A needle for extrusion forming of a pipe with variable internal diameter, a device and a method for extrusion forming

Abstract

The application discloses a kind of unequal inner diameter pipe extrusion forming needle tip, device and extrusion forming method, it is related to metal pipe extrusion forming technical field, including needle tip main body, needle tip main body includes the sizing section for the sizing of pipe inner diameter, sizing section includes main sizing band and vice sizing band, vice sizing band is set to one side of main sizing band along axial direction, when main sizing band is separated from effective working position along predetermined axial offset direction, vice sizing band can enter effective working position;The diameter of vice sizing band is not greater than the diameter of main sizing band, and the diameter difference between vice sizing band and main sizing band is not greater than the allowable deviation value of pipe target inner diameter corresponding to main sizing band.The technical scheme effectively solves the problem that the main sizing band is separated from effective working position due to axial position deviation when needle tip moves along axial direction during forming process, and causes pipe inner diameter sizing failure.

Description

Technical Field

[0001] This invention relates to the field of metal pipe extrusion molding technology, and in particular to an extrusion molding needle tip, apparatus and extrusion molding method for pipes with unequal inner diameters. Background Technology

[0002] Large-diameter aluminum alloy non-uniform cross-section pipes used in drilling, high-pressure fluid transportation, and other fields often employ an unequal inner diameter structure with a uniform outer diameter throughout the length and smaller inner diameters at both ends and a larger inner diameter in the middle, in order to achieve threaded connections at the ends and reduce weight. These pipes are typically formed directly in a single extrusion process using a double-action extrusion press with an independent piercing system and an extrusion needle method. The needle tip moves axially relative to the die to change the die orifice, and sizing bands of different diameters on the needle tip sequentially enter the effective working position, thus forming pipe sections with different inner diameters.

[0003] To obtain pipe sections with different inner diameters, the needle tip typically has two or more stages of sizing bands of different diameters and transition slopes. The sizing bands are paired with the die for sizing by the needle tip moving forward or backward relative to the die. However, during the extrusion process, the needle tip is subjected to complex and time-varying forces, making it difficult to guarantee its positioning accuracy relative to the die. If the control is inaccurate or the needle tip retracts excessively, the sizing band, which should be in an effective working position, will disengage, causing the sizing of the corresponding pipe section to fail. Existing solutions mainly focus on improving the accuracy of the control system, such as using a high-frequency response proportional servo valve for synchronous control to suppress needle tip displacement overshoot. However, these systems are complex, costly, and still cannot solve the problem of needle tip positioning deviation. Summary of the Invention

[0004] This invention provides a needle tip, device, and extrusion molding method for pipes with unequal inner diameters, aiming to solve the technical problem that the main sizing zone fails to sizing the inner diameter of the pipe due to axial position deviation when the needle tip moves axially during the molding process.

[0005] To achieve the above objectives, the first aspect of the present invention provides a needle tip for extruding pipes with unequal inner diameters, comprising a needle tip body, the needle tip body including a sizing section for sizing the inner diameter of the pipe, the sizing section including a main sizing band and a secondary sizing band, the secondary sizing band being axially disposed on one side of the main sizing band, the secondary sizing band being able to enter the effective working position when the main sizing band is displaced from the effective working position in a predetermined axial offset direction, the diameter of the secondary sizing band not being greater than the diameter of the main sizing band, and the diameter difference between the secondary sizing band and the main sizing band not being greater than the allowable deviation value of the target inner diameter of the pipe corresponding to the main sizing band.

[0006] By adding a secondary sizing band to the sizing section of the needle tip body at an axially adjacent position to the main sizing band, and ensuring that the diameter of the secondary sizing band is no greater than that of the main sizing band, the secondary sizing band does not interfere with the inner diameter of the pipe when the main sizing band is in an effective working position. When the main sizing band deviates from its axial position or leaves its effective working position due to complex forces on the needle tip body or inaccurate control during the extrusion process, and is unable to sizing the inner diameter of the pipe, the adjacent secondary sizing band connects to sizing the inner diameter of the pipe. At the same time, since the diameter difference between the secondary sizing band and the main sizing band is no greater than the allowable deviation value of the target inner diameter of the pipe corresponding to the main sizing band, the secondary sizing band can also control the inner diameter of the pipe within the allowable deviation value, reducing the risk of pipe scrap due to positioning deviation of the needle tip body.

[0007] By setting a secondary sizing belt, the precision requirements for the movement control of the needle tip are reduced, thereby simplifying the extrusion equipment and control system and reducing equipment costs.

[0008] Preferably, the secondary sizing band is tapered, the large-diameter end of the secondary sizing band is connected to the main sizing band, and the diameter of the large-diameter end is the same as the diameter of the main sizing band. The difference between the diameter of the small-diameter end of the secondary sizing band and the diameter of the main sizing band is not greater than the allowable deviation value of the target inner diameter of the pipe corresponding to the main sizing band.

[0009] The secondary sizing band is tapered, with its large-diameter end connecting to the main sizing band and having the same diameter, ensuring a smooth connection between the two bands and facilitating metal flow. When the secondary sizing band enters the effective working position, the inner diameter of the pipe is slightly smaller than the target inner diameter, but the deviation is within the allowable range, maintaining its sizing function even if the needle tip body deviates from its movement. Furthermore, the tapered shape of the secondary sizing band minimizes the axial movement deviation of the needle tip body, resulting in a diameter closer to the main sizing band at the effective working position and a smaller deviation between the inner diameter of the formed pipe and the target pipe inner diameter.

[0010] Preferably, the main sizing zone includes a first main sizing zone and a second main sizing zone, and a second guide slope connects the first main sizing zone and the second main sizing zone. The sizing section further includes a first guide slope. The first guide slope, the first main sizing zone, the second guide slope, the second main sizing zone and the secondary sizing zone are arranged sequentially along the axial direction. The small-diameter end of the first guide slope is connected to the first main sizing belt and has the same diameter; The large-diameter end of the second guide slope is connected to the first main sizing belt and has the same diameter, and the small-diameter end of the second guide slope is connected to the second main sizing belt and has the same diameter. The diameter of the first main sizing belt is larger than the diameter of the second main sizing belt; The large-diameter end of the secondary sizing belt is connected to the second main sizing belt and has the same diameter.

[0011] The first and second main sizing zones correspond to the large and small inner diameter sections of the pipe, respectively. This allows the needle tip body to sizing different inner diameter sections of the pipe as it moves between the front and rear positions. Furthermore, the guide slope forms a transition section with a gradually changing inner diameter during the movement of the needle tip body, making the inner diameter dimensions of each section of the pipe controllable.

[0012] The second aspect of the present invention provides an extrusion molding apparatus for tubular materials with unequal inner diameters, including the extrusion molding needle tip for tubular materials with unequal inner diameters as described in the first aspect, and further including a needle seat, an extrusion shaft, an extrusion needle, an extrusion pad, an extrusion cylinder, and a mold assembly; The extrusion shaft passes through the extrusion cylinder, and the extrusion shaft has a through hole along its central axis. The extrusion needle passes through the through hole of the extrusion shaft. One end of the extrusion needle is connected to the needle seat, and the needle tip body is assembled to the other end of the extrusion needle; The die assembly is disposed at one end of the extrusion cylinder, the extrusion pad is disposed inside the extrusion cylinder and located between the extrusion shaft and the billet, and the extrusion needle extends through the extrusion pad into the die assembly; The extrusion needle and the needle tip body are axially movable relative to the mold assembly to change the axial relative position of the needle tip body and the mold assembly.

[0013] The needle seat, extrusion shaft, extrusion needle, extrusion pad, extrusion cylinder and die assembly constitute a complete forming structure. The extrusion needle and needle tip body can move axially relative to the die assembly, so that the shape or size of the die hole can change during the extrusion process, thereby directly extruding and forming non-uniform cross-section tubes.

[0014] Preferably, the needle tip body further includes an assembly section, which is provided with a first assembly cone surface, a positioning boss, a tool relief groove and a connecting thread in sequence along the axial direction; The end face of the extrusion needle is provided with a conical hole that is adapted to the first mounting conical surface. The first mounting conical surface and the conical hole cooperate to make the needle tip body and the extrusion needle coaxially positioned. The diameter of the positioning boss is larger than the diameter of the connecting thread; The tool relief groove is disposed between the positioning boss and the connecting thread, and the diameter of the tool relief groove is smaller than the minor diameter of the connecting thread; The connecting thread is threaded to the internal thread of the extrusion needle.

[0015] The first assembly tapered surface mates with the tapered hole on the end face of the extrusion needle, and a positioning boss is engaged to achieve coaxial positioning of the needle tip body and the extrusion needle. The connecting thread makes the needle tip body and the extrusion needle rigidly connected. The sizing position of the needle tip body is stable during axial movement, which helps to maintain the consistency of the inner diameter of the pipe.

[0016] Preferably, the mold assembly includes a mold sleeve, a mold, and a mold pad; The mold and the mold pad are assembled inside the mold sleeve, which supports the mold and the mold pad. The mold pad is located on the side of the mold away from the extrusion cylinder and is used to axially limit the mold.

[0017] The mold and mold pad are assembled inside the mold sleeve and supported by the mold sleeve, which helps to maintain the rigidity of the mold. The mold pad axially limits the mold, making the mold stable in position during extrusion, which helps to maintain the stability of the mold hole size and improve the consistency of the outer diameter of the pipe.

[0018] Preferably, the inner hole of the mold is provided with a third main sizing band, which is used to sizing the outer diameter of the pipe; The third main sizing band and the main sizing band of the needle tip body are arranged opposite each other in the radial direction, and the gap between the third main sizing band and the main sizing band of the needle tip body forms a mold hole.

[0019] The gap between the third main sizing zone and the main sizing zone of the needle tip body forms the mold hole. The outer diameter and inner diameter of the tube are determined by the third main sizing zone and the main sizing zone of the needle tip body, respectively, and the forming size is controllable.

[0020] Preferably, the inner hole of the mold is further provided with a first empty cutter and a second empty cutter along the axial direction, and the first empty cutter and the second empty cutter are located on the discharge side of the third main sizing zone and arranged sequentially along the axial direction; The diameter of the first empty cutter is greater than the diameter of the third main sizing band, and the diameter of the second empty cutter is greater than the diameter of the first empty cutter.

[0021] The first and second empty cutters are located on the discharge side of the third main sizing zone, and their diameters increase gradually. This ensures that the die has sufficient axial length to guarantee its rigidity and strength, while also providing clearance for the pipe to pass through the die, reducing friction between the pipe and the die, and facilitating the smooth passage of the pipe through the die.

[0022] A third aspect of the present invention provides a method for extruding tubing with unequal inner diameters, using the extrusion molding apparatus described in the second aspect, comprising the following steps: Place the billet into the extrusion cylinder, place the die assembly against one end of the extrusion cylinder, insert the extrusion pad from the other end of the extrusion cylinder, pass the extrusion needle equipped with the needle tip body through the extrusion pad and the billet, and extend the needle tip body into the die assembly to the rear position of the needle. Keep the needle tip body in the rear position of the needle, so that the second main sizing band of the needle tip body cooperates with the third main sizing band of the mold to form a mold hole, the extrusion shaft pushes the extrusion pad to extrude the ingot, and the ingot metal flows out through the mold hole to form the first small inner diameter section; When the length of the first small inner diameter section reaches the preset length, the extrusion shaft stops extruding and advances the needle tip body along the extrusion direction to the front position of the needle. During the advance of the needle tip body, the second guide slope of the needle tip body cooperates with the third main sizing band of the mold to form a mold hole with gradually changing size, forming the first transition section. Keep the needle tip body in the front position of the needle, so that the first main sizing band of the needle tip body cooperates with the third main sizing band of the mold to form a mold hole, and the extrusion shaft continues to extrude and form a large inner diameter section; When the length of the large inner diameter section reaches the preset length, the extrusion shaft continues to extrude, and the needle tip body is retracted to the rear position in the opposite direction of the extrusion direction. During the retraction of the needle tip body, the second guide slope of the needle tip body cooperates with the third main sizing band of the mold to form a mold hole with gradually changing size, forming the second transition section. Keep the needle tip body in the rear position of the needle, so that the second main sizing band of the needle tip body cooperates with the third main sizing band of the mold to form a mold hole, and the extrusion shaft continues to extrude to form the second small inner diameter section; The inner diameters of the first small inner diameter segment and the second small inner diameter segment are smaller than the inner diameter of the large inner diameter segment, and the inner diameters of the first transition segment and the second transition segment gradually change along the axial direction.

[0023] The above method moves the needle tip body during the extrusion process, changes the relative position of the needle tip body and the die, and causes the die hole size to change in segments, sequentially forming the first small inner diameter segment, the first transition segment, the large inner diameter segment, the second transition segment and the second small inner diameter segment. This directly obtains a non-uniform cross-section tube with unequal inner diameters and large inner diameters at both ends, without the need for machining the tube, thus reducing metal waste and processing costs.

[0024] Preferably, after the second small inner diameter section is formed, the needle tip body is advanced along the extrusion direction to the front position of the needle, and the extrusion shaft continues to extrude to form a process section, so as to consume the axial length of the billet residue in the extrusion cylinder to a preset length range.

[0025] After the second small inner diameter section is formed, the needle tip body advances and continuously extrudes to form the process section, consuming the remaining billet material in the extrusion cylinder to the preset length range, so that the axial length of the remaining billet material in the cylinder after the extrusion ends meets the operation requirements of the subsequent separation equipment, avoiding interference between the separation equipment and the remaining billet material when separating the extrusion pad. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of the pipe with unequal inner diameter provided in an embodiment of the present invention.

[0028] Figure 2 This is an exploded view of the extrusion molding apparatus provided in an embodiment of the present invention.

[0029] Figure 3 This is a front sectional view of the extrusion molding apparatus provided in an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the extrusion shaft provided in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the extrusion needle provided in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the structure of the needle tip body provided in an embodiment of the present invention.

[0033] Figure 7 This is a schematic diagram of the structure of the extrusion pad provided in an embodiment of the present invention.

[0034] Figure 8 This is a front sectional view of the mold provided in an embodiment of the present invention.

[0035] Figure 9 This is a schematic diagram of the extrusion molding apparatus provided in an embodiment of the present invention during the molding of the first small inner diameter section.

[0036] Figure 10 This is a schematic diagram of the extrusion molding apparatus provided in an embodiment of the present invention when molding a large inner diameter section.

[0037] Figure 11 This is a schematic diagram of the extrusion molding apparatus provided in an embodiment of the present invention when molding the second small inner diameter section.

[0038] Figure 12 This is a schematic diagram of the extrusion molding apparatus provided in the embodiment of the present invention during the molding process.

[0039] Explanation of reference numerals in the attached figures: 1. Needle tip body, 2. Sizing section, 3. Main sizing band, 4. Secondary sizing band, 5. First guide slope, 6. First main sizing band, 7. Second guide slope, 8. Second main sizing band, 9. Chamfer, 10. Needle seat, 11. Extrusion shaft, 12. Extrusion needle, 13. Extrusion pad, 14. Extrusion cylinder, 15. Mold assembly, 16. Limiting platform, 17. Guide sleeve, 18. Nut, 19. Assembly section, 20. First assembly cone surface, 21. Positioning boss, 22. Relief groove, 23. Connecting thread, 24. Loading and unloading section, 25. Round hole, 26. Mold sleeve, 27. Mold pad, 28. Third main sizing band, 29. Mold hole, 30. First empty cutter, 31. Second empty cutter, 32. First small inner diameter section, 33. First transition section, 34. Large inner diameter section, 35. Second transition section, 36. Second small inner diameter section, 37. Process section, 38. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] This invention is applicable to the extrusion production of non-uniform cross-section tubes with unequal inner diameters from metals such as aluminum and aluminum alloys, and magnesium and magnesium alloys, especially suitable for the extrusion production of high-strength aluminum alloys. Exemplarily, a non-uniform cross-section tube with unequal inner diameters refers to a tube with a smaller inner diameter at both ends, a larger inner diameter in the middle, and a consistent outer diameter throughout its length. This tube is mainly used in drilling, fluid transport, and other scenarios where adjacent tube parts forming long-distance pipelines require threaded connections to flexibly extend or shorten the total pipeline length while ensuring overall pipeline strength and extending pipeline service life. Since threads need to be machined at both ends of each tube section, the wall thickness at both ends needs to be increased to ensure strength. The tube formed by this invention only increases the wall thickness at both ends, maintaining a smaller wall thickness in the middle section, thus reducing the weight of the tube while meeting the strength requirements of the threaded connection. Exemplarily, the cross-section of the tube can be circular or rectangular, etc. The following explanation uses a tube with a circular cross-section as an example.

[0043] The following are some embodiments of the extrusion molding of needle tips for tubular materials with unequal inner diameters according to the present invention.

[0044] In some embodiments, reference Figure 2 and Figure 6The needle tip for extruding pipes with unequal inner diameters includes a needle tip body 1. The needle tip body 1 is used to determine the inner cavity shape and inner diameter of the pipe. Its structure is generally in the form of a rotating body. For example, the needle tip body 1 is provided with a sizing section 2 along the axis of its rotating body. The sizing section 2 is used to sizing the inner diameter of the pipe.

[0045] The sizing section 2 includes a main sizing band 3 and a secondary sizing band 4, with the secondary sizing band 4 axially positioned on one side of the main sizing band 3. During pipe forming, the inner metal of the pipe is constrained by the main sizing band 3, and the size of the main sizing band 3 determines the inner diameter of the pipe. When the main sizing band 3 is in an axial position capable of sizing the inner diameter of the pipe flowing out of the die 30, this position is called the effective working position. When extruding non-uniform cross-section pipes with unequal inner diameters, the needle tip body 1 needs to move axially during a complete extrusion process to change the shape or size of the die 30, thereby resulting in a non-uniform cross-section of the obtained pipe along the axial direction. The movement of the needle tip body 1 is achieved through manipulation. If there is a deviation in the manipulation, the needle tip body 1 may retract too far, causing the main sizing band 3 to disengage from the effective working position along the predetermined axial offset direction. The inner diameter of the pipe will lose its sizing constraint, and without other constraints, pipe forming will fail.

[0046] The secondary sizing belt 4 is used to take over the sizing function when the primary sizing belt 3 leaves its effective working position. When the primary sizing belt 3 leaves its effective working position along a predetermined axial offset direction, the secondary sizing belt 4 can enter its effective working position to continue sizing the pipe's inner diameter. The diameter of the secondary sizing belt 4 is not greater than the diameter of the primary sizing belt 3, and the difference between the diameters of the secondary sizing belt 4 and the primary sizing belt 3 is not greater than the allowable deviation value of the pipe's target inner diameter. The target inner diameter of the pipe refers to the inner diameter of the pipe corresponding to the primary sizing belt 3. The allowable deviation value of the target inner diameter of the pipe refers to the range within which the inner diameter of the pipe is allowed to deviate from the target value, i.e., the dimensional tolerance of the inner diameter of the pipe. Since the diameter of the secondary sizing belt 4 is not greater than the diameter of the primary sizing belt 3, when the secondary sizing belt 4 is in its effective working position, the inner diameter of the pipe will be slightly smaller than the target inner diameter, but the deviation can be controlled within the allowable tolerance range, and the product can still be delivered for use. The secondary sizing belt 4 mitigates the adverse consequences caused by the primary sizing belt 3 leaving its effective working position in this way.

[0047] For example, when the needle tip body 1 retracts, the main sizing belt 3 shifts in the opposite direction to the extrusion direction, and the secondary sizing belt 4 is positioned on the side of the main sizing belt 3 away from the extrusion direction. During the retraction of the needle tip body 1, after the main sizing belt 3 disengages from its effective working position, the secondary sizing belt 4 immediately enters its effective working position. It should be noted that the specific position of the secondary sizing belt 4 can be determined according to the movement method of the needle tip body 1, as long as the secondary sizing belt 4 can enter its effective working position when the main sizing belt 3 disengages from its effective working position.

[0048] In some embodiments, reference Figure 6The secondary sizing band 4 is tapered. Its large-diameter end connects to the main sizing band 3, and the diameter of the large-diameter end is the same as that of the main sizing band 3. This ensures a smooth connection between the secondary sizing band 4 and the main sizing band 3, allowing for continuous change in cross-sectional dimensions as the metal flows through this point, resulting in a stable and smooth metal flow. The diameter of the small-diameter end of the secondary sizing band 4 is not greater than the diameter of the main sizing band 3, and the difference between the small-diameter end and the main sizing band 3 is not greater than the allowable deviation value of the target inner diameter of the pipe. In other words, the axial length of the secondary sizing band 4 is greater than the axial length of the effective working position. Regardless of which axial position of the secondary sizing band 4 is in the effective working position, the difference between the inner diameter of the formed pipe and the target inner diameter of the pipe is within the allowable deviation value.

[0049] For example, the smaller diameter of the secondary sizing belt 4 is 0.5 mm to 3 mm smaller than the larger diameter, for example, 1 mm smaller. In one specific embodiment, the larger diameter of the secondary sizing belt 4 is 120 mm and the smaller diameter is 119 mm. The axial length of the secondary sizing belt 4 is, for example, 15 mm to 35 mm, for example, 25 mm. The tapered secondary sizing belt 4 has a tapered surface with a gradually decreasing diameter in the axial direction. When there is a deviation in operation that causes the secondary sizing belt 4 to be in a pre-set effective working position, the secondary sizing belt 4 can still sizing the inner diameter of the pipe. At this time, the inner diameter of the pipe is slightly smaller than the target inner diameter, and the dimensional deviation is within the allowable tolerance range, so the product can still be delivered for use.

[0050] It should be noted that the secondary sizing band 4 is not limited to a tapered shape; it can also be a cylindrical surface of equal diameter, as long as the diameter difference between it and the primary sizing band 3 does not exceed the allowable deviation value. The diameter and length of the secondary sizing band 4 can be adjusted according to the specifications of the pipe.

[0051] In some embodiments, reference Figure 6 The sizing section 2 of the needle tip body 1 is provided axially with a first guide slope 5, a first main sizing band 6, a second guide slope 7, a second main sizing band 8, and a secondary sizing band 4. The large-diameter end of the first guide slope 5 is used to connect with the working section of the extrusion needle 12. The diameter of the large-diameter end of the first guide slope 5 is smaller than the diameter of the working section of the extrusion needle 12. The small-diameter end of the first guide slope 5 is connected to the first main sizing band 6 and has the same diameter. The large-diameter end of the second guide slope 7 is connected to the first main sizing band 6 and has the same diameter. The small-diameter end of the second guide slope 7 is connected to the second main sizing band 8 and has the same diameter. The diameter of the first main sizing band 6 is larger than the diameter of the second main sizing band 8. The large-diameter end of the secondary sizing band 4 is connected to the second main sizing band 8 and has the same diameter.

[0052] The first guide slope 5 is used to guide the metal on one side of the working section of the extrusion needle 12 toward the die hole 30. For example, the angle between the first guide slope 5 and the radial direction is 45° to 75°, such as 60°. The large-diameter end of the first guide slope 5 is smaller than the diameter of the working section of the extrusion needle 12. For example, the large-diameter end of the first guide slope 5 is 230 mm, and the diameter of the working section of the extrusion needle 12 is 250 mm. The axial length of the first guide slope 5 is, for example, 75 mm.

[0053] The first main sizing band 6 is used to sizing the inner diameter of the large inner diameter section 35 of the pipe. During pipe forming, the inner metal of the pipe is no longer subject to other constraints after separating from the first main sizing band 6. The size of the first main sizing band 6 plays a decisive role in the inner diameter of the large inner diameter section 35. For example, the diameter of the first main sizing band 6 is 147 mm. The axial length of the first main sizing band 6 should not be too long, as excessive length may cause scratches on the inner surface of the pipe and increase extrusion pressure, while excessive shortness may not achieve a good sizing effect. For example, the axial length of the first main sizing band 6 is 40 mm to 80 mm, for example, 60 mm.

[0054] The second guide slope 7 connects the first main sizing belt 6 and the second main sizing belt 8. The axial length of the second guide slope 7 is, for example, 70 mm.

[0055] The second main sizing band 8 is used to sizing the inner diameter of the small inner diameter section of the pipe. Its diameter is exemplarily 120 mm, and its axial length is exemplarily 40 mm to 80 mm, for example, 60 mm. Since the first main sizing band 6 corresponds to the large inner diameter section 35 of the pipe, and the second main sizing band 8 corresponds to the small inner diameter section of the pipe, the diameter of the first main sizing band 6 is larger than the diameter of the second main sizing band 8.

[0056] The large-diameter end of the secondary sizing belt 4 is connected to the second main sizing belt 8 and has the same diameter. The secondary sizing belt 4 is located on the side of the second main sizing belt 8 away from the second guide slope 7. During the retraction of the needle tip body 1, when the second main sizing belt 8 disengages from the effective working position along the predetermined axial offset direction, the secondary sizing belt 4 enters the effective working position and continues to sizing the inner diameter of the small inner diameter section of the pipe.

[0057] Optionally, the end of the sizing section 2 is also provided with a chamfer 9 to facilitate the separation of the pipe metal from the sizing section 2.

[0058] The following are some embodiments of the unequal inner diameter tube extrusion molding apparatus of the present invention.

[0059] In some embodiments, reference Figure 2The unequal inner diameter tube extrusion forming apparatus includes the unequal inner diameter tube extrusion forming needle tip as described in the above embodiment, and also includes a needle seat 10, an extrusion shaft 11, an extrusion needle 12, an extrusion pad 13, an extrusion cylinder 14, and a die assembly 15. The extrusion shaft 11 passes through the extrusion cylinder 14, and has a through hole along its central axis. The extrusion needle 12 passes through the through hole of the extrusion shaft 11. One end of the extrusion needle 12 is connected to the needle seat 10, and the needle tip body 1 is assembled to the other end of the extrusion needle 12. The die assembly 15 is disposed at one end of the extrusion cylinder 14, and the extrusion pad 13 is disposed within the extrusion cylinder 14 and located between the extrusion shaft 11 and the billet. The extrusion needle 12 passes through the extrusion pad 13 and extends into the die assembly 15. The extrusion needle 12 and the needle tip body 1 can move axially relative to the die assembly 15 to change the axial relative position of the needle tip body 1 and the die assembly 15.

[0060] The needle holder 10 supports the extrusion needle 12 and transmits power to ensure that the extrusion needle 12 moves back and forth along the axial direction. For example, one end of the needle holder 10 is provided with an internal thread and the other end is provided with an external thread. The internal thread end is threaded to the extrusion needle 12, and the external thread end is connected to related parts.

[0061] refer to Figure 4 The extrusion shaft 11 is used to transmit extrusion pressure and has a rear section and a front section. The rear section is used for assembly and has an inclined surface for assembling with related parts to ensure the coaxiality of the extrusion shaft 11 and the extrusion needle 12. The front section is the working section, which mates with the inner wall of the extrusion cylinder 14. Its outer diameter is smaller than the inner diameter of the extrusion cylinder 14, and the end face of the front section contacts the extrusion pad 13 to apply extrusion pressure to the billet through the extrusion pad 13. The extrusion shaft 11 has a through hole along its central axis. The diameter of the hole in the extrusion shaft 11 is larger than the diameter of the extrusion needle 12 to ensure the passage of the extrusion needle 12.

[0062] refer to Figure 5The extrusion needle 12 supports the needle tip body 1 and drives its axial movement. Exemplarily, the extrusion needle 12 is cylindrical and includes a working section, a limiting platform 16, a guide sleeve 17, and a nut 18, as well as internal and external threads. The working section is the main body of the extrusion needle 12, which is clearance-fitted with the extrusion shaft 11 and the extrusion pad 13, and its outer surface contacts the ingot metal. The diameter of the working section is not less than the maximum diameter of the first mounting cone surface of the needle tip body 1; exemplarily, the diameter of the working section is 200mm to 300mm, for example, 250mm. The length of the working section is greater than the sum of the ingot length and the axial length of the extrusion pad 13; exemplarily, it is 1500mm to 2500mm. One end of the working section has an internal thread for engaging with the connecting thread 23 of the needle tip body 1. The guide sleeve 17 guides and positions the extrusion needle 12 within the through hole of the extrusion shaft 11 to ensure the coaxiality of the extrusion needle 12 and the extrusion shaft 11; the guide sleeve 17 is made of copper. The diameter of the limiting platform 16 is larger than the diameter of the working section, used to limit the guide sleeve 17 to prevent it from moving towards the working section. Simultaneously, the diameter of the limiting platform 16 is smaller than the outer diameter of the guide sleeve 17 to avoid interference with the inner wall of the extrusion shaft 11. The nut 18 is used to limit the guide sleeve 17 to prevent it from moving towards the external thread. The outer diameter of the nut 18 is smaller than the outer diameter of the guide sleeve 17 to avoid interference with the inner wall of the extrusion shaft 11. The external thread connects to the needle seat 10, and its diameter is smaller than the diameter of the working section of the extrusion needle 12.

[0063] refer to Figure 7 The extrusion pad 13 is annular and is positioned between the billet and the extrusion shaft 11 during use. It transmits extrusion pressure and seals the metal in the billet, preventing metal from overflowing towards the extrusion shaft 11. The extrusion pad 13 has a two-step shape, with a large-diameter end and a small-diameter end. The outer surface of the large-diameter end is the working surface, which mates with the inner hole of the extrusion cylinder 14. The diameter of the large-diameter end is smaller than the inner diameter of the extrusion cylinder 14, and the clearance between them is, for example, 0.3 mm to 1.0 mm. The axial length of the large-diameter end is, for example, 30 mm to 80 mm, such as 50 mm. The function of the small-diameter end is to reduce the mating length with the inner wall of the extrusion cylinder 14 while maintaining sufficient axial length of the extrusion pad 13 to meet strength requirements, thereby reducing sliding resistance. For example, the axial length of the extrusion pad 13 is 120 mm to 200 mm, such as 150 mm. The inner hole of the extrusion pad 13 is used in conjunction with the extrusion needle 12. The diameter of the inner hole is larger than the diameter of the extrusion needle 12, and the gap between the two is exemplarily 0.2 mm to 2.0 mm.

[0064] The extrusion cylinder 14 is a circular cylinder with a central through-hole of equal diameter for holding the ingot. The extrusion cylinder 14 has a heating and heat preservation function to ensure that the ingot placed inside is kept warm or subjected to auxiliary heating. Exemplarily, the extrusion cylinder 14 is made of hot work die steel, such as H13. The inner diameter of the extrusion cylinder 14 is exemplary from 400mm to 700mm, for example, 500mm. The length of the extrusion cylinder 14 is exemplary from 1400mm to 1800mm.

[0065] The die assembly 15 is disposed at one end of the extrusion cylinder 14. The extrusion needle 12 passes through the extrusion pad 13 and extends into the die assembly 15. The needle tip body 1 extends into the die assembly 15, and an annular gap is formed between the needle tip body 1 and the die assembly 15. This annular gap is the die hole 30 for metal to flow out.

[0066] refer to Figure 3 During operation, the extrusion pad 13 moves towards the die assembly 15 under the push of the extrusion shaft 11, extruding the ingot. The ingot metal undergoes plastic deformation under high temperature and pressure, flowing out from the die hole 30 between the needle tip body 1 and the die assembly 15, forming a tube with a cross-section similar to that of the die hole 30. The inner diameter of the tube is determined by the sizing band size of the needle tip body 1, and the outer diameter is determined by the sizing band size of the die assembly 15. During the extrusion process, the extrusion needle 12 and the needle tip body 1 can move axially relative to the die assembly 15, changing the axial relative position of the needle tip body 1 and the die assembly 15. Combined with the different diameters of the needle tip body 1 at different axial positions, this causes the shape or size of the die hole 30 to change, resulting in a non-uniform cross-section of the obtained tube along the axial direction. The needle seat 10, the extrusion needle 12, and the needle tip body 1 are connected by threads to form a rigid whole, and no misalignment occurs between them during the extrusion process.

[0067] In some embodiments, reference Figure 6 The needle tip body 1 also includes an assembly section 19, which is provided axially with a first assembly conical surface 20, a positioning boss 21, a relief groove 22, and a connecting thread 23. The first assembly conical surface is located at the end of the assembly section 19 facing the sizing section 2, and the large-diameter end of the first assembly conical surface is connected to the large-diameter end of the first guide slope 5. For example, the angle between the first assembly conical surface and the radial direction is 30° to 45°, for example, 30°. The end face of the extrusion needle 12 is provided with a tapered hole adapted to the first assembly conical surface, and the first assembly conical surface and the tapered hole cooperate to make the needle tip body 1 and the extrusion needle 12 coaxially aligned and positioned.

[0068] The positioning boss 21 is used to ensure that the needle tip body 1 and the extrusion needle 12 have good coaxiality and positioning strength when they are assembled. The diameter of the positioning boss 21 is larger than the diameter of the connecting thread 23, and the axial length of the positioning boss 21 is unlimited.

[0069] The connecting thread 23 is used to mate with the internal thread of the extrusion needle 12 to form a threaded pair. For example, the axial length of the connecting thread 23 is 110 mm. The relief groove 22 is provided between the positioning boss 21 and the connecting thread 23 to provide relief space for thread processing. The diameter of the relief groove 22 is smaller than the minor diameter of the connecting thread 23. For example, the difference between the diameter of the relief groove 22 and the minor diameter of the connecting thread 23 does not exceed 3 mm.

[0070] For example, the total axial length of the assembly section 19 is 170mm. When the needle tip body 1 is assembled to the end of the extrusion needle 12, the connecting thread 23 is screwed into the internal thread of the extrusion needle 12, the first assembly cone surface fits with the cone hole on the end face of the extrusion needle 12, the positioning boss 21 abuts against the end face of the extrusion needle 12, and the needle tip body 1 and the extrusion needle 12 are coaxially positioned and rigidly connected.

[0071] Optionally, the needle tip body 1 is further provided with a loading / unloading section 24, connected to the end of the sizing section 2 opposite to the assembly section 19. The loading / unloading section 24 is an auxiliary part used to facilitate the installation of the needle tip body 1 to the extrusion needle 12 or to separate the needle tip body 1 from the extrusion needle 12. Exemplarily, the loading / unloading section 24 is a hexagonal prism, the diameter of which is smaller than the diameter of the secondary sizing band 4, for example, 40mm to 100mm, and the axial length of the hexagonal prism is exemplarily 50mm. Further, a through-hole 25 is provided on the side of the hexagonal prism to allow the insertion of a round bar to assist in loading / unloading.

[0072] In some embodiments, reference Figure 2 and Figure 3 The mold assembly 15 includes a mold sleeve 26, a mold 27, and a mold pad 28. The mold 27 and the mold pad 28 are assembled inside the mold sleeve 26. The mold sleeve 26 is used to support the mold 27 and the mold pad 28. The mold pad 28 is located on the side of the mold 27 away from the extrusion cylinder 14 and is used to axially limit the mold 27.

[0073] Exemplarily, the die sleeve 26 has an annular structure, and the end of the die 27 facing the extrusion cylinder 14 is the inlet end. The outer wall of the die 27 and the inner wall of the die sleeve 26 are fitted together by a mounting conical surface to ensure good coaxiality between the die 27 and the die sleeve 26. Exemplarily, the angle between the mounting conical surface and the axis is 3° to 12°, for example, 6°. The axial length of the die 27 relates to the rigidity of the die 27 during the extrusion process, and the axial length of the die 27 is exemplary 120 mm. The material of the die 27 is hot work die steel, such as H13 that has undergone quenching and tempering heat treatment.

[0074] The die pad 28 is located on the side of the die 27 away from the extrusion cylinder 14, axially limiting the die 27 and preventing it from moving axially. Exemplarily, the outer diameter of the die pad 28 is consistent with the maximum outer diameter of the die 27, and the inner diameter of the die pad 28 is larger than the inner diameter of the die 27. The axial length of the die pad 28 is exemplarily 130 mm, and the sum of the axial lengths of the die pad 28 and the die 27 is approximately equal to the axial length of the die sleeve 26.

[0075] In some embodiments, reference Figure 8 The mold 27 has a hollow, rotating structure. A third main sizing band 29 is provided in the inner hole of the mold 27, which is used to sizing the outer diameter of the tube. The third main sizing band 29 and the main sizing band 3 of the needle tip body 1 are radially opposite each other, and the gap between the third main sizing band 29 and the main sizing band 3 of the needle tip body 1 forms a mold hole 30. When the needle tip body 1 is in different axial positions, the third main sizing band 29 and different main sizing bands 3 of the needle tip body 1 are radially opposite each other, forming mold holes 30 of different sizes, thereby forming tube segments with different inner diameters. During tube forming, the billet metal flows out from the mold hole 30 between the third main sizing band 29 and the main sizing band 3 of the needle tip body 1. The outer diameter of the tube is determined by the third main sizing band 29, and the inner diameter of the tube is determined by the main sizing band 3 of the needle tip body 1.

[0076] For example, the diameter of the third main sizing band 29 is 181 mm, and the axial length of the third main sizing band 29 is 3 mm to 20 mm, for example, 20 mm. The outer diameter of the mold 27 depends on the diameter of the third main sizing band 29. For example, the outer diameter of the mold 27 is 100 mm to 400 mm larger than the diameter of the third main sizing band 29. For example, the outer diameter of the outlet end of the mold 27 is 435 mm, and the outer diameter of the inlet end is 420 mm. A mounting cone surface that mates with the mold sleeve 26 is formed on the outer peripheral surface of the inlet end of the mold 27.

[0077] In some embodiments, reference Figure 8 The inner hole of the mold 27 is also provided with a first empty cutter 31 and a second empty cutter 32 along the axial direction. The first empty cutter 31 and the second empty cutter 32 are located on the discharge side of the third main sizing belt 29 and are arranged sequentially along the axial direction. The diameter of the first empty cutter 31 is larger than the diameter of the third main sizing belt 29, and the diameter of the second empty cutter 32 is larger than the diameter of the first empty cutter 31.

[0078] The first and second cutters 31 do not shape the product. Their function is to ensure that the mold 27 has sufficient axial length to guarantee its rigidity and strength, while forming a clearance between the pipe and the inner hole of the mold 27, reducing the friction between the pipe and the mold 27, and facilitating the smooth passage of the pipe through the mold 27.

[0079] For example, the diameter of the first blanking tool 31 is 4 mm to 10 mm larger than the diameter of the third main sizing band 29, for example, the diameter of the first blanking tool 31 is 186 mm. The diameter of the second blanking tool 32 is 5 mm to 12 mm larger than the diameter of the first blanking tool 31, for example, the diameter of the second blanking tool 32 is 192 mm. The axial length of the first blanking tool 31 is, for example, 30 mm, and the axial length of the second blanking tool 32 is, for example, 80 mm.

[0080] It should be noted that in some embodiments, the second empty tool 32 may not be provided, that is, the first empty tool 31 and the second empty tool 32 may be combined into one.

[0081] In some embodiments, reference Figure 1 , Figures 9 to 12 This invention provides a method for extruding tubing with unequal inner diameters, implemented using the extrusion molding apparatus described in the previous embodiment. The forming dimensions of the unequal cross-section tubing depend on the distance between the end face of the needle tip body 1 and the end face of the die 27, i.e., the position of the needle tip body 1 extending into the die hole 30 determines the inner diameter of the tubing, corresponding to obtaining different segment sizes of the tubing. Simultaneously, obtaining the pre-set length of the transition section is also related to the movement speed of the needle tip body 1 relative to the die 27 during the extrusion process.

[0082] Before extrusion, a billet is placed inside an extrusion cylinder 14. The billet is a deformable metal, such as aluminum and aluminum alloys, magnesium and magnesium alloys, etc. The billet is heated before extrusion to improve its deformability; exemplarily, the heating temperature is 380°C to 550°C. The billet is cylindrical, with an outer diameter smaller than the inner diameter of the extrusion cylinder 14 and an inner diameter larger than the diameter of the extrusion needle 12. The length of the billet is less than the length of the extrusion cylinder 14; exemplarily, the length of the billet is 500mm to 800mm. The die assembly 15 is placed against one end of the extrusion cylinder 14, and the extrusion pad 13 is inserted from the other end of the extrusion cylinder 14. The extrusion needle 12, equipped with a needle tip body 1, is passed through the extrusion pad 13 and the billet, and the needle tip body 1 extends into the die assembly 15 to the rear position.

[0083] refer to Figure 9The needle tip body 1 is kept in the rear position, so that the second main sizing band 8 of the needle tip body 1 mates with the third main sizing band 29 of the die 27, forming an annular gap between them. This annular gap is the die hole 30. The extrusion shaft 11 pushes the extrusion pad 13 to extrude the billet, and the billet metal flows out through the die hole 30, forming the first small inner diameter segment 33. It should be noted that the rear position is the axial position of the needle tip body 1 in the radial relative position of the second main sizing band 8 and the third main sizing band 29. For example, the distance between the end face of the needle tip body 1 and the end face of the die 27 near the extrusion cylinder 14 is 60mm to 90mm, for example, 70mm. During this stage, the relative position of the needle tip body 1 and the die 27 remains unchanged, the shape and size of the die hole 30 are fixed, and the formed first small inner diameter segment 33 is a segment with a constant cross section. The outer diameter of the tube is determined by the third main sizing band 29, and the inner diameter of the tube is determined by the second main sizing band 8.

[0084] When the length of the first small inner diameter section 33 reaches the preset length, the extrusion shaft 11 stops extruding and advances the needle tip body 1 along the extrusion direction to the needle front position. During the advancement of the needle tip body 1, although the extrusion shaft 11 stops extruding, the second guide slope 7 of the needle tip body 1 will extrude and push the metal out of the die hole 30. At the same time, the second guide slope 7 and the third main sizing band 29 of the die 27 cooperate to form a die hole 30 with gradually changing size, forming the first transition section 34. The shape of the first transition section 34 is similar to the shape of the second guide slope 7. For example, the advancement speed of the needle tip body 1 is shown as 1.0 mm / s to 3.0 mm / s. It should be noted that the needle front position is the axial position of the needle tip body 1 when it is in the radial relative position of the first main sizing band 6 and the third main sizing band 29. For example, after the needle tip body 1 has advanced, the distance between the end face of the needle tip body 1 and the end face of the die 27 near the extrusion cylinder 14 is 180 mm to 200 mm, for example, 190 mm. The first transition section 34 is a transition section with a gradually changing inner diameter, and its length is the same as the axial length of the second guide slope 7.

[0085] refer to Figure 10 The needle tip body 1 remains in the front position. The first main sizing band 6 of the needle tip body 1 cooperates with the third main sizing band 29 of the mold 27 to form the mold hole 30. The extrusion shaft 11 continues to extrude, forming a large inner diameter section 35. During this stage, the relative position of the needle tip body 1 and the mold 27 remains unchanged. The formed large inner diameter section 35 is a section with a uniform cross section. The outer diameter of the tube is determined by the third main sizing band 29, and the inner diameter of the tube is determined by the first main sizing band 6.

[0086] When the length of the large inner diameter section 35 reaches the preset length, the extrusion shaft 11 continues to extrude, and the needle tip body 1 is retracted to the rear position in the opposite direction of the extrusion direction. During the retraction of the needle tip body 1, the second guide slope 7 of the needle tip body 1 cooperates with the third main sizing band 29 of the die 27 to form a die hole 30 with gradually changing size, forming the second transition section 36. During this process, the die hole 30 formed by the cooperation of the second guide slope 7 and the third main sizing band 29 is changing, and the billet metal continuously flows out of the die hole 30 under the extrusion action of the extrusion shaft 11, and the cross-sectional size of the formed tube is also changing, with the inner diameter of the tube showing a gradual change shape. The length and gradient size of the second transition section 36 depend on the extrusion speed and the moving speed of the needle tip body 1. For example, when forming the second transition section 36, the extrusion speed is 0.3 mm / s to 0.8 mm / s, and the moving speed of the needle tip body 1 in the opposite direction of the extrusion direction is 0.7 mm / s to 1.2 mm / s, for example, 0.8 mm / s.

[0087] refer to Figure 11 Keeping the needle tip body 1 in the rear position, the second main sizing band 8 of the needle tip body 1 mates with the third main sizing band 29 of the mold 27 to form the mold hole 30. The extrusion shaft 11 continues to extrude, forming the second small inner diameter segment 37. During this stage, the relative position of the needle tip body 1 and the mold 27 remains unchanged, and the formed second small inner diameter segment 37 is a segment with a constant cross-section.

[0088] Through the above steps, the inner diameters of the first small inner diameter section 33 and the second small inner diameter section 37 are smaller than the inner diameter of the large inner diameter section 35. The inner diameters of the first transition section 34 and the second transition section 36 gradually change along the axial direction, forming a non-uniform cross-section pipe with unequal inner diameters, small inner diameters at both ends, large inner diameters in the middle, and a uniform outer diameter throughout its length. The microstructure of the pipe is continuous and uniform in the cross-section, which is beneficial for meeting the requirements of use under harsh working conditions.

[0089] For example, the inner diameter of the small inner diameter sections at both ends of the pipe is 120mm and the length is 500mm, the inner diameter of the large inner diameter section 35 in the middle is 150mm, the axial length of the first transition section 34 is 70mm, the axial length of the second transition section 36 is 600mm, the outer diameter of the pipe is 178mm, the total length of the pipe is 9500mm, and the alloy of the pipe is 7-series high-strength aluminum alloy.

[0090] After forming the second small inner diameter segment 37, if the extrusion is terminated immediately, there will be a large amount of billet residue in the extrusion cylinder 14, which may cause interference with the separation equipment during the subsequent separation of the extrusion pad 13. In some embodiments, refer to Figure 12 After forming the second small inner diameter section 37, the needle tip body 1 is advanced along the extrusion direction to the front position of the needle, and the extrusion shaft 11 continues to extrude to form the process section 38. The process section 38 is a non-product section, and its purpose is to consume the axial length of the billet residue in the extrusion cylinder 14 to the preset length range.

[0091] Meanwhile, if the needle tip body 1 is located in the rear position, continuous extrusion will cause the extrusion pad 13 to detach from the working section of the extrusion needle 12 and enter the position of the needle tip body 1, resulting in the risk of deformed metal entering the inner hole of the extrusion pad 13 and causing an operational accident. Therefore, after forming the second small inner diameter section 37, the extrusion needle 12 and the needle tip body 1 are moved along the extrusion direction, so that the needle tip body 1 moves forward to the front position, and the extrusion shaft 11 is kept extruding continuously to form the process section 38, and the billet residue in the extrusion cylinder 14 is consumed to the preset length range.

[0092] For example, after extrusion is terminated, the axial length of the billet residue in the extrusion cylinder 14 is 80mm to 130mm, for example, 100mm. By consuming the billet residue to a preset length range, the axial length of the billet residue in the cylinder after extrusion is terminated meets the equipment operation requirements, and at the end of the extrusion, the extrusion pad 13 does not detach from the working section of the extrusion needle 12, thus improving operational safety.

[0093] It should be noted that if the length of the billet residue has reached the preset length range after the second small inner diameter segment 37 has been formed, then there is no need to continue the extrusion process segment 38 to consume the billet residue.

[0094] It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity from several other entities, and do not necessarily require or imply any such actual relationship or order between these entities.

[0095] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the present invention and its core ideas. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A needle tip formed by extrusion of tubing with unequal inner diameters, characterized in that, The device includes a needle tip body (1), which includes a sizing section (2) for sizing the inner diameter of the pipe. The sizing section (2) includes a main sizing band (3) and a secondary sizing band (4). The secondary sizing band (4) is axially disposed on one side of the main sizing band (3). When the main sizing band (3) moves away from the effective working position in a predetermined axial offset direction, the secondary sizing band (4) can enter the effective working position. The diameter of the secondary sizing band (4) is not greater than the diameter of the main sizing band (3), and the difference between the diameters of the secondary sizing band (4) and the main sizing band (3) is not greater than the allowable deviation value of the target inner diameter of the pipe corresponding to the main sizing band (3).

2. The needle tip formed by extruding tubing with unequal inner diameters according to claim 1, characterized in that, The secondary sizing band (4) is conical. The large diameter end of the secondary sizing band (4) is connected to the main sizing band (3), and the diameter of the large diameter end is the same as the diameter of the main sizing band (3). The difference between the diameter of the small diameter end of the secondary sizing band (4) and the diameter of the main sizing band (3) is not greater than the allowable deviation value of the target inner diameter of the pipe corresponding to the main sizing band (3).

3. The needle tip formed by extruding tubing with unequal inner diameters according to claim 2, characterized in that, The main sizing band (3) includes a first main sizing band (6) and a second main sizing band (8). A second guide slope (7) connects the first main sizing band (6) and the second main sizing band (8). The sizing section (2) also includes a first guide slope (5). The first guide slope (5), the first main sizing band (6), the second guide slope (7), the second main sizing band (8), and the secondary sizing band (4) are arranged sequentially along the axial direction. The small-diameter end of the first guide slope (5) is connected to the first main sizing belt (6) and has the same diameter; The large-diameter end of the second guide slope (7) is connected to the first main sizing belt (6) and has the same diameter; the small-diameter end of the second guide slope (7) is connected to the second main sizing belt (8) and has the same diameter. The diameter of the first main sizing band (6) is larger than the diameter of the second main sizing band (8); The large-diameter end of the secondary sizing belt (4) is connected to the second main sizing belt (8) and has the same diameter.

4. An extrusion molding apparatus for pipes with unequal inner diameters, characterized in that, The device includes the unequal inner diameter tube extrusion forming needle tip as described in claim 3, and also includes a needle seat (10), an extrusion shaft (11), an extrusion needle (12), an extrusion pad (13), an extrusion cylinder (14), and a mold assembly (15). The extrusion shaft (11) passes through the extrusion cylinder (14), and the extrusion shaft (11) has a through hole along the central axis. The extrusion needle (12) passes through the through hole of the extrusion shaft (11). One end of the extrusion needle (12) is connected to the needle seat (10), and the needle tip body (1) is assembled on the other end of the extrusion needle (12); The die assembly (15) is disposed at one end of the extrusion cylinder (14), the extrusion pad (13) is disposed inside the extrusion cylinder (14) and located between the extrusion shaft (11) and the billet, and the extrusion needle (12) passes through the extrusion pad (13) and extends into the die assembly (15); The extrusion needle (12) and the needle tip body (1) can move axially relative to the mold assembly (15) to change the axial relative position of the needle tip body (1) and the mold assembly (15).

5. The extrusion molding apparatus for unequal inner diameter pipes according to claim 4, characterized in that, The needle tip body (1) also includes an assembly section (19), which is provided with a first assembly cone surface (20), a positioning boss (21), a tool relief groove (22) and a connecting thread (23) in sequence along the axial direction. The end face of the extrusion needle (12) is provided with a conical hole that is adapted to the first assembly conical surface. The first assembly conical surface and the conical hole cooperate to make the needle tip body (1) and the extrusion needle (12) coaxially positioned. The diameter of the positioning boss (21) is larger than the diameter of the connecting thread (23); The tool relief groove (22) is disposed between the positioning boss (21) and the connecting thread (23), and the diameter of the tool relief groove (22) is smaller than the minor diameter of the connecting thread (23); The connecting thread (23) is threadedly connected to the internal thread of the extrusion needle (12).

6. The extrusion molding apparatus for unequal inner diameter pipes according to claim 4, characterized in that, The module assembly (15) includes a mold sleeve (26), a mold (27), and a mold pad (28); The mold (27) and the mold pad (28) are assembled inside the mold sleeve (26), and the mold sleeve (26) is used to support the mold (27) and the mold pad (28); the mold pad (28) is located on the side of the mold (27) away from the extrusion cylinder (14) and is used to axially limit the mold (27).

7. The extrusion molding apparatus for unequal inner diameter pipes according to claim 6, characterized in that, The inner hole of the mold (27) is provided with a third main sizing band (29), which is used to sizing the outer diameter of the pipe. The third main sizing band (29) and the main sizing band (3) of the needle tip body (1) are arranged opposite each other in the radial direction, and the gap between the third main sizing band (29) and the main sizing band (3) of the needle tip body (1) forms a die hole (30).

8. The extrusion molding apparatus for unequal inner diameter pipes according to claim 7, characterized in that, The inner hole of the mold (27) is also provided with a first empty knife (31) and a second empty knife (32) along the axial direction. The first empty knife (31) and the second empty knife (32) are located on the discharge side of the third main sizing belt (29) and are arranged sequentially along the axial direction. The diameter of the first empty cutter (31) is greater than the diameter of the third main sizing band (29), and the diameter of the second empty cutter (32) is greater than the diameter of the first empty cutter (31).

9. A method for extruding tubing with unequal inner diameters, characterized in that, The extrusion molding apparatus according to any one of claims 4-8 comprises the following steps: Place the billet into the extrusion cylinder (14), place the die assembly (15) against one end of the extrusion cylinder (14), insert the extrusion pad (13) from the other end of the extrusion cylinder (14), pass the extrusion needle (12) equipped with the needle tip body (1) through the extrusion pad (13) and the billet, and extend the needle tip body (1) into the die assembly (15) to the rear position of the needle; Keep the needle tip body (1) in the rear position of the needle, so that the second main sizing band (8) of the needle tip body (1) and the third main sizing band (29) of the mold (27) cooperate to form a mold hole (30), and the extrusion shaft (11) pushes the extrusion pad (13) to extrude the billet, and the billet metal flows out through the mold hole (30) to form the first small inner diameter section (33). When the length of the first small inner diameter section (33) reaches the preset length, the extrusion shaft (11) stops extruding and advances the needle tip body (1) along the extrusion direction to the front position of the needle. During the advance of the needle tip body (1), the second guide slope (7) of the needle tip body (1) cooperates with the third main sizing band (29) of the mold (27) to form a mold hole (30) with gradually changing size, forming the first transition section (34). Keep the needle tip body (1) in the front position of the needle, so that the first main sizing band (6) of the needle tip body (1) and the third main sizing band (29) of the mold (27) cooperate to form a mold hole (30), and the extrusion shaft (11) continues to extrude and form a large inner diameter section (35). When the length of the large inner diameter section (35) reaches the preset length, the extrusion shaft (11) is kept extruding continuously, and the needle tip body (1) is moved back to the needle rear position in the opposite direction of the extrusion direction. During the retraction of the needle tip body (1), the second guide slope (7) of the needle tip body (1) cooperates with the third main sizing band (29) of the mold (27) to form a mold hole (30) with gradually changing size, and the second transition section (36) is formed. Keep the needle tip body (1) in the rear position of the needle, so that the second main sizing band (8) of the needle tip body (1) and the third main sizing band (29) of the mold (27) cooperate to form a mold hole (30), and the extrusion shaft (11) continues to extrude to form the second small inner diameter section (37). The inner diameters of the first small inner diameter segment (33) and the second small inner diameter segment (37) are smaller than the inner diameter of the large inner diameter segment (35), and the inner diameters of the first transition segment (34) and the second transition segment (36) gradually change along the axial direction.

10. The extrusion molding method for pipes with unequal inner diameters according to claim 9, characterized in that, After the second small inner diameter section (37) is formed, the needle tip body (1) is advanced along the extrusion direction to the front position of the needle, and the extrusion shaft (11) continues to extrude to form the process section (38) so as to consume the axial length of the billet residue in the extrusion cylinder (14) to the preset length range.

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