Method for internal high-pressure forming of three-way pipe fittings

Abstract

The present application provides a method for internal high-pressure forming of a three-way pipe fitting. This method is executed by the following device, which includes a frame body, an upper mounting plate, a lower mounting plate, a left pushing head, a right pushing head, and a horizontal hydraulic cylinder; the left pushing head and the right pushing head are respectively arranged on the piston rods of the left hydraulic cylinder and the right hydraulic cylinder; the horizontal hydraulic cylinder is adjustably arranged on the lower mounting plate, the axis of the piston rod of the horizontal hydraulic cylinder and the first axis are in the same horizontal plane and the angle formed by the two axes is variable, and a pushing head is further arranged on the piston rod of the horizontal hydraulic cylinder. This method includes that when the pipe blank is inflated to contact the pushing head by boosting pressure, the pushing head is controlled to move away from the pipe blank along the branch cavity and apply a pushing force to the pipe blank. The method provided by the present application controls the forming speed of the branch pipe of the inclined three-way pipe fitting through the pushing head on the horizontal hydraulic cylinder, reduces the usage amount of raw materials, saves labor, and reduces the rejection rate.

Description

Technical Field

[0001] This application relates to the technical field of basic non-cutting machining or treatment of metal plates, tubes, bars or profiles, and specifically relates to a method for internal high-pressure forming of three-way pipe fittings. Background Art

[0002] Internal High Pressure Forming (IHPF) is an advanced process for manufacturing pipe fittings with complex shapes and is suitable for forming pipe fittings such as tees. The internal high-pressure forming method forms the required shape by applying high-pressure liquid inside the pipe, causing the pipe to expand inside the mold and conform to the mold cavity. This process combines the advantages of hydroforming and die forming and can manufacture three-way pipe fittings with high precision, complex geometries, no welds, and high strength.

[0003] Currently, when using existing internal high-pressure forming equipment to form inclined three-way pipe fittings, it is difficult to control the pressure. During the pressing process, it is easy for some parts of the pipe wall to be too thin, resulting in quality problems. Once the pressure is too high, the pipe blank may even explode, leading to the scrapping of the pipe blank and causing waste of materials, energy, and labor. Summary of the Invention

[0004] To at least partially solve the above problems, an embodiment of this application provides a method for internal high-pressure forming of three-way pipe fittings. This method is executed by the following device, which includes: a frame body that is respectively provided with an upper hydraulic cylinder and a lower hydraulic cylinder that are opposite up and down, and a left hydraulic cylinder and a right hydraulic cylinder that are opposite left and right; an upper mounting plate connected to the piston rod of the upper hydraulic cylinder for mounting the upper mold of the three-way pipe fitting mold; a lower mounting plate arranged on the frame body and opposite to the upper mounting plate. The lower mounting plate is provided with a through hole for the piston rod of the lower hydraulic cylinder to pass through, and the lower mounting plate is used for mounting the lower mold of the three-way pipe fitting mold; a left push head and a right push head are respectively arranged on the piston rods of the left hydraulic cylinder and the right hydraulic cylinder and are arranged on the same first axis; a horizontal hydraulic cylinder is adjustably arranged on the lower mounting plate. The axis of the piston rod of the horizontal hydraulic cylinder and the first axis are in the same horizontal plane and the angle formed by the two axes is variable, so that the axis of the piston rod of the horizontal hydraulic cylinder can be collinear with the axis of the branch cavity of the three-way pipe fitting mold. The piston rod of the horizontal hydraulic cylinder is provided with a pushing head, and the radial dimension of the pushing head is the same as the radial dimension of the branch cavity of the three-way pipe fitting mold. The method includes: after placing the pipe blank and closing the mold, adjusting the horizontal hydraulic cylinder so that the angle between the axis of the piston rod of the horizontal hydraulic cylinder and the first axis is the angle between the main pipe and the branch pipe of the three-way pipe fitting to be formed, controlling the pushing head to enter the branch cavity, and when the pipe blank expands to contact the pushing head under pressure increase, controlling the pushing head to move away from the pipe blank along the branch cavity and applying a pushing force to the pipe blank.

[0005] In some embodiments, the left pusher and the right pusher are controlled to synchronously apply an axial thrust to the tube blank and feed axially along the tube blank for feeding; after the tube blank contacts the pusher head, the axial feeding distances of the left pusher and the right pusher are controlled to be different. Among them, the axial feeding distance of the pusher head in the main pipe cavity on the side where the angle formed with the branch pipe cavity is an obtuse angle is M1, and the axial feeding distance of the pusher head in the main pipe cavity on the side where the angle formed with the branch pipe cavity is an acute angle is M2, and M1 > M2.

[0006] In some embodiments, after the tube blank contacts the pusher head, the pressure is continuously increased, and the speed at which the pusher head exits the branch pipe cavity is controlled to be less than or equal to the speed at which the top end of the branch pipe expands along the branch pipe cavity.

[0007] In some embodiments, the magnitude of the pushing force applied by the pusher head to the tube blank is collected in real time; in response to the pushing force being less than a preset threshold, the speed at which the pusher head exits the branch pipe cavity is reduced, and the value range of the preset threshold is 50 - 500 N.

[0008] In some embodiments, in response to the pusher head moving to a preset position, the pusher head, the left pusher, and the right pusher are controlled to stop moving, and at the same time, the pressure increase is stopped and the pressure is maintained. The preset position is related to the length of the branch pipe to be formed.

[0009] In some embodiments, after maintaining the pressure for a preset time, the pusher head is controlled to move a preset distance in the direction close to the branch pipe along the branch pipe cavity, and the value range of the preset distance is 5 - 30 mm.

[0010] In some embodiments, before the tube blank contacts the pusher head, the internal pressure range is 50 - 100 MPa; after the tube blank contacts the pusher head, the pressure is continuously increased, and the internal pressure range is 150 - 250 MPa; when the pressure increase is stopped and the pressure is maintained, the internal pressure range is 300 - 400 MPa; after maintaining the pressure for a preset time, the pressure is reduced in stages.

[0011] In some embodiments, a first lubricant is coated on the inner wall of the main pipe cavity of the mold, and a second lubricant is coated on the inner wall of the branch pipe cavity of the mold and at the transition position between the branch pipe cavity and the main pipe cavity. The friction coefficient of the first lubricant is greater than that of the second lubricant.

[0012] The method for internal high-pressure forming of a three-way pipe fitting provided by the embodiments of the present application, with the aid of a device for internal high-pressure forming of a three-way pipe fitting, during the process of expanding and forming a branch pipe from a tube blank, the pushing head of the control device continuously applies a pushing force to the tube blank and moves along with the expansion of the branch pipe part of the tube blank, can control the forming speed of the branch pipe during the forming process of the branch pipe, effectively prevent some pipe walls from being too thin or the tube blank from exploding, reduce the occurrence of tube blank scrapping, and moreover, there is no need to additionally increase too much pipe wall thickness to prevent the tube blank from exploding, reducing the waste of materials, energy, and labor. The present invention solves the problems in the traditional forming of three-way pipe fittings, such as difficult to accurately control the deformation of the tube blank, unstable forming quality, and low forming efficiency, through multi-directional collaborative forming technology and refined control. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0014] Figure 1 is a schematic structural diagram of a device for internal high-pressure forming of a three-way pipe fitting provided by the embodiments of the present application;

[0015] Figure 2 is a partial structural schematic diagram of a device for internal high-pressure forming of a three-way pipe fitting provided by the embodiments of the present application;

[0016] Figure 3 is an exploded partial structural diagram of a device for internal high-pressure forming of a three-way pipe fitting provided by the embodiments of the present application;

[0017] Figure 4 is a top view of another partial structure of a device for internal high-pressure forming of a three-way pipe fitting provided by the embodiments of the present application;

[0018] Figure 5 is a schematic structural diagram of a lower mounting plate with a vertical plate installed provided by the embodiments of the present application;

[0019] Figure 6 is a schematic structural diagram of a vertical plate provided by the embodiments of the present application;

[0020] Figure 7 is a schematic structural diagram of a fixing block provided by the embodiments of the present application;

[0021] Figure 8 is a schematic structural diagram of an upper mounting plate with an upper mold installed provided by the embodiments of the present application.

[0022] The reference numerals are as follows:

[0023] 10. Frame body; 11. Upper hydraulic cylinder; 12. Lower hydraulic cylinder; 13. Left hydraulic cylinder; 14. Right hydraulic cylinder; 15. Horizontal hydraulic cylinder; 151. Piston rod of the horizontal hydraulic cylinder; 152. End cover; 21. Upper mounting plate; 211. First limiting groove; 212. Second limiting groove; 213. Third limiting groove; 22. Lower mounting plate; 221. First mounting groove; 222. Second mounting groove; 223. Third mounting groove; 224. Through hole; 231. Mounting hole; 232. Insertion part; 233. Clamping groove; 234. Limiting part; 235. Limiting pad; 23. Vertical plate; 24. Fixed block; 241. First end; 242. Second end; 2421. Protrusion; 243. Through hole; 25. Bolt; 31. Left pushing head; 32. Right pushing head; 33. Top pushing head; 41. Upper die; 42. Lower die; 43. Main pipe cavity; 44. Branch pipe cavity.

[0024] It should be understood that the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationship. In addition, the same or similar reference numerals represent the same or similar components. Detailed implementation manners

[0025] Next, the technical solutions of the preferred embodiments of the present application will be clearly and completely described in conjunction with the drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection required by the present application.

[0026] The "first", "second" and similar terms used in the present application do not indicate any order, quantity or importance, but are only used to distinguish different parts. The terms such as "including" or "comprising" mean that the elements before this word cover the elements listed after this word, and do not exclude the possibility of also covering other elements. The terms such as "upper", "lower", "left", "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0027] When the inventor of the present application uses an existing internal high-pressure forming device to produce inclined tee pipe fittings (such as the included angles between the main pipe and the branch pipe are 30°, 45°, 60°, etc.), it is found that it is difficult to control the forming speed of the branch pipe. If the forming speed is too fast, on the one hand, part of the pipe wall is too thin, which does not meet the quality requirements, and even the pipe blank explodes; on the other hand, it is also difficult to control the length of the branch pipe, resulting in material waste and increased labor costs.

[0028] To obtain an inclined tee fitting that meets the quality requirements, the inventor has tried to avoid the above situation by reducing the pressure used during forming, increasing the thickness of the tube blank, and other methods. However, reducing the pressure used during forming will lead to an increase in the number of forming times, and at the same time, the corresponding number of manual processing times will also increase; increasing the thickness of the tube blank will lead to an increase in the amount of raw materials used, and after forming, machining is still required to obtain fittings that meet the thickness requirements and length requirements. Therefore, the above methods will all result in cumbersome operations, more material waste, and higher labor costs. Moreover, even if the above methods are adopted, there is still a high rejection rate.

[0029] To at least partially solve the above problems, the inventor of the present application has obtained the present invention through continuous attempts and improvements.

[0030] An embodiment of the present application provides a method for internal high-pressure forming of a tee fitting. This method is executed by the following device. Please refer to Figure 1 , and this device includes: a frame body, which is respectively provided with an upper hydraulic cylinder and a lower hydraulic cylinder that are opposite up and down, and a left hydraulic cylinder and a right hydraulic cylinder that are opposite left and right; an upper mounting plate, which is connected to the piston rod of the upper hydraulic cylinder and is used to mount the upper die of the tee fitting mold; a lower mounting plate, which is arranged on the frame body and is opposite to the upper mounting plate. The lower mounting plate is provided with a through hole for the piston rod of the lower hydraulic cylinder to pass through, and the lower mounting plate is used to mount the lower die of the tee fitting mold; a left push head and a right push head, which are respectively arranged on the piston rods of the left hydraulic cylinder and the right hydraulic cylinder and are arranged on the same first axis; a horizontal hydraulic cylinder, which is adjustably arranged on the lower mounting plate. The axis of the piston rod of the horizontal hydraulic cylinder and the first axis are in the same horizontal plane and the angle formed by the two axes is variable, so that the axis of the piston rod of the horizontal hydraulic cylinder can be collinear with the axis of the branch cavity of the tee fitting mold. The piston rod of the horizontal hydraulic cylinder is provided with a pushing head, and the radial dimension of the pushing head is the same as the radial dimension of the branch cavity of the tee fitting mold.

[0031] This method includes: after placing the tube blank and closing the mold, adjust the horizontal hydraulic cylinder so that the angle between the axis of the piston rod of the horizontal hydraulic cylinder and the first axis is the angle between the main pipe and the branch pipe of the tee fitting to be formed. Control the pushing head to enter the branch cavity. When the pressure is increased and the tube blank expands to contact the pushing head, control the pushing head to move away from the tube blank along the branch cavity and apply a pushing force to the tube blank.

[0032] Specifically, the selected material for the tube blank can be aluminum alloy, stainless steel, titanium alloy or high-strength steel, which should have good plasticity (for example, elongation ≥ 20%) and tensile strength. Cut the tube to the designed length, and the end face should be flat (for example, the perpendicularity error is usually ≤ 0.1 mm) to obtain the tube blank. When pushing a reducing tee by the internal high-pressure process, due to the asymmetric structure of the reducing tee, the tube blank can be preformed first to adapt to the die space and facilitate subsequent internal high-pressure forming. Place the tube blank into the tee fitting die and close the die. When making a reducing tee, the axis of the main pipe cavity of the tee fitting die forms an angle less than 90° with the axis of the branch pipe cavity, for example, it can be angles such as 30°, 45°, 60°, etc. Control the left pusher and the right pusher to enter the main pipe cavity and respectively seal the openings at both ends of the tube blank. Control the pusher to enter the branch pipe cavity, fill the inner cavity of the tube blank with a liquid medium and increase the pressure, so that the tube wall corresponding to the branch pipe cavity of the tube blank expands into the branch pipe cavity and gradually forms a branch pipe. When the tube blank does not contact the pusher, the pusher can remain stationary; once it is detected that the tube blank contacts the pusher, control the pusher to move away from the tube blank along the branch pipe cavity and apply a pushing force to the tube blank.

[0033] The method for internal high-pressure forming of a tee fitting provided by the embodiment of the present application, with the aid of the device for internal high-pressure forming of a tee fitting, during the process of the tube blank expanding to form a branch pipe, the pusher of the control device continuously applies a pushing force to the tube blank and moves together with the expansion of the branch pipe part of the tube blank, which can control the forming speed of the branch pipe during the forming process of the branch pipe, effectively prevent some tube walls from being too thin or the tube blank from exploding, reduce the occurrence of tube blank scrapping, and moreover, there is no need to additionally increase too much tube wall thickness to prevent the tube blank from exploding, reducing the waste of materials, energy and labor.

[0034] In some embodiments, the left pusher and the right pusher are controlled to synchronously apply an axial thrust to the tube blank and feed axially along the tube blank to replenish materials; after the tube blank contacts the pusher head, the axial feeding distances of the left pusher and the right pusher are controlled to be different. Among them, the axial feeding distance of the pusher head in the main pipe cavity on the side where the angle formed with the branch pipe cavity is an obtuse angle is M1, and the axial feeding distance of the pusher head in the main pipe cavity on the side where the angle formed with the branch pipe cavity is an acute angle is M2, and M1 > M2. It can be understood that in the inclined tee mold, taking the intersection point of the branch pipe cavity and the main pipe cavity as the demarcation point, the angle formed by the main pipe cavity on one side of the demarcation point and the branch pipe cavity can be an obtuse angle, and the angle formed by the main pipe cavity on the other side of the demarcation point and the branch pipe cavity can be an acute angle. In this embodiment, by applying an axial thrust and feeding axially along the tube blank to replenish materials, the material loss during the forming of the branch pipe of the tube blank is compensated. Before the tube blank contacts the pusher head, the axial feeding distances of the left pusher and the right pusher can be the same or different; after the tube blank contacts the pusher head, due to the asymmetric characteristics of the inclined tee, the left pusher and the right pusher can feed differentially. On the side where the branch pipe and the main pipe form an obtuse angle, a larger amount of deformation needs to be generated. Therefore, in this embodiment, a larger axial feeding distance is provided on this side to prevent the wall thickness of this side from being too thin and causing quality problems. Specifically, in view of the forming characteristics of the inclined tee pipe fitting, the pusher head always supports the top of the branch pipe during forming, and cooperates with the asymmetric feeding of the left and right filling to realize the gradual bulging of the branch pipe, avoiding the excessive thinning of the middle large arc during the bulging of the branch pipe and resulting in cracking.

[0035] In some embodiments, after the tube blank contacts the pusher head, the pressure is continuously increased, and the speed at which the pusher head withdraws from the branch pipe cavity is controlled to be less than or equal to the speed at which the top end of the branch pipe expands along the branch pipe cavity. In this embodiment, continuously increasing the pressure after the tube blank contacts the pusher head can increase the forming speed of the branch pipe and prevent the premature increase in pressure from causing the explosion of the tube blank; controlling the movement speed of the pusher head can ensure that the pusher head is always in contact with the branch pipe and continuously applies a pushing force to the branch pipe. Exemplarily, the speed at which the pusher head withdraws from the branch pipe cavity can be 0.1 - 0.3 mm / s.

[0036] In some embodiments, the magnitude of the pushing force applied by the pusher head to the tube blank is collected in real time; in response to the pushing force being less than a preset threshold, the speed at which the pusher head withdraws from the branch pipe cavity is reduced. Preferably, the value range of the preset threshold is 50 - 500 N. In this embodiment, a force sensor can be provided on the horizontal hydraulic cylinder to collect the pushing force in real time. By monitoring the magnitude of the pushing force, the relationship between the movement speed of the pusher head and the expansion speed of the branch pipe is analyzed in real time, so as to finely control the movement of the pusher head, prevent the pusher head from detaching from the tube blank, and cause the forming speed of the tube blank to get out of control without the pushing force, resulting in local thinning of the wall thickness and generating quality defects.

[0037] In some embodiments, in response to the push head moving to a preset position, the movement of the push head, the left push head, and the right push head is controlled to stop, and at the same time, the pressure boosting is stopped and the pressure is maintained. The preset position is related to the length of the branch pipe to be formed. In this embodiment, the preset position is determined according to the designed length of the branch pipe. For example, the distance between adjacent preset positions and the distance between the preset position and the initial position of the push head can both be 1 / N of the length of the branch pipe, where N is an integer. Alternatively, the preset position can be a plurality of position points sequentially marked on the expansion path during the process of the branch pipe expanding to the length of the branch pipe. When the push head moves to the preset position, its movement stops to ensure that a branch pipe with the designed length is obtained. At this time, the pressure boosting is stopped and the pressure is maintained. The internal pressure reaches the maximum value, and the left push head and the right push head also stop the axial feeding and remain stationary, only maintaining the axial seal. The tube blank expands under the action of the internal pressure, fully adheres to the mold, and eliminates local depressions or wrinkles.

[0038] In some embodiments, after maintaining the pressure for a preset time, the push head is controlled to move a preset distance in the direction close to the branch pipe along the branch pipe cavity. The value range of the preset distance is 5 - 30 mm. In this embodiment, after the pressure maintaining ends, under the condition that the tube blank is under pressure, the push head can perform a reverse push to reduce the fillet of the expanded branch pipe, increase the length of the effective straight section of the branch pipe, effectively improve the material utilization rate, reduce the difficulty of bulging, and reduce the material length of the tube blank. When forming a partial tee pipe fitting, the end of the push head in contact with the tube blank can be formed into a stepped shape, so as to directly punch holes under pressure during the reverse push, cut off the end of the branch pipe, and improve the working efficiency.

[0039] In some embodiments, before the tube blank contacts the push head, the internal pressure range is 50 - 100 MPa; after the tube blank contacts the push head, the pressure is continuously increased, and the internal pressure range is 150 - 250 MPa; when the pressure boosting is stopped and the pressure is maintained, the internal pressure range is 300 - 400 MPa; after maintaining the pressure for a preset time, the pressure is reduced in stages to prevent the springback amount of the tube blank from exceeding the standard. Due to the asymmetric structure of the partial tee pipe fitting, during forming, the device needs to push and form a single tube blank multiple times to obtain the tee pipe fitting. After each push and forming, the tube blank is heat-treated to eliminate stress. In this embodiment, according to the positional relationship between the tube blank and the push head and the forming stage, the pressure is increased in stages, so as to reach a higher internal pressure value, which can improve the deformation amount of a single push under the condition of ensuring product quality, and then reduce the number of forming times and improve the forming efficiency. Specifically, in the actual production process, when forming a partial tee pipe fitting in a device without a push head, the internal pressure range usually used is 50 - 100 MPa, and usually 11 times of push and forming and corresponding heat treatments are required; when forming the same partial tee pipe fitting in the device with a push head provided by the embodiments of the present application, only 5 - 6 times of push and forming and corresponding heat treatments are required, which greatly reduces the costs of heat treatment and pushing.

[0040] In some embodiments, a first lubricant is coated on the inner wall of the main cavity of the mold, and a second lubricant is coated on the inner wall of the branch cavity of the mold and at the transition position between the branch cavity and the main cavity. The friction coefficient of the first lubricant is greater than that of the second lubricant. It can be understood that when forming an inclined tee, it is usually necessary to coat lubricants in the main cavity and the branch cavity of the mold to facilitate the material flow of the tube blank. However, since the overall material flow direction of the tube blank is from the main cavity to the branch cavity, this will bring some lubricants in the main cavity into the branch cavity, resulting in too low a friction coefficient on the inner wall of the branch cavity and too high a friction coefficient on the inner wall of the main cavity. As a result, a relatively large friction coefficient gradient is generated at the junction between the main cavity and the branch cavity. When the tube blank material flows here, the flow path deviates from the ideal direction, causing the tube fitting to have corrugated or spiral surface defects. Moreover, the material replenishment in the main pipe area is blocked, while the material in the branch pipe area flows too fast, which is also likely to cause the pipe wall to be over-stretched and thinned, resulting in quality defects. In this embodiment, through this setting method, the main cavity has a relatively large friction coefficient. After the lubricant is reduced, while ensuring the lubrication effect, the increase in the friction coefficient is small. And because the branch cavity is mixed with the lubricant with a relatively large friction coefficient in the main cavity, while ensuring the lubrication effect, the decrease in the friction coefficient is small. Thus, the friction coefficient gradient between the main cavity area and the branch cavity area is reduced, the occurrence of corrugated or spiral surface defects is reduced, and the occurrence of quality defects of excessive wall thinning is prevented. In some embodiments, the first lubricant is molybdenum disulfide and the second lubricant is graphene. The friction coefficient range of molybdenum disulfide is 0.08 - 0.12, and the friction coefficient range of graphene is 0.05 - 0.08. The difference in the two friction coefficients is small, which can form a small friction coefficient gradient after the lubricant is transferred, reducing the appearance of product surface defects and quality defects.

[0041] Each technical feature of the present invention (such as multi-direction hydraulic cylinders, dynamically adjustable horizontal hydraulic cylinders, dual lubricant systems, staged pressurization and pressure holding, etc.) cooperate with each other to jointly constitute a complete forming process. There are obvious synergistic effects between these features, jointly improving the forming quality and efficiency. The invention not only solves a single technical problem, but through overall optimization, realizes the high efficiency, stability and high quality of the forming process.

[0042] The device for internal high-pressure forming of three-way pipe fittings provided by the embodiments of the present application will be described more comprehensively below.

[0043] Please refer to Figures 1-8 , the device includes a frame body 10, an upper mounting plate 21, a lower mounting plate 22, a left push head 31, a right push head 32, and a horizontal hydraulic cylinder 15.

[0044] Upper hydraulic cylinders 11, lower hydraulic cylinders 12, left hydraulic cylinders 13, and right hydraulic cylinders 14 are respectively arranged on the upper, lower, left, and right sides of the frame body 10. The upper hydraulic cylinders 11 and the lower hydraulic cylinders 12 are arranged oppositely, and the left hydraulic cylinders 13 and the right hydraulic cylinders 14 are arranged oppositely. The upper mounting plate 21 is connected to the piston rod of the upper hydraulic cylinder 11, and the upper mounting plate 21 is used for mounting the upper die 41 of the three-way pipe fitting mold; the lower mounting plate 22 is arranged on the frame body 10 and is arranged oppositely to the upper mounting plate 21. The lower mounting plate 22 is provided with a through hole 224 for the piston rod of the lower hydraulic cylinder 12 to pass through, and the lower mounting plate 22 is used for mounting the lower die 42 of the three-way pipe fitting mold; the left pushing head 31 and the right pushing head 32 are respectively arranged on the piston rods of the left hydraulic cylinder 13 and the right hydraulic cylinder 14. The left pushing head 31 and the right pushing head 32 are arranged on the same axis. For the convenience of description, this axis is hereinafter referred to as the first axis; the horizontal hydraulic cylinder 15 is arranged on the lower mounting plate 22 with adjustable position. The axis of the piston rod 151 of the horizontal hydraulic cylinder is in the same horizontal plane as the first axis and the angle formed by the two axes is variable, so that the axis of the piston rod 151 of the horizontal hydraulic cylinder can be collinear with the axis of the branch cavity 44 of the three-way pipe fitting mold. A pushing head 33 is also arranged on the piston rod 151 of the horizontal hydraulic cylinder. The radial dimension of the pushing head 33 is the same as the radial dimension of the branch cavity 44 of the three-way pipe fitting mold.

[0045] Specifically, please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 . The frame body 10 can be formed by welding a plurality of metal plates. The frame body 10 can be a cuboid. An open space can be formed in the middle of the frame body 10 for mounting other components. The internal high-pressure forming of the three-way pipe fitting can also be carried out here. The extending directions of the upper hydraulic cylinders 11, the lower hydraulic cylinders 12, the left hydraulic cylinders 13, the right hydraulic cylinders 14, and the piston rod 151 of the horizontal hydraulic cylinder can all face this open space.

[0046] The upper hydraulic cylinder 11 can be used to drive the upper die 41 to move, change the distance between the upper die 41 and the lower die 42, so as to realize mold closing and mold opening. The upper hydraulic cylinder 11 can also provide the clamping force between the upper die 41 and the lower die 42 during mold closing. The upper hydraulic cylinder 11 can have a larger size than the lower hydraulic cylinder 12 and can provide a greater output force.

[0047] The lower hydraulic cylinder 12 can be disposed relative to the upper hydraulic cylinder 11 and below the upper hydraulic cylinder 11. The lower hydraulic cylinder 12 can have a size and output force smaller than those of the upper hydraulic cylinder 11. When forming a straight three-way pipe fitting, the piston rod of the lower hydraulic cylinder 12 can pass through the through hole 224 of the lower mounting plate 22 and enter the branch cavity 44 of the straight three-way pipe fitting mold, and abut against the side wall of the pipe blank. When forming a straight three-way pipe fitting, the piston rod of the lower hydraulic cylinder 12 can gradually retract as the branch of the straight three-way pipe bulges, so as to control the forming speed of the branch of the straight three-way pipe. At the same time, when demolding, the piston rod of the lower hydraulic cylinder 12 can eject the straight three-way pipe by acting on the branch of the straight three-way pipe. At this time, the upper and lower molds 42 of the straight three-way pipe fitting mold can be of an asymmetric structure, and the branch cavity 44 of the straight three-way pipe fitting mold can be disposed at the bottom of the lower mold 42, and the upper mold 41 does not have the branch cavity 44.

[0048] In this embodiment, the three-way pipe fitting mold can include an upper mold 41 and a lower mold 42, and the upper mold 41 and the lower mold 42 can have a mirror-symmetrical structure or a non-mirror-symmetrical structure. The three-way pipe fitting mold can include a straight three-way pipe fitting mold and an inclined three-way pipe fitting mold. In the straight three-way pipe fitting mold, the angle formed by the axis of the main pipe cavity 43 and the axis of the branch cavity 44 is 90°. In the inclined three-way pipe fitting mold, the angle formed by the axis of the main pipe cavity 43 and the axis of the branch cavity 44 can be, for example, 30°, 45°, 60°, etc. In this embodiment, the inclined three-way pipe fitting mold can have an upper mold 41 and a lower mold 42 with a mirror-symmetrical structure, and the main pipe cavity 43 and the branch cavity 44 are simultaneously formed by the upper mold 41 and the lower mold 42. Compared with a mold in which the branch cavity 44 is formed by a separate lower mold 42, this mold can facilitate the demolding of the inclined three-way pipe fitting after forming. In the actual production process, both the upper mold 41 and the lower mold 42 are in a horizontal state, and the branch cavity 44 can also be located in a horizontal plane.

[0049] A left push head 31 is installed on the piston rod of the left hydraulic cylinder 13, and a right push head 32 is installed on the piston rod of the right hydraulic cylinder 14. When forming a three-way pipe fitting, the left push head 31 and the right push head 32 enter the main pipe cavity 43 of the three-way pipe fitting mold and are hermetically connected to both ends of the pipe blank. The left hydraulic cylinder 13 and the right hydraulic cylinder 14 can drive the left push head 31 and the right push head 32 to move in the main pipe cavity 43. The pipe blank can be filled with a liquid medium, and the liquid medium can be pressurized to generate an internal high pressure, so as to push the side wall of the pipe blank at the entrance of the branch cavity 44 into the branch cavity 44 and expand into a branch. The left push head 31 and the right push head 32 can be provided with a double-layer stepped structure in the sealing structure, that is, the ends of the left push head 31 and the right push head 32 for contacting the pipe blank can be formed by connecting a plurality of coaxial cylinders with gradually decreasing diameters. The adjacent two cylinders form a stepped surface due to the diameter difference, which is used for sealing with the end of the pipe blank. Specifically, the pipe blank is locally extruded by the steps, and reliable sealing is achieved by using the plastic deformation in the thickness direction of the pipe blank.

[0050] The horizontal hydraulic cylinder 15 is disposed on the lower mounting plate 22 in a position-adjustable manner. In this embodiment, the manner of achieving position adjustment for the horizontal hydraulic cylinder 15 is not limited. Exemplarily, the horizontal hydraulic cylinder 15 can be disposed on a slide rail fixedly connected to the frame body 10, thereby achieving position adjustment. At the same time, the horizontal hydraulic cylinder 15 can also be swingably connected to the slide rail in the horizontal plane, thereby achieving angle adjustment of the piston rod of the horizontal hydraulic cylinder 15. The axis of the piston rod 151 of the horizontal hydraulic cylinder is located in the same horizontal plane as the axes of the left push head 31 and the right push head 32, and the angle formed by the two axes (i.e., the axis of the piston rod 151 of the horizontal hydraulic cylinder and the common axis of the left push head 31 and the right push head 32) is variable, so that the axis of the piston rod 151 of the horizontal hydraulic cylinder can be collinear with the axis of the branch cavity 44 of the three-way pipe fitting mold. In this embodiment, this setting manner can enable the push head 33 disposed on the piston rod 151 of the horizontal hydraulic cylinder to adapt to three-way pipe fitting molds for forming branches with different angles, and achieve control of the forming speed of the branch.

[0051] The radial dimension of the push head 33 is the same as the radial dimension of the branch cavity 44 of the three-way pipe fitting mold, which enables the push head 33 to enter the branch cavity 44 and move along the branch cavity 44. In this embodiment, the push head 33 can be cylindrical. In some embodiments, one end of the push head 33 away from the horizontal hydraulic cylinder 15 can form an inclined surface, and the inclination angle of the inclined surface can correspond to the included angle between the main pipe and the branch pipe of the three-way pipe fitting. In this way, the push head 33 can fit more closely to the side wall of the pipe blank, and achieve control of the forming rate at the initial stage of branch forming. Exemplarily, when the included angle between the main pipe and the branch pipe is 60°, the included angle between the inclined surface and the axis of the branch cavity 44 can be 60°. In some embodiments, the end of the push head for contacting the pipe blank can form a stepped shape to directly punch the end of the branch under pressure and cut off the top end of the branch, improving work efficiency. In some embodiments, the push head 33 can be detachably connected to the piston rod 151 of the horizontal hydraulic cylinder. This setting manner can achieve cooperation with molds of different diameters of the branch cavity 44 by replacing push heads 33 with different radial dimensions. Exemplarily, the push head 33 and the piston rod 151 of the horizontal hydraulic cylinder can be detachably connected by bolt connection. Preferably, when the push head 33 is fixed to the horizontal hydraulic cylinder 15 by bolts, the bolts can be located on the side surface of the push head 33, so that the end surface of the push head 33 for contacting the pipe blank is smoother, preventing the uneven end surface of the push head 33 from affecting the control of the branch forming rate.

[0052] The embodiment of the present application provides a device for high-pressure internal forming of tee pipe fittings. By setting a horizontal hydraulic cylinder 15 with adjustable position, the pushing head 33 on the piston rod 151 of the horizontal hydraulic cylinder can enter the branch pipe cavity 44 of the tee pipe fitting mold with various angles when forming the tee branch pipe, and interfere with the side wall of the tube blank used to form the tee pipe fitting, so as to control the branch pipe forming speed of tee pipe fittings with various angles such as oblique tee pipe fittings, thereby eliminating the need to reserve a large thickness of the tube blank in advance, reducing the amount of raw materials used, reducing the workload of subsequent machining, saving labor, and reducing the scrap rate. In addition, due to the use of the horizontal hydraulic cylinder 15 and the pushing head 33, higher pressure can be used for internal high-pressure forming when forming the oblique tee, reducing the number of forming times, and further reducing labor costs and energy consumption costs. In addition, due to the presence of the pushing head 33, the shape and length of the end of the oblique tee branch pipe can be controlled, reducing the cutting length of the end of the oblique tee branch pipe, further reducing material consumption and labor costs. The device for internal high-pressure forming of tee pipe fittings provided in the embodiments of the present application can achieve the forming of straight tee pipe fittings and oblique tee pipe fittings using a single device by increasing the functionality of the equipment at low equipment cost (without increasing the number of internal high-pressure forming equipment).

[0053] See also Figure 5 as well as Figure 6 In some embodiments, the apparatus for high-pressure forming of tee pipe fittings further includes a vertical plate 23, which is vertically disposed on the lower mounting plate 22. The horizontal hydraulic cylinder 15 is disposed on the vertical plate 23, and the axis of the piston rod 151 of the horizontal hydraulic cylinder is perpendicular to the vertical plate 23. In this embodiment, the connection between the horizontal hydraulic cylinder 15 and the lower mounting plate 22 is achieved through the vertical plate 23. The horizontal hydraulic cylinder 15 and the lower mounting plate 22 can be separated in the height direction, thereby compensating for the thickness of the lower mold 42 and allowing the piston rod 151 of the horizontal hydraulic cylinder to enter the branch pipe cavity 44 of the mold. This structure is simple and reliable. Preferably, the vertical plate 23 is detachably connected to the lower mounting plate 22. With this arrangement, when producing some straight tee pipe fittings, the vertical plate 23 with the horizontal hydraulic cylinder 15 can be completely removed to facilitate the installation of the mold in which the branch pipe cavity 44 is disposed in the lower mold 42.

[0054] In some embodiments, the lower mounting plate 22 is provided with a mounting groove, and the extending direction of the mounting groove forms an angle with the axes of the left pushing head 31 and the right pushing head 32, which is determined based on the angle between the main pipe and the branch pipe of the three-way pipe fitting; the bottom end of the vertical plate 23 forms a plugging portion 232, and the plugging portion 232 is plugged into the mounting groove. Exemplarily, the angle formed by the extending direction of the mounting groove and the common axis of the left pushing head 31 and the right pushing head 32 can be 30° or 45°, corresponding to the three-way pipe fittings with the angles between the main pipe and the branch pipe being 60° and 45° respectively. In this embodiment, the vertical plate 23 is plugged into the mounting groove, and the mounting groove can define the angle of the vertical plate 23 to adapt to the extending direction of the branch pipe cavity 44 of the corresponding three-way pipe fitting mold. The vertical plate 23 is installed in the mounting groove by plugging, with a simple structure and easy disassembly.

[0055] In some embodiments, the mounting groove includes a first mounting groove 221, a second mounting groove 222, and a third mounting groove 223; the angle formed by the extending direction of the first mounting groove 221 and the first axis is 45°; the angle formed by the extending direction of the second mounting groove 222 and the first axis is 30°; the extending direction of the third mounting groove 223 is parallel to the first axis. In this embodiment, the first mounting groove 221, the second mounting groove 222, and the third mounting groove 223 are provided on the lower mounting plate 22, making full use of the space of the lower mounting plate 22. The above angles can cover the mainstream 45° and 60° inclined three-way pipe fitting products, and at the same time take into account some straight three-way products, increasing the versatility of the device. It can be understood that in other embodiments, mounting grooves with other angles can be provided.

[0056] Please refer to Figure 7 , in some embodiments, the device for internal high-pressure forming of three-way pipe fittings further includes a plurality of fixing blocks 24. The plurality of fixing blocks 24 are arranged on the lower mounting plate 22 and are evenly distributed on both sides of the mounting groove; clamping grooves 233 are provided at positions corresponding to the fixing blocks 24 on both sides of the plugging portion 232 of the vertical plate 23, and the first end portion 241 of the fixing block 24 is located in the clamping groove 233 to limit the plugging portion 232. In this embodiment, the vertical plate 23 is fixed by the cooperation of the fixing block 24 and the clamping groove 233, further ensuring the stability of the vertical plate 23, and at the same time facilitating the disassembly and installation of the vertical plate 23; in addition, by using the fixing block 24 for limiting, the structure of the lower mounting plate 22 can be simplified, and only the mounting groove and the screw holes need to be provided on the lower mounting plate 22, without making excessive adjustments to the structure of the lower mounting plate 22.

[0057] In some embodiments, a plurality of screw holes are formed on both sides of the installation groove, and the fixing block 24 is fixed to the lower mounting plate 22 by bolts 25; a protrusion 2421 is formed at the bottom of the second end 242 of the fixing block 24 opposite to the first end 241, and the protrusion 2421 abuts against the lower mounting plate 22. When the bolt 25 passes through the fixing block 24 and fixes the fixing block 24 at the screw hole position of the lower mounting plate 22, the bolt 25 is located between the first end 241 and the second end 242. A through hole 243 may be provided in the middle of the fixing block 24. When the insertion portion 232 is inserted into the installation groove, the clamping groove 233 may be slightly higher than the surface of the lower mounting plate 22. In this embodiment, when fixing the vertical plate 23 through the fixing block 24, the protrusion 2421 can serve as a fulcrum. The bolt 25 passes through the through hole 243 and is located in the middle of the fixing block 24. The nut applies a downward force to the fixing block 24, generating a lever effect, so that the first end 241 of the fixing block 24 generates a force to press down on the side wall of the clamping groove 233, and the vertical plate 23 can be more reliably fixed to the lower mounting plate 22.

[0058] In some embodiments, the length of the installation groove is greater than the length of the insertion portion 232, the number of screw holes is greater than the number of fixing blocks 24, the plurality of screw holes are evenly distributed on both sides of the installation groove, and the distance between adjacent two screw holes is equal. In this embodiment, through the above structure, the vertical plate 23 can be fixed at different positions in the extending direction of the installation groove, realizing fine adjustment of the position of the vertical plate 23 in the extending direction of the installation groove, so as to adapt to more different three-way molds. In this embodiment, the screw holes can be divided into two rows, and the two rows of screw holes are respectively located on both sides of the installation groove. In each row of screw holes, the distance between adjacent two screw holes is equal, and the distance between one row of screw holes is equal to the distance between the other row of screw holes. With this setting method, when using different three-way pipe fitting molds, the installation position of the vertical plate 23 can be determined by counting the number of screw holes, and the operation is simple.

[0059] In some embodiments, an installation hole 231 is formed on the vertical plate 23, and the diameter of the installation hole 231 is the same as the diameter of the cylinder barrel of the horizontal hydraulic cylinder 15. The cylinder barrel is sleeved in the installation hole 231, and an end cover 152 with a diameter larger than that of the cylinder barrel is provided at one end of the cylinder barrel close to the pushing head 33. The end cover 152 is fixedly connected to the vertical plate 23 and is located on the side of the vertical plate 23 close to the pushing head 33. It can be understood that during the working process of the horizontal hydraulic cylinder 15, it will be subjected to the reaction force of the pipe blank. To ensure the reliable fixation of the horizontal hydraulic cylinder 15, in this embodiment, by providing the end cover 152, since the diameter of the end cover 152 is larger than that of the cylinder barrel and is located on the side of the vertical plate 23 close to the pushing head 33, when the pipe blank applies a reaction force to the horizontal hydraulic cylinder 15, the force will be transmitted to the vertical plate 23 through the outer edge of the end cover 152, thus avoiding the force on the bolt 25 for fixing the horizontal hydraulic cylinder 15 and realizing the reliable fixation of the horizontal hydraulic cylinder 15.

[0060] In some embodiments, a limiting portion 234 is formed at the top end of the vertical plate 23; a limiting groove is provided at a position corresponding to the limiting portion 234 on the upper mounting plate 21. When the three-way pipe fitting mold is closed, the distance between the upper mounting plate 21 and the lower mounting plate 22 is less than the height of the vertical plate 23. The upper mounting plate 21 and the lower mounting plate 22 can be arranged in parallel and have the same or similar sizes. In this embodiment, through this setting method, when the three-way pipe fitting mold is closed, the top end of the vertical plate 23 can enter the limiting groove. At this time, in the extending direction of the plane where the upper mounting plate 21 and the lower mounting plate 22 are located, the bottom end of the vertical plate 23 is limited by the mounting groove of the lower mounting plate 22, and the top end of the vertical plate 23 is limited by the limiting groove of the upper mounting plate 21. The vertical plate 23 can be supported more reliably and evenly, reducing the risk of the vertical plate 23 breaking due to excessive reaction force. Exemplarily, a first limiting groove 211 can be provided at a position corresponding to the first mounting groove 221 of the upper mounting plate 21 and the lower mounting plate 22, a second limiting groove 212 can be provided at a position corresponding to the second mounting groove 222 of the upper mounting plate 21 and the lower mounting plate 22, and a third limiting groove 213 can be provided at a position corresponding to the third mounting groove 223 of the upper mounting plate 21 and the lower mounting plate 22.

[0061] In some embodiments, a plurality of limiting pads 235 are provided on both sides of the limiting portion 234, and the limiting pads 235 are detachably provided on the limiting portion 234. In this embodiment, by providing the limiting pads 235 on both sides of the limiting portion 234, it is possible to prevent the top end of the vertical plate 23 from directly contacting the limiting groove of the upper mounting plate 21, thereby reducing the wear of the top end of the vertical plate 23 after multiple mold closings and mold openings, and increasing the service life of the vertical plate 23. The limiting pads 235 are detachably provided on the limiting portion 234. When the limiting pads 235 are severely worn, it is convenient to remove the limiting pads 235 and replace them with new ones, preventing the situation of poor limiting effect due to the wear of the limiting pads 235 and the inclination of the vertical plate 23, and preventing damage to the three-way pipe fitting mold, the horizontal hydraulic cylinder 15 or the vertical plate 23.

[0062] Example 1

[0063] Obtain stainless steel pipes, cut the pipes to 50 cm, with the end face perpendicularity error ≤ 0.1 mm to form pipe blanks. The included angle between the axes of the main pipe cavity and the branch pipe cavity of the mold is 45°. Pretreat the pipe blanks to adapt to the mold space, and add lubricant molybdenum disulfide to the inner wall of the mold cavity. Figure 1Internal high-pressure forming is carried out in the shown device. The preformed tube blank is placed into the lower mold cavity, and the upper mold is closed to complete mold clamping. The left pusher and the right pusher move towards both ends of the tube blank to complete sealing, and water is injected into the tube. The left pusher and the right pusher synchronously apply axial thrust for feeding, with the axial feeding distance on both sides being 20 mm. Meanwhile, the internal pressure is gradually increased to 100 MPa to enable free bulging of the middle section of the tube blank. When the top of the branch tube contacts the pusher head, the pusher head starts to retreat along the preset path at a speed of 0.2 mm / s. The left pusher has an axial feeding distance of 10 mm, and the right pusher has an axial feeding distance of 15 mm. Meanwhile, the internal pressure continues to increase to 200 MPa. When the pusher head retreats, the pushing force applied by the pusher head to the tube blank is collected in real time. When the pushing force is less than 200 N, the speed at which the pusher head exits the branch tube cavity is reduced. After the pusher head moves to the specified position, the internal pressure rises to the peak value of 400 MPa. The left pusher and the right pusher stop feeding and only maintain sealing, and the middle punch stops retreating. After the pressure holding is completed, the pressure is reduced in stages, and the pressure reduction gradient is 400→200→50→0 MPa. After the pressure reduction, the tube blank is taken out for heat treatment to eliminate stress. Then it is put into the mold again, and the above steps are repeated until the length of the branch tube reaches 20 cm.

[0064] Example 2

[0065] When the top of the branch tube contacts the pusher head, the pusher head starts to retreat along the preset path at a speed of 0.2 mm / s. The left pusher has an axial feeding distance of 10 mm, and the right pusher has an axial feeding distance of 10 mm. Meanwhile, the internal pressure continues to increase to 200 MPa. The remaining steps are the same as those in Example 1.

[0066] Example 3

[0067] When the pusher head retreats, the pushing force applied by the pusher head to the tube blank is collected in real time. When the pushing force is less than 40 N, the speed at which the pusher head exits the branch tube cavity is reduced. The remaining steps are the same as those in Example 1.

[0068] Example 4

[0069] After the pressure holding is completed, the pressure is directly reduced from 400 MPa to 0 MPa. The remaining steps are the same as those in Example 1.

[0070] Example 5

[0071] The tube blank is pretreated to adapt to the mold space. Molybdenum disulfide, a lubricant, is added to the inner wall of the main tube cavity of the mold, and graphene, a lubricant, is added to the inner wall of the branch tube cavity of the mold and at the transition position between the branch tube cavity and the main tube cavity. The remaining steps are the same as those in Example 1.

[0072] Comparative Example

[0073] Obtain stainless steel pipes, cut the pipes to 50 cm, with the end face perpendicularity error ≤ 0.1 mm, to form pipe blanks. The included angle between the axis of the main pipe cavity and the branch pipe cavity of the mold is 45°. Pretreat the pipe blanks to adapt to the mold space, and add molybdenum disulfide lubricant to the inner wall of the mold cavity. Figure 1 Perform internal high-pressure forming in the equipment shown in Figure 1 , but do not install the vertical plate and auxiliary structures such as the horizontal hydraulic cylinder on the vertical plate. Place the preformed pipe blank into the lower mold cavity, and close the upper mold to complete mold clamping. The left pusher and the right pusher move towards both ends of the pipe blank to complete sealing, and inject water into the pipe. The left pusher and the right pusher synchronously apply axial thrust for feeding, with the axial feeding distance on both sides being 20 mm. At the same time, gradually increase the internal pressure to 100 MPa to cause free bulging of the middle section of the pipe blank. Continue to increase the pressure. During the pressure increase process, the axial feeding distance of the left pusher and the right pusher is 10 mm. Start pressure holding when the pressure increases to 150 MPa. The left pusher and the right pusher stop feeding and only maintain sealing. After the pressure holding ends, release the pressure, take out the pipe blank for heat treatment to eliminate stress. Then put it into the mold again and repeat the above steps until the length of the branch pipe reaches 20 cm.

[0074] Produce 50 inclined tee pipe fittings respectively by the methods of the examples and the comparative examples, and collect relevant data. Among them, the pipe blank explodes during the forming process, some areas of the pipe wall of the formed tee pipe fitting are too thin, and there are surface quality defects on the pipe wall of the formed tee pipe fitting are unqualified, as shown in the following table.

[0075] Maximum pressure Number of pushing operations required for forming a single inclined three-way pipe fitting Number of heat treatment operations required for forming a single inclined three-way pipe fitting Qualified rate Example 1 400 MPa 5~6 5~6 96% Example 2 400 MPa 5~6 5~6 90% Example 3 400 MPa 5~6 5~6 92% Example 4 400 MPa 5~6 5~6 86% Example 5 400 MPa 5~6 5~6 100% Comparative example 150 MPa 10~11 10~11 72%

[0076] As can be seen from the above table, by the method of the examples, during internal high-pressure forming, compared with the method of the comparative examples, a greater pressure can be used, reducing the number of pushing times and heat treatment times, and significantly improving the qualification rate. From the comparison between Example 1 and Example 2, it can be known that without differential feeding of the left pusher and the right pusher, the qualification rate of the inclined tee pipe fitting will be reduced; from the comparison between Example 1 and Example 3, it can be known that if the threshold value of the top thrust is set too small, the qualification rate of the inclined tee pipe fitting will be reduced; from the comparison between Example 1 and Example 4, it can be known that without staged pressure relief, the qualification rate of the inclined tee pipe fitting will be reduced; from the comparison between Example 1 and Example 5, it can be known that adding molybdenum disulfide and graphene lubricants to the main pipe cavity and the branch pipe cavity respectively will improve the qualification rate of the inclined tee pipe fitting.

[0077] Based on the above embodiments of the present application, without explicit negation or conflict, the technical features of one embodiment can be beneficially combined with one or more other embodiments.

[0078] Although some specific embodiments of the present application have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration purposes and not for limiting the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified or equivalent substitutions can be made for some technical features without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for internal high-pressure forming of a tee pipe fitting, characterized in that, The method is executed by the following device, which comprises: A frame body, which is respectively provided with an upper hydraulic cylinder and a lower hydraulic cylinder that are opposite up and down, and a left hydraulic cylinder and a right hydraulic cylinder that are opposite left and right; An upper mounting plate, which is connected to the piston rod of the upper hydraulic cylinder and is used for mounting the upper die of the three-way pipe fitting mold; A lower mounting plate, which is arranged on the frame body and is opposite to the upper mounting plate. The lower mounting plate is provided with a through hole for the piston rod of the lower hydraulic cylinder to pass through, and the lower mounting plate is used for mounting the lower die of the three-way pipe fitting mold; A left push head and a right push head, which are respectively arranged on the piston rods of the left hydraulic cylinder and the right hydraulic cylinder and are arranged on the same first axis; A horizontal hydraulic cylinder, which is arranged on the lower mounting plate with adjustable position. The axis of the piston rod of the horizontal hydraulic cylinder and the first axis are in the same horizontal plane and the angle formed by the two axes is variable, so that the axis of the piston rod of the horizontal hydraulic cylinder can be collinear with the axis of the branch cavity of the three-way pipe fitting mold. The piston rod of the horizontal hydraulic cylinder is provided with a pushing head, and the radial dimension of the pushing head is the same as the radial dimension of the branch cavity of the three-way pipe fitting mold; The method includes: after putting the pipe blank and closing the mold, adjusting the horizontal hydraulic cylinder so that the angle between the axis of the piston rod of the horizontal hydraulic cylinder and the first axis is the angle between the main pipe and the branch pipe of the to-be-formed three-way pipe fitting. Controlling the pushing head to enter the branch cavity. When the pipe blank expands to contact the pushing head under increased pressure, controlling the pushing head to move away from the pipe blank along the branch cavity and applying a pushing force to the pipe blank; Controlling the left push head and the right push head to synchronously apply an axial thrust to the pipe blank and feed along the axial direction of the pipe blank for replenishing materials; After the pipe blank contacts the pushing head, controlling the axial feeding distances of the left push head and the right push head to be different. Among them, the axial feeding distance of the push head in the main pipe cavity on the side where the angle formed with the branch cavity is an obtuse angle is M1, and the axial feeding distance of the push head in the main pipe cavity on the side where the angle formed with the branch cavity is an acute angle is M2, and M1 > M2; After the pipe blank contacts the pushing head, continue to increase the pressure, and control the speed of the pushing head exiting the branch cavity to be less than or equal to the speed of the top end of the branch expanding along the branch cavity; In response to the pushing head moving to a preset position, controlling the pushing head, the left push head and the right push head to stop moving, and at the same time stopping increasing the pressure and maintaining the pressure. The preset position is related to the length of the to-be-formed branch pipe; After maintaining the pressure for a preset time, controlling the pushing head to move a preset distance along the branch cavity towards the branch pipe. Among them, the end of the pushing head used to contact the pipe blank forms a stepped shape; Before the pipe blank contacts the pushing head, the internal pressure range is 50 - 100 MPa; after the pipe blank contacts the pushing head, continue to increase the pressure, and the internal pressure range is 150 - 250 MPa; when stopping increasing the pressure and maintaining the pressure, the internal pressure range is 300 - 400 MPa.

2. The method according to claim 1, wherein The magnitude of the pushing force applied by the pushing head to the pipe blank is collected in real time; In response to the pushing force being less than a preset threshold value, reducing the speed of the pushing head exiting the branch cavity, and the value range of the preset threshold value is 50 - 500 N.

3. The method according to claim 1, wherein The value range of the preset distance is 5 - 30 mm.

4. The method according to claim 1, wherein Apply a first lubricant to the inner wall of the main pipe cavity of the three-way pipe fitting mold, and apply a second lubricant to the inner wall of the branch pipe cavity of the three-way pipe fitting mold and the transition position between the branch pipe cavity and the main pipe cavity. The friction coefficient of the first lubricant is greater than that of the second lubricant.

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