The working surface of the base (1) is designed in a "T" shape to embed the pre-processed vertical ribs of the profile. The upper surface is in close contact with the pre-processed surface of the inner side of the web of the profile, forming a "convex" structure. A baffle (2) is provided at one end of the base (1) and is tightened with bolts (5) to restrict the position movement of the part during milling in the length direction. A positioning plate (3) is provided at the other end of the base (1), which is connected to the base (1) by a cylindrical pin (4) and tightened with bolts (5) to position the part in the length direction. The hexagonal head clamping screw (6) is located on the side of the positioning plate (3) and the base (1), and the positioning pin (7) is located at the bottom of the base; The die handle (12) is used to connect the "bending die" to the stamping equipment, and the die handle (12) is connected to the upper die by screws; The stop block (15) is connected to the tire body by a cylindrical pin (16) and fixed with a screw (17); the eye bolt (18) is installed on the tire body for lifting and transporting the repair mold.

2. The method for manufacturing a T-shaped cross-section variable thickness stringer part as described in claim 1, characterized in that, The body (14) of the repair mold is designed according to the bottom surface of the web of the part and the edge line of the part is drawn on it. The stop block (15) adopts a detachable split structure and is set at the ends of both sides of the tooling and at 1 / 4, 1 / 2, and 3 / 4 positions respectively. The working surface is designed according to the vertical rib surface of the corresponding position of the part, and the lower end leaves an appropriate gap so that the web of the part can be embedded.

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