Manufacturing method for thickness-variable stringer part with T-shaped section

Abstract

The invention belongs to the technical field of aviation aircraft sheet metal part machining, and relates to a manufacturing method of a T-shaped section variable-thickness stringer part. A material is changed into a T-section profile material, the technological process of numerical control milling-stamping forming-manual forming is used for replacing the technological process of numerical control milling-manual finishing, three sets of newly-designed tools are matched for milling and sheet metal forming, the structure of the milling clamp is simplified, the machining efficiency is improved, and the machining cost is reduced. The milling difficulty and manufacturing cost of the part are reduced, profile distortion, residual stress and the like in the machining process are reduced, the material utilization rate and the product quality are improved, and precise manufacturing and lean manufacturing of the thickness-variable stringer part with the T-shaped section are achieved through the simple technological process combining numerical control milling and sheet metal forming. The method has generalizability and can be widely applied to machining and manufacturing of complex stringer parts.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation aircraft sheet metal parts processing, and relates to a method for manufacturing a "T"-shaped cross-section variable thickness long stringer part. Background Art

[0002] As the longitudinal member 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, increase the critical stress of the skin under compression and shear instability, bear part of the aerodynamic force acting on the fuselage skin and transmit it to the bulkhead. Since the long stringer has a very important influence on the strength of the aircraft, its processing quality directly affects the overall quality of the aircraft, especially in key parts such as the fuselage and wings, long stringers with variable thickness and complex shapes are often used, and their manufacturability and economy are both very challenging. The bottleneck currently faced 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 surface distortion is difficult to repair, which ultimately leads to problems such as low raw material utilization, low production efficiency, manufacturing accuracy, and poor surface quality in the processing of the part, 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, there is an increase in difficulty in the processing of complex long stringer parts with variable cross-sections. Summary of the invention

[0003] The purpose of the present invention is to invent a manufacturing method for a long stringer part with a "T"-shaped cross section and variable thickness. The manufacturing method changes the process of "CNC milling-manual trimming" to "CNC milling-stamping-manual forming" by replacing the raw materials and designing a set of fixed fixtures for milling and cutting, a set of knocking and trimming dies, and a set of bending dies for sheet metal forming. The "T"-shaped cross-section raw materials used in the present invention are close to the final size of the parts, with low material removal rate and high utilization rate. The milling fixture used in the present invention only processes the straightened state of the parts, and the tooling structure is simple, the difficulty of part processing is small, and the processing efficiency is high. The knocking and trimming dies and the bending dies can realize the processing of the straightened blank after milling to the final state of the parts. Although the number of tooling increases and the sheet metal forming links are added, the cost of raw materials for part processing is reduced, the processing difficulty is reduced, and the processing accuracy and surface quality are improved, so the precise manufacturing of long stringer parts with a "T"-shaped cross section and variable thickness can be achieved.

[0004] In order to achieve the above object, the technical solution of the present invention is:

[0005] A method for manufacturing a "T"-shaped cross-section variable-thickness long stringer part comprises three processes: numerical control milling, stamping and manual forming.

[0006] The first process is CNC milling.

[0007] The raw material of the parts used in the CNC milling process is a "T"-shaped cross-section aluminum alloy profile.

[0008] The aluminum alloy profile described above can realize all edge and thickness processing of the parts in the straight state, and the vertical ribs and the web are at 90 degrees, which is convenient for subsequent sheet metal forming. When milling, the profile raw material is first milled according to the straight state of the parts to complete the inner thickness of the web, the thickness of the vertical ribs and the edge. Since the rough material thickness is relatively large at this time, the deformation during milling is relatively small, and it can be completed by using a milling fixture. After completing the above milling, the outer thickness and edge milling of the web are carried out. At this time, the material removal rate of the milling area is relatively high, and the remaining thickness is only 2mm to 8mm, which is easy to deform, so a special milling fixture is used to clamp it.

[0009] The "fixed fixture" includes: a base, a baffle, a positioning plate, a cylindrical pin, a bolt, a hexagonal head clamping screw and a positioning pin.

[0010] The tooling "fixed fixture" can realize milling of aluminum alloy profiles with completed vertical ribs and inner thickness processing of the web to the edge and thickness of the parts in the straight state, with the vertical ribs and the web forming a 90° angle, and ensuring the minimum deformation during milling. The working surface of the structural base is designed to be "T" shaped, which is used to embed the processed vertical ribs of the profile into it, and the upper surface is close to the processed surface of the inner side of the web of the profile. Considering the slender structural characteristics of the tooling, the bottom of the base is widened to increase the rigidity and stability and facilitate clamping, and the overall structure is a "convex" structure. A baffle is set at one end of the base and is tightened and fixed with bolts to limit the position movement of the parts during milling in the length direction. A positioning plate is set at the other end of the base, which is connected to the base through a cylindrical pin and tightened and fixed with bolts to position the parts in the length direction. The hexagonal head clamping screw is set on the side of the positioning plate and the base, and the depth is adjustable to fix the parts in the base from the end and the side to prevent the parts from moving in the horizontal and vertical positions during milling. The positioning pin is set at the bottom of the base for quick positioning and installation of the milling fixture 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 is not higher than Ra1.6.

[0011] The second stamping process.

[0012] The tooling used in the stamping process is a "bending die", which includes: a lower die, a cylindrical pin, a clamping pin, an upper die, a die handle and screws.

[0013] The tooling "bending die" can realize bending the parts with all edges and thicknesses cut by CNC milling from a straight state to a part angle close to the final angle of the part, with the part angle being 63° to 66°. Considering that the parts are long and the bending angles are close, the bending forming can be pressed by feeding in sections, so the "bending die design" is based on the length of the intercepted parts of about 300mm. The lower die of its structure adopts a left and right split structure, and its working surface is designed according to the inner profile of the web of the intercepted part. The gap between the two lower dies is determined according to the maximum thickness of the part ribs of 4mm, and a cylindrical pin is used for connection. A rectangular slot is set at the bottom of the lower die for easy installation on the press. The clamping pin is used to quickly align the upper die with the lower die to prevent the upper and lower die positions from moving, resulting in errors in the profile during forming and even damage to the die. The working surface of the upper die is designed according to the profile of the bottom end of the web of the intercepted part, and cooperates with the lower die under the impact force of the stamping equipment to complete the bending of the part. The die handle is used to connect the "bending die" with the stamping equipment, and transmits the stamping force with the up and down movement of the equipment during work. The die handle is connected to the upper die by screws. For the above structure, the profile manufacturing tolerance is ±0.1mm, and the working profile roughness is not higher than Ra1.6.

[0014] The third process is manual forming.

[0015] The tooling used for manual forming is a "knock-and-repair die", which includes: a carcass, a block, a cylindrical pin, a screw and a lifting eye screw.

[0016] The tooling "knocking and trimming mold" can realize the forming of parts to the final shape, and can be used for the trimming of deformation after heat treatment and quenching. Its structural carcass is designed according to the bottom end profile of the part's web and the part edge line is drawn on it, which is used to find the position when the part is formed, and the thickness change transition zone is appropriately increased to avoid. The block adopts a detachable split structure, which is respectively set at the ends of the two sides of the tooling and the 1 / 4, 1 / 2, and 3 / 4 positions. The working surface is designed according to the vertical rib profile of the corresponding position of the part, and the lower end is left with an appropriate gap so that the part's web is embedded. The block and the carcass are connected by a cylindrical pin and fixed with screws. During the forming and trimming process, the block can be disassembled according to the needs of use. When the block is installed, the part's web and vertical rib profile are formed and trimmed. When the block is disassembled, the web is formed and trimmed separately. The eye screw is installed on the carcass for the lifting and transportation of the tooling. The above is designed and manufactured according to the part engineering data set, the profile manufacturing tolerance is ±0.1mm, and the working profile roughness is not higher than Ra1.6.

[0017] Effects of the present invention

[0018] By changing the material to "T" section profile material, using the process flow of "CNC milling-stamping-manual forming" instead of "CNC milling-manual finishing", and using three sets of newly designed tooling for milling and sheet metal forming, the milling fixture structure is simplified, the difficulty of part milling, manufacturing costs, and surface distortion and residual stress during processing are reduced, and the material utilization rate and product quality are improved. Through the process flow of combining simple CNC milling and sheet metal forming, the precise manufacturing and lean manufacturing of long truss parts with "T" section and variable thickness are realized. This invention is scalable and can be widely used in the processing and manufacturing of complex long truss parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 For parts drawing;

[0020] Figure 2 It is the cross-section diagram of the milled part;

[0021] Figure 3 This is the overall structure diagram of the fixed fixture;

[0022] Figure 4 This is a top view of the detailed structure of the fixed fixture;

[0023] Figure 5 It is the left view of the detailed structure of the fixed fixture;

[0024] Figure 6 It is the right view of the detailed structure of the fixed fixture;

[0025] Figure 7 It is a top view of the bending mold structure;

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

[0027] Fig. 9 It is the AA section view of the bending die structure;

[0028] Fig.10 This is the front view of the knocking and repairing mold structure;

[0029] Fig.11 This is the AA cross-section view of the mold repair structure.

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

[0031] The specific method for manufacturing a variable thickness long stringer part with a "T" shaped cross section includes the following steps:

[0032] Step 1: CNC milling

[0033] Aluminum alloy profiles with material grade 7B04 T74 and specification XC212-87 are used for milling. The cross-section of the material is "T" shaped, with a web width of 100mm and a thickness of 12.5mm, a vertical rib height of 100mm and a thickness of 8mm.

[0034] Milling is performed on a 1550mm long rough material. First, fix the rough material horizontally on the milling platform with the ribs facing upwards. After fixing it with a pressure plate, use a Φ30R3 milling cutter to mill the inner thickness of the web, the thickness of the ribs and the edge of the ribs according to the pre-compiled CNC program. When milling, you can first do rough milling and then fine milling. After completing the above milling, remove the pressure plate and remove the blank. Lift the "fixed fixture" to the milling platform, align the positioning pin 7 of the base with the positioning hole on the milling platform to complete the quick positioning and fix it with a pressure plate. Loosen the hexagonal clamping screws 6 on the side of the positioning plate 3 and the base 1, put in the blank after the ribs and the inner side of the web have been milled, and ensure that one side of the blank is close to the baffle 2. At the same time, tighten the hexagonal clamping screws 6 on the side of the positioning plate 3 and the base 1 to completely fix the blank in the length direction and close to one side of the base in the width direction, thereby completing the clamping of the parts. Align the coordinate system so that the coordinate system of the machine tool coincides with the programming coordinate system, run the CNC milling program, and complete the milling of the bottom thickness of the web and the edge shape of the part according to the pre-compiled CNC program. After completing the milling, turn off the machine button, clean the aluminum chips on the surface of the part, and check the edge size of the part and whether there are any bruises or other mechanical damages on the surface. After completing the above operations, loosen the hexagonal clamping screws 6 on the side of the positioning plate 3 and the base 1, and remove the part; compared with using 7B04 T74, δ80mm forgings to directly mill the entire shape and profile of the part, the milling process of the present invention has a low material removal rate and a simple milling profile, so the milling difficulty is low, the residual stress is small, and the deformation after milling is small;

[0035] Step 2: Stamping

[0036] Place the "bending die" in the center of the universal die base of the press, pull the deflection wheel handle of the universal die base, use the jaws of the universal die base to clamp and fix the lower die 8 of the bevel die, align the upper and lower dies through the cylindrical pin 9, and align the die handle 12 with the die handle hole of the slider, start the equipment, slide the slider downward, make the "bending die" die handle 12 enter the die handle hole of the slider, manually lock the die handle hole, so that the "bending die" upper die 11 is clamped and fixed on the slider. Operate the press to slide the slider upward, separate the upper and lower dies of the "bending die", and place the milled "T"-shaped section blank with the ribs facing downward into the gap between the two lower dies, ensuring that one side of the blank is completely placed in the die. Control the press to move the slider downward, and move the upper die of the "bending die" to the lower die. The blank is deformed under pressure, and the web gradually fits the working surface of the lower die. The angle between the ribs 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, and the pressure switch of the hydraulic press is released, and the slider slides upward to the initial position. Repeat the above actions, and gradually perform bevel forming in sections, and punch the 90° ribs to 63°~66°;

[0037] Step 3: Manual Forming

[0038] Place the "knocking and repairing mold" on a horizontal workbench, remove the screws 17, cylindrical pins 16 and all the blocks 15, place the stamped blank on the tire body 14 and fix it with a universal clamp, use a hammer and an aluminum hammer to manually shape the blank, and ensure that the part is close to the tire body when the edge line of the blank web coincides with the edge of the tooling. Then, install the cylindrical pins 16 and the blocks 15 and fix them with the cylindrical pins 16, use a hammer and an aluminum hammer to shape the ribs, so that the ribs fit tightly with the blocks; after completing the above, the shape of the part is obtained; the blank is less deformed during CNC milling of the present invention, and the angle of the ribs has been suppressed by stamping, so manual shaping is less difficult;

[0039] Step 4: Quenching

[0040] The purpose of quenching parts is to improve the strength and hardness of parts. The purpose of quenching parts is to improve the strength and hardness of parts. Specific operation: clean the parts and put them into nitrate heat treatment equipment. The heating temperature range is 465℃~475℃ and the holding time is 20min. After quenching, put them into running cold water at 10℃~40℃ to completely cool them for no less than 2min.

[0041] Step 5: Trimming

[0042] Due to deformation caused by quenching, in this process, the parts are placed on the knocking and repairing die and fixed with a universal quick clamp. After ensuring that the edge of the part is aligned with the edge line of the part on the knocking and repairing die, the quenching deformation is trimmed manually with tools such as hammers and aluminum hammers to ensure that the gap between the part and the tooling is no more than 0.5mm;

[0043] Step 6: Artificial Aging

[0044] The purpose of artificial aging is to eliminate internal stress and stabilize the structure and size. First, clean the parts to ensure that the surface is dry and free of dirt, oil and grease. When all temperature sensors of the equipment reach the temperature range required by the process, the parts are put into the furnace. Primary aging: Heating temperature range: 115±5℃, aging insulation time: 7h~8h; After the primary aging, the parts are not taken out of the furnace and are directly heated to enter the secondary aging, heating temperature range: 165±5℃, insulation time: 15h~16h. After the aging is completed, the parts are cooled by air cooling;

[0045] Step 7: 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 parts' hardness, strength and other properties are qualified. First, clean the parts, and then perform fluorescent penetrant crack inspection. If there are no cracks, conduct conductivity or hardness inspection. If there are cracks, the parts will be scrapped. If both conductivity and hardness inspections fail, repeat heat treatment and trimming, and then perform this step inspection again until the physical and chemical properties are qualified before entering the subsequent process;

[0047] Step 8: Surface treatment

[0048] The parts are anodized and painted to improve their corrosion resistance.

[0049] (1) Anodizing: Place the parts in a sulfuric acid anodizing tank for oxidation treatment at a temperature of 13°C to 25°C and a voltage of 13V to 24V for 15min to 40min, and then rinse in a cold water tank for 1min to 2min;

[0050] (2) Potassium dichromate sealing: At a temperature of 90℃ to 100℃, the parts are treated in a potassium dichromate sealing tank for 15min to 20min, placed in a 40℃ to 60℃ warm water tank for cleaning for 1min to 2min, and blown dry with compressed air;

[0051] (3) Painting: Use the prepared paint for spraying within the validity period, and the thickness of the paint should be controlled within the range of 25μm to 35μm. The painted parts are dried at a temperature of 100℃ to 110℃ for 1h to 3h.

[0052] Complete the above steps to obtain the final part.

Claims

1. A method for manufacturing a "T"-shaped cross-section variable thickness long stringer part, characterized in that: It includes three processes: CNC milling, stamping and manual forming; The first process is CNC milling; The raw material of the parts used is a "T"-shaped cross-section aluminum alloy profile; The aluminum alloy profile can process all edges and thicknesses of the parts in a straight state, and the ribs and the web are at 90 degrees, which is convenient for subsequent sheet metal forming. When milling, the profile raw material is first milled according to the straight state of the parts to complete the inner thickness of the web, the thickness of the ribs and the edges. After completing the above milling, the outer thickness and edge of the web are milled. At this time, the material removal rate of the milling area is high, and the remaining thickness is only 2mm to 8mm, which is easy to deform, so a special milling fixture is used for clamping; The special milling fixture comprises: 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 tooling-specific milling fixture can mill the aluminum alloy profiles that have completed the thickness processing of the vertical ribs and the inner side of the web to the edge and thickness of the parts in the straight state, with the vertical ribs and the web forming a 90° angle, and ensure that the deformation during the milling process is minimal; The second stamping process; The tooling used in the stamping process is a "bending die", which includes: a lower die (8), a cylindrical pin (9), a clamping pin (10), an upper die (11), a die handle (12) and a screw (13); The lower die (8) adopts a left-right split structure, and its working surface is designed according to the inner profile of the web of the intercepted part. The gap between the two lower dies is determined according to the maximum thickness of the part ribs of 4 mm, and is connected by a cylindrical pin (9). A rectangular slot is arranged at the bottom of the lower die for easy installation on a press; the clamping pin (10) is used to quickly align the upper die (11) and the lower die (8) to prevent the upper and lower dies from moving in position, resulting in errors in the profile during forming and even damage to the die; the working surface of the upper die (11) is designed according to the bottom end profile of the web of the intercepted part, and cooperates with the lower die under the impact force of the stamping equipment to complete the bending forming of the part; The third process is manual forming; The tooling used for manual forming is a "knocking and repairing mold", and the "knocking and repairing mold" tooling includes: a carcass (14), a stopper (15), a cylindrical pin (16), a screw (17) and a lifting eye screw (18).

2. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 1, characterized in that: The working surface of the base (1) is designed to be in a "T" shape, and is used to embed the processed vertical ribs of the profile into it, and the upper surface is closely attached to the processed surface on the inner side of the web of the profile, forming a "convex" structure as a whole; a baffle (2) is provided at one end of the base (1) and is tightened and fixed with bolts (5) to limit the position movement of the part in the length direction during milling; a positioning plate (3) is provided at the other end of the base (1), which is connected to the base (1) through a cylindrical pin (4) and is tightened and fixed with bolts (5) to position the part in the length direction.

3. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 1 or 2, characterized in that: The hexagonal clamping screw (6) is arranged on the side of the positioning plate (3) and the base (1), and the positioning pin (7) is arranged at the bottom end of the base, which is used for quickly positioning and installing the milling fixture on the milling platform; the above structure is manufactured according to the data set, the manufacturing tolerance of the profile is ±0.1mm, and the surface roughness of the working profile is not higher than Ra1.

6.

4. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 1 or 2, characterized in that: The die handle (12) is used to connect the "bending die" and the punching equipment, and the die handle (12) is connected to the upper die via screws.

5. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 3, characterized in that: The die handle (12) is used to connect the "bending die" and the punching equipment, and the die handle (12) is connected to the upper die via screws.

6. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 1, 2 or 5, characterized in that: The carcass (14) of the tooling "knocking and repairing mold" is designed according to the bottom end profile of the web of the part and the edge line of the part is marked on it. The stopper (15) adopts a detachable split structure and is respectively arranged at the ends of both sides of the tooling and at the 1 / 4, 1 / 2 and 3 / 4 positions. The working surface is designed according to the vertical rib profile of the corresponding position of the part, and an appropriate gap is left at the lower end so that the web of the part can be embedded; the stopper and the carcass are connected by a cylindrical pin (16) and fixed by a screw (17); the eye screw (18) is installed on the carcass for hoisting and carrying the tooling.

7. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 3, characterized in that: The carcass (14) of the tooling "knocking and repairing mold" is designed according to the bottom end profile of the web of the part and the edge line of the part is marked on it. The stopper (15) adopts a detachable split structure and is respectively arranged at the ends of both sides of the tooling and at the 1 / 4, 1 / 2 and 3 / 4 positions. The working surface is designed according to the vertical rib profile of the corresponding position of the part, and an appropriate gap is left at the lower end so that the web of the part can be embedded; the stopper and the carcass are connected by a cylindrical pin (16) and fixed by a screw (17); the eye screw (18) is installed on the carcass for hoisting and carrying the tooling.

8. A method for manufacturing a T-shaped cross-section variable thickness long stringer part as claimed in claim 4, characterized in that: The carcass (14) of the tooling "knocking and repairing mold" is designed according to the bottom end profile of the web of the part and the edge line of the part is marked on it. The stopper (15) adopts a detachable split structure and is respectively arranged at the ends of both sides of the tooling and at the 1 / 4, 1 / 2 and 3 / 4 positions. The working surface is designed according to the vertical rib profile of the corresponding position of the part, and an appropriate gap is left at the lower end so that the web of the part can be embedded; the stopper and the carcass are connected by a cylindrical pin (16) and fixed by a screw (17); the eye screw (18) is installed on the carcass for hoisting and carrying the tooling.

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