A Carbon Steel Press-Fit Pipe Fitting Die and Forming Method

Abstract

The present invention relates to the technical field of pipe fitting processing, and discloses a carbon steel press-fitting type pipe fitting mold and a forming method. The mold includes a base, an upper mold, a lower mold and a pressurizing mechanism. A lower die base is fixedly installed on the base, and the lower mold is fixedly installed on the lower die base. The bottom of the upper mold and the top of the lower mold are both provided with the same number of model grooves. After the upper mold and the lower mold are closed, the corresponding two model grooves form a mold cavity. Punch mechanisms are arranged at both ends of the mold cavity. The punch mechanisms can move in a direction close to or away from the mold cavity. The punch mechanisms move in a direction close to the mold cavity and abut against the ends of the pipe fittings located in the mold cavity. The punch mechanisms can inject liquid into the pipe fittings. The pressurizing mechanism is used to pressurize the liquid in the pipe fittings, so that the outer wall of the pipe fittings is completely attached to the inner wall of the mold cavity. The present invention avoids the continuous extrusion action of the punch during the high-pressure stage, and significantly reduces the friction loss between the punch and the pipe fittings.

Description

Technical Field

[0001] The present invention relates to the technical field of pipe fitting processing, and particularly to a carbon steel press-fit pipe fitting mold and a forming method thereof. Background Art

[0002] A press-fit pipe fitting mold is a professional mold for manufacturing press-fit pipe fittings. It connects pipe fittings and accessories together through a press-fitting or cold pressing process, and is commonly used in fields such as pipe systems and automotive parts.

[0003] Chinese invention patent with publication number CN111872212B discloses a pipe fitting sealing method, which specifically includes the following steps: S1. Exhausting: Liquid medium is injected into the inner cavity of the pipe blank through the perforation of the punch, and at the same time, the gas in the pipe blank is discharged; S2. Establishing a low-pressure sealing surface: The punch moves towards the inner cavity of the pipe blank, and at the same time, liquid medium is injected into the inner cavity of the pipe blank. The pressure of the liquid medium is not greater than the yield strength of the pipe blank until the end of the pipe blank abuts against the high-pressure sealing section; S3. Establishing a high-pressure sealing surface: The punch continues to move towards the inner cavity of the pipe blank, and the punch squeezes the end of the pipe blank. At the same time, liquid medium is continuously injected into the inner cavity of the pipe blank. The pressure of the liquid medium is greater than the yield strength of the pipe blank until the end of the pipe blank undergoes bending deformation, and the bent end of the pipe blank fits against the high-pressure sealing section.

[0004] The above solution has some defects in the use process. For example, it is necessary to establish a low-pressure sealing surface and a high-pressure sealing surface respectively in two processes. Moreover, when establishing the high-pressure sealing surface, the punch needs to continue to move towards the inner cavity of the pipe blank, which inevitably causes damage to the punch and reduces the service life of the punch;

[0005] In the high-pressure stage, the pressure of the liquid medium needs to be greater than the yield strength of the pipe blank until the end of the pipe blank undergoes bending deformation. Currently, the yield strength of the pipe blank material used for carbon steel crimped pipe fittings is generally above 200 Mpa. In a long-term high-pressure working state, key components of the equipment (such as the pipeline for transporting liquid medium) are extremely easy to be damaged due to fatigue. Frequent maintenance and replacement of components increase the use cost and downtime, and reduce the production efficiency.

[0006] Therefore, a carbon steel press-fit pipe fitting mold and a forming method thereof are proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a carbon steel press-fit pipe fitting mold and a forming method thereof, so as to solve or at least alleviate one or more of the above problems and other problems existing in the prior art.

[0008] To achieve the above purpose, the present invention provides the following technical solution: A carbon steel press-fit pipe fitting mold, comprising:

[0009] A base, on which a lower die holder is fixedly installed;

[0010] An upper die and a lower die, the lower die is fixedly installed on the lower die holder;

[0011] The upper die can move in the vertical direction to complete the mold opening and closing actions. The bottom of the upper die and the top of the lower die are both provided with the same number of model cavities. The model cavities on the upper die correspond to the model cavities on the lower die one by one. After the upper die and the lower die are closed, the corresponding two model cavities form a mold cavity;

[0012] Punch mechanisms are arranged at both ends of the mold cavity, and the punch mechanisms can move towards or away from the mold cavity;

[0013] The punch mechanism moves towards the mold cavity and abuts against the end of the pipe fitting located in the mold cavity. The punch mechanism can inject liquid into the pipe fitting;

[0014] A pressurizing mechanism, which is used to pressurize the liquid in the pipe fitting, so that the outer wall of the pipe fitting is completely attached to the inner wall of the mold cavity.

[0015] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, the two groups of punch mechanisms have the same structure. The two groups of punch mechanisms both include a punch seat and a punch body. The number of punch bodies is the same as that of the mold cavities. The punch seat is fixedly connected to the punch body. The punch body is respectively provided with a flaring part and a positioning and sealing part. The flaring part is arranged at one end of the punch body close to the mold cavity, and the positioning and sealing part is arranged at one end of the flaring part away from the mold cavity. A water injection channel is opened inside the punch body, and a connection channel is opened inside the punch seat. The water outlet of the connection channel is communicated with the water injection channel, and the liquid inlet of the connection channel is communicated with the liquid outlet of the pressurizing mechanism through a pipeline.

[0016] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, the punch mechanism further includes a first driving oil cylinder, the first driving oil cylinder is fixedly installed on the base, and the end of the piston rod of the first driving oil cylinder is fixedly connected to the end of the punch seat away from the punch body.

[0017] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, a positioning block is fixedly connected to the end of the piston rod of the first driving oil cylinder away from the punch body after penetrating through the cylinder body of the first driving oil cylinder in a sealed and sliding manner. When the positioning and sealing part abuts against the end of the pipe fitting, the positioning block abuts against the end of the cylinder body of the first driving oil cylinder.

[0018] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, the pressurizing mechanism includes an oil cylinder body and a pressurizing cylinder. One end of the oil cylinder body is open, the pressurizing cylinder is fixedly installed at the opening of the oil cylinder body, a pressurizing inner cavity is formed inside the pressurizing cylinder, a fixed sealing seat is fixedly installed inside one end of the oil cylinder body close to the pressurizing cylinder, a piston seat is slidably installed inside the oil cylinder body, a piston rod member is fixedly installed on the piston seat, and one end of the piston rod member away from the piston seat hermetically slides through the fixed sealing seat and extends into the pressurizing inner cavity. A connector is fixedly installed at one end of the pressurizing cylinder away from the oil cylinder body, a pressurizing channel is formed inside the connector, one end of the pressurizing channel is communicated with the pressurizing inner cavity, and the liquid outlet of the pressurizing channel is communicated with the liquid inlet of the connection channel through the pipeline.

[0019] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, a sealing ring is fixedly installed on the inner wall of one end of the pressurizing inner cavity close to the oil cylinder body, and the piston rod member slidably seals through the inside of the sealing ring.

[0020] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, the pressurizing channel includes a transverse channel and a longitudinal channel. The transverse channel is communicated with the longitudinal channel, one end of the transverse channel is communicated with the inside of the pressurizing inner cavity, a one - way valve is installed at the liquid inlet of the longitudinal channel, and the liquid outlet of the longitudinal channel is communicated with the liquid inlet of the connection channel through the pipeline.

[0021] In a carbon steel press - fitting pipe fitting mold according to the present invention, optionally, the transverse channel and the longitudinal channel are distributed in a cross - shape, and a pressure sensor for monitoring the internal pressure of the pipe fitting is fixedly installed at one end of the transverse channel away from the pressurizing inner cavity.

[0022] The present invention also provides a method for forming a carbon steel press - fitting pipe fitting, which uses the above - mentioned carbon steel press - fitting pipe fitting mold for processing, and specifically includes the following steps:

[0023] S1. Closing the mold: Place the pipe fitting in the model groove of the lower mold, and then move the upper mold towards the lower mold to perform the closing - mold operation.

[0024] S2. Centering: Control the piston rods of the two first driving oil cylinders to extend, and then drive the punch body to move towards the mold cavity, so that the flared part is closely attached to the end of the pipe fitting. At this time, the punch body reaches the centering position. During the movement of the punch body, inject liquid into the inside of the pipe fitting through the water injection channel to discharge the air inside the pipe fitting.

[0025] S3. Preliminary forming: After reaching the centering position, the punch body continues to move inward into the pipe fitting, causing the positioning and sealing part to be in close contact with the end of the pipe fitting. At this time, the positioning block abuts against the end of the cylinder body of the first driving oil cylinder, and the punch body stops moving.

[0026] S4. Pressurized forming: The piston rod of the first driving oil cylinder stops moving, and the pressurizing mechanism is started to drive the piston rod part to move towards the pressurizing inner cavity, pressurizing the liquid inside the pipe fitting. After reaching the set required pressure, the high-pressure liquid makes the outer wall of the pipe fitting fully fit the inner wall of the mold cavity, obtaining a formed pipe.

[0027] S5. Mold opening: Control the piston rod of the first driving oil cylinder to retract, thereby driving the punch body to move away from the mold cavity, separating the punch body from the formed pipe. Then move the upper mold upward to take out the formed pipe from the mold groove of the lower mold.

[0028] In step S2, when the flaring part is in close fit with the end of the pipe fitting, the pressure inside the pipe fitting is 0 - 30 MPa. In step S4, the forming pressure inside the pipe fitting is 80 - 130 MPa.

[0029] In a method for forming a carbon steel press - fitting pipe fitting according to the present invention, optionally, in step S2, when the flaring part forms a sealing fit with the end of the pipe fitting, an initial pressure PA inside the pipe fitting is established, where 0 MPa < PA ≤ 30 MPa;

[0030] In step S4, the pressure inside the pipe fitting is increased to the forming pressure PB through the pressurizing mechanism, where 80 MPa ≤ PB ≤ 130 MPa.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] The punch body adopts a combined design of a flaring part and a positioning and sealing part, which can form an initial seal with the end of the pipe fitting through the flaring part during the centering stage. Subsequently, only the positioning and sealing part is required to maintain the seal, avoiding the continuous extrusion action of the punch during the high - pressure stage in the traditional process, significantly reducing the frictional loss between the punch and the pipe fitting, and prolonging the service life of the punch;

[0033] The pressurizing mechanism adopts an integrated design of an oil cylinder and a pressurizing cylinder, and realizes liquid pressurization through the linear motion of the piston rod part, avoiding the pipeline fatigue problem caused by the continuous high - pressure operation of the traditional high - pressure pump. At the same time, the setting of the one - way valve and the pressure sensor can accurately control the pressure fluctuation, reduce the equipment damage caused by unstable pressure, and reduce the maintenance frequency and cost;

[0034] The forming pressure of the pipe fitting is reduced to 8 MPa - 130 MPa, which can significantly improve the service life of the liquid medium transmission pipeline;

[0035] By setting the centering position, ensure that the sizes of both ends are consistent after the pipe fitting is formed, and guarantee the product quality. Brief Description of the Drawings

[0036] Figure 1 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention;

[0037] Figure 2 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention in the centering stage;

[0038] Figure 3 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention in the initial sealing and forming stage;

[0039] Figure 4 It is a schematic structural diagram of the lower mold of the carbon steel press-fit pipe fitting mold of the present invention;

[0040] Figure 5 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention when the punch is not pressed into the pipe fitting;

[0041] Figure 6 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention when the flaring part of the punch abuts against the end of the pipe fitting;

[0042] Figure 7 It is a schematic structural diagram of the carbon steel press-fit pipe fitting mold of the present invention when the positioning and sealing part of the punch abuts against the end of the pipe fitting;

[0043] Figure 8 It is a schematic cross-sectional structure diagram of the formed pipe;

[0044] Figure 9 It is a schematic structural diagram of an additional mechanism in a carbon steel press-fit pipe fitting mold.

[0045] In the figure: 100, base; 200, upper mold; 300, lower die base; 400, lower mold; 401, model groove; 500, punch mechanism; 501, first driving oil cylinder; 502, punch body; 5021, flaring part; 5022, positioning and sealing part; 5023, water injection channel; 5024, punch seat; 5025, connecting channel; 503, positioning block; 600, pipe fitting; 601, formed pipe; 700, pressurizing mechanism; 701, cylinder body; 702, piston seat; 703, piston rod; 704, fixed sealing seat; 705, pressurizing cylinder; 706, pressurizing cavity; 7061, sealing ring; 707, connector; 708, transverse channel; 709, longitudinal channel; 710, one-way valve; 711, pressure sensor. Detailed Embodiments

[0046] The following further illustrates the technical solution of the present invention in conjunction with the drawings and through specific embodiments.

[0047] Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams rather than physical drawings, and should not be construed as a limitation on this patent; in order to better illustrate the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, which does not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0048] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if terms such as "upper", "lower", "left", "right", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the attached drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms used to describe the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as a limitation on this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0049] In the description of the present invention, unless otherwise clearly specified and limited, if terms such as "connection" are used to indicate the connection relationship between components, this term should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] Embodiment

[0051] Please refer to Figures 1 to 9 , this embodiment provides a carbon steel press - fitting pipe fitting mold, including: a base 100, an upper mold 200, a lower mold 400, and a boosting mechanism 700, where:

[0052] A lower die base 300 is fixedly installed on the base 100; the lower mold 400 is fixedly installed on the lower die base 300;

[0053] The upper mold 200 can move in the vertical direction to complete the mold - opening and mold - closing actions. The bottom of the upper mold 200 and the top of the lower mold 400 are both provided with the same number of model cavities 401. The model cavities 401 on the upper mold 200 and the model cavities 401 on the lower mold 400 correspond one by one. After the upper mold 200 and the lower mold 400 are closed, the corresponding two model cavities 401 form a mold cavity; punch mechanisms 500 are arranged at both ends of the mold cavity, and the punch mechanisms 500 can move in a direction close to or away from the mold cavity;

[0054] The punch mechanism 500 moves towards the cavity, abuts against the end of the pipe fitting 600 located in the cavity, and the punch mechanism 500 can inject liquid into the pipe fitting 600.

[0055] The pressure boosting mechanism 700 is used to boost the pressure of the liquid in the pipe fitting 600, so that the outer wall of the pipe fitting 600 is fully attached to the inner wall of the cavity.

[0056] By adopting the above scheme, the base 100 provides support and an installation foundation for the whole mold. The lower die base 300 is fixed on the base 100 and is used to install the lower die 400. The up-and-down movement of the upper die 200 realizes mold opening and closing. After mold closing, the mold cavity 401 is formed for placing the pipe fitting 600. The punch mechanism 500 moves to the end of the pipe fitting 600 and injects liquid. The pressure boosting mechanism 700 boosts the pressure of the liquid in the pipe fitting 600, so that the outer wall of the pipe fitting 600 is attached to the inner wall of the cavity under the action of pressure, and the forming of the pipe fitting is completed.

[0057] In this embodiment, the two groups of punch mechanisms 500 have the same structure. The two groups of punch mechanisms 500 both include a punch seat 5024 and a punch body 502. The number of punch bodies 502 is the same as that of the cavities. The punch seat 5024 is fixedly connected to the punch body 502. The punch body 502 is respectively provided with a flaring portion 5021 and a positioning and sealing portion 5022. The flaring portion 5021 is arranged at one end of the punch body 502 close to the cavity, and the positioning and sealing portion 5022 is arranged at one end of the flaring portion 5021 away from the cavity. A water injection channel 5023 is opened inside the punch body 502, and a connection channel 5025 is opened inside the punch seat 5024. The water outlet of the connection channel 5025 is communicated with the water injection channel 5023, and the liquid inlet of the connection channel 5025 is communicated with the liquid outlet of the pressure boosting mechanism 700 through a pipeline.

[0058] The punch seat 5024 is used to fix the punch body 502. The flaring portion 5021 facilitates the cooperation between the punch body 502 and the end of the pipe fitting 600 to form the centering operation of the pipe fitting 600, and the positioning and sealing portion 5022 ensures the sealing between the punch body 502 and the end of the pipe fitting 600. The liquid enters the inside of the pipe fitting 600 from the pressure boosting mechanism 700 through the pipeline, the connection channel 5025 and the water injection channel 5023.

[0059] Furthermore, the punch mechanism 500 further includes a first driving oil cylinder 501. The first driving oil cylinder 501 is fixedly installed on the base 100, and the end of the piston rod of the first driving oil cylinder 501 is fixedly connected to the end of the punch seat 5024 away from the punch body 502.

[0060] The first driving oil cylinder 501 is fixed on the base 100, and the expansion and contraction of its piston rod drives the punch seat 5024 and the punch body 502 to move, realizing the operation of the punch body 502 approaching or departing from the cavity.

[0061] In this embodiment, one end of the piston rod of the first driving oil cylinder 501, which is far away from the punch body 502, hermetically and slidably penetrates through the cylinder block of the first driving oil cylinder 501 and is fixedly connected with a positioning block 503. When the positioning and sealing part 5022 abuts against the end of the pipe fitting 600, the positioning block 503 abuts against the end of the cylinder block of the first driving oil cylinder 501.

[0062] When the punch body 502 moves to the position where the positioning and sealing part 5022 abuts against the end of the pipe fitting 600, the positioning block 503 abuts against the end of the cylinder block of the first driving oil cylinder 501, playing a limiting role to prevent the punch body 502 from moving excessively.

[0063] In this embodiment, the pressurizing mechanism 700 includes an oil cylinder block 701 and a pressurizing cylinder 705. One end of the oil cylinder block 701 is open. The pressurizing cylinder 705 is fixedly installed at the opening of the oil cylinder block 701. A pressurizing inner cavity 706 is formed inside the pressurizing cylinder 705. A fixed sealing seat 704 is fixedly installed inside one end of the oil cylinder block 701 close to the pressurizing cylinder 705. A piston seat 702 is slidably installed inside the oil cylinder block 701. A piston rod part 703 is fixedly installed on the piston seat 702. One end of the piston rod part 703, which is far away from the piston seat 702, hermetically and slidably penetrates through the fixed sealing seat 704 and extends into the pressurizing inner cavity 706. A connecting head 707 is fixedly installed at one end of the pressurizing cylinder 705 far away from the oil cylinder block 701. A pressurizing channel is formed inside the connecting head 707. One end of the pressurizing channel is communicated with the pressurizing inner cavity 706. The liquid outlet of the pressurizing channel is communicated with the liquid inlet of the connecting channel 5025 through a pipeline.

[0064] The piston seat 702 slides inside the oil cylinder block 701, driving the piston rod part 703 to move inside the pressurizing inner cavity 706. When the piston rod part 703 moves into the pressurizing inner cavity 706, the liquid pressure inside the pressurizing inner cavity 706 increases. The high-pressure liquid enters the inside of the pipe fitting 600 through the pressurizing channel, the pipeline and the connecting channel 5025, thereby increasing the liquid pressure inside the pipe fitting 600.

[0065] In this embodiment, a sealing ring 7061 is fixedly installed on the inner wall of one end of the pressurizing inner cavity 706 close to the oil cylinder block 701. The piston rod part 703 slidably and hermetically penetrates through the inside of the sealing ring 7061.

[0066] The sealing ring 7061 ensures the sealing between the piston rod part 703 and the pressurizing inner cavity 706, prevents the liquid inside the pressurizing inner cavity 706 from leaking, and ensures the pressurizing effect.

[0067] In this embodiment, the pressurization channel includes a transverse channel 708 and a longitudinal channel 709. The transverse channel 708 communicates with the longitudinal channel 709. One end of the transverse channel 708 is internally connected to the pressurization cavity 706. A check valve 710 is installed at the liquid inlet of the longitudinal channel 709. The liquid outlet of the longitudinal channel 709 is connected to the liquid inlet of the connection channel 5025 through a pipeline.

[0068] The transverse channel 708 and the longitudinal channel 709 form the pressurization channel, enabling the liquid in the pressurization cavity 706 to flow to the pipe fitting 600. The check valve 710 ensures that the liquid can only flow from the pressurization cavity 706 to the pipe fitting 600, preventing the liquid from flowing back from the liquid inlet of the longitudinal channel 709. It should be noted that the liquid inlet of the check valve 710 is connected to the liquid outlet of an external water pump.

[0069] In this embodiment, the transverse channel 708 and the longitudinal channel 709 are arranged in a cross shape. A pressure sensor 711 for monitoring the internal pressure of the pipe fitting 600 is fixedly installed at one end of the transverse channel 708 away from the pressurization cavity 706.

[0070] The pressure sensor 711 is installed at one end of the transverse channel 708 away from the pressurization cavity 706, and can monitor the internal pressure of the pipe fitting 600 in real time, so as to control the pressurization process and ensure that the pipe fitting 600 is formed under appropriate pressure.

[0071] Among them, the pressure sensor 711 is signal-connected to the controller. The driving device of the upper mold 200 is a second driving oil cylinder. The output end of the controller is respectively connected to the control end of the first driving oil cylinder 501, the oil cylinder control valve (for controlling the movement of the piston rod part 703) that drives the piston seat 702 to move in the pressurization mechanism 700, and the control end of the second driving oil cylinder of the driving device of the upper mold 200 (for realizing the vertical movement of the upper mold 200); the input end of the controller is connected to the signal output end of the pressure sensor 711. Through the above connections, the controller can implement the following control logics:

[0072] Send an instruction to the control end of the second driving oil cylinder to drive the upper mold 200 to move up and down to complete the mold closing and mold opening actions. Send a signal to the control end of the first driving oil cylinder 501 to control the telescopic movement of its piston rod, drive the punch body 502 to approach or move away from the mold cavity, and realize the operations of centering, preliminary forming and separating from the formed pipe fitting;

[0073] Control the oil cylinder control valve of the pressurization mechanism 700 to drive the piston rod part 703 to move towards the pressurization cavity 706 to pressurize the liquid in the pipe fitting 600;

[0074] Receive the pressure signal feedback from the pressure sensor 711, monitor the internal pressure of the pipe fitting 600, and when the set pressure is reached (e.g., 80 MPa ≤ PB ≤ 130 MPa), adjust or stop the boosting operation to ensure that the outer wall of the pipe fitting 600 is fully fitted with the inner wall of the mold cavity, achieving precise forming control;

[0075] To further achieve precise forming control, the controller uses the pressure dynamic control equation to control the operation of the carbon steel press - fitting pipe mold. The specific pressure dynamic control equation is as follows:

[0076] ;

[0077] Parameter description table:

[0078] Parameter Physical meaning Typical range σy Yield strength of material 235 - 500 MPa t Wall thickness of pipe fitting 1.5 - 3.5 mm D Nominal diameter of pipe fitting 15 - 100 mm α Strain rate sensitivity coefficient 0.12-0.25 β Pressure gradient correction coefficient 0.05 - 0.15 s·MPa-1 P Actual pressure increase rate 20 - 50 MPa / s E Elastic modulus of material 200 GPa K Material hardening coefficient 500 - 800 MPa <![CDATA[V0]]> Initial volume of pipe fitting 50 - 500 cm³ ΔV Liquid incremental volume 10 - 50 cm³ γ Volume correction index 0.6-0.8

[0079] For example, when forming a DN50 carbon steel pipe fitting (σ y = 345 MPa, t = 2 mm, D = 50 mm), set:

[0080] α = 0.18, β = 0.1, P = 35 MPa / s, E = 200 GPa, K = 600 MPa, V0 = 120 cm³,

[0081] ΔV = 30 cm³, γ = 0.7;

[0082] Calculation process:

[0083] 1. Calculate the material correction term:

[0084] ;

[0085] 2. Calculate the volume correction term:

[0086] ;

[0087] Substitute into the equation:

[0088]

[0089] At this time, the pressure is increased to 16.2 MPa through the boosting mechanism in cooperation with the pressure sensor and the controller.

[0090] Technical effects:

[0091] Dynamic compensation effect: The adaptive adjustment of the pressure rate is achieved through the P parameter, avoiding local overload of the pipe fitting;

[0092] Material adaptability: The elastic - plastic conversion characteristics of different batches of materials are corrected by introducing the E / K ratio;

[0093] Volume compensation: Considering the volume change caused by liquid compressibility and pipe fitting deformation to improve dimensional accuracy;

[0094] Process window expansion: Compared with traditional empirical formulas, the forming pressure error is significantly reduced.

[0095] The working principle process is as follows:

[0096] 1. Preset the parameters of σy, E, and K in the material database;

[0097] 2. Collect the data of the pressure sensor in real time;

[0098] 3. Calculate P and automatically obtain the parameters of D and t according to the mold size;

[0099] 4. Measure the change amount of ΔV through a laser rangefinder;

[0100] 5. Solve the target value of PB by the dynamic equation;

[0101] 6. Feedback control the piston movement speed of the supercharging mechanism;

[0102] 7. Enter the pressure holding stage after reaching the target pressure.

[0103] Experimental verification data comparison:

[0104] Forming method Roundness error (mm) Springback amount (μm) Qualified rate Traditional method 0.15-0.25 80-120 92.3% This equation method 0.06-0.12 25-40 98.7%

[0105] This equation couples the material constitutive relationship, the dynamic supercharging process, and the volume change. By introducing the logarithmic pressure gradient term and the volume correction exponent, it breaks through the limitation of the static setting of pressure parameters in traditional forming processes and is particularly suitable for the forming of high-precision thin-walled pipe fittings.

[0106] The present invention also provides a forming method for carbon steel press-fitting pipe fittings, which uses the above-mentioned carbon steel press-fitting pipe fitting mold for processing, and specifically includes the following steps:

[0107] S1. Close the mold, place the pipe fitting 600 in the model groove 401 of the lower mold 400, and then move the upper mold 200 towards the lower mold 400 to perform the mold closing operation;

[0108] S2. Center, control the piston rods of the two first driving oil cylinders 501 to extend, and then drive the punch body 502 to move towards the mold cavity, so that the flared part 5021 is closely attached to the end of the pipe fitting 600. At this time, the punch body 502 reaches the centered position. During the movement of the punch body 502, liquid is injected into the inside of the pipe fitting 600 through the water injection channel 5023 to discharge the air inside the pipe fitting 600;

[0109] S3. Preliminary forming: After reaching the centering position, the punch body 502 continues to move into the interior of the pipe fitting 600, causing the positioning and sealing portion 5022 to come into close contact with the end of the pipe fitting 600. At this time, the positioning block 503 abuts against the end of the cylinder body of the first driving oil cylinder 501, and the punch body 502 stops moving.

[0110] S4. Pressurized forming: The piston rod of the first driving oil cylinder 501 stops moving, and the pressurizing mechanism 700 is started to drive the piston rod member 703 to move towards the pressurizing inner cavity 706, pressurizing the liquid inside the pipe fitting 600. After reaching the set required pressure, the high-pressure liquid causes the outer wall of the pipe fitting 600 to completely fit the inner wall of the mold cavity, obtaining the formed pipe 601.

[0111] S5. Mold opening: Control the piston rod of the first driving oil cylinder 501 to retract, thereby driving the punch body 502 to move away from the mold cavity, separating the punch body 502 from the formed pipe 601. Then move the upper mold 200 upward to take out the formed pipe 601 from the mold groove 401 of the lower mold 400.

[0112] It should be noted that in step S2, when the flaring portion 5021 forms a sealing fit with the end of the pipe fitting 600, an initial pressure PA is established inside the pipe fitting 600, where 0 MPa < PA ≤ 30 MPa.

[0113] In step S4, the pressure inside the pipe fitting 600 is increased to the forming pressure PB through the pressurizing mechanism 700, where 80 MPa ≤ PB ≤ 130 MPa.

[0114] This embodiment also provides the following experiment to verify the improvement effect of pressure optimization on the reliability of the equipment.

[0115] I. Experimental objectives

[0116] Verify that when the forming pressure is within the range of 80 - 130 MPa, the service life of the liquid medium conveying pipeline (measured by the number of cycles or leakage rate) is significantly improved compared to traditional high pressure (such as above 200 MPa).

[0117] Experimental variable table

[0118] Parameter Control group (traditional pressure) Experimental group (optimized pressure) Forming pressure 200 - 250 MPa 80 - 130 MPa Pressure fluctuation range ±10% ±5% (closed-loop control) Number of test cycles 5000 times 5000 times Pipeline material 304 stainless steel 304 stainless steel

[0119] Experimental method

[0120] 1. Pipeline life test:

[0121] Under traditional pressure (200 - 250 MPa) and optimized pressure (80 - 130 MPa), respectively conduct

[0122] 5000 - cycle liquid filling tests.

[0123] Record the number of pipeline leaks, the inner wall wear amount, and the seal life.

[0124] 2. Pressure stability test:

[0125] Use a pressure sensor (such as the pressure sensor 711 in the embodiment) to monitor the pressure fluctuation in real time and analyze the influence of pressure stability on pipeline fatigue.

[0126] 3. Material fatigue analysis:

[0127] Conduct metallographic analysis and microhardness test on the pipeline after testing to observe the changes in the material microstructure.

[0128] Experimental data:

[0129] 1. Pipeline life comparison table

[0130] Index Control group (200 - 250 MPa) Experimental group (80 - 130 MPa) Improvement range Average number of leakage times / 5000 times 12 times 0 times 100% Seal replacement cycle 1000 hours 3000 hours 200% Wear amount of pipeline inner wall (μm) 5.2 1.8 65%

[0131] 2. Pressure stability analysis table

[0132] Detection item Control group (200 - 250 MPa) Experimental group (80 - 130 MPa) Intergranular crack density (number / mm²) 12.5 3.8 Microhardness change (HV) +15% +5%

[0133] 3. Material fatigue analysis table

[0134] Detection item Control group (200 - 250 MPa) Experimental group (80 - 130 MPa) Intergranular crack density (number / mm²) 12.5 3.8 Microhardness change (HV) +15% +5%

[0135] Data analysis and mechanism explanation

[0136] 1. Relationship between pressure and pipeline life

[0137] 1.1 Pressure reduction reduces material fatigue:

[0138] According to the material fatigue curve (S-N curve), for every 20% reduction in stress, the fatigue life can be increased by 1-2 orders of magnitude. The pressure of the experimental group is reduced by about 40% compared with the control group, and the cyclic life is significantly improved (such as the seal life increasing from 1000 hours to 3000 hours).

[0139] 1.2 Reduction of pressure fluctuation rate:

[0140] The experimental group adopts closed-loop control (±5% fluctuation), reducing the impact load by 50% compared with the control group (±10%) and reducing the high-frequency fatigue damage of the pipeline.

[0141] 2. Failure mechanism of liquid medium transmission pipeline

[0142] 2.1 Failure mode under high pressure:

[0143] 2.11 Increased corrosion: High pressure causes the local flow rate of the liquid medium to accelerate, scouring the inner wall of the pipeline and accelerating corrosion (the inner wall wear amount of the control group is 5.2 μm).

[0144] 2.12 Stress corrosion cracking: Under high pressure, stress concentration occurs at the grain boundaries of metals, and intergranular cracks are likely to occur (the density of intergranular cracks in the control group is 12.5 cracks / mm²).

[0145] 2.2 Improvements after low-pressure optimization:

[0146] Reducing the pressure reduces erosion and stress concentration, and delays material fatigue (the density of intergranular cracks in the experimental group is only 3.8 cracks / mm²).

[0147] 3. Synergistic effect of the control system

[0148] 3.1 Closed-loop pressure control:

[0149] The controller in the embodiment feeds back in real time through the pressure sensor 711, limits the pressure fluctuation within ±5%, and avoids instantaneous overload under traditional high pressure (the peak impact frequency is reduced by 66.7%).

[0150] 3.2 Precise pressure boost matching:

[0151] The pressure booster cylinder 705 of the pressure boosting mechanism 700 and the cylinder block 701 of the oil cylinder are designed, combined with the anti-backflow function of the one-way valve 710, to ensure stable pressure output and reduce pipeline vibration.

[0152] Conclusion

[0153] Experimental data shows that:

[0154] When the forming pressure is reduced from 200 - 250 MPa to 80 - 130 MPa, the leakage rate of the liquid medium conveying pipeline is reduced by 100%, and the service life of the seal is extended by 200%.

[0155] The pressure fluctuation rate is reduced from 8.5% to 2.3%, the wear amount on the inner wall of the pipeline is reduced by 65%, and the material fatigue damage is significantly reduced.

[0156] The synergistic effect of the closed-loop pressure control and the design of the pressure boosting mechanism realizes the overall improvement of the pipeline service life.

[0157] This data is used to support the technical solution in the embodiment and prove the improvement effect of pressure optimization on the equipment reliability.

[0158] Parts not involved in the present invention are the same as or can be implemented by using the prior art. Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A carbon steel press-fit pipe fitting mold, characterized in that, Including: A base (100), on which a lower die holder (300) is fixedly installed; An upper die (200) and a lower die (400), the lower die (400) is fixedly installed on the lower die holder (300); the upper die (200) can move in the vertical direction to complete the die opening and closing actions. The bottom of the upper die (200) and the top of the lower die (400) are both provided with the same number of model cavities (401). The model cavities (401) on the upper die (200) correspond to the model cavities (401) on the lower die (400) one by one. After the upper die (200) and the lower die (400) are closed, the corresponding two model cavities (401) form a die cavity; punch mechanisms (500) are arranged at both ends of the die cavity, and the punch mechanisms (500) can move towards or away from the die cavity; when the punch mechanisms (500) move towards the die cavity and abut against the ends of the pipe fittings (600) located in the die cavity, the punch mechanisms (500) can inject liquid into the pipe fittings (600); the two groups of punch mechanisms (500) have the same structure. The two groups of punch mechanisms (500) both include a punch seat (5024) and a punch body (502). The number of punch bodies (502) is the same as that of the die cavities. The punch seat (5024) is fixedly connected to the punch body (502). An expanding part (5021) and a positioning and sealing part (5022) are respectively arranged on the punch body (502). The expanding part (5021) is arranged at one end of the punch body (502) close to the die cavity, and the positioning and sealing part (5022) is arranged at one end of the expanding part (5021) away from the die cavity. A water injection channel (5023) is opened inside the punch body (502), and a connection channel (5025) is opened inside the punch seat (5024). The water outlet of the connection channel (5025) is communicated with the water injection channel (5023). The liquid inlet of the connection channel (5025) is communicated with the liquid outlet of a pressurizing mechanism (700) through a pipeline; the pressurizing mechanism (700) is used to pressurize the liquid in the pipe fittings (600) so that the outer wall of the pipe fittings (600) is completely attached to the inner wall of the die cavity; The carbon steel press-fit pipe fitting mold calculates the forming pressure by the controller executing the pressure dynamic control equation, and the equation is: ; Wherein: σ y is the yield strength of the material, with a range of 235 - 500 MPa; t is the wall thickness of the pipe fitting, and the range is 1.5 - 3.5 mm; D is the nominal diameter of the pipe fitting, and the range is 15 - 100 mm; α is the strain rate sensitivity coefficient, and the range is 0.12 - 0.25; β is the pressure gradient correction coefficient, with a range of 0.05 - 0.15 s·MPa -1 ; P is the actual pressurizing rate, and the range is 20 - 50 MPa / s; E is the elastic modulus of the material, and the range is 200 GPa; K is the material hardening coefficient, and the range is 500 - 800 MPa; V0 is the initial volume of the pipe fitting, and the range is 50 - 500 cm 3 ; ΔV is the incremental volume of the liquid, with a range of 10 - 50 cm 3 ; γ is the volume correction index, and the range is 0.6 - 0.8; The controller adjusts the moving speed of the piston rod part (703) of the pressurizing mechanism (700) according to the feedback signal of the pressure sensor (711) so that the internal pressure of the pipe fitting (600) reaches the forming pressure PB, and 80 MPa ≤ PB ≤ 130 MPa.

2. The carbon steel press - fitting pipe fitting die according to claim 1, characterized in that: The punch mechanism (500) further includes a first driving oil cylinder (501). The first driving oil cylinder (501) is fixedly installed on the base (100), and the end of the piston rod of the first driving oil cylinder (501) is fixedly connected to one end of the punch seat (5024) away from the punch body (502).

3. The carbon steel press - fitting pipe fitting mold according to claim 2, characterized in that: One end of the piston rod of the first driving oil cylinder (501) away from the punch body (502) hermetically slides through the cylinder body of the first driving oil cylinder (501) and is fixedly connected with a positioning block (503). When the positioning and sealing part (5022) abuts against the end of the pipe fitting (600), the positioning block (503) abuts against the end of the cylinder body of the first driving oil cylinder (501).

4. A carbon steel press-fit pipe fitting mold according to claim 3, characterized in that: The pressurizing mechanism (700) includes an oil cylinder body (701) and a pressurizing cylinder (705). One end of the oil cylinder body (701) is open. The pressurizing cylinder (705) is fixedly installed at the opening of the oil cylinder body (701). A pressurizing inner cavity (706) is formed inside the pressurizing cylinder (705). A fixed sealing seat (704) is fixedly installed inside one end of the oil cylinder body (701) close to the pressurizing cylinder (705). A piston seat (702) is slidably installed inside the oil cylinder body (701). A piston rod part (703) is fixedly installed on the piston seat (702). One end of the piston rod part (703) away from the piston seat (702) hermetically slides through the fixed sealing seat (704) and extends into the pressurizing inner cavity (706). A connecting head (707) is fixedly installed at one end of the pressurizing cylinder (705) away from the oil cylinder body (701). A pressurizing channel is formed inside the connecting head (707). One end of the pressurizing channel is communicated with the pressurizing inner cavity (706), and the liquid outlet of the pressurizing channel is communicated with the liquid inlet of the connecting channel (5025) through the pipeline.

5. A carbon steel press-fit pipe fitting mold according to claim 4, characterized in that: A sealing ring (7061) is fixedly installed on the inner wall of one end of the pressurizing inner cavity (706) close to the oil cylinder body (701). The piston rod part (703) slidably seals through the inside of the sealing ring (7061).

6. The die for carbon steel press-fit pipe fittings according to claim 5, characterized in that: The pressurizing channel includes a transverse channel (708) and a longitudinal channel (709). The transverse channel (708) is communicated with the longitudinal channel (709). One end of the transverse channel (708) is communicated with the inside of the pressurizing inner cavity (706). A one-way valve (710) is installed at the liquid inlet of the longitudinal channel (709). The liquid outlet of the longitudinal channel (709) is communicated with the liquid inlet of the connecting channel (5025) through the pipeline.

7. The die for carbon steel press-fit pipe fittings according to claim 6, characterized in that: The transverse channel (708) and the longitudinal channel (709) are distributed in a cross shape. At one end of the transverse channel (708) far from the pressurizing inner cavity (706), a pressure sensor (711) for monitoring the internal pressure of the pipe fitting (600) is fixedly installed.

8. A forming method for carbon steel press-fitting pipe fittings, characterized in that: Using the carbon steel crimping type pipe fitting mold according to any one of claims 4-7 for processing, specifically including the following steps: S1. Closing the mold: Place the pipe fitting (600) in the mold cavity (401) of the lower mold (400), and then move the upper mold (200) towards the lower mold (400) to perform the mold closing operation. S2. Centering: Control the piston rods of the two first driving oil cylinders (501) to extend, thereby driving the punch body (502) to move towards the mold cavity, so that the flaring portion (5021) is in close contact with the end of the pipe fitting (600). At this time, the punch body (502) reaches the centering position. During the movement of the punch body (502), liquid is injected into the interior of the pipe fitting (600) through the water injection channel (5023) to discharge the air inside the pipe fitting (600). S3. Preliminary forming: After reaching the centering position, the punch body (502) continues to move into the interior of the pipe fitting (600), so that the positioning and sealing portion (5022) is in close contact with the end of the pipe fitting (600). At this time, the positioning block (503) abuts against the end of the cylinder body of the first driving oil cylinder (501), and the punch body (502) stops moving. S4. Pressurizing and forming: The piston rod of the first driving oil cylinder (501) stops moving, and the pressurizing mechanism (700) is started to drive the piston rod member (703) to move towards the pressurizing inner cavity (706) to pressurize the liquid inside the pipe fitting (600). After reaching the set required pressure, the high-pressure liquid makes the outer wall of the pipe fitting (600) completely fit the inner wall of the mold cavity to obtain the formed pipe (601). S5. Opening the mold: Control the piston rod of the first driving oil cylinder (501) to retract, thereby driving the punch body (502) to move away from the mold cavity, so as to separate the punch body (502) from the formed pipe (601). Then move the upper mold (200) upward to take out the formed pipe (601) from the mold cavity (401) of the lower mold (400).

9. A forming method for carbon steel press - fitting pipe fittings according to claim 8, characterized in that: In step S2, when the flaring portion (5021) forms a sealing fit with the end of the pipe fitting (600), an initial pressure PA inside the pipe fitting (600) is established, where 0 MPa < PA ≤ 30 MPa. In step S4, the internal pressure of the pipe fitting (600) is increased to the forming pressure PB through the pressurizing mechanism (700), where 80 MPa ≤ PB ≤ 130 MPa.

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