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CN-121972558-A - Forming method of axially-assisted thin-wall pipe fitting thermal expansion graphite

CN121972558ACN 121972558 ACN121972558 ACN 121972558ACN-121972558-A

Abstract

An axial auxiliary thin-wall pipe thermal expansion graphite forming method belongs to the technical field of metal pipe precise forming. The invention selects thermal expansion graphite with different performances at the inner part and the two end parts of the thin-wall pipe fitting, and provides internal pressure for forming the thin-wall pipe fitting and load required by feeding the axial end parts by utilizing different thermal expansion effects and generated thermal-force performances of the thermal expansion graphite under a certain temperature condition, thereby realizing near-equal wall thickness and high-quality forming of the parts. The method provided by the invention has the advantages of simple structure of the die, convenient process operation and the like, and has stronger engineering application and popularization values in the aspects of forming thin-wall pipe fittings in the fields of aerospace, machinery, automobiles and the like.

Inventors

  • GAO TIEJUN
  • LIU YU
  • DENG XIWEN
  • CHEN ZIHANG
  • YANG DAYONG

Assignees

  • 沈阳航空航天大学

Dates

Publication Date
20260505
Application Date
20260130

Claims (10)

  1. 1. The forming method of the axially auxiliary thin-wall pipe fitting thermal expansion graphite is characterized by comprising the following steps of: step 1, determining the length of a tube blank according to the shape and the size of a target thin-wall tube and the deformation; Step 2, selecting thermal expansion graphite I and thermal expansion graphite II with initial expansion temperature and complete expansion temperature matched with the tube blank material and the thermal forming temperature, and respectively filling graphite into the tube blank and the tube blank end, wherein the expansion rate and the volume of the thermal expansion graphite I are matched with the deformation of the tube blank, and the expansion rate and the volume of the thermal expansion graphite II are matched with the end material supplementing quantity required by tube blank forming; Step 3, filling the thermal expansion graphite I into the tube blank, placing rigid sealing pistons on two sides of the tube blank, then placing the rigid sealing pistons together with the tube blank filled with the thermal expansion graphite I into a preset position in a cavity of a rigid die integrally, and closing the die; Step 4, filling thermal expansion graphite II required by the end part of the tube blank into two ends of a cavity of a rigid die, fixing a rigid plug on the end face of the die, and sealing through the rigid plug; Step 5, heating the rigid die to initial expansion temperatures of the thermal expansion graphite I and the thermal expansion graphite II, and expanding the thermal expansion graphite I in the tube blank to start increasing the diameter of the tube blank; step 6, continuously heating the rigid die to the thermal forming temperature of the tube blank and preserving heat until the tube blank is completely attached to the cavity of the rigid die; and 7, stopping heating, cooling to room temperature, opening the die, and taking out the thermal expansion graphite I and the thermal expansion graphite II to obtain the formed target thin-wall pipe fitting.
  2. 2. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 1, the length of the pipe blank consists of the length required by forming the part and the process allowance; Wherein the process allowance is 4% -6% of the length required by part forming.
  3. 3. The method for forming the axially auxiliary thin-walled pipe fitting by thermal expansion graphite according to claim 1, wherein in the step 2, the initial expansion temperature and the complete expansion temperature of the thermal expansion graphite I are respectively the same as the initial expansion temperature and the complete expansion temperature of the thermal expansion graphite II, the initial expansion temperature is 100 ℃ or more lower than the tube blank thermoforming temperature, and the complete expansion temperature is 150 ℃ or more higher than the tube blank thermoforming temperature.
  4. 4. The method for forming the thermal expansion graphite of the axially auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 2, the expansion ratio of the thermal expansion graphite I in a free state is more than 50 times of the deformation amount of a pipe blank, and the filling volume of the thermal expansion graphite I is 1.1-1.5 times of the corresponding volume of a deformation area of the pipe blank.
  5. 5. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 2, the expansion rate of the thermal expansion graphite II in a free state is more than 80 times of the deformation of a pipe blank, and the single-side filling volume of the thermal expansion graphite II in a die cavity at two sides of the pipe blank is 8-12 times of the corresponding cavity volume of the single-side feeding length of the end part, and can be equivalently that the single-side filling length of the thermal expansion graphite II is 8-12 times of the single-side axial feeding length of the end part.
  6. 6. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 3, the rigid sealing piston is in a stepped structure or a follow-up structure matched with the cross section of the pipe blank, one end of the rigid sealing piston has the same diameter as the inner diameter of the pipe blank and is arranged in the pipe blank, and the other end of the rigid sealing piston has the same diameter as the outer diameter of the pipe blank; the specified position is a preset positioning area in the rigid mold cavity, and the positioning area is arranged at the geometric symmetry center of the mold cavity or at a corresponding preset position in the mold cavity according to the specific forming process.
  7. 7. The method for forming the thermal expansion graphite of the axially auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 4, the inner diameter of the rigid plug is the same as the outer diameter of the pipe blank, the outer diameter of the rigid plug is the same as or similar to the contour of the end face of the die, and the rigid plug is fixed on the end face of the die through bolts or other fastening modes, so that reliable end sealing and supporting are formed in the closed state of the die, and the thermal expansion graphite II filled at the two ends of the pipe blank is prevented from overflowing in the thermal expansion process.
  8. 8. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 5, a heating device adopts an internal electric heating element of a die or an external heating furnace of the die to heat, the temperature of a region corresponding to the internal thermal expansion graphite I of the pipe blank and the temperature of a region corresponding to the end thermal expansion graphite II are the same, or different temperatures are applied by adopting zonal temperature control.
  9. 9. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 6, heating and heat preservation time is 30-60 min.
  10. 10. The method for forming the thermal expansion graphite of the axial auxiliary thin-wall pipe fitting according to claim 1, wherein in the step 7, natural cooling or air cooling is adopted for cooling to room temperature; And after cooling, sequentially disassembling the rigid plug, opening the rigid mold, removing the thermal expansion graphite II at the two ends of the thin-wall pipe fitting, disassembling the rigid sealing piston, and removing the thermal expansion graphite I in the thin-wall pipe fitting to obtain the target thin-wall pipe fitting.

Description

Forming method of axially-assisted thin-wall pipe fitting thermal expansion graphite Technical Field The invention belongs to the technical field of metal pipe fitting precision forming, in particular to an axial auxiliary thin-wall pipe fitting thermal expansion graphite forming method, which comprises the steps of selecting thermal expansion graphite with different performances in the thin-wall pipe fitting and at two end parts, the internal pressure for forming the thin-wall pipe and the load required by the axial end part feeding are provided by utilizing different thermal expansion effects and generated thermal-force performances under a certain temperature condition, so that the near-equal wall thickness and high-quality forming of the part are realized. Background The thin-wall pipe fitting has the advantages of compact structure, light weight, strong bearing capacity and the like, and is widely applied to the fields of aviation, aerospace, automobiles and the like. Currently, in order to improve the forming quality and wall thickness distribution uniformity of such parts, forming is mainly performed under the combined action of the internal pressure of the tube blank and the axial load of the end part. For metal pipe fittings with better plasticity or smaller deformation, a liquid or flexible medium internal pressure forming method under normal temperature condition is mostly adopted. For metal pipe fittings with poor plasticity or large deformation, the rupture of the forming process and the improvement of the uniformity of wall thickness are required to be prevented by an axial feeding method in the internal pressure forming process, for example, a method for forming metal pipe fittings by establishing pressure inside a pipe blank through a liquid medium and matching with an external axial loading device is disclosed in Chinese patent (patent application number: CN00208694.8, publication number: CN2427399Y, publication date 2001.04.25). In addition, for example, chinese patent No. CN200910227958.3, publication No. CN101722225A, publication No. 2010.06.09 discloses a metal pipe fitting forming method using rubber or polyurethane core to bear liquid pressure, and the pipe fitting is formed under the combined action of internal pressure and axial feeding by arranging external actuating mechanisms at two ends of the pipe fitting to push inwards. At present, with the increase of application requirements of difficult-to-deform materials such as high-strength steel, titanium alloy and the like, the forming of the parts is difficult to meet at room temperature, a pipe blank is required to be heated to a certain temperature to be formed by means of the high-temperature softening effect of the materials, hot fluid or hot gas forming and the like are derived on the basis, and meanwhile, the complex shape forming is realized by matching with the axial feeding of the end part. For example, chinese patent (CN 201410741143.8, publication No. CN104525676A, publication No. 2015.04.22) proposes a hot forming process of boron steel tube, which uses high-temperature high-pressure gas or liquid system and realizes synchronous matching of internal pressure and axial force with external actuator to form boron steel tube blank. The thermal expansion graphite as one new kind of carbon material is prepared through artificial synthesis of natural graphite flake and through inserting other molecules, atoms and ions between them, and has the advantages of high heat resistance, homogeneous heat conduction, etc. in addition, the thermal expansion graphite intercalation material in certain temperature condition, called initial expansion temperature, absorbs heat and evaporates fast to produce thrust force to the graphite flake structure, so that the volume is expanded greatly and reaches the maximum value at full expansion temperature and expansion rate of tens to hundreds times in free state. At present, the thermal expansion graphite is mainly applied to sealing, flame retardance, adsorption and other aspects of materials, and can be used as a force transfer medium and a filling medium in sheet metal forming and pipe bending. In addition, the high-temperature expansion effect of the thermal expansion graphite can be used for thermal forming of pipe parts, such as the thermal forming method of metal pipe fittings with complex shapes (application number CN202311267897.X, publication number CN117259551A, publication date 2023.12.22) of Chinese patent, the method simplifies the form of forming medium to a certain extent, but still the external loading device is needed to match the internal pressure with the axial force to form the pipe blanks. Disclosure of Invention In order to facilitate operation and simplify process flow, the invention provides the method for forming the axial auxiliary thin-wall pipe fitting by using the thermal expansion graphite, wherein in the forming process, the axial load at the end part and the interna