Method for determining size of forward extrusion initial tube blank of bimetal composite tube

Abstract

The invention relates to a method for determining the size of an initial forward extrusion pipe blank of a bimetal composite pipe, the bimetal composite pipe comprises an inner pipe blank and an outer pipe blank which are coaxially arranged, and when the initial sizes of the inner pipe blank and the outer pipe blank before forward extrusion are determined, the initial sizes of the inner pipe blank and the outer pipe blank are determined according to the principle that the plastic deformation volume of the bimetal composite pipe is not changed. Establishing a relation equation between the initial sizes of the inner pipe blank and the outer pipe blank and the finished product sizes of the inner pipe blank and the outer pipe blank after forward extrusion under the condition that the outflow speeds of the inner pipe blank and the outer pipe blank after forward extrusion deformation are equal; and then determining the size of the initial tube blank according to the deformation mode of forward extrusion of the bimetal composite tube and the relation equation. According to the determination method, the problem of bonding interface layering caused by too large flow velocity difference can be avoided, and operation is easy, convenient and rapid.

Description

Technical Field

[0001] The invention relates to the technical field of metal plastic forming, in particular to a method for determining the size of an initial tube blank of a bimetallic composite tube in forward extrusion. Background Art

[0002] Bimetallic composite pipes take into account the advantages of two different metal materials and are widely used in machinery, petroleum, chemical industry, electric power and other industrial fields due to their high reliability. Compared with mechanically bonded bimetallic composite pipes, metallurgically bonded composite pipes have better comprehensive performance. In the manufacturing process of metallurgically bonded composite pipes, rolling, extrusion and explosive compounding are three commonly used methods; compared with the first two processes, extrusion forming can make the composite pipe interface easy to achieve metallurgical bonding, wide interface bandwidth, high bonding strength, consistent hot and cold shrinkage and expansion, and no limits on thermal conductivity, electrical conductivity and sound transmission; secondly, the tube blank is in a strong three-dimensional compressive stress state during extrusion, which is conducive to the plastic deformation of the material, especially for low plasticity and difficult to deform alloys, thus becoming the preferred process for preparing bimetallic composite pipes.

[0003] However, in the bimetallic composite tube extrusion process, due to the large differences in the strength and plasticity of the two metals, the deformation of the two metal tube blanks is not coordinated and uneven during the extrusion process, resulting in differences in the flow rate of the material near the interface, which can easily cause macro defects such as interface stratification and cracking, and ultimately lead to poor interface bonding quality and low bonding strength, and the performance of the composite tube cannot meet the requirements. In order to ensure the smooth implementation of bimetallic composite tube extrusion and obtain excellent interface bonding quality, it is first necessary to control the uniform and coordinated deformation and flow of the two metal tube blanks and suppress the flow rate difference of the material near the interface. For a given bimetallic composite tube, the size of the two metal initial tube blanks is crucial to the extrusion process, the deformation and coordination of the materials, and especially the flow rate difference of the materials near the interface. Therefore, reasonable initial blank design is the key to ensuring the extrusion quality of bimetallic composite tubes.

[0004] The literature (Knezevic M, Jahedi M, Korkolis YP, et al. Material-based design of the extrusion of bimetallic tubes [J]. Computational Materials Science, 2014, 95: 63-73.) designed three bimetallic tube forward extrusion deformation modes, and analyzed the strain distribution and forming peak load of the composite tube under the three deformation modes through finite element simulation, but did not pay attention to the interface bonding quality after forming. The literature (Liu Jianbin, Zhang Qi, Wang Tao. Numerical simulation of hot extrusion process of bimetallic composite tube [J]. Steel Pipe, 2022, 51 (04): 16-21.) simulated the hot extrusion forming process of bimetallic composite tubes and found that the maximum equivalent stress difference in the deformed body and the plastic flow difference between the inner and outer metal layers were reduced when using differential temperature extrusion, but the factors affecting the flow velocity difference and how to control the flow velocity difference between the inner and outer metal layers were not analyzed.

[0005] Patent CN 102226486 B discloses a copper-aluminum bimetallic composite tube extrusion forming method, first preheating the outer tube blank and the inner tube blank, loading the inner tube blank into the outer tube blank, and then loading the mold and extruding the bimetallic tube under the action of the hydraulic press extrusion block through the punch, and the two metals are composited after the outer metal cools and shrinks. Patent CN 109570253 B discloses a magnesium / aluminum alloy bimetallic composite tube forming mold and method, by introducing the rotation of the concave die on the basis of the traditional positive extrusion process, so that the blank is simultaneously subjected to extrusion and torsion, thereby reducing the metal flow resistance, the preheating temperature of the blank and the mold, and improving the interface quality and dimensional accuracy of the composite tube. Patent CN 115805257 A discloses a bimetallic composite tube forming method, after uniformly brushing a layer of paste-like low-melting-point metal or intermetallic compound on the outer surface of the inner tube, the inner tube is sleeved in the outer tube, the deformation zone is locally and rapidly heated, and the composite tube is obtained by external expansion and spinning deformation using a spinning device. Patent CN 102248022 B discloses a preparation process for a bimetallic thin-walled composite tube, in which a rod-shaped blank as an outer tube is first squeezed into a mold cavity, the rod-shaped blank is deformed and coated on the surface of the inner tube along two symmetrical surfaces to obtain a thick-walled composite tube, and finally a bimetallic thin-walled composite tube is obtained by drawing. The manufacturing methods of bimetallic composite tubes disclosed in patents CN 104028957B, CN102672438B and CN 104384859A are similar in that the inner and outer tubes are mechanically sleeved, welded and fixed at the joints at both ends, and then the bimetallic composite tube is obtained by hot extrusion. Patent CN 113305166 B discloses a hot extrusion expansion process for bimetallic composite steel pipes, and provides a method for determining the extrusion temperature and extrusion ratio by the thickness of the blank, but this method is an empirical formula and is limited to specific metal materials. Patent CN 114769322 B discloses a hot rolling process optimization method for bimetallic composite seamless steel pipes. This method uses the reverse rolling pass direction to calculate the tube size of the seamless steel pipe, which can reasonably distribute the deformation of each rolling mill, so that the burden of the piercing machine, tube rolling mill and diameter reducing mill is balanced. Patent CN 117505571 A discloses a bimetallic composite pipe extrusion structure and extrusion method. First, an external thread is set on the inner tube core, and an internal thread is set on the outer tube shell. The inner and outer tube blanks are connected by threads and then extruded, and finally the mechanical combination of the bimetallic tube is realized.

[0006] The existing work on bimetallic composite tubes mentioned above focuses on providing different extrusion forming processes or methods, but does not involve the forming quality after extrusion, especially the forming quality of the composite tube interface. There are even fewer reports on the initial tube size design, especially the work on suppressing the interface material flow rate difference and improving the interface forming quality through the initial tube size design. Summary of the invention

[0007] The purpose of the present invention is to avoid the shortcomings of the prior art and provide a method for determining the initial tube size under different extrusion deformation modes, so as to ensure that the flow rates of the two tubes are equal during the extrusion process, thereby avoiding the problem of interface stratification caused by excessive flow rate difference.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for determining the initial tube size of a bimetallic composite tube forward extrusion, wherein the bimetallic composite tube comprises an inner tube and an outer tube arranged coaxially, and when determining the initial size of the inner tube and the outer tube before forward extrusion, the method comprises the following steps:

[0009] Step 1: According to the principle that the plastic deformation volume of the bimetallic composite tube remains unchanged, under the condition that the outflow speeds of the inner tube blank and the outer tube blank after positive extrusion deformation are equal, a relationship equation between the initial dimensions of the inner tube blank and the outer tube blank and the finished dimensions of the inner tube blank and the outer tube blank after positive extrusion is established;

[0010] Step 2: determining the initial tube blank size according to the deformation mode of the bimetallic composite tube forward extrusion and the relationship equation.

[0011] Furthermore, the step 1 is specifically as follows:

[0012] Before forward extrusion, the initial inner diameter of the inner tube blank is D1, the initial outer diameter and the inner diameter of the outer tube blank are both D2, and the initial outer diameter of the outer tube blank is D3;

[0013] After extrusion, the inner diameter of the inner tube blank is d1, the outer diameter of the inner tube blank is d2, and the outer diameter of the outer tube blank is d3;

[0014] During positive extrusion, the extrusion speed is v0, and the speeds of the inner and outer tube billets flowing out of the die after deformation are v in and v out , the outflow velocity of the inner tube and the outer tube is equal, that is, to ensure v in =v out , then according to the principle of volume invariance of plastic deformation, we can obtain formula (1) and formula (2):

[0015]

[0016] When v in =v out When , we get formula (3):

[0017]

[0018] At the same time, since the extrusion ratio λ of the forward extrusion is expressed by the sizes of the inner tube billet and the outer tube billet as formula (4):

[0019]

[0020] The formulas (3) and (4) are relationship equations between the initial dimensions of the inner tube blank and the outer tube blank and the finished dimensions of the inner tube blank and the outer tube blank after positive extrusion.

[0021] Furthermore, the bimetallic composite tube forward extrusion deformation mode described in step 2 is an inner fixed outer shrinkage mode, that is, a deformation mode in which the inner diameter of the inner tube blank remains unchanged and the outer diameter of the outer tube blank is reduced, and the initial inner diameter D1 of the inner tube blank is the same as the finished inner diameter d1 of the inner tube blank, then:

[0022] D1=d1,

[0023]

[0024] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, that is, it is determined by the actual production requirements, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, d2, and d3 are all the finished tube diameter sizes given according to the actual service requirements;

[0025] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0026] Further, the positive extrusion deformation mode of the bimetallic composite tube described in step 2 is an inner expansion and outer contraction mode, that is, a deformation mode in which the inner diameter of the inner tube billet is expanded and the outer diameter of the outer tube billet is reduced. At this time, the angle of the concave die for reducing the outer diameter of the outer tube billet is equal to the angle of the core die for expanding the inner diameter of the inner tube billet, that is, α=β, then:

[0027]

[0028]

[0029] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, d2, and d3 are all the finished tube diameter sizes given according to actual service requirements;

[0030] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0031] Furthermore, the forward extrusion deformation mode of the bimetallic composite tube described in step 2 is an overall diameter reduction mode, that is, a deformation mode in which both the inner diameter of the inner tube blank and the outer diameter of the outer tube blank are reduced, then:

[0032]

[0033] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, d2, and d3 are all the finished tube diameter sizes given according to actual service requirements;

[0034] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0035] Furthermore, the forward extrusion deformation of the inner tube blank and the outer tube blank is carried out in a forward extrusion die, and the forward extrusion die is composed of a coaxially arranged male die, a female die, a core die and a sleeve;

[0036] The core mold is arranged in the mold cavity of the sleeve, the male mold is installed at one end of the mold cavity between the core mold and the sleeve, the female mold is installed at the other end of the mold cavity between the core mold and the sleeve, the inner tube blank is embedded on the core mold, and the outer tube blank is embedded on the inner tube blank. As the male mold is loaded, the inner tube blank and the outer tube blank are plastically deformed in the mold cavity and are finally extruded from the female mold opening.

[0037] Furthermore, the positive extrusion deformation mode is an inner-fixed outer-shrinkage mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is a straight line.

[0038] Furthermore, the positive extrusion deformation mode is an inward expansion and outward contraction mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is provided with an inclined convex surface for expanding the inner diameter of the inner tube blank, and the inclination angles of the inclined convex surfaces are the same.

[0039] Furthermore, the positive extrusion deformation mode is an overall diameter reduction mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is provided with an inclined concave surface for reducing the inner diameter of the inner tube blank.

[0040] The beneficial effects of the present invention are:

[0041] 1. According to the flow law of bimetallic composite tubes during the extrusion process, a method for quickly determining the initial tube size is proposed. The initial tube size can be determined only according to the finished tube size and the extrusion ratio, thereby ensuring that the flow velocities of the two tubes are equal during the extrusion process, avoiding the problem of interface stratification caused by excessive flow rate difference. The operation is simple, convenient and fast.

[0042] 2. This method is based on the most basic tube billet geometric relationship in the forward extrusion process, so it is not limited to specific metal materials and can be applied to the forward extrusion process of bimetallic composite tubes with various strengths and plasticities. It has strong applicability and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the structure of three deformation modes of the bimetallic composite tube extrusion of the present invention;

[0044] Figure 2 It is a schematic diagram of the die structure of three deformation modes of the bimetallic composite tube forward extrusion of the present invention. DETAILED DESCRIPTION

[0045] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0046] The inventors have found that there are three deformation modes for the forward extrusion of bimetallic composite tubes: the first deformation mode is the inner fixed outer shrinkage mode, that is, the inner diameter of the inner tube blank remains unchanged, and the outer diameter of the outer tube blank is reduced. Figure 1 (a) as shown; the second deformation mode is the inner expansion and outer contraction mode, that is, the inner diameter of the inner tube is expanded and the outer diameter of the outer tube is reduced (at this time, the angle of the die for reducing the outer diameter of the outer tube is equal to the angle of the core die for expanding the inner diameter of the inner tube, that is, α = β,). Figure 1 (b) As shown; The third deformation mode is the overall diameter reduction mode, that is, the deformation mode in which the inner diameter of the entire inner tube blank and the outer diameter of the outer tube blank are reduced, such as Figure 1 (c) as shown.

[0047] For the above three deformation modes, when other process parameters are given and the initial tube size and the finished tube size satisfy a certain geometric relationship, the flow rate of the two tubes at the interface will remain consistent during extrusion. Therefore, for a certain target finished composite tube, a reasonable initial tube size can be determined through this geometric relationship to achieve the control of the flow rate difference between the two tubes at the interface during the extrusion process. Therefore, in order to achieve the above purpose, the present invention provides the following specific implementation methods:

[0048] Embodiment 1: A method for determining the initial tube size of a bimetallic composite tube by forward extrusion, wherein the bimetallic composite tube comprises an inner tube and an outer tube that are coaxially arranged, and the forward extrusion deformation of the inner tube and the outer tube is carried out in a forward extrusion die, wherein the forward extrusion die is composed of a punch, a die, a core die and a sleeve, wherein the core die is arranged in a die cavity of the sleeve, and the die is installed on one side of the sleeve, wherein the inner tube is sleeved on the core die, and the outer tube is sleeved on the inner tube, and as the punch is loaded, the inner tube and the outer tube undergo plastic deformation in the die cavity and are finally extruded from the die mouth, and when determining the initial size of the inner tube and the outer tube before forward extrusion, the following steps are included:

[0049] Step 1: According to the principle that the volume of the bimetallic composite tube remains unchanged after plastic deformation, under the condition that the outflow speeds of the inner and outer tube billets after positive extrusion deformation are equal, a relationship equation between the initial dimensions of the inner and outer tube billets and the finished dimensions of the inner and outer tube billets after positive extrusion is established, specifically:

[0050] Before forward extrusion, the initial inner diameter of the inner tube blank is D1, the initial outer diameter and the inner diameter of the outer tube blank are both D2, and the initial outer diameter of the outer tube blank is D3;

[0051] After extrusion, the inner diameter of the inner tube blank is d1, the outer diameter of the inner tube blank is d2, and the outer diameter of the outer tube blank is d3;

[0052] During positive extrusion, the extrusion speed is v0, and the speeds of the inner and outer tube billets flowing out of the die after deformation are v in and v out , the outflow velocity of the inner tube and the outer tube is equal, that is, to ensure v in =v out , then according to the principle of volume invariance of plastic deformation, we can obtain formula (1) and formula (2):

[0053]

[0054] When v in =v out When , we get formula (3):

[0055]

[0056] At the same time, since the extrusion ratio λ of the forward extrusion is expressed by the sizes of the inner tube billet and the outer tube billet as formula (4):

[0057]

[0058] The formulas (3) and (4) are relationship equations between the initial dimensions of the inner tube blank and the outer tube blank and the finished dimensions of the inner tube blank and the outer tube blank after positive extrusion.

[0059] Step 2: Determine the initial tube size according to the deformation mode of the bimetallic composite tube forward extrusion and the relationship equation, specifically:

[0060] The positive extrusion deformation mode of the bimetallic composite tube is an inner fixed outer shrinkage mode, that is, the inner diameter of the inner tube billet remains unchanged, and the outer diameter of the outer tube billet is reduced. The initial inner diameter D1 of the inner tube billet is the same as the finished inner diameter d1 of the inner tube billet, then:

[0061]

[0062] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, D2, and d3 are all the finished tube diameter sizes given according to actual service requirements;

[0063] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0064] In order to further illustrate the solution of Example 1, the present invention provides the following specific calculation examples:

[0065] Given that the inner diameter d1 of the finished tube is 24 mm, the inner diameter d2 of the outer tube is 29.5 mm, the outer diameter d3 of the outer tube is 35 mm, and the extrusion ratio λ is 3, the initial tube size is determined to ensure that the flow rate of the two tubes is equal during the extrusion process, then:

[0066] Step S1: Determine the initial inner tube inner diameter D1. For this deformation mode, the initial inner tube inner diameter D1 is the same as the finished inner tube inner diameter d1, that is, D1 = 24 mm;

[0067] Step S2: Determine the initial outer diameter D3 of the outer tube. D3 can be determined by the following formula, where λ is known to be 3 according to actual engineering requirements, then:

[0068]

[0069] Step S3: Determine the initial inner tube outer diameter D2, that is, the initial outer tube inner diameter, according to the following formula:

[0070]

[0071] Therefore, under the internal fixed external shrinkage deformation mode, the initial tube blank dimensions D1 are 24 mm, D2 are 28.2 mm, and D3 are 50.2 mm.

[0072] At the same time, the forward extrusion deformation of the inner tube blank and the outer tube blank described in this embodiment is carried out in a forward extrusion die, and the forward extrusion die is composed of a coaxially arranged male die, a female die, a core die and a sleeve;

[0073] The core mold is arranged in the mold cavity of the sleeve, the male mold is installed at one end of the mold cavity between the core mold and the sleeve, the female mold is installed at the other end of the mold cavity between the core mold and the sleeve, the inner tube blank is embedded on the core mold, and the outer tube blank is embedded on the inner tube blank. As the male mold is loaded, the inner tube blank and the outer tube blank are plastically deformed in the mold cavity and are finally extruded from the female mold opening.

[0074] like Figure 2 As shown in (a), the positive extrusion deformation mode of this embodiment is an inner-fixed outer-shrinkage mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is a straight line.

[0075] Embodiment 2: The same as Embodiment 1, except that step 2 is: the positive extrusion deformation mode of the bimetallic composite tube is an inner expansion and outer contraction mode, that is, a deformation mode in which the inner diameter of the inner tube is expanded and the outer diameter of the outer tube is reduced. At this time, the angle of the concave die for reducing the outer diameter of the outer tube is equal to the angle of the core die for expanding the inner diameter of the inner tube, that is, α=β, then:

[0076]

[0077]

[0078] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, d2, and d3 are all the finished tube diameter sizes given according to actual service requirements;

[0079] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0080] In order to further illustrate the solution of Example 2, the present invention provides the following specific calculation example:

[0081] Given that the inner diameter d1 of the finished tube is 24 mm, the inner diameter d2 of the outer tube is 29.5 mm, the outer diameter d3 of the outer tube is 35 mm, and the extrusion ratio λ is 3, the initial tube size is determined to ensure that the flow rate of the two tubes is equal during the extrusion process, then:

[0082] Step S1: Determine the initial inner diameter D1 of the inner tube. D1 can be determined by the following formula, where λ is known to be 3 according to actual engineering requirements:

[0083]

[0084] Step S2: Determine the initial outer diameter D3 of the outer tube. D3 can be determined by the following formula, where λ is known to be 3 according to actual engineering requirements, then:

[0085]

[0086] Step S3: Determine the initial inner tube outer diameter D2, that is, the initial outer tube inner diameter, according to the following formula:

[0087]

[0088] Therefore, under the internal expansion and external contraction deformation mode, the initial tube blank dimensions D1 are 13 mm, D2 are 32.4 mm, and D3 are 46 mm.

[0089] At the same time, the forward extrusion deformation of the inner tube blank and the outer tube blank described in this embodiment is carried out in a forward extrusion die, and the forward extrusion die is composed of a coaxially arranged male die, a female die, a core die and a sleeve;

[0090] The core mold is arranged in the mold cavity of the sleeve, the male mold is installed at one end of the mold cavity between the core mold and the sleeve, the female mold is installed at the other end of the mold cavity between the core mold and the sleeve, the inner tube blank is embedded on the core mold, and the outer tube blank is embedded on the inner tube blank. As the male mold is loaded, the inner tube blank and the outer tube blank are plastically deformed in the mold cavity and are finally extruded from the female mold opening.

[0091] like Figure 2 As shown in (b), the positive extrusion deformation mode of this embodiment is an inner expansion and outer contraction mode, then the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the mandrel corresponding to the die is provided with an inclined convex surface for expanding the inner diameter of the inner tube blank, and the inclined convex surface and the inclined convex surface have the same inclination angle, that is, Figure 1 The angles of the concave die and the core die shown in (b) are equal, that is, α=β.

[0092] Embodiment 3 is the same as Embodiment 1, except that step 2 is: the positive extrusion deformation mode of the bimetallic composite tube is an overall diameter reduction mode, that is, a deformation mode in which the inner diameter of the entire inner tube blank and the outer diameter of the outer tube blank are both reduced, then:

[0093]

[0094] Wherein, D3 is the initial outer diameter of the outer tube blank, D2 is the initial inner diameter of the outer tube blank and also the initial outer diameter of the inner tube blank, D1 is the initial inner diameter of the inner tube blank, the given λ is the extrusion ratio of the forward extrusion, d1 is the finished inner diameter of the inner tube blank, d2 is the finished outer diameter of the inner tube blank and also the finished inner diameter of the outer tube blank, d3 is the finished outer diameter of the outer tube blank, wherein d1, d2, and d3 are all the finished tube diameter sizes given according to actual service requirements;

[0095] That is, the initial dimensions of the inner tube blank and the outer tube blank before positive extrusion are determined, that is, the determination of D1, D2, and D3 is completed.

[0096] In order to further illustrate the solution of Example 3, the present invention provides the following specific calculation examples:

[0097] Given that the inner diameter d1 of the finished tube is 24 mm, the inner diameter d2 of the outer tube is 29.5 mm, the outer diameter d3 of the outer tube is 35 mm, and the extrusion ratio λ is 3, the initial tube size is determined to ensure that the flow rate of the two tubes is equal during the extrusion process, then:

[0098] Step S1: Determine the initial inner diameter D1 of the inner tube. D1 can be determined by the following formula, where λ is known to be 3 according to actual engineering requirements, then:

[0099]

[0100] Step S2: Determine the initial outer diameter D3 of the outer tube. D3 can be determined by the following formula, where λ is known to be 3 according to actual engineering requirements:

[0101]

[0102] Step S3: Determine the initial inner tube outer diameter D2, that is, the initial outer tube inner diameter, according to the following formula:

[0103]

[0104] Therefore, under the overall diameter reduction deformation mode, the initial tube blank dimensions D1 are 41.6 mm, D2 are 51.1 mm, and D3 are 60.6 mm.

[0105] At the same time, the forward extrusion deformation of the inner tube blank and the outer tube blank described in this embodiment is carried out in a forward extrusion die, and the forward extrusion die is composed of a coaxially arranged male die, a female die, a core die and a sleeve;

[0106] The core mold is arranged in the mold cavity of the sleeve, the male mold is installed at one end of the mold cavity between the core mold and the sleeve, the female mold is installed at the other end of the mold cavity between the core mold and the sleeve, the inner tube blank is embedded on the core mold, and the outer tube blank is embedded on the inner tube blank. As the male mold is loaded, the inner tube blank and the outer tube blank are plastically deformed in the mold cavity and are finally extruded from the female mold opening.

[0107] like Figure 2 As shown in (c), the positive extrusion deformation mode of this embodiment is an overall diameter reduction mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is provided with an inclined concave surface for reducing the inner diameter of the inner tube blank.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the initial tube size of a bimetallic composite tube in forward extrusion, It is characterized in that The bimetallic composite tube comprises an inner tube blank and an outer tube blank which are coaxially arranged. When determining the initial sizes of the inner tube blank and the outer tube blank before forward extrusion, the following steps are included: Step 1: According to the principle that the plastic deformation volume of the bimetallic composite tube remains unchanged, under the condition that the outflow speeds of the inner tube blank and the outer tube blank after positive extrusion deformation are equal, a relationship equation between the initial dimensions of the inner tube blank and the outer tube blank and the finished dimensions of the inner tube blank and the outer tube blank after positive extrusion is established; Step 2: determining the initial tube blank size according to the deformation mode of the bimetallic composite tube forward extrusion and the relationship equation.

2. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 1, It is characterized in that The step 1 is specifically as follows: Before forward extrusion, the initial inner diameter of the inner tube blank is D 1 The initial outer diameter and the inner diameter of the outer tube are both D 2 , the initial outer diameter of the outer tube is D 3 ; After extrusion, the inner diameter of the inner tube blank is d 1 The finished outer diameter of the inner tube is the finished inner diameter of the outer tube, which is d. 2 The finished outer diameter of the outer tube is d 3 ; The extrusion speed is v during positive extrusion. 0 The speeds of the inner and outer tube billets flowing out of the die after deformation are v in and v out , the outflow velocity of the inner tube and the outer tube is equal, that is, to ensure v in =v out , According to the principle of volume invariance of plastic deformation, we can obtain formula (1) and formula (2): When v in =v out When , we get formula (3): At the same time, since the extrusion ratio λ of the forward extrusion is expressed by the sizes of the inner tube billet and the outer tube billet as formula (4): The formulas (3) and (4) are relationship equations between the initial dimensions of the inner tube blank and the outer tube blank and the finished dimensions of the inner tube blank and the outer tube blank after positive extrusion.

3. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 1, It is characterized in that The bimetallic composite tube forward extrusion deformation mode described in step 2 is an inner fixed outer shrinkage mode, that is, a deformation mode in which the inner diameter of the inner tube billet remains unchanged and the outer diameter of the outer tube billet is reduced. The initial inner diameter D of the inner tube billet is 1 The inner diameter of the inner tube blank is d 1 The same, then: D 1 =d 1 , Where D 3 is the initial outer diameter of the outer tube, D 2 is the initial inner diameter of the outer tube and also the initial outer diameter of the inner tube, D 1 is the initial inner diameter of the inner tube, the given λ is the extrusion ratio of the forward extrusion, d 1 is the finished inner diameter of the inner tube blank, d 2 The finished outer diameter of the inner tube is also the finished inner diameter of the outer tube, d 3 is the finished outer diameter of the outer tube blank, where d 1 , d 2 , d 3 The finished pipe diameters are all given according to actual service requirements; That is, the initial dimensions of the inner and outer tube blanks before positive extrusion are determined, that is, the D 1 , D 2 , D 3 of determination.

4. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 1, It is characterized in that The positive extrusion deformation mode of the bimetallic composite tube described in step 2 is an inner expansion and outer contraction mode, that is, a deformation mode in which the inner diameter of the inner tube billet is expanded and the outer diameter of the outer tube billet is reduced. At this time, the angle of the concave die for reducing the outer diameter of the outer tube billet is equal to the angle of the core die for expanding the inner diameter of the inner tube billet, that is, α=β, then: Where D 3 is the initial outer diameter of the outer tube, D 2 is the initial inner diameter of the outer tube and also the initial outer diameter of the inner tube, D 1 is the initial inner diameter of the inner tube, the given λ is the extrusion ratio of the forward extrusion, d 1 is the finished inner diameter of the inner tube blank, d 2 The finished outer diameter of the inner tube is also the finished inner diameter of the outer tube, d 3 is the finished outer diameter of the outer tube blank, where d 1 , d 2 , d 3 The finished pipe diameters are all given according to actual service requirements; That is, the initial dimensions of the inner and outer tube blanks before positive extrusion are determined, that is, the D 1 , D 2 , D 3 of determination.

5. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 1, It is characterized in that The forward extrusion deformation mode of the bimetallic composite tube described in step 2 is an overall diameter reduction mode, that is, a deformation mode in which the inner diameter of the entire inner tube blank and the outer diameter of the outer tube blank are both reduced, then: Where D 3 is the initial outer diameter of the outer tube, D 2 is the initial inner diameter of the outer tube and also the initial outer diameter of the inner tube, D 1 is the initial inner diameter of the inner tube, the given λ is the extrusion ratio of the forward extrusion, d 1 is the finished inner diameter of the inner tube blank, d 2 The finished outer diameter of the inner tube is also the finished inner diameter of the outer tube, d 3 is the finished outer diameter of the outer tube blank, where d 1 , d 2 , d 3 The finished pipe diameters are all given according to actual service requirements; That is, the initial dimensions of the inner and outer tube blanks before positive extrusion are determined, that is, the D 1 , D 2 , D 3 of determination.

6. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to any one of claims 1 to 5, It is characterized in that The forward extrusion deformation of the inner tube blank and the outer tube blank is carried out in a forward extrusion die, and the forward extrusion die is composed of a coaxially arranged male die, a female die, a core die and a sleeve; The core mold is arranged in the mold cavity of the sleeve, the male mold is installed at one end of the mold cavity between the core mold and the sleeve, the female mold is installed at the other end of the mold cavity between the core mold and the sleeve, the inner tube blank is embedded on the core mold, and the outer tube blank is embedded on the inner tube blank. As the male mold is loaded, the inner tube blank and the outer tube blank are plastically deformed in the mold cavity and are finally extruded from the female mold opening.

7. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 6, It is characterized in that The positive extrusion deformation mode is an inner-fixed outer-shrinkage mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is a straight line.

8. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 6, It is characterized in that The positive extrusion deformation mode is an inward expansion and outward contraction mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is provided with an inclined convex surface for expanding the inner diameter of the inner tube blank, and the inclination angles of the inclined convex surfaces are the same.

9. The method for determining the size of the initial tube blank for forward extrusion of a bimetallic composite tube according to claim 6, It is characterized in that The positive extrusion deformation mode is an overall diameter reduction mode, and the surface of the die is provided with an inclined convex surface for reducing the outer diameter of the outer tube blank, and the surface of the core mold corresponding to the die is provided with an inclined concave surface for reducing the inner diameter of the inner tube blank.

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