Method and die for reducing residual stress of large aluminum alloy whole frame through low-load cold pressing

Abstract

The invention discloses a method for reducing residual stress through low-load cold pressing of a large aluminum alloy whole frame, and the residual stress of a forged piece is reduced by pressing the forged piece subjected to heat treatment through a cold pressing die. The cold pressing die comprises an upper die and a lower die, the general shape of a cavity of the cold pressing die is consistent with that of the forge piece, on the basis of the forge piece, the height of the cavity of the die corresponding to a forge piece rib is reduced by 0.02 h-0. 05h (h is the height of the forge piece rib), the draft angle of the die is increased by 2-4 degrees, and the height of the cavity of the die corresponding to a forge piece web is increased by 0.02 h-0. 1h. In the whole cold pressing process of the forge piece, a cold pressing die is only in contact with the top of the forge piece rib and rib top convex fillets (R1 and R2), the die can wrap the top of the whole forge piece rib after cold pressing, the residual stress of the cross section of the large aluminum alloy whole frame after cold pressing is within + / -50 Mpa, and the load in the cold deformation process is always lower than the nominal pressure of a press.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy plastic forming, in particular to a method for reducing residual stress by low-load cold pressing of a large aluminum alloy whole frame and a mold thereof. Background Art

[0002] The rapid development of the aviation industry has put forward higher requirements on the mechanical properties, service stability and bearing capacity of large components, which has led to the increasingly prominent development trend of large components towards integration, large-scale and lightweight. Large aluminum alloy components have broad application prospects in the fields of aviation and aerospace. For aluminum alloy components, solid solution and rapid quenching are often used to obtain higher mechanical properties. However, during the quenching and cooling process, due to the temperature gradient between the core and the surface, uneven plastic deformation occurs between the various parts, and a large amount of residual stress is generated in the workpiece. The size and distribution of the residual stress generated by quenching have an important influence on the mechanical properties of the material, resulting in unstable dimensions of the parts after subsequent processing, prone to various defects such as warping, and difficult to guarantee material properties and dimensional accuracy. Through the heat treatment simulation of large aluminum alloy H-section forgings with complex shapes, it can be found that the surface of the forging, the fillet of the transition zone and the convex fillet of the ribs mainly concentrate compressive stress, and the core of the forging is mainly compressive stress. At present, the die pressing method is often used to eliminate the quenching residual stress for large aluminum alloy H-section forgings with complex shapes. The existing methods mainly reduce the tensile stress in the core of the forging by applying pressure to the sides, tops and webs of the ribs, and at the same time use metal flow to eliminate the compressive stress in the fillet of the forging. However, the area around the convex fillet of the forging rib top is a difficult deformation area during the cold deformation of the forging, and the stress elimination ability of the convex fillet of the forging rib is weak, and it is impossible to reduce the residual stress of the entire cross section of the forging. It can be seen that the existing residual elimination method cannot solve the problem of excessively high residual stress formed after quenching of large aluminum alloy frames and large cold pressing residual elimination load.

[0003] CN 115446610A discloses a method for eliminating residual stress by cold pressing, comprising the following steps: based on a forging to be cold pressed, obtaining a segmented cold pressing area; based on the segmented cold pressing area, obtaining a segmented cold pressing direction and a segmented cold pressing sequence; based on the segmented cold pressing area, obtaining a segmented cold pressing area mold; based on the segmented cold pressing area mold, obtaining a cold compression amount of the segmented cold pressing; based on the cold compression amount of the segmented cold pressing, cold pressing the segmented cold pressing area. For forgings with complex rib structures, the problem that the existing technology cannot effectively eliminate the residual stress in each part of the forging is solved. However, for large and complex forgings, this method requires a large number of molds to be designed; at the same time, the forging may be warped during the segmented cold pressing process, and a shaping mold is required for final shaping, resulting in a high production cost. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for reducing the residual stress of large aluminum alloy whole frames under low-load cold pressing, so as to solve the problems of excessively high residual stress formed after quenching of large aluminum alloy whole frames and large residual load during cold pressing.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A method for reducing residual stress by cold pressing a large aluminum alloy frame under low load, characterized in that the forging after heat treatment is pressed down by a cold pressing die to reduce the residual stress of the forging; Specifically, according to the structure of the forging, different cavity shapes of the upper and lower dies of the cold pressing residual elimination die are designed, and the downward pressure of the cold pressing upper die is adjusted so that during the cold deformation of the forging, the die only contacts the top of the forging rib and the convex fillet (R1, R2) of the rib top. After cold pressing, the die can wrap the top of the entire forging rib. The residual stress of the large aluminum alloy frame cross section after cold pressing is within ±50Mpa, and the load during the cold deformation process is always lower than the nominal pressure of the press, thereby achieving the reduction of the low-load cold pressing residual stress of large aluminum alloy frames with different structures.

[0006] Furthermore, according to the forging performance requirements, the cold pressing die structural parameters (forging ribs corresponding to the die cavity height, die draft angle, forging web corresponding to the die cavity height) and cold pressing process parameters (pressing amount) are optimized to reduce the forging residual stress to varying degrees. The specific method includes the following steps: S1. Design a cold pressing die based on the forging to be cold pressed, that is, adjust the die cavity structure parameters based on the forging, reduce the die cavity height corresponding to the forging rib, reduce the height H to 0.02h~0.05h (h is the forging rib height); increase the die draft angle, increase the angle A to 2°~4°; increase the die cavity height corresponding to the forging web, increase the height D to 0.02h~0.1h; S2. Control the cold pressing upper die to press down for 0.02h~0.05h, so that the load of the forging is always lower than the nominal pressure of the press during the entire cold pressing process. The cold pressing die only contacts the top of the forging rib and the convex fillets R1 and R2 of the rib top. After cold pressing, the die can wrap the entire top of the forging rib. S3. After simulation optimization, the large aluminum alloy frame is cold pressed. After cold pressing, the residual stress of the cross section of the large aluminum alloy frame is within ±50Mpa.

[0007] The present invention also provides a cold pressing die, the general shape of the cold pressing die cavity is consistent with the forging, the die cavity structural parameters are adjusted based on the forging, the die cavity height corresponding to the forging rib is reduced, and the height H is reduced to 0.02h~0.05h (H is the height of the forging rib); the die draft angle is increased, and the angle A is increased to 2°~4°; the die cavity height corresponding to the forging web is increased, and the height D is increased to 0.02h~0.1h.

[0008] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention applies pressure to the entire rib top and utilizes metal flow to achieve residual stress reduction in various parts of the forging, thereby solving the problem of residual stress reduction in the difficult-to-deform area of ​​the rib top that cannot be solved by the prior art; it applies compressive stress to the rib top of the component and the convex fillet (R1, R2) of the rib top to eliminate residual stress within the nominal pressure range of the press.

[0009] 2. The present invention can optimize the structural parameters and process parameters of the cold pressing die for forgings according to the performance requirements of the forgings, so that the residual stress of the large aluminum alloy frame cross section after cold pressing is within ±50Mpa, thereby achieving a significant reduction in the residual stress of the forgings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the aluminum alloy whole frame cold pressing method of the present invention; Figure 2 The positions of the typical cross sections of a large aluminum alloy forging before and after cold pressing in Example 1 of the present invention; Figure 3 The residual stress distribution cloud diagram of the cross section of a large aluminum alloy forging in the X direction and the Z direction before cold pressing in Example 1 of the present invention, wherein (a) is the residual stress in the X direction, and (b) is the residual stress in the Z direction; Figure 4 The residual stress distribution cloud diagram of the cross section of a large aluminum alloy forging in the X direction and the Z direction after cold pressing in Example 1 of the present invention, wherein (a) is the residual stress in the X direction, and (b) is the residual stress in the Z direction; DETAILED DESCRIPTION

[0011] The technical solution of the present invention is clearly and completely described below in conjunction with specific embodiments and drawings. Obviously, the embodiments are only representative of embodiments of the present invention and are not limited to the described embodiments. Therefore, the following detailed description of the embodiments provided in the drawings is not intended to limit the scope of the invention claimed for protection. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. The terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the figures, or the positions or positional relationships usually placed when the invention is used, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0013] Example 1 like Figure 1 As shown, a method for reducing residual stress by low-load cold pressing of a large aluminum alloy frame comprises the following steps: S1. Design the cold pressing die structure based on the forging to be cold pressed, that is, adjust the die structure parameters based on the forging, reduce the die cavity height corresponding to the forging rib, reduce the height H to 0.04h (h is the forging rib height); increase the die draft angle, increase the angle A to 2°; increase the die cavity height corresponding to the forging web, increase the height to 0.05h; S2. Control the cold pressing upper die to press down for 0.04h, so that during the whole cold pressing process of the forging, the cold pressing die only contacts the top of the forging rib and the convex fillet (R1, R2) of the rib top, and the die can wrap the top of the entire forging rib after cold pressing; S3. After simulation optimization, the large aluminum alloy frame is cold pressed. After cold pressing, the residual stress of the cross section of the large aluminum alloy frame is within ±50Mpa.

[0014] See also Figure 1 A cold pressing die, the general shape of the cold pressing die cavity is consistent with the forging, the die structure parameters are adjusted on the basis of the forging, the die cavity corresponding to the forging rib is lowered, and the height H is lowered to 0.04h (h is the height of the forging rib); the die draft angle is increased, and the angle A is increased to 2°; the die cavity height corresponding to the forging web is increased, and the height D is increased to 0.03h.

[0015] The method of reducing residual stress by cold pressing of large aluminum alloy whole frame under low load is adopted. Figure 2 A large aluminum alloy forging is processed. The outer contour size of the forging is large, the shape is complex, and it contains high ribs and high bosses. In the figure, CC is the position of the typical cross-section before cold pressing.

[0016] See also Figure 3 , for Figure 2 The simulation results of the heat treatment process of the large aluminum alloy frame forging before cold pressing were used to extract the residual stress distribution cloud diagram of a certain H-shaped section in the X and Z directions from the simulation results. Figure 3 (a) It can be clearly seen that after the aluminum alloy frame is heat treated, the stress range in the X direction of the cross section is -305Mpa~+138Mpa; Figure 3 (b) It can be clearly seen that the stress range in the Z direction is -312Mpa~+105Mpa, the residual stress is large and unevenly distributed, which has a great impact on the performance of the forging.

[0017] See also Figure 4 , using the cold pressing mold of the present invention Figure 2 The large aluminum alloy frame is subjected to residual stress cold pressing simulation treatment. The residual stress reduction simulation results are as follows: Figure 4 (a) It can be clearly seen that the stress range of the component in the X direction after cold pressing is -24.5Mpa~+31.8Mpa; Figure 4 (b) It can be clearly seen that the stress range in the Z direction is -39.4Mpa~+31.3Mpa, and the residual stress of the forging is within the expected range. Compared with before cold deformation, the residual stress is significantly reduced, the center of the forging web changes from tensile stress to compressive stress, and the residual stress is redistributed evenly.

[0018] In summary, the die and method provided by the present invention can significantly reduce the residual stress of the forging after quenching within the nominal pressure range of the press and redistribute the residual stress evenly.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing residual stress by low-load cold pressing of a large aluminum alloy frame, characterized in that: The heat-treated forgings are pressed down by cold pressing dies to reduce the residual stress of the forgings; Specifically, according to the structure of the forging, different cavity shapes of the upper and lower dies of the cold pressing residual elimination die are designed, and the downward pressure of the cold pressing upper die is adjusted so that during the cold deformation of the forging, the die only contacts the top of the forging rib and the convex fillet of the rib top. After cold pressing, the die can wrap the top of the entire forging rib. The residual stress of the cross-section of the large aluminum alloy frame after cold pressing is within ±50Mpa, and the load during the cold deformation process is always lower than the nominal pressure of the press, thereby achieving the reduction of the low-load cold pressing residual stress of large aluminum alloy frames with different structures.

2. According to claim 1, the method for reducing residual stress by low-load cold pressing of large aluminum alloy whole frame is characterized in that: According to the performance requirements of forgings, the structural parameters of the cold pressing die, namely the height of the forging rib corresponding to the die cavity, the die draft angle, the height of the forging web corresponding to the cavity and the pressing amount of the cold pressing process are optimized to reduce the residual stress of the forgings to varying degrees.

3. The method for reducing residual stress by low-load cold pressing of large aluminum alloy whole frame according to claim 1 is characterized in that: The following steps are involved: S1. Design a cold pressing die based on the forging to be cold pressed, that is, adjust the die cavity structure parameters based on the forging, reduce the die cavity height corresponding to the forging rib, reduce the height H to 0.02h~0.05h (h is the forging rib height); increase the die draft angle, increase the angle A to 2°~4°; increase the die cavity height corresponding to the forging web, increase the height D to 0.02h~0.1h; S2. Control the cold pressing upper die to press down for 0.02h~0.05h, so that the load of the forging is always lower than the nominal pressure of the press during the entire cold pressing process. The cold pressing die only contacts the top of the forging rib and the convex fillets R1 and R2 of the rib top. After cold pressing, the die can wrap the entire top of the forging rib. S3. After simulation optimization, the large aluminum alloy frame is cold pressed. After cold pressing, the residual stress of the cross section of the large aluminum alloy frame is within ±50Mpa.

4. The method for reducing residual stress by low-load cold pressing of large aluminum alloy whole frame according to claim 3 is characterized in that: The step S3 optimizes the cold pressing die structure parameters and process parameters with good residual stress reduction effect through simulation.

5. A cold pressing die, characterized in that: The general shape of the cold pressing die cavity is consistent with that of the forging. The die cavity structure parameters are adjusted based on the forging. The die cavity height corresponding to the forging ribs is reduced to 0.02h~0.05h (H is the height of the forging ribs); the die draft angle is increased to 2°~4°; the die cavity height corresponding to the forging web is increased to 0.02h~0.1h.

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