Metal pipe hot bending method using heat-expandable graphite as filler

Abstract

A method for hot bending of metal pipes using thermal expansion graphite as a filler belongs to the field of metal pipe processing. The method is to fill the metal pipe with thermal expansion graphite, and the initial expansion temperature of the filled thermal expansion graphite is within 20°C of the forming temperature of the metal pipe; the volume of the added thermal expansion graphite is: the volume corresponding to the bending deformation part required for the tube blank + the process margin = the volume of the thermal expansion graphite. During the bending process of the metal pipe, the metal pipe and the thermal expansion graphite are heated at the same time. Since the thermal expansion graphite expands under the heating condition, a certain pressure is generated to act on the inner wall of the pipe, thereby playing a supporting role and preventing the metal pipe from wrinkling; at the same time, the thermal expansion graphite can also improve the filling effect during the expansion process and inhibit the cross-sectional distortion of the bending area of ​​the metal pipe. In addition, the thermal expansion graphite has good heat resistance and a wide expansion temperature range. It can be filled in different types of metal pipes to provide expansion support and improve the forming quality of the metal pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of metal pipe processing, and in particular relates to a metal pipe thermal bending method using thermal expansion graphite as a filler. Background Art

[0002] In the fields of aviation, aerospace, automobiles, etc., improving component strength, reducing component mass, and saving space are the goals that people have long pursued. Since metal pipes are hollow inside, they have the advantages of light weight and strong load-bearing capacity. At the same time, they can also be bent to obtain complex parts. Therefore, they are widely used in the fields of aviation, aerospace, automobiles, etc.

[0003] At present, the commonly used metal pipe bending processing technologies include bending, push bending and stretch bending. However, under normal circumstances, the bending process of metal pipes is subject to tensile-compressive stress, which is prone to quality defects such as cracking, wrinkling and cross-sectional shape distortion, affecting the accuracy and performance of pipe fittings. In order to solve such problems, bending methods such as filling solid particles, low-melting-point alloys and other fillers in the pipe or heating bending methods under certain temperature conditions are often used.

[0004] However, the existing bending forming methods such as filling the tube with solid particles and low-melting point alloys still have the problem of wear between the filler and the tube wall and the problem that the filler transmits uneven force and it is difficult to ensure uniform support for the tube wall; at the same time, low-melting point alloys are only suitable for bending forming under room temperature conditions, and cannot meet the bending forming requirements of some alloy materials that are difficult to form under room temperature conditions (such as high-strength aluminum alloys, titanium alloys, etc.); filling with solid particles can be bent under warm conditions, but warm conditions aggravate the wear between the solid particles and the tube wall, and still cannot meet the accuracy and performance requirements of metal tubes.

[0005] Thermally expanded graphite is a new material formed by inserting other molecules, atoms or ions into the interlayers of natural graphite flakes through artificial synthesis. In a high temperature environment, the internal intercalation material will quickly absorb heat and vaporize, generating thrust on the graphite sheet structure, thus causing a large expansion in volume. It can generally be used as a sealing material, microbial carrier, etc. At the same time, the expanded graphite formed after heating can be used to prepare graphene. Summary of the invention

[0006] The present invention aims at the phenomenon of wrinkling and cross-sectional distortion of metal pipes during the bending process, and utilizes the characteristics of thermal expansion of thermal expansion graphite to propose a method for hot bending of metal pipes using thermal expansion graphite as a filler. Specifically, the thermal expansion graphite is filled inside the metal pipe, and during the bending process of the metal pipe, the metal pipe and the thermal expansion graphite are heated at the same time. Since the thermal expansion graphite expands under the heating condition, a certain pressure is generated to act on the inner wall of the pipe, thereby playing a supporting role and preventing the wrinkling of the metal pipe; at the same time, the thermal expansion graphite can also improve the filling effect during the expansion process and inhibit the cross-sectional distortion of the bending area of ​​the metal pipe. In comparison, thermal expansion graphite has good heat resistance and a wide expansion temperature range. It can be filled in different types of metal pipes to meet their forming temperature conditions, and a certain expansion occurs to provide support for the pipe wall, thereby improving the forming quality of the metal pipe.

[0007] In order to achieve the above purpose, the following technical solutions are adopted:

[0008] A method for hot bending a metal pipe using heat-expandable graphite as a filler according to the present invention comprises the following steps:

[0009] Step 1: Blank making

[0010] Forming metal pipes into required pipe blanks;

[0011] Step 2: Determine the type and amount of thermal expansion graphite

[0012] Determine the type of thermal expansion graphite according to the forming temperature and material properties of the tube blank, ensure that the initial expansion temperature of the thermal expansion graphite is less than the forming temperature of the tube blank, and the tube blank is not scratched during the bending process;

[0013] Calculate the required volume of thermal expansion graphite and prepare the thermal expansion graphite for filling;

[0014] Step 3: Filling

[0015] Putting heat-expandable graphite into the part of the tube blank that needs to be bent and deformed, and sealing both ends of the part filled with the heat-expandable graphite to obtain a tube blank filled with the heat-expandable graphite;

[0016] Step 4: Heating and insulation

[0017] The whole or a local area of ​​the tube blank filled with heat-expandable graphite is heated to the forming temperature of the tube blank and kept warm to obtain a heated tube blank;

[0018] Step 5: Bending and deformation

[0019] The heated tube is bent to a desired bending angle;

[0020] Step 6: Stop heating

[0021] Stop heating and let the temperature cool to room temperature;

[0022] Step 7: Take out the thermal expansion graphite

[0023] The thermally expanded graphite is taken out to obtain a bent metal pipe part.

[0024] In the step 1, the method used for blank making is one of wire cutting and laser cutting.

[0025] In the step 2, the volume of the required heat-expanded graphite is determined according to the volume corresponding to the required bending deformation part of the tube blank, and the specific calculation method is: the volume corresponding to the required bending deformation part of the tube blank + the process margin = the volume of the heat-expanded graphite. Among them, the process margin is 1 / 5 of the volume corresponding to the required bending deformation part of the tube blank.

[0026] In the step 2, the initial expansion temperature of the heat-expandable graphite is the lowest temperature at which the heat-expandable graphite starts to expand during the static heating process, and the measurement method is specifically: measuring the volume of the heat-expandable graphite during the heating process, and the temperature at which the volume of the heat-expandable graphite after expansion reaches 1.1 times the volume before expansion is taken as the initial expansion temperature of the heat-expandable graphite.

[0027] The thermally expandable graphite is preferably prepared by acid washing natural graphite flakes with acidic substances or by oxidation intercalation with strong oxidizing substances.

[0028] The initial expansion temperature of the thermal expansion graphite is from 150°C to 800°C. In the bending and forming of the tube, the initial expansion temperature of the selected thermal expansion graphite should be lower than the forming temperature of the tube blank, and the initial expansion temperature of the thermal expansion graphite is within 20°C of the forming temperature of the tube blank. In this temperature range, the expansion ratio of the thermal expansion graphite remains basically unchanged, which can ensure that the expansion force generated by the thermal expansion graphite during the forming process effectively provides support for the tube wall, and at the same time, the expansion force generated by the thermal expansion graphite is less than or equal to the pressure required for the plastic deformation of the tube.

[0029] In the step 3, sealing the two ends of the tube blank filled with the heat-expandable graphite has the following effects: first, preventing the heat-expandable graphite from leaking during the forming process; second, the heat-expandable graphite is heated in the tube blank and expands in the radial and axial directions, and the radial direction is constrained by the tube wall and basically does not change through temperature control. If the axial direction is not sealed, the heat-expandable graphite in this direction will flow. Therefore, the two ends of the tube blank filled with the heat-expandable graphite are sealed to ensure that the force generated by the heat-expandable graphite during the heating process acts on the tube wall to assist the tube blank in bending and forming.

[0030] In the step 4, the heating temperature set by the heating device is the forming temperature of the tube blank and the tube blank is kept warm, wherein the forming temperature of the tube blank and the holding time after forming are determined by the material properties of the metal tube blank.

[0031] In the step 4, there are two ways to heat the tube blank. One is a heating and forming integrated device, that is, the heating device is directly arranged inside the forming device, and the heating, insulation and forming of the tube blank can be completed directly on the heating and forming integrated device; the other is a heating and forming separate device including a heating device and a separate forming device, the heating process and the forming process are carried out independently, and the tube blank is heated and then transferred to a separate forming device for bending and forming.

[0032] The step five can be used for a variety of bending deformation processes, such as: bending around, pushing and pulling.

[0033] The metal pipe hot bending method using heat-expandable graphite as filler of the present invention has the following beneficial effects:

[0034] Thermal expansion graphite is used as a filler to assist the bending and deformation of metal pipes. During the bending process, the tube blank and the thermal expansion graphite are heated simultaneously. Under heating conditions, the plasticity of the metal pipe increases, the deformation resistance decreases, and the material is easy to deform; when the heating temperature exceeds the expansion temperature of the thermal expansion graphite, it will expand, which can generate a certain external force on the tube wall, and better play a filling and supporting role, thereby more effectively preventing the wrinkling and cross-sectional distortion of the metal pipe during bending. Thermal expansion graphite has good heat resistance and can achieve high-temperature expansion under different temperature conditions to meet the thermal bending temperature of different metal pipes and achieve a better filling effect on the metal pipe. If a certain amount of thermal expansion graphite is added as a filler during the hot bending process of the metal pipe, the heat resistance of the thermal expansion graphite can not only meet the hot bending temperature conditions of different metal pipes, but also use the external force generated by the thermal expansion graphite during the expansion process of a certain temperature to further improve the support of the thermal expansion graphite as a filler on the metal pipe, which has research significance for improving the quality of hot bending of metal pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a metal pipe hot bending method (initial state) using heat-expandable graphite as a filler according to Example 1 of the present invention;

[0036] Figure 2 This is a schematic diagram of a metal pipe hot bending method (forming state) using heat-expandable graphite as a filler according to Example 1 of the present invention;

[0037] Figure 3 This is a schematic diagram of a metal pipe hot bending method (initial state) using heat-expandable graphite as a filler according to Example 2 of the present invention;

[0038] Figure 4 This is a schematic diagram of a metal pipe hot bending method (forming state) using heat-expandable graphite as a filler according to Example 2 of the present invention;

[0039] Figure 5Schematic diagram of the metal pipe hot bending method (initial state) of Comparative Example 1 of the present invention;

[0040] Figure 6 Schematic diagram of the metal pipe hot bending method (forming state) of Comparative Example 1 of the present invention;

[0041] Figure 7 It is a schematic diagram of a hot bending method (initial state) of a metal pipe filled with metal particles according to Comparative Example 2 of the present invention;

[0042] Figure 8 It is a schematic diagram of a hot bending method (forming state) of a metal pipe filled with metal particles according to Comparative Example 2 of the present invention;

[0043] Fig. 9 It is a schematic diagram of a bending method (initial state) of a metal tube filled with a low melting point alloy according to Comparative Example 3 of the present invention;

[0044] Fig.10 It is a schematic diagram of a bending method (forming state) of a metal tube filled with a low melting point alloy according to Comparative Example 3 of the present invention;

[0045] Figure 1 and Figure 2 In the figure, 1 is a tube blank, 2 is a sealing piston, 3 is a heat-expandable graphite, 4 is a heating device, and 5 is a heating and forming integrated device;

[0046] Figure 3 and Figure 4 In the figure, 1 is a tube blank, 2 is a sealing piston, 3 is a thermal expansion graphite, and 6 is a separate forming device;

[0047] Figure 5 and Figure 6 In the figure, 1 is a tube blank, 4 is a heating device, and 5 is a heating and forming integrated device;

[0048] Figure 7 and Figure 8 In the figure, 1 is a tube blank, 2 is a sealing piston, 7 is a metal particle, and 6 is a separate forming device;

[0049] Fig. 9 and Fig.10 In the figure, 1 is a tube blank, 8 is a low melting point alloy, 9 is a solid wax block, and 6 is a separate forming device. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] In the following embodiments, the initial expansion temperature of the heat-expandable graphite is the lowest temperature at which the heat-expandable graphite begins to expand during static heating. The specific measurement method is: the volume of the heat-expandable graphite is measured during the heating process, and the temperature at which the volume of the heat-expandable graphite after expansion reaches 1.1 times the volume before expansion is taken as the initial expansion temperature of the heat-expandable graphite.

[0052] Example 1

[0053] A method for hot bending of metal pipes filled with heat-expandable graphite, schematic diagram of which is shown in Figure 1 and Figure 2 The equipment used includes a sealing piston 2 and a heating and forming integrated device 5, wherein the heating and forming integrated device 5 contains a heating device 4.

[0054] In this embodiment, the material of the tube blank 1 is aluminum alloy 5A06, the outer diameter of the tube blank 1 is 30 mm, the wall thickness is 1 mm, and the length is 310 mm. The tube blank 1 is made into a part with a bending radius of 100 mm, a bending angle of 90°, and a straight section length of 75 mm at one end. The forming temperature is 250°C.

[0055] A method for hot bending a metal pipe using heat-expandable graphite as a filler comprises the following steps:

[0056] Step 1: Cut the metal tube into the required tube blank 1 by laser cutting;

[0057] Step 2: Calculate the required volume of thermal expansion graphite 3 and prepare the thermal expansion graphite 3 for filling;

[0058] The forming temperature of tube blank 1 (aluminum alloy 5A06) is determined to be 250°C, therefore, thermal expansion graphite with an initial expansion temperature of 240°C is selected, and the initial expansion temperature of the thermal expansion graphite differs by 10°C from the forming temperature of the tube blank.

[0059] The method for calculating the required volume of the heat-expandable graphite 3 is as follows: the volume of the bending deformation part of the tube blank 1 is calculated to be 100 mL, the process margin is 20 mL, and the amount of the heat-expandable graphite 3 is determined to be 120 mL.

[0060] Step 3: Place the heat-expandable graphite 3 into the portion of the tube blank 1 that needs to be bent and deformed, and seal both ends of the portion filled with the heat-expandable graphite using a sealing piston 2 to obtain a tube blank filled with the heat-expandable graphite;

[0061] Step 4: Start the heating device 4 in the integrated heating and forming device 5 to heat the tube blank filled with heat-expandable graphite to the forming temperature and keep it warm to obtain a heated tube blank;

[0062] Step 5: The heated tube blank is bent by using the heating and forming integrated device 5 to reach the required bending angle;

[0063] Step 6: Stop heating and cool to room temperature;

[0064] Step 7: Take out the thermal expansion graphite 3 to obtain the bent metal pipe part.

[0065] By observing the bent metal pipe parts, it is found that this method effectively suppresses the defect of wrinkling of the tube wall due to pressure on the inner side, while the change in cross-sectional roundness is small.

[0066] Example 2

[0067] A method for hot bending of metal pipes filled with heat-expandable graphite, schematic diagram of which is shown in Figure 3 and Figure 4 The equipment used includes a sealing piston 2, a heating device and a separate forming device 6.

[0068] In this embodiment, the tube blank 1 is made of aluminum alloy 5A06, the outer diameter of the tube blank 1 is 30 mm, the wall thickness is 1 mm, and the length is 310 mm. The tube blank 1 is made into a part with a bending radius of 100 mm, a bending angle of 90°, and a straight section length of 75 mm at one end, and the local heating temperature is 250° C. Different from the embodiment 1, the metal tube filled with thermal expansion graphite is heated before bending, and then the bending is performed by a separate forming device 6 of the heating forming split device, which can also improve the forming quality and improve the accuracy of the parts.

[0069] A method for hot bending a metal pipe using heat-expandable graphite as a filler comprises the following steps:

[0070] Step 1: Cut the metal tube into the required tube blank 1 by wire cutting;

[0071] Step 2: Calculate the required volume of thermal expansion graphite 3 and prepare the thermal expansion graphite 3 for filling;

[0072] The forming temperature of tube blank 1 (aluminum alloy 5A06) is determined to be 250°C, therefore, thermal expansion graphite with a starting expansion temperature of 240°C is selected; the starting expansion temperature of the thermal expansion graphite differs by 10°C from the forming temperature of the tube blank.

[0073] The method for calculating the required volume of the heat-expandable graphite 3 is as follows: the volume of the bending deformation part of the tube blank 1 is calculated to be 100 mL, the process margin is 20 mL, and the amount of the heat-expandable graphite 3 is determined to be 120 mL.

[0074] Step 3: Place the heat-expandable graphite 3 into the portion of the tube blank 1 that needs to be bent and deformed, and seal both ends of the portion filled with the heat-expandable graphite using a sealing piston 2 to obtain a tube blank filled with the heat-expandable graphite;

[0075] Step 4: In a corresponding heating device, the tube blank filled with heat-expandable graphite is heated to a forming temperature and kept warm to obtain a heated tube blank;

[0076] Step 5: The heated tube blank is bent by a separate forming device 6 to a desired bending angle;

[0077] Step 6: Cool down to room temperature;

[0078] Step 7: Take out the thermal expansion graphite 3 to obtain the bent metal pipe part.

[0079] Example 3

[0080] A method for hot bending a metal tube filled with heat-expandable graphite, which is the same as that of Example 2, except that:

[0081] The specific method used is a bending forming method, and the material of the tube blank is titanium alloy TA1.

[0082] The outer diameter of the tube blank is 30mm, the wall thickness is 1mm, and the length is 310mm. The tube blank is made into a part with a bending radius of 100mm, a bending angle of 90°, and a straight section length of 75mm at one end. A heating forming split device is used, the heating temperature is 550℃, and the separate forming device is a bending forming device.

[0083] The forming temperature of the tube (titanium alloy TA1) is determined to be 550°C, and the thermal expansion graphite with an initial expansion temperature of 535°C is selected. The initial expansion temperature of the thermal expansion graphite differs from the forming temperature of the tube by 15°C. The required volume of thermal expansion graphite is calculated as follows: the volume of the bending deformation part of the tube is calculated to be 100mL, the process margin is 20mL, and the amount of thermal expansion graphite is determined to be 120mL.

[0084] Comparative Example 1

[0085] A method for hot bending of metal pipes, schematic diagram of which is shown in Figure 5 and Figure 6 The equipment used includes a heating and forming integrated device 5, which includes a heating device 4.

[0086] In this embodiment, the material of the tube blank 1 is aluminum alloy 5A06, the outer diameter of the tube blank 1 is 30 mm, the wall thickness is 1 mm, and the length is 310 mm. The tube blank 1 is made into a part with a bending radius of 100 mm, a bending angle of 90°, and a straight section length of 75 mm at one end. The forming temperature is 250°C.

[0087] A method for hot bending a metal pipe, using the forming device, comprises the following steps:

[0088] Step 1: Forming the metal tube into the required tube blank 1;

[0089] Step 2: Start the heating device 4 in the integrated heating and forming device 5 to heat the tube blank as a whole to the forming temperature and keep the temperature to obtain a heated tube blank;

[0090] Step 3: bend the heated tube blank by using the heating and forming integrated device 5 to reach the required bending angle;

[0091] Step 4: Stop heating and wait for the device to cool to room temperature;

[0092] Step 5: Remove the parts.

[0093] A method for heating and bending a metal pipe is different from Example 1 in that the hollow inside the pipe is directly subjected to hot bending, thereby improving the problem that the aluminum alloy pipe is difficult to form at room temperature, but there is no filling material in the pipe blank to provide support for the pipe wall, and quality problems such as wrinkling and cross-sectional distortion are prone to occur. Heat-expandable graphite is used as a filler to bend the metal pipe. Under the same heating conditions, the heat-expandable graphite absorbs heat and expands, effectively supporting the inner wall of the pipe blank, preventing the occurrence of wrinkling and cross-sectional distortion of the pipe blank, and improving the forming quality.

[0094] Comparative Example 2

[0095] A method for hot bending of metal pipes filled with metal particles, schematic diagram of which is shown in Figure 7 and Figure 8 The equipment used includes a separate forming device 6 and a sealing piston 2.

[0096] In this embodiment, the material of the tube blank 1 is aluminum alloy 5A06, the outer diameter of the tube blank 1 is 30 mm, the wall thickness is 1 mm, and the length is 310 mm. The tube blank 1 is made into a part with a bending radius of 100 mm, a bending angle of 90°, and a straight section length of 75 mm at one end. The local heating temperature is 250°C.

[0097] A method for bending a metal pipe filled with metal particles, using the forming device, comprises the following steps:

[0098] Step 1: Forming the metal tube into the required tube blank 1;

[0099] Step 2: Calculate the required volume of metal particles 7 and prepare the metal particles 7 for filling;

[0100] The volume of the bent and deformed portion of the tube blank 1 is calculated to be 100 mL, the process margin is 20 mL, and the amount of metal particles 7 is determined to be 120 mL.

[0101] Step 3: Put metal particles 7 into the part of the tube blank 1 that needs to be bent and deformed, and seal both ends with a sealing piston 2 to obtain a tube blank filled with metal particles;

[0102] Step 4: In a corresponding heating device, the tube blank filled with metal particles is heated to a forming temperature and kept warm to obtain a heated tube blank;

[0103] Step 5: The heated tube blank is bent by a separate forming device 6 to a desired bending angle;

[0104] Step 6: Wait for the device to cool to room temperature;

[0105] Step 7: Pour out the metal particles 7 to obtain parts.

[0106] A method for bending a metal tube filled with metal particles is different from Example 1 in that the filler is metal particles that are bent under heating conditions, and the metal particles are filled into the tube blank in a loose state. During the bending process, due to the discontinuity of the metal particles, it is difficult to ensure uniform support for the tube wall. The metal tube is bent by filling with heat-expanded graphite. The heat-expanded graphite is in powder form at room temperature, and the gap between the substances is small. The heat-expanded graphite itself expands when heated during the forming process, and expands in a closed tube blank and squeezes each other to provide support for the tube. Compared with the discontinuity of the metal particles, the heat-expanded graphite can be regarded as a continuous state after expansion, and can provide uniform support for the tube blank without applying additional pressure, which can further improve the forming quality.

[0107] Comparative Example 3

[0108] A method for bending a metal tube filled with a low melting point alloy, as shown in the schematic diagram Fig. 9 and Fig.10 The equipment used includes a separate forming device 6 and a sealing device, and the sealing device is a solid wax block 9.

[0109] In this embodiment, the material of the tube blank 1 is titanium alloy TA1, the outer diameter of the tube blank 1 is 30 mm, the wall thickness is 1 mm, and the length is 310 mm. The tube blank 1 is made into a part with a bending radius of 100 mm, a bending angle of 90°, and a straight section length of 75 mm at one end.

[0110] A method for bending a metal pipe filled with a low melting point alloy, using the forming device, comprises the following steps:

[0111] Step 1: Forming the metal tube into the required tube blank 1;

[0112] Step 2: Place the tube blank 1 vertically and seal the lower end with a solid wax block 9;

[0113] Step 3: placing the low melting point alloy 8 in a beaker and heating it to a molten state, injecting the low melting point alloy 8 into the tube blank 1 until it reaches the tube mouth, and waiting for the low melting point alloy 8 to completely cool and solidify;

[0114] Step 3: The tube blank 1 is bent by a separate forming device 6 to reach a desired bending angle;

[0115] Step 4: Take down the part, remove the solid wax block 9, and heat the part until the low melting point alloy 8 in the part is melted;

[0116] Step 6: Remove the low melting point alloy 8 to obtain the parts.

[0117] A method for bending a metal tube filled with a low melting point alloy is different from Example 3 in that the low melting point alloy is filled in the tube, and the characteristics of the low melting point alloy are utilized to inject the tube blank in a molten state, and the tube blank is removed by heating after forming, which does not damage the tube blank and has a supporting force on the tube wall after solidification. However, due to the heat resistance of the low melting point alloy, this method is mostly used for bending tubes at room temperature. Using heat-expandable graphite as a filler can achieve different temperature heating according to different materials, improve the plastic deformation ability of the tube blank, and the heat-expandable graphite in the tube absorbs heat and expands to achieve a better supporting effect.

[0118] Comparative Example 4

[0119] A method for hot bending a metal pipe using heat-expandable graphite as a filler, which is the same as Example 1, except that:

[0120] The forming temperature of the tube (aluminum alloy 5A06) was determined to be 250°C, and thermal expansion graphite with an initial expansion temperature of 300°C was selected.

[0121] During the static heating process, the temperature is 250°C, and the volume of the thermal expansion graphite does not change. When the temperature is 300°C, the expansion ratio of the thermal expansion graphite is 1.1 times. When this thermal expansion graphite is filled into the tube blank, during the forming process, because the thermal expansion graphite does not expand to reach the initial expansion temperature, it cannot provide sufficient support for the tube blank, and uneven wrinkling occurs after the tube blank is formed.

[0122] Comparative Example 5

[0123] A method for hot bending a metal pipe using heat-expandable graphite as a filler, which is the same as Example 3, except that:

[0124] The forming temperature of the tube blank (titanium alloy TA1) was determined to be 550°C, and thermal expansion graphite with an initial expansion temperature of 500°C was selected.

[0125] During the static heating process, when the temperature is 500℃, the expansion ratio of the heat-expanded graphite is 1.1 times, and when the temperature is 550℃, the expansion ratio of the heat-expanded graphite is 2.5 times. When this heat-expanded graphite is filled into the tube blank, during the forming process, because the temperature difference between the initial expansion temperature of the heat-expanded graphite and the forming temperature of the tube blank is 50℃, the pressure generated by the heat-expanded graphite in the tube blank is greater than the pressure required for the plastic forming of the tube blank. At this time, the expansion force of the heat-expanded graphite is too large, and the pressure in the tube blank is high, which leads to an increase in the diameter of the tube and plastic deformation.

[0126] Comparative Example 6

[0127] A method for hot bending a metal pipe using heat-expandable graphite as a filler, which is the same as Example 1, except that:

[0128] The volume of thermal expansion graphite required. The specific calculation method is: the volume corresponding to the bending deformation part of the tube blank required + process allowance = the volume of thermal expansion graphite. The process allowance is 1 / 2 of the volume of the deformation part. The calculation method for the required volume of thermal expansion graphite is: the volume of the bending deformation part of the tube blank is calculated to be 100mL, the process allowance is 50mL, and the amount of thermal expansion graphite is determined to be 150mL.

[0129] Filling an appropriate amount of thermal expansion graphite provides support for the tube wall during the forming process. The amount of thermal expansion graphite reaches the corresponding volume of the bent and deformed part, and the process margin is increased to 1 / 5 of the corresponding volume. The tube forming tends to be stable and the wrinkling phenomenon is significantly reduced. As the amount of thermal expansion graphite continues to increase, the tube forming effect is not significantly improved, and the production cost is increased.

Claims

1. A method for hot bending a metal pipe using heat-expandable graphite as a filler, characterized in that: Fill the metal tube to be bent with thermal expansion graphite, the initial expansion temperature of the filled thermal expansion graphite is within 20°C of the forming temperature of the metal tube to be bent; the volume of the added thermal expansion graphite is calculated as follows: the volume corresponding to the bending deformation part of the tube blank required + the process margin = the volume of the thermal expansion graphite; wherein the process margin is 1 / 5 of the volume corresponding to the bending deformation part of the tube blank required; The method comprises the following steps: Step 1: Blank making Forming metal pipes into required pipe blanks; Step 2: Determine the type and amount of thermal expansion graphite Determine the type of thermal expansion graphite according to the forming temperature and material properties of the tube blank, ensure that the initial expansion temperature of the thermal expansion graphite is less than the forming temperature of the tube blank, and the tube blank is not scratched during the bending process; Calculate the required volume of thermal expansion graphite and prepare the thermal expansion graphite for filling; Step 3: Filling Putting heat-expandable graphite into the part of the tube blank that needs to be bent and deformed, and sealing both ends of the part filled with the heat-expandable graphite to obtain a tube blank filled with the heat-expandable graphite; Step 4: Heating and insulation The whole or a local area of ​​the tube blank filled with heat-expandable graphite is heated to the forming temperature of the tube blank and kept warm to obtain a heated tube blank; Step 5: Bending and deformation Bending the heated tube to a desired bending angle; Step 6: Stop heating Stop heating and let the temperature cool to room temperature; Step 7: Take out the thermal expansion graphite Take out the thermal expansion graphite to obtain the bent metal pipe parts; In the step 2, the volume of the required heat-expandable graphite is determined according to the volume corresponding to the required bending deformation portion of the tube blank; The thermal expansion graphite is prepared by acid washing of natural graphite flakes with acidic substances or by oxidation intercalation with strong oxidizing substances. The initial expansion temperature of the thermal expansion graphite is from 150°C to 800°C.

2. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the step 1, the method used for blank making is one of wire cutting and laser cutting.

3. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the step 2, the initial expansion temperature of the heat-expandable graphite is the lowest temperature at which the heat-expandable graphite starts to expand during the static heating process, and the measurement method is specifically: measuring the volume of the heat-expandable graphite during the heating process, and the temperature at which the volume of the heat-expandable graphite after expansion reaches 1.1 times the volume before expansion is taken as the initial expansion temperature of the heat-expandable graphite.

4. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the tube bending forming, the starting expansion temperature of the selected heat-expandable graphite is lower than the forming temperature of the tube blank, the starting expansion temperature of the heat-expandable graphite is within 20°C of the forming temperature of the tube blank, and the expansion force generated by the heat-expandable graphite is ≤ the pressure required for the plastic deformation of the tube.

5. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the step 4, the heating temperature set by the heating device is the forming temperature of the tube blank and the tube blank is kept warm, wherein the forming temperature of the tube blank and the holding time after forming are determined by the material properties of the metal tube blank.

6. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the step 4, the following methods are selected to heat the tube blank: one is a heating and forming integrated device, that is, the heating device is directly arranged inside the forming device, and the heating, insulation and forming of the tube blank are directly completed on the heating and forming integrated device; the other is a heating and forming separate device including a heating device and a separate forming device, the heating process and the forming process are carried out independently, and the tube blank is heated and then transferred to a separate forming device for bending and forming.

7. The method for hot bending a metal pipe using heat-expandable graphite as a filler according to claim 1, characterized in that: In the step 5, the bending is selected from one of bending around, pushing or pulling.

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