A multi-directional loading spin forming method to improve the uniformity of corrugated pipe wall thickness

Abstract

A multi-directional loading spin forming method for improving the wall thickness uniformity of corrugated pipes includes: mounting the fixed end of the pipe blank on a mandrel, with the free end of the pipe blank contacting the end face of a thrust plate; assuming that the wall thickness of the pipe blank remains constant during the spin forming process, with only the shape changing, the pipe blank is discretized into n micro-elements along the axial direction, maintaining the volume of each micro-element after deformation equal to that before deformation; based on the length difference of each micro-element before and after deformation, the specific displacement of the thrust plate when the spinning wheel moves to different waveform regions during the spin forming process can be obtained, and the axial displacement curve of the thrust plate is plotted to obtain the tail axial loading path; rotating the mandrel so that the spinning wheel contacts the pipe blank radially, the spinning wheel feeds according to the target waveform curve of the corrugated pipe, and simultaneously the thrust plate feeds according to the tail axial loading path, obtaining a corrugated pipe with better wall thickness uniformity. Compared with the spin forming results of the prior art, the maximum wall thickness difference of the corrugated pipe formed by the process of this invention is reduced by 25%.

Description

Technical Field

[0001] This invention relates to the field of metal thin-walled complex component processing, specifically to a multi-directional loading spin forming method for improving the uniformity of corrugated pipe wall thickness. Background Technology

[0002] Metal bellows possess advantages such as high strength and high pressure resistance, and are widely used in the aerospace field. Spinning technology progressively forms complex components through the continuous point loading action of a spinning wheel, offering advantages such as good forming quality, low forming load, and high production efficiency, making it an advanced method for manufacturing bellows. In bellows spinning, one end of the tube blank is fixed by a clamping device and rotates along its central axis, while the other end is free and unrestrained; simultaneously, the spinning wheel feeds the tube blank axially and radially with a wave-shaped curve trajectory to achieve bellows forming.

[0003] However, in traditional bellows spinning, the tube blank undergoes a complex triaxial strain state under the progressive local loading of the spinning wheel. The radial feed of the spinning wheel induces circumferential compressive strain in the loading zone, the magnitude of which varies with the diameter reduction at different waveform positions. The axial feed of the spinning wheel induces axial tensile strain in the loading zone, the magnitude of which depends on the spinning loading parameters and die parameters (including the slope of the waveform tangent at the loading position, feed ratio, and spinning wheel fillet radius). The thickness strain in the loading zone varies dynamically under the constraint of a constant plastic deformation volume (the sum of axial, circumferential, and thickness strains is 0). In summary, in bellows spinning, the magnitude of the triaxial strain varies significantly with the loading area, leading to uneven thickness strain and wall thickness distribution, especially excessive wall thinning in the descent section of the spinning wheel and the straight wall section. Figure 1 As shown in the figure, this leads to a decrease in the pressure-bearing capacity of the bellows. Therefore, it is of great significance to study and develop methods to improve the wall thickness uniformity of bellows spinning.

[0004] To address the issue of uneven wall thickness distribution in the spinning process of corrugated pipes, traditional methods control wall thickness by altering spinning process parameters (including spinning passes, feed ratio, spindle speed, and die parameters such as the radius of the spinning wheel). However, these methods do not change the local loading pattern of the spinning wheel and the stress state of the billet during spinning, and cannot significantly control the magnitude of the three-dimensional strain of the billet, thus having limited effect on improving the wall thickness uniformity of the corrugated pipe. For example, the literature (Yang Xin, Xiao Gangfeng, Cheng Xiuquan, et al. Influence of process parameters on the quality of single-pass diameter reduction spinning of high-strength steel pipes [J]. Forging Technology, 2017, 42(3):84-89) addresses the problem of excessive wall thickness reduction in the diameter reduction spinning of pipes by optimizing the radius of the spinning wheel and the feed ratio, but the maximum wall thickness difference of the formed component is reduced by only 5%, and the effect of improving wall thickness uniformity is still not significant. Summary of the Invention

[0005] Based on this, the present invention provides a multi-directional loading spin forming method to improve the wall thickness uniformity of corrugated pipes, thereby solving the problem of uneven wall thickness distribution in corrugated pipes formed by existing spin forming techniques. The present invention adds tail loading to the traditional spin forming process, applying constraints to the free end of the corrugated pipe to control its stress state and regulate triaxial strain; and dynamically matches the displacement of the tail loading according to the spin wheel loading conditions in different waveform regions, so as to flexibly control the thickness compressive strain in different waveform regions, avoiding excessive wall thinning, thereby improving the wall thickness uniformity of the spin-formed corrugated pipe.

[0006] To achieve the above objectives, the present invention provides a multi-directional loading spin forming method for improving the uniformity of corrugated pipe wall thickness, used to process a pipe blank into a corrugated pipe, comprising the following steps:

[0007] S1. Define one end of the tube blank as the fixed end and the other end as the free end. Install the fixed end of the tube blank on the mandrel. The free end of the tube blank is in contact with the end face of the pusher plate. Set the rotating wheel on the outer circumference of the tube blank. The plane containing the central axis of the rotating wheel and the central axis of the tube blank coincides with the feed plane of the rotating wheel. The central axis of the pusher plate coincides with the central axis of the tube blank, and the pusher plate moves along its central axis.

[0008] S2. The design principle of the axial loading path at the tail end is to assume that the wall thickness of the tube blank remains unchanged during the spinning process, with only the shape changing. The bellows obtained from the tube blank is discretized into n continuous infinitesimal elements along the axial direction. The cross-section of each infinitesimal element is perpendicular to the feed plane of the spinning wheel through the central axis of the tube blank. Let the slope of the tangent line of the target waveform curve (also known as the ideal waveform) of the bellows at the i-th segment of the n infinitesimal elements be y. i ′, the length of the i-th infinitesimal element before deformation is h i The inner diameter is r0, the outer diameter is R0, and the length after deformation is h. i ′, inner diameter is r i The outer diameter is R i And if the volume of each infinitesimal element after deformation is equal to that before deformation, then the length difference Δh of the infinitesimal element at the i-th segment before and after deformation is... i Represented as:

[0009]

[0010] Based on the principle that the thrust plate always acts on the tail end of the deformed tube blank, the specific displacement of the thrust plate can be obtained when the spinning wheel moves to different waveform areas during the spinning process according to the length difference of each micro-element before and after deformation. The axial displacement curve of the thrust plate is plotted with the distance of the spinning wheel moving in the axial direction as the independent variable and the displacement of the thrust plate as the dependent variable, and the axial loading path at the tail end is obtained.

[0011] S3. Rotate the mandrel so that the swivel wheel contacts the tube blank in the radial direction. The swivel wheel feeds according to the target waveform curve of the corrugated pipe, while the counter-pushing disc feeds according to the axial loading path at the tail end, resulting in a corrugated pipe with a relatively uniform wall thickness.

[0012] As a further preferred embodiment of the present invention, the end face diameter of the thrust disk is larger than the diameter of the tube blank.

[0013] As a further preferred embodiment of the present invention, the length of the micro-element is 0.01-0.1 mm, preferably 0.1 mm.

[0014] As a further preferred technical solution of the present invention, in step S2, the calculation formula for ensuring that the volume of the i-th micro-element after deformation is equal to that before deformation is as follows:

[0015]

[0016] The multi-directional loading spin forming method for improving the uniformity of corrugated pipe wall thickness of the present invention, by adopting the above technical solution, can achieve the following beneficial effects:

[0017] ① The method for improving the wall thickness uniformity of corrugated pipes in this invention adds a loading constraint to the free end of the corrugated pipe during the traditional spinning process, thus changing the stress form during spinning. This effectively controls the stress state and triaxial strain, preventing excessive wall thinning and improving the wall thickness uniformity of the corrugated pipe. Compared with traditional spinning under the same process parameters, the maximum wall thickness difference of the corrugated pipe formed by the process of this invention is reduced by 25%, and the wall thickness uniformity is improved by 20% compared with the spinning results of existing wall thickness uniformity technologies.

[0018] ②The method of the present invention for improving the uniformity of the wall thickness of the corrugated pipe, compared with the traditional spinning method, produces a waveform that is more consistent with the ideal waveform.

[0019] ③ The multi-directional spinning process in this invention introduces a tail loading degree of freedom, increases process flexibility, and improves the flexibility of spinning forming. In the future, it can be extended to the forming of other thin-walled complex metal components, such as irregular curved surface parts. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a comparison diagram of the wall thickness distribution of the corrugated pipe formed by the present invention and that of ordinary spinning. In the diagram, traditional spinning refers to the spinning method commonly used before the improvement, and uniform wall thickness spinning refers to the spinning method of the present invention.

[0022] Figure 2 This is a diagram of the apparatus for multi-directional loading spin forming as described in this invention;

[0023] Figure 3 Schematic diagram of the multi-directional loading spinning forming process according to the present invention;

[0024] Figure 4 Schematic diagram of the division of the tube blank according to the present invention;

[0025] Figure 5 Schematic diagram of the shape and size of the micro-elements before and after deformation after discretization;

[0026] Figure 6 Schematic diagram of the height of the ideal waveform outer contour according to the present invention. In the figure, the radial height refers to the distance from the outer surface of the deformed tube blank to the central axis of the tube blank;

[0027] Figure 7 Loading path at the tail end calculated by the method of the present invention.

[0028] Figure 8 Comparison diagram of the waveform geometry of the bellows according to the present invention and traditional spinning;

[0029] In the figure: 1 - reverse pushing disk; 2 - spinning wheel; 3 - tube blank; 4 - core die.

[0030] The realization of the purpose, functional characteristics and advantages of the present invention will be further described in conjunction with embodiments and with reference to the accompanying drawings. Specific embodiments

[0031] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0032] [[ID=三十五]]The present invention provides a multi-directional loading spinning forming method for improving the wall thickness uniformity of bellows. In this process method, a loading device and a reverse pushing disk 1 are added to the tail of the existing spinning equipment. The reverse pushing disk 1 and its loading device are installed on one side of the free end of the tube blank 3 (the other end of the tube blank 3 is used as a fixed end for connection with the core die 4), and can move axially according to a preset path. The end face diameter of the reverse pushing disk 1 is larger than the diameter of the tube blank 3. For details, please refer to Figure 2 as shown.

[0033] A tube blank 3 made of Al1060 is selected, with a wall thickness of mm and an outer diameter of 100 mm. The ideal outer diameter of the straight wall section of the bellows to be formed is 80 mm, the height H of the corrugation is 10 mm, the radius of the wave peak fillet on the outer surface of the corrugated section is r = 5 mm, and the radius of the wave peak fillet on the outer surface is R = 5 mm, as Figure 3 shown.

[0034] The specific forming steps of the bellows of the present invention are as follows:

[0035] Step 1: Before forming begins, the tube blank 3 is installed on the mandrel 4, and the pusher plate 1 is configured to contact the other end of the tube blank 3 through its end face to provide a load that can be applied to the tube blank 3. The roller 2 is installed on both sides of the tube blank 3, and the position of the roller is adjusted so that the plane containing the central axis of the roller 2 and the central axis of the tube blank 3 coincides with the feed plane of the roller 2, the central axis of the pusher plate 1 coincides with the central axis of the tube blank 3, and the pusher plate 1 moves along its central axis.

[0036] Step 2: After the position adjustment is completed, rotate the core mold 4 so that the rotating wheel 2 contacts the tube blank in the radial direction and the end face of the pusher 1 contacts the free end of the tube blank 3.

[0037] Step 3: Forming begins. The spinning wheel 2 feeds according to the target waveform curve of the bellows, while the reverse thrust plate 1 feeds according to the axial loading path at the tail. The selected process parameters are: the radius of the rounded corner of the spinning wheel 2 is 10mm, the diameter of the reverse thrust plate 1 is 200mm, the feed rate of the spinning wheel 2 is 1mm / r, and the rotation speed of the core mold 4 is 60r / min.

[0038] Step 4: After the forming process is completed, the core mold 4 stops rotating and the corrugated pipe is removed.

[0039] The design principle for the axial loading path at the tail is as follows: The wall thickness of the tube blank 3 remains constant during the spinning process, with only the shape changing as a constraint, to design the axial loading path. The specific design method is as follows: The desired corrugated pipe (composed of several alternating straight and corrugated pipe segments) is discretized axially into n continuous micro-elements (when the outer contour is a straight line, n ≥ 2 for each straight segment; when the outer contour is a curve, n ≥ 50 for each curved segment). The micro-element cross-section passes through the central axis of the tube blank 3 and is perpendicular to the feed plane of the spinning wheel 2, such as... Figure 4 As shown, the length of each micro-element is 0.1 mm (the area between the two vertical lines in the figure is the i-th micro-element, and the distance is the length h of the i-th micro-element). i (The diagram shows the result of dividing the infinitesimal element into segments, but due to the large number of segments, only a portion is shown in the figure). The shape and size of the infinitesimal element before and after deformation are as follows: Figure 5 As shown, the infinitesimal element is a uniform hollow cylinder before deformation, and the blank after deformation is approximately a hollow frustum; the length of the i-th infinitesimal element before deformation is h. i The inner diameter is r0, the outer diameter is R0, and the length after deformation is h. i The inner diameter at the end face furthest from the four ends of the core mold is r. i The outer diameter is R i Let the slope of the tangent line of the target waveform curve at the i-th segment be y. i ',like Figure 6 As shown.

[0040] To ensure that the volume of the infinitesimal element remains the same after deformation as before deformation, the calculation formula is as follows:

[0041]

[0042] The length difference Δh of the i-th infinitesimal element before and after deformation i Represented as:

[0043]

[0044] Based on the principle that the thrust disc always acts on the tail end of the deformed tube blank, and according to the length difference of each micro-element before and after deformation, the specific displacement of the thrust disc when the spinning wheel 2 moves to different waveform regions during the spinning process can be obtained. Linearizing this displacement magnitude yields the axial loading path at the tail end, such as... Figure 7 As shown.

[0045] The waveform curves of the waveform tubes processed using conventional methods, the waveform curves of the waveform tubes processed using the process of this invention, and the target waveform curve (ideal waveform) are compared. The comparison curves are shown below. Figure 8 As shown, the traditional process corresponds to ordinary spinning in the figure, the process of the present invention corresponds to uniform wall thickness spinning in the figure, and the target waveform curve corresponds to the ideal waveform. Figure 8 It can be seen that, compared with the traditional spinning process under the same process parameters, the maximum wall thickness difference of the corrugated pipe formed by the process of the present invention is reduced by 25%, the wall thickness uniformity is improved by 20%, and the waveform formed by the process of the present invention is more in line with the ideal waveform.

[0046] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A multi-directional loading spinning forming method for improving the uniformity of the wall thickness of a corrugated pipe for processing a pipe blank into a corrugated pipe, characterized by, The method comprises the following steps: S1, one end of the pipe blank is installed on the core mold, the other end of the pipe blank is in contact with the end face of the reverse push plate, the spinning wheel is arranged on the outer peripheral surface of the pipe blank, the central axis of the spinning wheel and the plane where the central axis of the pipe blank are coincident with the spinning wheel feeding plane, the central axis of the reverse push plate is coincident with the central axis of the pipe blank, and the reverse push plate moves along the central axis; S2. Assume that the wall thickness of the tube blank remains unchanged during the spinning process, only the shape changes, and the corrugated pipe obtained from the tube blank is discretized axially as follows: The segment is a continuous infinitesimal element, and the cross section of each infinitesimal element passes through the central axis of the tube blank and is perpendicular to the feed plane of the rotary wheel. Let the target waveform curve of the bellows be... The first in Duan Weiyuan The slope of the tangent line at the segment is , No. The length of the segment before deformation is The inner diameter is The outer diameter is The length after deformation is The inner diameter is The outer diameter is And if the volume of each infinitesimal element after deformation is equal to that before deformation, then the volume of the first infinitesimal element before and after deformation is equal to that before deformation. Length difference of the segment element Represented as: ； According to the length difference of each micro-element before and after deformation, the specific displacement size of the reverse push plate when the spinning wheel moves to different waveform regions in the spinning forming process is obtained, the axial movement distance of the spinning wheel is taken as the independent variable, the displacement size of the reverse push plate is taken as the dependent variable, the axial displacement curve of the reverse push plate is drawn, and the tail axial loading path is obtained; S3, the core mold is rotated, the spinning wheel is in contact with the pipe blank in the radial direction, the spinning wheel feeds according to the target waveform curve of the corrugated pipe, the reverse push plate feeds according to the tail axial loading path, and the corrugated pipe with uniform wall thickness is obtained.

2. The multi-axial loading spinning forming method for improving the uniformity of the wall thickness of a bellows according to claim 1, characterized by, The end face diameter of the reverse push plate is greater than the diameter of the pipe blank.

3. The multi-axial loading spinning forming method for improving the uniformity of the wall thickness of a bellows according to claim 1, characterized by, The length of the micro-element is 0.01-0.1 mm.

4. The multi-axial loading spinning process for improving the uniformity of the wall thickness of a bellows according to any one of claims 1 to 3, characterized in that, In step S2, the first The calculation formula that the volume of the segment micro-element after deformation is equal to the volume before deformation is as follows: 。

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