Multi-degree-of-freedom rolling-extrusion-rotary drawing composite forming method for straight cylinder with high rib thin wall

Abstract

The invention relates to a multi-degree-of-freedom rolling-extrusion-rotary-drawing composite forming method for a high-rib thin-wall straight cylinder, which comprises the following steps of: firstly, obtaining a high-rib thin-wall straight cylinder pre-forge piece with smaller axial height through a rolling-extrusion forming process, and then forming the high-rib thin-wall straight cylinder pre-forge piece into a high-rib thin-wall straight cylinder with larger axial height through a two-pass rotary-drawing forming process. And in the rolling and extruding forming stage, the outer diameter and the axial height of the workpiece are kept unchanged, the workpiece generates continuous local plastic deformation of skin thinning-ring rib growth through coordinated movement of the constraint die, the roller and the check block, and finally the target high-rib thin-wall straight cylinder pre-forged piece with the small axial height is obtained. And in the rotary drawing forming stage, the outer diameter of the workpiece, the width of the ring rib and the inner diameter of the ring rib are kept unchanged, continuous local plastic deformation of wall thickness reduction-axial drawing is generated on the skin of the workpiece, and finally the target high-rib thin-wall straight cylinder with the large axial height is obtained. By means of the method, integral plastic forming of the high-rib thin-wall straight cylinder can be achieved, and then the mechanical property of the high-rib thin-wall straight cylinder is greatly improved.

Description

Technical Field

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

[0002] The thin-walled straight tube with high ribs is composed of a thin-walled skin and multiple inner ring ribs, and has the advantages of strong load-bearing capacity and light weight. However, the structure of the thin-walled straight tube with high ribs is extreme, with a thin skin, wide and high ribs, large dimensions, and the use of high-strength and lightweight materials that are difficult to deform, which brings great challenges to its high-performance and high-efficiency manufacturing.

[0003] At present, thin-walled straight tubes with high ribs are mainly manufactured by cutting + welding, but the cutting process cycle is long, the material utilization rate is extremely low, and the performance of the welding part is low, so it cannot meet the high-performance and high-efficiency manufacturing requirements of thin-walled straight tubes with high ribs. Rolling and extrusion forming is a new method that can achieve the overall plastic forming of thin-walled high-ribbed tubes. Its principle is to limit the increase in the outer diameter and axial height of the tube, forcing a large amount of metal at the skin to transfer axially to fill the high ribs, thereby achieving the coordinated forming of thin skin and high ribs. However, the axial height of aerospace thin-walled straight tubes with high ribs is relatively large. On the one hand, the axial contact length between the rolling and extrusion forming process and the core roller is relatively large, resulting in a large radial forming force of the core roller, which puts extremely high requirements on the rolling and extrusion forming equipment; on the other hand, during the rolling and extrusion forming process of thin-walled straight tubes with high ribs, the long-distance axial flow of metal will form a great flow resistance, causing the metal to tend to flow in the circumferential direction, which is very likely to cause plastic instability of the thin skin in the circumferential direction. Therefore, the rolling and extrusion forming method is not suitable for forming thin-walled straight tubes with high ribs with large axial height. The spinning forming method can realize the overall plastic forming of thin-walled cylinders. Its principle is to locally load the blank through the spinning wheel, thereby driving a large amount of metal to flow axially. It has the advantages of small forming force and good metal fluidity, so it is particularly suitable for forming thin-walled cylinders with large axial heights. However, during the spinning forming 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 spinning forming method cannot realize the overall 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 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: construct a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for a thin-walled straight tube with high ribs, which is used to form 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 tube with high ribs. The outer diameter of the pre-forged part is equal to the outer diameter of the thin-walled straight tube with high ribs, and the axial height of the pre-forged part is much smaller than the axial height of the thin-walled straight tube with high ribs.

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

[0008] S3, assemble the rolling extrusion forming die, which includes a constraint die, a roller and two blocks; the constraint die is a thick-walled equal-diameter ring, 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, whose two ends have the smallest diameters, and the middle end is a cylinder with an annular groove, and the upper and lower blocks are both rings, whose outer diameters are equal to the outer diameter of the constraint die, the inner diameter of the upper block is smaller than the inner diameter of the annular rib at the upper end of the pre-forging, and the inner diameter of the lower block is smaller than the inner diameter of the annular rib at the lower end of the pre-forging;

[0009] S4, assemble the spin-drawing forming mold, which includes a sleeve mold, a base, a rotating wheel and two pressing blocks; the sleeve mold is a straight cylinder with equal diameter, the inner diameter of the sleeve mold is equal to the outer diameter of the pre-forging, and the axial height of the sleeve mold 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 mold, the rotating wheel is a rotating part, the upper and lower end faces of the rotating wheel are both flat, and the side face of the rotating wheel is a curved surface;

[0010] S5, rolling and extruding the pre-forging;

[0011] S6. The pre-forged parts are formed into thin-walled straight tubes with high ribs 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 preforging 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 preforging 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 preforging 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 preforging and the middle end ring ribs is less than the distance between the ring ribs at the upper / lower ends and the middle end ring ribs of the thin-walled straight tube with high ribs.

[0013] According to the above scheme, 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 spacing between the upper ring ribs and the middle ring ribs of the pre-forged piece, b1 is the spacing between the lower ring ribs and the middle ring ribs of the pre-forged piece, a2 is the spacing between the upper ring ribs and the middle ring ribs of the thin-walled straight tube with high ribs, and b2 is the spacing between the lower ring ribs and the middle ring ribs of the thin-walled straight tube with high ribs.

[0016] According to the above scheme, 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 skin and 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 scheme, in step S2, the ring blank and the thin-walled straight tube with high ribs should satisfy the following dimensional relationship:

[0020]

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

[0022] According to the above scheme, in step S3, the pre-forging, the stopper and the roller satisfy the following dimensional relationship:

[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 tube 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 block is an arc-shaped plate 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 rolling and 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 rolling and extrusion forming stage, under the joint constraints of the constraint die and the block, the outer diameter and axial height of the ring blank remain unchanged; the constraint die drives the ring blank and the two blocks 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 constraint die, the block and the rollers, the metal in the loading area of ​​the ring blank gradually flows into the roller cavity, causing the ring blank to produce continuous local plastic deformation of skin thinning-ring rib growth, and finally forming a pre-forged part;

[0029] 3) In the demoulding stage of the pre-forging, the rolling roller is first pulled out from the inside of the pre-forging and the stopper, 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 forming method of a thin-walled straight tube with high ribs includes:

[0031] 1) 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 peripheral surface of the preforging is in contact with the inner peripheral surface of the sleeve die; the bottom of the inner peripheral surface of the upper skin of the preforging is in contact with the rotating wheel, and the rotating wheel 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 pressing block. By tightening the bolt, sufficient clamping force is generated between the pressing block and the ring rib at the lower end of the preforging to prevent the preforging from moving along the axial direction during the spinning and drawing process;

[0032] 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter of the preforging, the width of the annular ribs and the inner diameter of the annular ribs remain unchanged; the base drives the preforging, the sleeve die and the pressure block to rotate around its own axis, the rotating wheel passively rotates around its own axis and stops feeding in the radial direction after f1, and then the rotating wheel feeds f2 upward along the axial direction 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, the rotating wheel stops feeding in the radial direction after f1, and then the rotating wheel feeds f3 upward along the axial direction 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 / lower skins of the preforging all produce continuous local deformations of 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 forming method of a thin-walled straight tube with high ribs includes:

[0035] 1) Take the preforging out of the sleeve die and rotate it 180°, then put the rotated preforging 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 peripheral surface of the preforging is in contact with the inner peripheral surface of the sleeve die; the bottom of the inner peripheral surface of the upper skin of the preforging is in contact with the rotating wheel, and the rotating wheel is tilted upward at a certain angle along the axial direction; the bolt is screwed to the base, the cone of the bolt is fully matched with the inner cone of the pressing block, and by tightening the bolt, sufficient clamping force is generated between the pressing 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 of the preforging, the width of the annular ribs and the inner diameter of the annular ribs remain unchanged; the base drives the preforging, the sleeve die and the pressure block to rotate around its own axis, the rotating wheel passively rotates around its own axis and stops feeding in the radial direction after f1, and then the rotating wheel feeds f3 upward along the axial direction 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, the rotating wheel stops feeding in the radial direction after f1, and then the rotating wheel feeds f2 upward along the axial direction from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower end of the upper / lower skin of the preforging produces 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 molds in turn, 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 a thin-walled straight tube with high ribs of the present invention 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 thin-walled straight tube with high ribs of the present invention can realize the coordinated forming of thin skin and high ring ribs of the thin-walled straight tube with high ribs with large axial height, which significantly improves the forming size limit of the thin-walled straight tube with high ribs.

[0041] 3. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of the thin-walled straight tube with high ribs of the present invention has the significant advantage of small forming force, which significantly reduces the manufacturing requirements of the forming equipment, and therefore 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 It is a schematic diagram of the shaft 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 rolling and extrusion;

[0046] Figure 4 A schematic diagram of the pressing block required for spin-drawing;

[0047] Figure 5 It is a schematic diagram of the rolling and 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 spin-drawing 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] The 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 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 small 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 constraint die, the roller and the block, the workpiece produces continuous local plastic deformation of skin thinning-annular rib growth, and finally a target pre-forged thin-walled straight tube with high ribs having a small axial height is obtained. During the spinning and drawing forming stage, the outer diameter of the workpiece, the width of the ring ribs and the inner diameter of the ring ribs remain unchanged. Through the coordinated movement of the sleeve die, the rotating wheel and the pressing block, the skin of the workpiece undergoes continuous local plastic deformation of wall thickness reduction and axial elongation, and finally obtains a target high-ribbed thin-walled straight tube with a large axial height. The method of the present invention can realize the overall plastic forming of the high-ribbed thin-walled straight tube, thereby greatly improving the mechanical properties of the high-ribbed thin-walled straight tube.

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

[0053] Table 1. Cross-sectional dimensions of this example with high-ribbed thin-walled straight shaft

[0054]

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

[0056] S1. Design of preforgings of thin-walled straight tubes with high ribs (hereinafter referred to as preforgings): the outer diameter of preforgings 6 is equal to the outer diameter Φ1 of thin-walled straight tubes with high ribs 12, the axial height H1 of preforgings 6 is much smaller than the axial height H2 of thin-walled straight tubes with high ribs 12, the width of the ring ribs at the upper / middle / lower ends of preforgings 6 is equal to the width of the ring ribs at the upper / middle / lower ends of thin-walled straight tubes with high ribs 12, the inner diameter of the ring ribs at the upper / middle / lower ends of preforgings 6 is equal to the inner diameter of the ring ribs at the upper / middle / lower ends of thin-walled straight tubes with high ribs 12, the skin thickness t1 of preforgings 6 is greater than the skin thickness t2 of thin-walled straight tubes with high ribs 12, and the distance between the upper / lower end ring ribs and the middle end ring ribs of preforgings 6 is smaller than the distance between the upper / lower end ring ribs and the middle end ring ribs of thin-walled straight tubes with high ribs 12. The following dimensional relationship should be satisfied between the skin of preforgings 6 and the skin of thin-walled straight tubes 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 at the interface between the skin and the annular 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 skin and 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 amount 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 tube 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 diameters of the upper / middle / lower end ring ribs are all 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 rolling and extrusion of the pre-forging 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 skin wall thickness of the pre-forging 6, the axial height of the ring blank 3 is equal to the axial height of the pre-forging 6, and 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 ribs at the upper end of the thin-walled straight tube with high ribs 12, w2 is the width of the ring ribs at the middle end of the thin-walled straight tube with high ribs 12, w3 is the width of the ring ribs at the lower end of the thin-walled straight tube with high ribs 12, Φ2 is the inner diameter of the ring ribs at the upper end of the thin-walled straight tube with high ribs 12, Φ3 is the inner diameter of the ring ribs at the middle end of the thin-walled straight tube with high ribs 12, and Φ4 is the inner diameter of the ring ribs 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 roller 4 and two blocks 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 roller 4 is a stepped shaft, whose two ends have the smallest diameter (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 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 blocks 1 and 5 are both rings, and the outer diameter of the blocks 1 and 5 is equal to the outer diameter of the constraint mold 3, the inner diameter Φ5 of the upper block 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 block 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 stoppers 1, 5 and the pre-forging 6, the pre-forging 6, the stopper 1, the stopper 5 and the roller 4 should also meet the following dimensional relationship:

[0068] Φ7 <min{Φ3,Φ5,Φ6} (4)

[0069] Among them, 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 rotating wheel 8, two pressure blocks 9 and a bolt 10; the sleeve die 7 is an equal-diameter straight cylinder, 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 a plurality of threaded holes; the rotating wheel 8 is a rotating part, the upper and lower end faces of the rotating wheel 8 are both flat, the side face of the rotating wheel 8 is a curved surface, the radius of the rotating wheel 8 is much greater than the inner ring rib height of the thin-walled straight cylinder with high ribs 12, and the axial height of the rotating wheel 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 pressure blocks 9 are exactly the same, the pressure block 9 is an arc-shaped plate with a fan-shaped axial section, the outer diameter of the pressure 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 pressure block 9 is a conical surface, and the axial height of the pressure 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 in 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 pressure block 9, and the lower diameter of the frustum is greater than the small end diameter of the inner conical surface of the pressure 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 respectively fitted with the end faces of the S3 stoppers 1 and 5, and the inner circumference of the S2 ring blank 3 is fitted with the S3 rolling roller 4. 2) In the rolling and extrusion forming stage, under the joint constraints of the S3 constraint die 2 and the S3 blocks 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 blocks 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 blocks 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 firstly pulled out from the inside of the S1 preforging 6 and the S3 blocks 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 high-ribbed thin-walled straight tube 12.

[0073] S6-1, the first process of spin-drawing forming of the thin-walled straight tube 12 with high ribs is 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 annular rib at the lower end of the S1 preforging 6 is fitted with the S4 base 11, and the outer peripheral surface of the S1 preforging 6 is fitted 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 cone 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 S4 preforging 6 to prevent the S1 preforging 6 from moving axially during the spin-drawing forming process. 2) Under the joint constraints of the S4 rotating 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, the S4 rotating wheel 8 passively rotates around its own axis and feeds f1 in the radial direction (f1 is equal to the difference between the skin wall thickness of the S1 preforging 6 and the skin wall thickness of the thin-walled straight tube with high ribs 12) and then stops feeding, and then the S4 rotating 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 rotating 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 12 with high ribs); 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 elongation, and finally a preforged part 6-2 with a large axial height and uneven skin wall thickness is obtained. 3) Stop the movement of all molds, the S4 wheel 8 retreats to a position that does not affect the demolding of the preforged part 6-2, and unloads the S4 bolt 10, the pressure block 9 and the sleeve die 7 in turn.

[0074] S6-2, the second process of spin-drawing forming of thin-walled straight tube with high ribs is as follows: 1) taking out the S6-1 pre-forged piece 6-2 from the S4 sleeve die 7 and rotating it 180°, and then putting 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 circumference of the upper skin of the pre-forged piece 6-2 is in contact with the S4 roller 8, and the S4 roller 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 with the S4 base 11, and the cone of the S4 bolt 10 is fully matched with the inner cone 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 piece 6-2. 2) Under the joint constraints of the S4 rotary wheel 8 and the sleeve die 7, the outer diameter, the ring rib width and the inner diameter of the ring rib of the preforging 6-2 remain unchanged; the S4 base 11 drives the preforging 6-2, the S4 sleeve die 7 and the S4 pressing block 9 to rotate around its own axis, the S4 rotary wheel 8 passively rotates around its own axis and stops feeding after feeding f1 in the radial direction, and then the S4 rotary wheel 8 feeds f3 axially upward from the bottom of the upper skin of the preforging 6-3; on this basis, the S4 rotary wheel 8 quickly moves to the bottom of the lower skin of the preforging 6-3, and stops feeding after feeding f1 in the radial direction, 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 elongation, and finally the target thin-walled straight tube 12 with high ribs 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 12 with high ribs, and the S4 bolts 10, the pressure block 9 and the sleeve die 7 are unloaded in turn, and the thin-walled straight tube 12 with high ribs is ejected from the S4 sleeve die 7 along the axial direction.

[0075] The present invention innovates a multi-degree-of-freedom rolling-extrusion-spinning composite forming method for a thin-walled straight tube with high ribs, that is, firstly, a pre-forged thin-walled straight tube with high ribs having a small axial height is obtained by a rolling-extrusion forming process, so that the rolling-extrusion forming force is significantly reduced, and then the pre-forged thin-walled straight tube with high ribs having a large axial height and uniform skin wall thickness is formed by two-pass spin-drawing forming processes. The present invention combines the respective advantages of the rolling-extrusion forming method and the spin-drawing forming method, and can realize the overall plastic forming of the thin-walled straight tube with high ribs by using a small forming force, and has the advantages of high forming quality, high forming efficiency, high material utilization rate, etc., and has good application prospects in the field of 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 modes, which are merely illustrative rather than 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 within the protection of 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, the thin-walled straight tube with high ribs comprising a thin-walled skin and inner annular ribs located at the upper end, middle end and lower end of the tube, characterized in that: The forming method comprises the following steps: S1. Obtain parameters of a pre-forged thin-walled straight tube with high ribs. The outer diameter of the pre-forged part is equal to the outer diameter of the thin-walled straight tube with high ribs, and the axial height of the pre-forged part is much smaller than the axial height of the thin-walled straight tube with high ribs. S2. Obtain parameters of the ring blank required for the preforging rolling and extrusion forming. The ring blank required for the preforging rolling and extrusion forming is a ring blank with equal wall thickness, the outer diameter of the ring blank is equal to the outer diameter of the thin-walled straight tube with high ribs, the wall thickness of the ring blank is greater than the wall thickness of the preforging skin, and the axial height of the ring blank is equal to the axial height of the preforging; S3, assemble the rolling extrusion forming die, which includes a constraint die, a roller and two blocks; the constraint die is a thick-walled equal-diameter ring, 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, whose two ends have the smallest diameters, and the middle end is a cylinder with an annular groove, and the upper and lower blocks are both rings, whose outer diameters are equal to the outer diameter of the constraint die, the inner diameter of the upper block is smaller than the inner diameter of the annular rib at the upper end of the pre-forging, and the inner diameter of the lower block is smaller than the inner diameter of the annular rib at the lower end of the pre-forging; S4, assemble the spin-drawing forming mold, which includes a sleeve mold, a base, a rotating wheel and two pressing blocks; the sleeve mold is a straight cylinder with equal diameter, the inner diameter of the sleeve mold is equal to the outer diameter of the pre-forging, and the axial height of the sleeve mold 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 mold, the rotating wheel is a rotating part, the upper and lower end faces of the rotating wheel are both flat, and the side face of the rotating wheel is a curved surface; S5, rolling and extruding the pre-forging; S6. The pre-forged parts are formed into thin-walled straight tubes with high ribs by two-pass spinning.

2. The multi-degree-of-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 preforging 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 preforging 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 preforging 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 preforging and the middle end ring ribs is less than the distance between the ring ribs at the upper / lower ends and the middle end ring ribs 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 is 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 spacing between the upper ring ribs and the middle ring ribs of the pre-forged piece, b1 is the spacing between the lower ring ribs and the middle ring ribs of the pre-forged piece, a2 is the spacing between the upper ring ribs and the middle ring ribs of the thin-walled straight tube with high ribs, and b2 is the spacing between the lower ring ribs and the 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 is 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 skin and 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-degree-of-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 satisfy the following dimensional relationship: Among them, t0 is the wall thickness of the ring blank, w1 is the width of the ring ribs at the upper end of the thin-walled straight tube with high ribs, w2 is the width of the ring ribs in the middle end of the thin-walled straight tube with high ribs, w3 is the width of the ring ribs at the lower end of the thin-walled straight tube with high ribs, Φ2 is the inner diameter of the ring ribs at the upper end of the thin-walled straight tube with high ribs, Φ3 is the inner diameter of the ring ribs in the middle end of the thin-walled straight tube with high ribs, and Φ4 is the inner diameter of the ring ribs at the lower end of the thin-walled straight tube with high ribs.

6. The multi-degree-of-freedom rolling-extrusion-spinning composite forming method of a high-ribbed thin-walled straight tube according to claim 1 is characterized in that: In step S3, the following dimensional relationship is satisfied between the pre-forging, the stopper and the roller: 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 tube 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-degree-of-freedom rolling-extrusion-spinning composite forming method of a high-ribbed thin-walled straight tube according to claim 1, 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 fan-shaped axial cross-sections. The outer diameter of the pressing blocks 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 is characterized in that: In step S5, the pre-forging extrusion forming includes the following steps: 1) Before rolling and 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 rolling and extrusion forming stage, under the joint constraints of the constraint die and the block, the outer diameter and axial height of the ring blank remain unchanged; the constraint die drives the ring blank and the two blocks 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 constraint die, the block and the rollers, the metal in the loading area of ​​the ring blank gradually flows into the roller cavity, causing the ring blank to produce continuous local plastic deformation of skin thinning-ring rib growth, and finally forming a pre-forged part; 3) In the demoulding stage of the pre-forging, the rolling roller is first pulled out from the inside of the pre-forging and the stopper, 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 forming method of a thin-walled straight tube with high ribs includes: 1) 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 peripheral surface of the preforging is in contact with the inner peripheral surface of the sleeve die; the bottom of the inner peripheral surface of the upper skin of the preforging is in contact with the rotating wheel, and the rotating wheel 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 pressing block. By tightening the bolt, sufficient clamping force is generated between the pressing block and the ring rib at the lower end of the preforging to prevent the preforging from moving along the axial direction during the spinning and drawing process; 2) Under the joint constraints of the rotating wheel and the sleeve die, the outer diameter of the preforging, the width of the annular ribs and the inner diameter of the annular ribs remain unchanged; the base drives the preforging, the sleeve die and the pressure block to rotate around its own axis, the rotating wheel passively rotates around its own axis and stops feeding in the radial direction after f1, and then the rotating wheel feeds f2 upward along the axial direction 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, the rotating wheel stops feeding in the radial direction after f1, and then the rotating wheel feeds f3 upward along the axial direction 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 / lower skins of the preforging all produce continuous local deformations of 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-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 second-pass spin-drawing forming method of a thin-walled straight tube with high ribs includes: 1) Take the preforging out of the sleeve die and rotate it 180°, then put the rotated preforging 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 peripheral surface of the preforging is in contact with the inner peripheral surface of the sleeve die; the bottom of the inner peripheral surface of the upper skin of the preforging is in contact with the rotating wheel, and the rotating wheel is tilted upward at a certain angle along the axial direction; the bolt is screwed to the base, the cone of the bolt is fully matched with the inner cone of the pressing block, and by tightening the bolt, sufficient clamping force is generated between the pressing 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 of the preforging, the width of the annular ribs and the inner diameter of the annular ribs remain unchanged; the base drives the preforging, the sleeve die and the pressure block to rotate around its own axis, the rotating wheel passively rotates around its own axis and stops feeding in the radial direction after f1, and then the rotating wheel feeds f3 upward along the axial direction 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, the rotating wheel stops feeding in the radial direction after f1, and then the rotating wheel feeds f2 upward along the axial direction from the bottom of the lower skin of the preforging; under the joint action of the rotating wheel and the sleeve die, the lower end of the upper / lower skin of the preforging produces 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 molds in turn, and eject the target high-ribbed thin-walled straight cylinder from the sleeve mold along the axial direction.

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