Manufacturing method for improving the fatigue performance of an aircraft annular lip in the direction of travel

Abstract

The application discloses a manufacturing method for improving the fatigue performance of an annular lip of an aircraft. The raw material is cold-work hardened at normal temperature, and then subjected to recrystallization heat treatment to increase equiaxed grains in the fiber direction of the raw material. After that, the raw material is deep-drawn to form a semi-finished product. The semi-finished product is locally cold-work hardened, and the materials in the annular excess area are extruded to the annular riveting area, so that the annular riveting area is flattened along the circumferential direction. Then, the semi-finished product is subjected to heat treatment and cooling treatment at a ladder temperature, so that the grains in the annular riveting area of the semi-finished product form finer aluminum-based supersaturated solid solution. Finally, the semi-finished product is subjected to normal-temperature circumferential expansion, so that more grains in the annular riveting area are subjected to tensile force along the circumferential direction, and the circumferential grain ratio and length are increased.

Description

TECHNICAL FIELD

[0001] The application relates to a sheet metal manufacturing technology in the field of aircraft manufacturing, in particular to a manufacturing method for improving the heading fatigue performance of an annular lip of an aircraft, and is especially suitable for improving the heading anti-breaking performance of a hard aluminum alloy annular lip along the edges of the periphery. BACKGROUND

[0002] It is known that metal plates have anisotropy, and the advantages are that the tensile strength and elongation of the plate along the fiber direction are obviously better than those perpendicular to the fiber direction; and the disadvantage is that the anti-breaking performance along the fiber direction is obviously lower than that perpendicular to the fiber direction. At present, the engine lip is assembled by edge riveting, and the high-frequency continuous vibration is generated in the riveting area of the lip under the action of high-speed airflow during work; the riveting hole of the lip is the primary source of heading crack initiation and expansion, and therefore improving the heading anti-shear breaking fatigue durability of the edge of the riveting area can obviously improve the service life of the lip. At present, in order to realize the lightweight structure of the product, the main measures taken to solve the problem of insufficient anti-shear fatigue performance of the product are as follows: 1. installing a reinforcing pad in the anti-shear fatigue weak area; 2. manufacturing a variable wall thickness product to increase the thickness of the anti-shear fatigue weak area; and 3. adjusting the fiber direction of the sheet metal to be perpendicular to the crack propagation direction of the known fatigue weak area during forming. Measures one and two not only increase the weight, but also increase the assembly workload, especially the deformation of the weak and rigid thin-walled part is large after milling. The essence of measure three is to transfer the anti-shear fatigue weak area to other areas.

[0003] In order to solve the defects of poor assembly precision and low service life of the existing split lip, domestic patents with publication numbers CN110434216A, CN110899501A and CN114160700A disclose an engine lip integral forming method. The essence of the above-mentioned prior art is to realize integral forming, reduce the thinning rate and improve the uniformity of the wall thickness. The common defect is that the fiber organization along the heading direction is obviously generated under the combined action of the radial tensile stress and the tangential compressive stress of the side wall of the lip during deep drawing forming, especially in the riveting area of the outer side wall corresponding to the fiber direction of the raw material. By reducing the fiber ratio along the heading direction of the riveting area or even forming a circumferential fiber organization during the deformation process, the difficulty of crack penetration through the fiber organization of the material can be increased, the crack propagation speed can be obviously slowed down, and the heading anti-shear load performance of the riveting area can be improved as a whole. SUMMARY

[0004] In order to overcome the significant defects that the annular lip riveting zone along the edge of the annular lip manufactured by the prior art cannot improve the overall performance of the annular lip in the direction of the edge, the purpose of the present application is to provide a manufacturing method for improving the performance of the annular lip in the direction of the edge of the aircraft, which utilizes the staggered promotion of hard aluminum alloy deformation and heat treatment to form ring-shaped grains in the riveting zone of the annular lip, retain ring-shaped deformation strengthening organization, and increase the number of strengthening phases, so as to achieve the purpose of significantly improving the overall performance of the annular lip in the direction of the edge.

[0005] A manufacturing method for improving the performance of the annular lip in the direction of the edge of the aircraft, the annular lip being a deep groove shell structure comprising an annular inner wall and an outer wall, the cross section of the annular inner wall and the outer wall being a parabola, the ends of the parabola cross section being annular riveting zones prone to forming cracks in the direction of the edge, characterized by the following contents: 1) cold work hardening of the raw material at room temperature to break the fiber grains of the raw material; 2) recrystallization heat treatment of the cold work hardened raw material to increase the equiaxed grains in the fiber direction of the raw material; 3) deep drawing of the recrystallization heat treated raw material into a semi-finished product, the end of the annular inner wall and the outer wall of the semi-finished product containing annular riveting zones and annular excesses, respectively, and the annular riveting zones and annular excesses of the semi-finished product containing elliptical grains in the direction of the edge; 4) local cold work hardening of the semi-finished product to extrude part of the material in the annular excess zone to the annular riveting zone, so that the grains in the annular riveting zone are flattened in the direction of the edge; 5) step temperature heating treatment of the semi-finished product after local cold work hardening, followed by cooling treatment, so that the grains in the annular riveting zone of the semi-finished product form finer aluminum supersaturated solid solution; 6) circumferential expansion of the semi-finished product after cooling treatment at room temperature, so that more grains in the annular riveting zone are subjected to tensile force in the circumferential direction, increasing the ratio and length of the circumferential grains; 7) drying the semi-finished product after circumferential expansion, and then placing it in a refrigerator for low temperature refrigeration; 8) first heat thick extrusion shaping of the semi-finished product after low temperature refrigeration, and then cutting the annular excess of the semi-finished product.

[0006] Further, in step 1), when the raw material is cold work hardened, the raw material is first covered with soft protective film on both sides, and then pulled along the fiber direction through a mold provided with multiple sets of interlocking convex ribs and grooves.

[0007] Further, in step 2), when the raw material is recrystallized, the soft protective film on both sides of the raw material is first removed, the raw material is then curled into a cylindrical shape and preheated at a temperature of 300±20°C; then the preheated raw material is placed in a heating furnace, and the heating medium in the heating furnace flows in the same direction as the axis of the raw material cylinder.

[0008] Further, in step 3), when the semi-finished product is deep drawn, the frictional resistance along the fiber direction of the raw material is less than the frictional resistance perpendicular to the fiber direction, and the diameters of the end of the annular inner wall and the annular outer wall of the deep drawn semi-finished product are both less than the theoretical diameters of the inner wall and the outer wall at the corresponding positions of the annular lip.

[0009] Further, in step 4), when the semi-finished product is partially cold-hardened, a roller is used to roll the semi-finished product to transfer the material in the annular excess area to the annular riveting area, so as to increase the wall thickness of the annular riveting area.

[0010] Further, in step 5), when the semi-finished product is heated, the semi-finished product is first kept at an environment of 410±10℃ for 60±10 minutes, and then is transferred to an environment of 494±5℃ for 20±5 minutes; when the semi-finished product is cooled, the semi-finished product is first transferred from the environment of 494±5℃ to room temperature water for rapid cooling for 2-4 minutes, and then is transferred to warm water of 60±10℃ for slow cooling.

[0011] Further, in step 6), the semi-finished product is circumferentially expanded when the material is in the heat treatment incubation period, and before the circumferential expansion, solid powder is filled in the annular riveting area and the groove cavity below the semi-finished product, and then the upper part of the solid powder is sealed with a soft metal.

[0012] Further, in step 7), the semi-finished product is stored in a cold storage environment with a temperature lower than -16℃ for 1-3 days.

[0013] Further, in step 8), when the semi-finished product is heat thick extrusion shaped and kept, the heating temperature is 190±10℃, and the keeping time is 30-60 minutes.

[0014] The application has the following advantages:

[0015] 1) The application adopts the directional cold-hardening and recrystallization heat treatment method, has the advantages of large cold-hardening strength, high efficiency, and uniform cold-hardening effect, and the grain refinement after recrystallization treatment can improve the formability of the material and significantly reduce the anisotropy of the raw material.

[0016] 2) The application adopts the variable resistance deep drawing method, which is also beneficial to improving the uniformity of the elliptical grain distribution in the riveting area of the deep drawn semi-finished product, and can reduce the influence of deep drawing deformation on the anisotropy of the semi-finished product riveting area.

[0017] 3) The application adopts the method of local thickening cold-hardening of the lip riveting area combined with step temperature heating, quenching incubation period circumferential deformation, which is beneficial to grain refinement, material strength and plasticity improvement, and increasing the circumferential grain ratio through deformation.

[0018] 4) The application adopts internal pressure flexible support ring expansion method, which can avoid the distortion of the inner and outer walls of the semi-finished product during ring expansion, facilitate the increase of the ring expansion deformation amount of the edge riveting area of the semi-finished product after deep drawing, and increase the ratio of ring-shaped elongated grains.

[0019] 5) The application adopts quenching incubation period ring deformation, cold storage, hot extrusion shaping, and heat preservation method, which promotes the dislocation density and vacancy between grains by deformation, and makes the material accumulate elastic potential energy of strengthening phase precipitation by deformation and cold storage, which is beneficial to activate more and finer strengthening phase by heating.

[0020] Therefore, the annular lip prepared by the application can form ring-shaped grains in the riveting area, refine aluminum-based and strengthening phase grains, and completely retain the ring deformation strengthening structure, so that the overall shear fracture resistance of the annular lip riveting area is significantly improved.

[0021] The application will be further described below in combination with the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the grain distribution of the annular lip made by the existing method.

[0023] Figure 2 is a schematic diagram of the cold work hardening principle of the raw material of the annular lip of the application.

[0024] Figure 3 is a schematic diagram of the shape of the raw material of the annular lip of the application during recrystallization treatment.

[0025] Figure 4 is a schematic diagram of the grain distribution of the annular lip deep drawing semi-finished product of the application.

[0026] Figure 5 is a schematic diagram of the comparison of the cross-sectional shape of the annular lip and its deep drawing semi-finished product of the application.

[0027] Figure 6 is a schematic diagram of the local cold work hardening principle of the semi-finished product of the annular lip of the application.

[0028] Figure 7 is a schematic diagram of the internal pressure support ring expansion principle of the semi-finished product of the annular lip of the application.

[0029] Figure 8 is a schematic diagram of the grain distribution of the finished product of the annular lip of the application.

[0030] Figure number explanation: 1. annular lip, 2. inner side wall, 3. outer side wall, 4. direction crack, 5. annular riveting area, 6. raw material, 7. convex rib, 8. groove, 9. fiber direction, 10. protective film, 11. heating medium, 12. cylinder axis, 13. semi-finished product, 14. elliptical grain, 15. fiber grain, 16. annular grain, 17. annular allowance, 18. roller, 19. solid powder, 20. soft metal. DETAILED DESCRIPTION

[0031] Firstly, the defects of the annular lip manufactured by the known technology are introduced.

[0032] The present application relates to an annular lip 1 as shown in the attached Figure 1 The raw material of the annular lip 1 is 2A12 or 2024 hard aluminum alloy sheet. The annular lip 1 is a deep groove shell structure including an annular inner side wall 2 and an outer side wall 3. The cross section of the annular inner side wall and the outer side wall of the annular lip is a parabola, and the ends of the parabola cross section are annular riveting areas 5 prone to form direction cracks 4. Generally, the annular lip 1 is connected with the aircraft nacelle through the annular riveting area 5, and the annular riveting area 5 bears high-frequency direction shear load during flight. When the annular lip 1 is manufactured by the traditional method, the material is subjected to radial tension and compression force along the ring direction, and the direction elliptical grains 14 are formed in the annular riveting area 5 perpendicular to the fiber direction 9 of the raw material, and the direction fiber grains 15 with higher density are more prone to be formed in the annular riveting area 5 along the fiber direction 9 of the raw material, which causes obvious directional difference of the direction shear rupture performance of the annular riveting area 5. The adjustment of the fiber direction 9 of the material during the forming of the existing technology actually transfers the weak area of the shear load to other areas, and cannot realize the overall improvement of the direction shear load performance around the annular riveting area 5. In addition, the fiber direction 9 of the material is used randomly in actual production, which is affected by various uncontrollable factors such as machining and assembly accuracy, and it is necessary to determine the highest frequency area of the direction crack 4 generated in the service environment through a large number of flight tests, which has a long cycle and high cost.

[0033] Secondly, the manufacturing method for improving the direction fatigue performance of the annular lip of the aircraft is introduced.

[0034] The measures such as the formation of the annular grain, the grain refinement and the improvement of the material strength in the direction of the direction crack 4 initiation and expansion can slow down the crack propagation rate, and achieve the purpose of overall improvement of the direction rupture performance of the annular riveting area 5. In order to realize the invention idea of the present application, reference is made to the attached Figure 1 to the attached Figure 8 The preparation process is as follows:

[0035] Step 1) Cold work hardening of the raw material 6 at room temperature to break and refine the fiber grains 15 of the raw material 6. It needs to be explained that when the raw material 6 is cold work hardened, the raw material is first covered with soft protective film 10 on both sides, and then pulled through the mold provided with multiple sets of interlocking convex ribs 7 and grooves 8 along the fiber direction 9. The purpose is three-fold: first, the soft protective film 10 on both sides can avoid surface scratches during material deformation hardening; second, the raw material 6 pulled through the mold provided with multiple sets of interlocking convex ribs 7 and grooves 8 can improve the efficiency of uniform high-strength cold work hardening of the material; third, cold work hardening along the fiber direction 9 of the raw material has obvious directionality, and through the above measures, the equiaxed grains of the material after recrystallization increase more along the fiber direction 9, and the anisotropy of the raw material is reduced to the maximum.

[0036] Step 2) Recrystallization heat treatment of the cold work hardened raw material 6 to increase the equiaxed grains of the raw material in the fiber direction 9 and reduce the anisotropy of the raw material before forming. It needs to be explained that when the raw material is recrystallized, the soft protective film 10 on both sides of the raw material is first removed, and the raw material 6 is curled into a cylindrical shape and preheated at a temperature of 300±20℃. Then the preheated raw material is placed in a nitrate salt furnace, and the heating medium 11 in the nitrate salt furnace flows in the same direction as the cylindrical axis 12 of the raw material. The reason is two-fold: first, curling the raw material 6 into a cylinder can increase the stiffness of the sheet and reduce the deformation under heat; it is also conducive to the smooth flow of the heating medium 11 from the cylindrical axis 12, which reduces the space and improves the temperature uniformity. Second, the raw material 6 is preheated and transferred to the nitrate salt furnace for heat preservation. Because nitrate has high specific heat and is isolated from air, it can reduce the high-temperature heat preservation time under the condition of improving the recrystallization rate, and avoid overburning or oxidation of the material.

[0037] Step 3) Deep drawing of the raw material 6 after recrystallization heat treatment into a semi-finished product 13, which has a ring-shaped riveting area 5 and a ring-shaped excess 17 at the end of the ring-shaped inner and outer walls 2 and 3, and has directional elliptical grains 14 on the ring-shaped riveting area 5 and the ring-shaped excess 17. It needs to be explained that when the semi-finished product 13 is deep drawn, the frictional resistance along the fiber direction 9 of the raw material is less than the frictional resistance perpendicular to the fiber direction, and the diameters of the ring-shaped inner and outer walls 2 and 3 at the end of the semi-finished product are smaller than the theoretical inner and outer wall diameters at the corresponding positions of the ring-shaped lip. The purpose is two-fold: first, reducing the frictional resistance in the fiber direction 9 during deep drawing can further reduce the influence of deep drawing deformation on the anisotropy of the edge of the semi-finished product 13; second, in order to facilitate the subsequent ring-shaped riveting area 5 to change the grain direction through ring-shaped bulging, the diameters of the inner and outer walls of the semi-finished product 13 at the edge of the ring-shaped lip are smaller than the theoretical inner and outer wall diameters at the corresponding positions of the ring-shaped lip.

[0038] Step 4) Local cold work hardening of semi-finished product 13, partial material extrusion of annular excess 17 region to annular riveting zone 5, annular riveting zone 5 wall thickness increases. One of the purposes is to flatten the annular riveting zone 5 wall thickness. The other purpose is to shorten or break part of the annular fiber grains 15, which is beneficial to subsequent heat treatment to refine grains and increase the ratio of annular grains 16.

[0039] Step 5) After local cold work hardening, semi-finished product 13 is first subjected to step temperature heating treatment, and then cooling treatment, so that the semi-finished product annular riveting zone 5 grain forms a finer aluminum-based supersaturated solid solution. Two points need to be explained: first, during the heating treatment of the semi-finished product 13, the semi-finished product is first placed in a 410±10℃ environment nitrate salt furnace for 60±10 minutes, and then the semi-finished product 13 is transferred to a 494±5℃ environment nitrate salt furnace for 20±5 minutes. The purpose of 410±10℃ heat preservation is to refine the grains and shorten the high temperature time to increase the solubility of the solute, so that the aluminum-based supersaturated solid solution has finer grains and higher concentration. The second is that during the cooling treatment of the semi-finished product 13, the semi-finished product 13 is first transferred from the 494±5℃ environment to room temperature water for rapid cooling for 2-4 minutes, and then the semi-finished product is transferred to 60±10℃ warm water environment for slow cooling. The purpose of rapid cooling is to increase the concentration of solute in aluminum-based, which can increase the amount of strengthening phase. The purpose of slow cooling is to avoid deformation of the thin-walled part and quenching rupture.

[0040] Step 6) Normal temperature ring expansion of semi-finished product 13 after cooling treatment, more grains of annular riveting zone 5 are subjected to tensile force, increasing the ratio and length of annular grains 16. It needs to be explained that: the semi-finished product 13 is subjected to ring expansion during the incubation period of the material. During ring expansion, solid powder 19 is first filled in the annular riveting zone 5 and the lower cavity of the semi-finished product, and then the upper part of the solid powder is sealed with soft metal 20. There are three reasons for this: first, the plasticity of the material in the incubation period is good, which is beneficial to improving the dislocation, vacancy density and uniformity between grains through deformation, and improving the strengthening potential energy; second, the internal pressure support of the solid powder 19 can avoid distortion caused by the large difference in parabolic section, which is beneficial to increasing the ring deformation of the annular riveting zone 5 and improving the ratio of annular grains 16; third, ring expansion after solid solution can not only eliminate the deformation of heat treatment, but also completely retain the strengthening structure formed by ring expansion.

[0041] Step 7) After the semi-finished product 13 is cleaned and dried, it is placed in a refrigerator for low-temperature storage. It should be noted that the semi-finished product is stored at a temperature below -16°C for 1-3 days. The purpose of the storage is to strongly inhibit the precipitation of the strengthening phase, so that the material can further accumulate the potential energy of the precipitation of the strengthening phase, thereby improving the nucleation rate of the precipitation of the strengthening phase during heating, refining the strengthening phase, and increasing the number of the strengthening phase.

[0042] Step 8) The semi-finished product 13 is first subjected to hot thick extrusion shaping and heat preservation, and then the ring-shaped excess part 17 of the semi-finished product is cut to obtain a ring-shaped lip product. It should be noted that the semi-finished product 13 is subjected to hot thick extrusion shaping at a temperature of 190±10°C for 30-60 minutes. The advantages of this method are as follows: 1) the hot activation can improve the nucleation rate of the precipitation of the strengthening phase, so that more and finer strengthening phases are precipitated; 2) the heat preservation accelerates the aging process and reduces the deformation caused by natural aging; 3) the hot extrusion is beneficial to the welding deformation and can improve the density of the material; and 4) the warm thick extrusion can completely retain the deformation strengthening structure and reduce the uneven wall thickness defects caused by the deformation process.

Claims

1. A method for improving the azimuth fatigue performance of an aircraft annular lip, wherein the annular lip is a deep-groove shell structure comprising an annular inner wall and an annular outer wall, the cross-sections of the inner and outer walls of the annular lip being parabolic, and the two ends of the parabolic cross-sections being annular riveting areas, characterized by comprising: The following content: 1) at room temperature, the raw material is cold hardening along the fiber direction, the raw material fiber grain is broken; 2) the cold hardening raw material is recrystallized heat treatment, the raw material fiber direction of equiaxed grain increases; 3) the recrystallization heat treatment after the raw material is drawn into a semi finished product, the end of the annular inner side wall and the outer side wall of the semi finished product contains annular riveting area and annular surplus, the annular riveting area and the annular surplus of the semi finished product annular inner side wall and outer side wall contains the heading elliptical grain; 4) the semi finished product is locally cold hardening, the annular surplus area part material is extruded to the annular riveting area, the annular riveting area grain is flattened along the ring; 5) the semi finished product is first heated to step temperature treatment, then cooled, so that the grain of the annular riveting area of the semi finished product forms finer aluminum supersaturated solid solution; 6) the semi finished product is ring expansion at room temperature after cooling treatment, more grains in the annular riveting area are subjected to tensile force in the ring direction, the ratio and length of the ring grain are increased; 7) the semi finished product is cleaned and dried after ring expansion, and is placed in a refrigerator for low temperature refrigeration; 8) the semi finished product is first heat thick extrusion shaping and heat preservation, and then the annular surplus of the semi finished product is cut.

2. The method of claim 1, wherein the aircraft annular lip heading fatigue performance is improved by: In step 1), the raw material is cold hardening, the raw material is first covered with soft protective film on both sides, and then is pulled along the fiber direction through the mold provided with multiple groups of interlocking convex ribs and grooves.

3. The method of claim 1, wherein the method further comprises the step of: In step 2), the raw material is recrystallized heat treatment, the soft protective film on both sides of the raw material is removed, the raw material is curled into a cylindrical shape and preheated at 300±20℃; then the preheated raw material is placed in a heating furnace, and the heating medium in the heating furnace flows in the same direction as the axis of the raw material curling cylinder. ​ 4. The method of claim 1, wherein the method further comprises the step of: In step 3), the semi finished product is drawn, the friction resistance along the fiber direction of the raw material is less than the friction resistance perpendicular to the fiber direction, and the diameters of the end of the annular inner side wall and the outer side wall of the drawn semi finished product are smaller than the theoretical inner and outer side wall diameters corresponding to the position of the annular lip. ​ 5. The method of claim 1, wherein the method further comprises the step of: In step 4), the semi finished product is locally cold hardening, the annular surplus area of the semi finished product is rolled by a roller to transfer the material in the annular surplus area to the annular riveting area, so that the wall thickness of the annular riveting area is increased. ​ 6. The method of claim 1, wherein the aircraft annular lip heading fatigue performance is improved by: In step 5), the semi finished product is heated, the semi finished product is first heat treated at 410±10℃ for 60±10 minutes, and then is transferred to an environment of 494±5℃ for 20±5 minutes; the semi finished product is cooled, the semi finished product is first transferred from the environment of 494±5℃ to room temperature water for rapid cooling for 2-4 minutes, and then is transferred to the warm water environment of 60±10℃ for slow cooling.

7. The method of claim 1, wherein the method further comprises the step of: In step 6), the semi finished product is ring expanded during the heat treatment incubation period of the material, and the semi finished product is ring expanded, the groove in the annular riveting area and the lower part of the semi finished product is first filled with solid powder, and then the upper part of the solid powder is sealed with soft metal. ​ 8. The method of claim 1, wherein the method further comprises the step of: In step 7), the semi finished product is refrigerated at an environment temperature lower than-16℃ for 1-3 days. ​ 9. The method of claim 1, wherein the method further comprises the step of: In step 8), the semi-finished product is heated to 190±10℃ and kept for 30-60 minutes during the hot thick extrusion shaping and heat preservation. ​

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