A vertical extrusion molding device and method for variable diameter thin-walled aluminum tube

Abstract

The present invention belongs to the technical field of pipe forming, and specifically relates to a device and method for vertical extrusion forming of a variable diameter thin-walled aluminum tube. The device includes a base, a column, a servo extrusion unit, a core mold, an extrusion head and a die, wherein the servo extrusion unit is connected to the base through two columns, the die is arranged on the base and is sealed by a sealing structure, the core mold is arranged in the die, and an annular extrusion cavity for placing the pipe blank is formed between the core mold and the die; the extrusion head is slidably connected to the two columns, and the extrusion head is used to servo extrude the pipe blank at the upper end of the annular extrusion cavity, and the servo extrusion unit provides servo extrusion power to the extrusion head through a servo extrusion rod. The present invention uses back pressure extrusion and repeated back pressure and extrusion to cause the surface of the pipe in the crystallization process to repeatedly rub and crystallize and refine the mold, effectively improving the wettability and crystallization refinement of ceramic particles and aluminum-magnesium matrix, thereby improving the mechanical properties such as fatigue strength and plasticity of the pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe forming, and in particular relates to a vertical extrusion forming device and method for a variable-diameter thin-walled aluminum pipe. Background Art

[0002] Particle-reinforced aluminum-magnesium matrix composites have excellent comprehensive properties such as high specific strength and specific stiffness, fatigue resistance, good thermal conductivity, small thermal expansion coefficient, and good dimensional stability. They have broad application prospects as structural materials in the aerospace field. A large number of studies have shown that the mechanical properties of fatigue, strength, and plasticity, which are of great concern as structural materials, are affected by the wettability of ceramic particles and aluminum-magnesium matrix, crystal refinement, crystallization process temperature, and crystallization pressure, making the optimal hot extrusion temperature range of silicon carbide reinforced aluminum-magnesium alloy very narrow, resulting in coarse crystals on the inner and outer curved surfaces of thin-walled bell-shaped pipes, which has a great impact on their fatigue performance. Therefore, for the trumpet-shaped parts of composite materials, how to ensure the wettability of its ceramic particles will be a key factor to be considered in optimizing the pipe forming process. Summary of the invention

[0003] In view of the above problems, the object of the present invention is to provide a device and method for vertical extrusion molding of variable diameter thin-walled aluminum tubes to ensure the wettability of ceramic particles and improve the fatigue performance of pipe fittings.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] On the one hand, the present invention provides a vertical extrusion molding device for variable-diameter thin-walled aluminum tubes, comprising a base, a column, a servo extrusion unit, a core mold, an extrusion head and a die, wherein the servo extrusion unit is arranged above the base, and the servo extrusion unit is connected to the base through two columns, the die is arranged on the base and sealed by a sealing structure, the core mold is arranged in the die, and an annular extrusion cavity for placing a pipe blank is formed between the core mold and the die; the extrusion head is slidably connected to the two columns, the servo extrusion unit provides servo extrusion power to the extrusion head through a servo extrusion rod, and the extrusion head is used to servo extrude the pipe blank at the upper end of the annular extrusion cavity to obtain a formed pipe with a bell mouth and a barrel.

[0006] In one possible implementation, the annular extrusion chamber is divided into a clearance fit guide chamber, a transition guide chamber, an interference fit extrusion chamber, a curved surface chamber and a shrinkage chamber from top to bottom, wherein the diameter of the clearance fit guide chamber is larger than the diameter of the interference fit extrusion chamber, the clearance fit guide chamber is used to guide the pipe blank, the transition guide chamber is a conical transition chamber, and the interference fit extrusion chamber is interference fit with the pipe blank; the inner diameter of the curved surface chamber gradually shrinks from top to bottom, and the diameter of the lower port of the curved surface chamber is equal to the diameter of the shrinkage chamber; the curved surface chamber is used to form the bell mouth of the formed pipe, and the shrinkage chamber is used to form the barrel of the formed pipe.

[0007] In one possible implementation, a bottom heating module is provided in the base; an inner concave cavity connected to the annular extrusion cavity is provided on the upper plane of the base, and an upwardly protruding central column is provided at the center of the inner concave cavity, and the central column is used to coaxially install the core mold; high-pressure passage I and high-pressure passage II are respectively provided on both sides of the inner concave cavity, and the high-pressure passage I is connected to the water-cooled heat exchanger I and the high-pressure water preparation machine in sequence, and the high-pressure water preparation machine is used to provide a high-pressure water source to the inner concave cavity, and the high-pressure water in the inner concave cavity is used to perform back-pressure extrusion on the pipe blank; the high-pressure passage II is connected to the water-cooled heat exchanger II and the high-pressure accumulator in sequence, and the high-pressure accumulator is used to compensate for the pressure of the inner concave cavity.

[0008] In one possible implementation, the sealing structure includes a high-temperature and high-pressure upper sealing groove and a high-temperature and high-pressure lower sealing groove forming an annular sealing cavity, wherein the high-temperature and high-pressure lower sealing groove is circumferentially arranged on the upper plane of the base, and an annular high-temperature and high-pressure lower sealing cutting edge is provided in the high-temperature and high-pressure lower sealing groove; the high-temperature and high-pressure upper sealing groove is circumferentially arranged on the mounting surface of the bottom of the die, and an annular high-temperature and high-pressure upper sealing cutting edge is provided in the high-temperature and high-pressure upper sealing groove, the high-temperature and high-pressure upper sealing cutting edge corresponds to the high-temperature and high-pressure lower sealing cutting edge, and a high-temperature and high-pressure sealing ring band is provided between the high-temperature and high-pressure upper sealing cutting edge and the high-temperature and high-pressure lower sealing cutting edge to achieve high-temperature and high-pressure sealing.

[0009] In one possible implementation, the die includes a die body and a die cavity arranged at the center of the die body, an outer heating module is arranged in the die body, and the die cavity comprises a clearance fit hole, a transition guide hole, an interference fit hole, a concave curved hole and a shrinkage hole from top to bottom, wherein the diameter of the interference fit hole is smaller than the diameter of the clearance fit hole, the transition guide hole is a transition tapered hole, the concave curved hole is used for forming the outer surface of the bell mouth of the formed pipe fitting, and the shrinkage hole is used for forming the outer surface of the barrel of the formed pipe fitting.

[0010] In one possible implementation, the core mold includes a locking operating part, a clearance fit column, a transition guide column, an interference fit column, a convex curved surface section and a connecting part, which are arranged in sequence from top to bottom, wherein the diameter of the clearance fit column is larger than the diameter of the interference fit column, the convex curved surface section is used to form the inner surface of the bell-mouth part of the forming pipe, and the connecting part is used to connect with the base; an inner heating module is provided in the core mold.

[0011] In one possible implementation, the extrusion head includes an extrusion body and a pressing cylinder arranged at the bottom of the extrusion body, wherein guide holes are provided on both sides of the extrusion body and are respectively slidably matched with the two columns, and the pressing cylinder is used to extrude the pipe blank in the annular extrusion cavity.

[0012] In one possible implementation, a one-way limiting structure is provided between the servo extrusion unit and the extrusion head; the one-way limiting structure includes ratchets arranged on both sides of the extrusion body in the vertical direction and two ratchets hinged on both sides of the servo extrusion unit, and the two ratchets are respectively engaged with the two ratchets to limit the upward movement of the extrusion head.

[0013] Another aspect of the present invention provides an extrusion method using the above-mentioned variable diameter thin-walled aluminum tube vertical extrusion molding device, comprising the following steps:

[0014] Step S1: inserting the pipe blank into the clearance fitting guide cavity at the upper part of the annular extrusion cavity between the core die and the concave die;

[0015] Step S2: The servo extrusion unit presses down the extrusion head through the servo extrusion rod, and the extrusion head extrudes the pipe blank, so that the pipe blank passes through the transition guide cavity and enters the interference fit extrusion cavity, so that the inner concave cavity on the base forms a high-temperature and high-pressure cavity;

[0016] Step S3: High-temperature and high-pressure water is introduced into the high-temperature and high-pressure chamber to pressurize the pipe blank, so that the pipe blank is subjected to closed-die back-pressure extrusion; a one-way limiting structure prevents the pipe blank from moving upward during the back-pressure extrusion process;

[0017] Step S4: the extrusion die heats the pipe blank to a hot extrusion temperature and maintains a constant temperature;

[0018] Step S5: performing servo hot extrusion on the pipe blank to obtain a preliminarily formed pipe with a bell mouth portion and a barrel portion;

[0019] Step S6: performing grain refinement hot extrusion on the formed pipe;

[0020] Step S7: demolding to obtain a formed pipe fitting that meets the process requirements.

[0021] In a possible implementation, in step S6, the process of performing grain refinement hot extrusion on the pipe includes the following steps:

[0022] Step S6a: controlling the temperature of the formed pipe to be lowered to a set process temperature;

[0023] Step S6b: the servo extrusion rod is servo-pressed down for a set distance and then lifted up, the set distance being less than one tooth pitch of the ratchet bar, and the inner and outer surfaces of the formed pipe are rubbed against the mold and crystallized and refined;

[0024] Step S6c: the high temperature and high pressure chamber increases the pressure, causing the formed tube to move in the opposite direction for a set distance and then lift up, and the set distance is less than one tooth pitch of the ratchet; the ratchet prevents the formed tube from moving upward;

[0025] Step S6d: Repeat steps S6a to S6c in a loop until the temperature is lower than the recrystallization temperature of the formed pipe;

[0026] Step S6e: demoulding and taking out the formed pipe.

[0027] The advantages and beneficial effects of the present invention are as follows: the present invention provides a variable diameter thin-walled aluminum tube vertical extrusion molding device, which can effectively improve the wettability and crystallization refinement of ceramic particles and aluminum-magnesium matrix, strictly control the crystallization process temperature and crystallization pressure, and thus improve the mechanical properties such as fatigue strength and plasticity of the molded tube through back pressure extrusion and repeated action of back pressure extrusion and front extrusion, resulting in crystallization refinement.

[0028] The invention provides a vertical extrusion molding method for a variable-diameter thin-walled aluminum tube, in which a tube blank is heated to a suitable hot extrusion temperature, and the tube surface in the crystallization process is repeatedly rubbed against a mold by back pressure extrusion and repeated back pressure extrusion and front extrusion, so that the crystals are refined, and the optimal hot extrusion temperature range can be effectively increased to realize the inner and outer curved surface molding of a thin-walled bell-shaped tube and improve its smoothness.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 It is an axonometric view of a vertical extrusion molding device for a variable diameter thin-walled aluminum tube according to the present invention;

[0033] Figure 2 for Figure 1 A partial enlarged view of the middle part;

[0034] Figure 3 It is a cross-sectional view of a variable diameter thin-wall aluminum tube vertical extrusion molding device before extrusion of the present invention;

[0035] Figure 4 for Figure 3 A partial enlarged view of point B in the middle;

[0036] Figure 5 for Figure 4A partial enlarged view of point C in the middle;

[0037] Figure 6 It is an axonometric view of the core mold in the present invention;

[0038] Figure 7 It is a cross-sectional view of a variable diameter thin-wall aluminum tube vertical extrusion molding device after extrusion of the present invention;

[0039] Figure 8 It is an axonometric view of the formed pipe in the present invention.

[0040] In the figure: 1-pipe blank, 2-molded pipe, 201-barrel, 202-flare, 3-base, 303-center column, 304-inner concave cavity, 305-high pressure passage I, 306-high pressure passage II, 4-column, 5-servo extrusion unit, 6-core mold, 601-locking operation part, 602-clearance fit column, 603-transition guide column, 604-interference fit column, 605-convex curved surface section, 606-shaft shoulder, 607-positioning pin column, 608-external thread section, 7-extrusion Head, 701-extrusion body, 702-upper extrusion striking surface, 703-guide hole, 704-spike, 705-pressing cylinder, 8-die, 801-die body, 802-clearance fitting hole, 803-transition guide hole, 804-interference fit hole, 805-concave curved hole, 809-shrinkage hole, 10-servo extrusion rod, 11-high temperature and high pressure cavity, 12-ratchet, 13-hinge shaft, 14-water-cooled heat exchanger I, 15-water-cooled heat exchanger II, 16-high-pressure water preparation machine, 17-high-pressure accumulator. DETAILED DESCRIPTION

[0041] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0043] An embodiment of the present invention provides a variable diameter thin-wall aluminum tube vertical extrusion molding device to ensure the wettability of ceramic particles and optimize the hot extrusion molding process. Figures 1 to 8As shown, the variable diameter thin-walled aluminum tube vertical extrusion molding device includes a base 3, a column 4, a servo extrusion unit 5, a core mold 6, an extrusion head 7 and a die 8, wherein the servo extrusion unit 5 is arranged above the base 3, and the servo extrusion unit 5 is connected to the base 3 through two columns 4, the die 8 is arranged on the base 3 and sealed by a sealing structure, the core mold 6 is arranged in the die 8, and an annular extrusion cavity for placing the pipe blank 1 is formed between the core mold 6 and the die 8; the extrusion head 7 is slidably connected to the two columns 4; the servo extrusion unit 5 provides servo extrusion power to the extrusion head 7 through the servo extrusion rod 10, and the extrusion head 7 is used to servo extrude the pipe blank 1 at the upper end of the annular extrusion cavity to finally obtain a formed pipe 2, and the formed pipe 2 includes a barrel 201 and a bell mouth 202.

[0044] In the embodiment of the present invention, the pipe blank 1 is in a finely machined cylindrical shape and is made of silicon carbide reinforced aluminum-magnesium alloy. The hot extrusion temperature of the pipe blank 1 is 416°C±19°C, and the wall thickness of the pipe blank 1 is 3-8mm.

[0045] See also Figure 4 As shown, in the embodiment of the present invention, the annular extrusion cavity between the core mold 6 and the die 8 is divided into a clearance fit guide cavity, a transition guide cavity, an interference fit extrusion cavity, a curved cavity and a shrinkage cavity from top to bottom, wherein the diameter of the clearance fit guide cavity is larger than the diameter of the interference fit extrusion cavity, the clearance fit guide cavity is used to guide the pipe blank 1, the transition guide cavity is a conical transition cavity, and the interference fit extrusion cavity is interference fit with the pipe blank 1; the inner diameter of the curved cavity gradually shrinks from top to bottom, and the diameter of the lower port of the curved cavity is equal to the diameter of the shrinkage cavity; the curved cavity is used to form the bell mouth portion 202 of the formed pipe fitting 2, and the shrinkage cavity is used to form the barrel portion 201 of the formed pipe fitting 2.

[0046] See also Figure 4 As shown, in the embodiment of the present invention, a bottom heating module is provided in the base 3; an inner concave cavity 304 connected to the annular extrusion cavity is provided on the upper plane of the base 3, and an upwardly protruding central column 303 is provided at the center of the inner concave cavity 304, and the central column 303 is used to coaxially install the core mold 6; high-pressure passages I 305 and II 306 are provided on both sides of the inner concave cavity 304, respectively, and the high-pressure passage I 305 is connected with the water-cooled heat exchanger I 14 and the high-pressure water preparation machine 16 in sequence, and the high-pressure water preparation machine 16 is used to provide a high-pressure water source to the inner concave cavity 304, and the high-pressure water in the inner concave cavity 304 is used to perform back-pressure extrusion on the pipe blank 1; the high-pressure passage II 306 is connected with the water-cooled heat exchanger II 15 and the high-pressure accumulator 17 in sequence, and the high-pressure accumulator 17 is used to perform pressure compensation on the inner concave cavity 304.

[0047] Specifically, the high-pressure water preparation machine 16 uses mature components of the high-pressure water expansion machine, and its pressure can reach 400MPa. The high-pressure accumulator 17 uses hydraulic system components, which belongs to mature technology. The application function of the high-pressure accumulator 17 is to compensate the volume of the high-temperature and high-pressure chamber 11 during the extrusion process of the high-temperature and high-pressure chamber 11.

[0048] In an embodiment of the present invention, the sealing structure includes a high-temperature and high-pressure upper sealing groove and a high-temperature and high-pressure lower sealing groove forming an annular sealing cavity, wherein the high-temperature and high-pressure lower sealing groove is circumferentially arranged on the upper plane of the base 3, and an annular high-temperature and high-pressure lower sealing cutting edge is provided in the high-temperature and high-pressure lower sealing groove; the high-temperature and high-pressure upper sealing groove is circumferentially arranged on the mounting surface at the bottom of the die 8, and an annular high-temperature and high-pressure upper sealing cutting edge is provided in the high-temperature and high-pressure upper sealing groove, the high-temperature and high-pressure upper sealing cutting edge corresponds to the high-temperature and high-pressure lower sealing cutting edge, and a high-temperature and high-pressure sealing ring band is provided between the high-temperature and high-pressure upper sealing cutting edge and the high-temperature and high-pressure lower sealing cutting edge to achieve high-temperature and high-pressure sealing.

[0049] See also Figure 4 , Figure 5 As shown, in an embodiment of the present invention, the die 8 includes a die body 801 and a die inner cavity arranged at the center of the die body 801, an outer heating module is arranged in the die body 801, and the die inner cavity comprises a clearance fit hole 802, a transition guide hole 803, an interference fit hole 804, a concave curved hole 805 and a shrinkage hole 809 from top to bottom, wherein the diameter of the interference fit hole 804 is smaller than the diameter of the clearance fit hole 802, the transition guide hole 803 is a transition tapered hole, the concave curved hole 805 is used for forming the outer surface of the bell mouth portion 202 of the forming pipe fitting 2, and the shrinkage hole 809 is used for forming the outer surface of the barrel portion 201 of the forming pipe fitting 2.

[0050] In this embodiment, the mounting surface below the die 8 and the upper plane of the base 3 are positioned and locked by screws and pins, and the die 8 and the base 3 contain a high-temperature and high-pressure soft metal seal. The high-temperature and high-pressure upper sealing edge of the die 8 and the high-temperature and high-pressure lower sealing edge corresponding to the base 3 form a high-temperature and high-pressure soft metal seal through plastic deformation of the high-temperature and high-pressure sealing ring belt. The material of the high-temperature and high-pressure sealing ring belt is annealed copper, and the working temperature of the high-temperature and high-pressure sealing ring belt can reach up to 700°C. The central column 303 of the base 3, the die 8 and the core mold 6 contain heating coils and sensors.

[0051] See also Figure 6 As shown, in an embodiment of the present invention, the core mold 6 includes a locking operating part 601, a clearance fit column 602, a transition guide column 603, an interference fit column 604, a convex curved surface section 605 and a connecting part which are arranged in sequence from top to bottom, wherein the diameter of the clearance fit column 602 is larger than the diameter of the interference fit column 604, the convex curved surface section 605 is used to form the inner surface of the bell mouth portion 202 of the forming pipe 2, and the connecting part is used to connect with the base 3; an inner heating module is provided in the core mold 6.

[0052] Specifically, the locking operation part 601 is a hexagonal locking part, which is convenient for screwing operation. The connecting part includes a shoulder 606, a positioning pin 607 and an external thread section 608 arranged in sequence from top to bottom. The shoulder 606 is positioned and fitted with the upper end surface of the center column 303, and the positioning pin 607 and the external thread section 608 are respectively positioned and connected with the guide hole and the threaded hole on the center column 303. In other words, the core mold 6 forms a positioning and centering relationship with the upper end of the center column 303 of the base 3 through the shoulder 606 and the positioning pin 607. The core mold 6 is locked by the hexagon, and the external thread section 608 forms a temporary fixing relationship with the base 3. The outer cylindrical surface of the center column 303 is also a part of the convex curved surface section 605. The convex curved surface section 605 of the core mold 6 and the outer cylindrical surface of the center column 303 are the same as the inner curved surface of the forming pipe 2.

[0053] Specifically, after the core mold 6 is connected to the center column 303 through the external thread section 608, the clearance fit column 602, transition guide column 603, interference fit column 604 and convex curved surface section 605 of the core mold 6 correspond one by one to the clearance fit hole 802, transition guide hole 803, interference fit hole 804 and concave curved surface hole 805 of the die 8, and the center column 303 is located in the shrinkage hole 809, and a shrinkage cavity of equal diameter is formed between the outer circumference of the center column 303 and the inner surface of the shrinkage hole 809.

[0054] See also Figure 1 , Figure 2 As shown, in the embodiment of the present invention, the extrusion head 7 includes an extrusion body 701 and a pressing cylinder 705 arranged at the bottom of the extrusion body 701, wherein the extrusion body 701 is provided with guide holes 703 on both sides thereof respectively slidingly matched with two columns 4, and the pressing cylinder 705 is used to extrude the pipe blank 1 in the annular extrusion cavity. The servo extrusion unit 5 performs the required servo extrusion on the upper extrusion striking surface 702 of the extrusion head 7.

[0055] Furthermore, a one-way limiting structure is provided between the servo extrusion unit 5 and the extrusion head 7; the one-way limiting structure includes ratchets 704 provided on both sides of the extrusion body 701 in the vertical direction and two ratchets 12 hinged on both sides of the servo extrusion unit 5, the two ratchets 12 respectively engage with the two ratchets 704 to form a ratchet-pawl mechanism, allowing the extrusion head 7 to move downward in one direction for a certain height, thereby limiting the upward movement of the extrusion head 7. The hinge shaft 13 of the ratchets 12 contains a torsion spring, so that the ratchets 12 and the ratchets 704 are always engaged.

[0056] In this embodiment, the high-temperature and high-pressure chamber 11 is filled with high-temperature and high-pressure water for back pressure extrusion; under the repeated action of back pressure and front extrusion, the surface of the pipe during the crystallization process repeatedly rubs against the mold, resulting in crystal refinement, which can effectively improve the wettability and crystal refinement of the ceramic particles and the aluminum-magnesium matrix, accurately control the crystallization process temperature and crystallization pressure, and thereby improve the mechanical properties of the structural material such as fatigue strength and plasticity.

[0057] The mold of the present invention heats the pipe blank to a suitable hot extrusion temperature, which can effectively solve the problem that the optimal hot extrusion temperature range of silicon carbide reinforced aluminum-magnesium alloy is very narrow, and can realize the forming of the inner and outer curved surfaces of the thin-walled bell mouth of the pipe and improve its smoothness.

[0058] See also Figures 1 to 8 As shown, another embodiment of the present invention provides an extrusion molding method using the variable diameter thin-walled aluminum tube vertical extrusion molding device in the above embodiment, comprising the following steps:

[0059] Step S1: inserting the pipe blank 1 into the clearance fitting guide cavity at the upper part of the annular extrusion cavity between the core die 6 and the concave die 8;

[0060] Step S2: The servo extrusion unit 5 presses down the extrusion head 7 through the servo extrusion rod 10, and the extrusion cylinder 705 of the extrusion head 7 extrude the pipe blank 1, so that the pipe blank 1 passes through the transition guide cavity and enters the interference fit extrusion cavity, so that the inner concave cavity 304 on the base 3 forms a high-temperature and high-pressure cavity 11;

[0061] Step 3: High-temperature and high-pressure water is introduced into the high-temperature and high-pressure chamber 11 for pressurization. The pressure of the high-temperature and high-pressure chamber 11 is increased to 176±5MPa, so that the pipe blank 1 is subjected to closed die back pressure extrusion; the ratchet 12 in the one-way limiting structure cooperates with the ratchet bar 704 to prevent the pipe blank 1 from moving upward during the back pressure extrusion process;

[0062] Step S4: the extrusion die heats the pipe blank 1 to a hot extrusion temperature and maintains a constant temperature;

[0063] Specifically, the central column 303 of the base 3, the heating coils and sensors inside the die 8 and the core die 6 work together to heat the pipe blank 1 to the hot extrusion temperature of the aluminum-magnesium alloy 416°C ± 19°C and maintain it until the forming is completed;

[0064] Step S5: Perform servo hot extrusion on the pipe blank 1 to obtain a preliminarily formed pipe 2 having a bell mouth portion 202 and a barrel portion 201, see Figure 7 As shown;

[0065] Step S6: performing grain refinement hot extrusion on the formed pipe 2;

[0066] Step S7: demoulding to obtain a formed pipe fitting 2 that meets the process requirements.

[0067] In the embodiment of the present invention, in step S6, the process of performing grain refinement hot extrusion on the formed pipe 2 includes the following steps:

[0068] Step S6a: controlling the temperature of the formed tube 2 to be lowered to a set process temperature;

[0069] Step S6b: the servo extrusion rod 10 is servo-pressed down for a set distance and then lifted up, the set distance being less than one pitch of the ratchet bar 704, and the inner and outer surfaces of the formed tube 2 rub against the mold and crystallize and refine;

[0070] Step S6c; the high temperature and high pressure chamber 11 increases the pressure, causing the molded tube 2 to move in the opposite direction for a set distance and then lift up, and the set distance is less than one tooth pitch of the ratchet 704; the ratchet 12 prevents the molded tube 2 from moving upward;

[0071] Step S6d: Repeat steps S6a to S6c in a loop until the temperature is lower than the recrystallization temperature of the molded tube 2;

[0072] Step S6e: dismantle the mold, take out the formed pipe 2, and disassemble and return the extrusion device and the press to their original positions.

[0073] The present invention provides a vertical extrusion molding method for a variable-diameter thin-walled aluminum tube. Through back pressure and repeated action of back pressure and upper extrusion, the surface of the tube in the crystallization process is repeatedly rubbed against the mold, resulting in crystal refinement. The wettability and crystal refinement of ceramic particles and aluminum-magnesium matrix can be effectively improved, and the temperature and crystallization pressure of the crystallization process can be strictly controlled, thereby improving the mechanical properties such as fatigue strength and plasticity of the structural material.

[0074] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A vertical extrusion molding device for variable diameter thin-walled aluminum tubes, characterized in that: The invention comprises a base (3), a column (4), a servo extrusion unit (5), a core mold (6), an extrusion head (7) and a die (8), wherein the servo extrusion unit (5) is arranged above the base (3) and connected to the base (3) via two columns (4); the die (8) is arranged on the base (3) and sealed via a sealing structure; the core mold (6) is arranged in the die (8) and forms an annular extrusion cavity for placing a pipe blank (1) between the core mold (6) and the die (8); the extrusion head (7) is slidably connected to the two columns (4); the servo extrusion unit (5) provides servo extrusion power to the extrusion head (7) via a servo extrusion rod (10); the extrusion head (7) is used to servo extrude the pipe blank (1) at the upper end of the annular extrusion cavity to obtain a formed pipe (2) having a bell mouth portion (202) and a barrel portion (201); The annular extrusion chamber is divided into a clearance fit guide chamber, a transition guide chamber, an interference fit extrusion chamber, a curved surface chamber and a shrinkage chamber from top to bottom, wherein the diameter of the clearance fit guide chamber is larger than the diameter of the interference fit extrusion chamber, the clearance fit guide chamber is used to guide the pipe blank (1), the transition guide chamber is a conical transition chamber, and the interference fit extrusion chamber is interference fit with the pipe blank (1); the inner diameter of the curved surface chamber gradually shrinks from top to bottom, and the diameter of the lower end of the curved surface chamber is equal to the diameter of the shrinkage chamber; the curved surface chamber is used to form the bell mouth portion (202) of the formed pipe (2), and the shrinkage chamber is used to form the barrel portion (201) of the formed pipe (2); The base (3) is provided with a bottom heating module; an inner concave cavity (304) communicating with the annular extrusion cavity is provided on the upper plane of the base (3); a center column (303) protruding upward is provided at the center of the inner concave cavity (304); the center column (303) is used to coaxially install the core mold (6); high-pressure passages I (305) and II (306) are provided on both sides of the inner concave cavity (304); the high-pressure passage I (305) is connected to the water-cooled heat exchanger I (14) and the high-pressure water preparation machine (16) in sequence; the high-pressure water preparation machine (16) is used to provide a high-pressure water source to the inner concave cavity (304); the high-pressure water in the inner concave cavity (304) is used to perform back pressure extrusion on the pipe blank (1); the high-pressure passage II (306) is connected to the water-cooled heat exchanger II (15) and the high-pressure accumulator (17) in sequence; the high-pressure accumulator (17) is used to perform pressure compensation on the inner concave cavity (304); The concave mold (8) comprises a concave mold body (801) and a concave mold inner cavity arranged at the center of the concave mold body (801), and an outer heating module is arranged in the concave mold body (801); and an inner heating module is arranged in the core mold (6).

2. The variable diameter thin-walled aluminum tube vertical extrusion molding device according to claim 1 is characterized in that: The sealing structure comprises a high-temperature and high-pressure upper sealing groove and a high-temperature and high-pressure lower sealing groove forming an annular sealing cavity, wherein the high-temperature and high-pressure lower sealing groove is circumferentially arranged on the upper plane of the base (3), and an annular high-temperature and high-pressure lower sealing edge is arranged in the high-temperature and high-pressure lower sealing groove; the high-temperature and high-pressure upper sealing groove is circumferentially arranged on the mounting surface of the bottom of the die (8), and an annular high-temperature and high-pressure upper sealing edge is arranged in the high-temperature and high-pressure upper sealing groove, the high-temperature and high-pressure upper sealing edge corresponds to the high-temperature and high-pressure lower sealing edge, and a high-temperature and high-pressure sealing ring is arranged between the high-temperature and high-pressure upper sealing edge and the high-temperature and high-pressure lower sealing edge to achieve high-temperature and high-pressure sealing.

3. The variable diameter thin-walled aluminum tube vertical extrusion molding device according to claim 1 is characterized in that: The inner cavity of the die comprises, from top to bottom, a clearance fit hole (802), a transition guide hole (803), an interference fit hole (804), a concave curved hole (805) and a shrinkage hole (809), wherein the diameter of the interference fit hole (804) is smaller than the diameter of the clearance fit hole (802), the transition guide hole (803) is a transition cone hole, the concave curved hole (805) is used for forming the outer surface of the bell mouth portion (202) of the formed pipe fitting (2), and the shrinkage hole (809) is used for forming the outer surface of the barrel portion (201) of the formed pipe fitting (2).

4. The variable diameter thin-walled aluminum tube vertical extrusion molding device according to claim 1 is characterized in that: The core mold (6) comprises a locking operation portion (601), a clearance fit column (602), a transition guide column (603), an interference fit column (604), a convex curved surface section (605) and a connecting portion, which are arranged in sequence from top to bottom, wherein the diameter of the clearance fit column (602) is greater than the diameter of the interference fit column (604), the convex curved surface section (605) is used to shape the inner surface of the bell mouth portion (202) of the forming pipe (2), and the connecting portion is used to connect to the base (3).

5. The variable diameter thin-walled aluminum tube vertical extrusion molding device according to any one of claims 1 to 4, characterized in that: The extrusion head (7) comprises an extrusion body (701) and a pressing cylinder (705) arranged at the bottom of the extrusion body (701), wherein guide holes (703) respectively slidably matched with the two uprights (4) are provided on both sides of the extrusion body (701), and the pressing cylinder (705) is used to extrude the pipe blank (1) in the annular extrusion cavity.

6. The variable diameter thin-walled aluminum tube vertical extrusion molding device according to claim 5, characterized in that: A one-way limiting structure is provided between the servo extrusion unit (5) and the extrusion head (7); the one-way limiting structure comprises ratchets (704) arranged on both sides of the extrusion body (701) in the vertical direction and two ratchets (12) hinged on both sides of the servo extrusion unit (5), the two ratchets (12) respectively engaging with the two ratchets (704) to limit the upward movement of the extrusion head (7).

7. An extrusion molding method using the variable diameter thin-walled aluminum tube vertical extrusion molding device according to claim 6, characterized in that: The following steps are involved: Step S1: inserting the pipe blank (1) into the clearance fitting guide cavity at the upper part of the annular extrusion cavity between the core die (6) and the concave die (8); Step S2: the servo extrusion unit (5) presses down the extrusion head (7) via the servo extrusion rod (10), and the extrusion cylinder (705) of the extrusion head (7) extrudes the pipe blank (1), so that the pipe blank (1) passes through the transition guide cavity and enters the interference fit extrusion cavity, so that the inner concave cavity (304) on the base (3) forms a high-temperature and high-pressure cavity (11); Step S3: high-temperature and high-pressure water is introduced into the high-temperature and high-pressure chamber (11) to pressurize the pipe blank (1) so that the pipe blank (1) is subjected to closed die back pressure extrusion; a one-way limiting structure prevents the pipe blank (1) from moving upward during the back pressure extrusion process; Step S4: the extrusion die heats the pipe blank (1) to a hot extrusion temperature and maintains a constant temperature; Step S5: performing servo hot extrusion on the pipe blank (1) to obtain a preliminarily formed shaped pipe (2) having a bell mouth portion (202) and a barrel portion (201); Step S6: performing grain refinement hot extrusion on the formed pipe (2); Step S7: demoulding the mold to obtain a formed pipe (2) that meets the process requirements.

8. The extrusion molding method according to claim 7, characterized in that: In step S6, the process of performing grain refinement hot extrusion on the formed pipe (2) comprises the following steps: Step S6a: controlling the temperature of the formed pipe (2) to be lowered to a set process temperature; Step S6b: the servo extrusion rod (10) is servo-pressed down for a set distance and then lifted up, the set distance being less than a tooth pitch of the spine (704), so that the inner and outer surfaces of the formed tube (2) rub against the mold and crystallize and refine; Step S6c: the high temperature and high pressure chamber (11) increases the pressure, causing the formed tube (2) to move in the opposite direction for a set distance and then be lifted, and the set distance is less than one tooth pitch of the ratchet (704); the ratchet (12) prevents the formed tube (2) from moving upward; Step S6d: Repeating steps S6a to S6c in a loop until the temperature is lower than the recrystallization temperature of the formed tube (2); Step S6e: demoulding and taking out the formed tube (2).

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