Water expansion forming device and elbow joint machining method

Abstract

The invention discloses a water expansion forming device and an elbow joint machining method. The water expansion forming device comprises an upper die, a lower die and a water expansion forming device, the lower die and the upper die are combined to form a water expansion forming cavity, a first clearance position and a second clearance position, the first clearance position and the second clearance position are communicated with openings in the two sides of the water expansion forming cavity respectively, and a containing space capable of containing a screw head is formed in the position, close to the water expansion forming cavity, of the first clearance position; the first punching needle extends into the containing space through the first clearance position, an injection channel is formed in the first punching needle, a first near-end shaft shoulder is arranged at the end of the first punching needle, a far-end shaft shoulder is arranged at the position, away from the end, of the first punching needle, and the size of the far-end shaft shoulder is larger than that of the first near-end shaft shoulder; and the second punching needle extends into the water expansion forming cavity through the second clearance position, and a second near-end shaft shoulder is arranged at the end of the second punching needle. By means of the water expansion forming device, the stainless steel pipe joint with the screw head can be directly machined, and the requirement of an engineering project is met.

Description

Technical Field

[0001] The invention relates to the technical field of pipe processing, in particular to a water expansion forming device and a method for processing an elbow joint. Background Art

[0002] In drinking water projects, thin-walled stainless steel water pipes have many technical advantages over plastic water pipes, in addition to cost. Thin-walled stainless steel water pipes have high strength and good impact resistance. Their ability to resist external impact is 8 to 10 times that of plastic water pipes. They also have excellent corrosion resistance. The oxide film on the inner and outer walls can withstand high concentrations of chloride content, effectively resisting rust and corrosion. Stainless steel is a healthy material that can be implanted in the human body. It is non-toxic and harmless, and will not cause secondary pollution to the water quality, meeting the national direct drinking water quality standards. In addition, thin-walled stainless steel water pipes can be connected in a variety of ways, such as clamping, ring pressing, and groove, to avoid environmental pollution and health hazards caused by glue bonding, effectively improving the installation efficiency of the project and the quality of drinking water.

[0003] At present, the components of thin-walled stainless steel water pipes include at least stainless steel pipes, straight pipe joints and bent pipe joints. For the processing of straight pipe joints and bent pipe joints, reference can be made to "A water expansion forming device and forming process" with publication number CN112808836A. The water expansion forming process is performed by a water expansion forming device, and the production efficiency far exceeds the traditional machining process.

[0004] According to customer feedback, in order to meet the needs of engineering projects, a screw head needs to be set at one end of the stainless steel pipe joint so that accessories with external threads such as faucets can be directly installed. However, there is no water expansion forming device that matches this in the existing technology. Summary of the invention

[0005] The invention aims to provide a water expansion forming device, which can perform water expansion forming on a pipe blank with a screw head at one end and can protect the inner thread of the screw head from the impact of ultra-high water pressure.

[0006] According to a first aspect of the present invention, a water expansion molding device comprises:

[0007] upper mold;

[0008] A lower mold, which is combined with the upper mold to form a water expansion molding cavity, a first avoidance position and a second avoidance position, wherein the first avoidance position and the second avoidance position are respectively connected to the openings on both sides of the water expansion molding cavity, and the first avoidance position is provided with an accommodating space for accommodating a screw head at a position close to the water expansion molding cavity;

[0009] A first punch needle, which extends into the accommodating space through the first avoidance position, an injection channel is provided in the first punch needle, a first proximal shoulder is provided at the end of the first punch needle, and a distal shoulder is provided at a position away from the end of the first punch needle, and the size of the distal shoulder is larger than the size of the first proximal shoulder;

[0010] A second punching needle extends into the water expansion forming cavity through the second avoidance position, and a second proximal shoulder is provided at the end of the second punching needle.

[0011] The water expansion forming device according to the embodiment of the present invention has at least the following beneficial effects: during processing, the pipe blank with the screw head is first placed on the lower die, at which time the position of the screw head is located at the corresponding position of the accommodating space, and then the upper die moves toward the lower die and closes the die; thereafter, the first punch needle gradually extends to the first avoidance position until the first proximal shoulder of the first punch needle seals against the narrowing position between the pipe blank and the screw head, and at this time, the distal shoulder of the first punch needle also abuts against the outer end face of the screw head, and at the same time, the second punch needle gradually extends to the second avoidance position until the second proximal shoulder of the second punch needle seals against the pipe mouth of the pipe blank; due to the pipe The narrowed position between the pipe blank and the screw head is sealed by the first proximal shoulder of the first punch needle, and the other end of the pipe blank is sealed by the second proximal shoulder of the second punch needle. Therefore, during the water expansion forming process, the internal seal of the pipe blank can be maintained, and the high-pressure liquid cannot enter the thread section of the screw head from the injection channel to prevent the internal thread of the screw head from being deformed by the impact of ultra-high water pressure. The setting of the distal shoulder can limit the position of the screw head and prevent the connection between the screw head and the pipe blank from being broken under the impact of ultra-high water pressure. Through the above-mentioned water expansion forming device, the present invention can directly process a stainless steel pipe joint with a screw head to meet the needs of engineering projects.

[0012] According to some embodiments of the present invention, the first punch needle includes a fixed portion and a movable portion, the movable portion is movably nested in the fixed portion, the movable portion and the fixed portion are both provided with the injection channel, the first proximal shoulder is provided on the movable portion, and the distal shoulder is provided on the fixed portion. Through such an arrangement, the first proximal shoulder and the distal shoulder of the first punch needle can move relative to each other to meet different working conditions.

[0013] According to some embodiments of the present invention, specifically, the outer peripheral surface of the movable portion is provided with a plurality of sliding grooves arranged along the axial direction, and the fixed portion is provided with a sliding block slidably connected to the sliding groove.

[0014] According to some embodiments of the present invention, in order to prevent leakage of high-pressure water from the connection position between the movable part and the fixed part during the water expansion forming process, a sealing element is provided between the end of the slide groove close to the fixed part and the slider.

[0015] According to some embodiments of the present invention, in order to guide the upper mold, the upper mold is connected to at least two guide pillars, and the lower mold is provided with guide holes corresponding to the guide pillars.

[0016] According to some embodiments of the present invention, in order to achieve positioning of the upper mold, the upper mold is connected to a plurality of positioning columns, and the lower mold is provided with positioning holes corresponding to the positioning columns.

[0017] According to some embodiments of the present invention, the number of the water expansion molding cavities is multiple, and the number of the water expansion molding cavities determines the number of products that can be molded by the mold in one processing step.

[0018] According to some embodiments of the present invention, the two side openings of the water expansion molding cavity respectively have intersecting central axes, and in this case, the water expansion molding cavity is used to form an elbow joint.

[0019] According to some embodiments of the present invention, the two side openings of the water expansion molding cavity have a coaxial central axis, and in this case, the water expansion molding cavity is used to form a straight pipe joint.

[0020] According to the second aspect of the present invention, a method for processing an elbow joint, using the above-mentioned water expansion forming device, comprises the following steps:

[0021] Cutting the stainless steel pipe to obtain multiple straight pipes;

[0022] Arranging and positioning the plurality of straight tubes, and welding a screw head on one end of each of the straight tubes one by one, so as to obtain a plurality of straight tube blanks;

[0023] Arranging and positioning the plurality of straight tube blanks, and bending each of the straight tube blanks one by one to obtain a plurality of bent tube blanks;

[0024] The water expansion forming device is used to perform water expansion forming on the elbow blank to obtain an elbow joint with a screw head.

[0025] The elbow joint processing method according to the embodiment of the present invention has at least the following beneficial effects: before the present technology, due to the lack of corresponding water expansion forming devices in the industry, the welding process of the screw head was always placed after the water expansion forming process, but since the elbow has directionality, it is very difficult to automatically position and discharge the material through welding equipment, so manual auxiliary welding is required, and the welding efficiency is low, and since the water expansion forming device is generally one-out-two or one-out-four, the method of manual auxiliary welding cannot meet the requirements of mass production; since the present technology develops a water expansion forming device suitable for the elbow blank, the process of welding the screw head can be placed before the elbow process and the water expansion forming process, and the existing welding equipment can automatically position and weld multiple straight pipes, and the existing bending equipment can also automatically position and bend multiple straight pipe blanks, which greatly improves production efficiency, reduces the labor intensity of workers, reduces production costs, and provides a technical basis for automated production.

[0026] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0028] Figure 1 is a half-section view of a water expansion forming device provided in an embodiment of the present invention;

[0029] Figure 2 is a schematic structural diagram of a lower mold provided by an embodiment of the present invention;

[0030] Figure 3 It is a half-section view of the first punch needle and the second punch needle provided in an embodiment of the present invention.

[0031] In the accompanying drawings: 100-lower mold, 110-water expansion molding cavity, 120-first avoidance position, 130-second avoidance position, 140-guide hole, 150-positioning hole, 210-screw head, 200-bend pipe blank, 121-accommodating space, 300-first punch needle, 400-second punch needle, 500-power device, 330-injection channel, 510-injection chamber, 321-first proximal shoulder, 311-distal shoulder, 421-second proximal shoulder, 220-narrowing position, 310-fixed part, 320-movable part, 312-groove, 323-slide groove, 313-slider, 331-gap, 322-sealing element. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0033] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0034] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0035] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0036] like Figure 1 and Figure 2 As shown, the water expansion molding device according to the first embodiment of the present invention comprises an upper mold and a lower mold 100, both of which are provided with a half cavity, and the two molds can form a water expansion molding cavity 110, a first avoidance position 120 and a second avoidance position 130, and an opening is provided on each side of the water expansion molding cavity 110, and the two openings are respectively connected with the first avoidance position 120 and the second avoidance position 130. In order to guide the upper mold, the upper mold is connected with at least two guide pillars, and the lower mold 100 is provided with guide holes 140 corresponding to the guide pillars; in order to position the upper mold, the upper mold is connected with a plurality of positioning pillars, and the lower mold 100 is provided with positioning holes 150 corresponding to the positioning pillars.

[0037] The above structures are conventional settings of existing water expansion molding devices, wherein the first avoidance position 120 and the second avoidance position 130 are connected to the outer surface of the mold, and the two are respectively used for the punch needle to extend into the water expansion molding cavity 110, and the water expansion molding cavity 110 is divided into a straight tube molding cavity and a curved tube molding cavity according to different products. When the water expansion molding cavity 110 is a straight tube molding cavity, the two side openings of the water expansion molding cavity 110 have a coaxial central axis; when the water expansion molding cavity 110 is a curved tube molding cavity, the two side openings of the water expansion molding cavity 110 respectively have intersecting central axes. If further subdivided, if the central axes of the two side openings form an angle of ∠90°, then the water expansion molding cavity 110 is used to produce a 90° curved tube joint, and if the central axes of the two side openings form an angle of ∠45°, then the water expansion molding cavity 110 is used to produce a 45° curved tube joint. For ease of understanding, the following description is based on the water expansion molding cavity 110 as a curved tube molding cavity.

[0038] In order to adapt to the bent tube blank 200 with the screw head 210, the first avoidance position 120 is provided with a receiving space 121 for receiving the screw head 210 near the water expansion molding cavity 110. Since the outer dimension of the screw head 210 is larger than the outer diameter of the bent tube joint, the cross-sectional dimension of the receiving space 121 is also larger than the cross-sectional dimension of the water expansion molding cavity 110. When water expansion molding is required, the bent tube blank 200 with the screw head 210 only needs to be placed in the half-cavity of the lower mold 100. At this time, the screw head 210 of the bent tube blank 200 is located at the corresponding position of the receiving space 121 and is positioned by the receiving space 121, so as to limit the position of the bent tube blank 200 on the mold. After that, the upper mold moves toward the lower mold 100 under the drive of the hydraulic cylinder, and finally completes the mold closing of the upper mold and the lower mold 100. After the mold is closed, the parting surface of the water expansion molding cavity 110 is sealed, and the water expansion molding cavity 110 is connected to the outside only through the first escape position 120 and the second escape position 130 .

[0039] On the other hand, the water expansion molding device also includes a first punch needle 300 and a second punch needle 400, which are respectively connected to two power devices 500, and the position of the first punch needle 300 is exactly opposite to the position of the first avoidance position 120, and the position of the second punch needle 400 is exactly opposite to the position of the second avoidance position 130. The two power devices 500 control the first punch needle 300 and the second punch needle 400 to extend into the first avoidance position 120 and the second avoidance position 130 respectively. The first punch needle 300 is provided with an injection channel 330, and the injection channel 330 is connected to the injection chamber 510 controlled by the hydraulic press. During processing, the hydraulic press injects the liquid (usually water) into the bent tube blank 200 through the injection channel 330 by compressing the liquid (generally water). The hydraulic press continuously applies pressure, causing the water pressure in the bent tube blank 200 to rise to 100MPa to 400MPa. The bent tube blank 200 deforms under the ultra-high water pressure and fits the water expansion molding cavity 110, thereby forming a specific shape. The key point of this technology is that the first punch needle 300 and the second punch needle 400 must seal the inner cavity of the bent tube blank 200 to prevent liquid from leaking from the bent tube blank 200, and the pressure needs to be released after the processing is completed to prevent the high-pressure liquid from being ejected out at a very high speed, thereby causing damage to personnel or equipment.

[0040] Since the first avoidance position 120 is provided with a receiving space 121 for accommodating the screw head 210 near the water expansion molding cavity 110, the present technology can directly process the bent tube blank 200 with the screw head 210. At this time, the screw head 210 is welded to one end of the bent tube blank 200, and the other end of the bent tube blank 200 maintains the existing structure. In order to prevent the internal thread of the screw head 210 from being deformed by the impact of the high-pressure liquid during water expansion molding, thereby affecting the threaded connection after processing, it is necessary to improve the structure of the first punch 300.

[0041] like Figure 3 As shown, in addition to the first proximal shoulder 321 at the end of the first punching needle 300, the first punching needle 300 is provided with a distal shoulder 311 at a position away from the end, and the size of the distal shoulder 311 is larger than the size of the first proximal shoulder 321, and the distance between the distal shoulder 311 and the first proximal shoulder 321 should be set reasonably. In contrast, the second punching needle 400 is only provided with a second proximal shoulder 421 at the end.

[0042] The structure of the second punch needle 400 is of conventional design. During the process of water expansion forming, the front section of the second proximal shoulder 421 can extend into the interior of the elbow blank 200. At this time, the second proximal shoulder 421 is in sealing contact with the tube mouth of the elbow blank 200, and a sealing structure is formed between the two. The high-pressure liquid in the elbow blank 200 cannot leak to the outside through the tube mouth of the elbow blank 200. The structure of the first punch needle 300 is of special design. During the process of water expansion forming, the first punch needle 300 gradually extends into the first avoidance position 120 until the first proximal shoulder 321 of the first punch needle 300 is in sealing contact with the narrowing position 220 between the elbow blank 200 and the screw head 210. The formation of the narrowing position 220 is based on the condition that the outer dimension of the screw head 210 is greater than the outer diameter of the elbow joint. It exists as an inherent structure. At this time, the distal shoulder 311 of the first punch needle 300 also contacts the outer end face of the screw head 210.

[0043] Since the narrowed portion 220 between the elbow blank 200 and the screw head 210 is sealed by the first proximal shoulder 321 of the first punch needle 300, and the other end of the pipe blank is sealed by the second proximal shoulder 421 of the second punch needle 400, the internal seal of the elbow blank 200 can be maintained during the water expansion forming process. Since the position of the first proximal shoulder 321 exceeds the internal thread of the screw head 210, the high-pressure liquid cannot enter the thread section of the screw head 210 from the injection channel 330, so as to prevent the internal thread of the screw head 210 from being deformed by the impact of the ultra-high water pressure. The setting of the distal shoulder 311 can limit the position of the screw head 210, and prevent the connection between the screw head 210 and the elbow blank 200 from being broken under the impact of the ultra-high water pressure.

[0044] In view of the tolerance of the screw head 210 and the size difference of different screw heads 210, it is quite difficult to achieve that when the first proximal shoulder 321 of the first punch needle 300 is sealed against the narrowed position 220 between the bent tube blank 200 and the screw head 210, the distal shoulder 311 of the first punch needle 300 is also abutted against the outer end face of the screw head 210. In most cases, it is only possible to ensure that the first proximal shoulder 321 of the first punch needle 300 is sealed against the narrowed position 220 between the bent tube blank 200 and the screw head 210, but it is impossible to simultaneously ensure that the distal shoulder 311 of the first punch needle 300 is abutted against the outer end face of the screw head 210. For this reason, the structure of the first punch needle 300 needs to be further improved.

[0045] Specifically, the first punching needle 300 includes a fixed portion 310 and a movable portion 320. The fixed portion 310 is fixedly connected to the power device 500. The fixed portion 310 is provided with a groove 312 at one end away from the power device 500, and the groove 312 can accommodate the movable portion 320. The outer peripheral surface of the movable portion 320 is provided with a plurality of chute grooves 323 arranged in the axial direction. The fixed portion 310 is provided with a slider 313 slidably connected to the chute groove 323, so that the movable portion 320 can be movably nested in the fixed portion 310 in the axial direction. At this time, the first proximal shoulder 321 is provided at the end of the movable portion 320, and the distal shoulder 311 is provided at the end of the fixed portion 310. Since the chute 323 has two extreme positions, when any extreme position of the chute 323 abuts against the slider 313, the movable portion 320 cannot continue to move in the predetermined direction, thereby limiting the moving path of the movable portion 320 relative to the fixed portion 310, so that the movable portion 320 cannot be separated from the fixed portion 310.

[0046] The movable part 320 and the fixed part 310 are both provided with an injection channel 330. However, since the movable part 320 and the fixed part 310 are in a separable state, when the movable part 320 is away from the fixed part 310, there is a gap 331 between the injection channel 330 of the movable part 320 and the injection channel 330 of the fixed part 310. During the water expansion forming process, the high-pressure liquid will also fill the entire gap 331. In order to prevent the high-pressure liquid from leaking to the outside from the connection between the movable part 320 and the fixed part 310 through the gap 331, it is first necessary to ensure that the outer dimension of the movable part 320 and the inner dimension of the groove 312 are matched with high precision. Secondly, it is necessary to provide a sealing element 322 between the end of the slide groove 323 close to the fixed part 310 and the slider 313. The sealing element 322 can be a rubber gasket. When the high-pressure liquid acts on the sealing element 322, the sealing element 322 is deformed by force to provide a sealing effect.

[0047] During operation, the first punch 300 is driven by the power device 500 to gradually extend into the screw head 210 of the bent tube blank 200 until the first proximal shoulder 321 of the movable part 320 seals and abuts against the narrowed position 220 between the bent tube blank 200 and the screw head 210. Since the distal shoulder 311 of the fixed part 310 does not abut against the outer end face of the screw head 210 at this time, and the relative position of the movable part 320 and the fixed part 310 is adjustable, the power device 500 can continue to drive the fixed part 310 to move toward the screw head 210 until the distal shoulder 311 of the fixed part 310 abuts against the outer end face of the screw head 210. Not limited to the tolerance of the screw head 210 and the size difference of different screw heads 210, as long as the first proximal shoulder 321 of the movable part 320 can seal and abut against the narrowed position 220 between the bent pipe blank 200 and the screw head 210, the distal shoulder 311 of the fixed part 310 can also abut against the outer end face of the screw head 210.

[0048] During the water expansion forming process, the high-pressure liquid will also fill the gap 331 between the movable part 320 and the fixed part 310. At this time, the high-pressure liquid exerts a force on the movable part 320, so that the first proximal shoulder 321 of the movable part 320 can further seal against the narrowed portion 220 between the elbow blank 200 and the screw head 210, thereby converting the thrust of the high-pressure liquid into a partial compression force of the power device 500, so as to effectively reduce the configuration requirements of the power device 500. Through the above-mentioned water expansion forming device, the present invention can directly process an elbow joint with a screw head 210 to meet the needs of engineering projects.

[0049] like Figure 1 and Figure 2 As shown, in some embodiments of the present invention, the number of water expansion molding cavities 110 is set to be multiple, and the number of water expansion molding cavities 110 determines the number of products that the mold can form in one processing step. When the number of water expansion molding cavities 110 is two, two elbow joints can be produced in one processing step, which is commonly known as "one out of two" in the industry; when the number of water expansion molding cavities 110 is four, four elbow joints can be produced in one processing step, which is commonly known as "one out of four" in the industry.

[0050] According to the second embodiment of the present invention, a method for processing an elbow joint uses the water expansion forming device according to the first embodiment of the present invention, and comprises the following steps:

[0051] S100. Use a slitting device to slit the stainless steel pipe into a plurality of straight pipes with fixed lengths.

[0052] S200. Use welding equipment to arrange and position multiple straight pipes, and weld a screw head 210 at one end of each straight pipe one by one to obtain multiple straight pipe blanks. Since the directionality of the straight pipes at all angles remains consistent, the multiple straight pipes can be automatically positioned and arranged by a vibration plate. During welding, the manipulator grabs the screw head 210 and moves it to the end of the straight pipe, and the welding robot welds along the weld, thereby realizing automated welding.

[0053] S300. Use a pipe bending device to arrange and position a plurality of straight pipe blanks, and bend each straight pipe blank one by one to obtain a plurality of bent pipe blanks 200. Since the directionality of the straight pipe blanks at all angles is consistent, the plurality of straight pipe blanks can be automatically positioned and arranged by a vibrating plate. When bending the pipe, the straight pipe blank passes through a plurality of bending rotating rollers. Since there is an angle difference between different bending rotating rollers, the pipe bending device can bend the straight pipe blank into a bent pipe blank 200, and the processing process does not require manual intervention.

[0054] S400. Use a water expansion forming device to perform water expansion forming on the bent pipe blank 200 to obtain a bent pipe joint with a screw head 210. Before this technology, due to the lack of corresponding water expansion forming devices in this industry, the welding process of the screw head 210 was placed after the water expansion forming process, but because the bent pipe has directionality, it is very difficult to automatically position and discharge it through a vibration plate, so manual auxiliary welding is required, and the welding efficiency is low. In addition, since the water expansion forming device is generally one out of two or one out of four, the method of manual auxiliary welding cannot meet the requirements of mass production. Since this technology has developed a water expansion forming device suitable for the bent pipe blank 200, the process of welding the screw head 210 can be placed before the bending process and the water expansion forming process, and the existing welding equipment can automatically position and weld multiple straight pipes, and the existing bending equipment can also automatically position and bend multiple straight pipe blanks, which greatly improves production efficiency, reduces the labor intensity of workers, reduces production costs, and provides a technical basis for automated production.

[0055] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A water expansion forming device, characterized in that: include: upper mold; A lower mold (100) is molded together with the upper mold to form a water expansion molding cavity (110), a first avoidance position (120) and a second avoidance position (130), wherein the first avoidance position (120) and the second avoidance position (130) are respectively connected to openings on both sides of the water expansion molding cavity (110), and the first avoidance position (120) is provided with an accommodating space (121) capable of accommodating a screw head (210) at a position close to the water expansion molding cavity (110); A first punching needle (300), which extends into the accommodating space (121) through the first avoidance position (120), an injection channel (330) is provided in the first punching needle (300), a first proximal shoulder (321) is provided at the end of the first punching needle (300), and a distal shoulder (311) is provided at a position away from the end of the first punching needle (300), and the size of the distal shoulder (311) is larger than the size of the first proximal shoulder (321); A second punching needle (400) extends into the water expansion molding cavity (110) through the second avoidance position (130), and a second proximal shoulder (421) is provided at the end of the second punching needle (400).

2. The water expansion forming device according to claim 1, characterized in that: The first punch needle (300) includes a fixed part (310) and a movable part (320), the movable part (320) is movably nested in the fixed part (310), the movable part (320) and the fixed part (310) are both provided with the injection channel (330), the first proximal shoulder (321) is provided on the movable part (320), and the distal shoulder (311) is provided on the fixed part (310).

3. The water expansion forming device according to claim 2, characterized in that: The outer peripheral surface of the movable part (320) is provided with a plurality of sliding grooves (323) arranged along the axial direction, and the fixed part (310) is provided with a sliding block (313) slidably connected to the sliding groove (323).

4. The water expansion molding device according to claim 3, characterized in that: A sealing element (322) is provided between the sliding groove (323) at one end close to the fixing portion (310) and the sliding block (313).

5. The water expansion forming device according to claim 1, characterized in that: The upper die is connected to at least two guide pillars, and the lower die (100) is provided with guide holes (140) corresponding to the guide pillars.

6. The water expansion molding device according to claim 1, characterized in that: The upper die is connected to a plurality of positioning columns, and the lower die (100) is provided with positioning holes (150) corresponding to the positioning columns.

7. The water expansion molding device according to claim 1, characterized in that: The water expansion molding cavities (110) are provided in a plurality.

8. The water expansion molding device according to claim 1 or 7, characterized in that: The openings on both sides of the water expansion molding cavity (110) respectively have intersecting central axes.

9. The water expansion molding device according to claim 1 or 7, characterized in that: The two side openings of the water expansion molding cavity (110) have a coaxial central axis.

10. A method for processing an elbow joint, characterized in that: The use of the water expansion forming device according to any one of claims 1 to 8 comprises the following steps: Cutting the stainless steel pipe to obtain multiple straight pipes; Arranging and positioning the plurality of straight tubes, and welding a screw head (210) at one end of each of the straight tubes one by one, so as to obtain a plurality of straight tube blanks; Arranging and positioning a plurality of the straight tube blanks, and bending each of the straight tube blanks one by one to obtain a plurality of bent tube blanks (200); The water expansion forming device is used to perform water expansion forming on the elbow blank (200) to obtain an elbow joint with a screw head (210).

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