Multi-degree-of-freedom rolling-extrusion-spinning composite forming method for thin-walled straight tubes with high ribs

Abstract

The present invention relates to a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for a thin-walled straight tube with high ribs, wherein a pre-forged thin-walled straight tube with high ribs having a relatively small axial height is first obtained through a rolling-extrusion forming process, and then the pre-forged thin-walled straight tube with high ribs having a relatively large axial height is formed into a thin-walled straight tube with high ribs having a relatively large axial height through two-pass spin-drawing forming processes. During the rolling-extrusion forming stage, the outer diameter and axial height of the workpiece remain unchanged, and through the coordinated movement of the constraining die, the rollers, and the block, the workpiece undergoes continuous local plastic deformation of thinning of the skin and growth of the annular ribs, and finally the target pre-forged thin-walled straight tube with high ribs having a relatively small axial height is obtained. During the spin-drawing forming stage, the outer diameter, the width of the annular ribs, and the inner diameter of the annular ribs remain unchanged, and the skin of the workpiece undergoes continuous local plastic deformation of reducing the wall thickness and extending the axial length, and finally the target thin-walled straight tube with high ribs having a relatively large axial height is obtained. The method of the present invention can realize the overall plastic forming of the thin-walled straight tube with high ribs, thereby greatly improving the mechanical properties of the thin-walled straight tube with high ribs.

Description

Technical Field

[0001] The invention relates to the field of manufacturing thin-walled ribbed tubes, and more particularly to a multi-freedom rolling-extrusion-spinning composite forming method for thin-walled straight tubes with high ribs. Background Art

[0002] Highly ribbed thin-walled straight tubes, consisting of a thin-walled skin and multiple internal ring ribs, offer advantages such as high load-bearing capacity and light weight. However, the extreme structure of highly ribbed thin-walled straight tubes, with their thin skin, wide and tall ribs, large dimensions, and use of highly deformable, high-strength, lightweight materials, pose significant challenges to their high-performance and efficient manufacturing.

[0003] Currently, thin-walled straight tubes with high ribs are primarily manufactured using a cutting-and-welding process. However, this process suffers from long cutting cycles, extremely low material utilization, and poor weld performance, making it unable to meet the high-performance and efficient manufacturing requirements for thin-walled straight tubes with high ribs. Roll-extrusion is a new method for achieving integral plastic forming of thin-walled, high-ribbed tubes. This method limits the increase in the outer diameter and axial height of the tube, forcing a large amount of metal from the skin to axially transfer to fill the ribs, thereby achieving coordinated forming of the thin skin and ribs. However, thin-walled straight tubes with high ribs in aerospace applications have a large axial height. This, on the one hand, results in a long axial contact length between the core roller and the roller during the roll-extrusion process, resulting in extremely high radial forming forces on the core roller, placing extremely high demands on the roll-extrusion equipment. Furthermore, during the roll-extrusion process, the long axial flow of metal creates significant flow resistance, resulting in a preference for circumferential flow, which can easily lead to circumferential plastic instability of the thin skin. Therefore, roll-extrusion is not suitable for forming thin-walled straight tubes with high ribs with large axial heights. The spinning method can achieve integral plastic forming of thin-walled cylindrical parts. Its principle is to locally load the blank through a spinning wheel, thereby driving a large amount of metal to flow axially. This method has the advantages of low forming force and good metal fluidity, making it particularly suitable for forming thin-walled cylindrical parts with large axial heights. However, during the spin-drawing process, a large amount of metal flows axially to increase the axial height, making it difficult for the metal to flow radially to fill the high ribs. Therefore, the spin-drawing method cannot achieve integral plastic forming of thin-walled straight cylinders with high ribs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for a thin-walled straight tube with high ribs, which can achieve the overall plastic forming of the thin-walled straight tube with high ribs using a relatively small forming force.

[0005] The technical solution adopted by the present invention to solve the technical problem is to construct a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for forming a thin-walled straight tube with high ribs. The thin-walled straight tube with high ribs includes a thin-walled skin and inner annular ribs located at the upper end, middle end and lower end of the tube. The forming method includes the following steps:

[0006] S1. Obtain parameters of a pre-forged thin-walled straight cylinder with high ribs. The outer diameter of the pre-forged is equal to the outer diameter of the thin-walled straight cylinder with high ribs, and the axial height of the pre-forged is much smaller than the axial height of the thin-walled straight cylinder with high ribs.

[0007] S2. Obtain parameters of a ring blank required for roll extrusion of a preforging. The ring blank required for roll extrusion of the preforging is a ring blank of uniform wall thickness, with an outer diameter equal to that of a thin-walled straight cylinder with high ribs, a wall thickness greater than that of a skin of the preforging, and an axial height equal to that of the preforging;

[0008] S3. Assemble the extrusion die, which includes a constraining die, a roller, and two stoppers. The constraining die is a thick-walled, equal-diameter ring member, whose axial height is equal to the circumferential height of the ring blank and whose inner diameter is equal to the outer diameter of the ring blank. The roller is a stepped shaft member, whose two ends have the smallest diameters, and whose middle end is a cylinder with an annular groove. The upper and lower stoppers are both ring members, and their outer diameters are equal to the outer diameter of the constraining die. The inner diameter of the upper stopper is smaller than the inner diameter of the annular rib at the upper end of the preforging, and the inner diameter of the lower stopper is smaller than the inner diameter of the annular rib at the lower end of the preforging.

[0009] S4. Assemble the spin-drawing forming die, which includes a sleeve die, a base, a roller, and two pressing blocks; the sleeve die is a straight cylinder with a constant diameter, the inner diameter of the sleeve die is equal to the outer diameter of the pre-forging, and the axial height of the sleeve die is greater than the axial height of the straight cylinder with high ribs and thin walls; the diameter of the base is greater than or equal to the outer diameter of the sleeve die, the roller is a rotating part, the upper and lower end surfaces of the roller are flat, and the side surface of the roller is a curved surface;

[0010] S5, performing rolling and extrusion forming of pre-forgings;

[0011] S6. The pre-forged parts are formed into straight tubes with high ribs and thin walls by two-pass spinning.

[0012] According to the above scheme, in step S1, the width of the ring ribs at the upper / middle / lower ends of the pre-forging is equal to the width of the ring ribs at the upper / middle / lower ends of the thin-walled straight tube with high ribs, the inner diameter of the ring ribs at the upper / middle / lower ends of the pre-forging is equal to the inner diameter of the ring ribs at the upper / middle / lower ends of the thin-walled straight tube with high ribs, the skin thickness t1 of the pre-forging is greater than the skin thickness t2 of the thin-walled straight tube with high ribs, and the distance between the ring ribs at the upper / lower ends of the pre-forging and the middle end is less than the distance between the ring ribs at the upper / lower ends and the middle end of the thin-walled straight tube with high ribs.

[0013] According to the above solution, in step S1, the following dimensional relationship is satisfied between the pre-forged skin and the thin-walled straight tube skin with high ribs:

[0014]

[0015] Among them, Φ1 is the outer diameter of the thin-walled straight tube with high ribs, H1 is the axial height of the pre-forged piece, H2 is the axial height of the thin-walled straight tube with high ribs, a1 is the distance between the upper and middle ring ribs of the pre-forged piece, b1 is the distance between the lower and middle ring ribs of the pre-forged piece, a2 is the distance between the upper and middle ring ribs of the thin-walled straight tube with high ribs, and b2 is the distance between the lower and middle ring ribs of the thin-walled straight tube with high ribs.

[0016] According to the above solution, in step S1, the pre-forging size also meets the following requirements:

[0017]

[0018] Among them, σ r is the axial stress at the interface between the skin and the reinforcement, σ c is the critical stress of axial instability at the interface between the skin and the ring reinforcement, σ s is the yield stress of the preforging material, h is the radial height of the preforging ring rib, m is the friction coefficient between the preforging and the die, l is the circumferential contact length between the roller and the preforging, w is the width of the preforging ring rib, t1 is the wall thickness of the preforging skin, E is the elastic modulus of the preforging material, μ is the Poisson's ratio of the preforging material, r is the radius of the roller working surface, R is the radius of the inner surface of the preforging skin, and f is the radial feed of the roller corresponding to one rotation of the preforging.

[0019] According to the above solution, in step S2, the ring blank and the thin-walled straight tube with high ribs should meet the following dimensional relationship:

[0020]

[0021] Among them, t0 is the wall thickness of the ring blank, w1 is the width of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs, w2 is the width of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs, w3 is the width of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs, Φ2 is the inner diameter of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs, Φ3 is the inner diameter of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs, and Φ4 is the inner diameter of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs.

[0022] According to the above solution, in step S3, the following dimensional relationship is satisfied between the pre-forging, the stopper, and the roll:

[0023] Φ7 <min{Φ3,Φ5,Φ6} (4)

[0024] Among them, Φ3 is the inner diameter of the ring rib at the middle end of the thin-walled straight cylinder with high ribs, Φ5 is the inner diameter of the upper stopper, Φ6 is the inner diameter of the lower stopper, and Φ7 is the outermost diameter of the roller.

[0025] According to the above scheme, in step S4, the shapes of the two pressing blocks are exactly the same. The pressing blocks are arc-shaped plates with a fan-shaped axial cross-section. The outer diameter of the pressing block is equal to the smaller value of the inner diameter of the ring ribs at the upper end of the thin-walled straight tube with high ribs and the inner diameter of the ring ribs at the small end. The inner side of the pressing block is a conical surface, and the axial height of the pressing block is less than the smaller value of the width of the ring ribs at the upper end of the thin-walled straight tube with high ribs and the width of the ring ribs at the lower end.

[0026] According to the above scheme, in step S5, the pre-forging extrusion forming includes the following steps:

[0027] 1) Before extrusion, the outer circumference of the ring blank is in contact with the inner circumference of the constraining die, the end faces on both sides of the ring blank are in contact with the end faces of the block respectively, and the inner circumference of the ring blank is in contact with the roller;

[0028] 2) In the extrusion forming stage, under the joint constraints of the constraining die and the stopper, the outer diameter and axial height of the ring blank remain unchanged; the constraining die drives the ring blank and the two stoppers to rotate around their own axes, and the rollers passively rotate around their own axes and feed a predetermined amount in the radial direction; under the joint action of the constraining die, the stopper and the rollers, the metal in the loading area of ​​the ring blank gradually flows into the roller cavity, causing the ring blank to undergo continuous local plastic deformation of skin thinning and ring rib growth, and finally forming a pre-forged part;

[0029] 3) In the demoulding stage of the pre-forging, the roller is first pulled out from the inside of the pre-forging and the block, and then the pre-forging is ejected from the constraining die along the axial direction.

[0030] According to the above scheme, in step S6, the first-pass spin-drawing method for a thin-walled straight tube with high ribs includes:

[0031] 1) The lower end face of the sleeve die is integrally connected to the base, the outer end face of the annular rib at the lower end of the pre-forging is in contact with the base, and the outer circumference of the pre-forging is in contact with the inner circumference of the sleeve die; the bottom of the inner circumference of the upper skin of the pre-forging is in contact with the roller, and the roller is tilted upward at a certain angle along the axial direction; the bolts are screwed to the base, and the frustum of the bolts is fully matched with the inner conical surface of the pressing block. By tightening the bolts, sufficient clamping force is generated between the pressing block and the annular rib at the lower end of the pre-forging to prevent the pre-forging from moving axially during the spinning and drawing process;

[0032] 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter, ring rib width and inner diameter of the preforging remain unchanged; the base drives the preforging, the sleeve die and the pressing block to rotate around its own axis, the rotating wheel passively rotates around its own axis and feeds f1 in the radial direction and then stops feeding, and then the rotating wheel feeds f2 axially upward from the bottom of the upper skin of the preforging; on this basis, the rotating wheel quickly moves to the bottom of the lower skin of the preforging, feeds f1 in the radial direction and then stops feeding, and then the rotating wheel feeds f3 axially upward from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower ends of the upper and lower skins of the preforging undergo continuous local deformation with reduced wall thickness and axial elongation, and finally a preforging with a large axial height and uneven skin wall thickness is obtained;

[0033] 3) Stop the movement of all dies, retract the rotary wheel to a position that does not affect the demoulding of the pre-forged parts, and unload the bolts, pressure blocks and sleeve dies in turn.

[0034] According to the above scheme, in step S6, the second-pass spin-drawing method for a thin-walled straight tube with high ribs includes:

[0035] 1) The preforging is removed from the sleeve die and rotated 180°, then the rotated preforging is placed into the sleeve die. The lower end face of the sleeve die is connected to the base as a whole, the outer end face of the ring rib at the lower end of the preforging is in contact with the base, and the outer circumference of the preforging is in contact with the inner circumference of the sleeve die; the bottom of the inner circumference of the upper skin of the preforging contacts the roller, and the roller is tilted upward at a certain angle along the axial direction; the bolt is screwed to the base, and the frustum of the bolt is fully matched with the inner conical surface of the pressure block. By tightening the bolt, sufficient pressing force is generated between the pressure block and the ring rib at the lower end of the preforging;

[0036] 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter, ring rib width and inner diameter of the preforging remain unchanged; the base drives the preforging, the sleeve die and the pressing block to rotate around its own axis, the rotating wheel passively rotates around its own axis and feeds f1 radially and then stops feeding, then the rotating wheel feeds f3 axially upward from the bottom of the upper skin of the preforging; on this basis, the rotating wheel quickly moves to the bottom of the lower skin of the preforging, feeds f1 radially and then stops feeding, then the rotating wheel feeds f2 axially upward from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower ends of the upper and lower skins of the preforging undergo continuous local deformation of reduced wall thickness and axial elongation, and finally the target thin-walled straight tube with high ribs is obtained;

[0037] 3) Stop the movement of all molds, retract the rotary wheel to a position that does not affect the demoulding of the target high-ribbed thin-walled straight cylinder, unload the bolts, pressure blocks and sleeve mold in sequence, and eject the target high-ribbed thin-walled straight cylinder from the sleeve mold along the axial direction.

[0038] The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of the present invention for a thin-walled straight tube with high ribs has the following beneficial effects:

[0039] 1. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of the high-ribbed thin-walled straight tube of the present invention not only has low manufacturing cost, high forming efficiency, and high material utilization rate, but also can cause the high-ribbed thin-walled straight tube to undergo plastic deformation to obtain fine grains and continuous metal streamlines, thereby significantly improving the mechanical properties of the high-ribbed thin-walled straight tube.

[0040] 2. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of the present invention can realize the coordinated forming of thin skin and high ring ribs of thin-walled straight tubes with high ribs with large axial height, significantly improving the forming size limit of thin-walled straight tubes with high ribs.

[0041] 3. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of the present invention for a thin-walled straight tube with high ribs has the significant advantage of low forming force, which significantly reduces the manufacturing requirements of the forming equipment. Therefore, it has good application prospects in the field of aerospace manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0043] Figure 1 Schematic diagram of the cross section of the target thin-walled straight cylindrical shaft with high ribs;

[0044] Figure 2 This is a schematic diagram of the shaft cross section of a thin-walled straight pre-forged part with high ribs;

[0045] Figure 3 A schematic diagram of the axial cross section of the ring blank required for roll extrusion;

[0046] Figure 4 Schematic diagram of the pressing block required for spin forming;

[0047] Figure 5 This is a schematic diagram of the rolling extrusion forming principle of a thin-walled straight-tube pre-forging with high ribs;

[0048] Figure 6 This is a schematic diagram of the first-pass spinning forming principle of a thin-walled straight tube with high ribs;

[0049] Figure 7 This is a schematic diagram of the second-pass spinning forming principle of a thin-walled straight tube with high ribs. DETAILED DESCRIPTION

[0050] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0051] A thin-walled straight tube with high ribs is composed of a thin-walled skin and a plurality of inner annular ribs located at the upper, middle and lower ends of the tube. It is the main light-weight load-bearing structure of aerospace equipment. How to achieve its high-performance overall manufacturing is an engineering problem that urgently needs to be solved in the aerospace field. To this end, the present invention proposes a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for a thin-walled straight tube with high ribs, that is, a pre-forged thin-walled straight tube with high ribs having a smaller axial height is first obtained through a rolling-extrusion forming process, and then the pre-forged thin-walled straight tube with high ribs is formed into a thin-walled straight tube with high ribs having a larger axial height through two-pass spin-extrusion forming processes. During the rolling-extrusion forming stage, the outer diameter and axial height of the workpiece remain unchanged. Through the coordinated movement of the constraining die, rollers and blocks, the workpiece undergoes continuous local plastic deformation of skin thinning and annular rib growth, and finally obtains a target pre-forged thin-walled straight tube with high ribs having a smaller axial height. During the spin-drawing stage, the workpiece's outer diameter, rib width, and inner diameter remain constant. Through the coordinated movement of the die, spinner, and pressure block, the workpiece skin undergoes continuous localized plastic deformation, resulting in a reduction in wall thickness and axial elongation. Ultimately, the target high-ribbed, thin-walled straight tube with a greater axial height is achieved. This method enables the integral plastic forming of the high-ribbed, thin-walled straight tube, significantly improving its mechanical properties.

[0052] Figure 1 This is a cross-sectional diagram of the target high-ribbed thin-walled straight shaft in the example. Figure 2 This is a schematic diagram of the axial cross-section of a thin-walled straight cylindrical pre-forging with high ribs required for spin-drawing. Figure 3 Schematic diagram of the axial section of the ring blank required for rolling forming. Figure 4 This is a schematic diagram of the pressing block required for spin-drawing. The cross-sectional dimensions of this example's high-ribbed thin-walled straight cylindrical shaft are shown in Table 1:

[0053] Table 1. Cross-sectional dimensions of the thin-walled straight cylindrical shaft with high ribs in this example

[0054]

[0055] The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs of the present invention comprises the following steps:

[0056] S1. Design of preforged thin-walled straight tube with high ribs (hereinafter referred to as preforged): The outer diameter of the preforged 6 is equal to the outer diameter Φ1 of the thin-walled straight tube with high ribs 12; the axial height H1 of the preforged 6 is much smaller than the axial height H2 of the thin-walled straight tube with high ribs 12; the width of the upper / middle / lower ring ribs of the preforged 6 is equal to the width of the upper / middle / lower ring ribs of the thin-walled straight tube with high ribs 12; the inner diameter of the upper / middle / lower ring ribs of the preforged 6 is equal to the inner diameter of the upper / middle / lower ring ribs of the thin-walled straight tube with high ribs 12; the skin thickness t1 of the preforged 6 is greater than the skin thickness t2 of the thin-walled straight tube with high ribs 12; the distance between the upper / lower ring ribs and the middle ring ribs of the preforged 6 is smaller than the distance between the upper / lower ring ribs and the middle ring ribs of the thin-walled straight tube with high ribs 12. The following dimensional relationship should be met between the skin of the preforged 6 and the skin of the thin-walled straight tube with high ribs 12:

[0057]

[0058] Among them, a1 is the distance between the upper end ring rib and the middle end ring rib of the pre-forged part 6, b1 is the distance between the lower end ring rib and the middle end ring rib of the pre-forged part 6, a2 is the distance between the upper end ring rib and the middle end ring rib of the thin-walled straight tube with high ribs 12, and b2 is the distance between the lower end ring rib and the middle end ring rib of the thin-walled straight tube with high ribs 12.

[0059] In order to prevent plastic instability in the interface between the skin and the ring reinforcement during the rolling and extrusion process of the pre-forging 6, the size of the pre-forging 6 should also meet the following requirements:

[0060]

[0061] Among them, σ r is the axial stress at the interface between the skin and the reinforcement, σ c is the critical stress of axial instability at the interface between the skin and the ring reinforcement, σ s is the yield stress of the preforging 6 material, h is the radial height of the annular rib of the preforging 6, m is the friction coefficient between the preforging 6 and the die, l is the circumferential contact length between the roller 4 and the preforging 6, w is the width of the annular rib of the preforging 6, t1 is the wall thickness of the skin of the preforging 6, E is the elastic modulus of the preforging 6 material, μ is the Poisson's ratio of the preforging 6 material, r is the working surface radius of the roller 4, R is the inner surface radius of the skin of the preforging 6, and f is the radial feed of the roller 4 corresponding to one rotation of the preforging 6.

[0062] By combining Table 1 and formulas (1)-(2), the dimensions of the thin-walled straight cylindrical pre-forging 6 with high ribs in this example are determined as follows: the skin wall thickness t1 is 5 mm, the width of the upper / middle / lower end ring ribs is 10 mm, the inner diameter of the upper / middle / lower end ring ribs is 454 mm, the axial height H1 is 373.4 mm, the outer diameter Φ1 is 500 mm, and the distance between the upper / lower end ring ribs and the middle end ring ribs is 171.7 mm.

[0063] S2. Ring blank design: The ring blank 3 required for the roll extrusion of the preforging 6 is a ring blank of equal wall thickness. The outer diameter of the ring blank 3 is equal to the outer diameter of the thin-walled straight tube 12 with high ribs. The wall thickness t0 of the ring blank 3 is greater than the wall thickness of the skin of the preforging 6. The axial height of the ring blank 3 is equal to the axial height of the preforging 6. The ring blank 3 and the thin-walled straight tube 12 with high ribs should meet the following dimensional relationship:

[0064]

[0065] Among them, t0 is the wall thickness of the ring blank 3, w1 is the width of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs 12, w2 is the width of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs 12, w3 is the width of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs 12, Φ2 is the inner diameter of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs 12, Φ3 is the inner diameter of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs 12, and Φ4 is the inner diameter of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs 12.

[0066] Combining Table 1 and formula (3), the dimensions of the ring blank 3 in this example are determined as follows: axial height H1 is 373.4 mm, outer diameter Φ1 is 500 mm, and wall thickness t0 is 9.5 mm.

[0067] S3. Design of the mold required for roll extrusion: The mold required for roll extrusion includes a constraint mold 2, a rolling roller 4 and two stops 1 and 5; the constraint / 2 is a thick-walled equal-diameter ring, whose axial height is equal to the circumferential height of the S2 ring blank 3, and its inner diameter is equal to the outer diameter of the S2 ring blank 3; the rolling roller 4 is a stepped shaft with the smallest diameter at both ends (connected to the machine tool), and the middle end is a cylinder with an annular groove (the cylindrical surface matches the inner surface of the thin-walled straight cylinder pre-forging with high ribs), and the radial feed amount of the rolling roller 4 is equal to the difference between the wall thickness of the S2 ring blank 3 and the skin wall thickness of the S1 pre-forging 6; the stops 1 and 5 are both rings, and the outer diameter of the stops 1 and 5 is equal to the outer diameter of the constraint mold 3, the inner diameter Φ5 of the upper stopper 1 is smaller than the inner diameter of the ring rib at the upper end of the pre-forging 6, and the inner diameter Φ6 of the lower stopper 5 is smaller than the inner diameter of the ring rib at the lower end of the pre-forging 6. In order to ensure that the roller 4 can smoothly move in and out of the blocks 1, 5 and pre-forging 6, the pre-forging 6, block 1, block 5 and roller 4 should also meet the following dimensional relationship:

[0068] Φ7 <min{Φ3,Φ5,Φ6} (4)

[0069] Wherein, Φ7 is the outermost diameter of the roller 4.

[0070] S4. Design of the mold required for spin-drawing: The mold required for spin-drawing includes a sleeve die 7, a base 11, a roller 8, two pressure blocks 9 and a bolt 10; the sleeve die 7 is a straight cylinder of equal diameter, the inner diameter of the sleeve die 7 is equal to the outer diameter of the S1 pre-forging 6, and the axial height of the sleeve die is greater than the axial height of the thin-walled straight cylinder with high ribs 12; the base 11 is a cylinder (connected to the machine tool), the base diameter is greater than or equal to the outer diameter of the sleeve die 7, and the upper end face of the base 11 is provided with multiple threaded holes; the roller 8 is a rotating part, the upper and lower end faces of the roller 8 are both flat, the side face of the roller 8 is a curved surface, the radius of the roller 8 is much greater than the height of the inner ring rib of the thin-walled straight cylinder with high ribs 12, and the axial height of the roller 8 is much less than the axial height of the thin-walled straight cylinder with high ribs 12 The distance between the upper / lower end ring ribs and the middle end ring ribs; the shapes of the two pressing blocks 9 are exactly the same, the pressing block 9 is an arc-shaped plate with a fan-shaped axial section, the outer diameter of the pressing block 9 is equal to the smaller value of the inner diameter of the upper end ring rib of the thin-walled straight tube with high ribs 12 and the inner diameter of the small end ring rib, the inner side of the pressing block 9 is a conical surface, and the axial height of the pressing block 9 is less than the smaller value of the width of the upper end ring rib of the thin-walled straight tube with high ribs 12 and the width of the lower end ring rib; the lower end of the bolt 10 has the smallest diameter and is provided with an external thread, and the upper end of the bolt 10 is a frustum (a hexagonal blind hole is provided at the center of the upper end face of the frustum, the upper diameter of the frustum is greater than the lower diameter of the frustum, the upper diameter of the frustum is equal to the large end diameter of the inner conical surface of the pressing block 9, and the lower diameter of the frustum is greater than the small end diameter of the inner conical surface of the pressing block).

[0071] S5, pre-forging rolling extrusion forming includes the following steps: 1) Before rolling extrusion forming, the outer circumference of the S2 ring blank 3 is fitted with the inner circumference of the S3 constraint die 2, the end faces on both sides of the S2 ring blank 3 are fitted with the end faces of the S3 stoppers 1 and 5 respectively, and the inner circumference of the S2 ring blank 3 is fitted with the S3 rolling roller 4. 2) In the extrusion forming stage, under the joint constraints of the S3 constraint die 2 and the S3 stops 1 and 5, the outer diameter and axial height of the S2 ring blank 3 remain unchanged; the S3 constraint die 2 drives the S2 ring blank 3 and the two S3 stops 1 and 5 to rotate around their own axes, and the S3 rolling roller 4 passively rotates around its own axis and feeds a predetermined amount in the radial direction; under the joint action of the S3 constraint die 2, the stops 1 and 5 and the rolling roller 4, the metal in the loading area of ​​the S2 ring blank 3 gradually flows into the cavity of the S3 rolling roller 4, causing the S2 ring blank 3 to produce continuous local plastic deformation of skin thinning and ring rib growth, and finally forming the S1 preforging 6. 3) In the demolding stage of the preforging 6, the S3 rolling roller 4 is first pulled out from the inside of the S1 preforging 6 and the S3 stops 1 and 5, and then the S1 preforging 6 is ejected from the S3 constraint die 2 along the axial direction.

[0072] S6. In order to ensure the uniformity of the skin wall thickness during the spin-drawing process, a two-pass spin-drawing scheme is adopted to form a thin-walled straight tube 12 with high ribs.

[0073] S6-1, the first rotary drawing forming steps of the thin-walled straight tube 12 with high ribs are as follows: 1) the lower end face of the S4 sleeve die 7 is connected to the S4 base 11 as a whole, the outer end face of the ring rib at the lower end of the S1 preforging 6 is in contact with the S4 base 11, and the outer peripheral surface of the S1 preforging 6 is in contact with the inner peripheral surface of the S4 sleeve die 11; the bottom of the inner peripheral surface of the upper skin of the S1 preforging 6 is in contact with the S4 rotating wheel 8, and the S4 rotating wheel 8 is tilted upward at a certain angle along the axial direction (the tilt angle is in the range of 5°-20°); the S4 bolt 10 is screwed to the S4 base 11, and the cone of the S4 bolt 10 is fully matched with the inner conical surface of the S4 pressure block 9. By tightening the S4 bolt 10, sufficient clamping force is generated between the S4 pressure block 9 and the ring rib at the lower end of the S4 preforging 6 to prevent the S1 preforging 6 from moving axially during the rotary drawing forming process. 2) Under the joint constraints of the S4 wheel 8 and the sleeve die 7, the outer diameter, the ring rib width and the inner diameter of the ring rib of the S1 preforging 6 remain unchanged; the S4 base 11 drives the S1 preforging 6, the S4 sleeve die 7 and the S4 pressing block 9 to rotate around its own axis, and the S4 wheel 8 passively rotates around its own axis and feeds f1 in the radial direction (f1 is equal to the difference between the wall thickness of the skin of the S1 preforging 6 and the wall thickness of the skin of the thin-walled straight tube with high ribs 12) and stops feeding. Then, the S4 wheel 8 feeds f2 in the axial direction upward from the bottom of the upper skin of the S1 preforging 6 (f2 is equal to half of the axial height of the upper skin of the thin-walled straight tube with high ribs 12); on this basis, the S4 wheel 8 quickly moves to the lower skin of the preforging 6-1 At the bottom of the skin, the S4 wheel 8 feeds f1 radially and then stops feeding, and then the S4 wheel 8 feeds f3 axially upward from the bottom of the lower skin of the preforged part 6-1 (f3 is equal to half of the axial height of the lower skin of the thin-walled straight tube with high ribs 12); under the joint action of the S4 wheel 8 and the sleeve die 7, the preforged part 6 and the lower end of the upper / lower skin of the preforged part 6-1 produce continuous local deformation of reduced wall thickness and axial stretching, and finally a preforged part 6-2 with a large axial height and uneven skin wall thickness is obtained. 3) The movement of all molds is terminated, and the S4 wheel 8 retreats to a position where it does not affect the demoulding of the preforged part 6-2, and the S4 bolt 10, the pressure block 9 and the sleeve die 7 are unloaded in turn.

[0074] S6-2, the second spin-drawing forming steps of the thin-walled straight tube with high ribs are as follows: 1) take out the S6-1 pre-forged piece 6-2 from the S4 sleeve die 7 and rotate it 180 degrees, then install the rotated pre-forged piece 6-2 into the S4 sleeve die 7, the lower end face of the S4 sleeve die 7 is connected to the S4 base 11 as a whole, the outer end face of the lower end ring rib of the pre-forged piece 6-2 is fitted with the S4 base 11, and the outer peripheral surface of the pre-forged piece 6-2 is fitted with the inner peripheral surface of the S4 sleeve die 7. The bottom of the inner peripheral surface of the upper skin of the pre-forged part 6-2 contacts the S4 roller 8, and the S4 roller 8 is tilted upward at a certain angle along the axial direction (the tilt angle is within the range of 5°-20°); the S4 bolt 10 is screwed to the S4 base 11, and the cone of the S4 bolt 10 is fully matched with the inner conical surface of the S4 pressure block 9. By tightening the S4 bolt 10, sufficient clamping force is generated between the S4 pressure block 9 and the annular rib at the lower end of the pre-forged part 6-2. 2) Under the joint constraints of the S4 wheel 8 and the sleeve die 7, the outer diameter, the ring rib width and the inner diameter of the ring rib of the preforged part 6-2 remain unchanged; the S4 base 11 drives the preforged part 6-2, the S4 sleeve die 7 and the S4 pressing block 9 to rotate around its own axis, the S4 wheel 8 passively rotates around its own axis and feeds f1 in the radial direction and then stops feeding, then the S4 wheel 8 feeds f3 axially upward from the bottom of the upper skin of the preforged part 6-3; on this basis, the S4 wheel 8 quickly moves to the bottom of the lower skin of the preforged part 6-3, and the S4 wheel 8 feeds f1 in the radial direction and then stops feeding, Then the S4 wheel feeds f2 axially upward from the bottom of the lower skin of the pre-forged part 6-3; under the joint action of the S4 wheel 8 and the sleeve die 7, the lower ends of the upper / lower skin of the pre-forged parts 6-2 and 6-3 produce continuous local deformation of reduced wall thickness and axial stretching, and finally the target thin-walled straight tube with high ribs 12 is obtained. 3) The movement of all molds is terminated, and the S4 wheel 8 retreats to a position that does not affect the demoulding of the target thin-walled straight tube with high ribs 12, and the S4 bolts 10, the pressure block 9 and the sleeve die 7 are unloaded in turn, and the thin-walled straight tube with high ribs 12 is ejected from the S4 sleeve die 7 along the axial direction.

[0075] This invention innovates a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for high-ribbed, thin-walled straight tubes. This method first uses a rolling-extrusion process to produce a pre-forged high-ribbed, thin-walled straight tube with a relatively low axial height, significantly reducing the rolling forming force. This pre-forged tube is then formed into a high-ribbed, thin-walled straight tube with a relatively high axial height and uniform skin wall thickness through a two-pass spinning process. Combining the advantages of rolling-extrusion and spinning, this method achieves integral plastic forming of the high-ribbed, thin-walled straight tube using relatively low forming forces. This method offers advantages such as high forming quality, high forming efficiency, and high material utilization, and has promising application prospects in aerospace manufacturing.

[0076] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A multi-degree-of-freedom rolling-extrusion-spinning composite forming method for forming a thin-walled straight tube with high ribs, which comprises a thin-walled skin and inner ring ribs at the upper, middle and lower ends of the tube, characterized in that: The forming method comprises the following steps: S1. Obtain parameters of a pre-forged thin-walled straight cylinder with high ribs. The outer diameter of the pre-forged is equal to the outer diameter of the thin-walled straight cylinder with high ribs, and the axial height of the pre-forged is much smaller than the axial height of the thin-walled straight cylinder with high ribs. S2. Obtain parameters of a ring blank required for roll extrusion of a preforging. The ring blank required for roll extrusion of the preforging is a ring blank of uniform wall thickness, with an outer diameter equal to that of a thin-walled straight cylinder with high ribs, a wall thickness greater than that of a skin of the preforging, and an axial height equal to that of the preforging; S3. Assemble the extrusion die, which includes a constraining die, a roller, and two stoppers. The constraining die is a thick-walled, equal-diameter ring member, whose axial height is equal to the circumferential height of the ring blank and whose inner diameter is equal to the outer diameter of the ring blank. The roller is a stepped shaft member, whose two ends have the smallest diameters, and whose middle end is a cylinder with an annular groove. The upper and lower stoppers are both ring members, and their outer diameters are equal to the outer diameter of the constraining die. The inner diameter of the upper stopper is smaller than the inner diameter of the annular rib at the upper end of the preforging, and the inner diameter of the lower stopper is smaller than the inner diameter of the annular rib at the lower end of the preforging. S4. Assemble the spin-drawing forming die, which includes a sleeve die, a base, a roller, and two pressing blocks; the sleeve die is a straight cylinder with a constant diameter, the inner diameter of the sleeve die is equal to the outer diameter of the pre-forging, and the axial height of the sleeve die is greater than the axial height of the straight cylinder with high ribs and thin walls; the diameter of the base is greater than or equal to the outer diameter of the sleeve die, the roller is a rotating part, the upper and lower end surfaces of the roller are flat, and the side surface of the roller is a curved surface; S5, performing rolling and extrusion forming of pre-forgings; S6. The pre-forged parts are formed into straight tubes with high ribs and thin walls by two-pass spinning.

2. The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1 is characterized in that: In step S1, the width of the ring ribs at the upper / middle / lower ends of the pre-forging is equal to the width of the ring ribs at the upper / middle / lower ends of the thin-walled straight tube with high ribs, the inner diameter of the ring ribs at the upper / middle / lower ends of the pre-forging is equal to the inner diameter of the ring ribs at the upper / middle / lower ends of the thin-walled straight tube with high ribs, the skin thickness t1 of the pre-forging is greater than the skin thickness t2 of the thin-walled straight tube with high ribs, and the distance between the ring ribs at the upper / lower ends of the pre-forging and the middle end is less than the distance between the ring ribs at the upper / lower ends and the middle end of the thin-walled straight tube with high ribs.

3. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 2, characterized in that: In step S1, the following dimensional relationship is satisfied between the pre-forged skin and the thin-walled straight tube skin with high ribs: Among them, Φ1 is the outer diameter of the thin-walled straight tube with high ribs, H1 is the axial height of the pre-forged piece, H2 is the axial height of the thin-walled straight tube with high ribs, a1 is the distance between the upper and middle ring ribs of the pre-forged piece, b1 is the distance between the lower and middle ring ribs of the pre-forged piece, a2 is the distance between the upper and middle ring ribs of the thin-walled straight tube with high ribs, and b2 is the distance between the lower and middle ring ribs of the thin-walled straight tube with high ribs.

4. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 3, characterized in that: In step S1, the pre-forging size also meets the following requirements: Among them, σ r is the axial stress at the interface between the skin and the reinforcement, σ c is the critical stress of axial instability at the interface between the skin and the ring reinforcement, σ s is the yield stress of the preforging material, h is the radial height of the preforging ring rib, m is the friction coefficient between the preforging and the die, l is the circumferential contact length between the roller and the preforging, w is the width of the preforging ring rib, t1 is the wall thickness of the preforging skin, E is the elastic modulus of the preforging material, μ is the Poisson's ratio of the preforging material, r is the radius of the roller working surface, R is the radius of the inner surface of the preforging skin, and f is the radial feed of the roller corresponding to one rotation of the preforging.

5. The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1 is characterized in that: In step S2, the ring blank and the thin-walled straight tube with high ribs should meet the following dimensional relationship: Among them, t0 is the wall thickness of the ring blank, w1 is the width of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs, w2 is the width of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs, w3 is the width of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs, Φ2 is the inner diameter of the ring reinforcement at the upper end of the thin-walled straight tube with high ribs, Φ3 is the inner diameter of the ring reinforcement at the middle end of the thin-walled straight tube with high ribs, and Φ4 is the inner diameter of the ring reinforcement at the lower end of the thin-walled straight tube with high ribs.

6. The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1 is characterized in that: In step S3, the following dimensional relationships are satisfied between the pre-forging, the stopper, and the roll: Φ7 <min{Φ3,Φ5,Φ6} (4) Among them, Φ3 is the inner diameter of the ring rib at the middle end of the thin-walled straight cylinder with high ribs, Φ5 is the inner diameter of the upper stopper, Φ6 is the inner diameter of the lower stopper, and Φ7 is the outermost diameter of the roller.

7. The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1 is characterized in that: In step S4, the shapes of the two pressing blocks are exactly the same. The pressing blocks are arc-shaped plates with a fan-shaped axial cross-section. The outer diameter of the pressing block is equal to the smaller value of the inner diameter of the ring ribs at the upper end of the thin-walled straight tube with high ribs and the inner diameter of the ring ribs at the small end. The inner side of the pressing block is a conical surface, and the axial height of the pressing block is less than the smaller value of the width of the ring ribs at the upper end of the thin-walled straight tube with high ribs and the width of the ring ribs at the lower end.

8. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1, characterized in that: In step S5, the pre-forging extrusion forming includes the following steps: 1) Before extrusion, the outer circumference of the ring blank is in contact with the inner circumference of the constraining die, the end faces on both sides of the ring blank are in contact with the end faces of the block respectively, and the inner circumference of the ring blank is in contact with the roller; 2) In the extrusion forming stage, under the joint constraints of the constraining die and the stopper, the outer diameter and axial height of the ring blank remain unchanged; the constraining die drives the ring blank and the two stoppers to rotate around their own axes, and the rollers passively rotate around their own axes and feed a predetermined amount in the radial direction; under the joint action of the constraining die, the stopper and the rollers, the metal in the loading area of ​​the ring blank gradually flows into the roller cavity, causing the ring blank to undergo continuous local plastic deformation of skin thinning and ring rib growth, and finally forming a pre-forged part; 3) In the demoulding stage of the pre-forging, the roller is first pulled out from the inside of the pre-forging and the block, and then the pre-forging is ejected from the constraining die along the axial direction.

9. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1, characterized in that: In step S6, the first-pass spin-drawing method for a thin-walled straight tube with high ribs includes: 1) The lower end face of the sleeve die is integrally connected to the base, the outer end face of the annular rib at the lower end of the pre-forging is in contact with the base, and the outer circumference of the pre-forging is in contact with the inner circumference of the sleeve die; the bottom of the inner circumference of the upper skin of the pre-forging is in contact with the roller, and the roller is tilted upward at a certain angle along the axial direction; the bolts are screwed to the base, and the frustum of the bolts is fully matched with the inner conical surface of the pressing block. By tightening the bolts, sufficient clamping force is generated between the pressing block and the annular rib at the lower end of the pre-forging to prevent the pre-forging from moving axially during the spinning and drawing process; 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter, ring rib width and inner diameter of the preforging remain unchanged; the base drives the preforging, the sleeve die and the pressing block to rotate around its own axis, the rotating wheel passively rotates around its own axis and feeds f1 in the radial direction and then stops feeding, and then the rotating wheel feeds f2 axially upward from the bottom of the upper skin of the preforging; on this basis, the rotating wheel quickly moves to the bottom of the lower skin of the preforging, feeds f1 in the radial direction and then stops feeding, and then the rotating wheel feeds f3 axially upward from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower ends of the upper and lower skins of the preforging undergo continuous local deformation with reduced wall thickness and axial elongation, and finally a preforging with a large axial height and uneven skin wall thickness is obtained; 3) Stop the movement of all dies, retract the rotary wheel to a position that does not affect the demoulding of the pre-forged parts, and unload the bolts, pressure blocks and sleeve dies in turn.

10. The multi-freedom rolling-extrusion-spinning composite forming method of a thin-walled straight tube with high ribs according to claim 1, characterized in that: In step S6, the second-pass spin-drawing method for a thin-walled straight tube with high ribs includes: 1) The preforging is removed from the sleeve die and rotated 180°, then the rotated preforging is placed into the sleeve die. The lower end face of the sleeve die is connected to the base as a whole, the outer end face of the ring rib at the lower end of the preforging is in contact with the base, and the outer circumference of the preforging is in contact with the inner circumference of the sleeve die; the bottom of the inner circumference of the upper skin of the preforging contacts the roller, and the roller is tilted upward at a certain angle along the axial direction; the bolt is screwed to the base, and the frustum of the bolt is fully matched with the inner conical surface of the pressure block. By tightening the bolt, sufficient pressing force is generated between the pressure block and the ring rib at the lower end of the preforging; 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter, ring rib width and inner diameter of the preforging remain unchanged; the base drives the preforging, the sleeve die and the pressing block to rotate around its own axis, the rotating wheel passively rotates around its own axis and feeds f1 radially and then stops feeding, then the rotating wheel feeds f3 axially upward from the bottom of the upper skin of the preforging; on this basis, the rotating wheel quickly moves to the bottom of the lower skin of the preforging, feeds f1 radially and then stops feeding, then the rotating wheel feeds f2 axially upward from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower ends of the upper and lower skins of the preforging undergo continuous local deformation of reduced wall thickness and axial elongation, and finally the target thin-walled straight tube with high ribs is obtained; 3) Stop the movement of all molds, retract the rotary wheel to a position that does not affect the demoulding of the target high-ribbed thin-walled straight cylinder, unload the bolts, pressure blocks and sleeve mold in sequence, and eject the target high-ribbed thin-walled straight cylinder from the sleeve mold along the axial direction.

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