Tool structure and method for prolonging fatigue life of 35MPa flaring-free rolling connecting piece

Abstract

The invention discloses a tool structure and method for prolonging the fatigue life of a 35 MPa flaring-free rolling connecting piece. The tool structure comprises a die clamping assembly, a positioning sleeve assembled in the die clamping assembly and a pipe sleeve assembled in the positioning sleeve, and a guide pipe is assembled in the pipe sleeve; the clamping die assembly comprises a first clamping die body and a second clamping die body corresponding to the first clamping die body, and a limiting cavity used for assembling a positioning sleeve is formed in the first clamping die body and the second clamping die body. A tool structure is used for limiting the guide pipe and the pipe sleeve which are connected in a rolling mode and controlling structural deformation, so that structural stress is improved, the problem of fatigue test failure of the 35 MPa high-pressure combined guide pipe is solved, the stress distribution condition of the connecting position is improved, beneficial residual stress of a connecting piece is increased, and the service life of the connecting piece is prolonged. And the fatigue strength of the connecting piece under the bending stress load is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rolled flare-free connections, and in particular to a tooling structure and method for improving the fatigue life of a 35MPa flare-free rolled connection. Background Art

[0002] Flareless rolled connectors are mainly used in aircraft hydraulic systems. They replace traditional flared connectors in high-pressure systems and are important components that affect aircraft safety and reliability. The advantages of flareless connectors are good sealing performance and high connection strength. Compared with traditional flared connectors, they are more reliable. At present, the maximum working pressure of domestic flareless rolled series products has reached 35MPa. The rolling flareless connection technology is to connect the catheter and the 24° cone-plated sealed sleeve by inner diameter rolling. The catheter and the sleeve will be connected by rolling equipment. In this process, the catheter will be plastically deformed and pressed into the internal notch of the sleeve to achieve the purpose of permanent connection. The rolled catheter assembly uses the sleeve and the joint with a 24° cone surface to be connected together by threading to ensure the sealing of the catheter connection. It is a detachable connection technology. During the rolling connection process of the catheter and the sleeve, due to the deformation of the catheter material, the connection position has become the weak point of the product life under the flareless connection technology.

[0003] With the development of high pressure of flareless connection products, their application conditions are becoming more and more demanding. Facing high pressure working conditions, the reliability and safety of the connectors themselves are also put to the test. At present, the higher the pressure or the larger the specification of domestic flareless rolled connectors, the greater the risk of fatigue failure. The factors affecting the life of flareless connection pipe fittings are mainly concentrated in the rolling connection process, including tooling design, rolling equipment, selection of process parameters, etc. Limited by the level of domestic equipment and rolling process, the problem of fatigue failure caused by process equipment still exists in the product development process.

[0004] The main mechanism that affects the fatigue life of rolled connectors is stress concentration caused by material deformation or micro-wear in the contact parts. The most direct way to solve the stress concentration problem is to control the deformation degree of the material after rolling. In the patents "A Process for Rolling Transition Zone of Stainless Steel Non-Flaring Tube" and "A Process for Forming Stainless Steel Tube Non-Flaring with Working Pressure 28MPa", the author controlled the deformation of the inner wall of the tube after rolling by changing the inner diameter tooling needle structure and rolling parameters, and changed the stress concentration problem of the inner wall of the tube. This solution has a good improvement on the stress problem of the inner wall, but in addition to the inner diameter tooling, the outer diameter tooling also plays a very important role in affecting the life of the tube in the process link, especially for high-pressure and titanium alloy tubes. The risk of fatigue failure of simply adjusting the internal process connectors is still relatively large. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a tooling structure and method for improving the fatigue life of a 35MPa non-flaring rolled connector.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a tooling structure for improving the fatigue life of a 35MPa non-flaring rolled connector, comprising a clamping die assembly, a positioning sleeve assembled in the clamping die assembly, and a pipe sleeve assembled in the positioning sleeve, wherein a guide tube is assembled in the pipe sleeve;

[0007] The clamping mold assembly includes a first clamping mold body and a second clamping mold body corresponding to the first clamping mold body, and a limiting cavity for positioning sleeve assembly is formed in the first clamping mold body and the second clamping mold body.

[0008] Furthermore, the positioning sleeve includes a positioning column and a positioning ring arranged on the outer surface of the positioning column, the positioning ring and the positioning column form a step-like structure, the positioning ring is assembled in the limiting cavity, the positioning column is assembled in the step groove of the first clamping body and the second clamping body, and the catheter is assembled in the positioning column.

[0009] Furthermore, the end surface of the positioning column is flush with the end surface of the clamping assembly.

[0010] The present invention also provides a method for improving the fatigue life of a 35MPa non-flaring rolled connector, which is operated using a tooling structure and includes the following steps:

[0011] S1: Prepare the sleeve and conduit required for the rolling connection process, and measure the outer diameter, length, inner diameter and outer diameter of the conduit to ensure that the part size is within the tolerance range;

[0012] S2: According to the size of the catheter, select the tooling structure of the corresponding size, including the clamping die assembly and the positioning sleeve;

[0013] S3: Clean the tooling structure, pre-install the catheter and the pipe sleeve, put them into the positioning sleeve after assembly, press down the clamping die assembly to fix the catheter end, and complete the installation of the tooling structure;

[0014] S4: Debug the rolling equipment and complete the permanent connection between the casing and the conduit through the rolling equipment operation;

[0015] S5: For the combined conduit connected in S4, use a special measuring tool to measure the dimensional parameters of the diameter of the rolled part at the root of the sleeve, the inner diameter of the conduit after rolling, the elongation of the conduit after rolling, and the extension of the conduit end;

[0016] S6: Measure the bending strain of the catheter at the tail end of the sleeve. When the strain reaches the required value, pressurize the catheter to 35MPa and perform fatigue test according to the strain value.

[0017] Furthermore, step S4 specifically includes the following steps:

[0018] S4.1: Determine rolling parameters based on the catheter specifications;

[0019] S4.2: According to the rolling parameters, the rolling equipment is pressed against the end of the catheter to start the rolling operation and complete the permanent connection between the casing and the catheter.

[0020] Furthermore, in step S6, a strain gauge is arranged on the outer wall of the catheter at a distance of 5 mm to 7 mm from the rear end of the sleeve, and a strain gauge is also arranged in the vertical direction, and then the combined catheter is installed in the rotary bending fatigue test equipment.

[0021] Furthermore, when measuring strain, first adjust the position of the headstock and tailstock to ensure that the specimen catheter is coaxial, and use the micrometer to determine the coaxiality. The asymmetric offset indicated by the micrometer should not be greater than 0.08mm. After determining the coaxiality, clear the measured strain data to zero, and use the deflection adjustment rod to give the catheter a certain offset. The catheter obtains a flexural displacement through the offset. Set the speed to 100r / min to start rotating the equipment. At this time, the strain gauge reading is the bending strain. When the bending strain reaches the required value, stop adjusting the offset.

[0022] The present invention has the following beneficial effects: the present invention provides a tooling structure and method for improving the fatigue life of a 35MPa non-flaring rolled connector, which has a reliable structure and good performance. The tooling structure is used to limit the position and control the structural deformation of the rolled connected conduit and pipe sleeve to improve the structural stress, solve the problem of fatigue test failure of the 35MPa high-pressure combined conduit, improve the stress distribution at the connection, increase the beneficial residual stress of the connector, and improve the fatigue strength of the connector under bending stress load. Finally, the matching relationship between the rolling tooling size structure and the applicable conduit is specified, the rolling connection process is optimized, and the product safety performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the tooling structure in the present invention;

[0024] Figure 2 It is a schematic diagram of the assembly of the tooling structure in the present invention;

[0025] Figure 3 It is a cross-sectional view of the tooling structure of the present invention;

[0026] Figure 4 It is a schematic diagram of the positioning sleeve structure in the present invention;

[0027] Figure 5 It is a schematic diagram of the measurement position after rolling in the present invention;

[0028] Figures 1 to 5 The reference numerals shown in the figure represent respectively: 1-clamping mold assembly, 2-positioning sleeve, 3-tube sleeve, 10-first clamping mold body, 11-second clamping mold body, 20-positioning column, 21-positioning ring. DETAILED DESCRIPTION

[0029] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0030] like Figures 1 to 3 As shown, a tooling structure for improving the fatigue life of a 35MPa non-flaring rolled connector includes a clamping die assembly 1, a positioning sleeve 2 assembled in the clamping die assembly 1, and a pipe sleeve 3 assembled in the positioning sleeve 2, wherein a catheter 4 is assembled in the pipe sleeve 3; the clamping die assembly 1 includes a first clamping die body 10 and a second clamping die body 11 corresponding to the first clamping die body 10, and the first clamping die body 10 and the second clamping die body 11 are respectively provided with limiting grooves, and the two limiting grooves are assembled to form a limiting cavity for assembling the positioning sleeve 2. The tooling plays a role in limiting and shaping the pipe sleeve 3. According to the rolling principle, during the rolling process of the part, the catheter 4 expands outward, causing the pipe sleeve 3 to deform, and the positioning sleeve 2 limits the elongation of the end of the catheter 4 on the one hand, and limits the deformation degree of the pipe sleeve 3 on the other hand, and changes the stress concentration at the root of the catheter 4 and the pipe sleeve 3 through the limiting of the two.

[0031] like Figure 4 As shown, the positioning sleeve 2 includes a positioning column 20 and a positioning ring 21 arranged on the outer surface of the positioning column 20, the positioning ring 21 and the positioning column 20 form a step-like structure, the positioning ring 21 is assembled in the limiting cavity, the positioning column 20 is assembled in the step groove of the first clamping mold body 10 and the second clamping mold body 11, the catheter 4 is assembled in the positioning column 20, and the end face of the positioning column 20 is flush with the end face of the clamping mold assembly 1.

[0032] The present invention also provides a method for improving the fatigue life of a 35MPa non-flaring rolled connector, which is operated using a tooling structure and includes the following steps:

[0033] S1: Prepare the pipe sleeve 3, conduit 4 and outer nut required for the rolling connection process, and measure the outer diameter and length of conduit 4, inner diameter and outer diameter of pipe sleeve 3 before rolling to ensure that the size of the parts is within the tolerance range. The length of conduit 4 is prepared according to the requirements of HB6442, and the end burrs of both ends of conduit 4 are removed to ensure that the ends of conduit 4 will not cause damage to the rolling tooling.

[0034] Table 1 Key dimensions of outer diameter tooling

[0035] Pipe sleeve specifications Size a Size b 6 1.8±0.1 R1.5 8 1.8±0.1 R1.5 10 1.6±0.1 R1.5 12 1.6±0.1 R1.75 14 1.6±0.1 R1.75 16 1.5±0.1 R1.75 18 1.5±0.1 R1.75 20 1.5±0.1 R1.75 25 1.3±0.1 R1.5

[0036] Before rolling, the sleeve 3 and the titanium alloy conduit 4 are measured, and the measured values ​​are required to meet the requirements in Table 2.

[0037] Table 2 Data measurement before rolling

[0038]

[0039] S2: According to the size of the catheter 4, a tooling structure of corresponding size is selected, including a clamping die assembly 1 and a positioning sleeve 2; the clamping die assembly 1 is a first clamping die body 10 and a second clamping die body 11, and the tooling structure is subjected to blanking, heat treatment, machining, inner hole machining, passivation and bluing processes to realize the trial production of the rolling outer diameter tooling;

[0040] S3: Clean the tooling structure, pre-install the catheter 4 and the pipe sleeve 3, put them into the positioning sleeve 2 after assembly, press down the clamping mold assembly 1 to fix the end of the catheter 4, and complete the installation of the tooling structure;

[0041] Among them, the installation of the rolling inner diameter tooling expander is carried out, and then the clamping die of the outer diameter tooling is installed, the positioning sleeve 2 is placed, and then the one end of the catheter 4 and the pipe sleeve 3 are pre-installed, placed in the positioning sleeve 2, and the clamping die is pressed down to fix the end of the catheter 4, and the equipment is locked, and the installation is completed. The inner diameter tooling expander includes an expander, a retainer, and a roller needle. The outer diameter tooling is the tooling structure in the present invention.

[0042] S4: Debugging the rolling equipment and completing the permanent connection between the casing and the conduit 4 through the rolling equipment operation;

[0043] The specific steps include:

[0044] S4.1: Determine rolling parameters according to the specifications of the catheter 4;

[0045] S4.2: According to the rolling parameters, the rolling equipment is pressed against the end of the catheter 4 to start the rolling operation, thereby completing the permanent connection between the casing and the catheter 4.

[0046] S5: For the combined conduit 4 connected in S4, use a special measuring tool to measure the diameter of the rolled part at the root of the sleeve 3, the inner diameter of the conduit 4 after rolling, the elongation of the conduit 4 after rolling, and the extension of the end of the conduit 4, such as Figure 5 shown.

[0047] After rolling, data measurements are taken, including the diameter of the rolled portion at the root of the sleeve 3, the inner diameter of the catheter 4 after rolling, the elongation of the catheter 4 after rolling, the extension of the end of the catheter 4 and other dimensions. See the table for specific data.

[0048] Table 3 Key dimension measurement results after rolling

[0049] Dimensions in mm L L0 d d1 Pipe sleeve expansion 16×1.4 301.3 1.67 13.63 0.05 0 20×1.7 339.1 1.5 17.08 0.05 0.01

[0050] S6: measuring the bending strain of the conduit 4 at the tail end of the sleeve 3. When the strain reaches the required value, the conduit 4 is pressurized to 35 MPa and a fatigue test is performed according to the strain value.

[0051] In step S6, a strain gauge is set on the outer wall of the catheter 4 at a distance of 5mm-7mm from the tail end of the sleeve 3, and a strain gauge is also set in the vertical direction, and then the combined catheter 4 is installed in the rotating bending fatigue test equipment. When measuring the strain, first adjust the position of the headstock and tailstock to ensure that the specimen catheter 4 is coaxial, and use the micrometer to determine the coaxiality. The asymmetric offset indicated by the micrometer should not be greater than 0.08mm; when the coaxiality is determined, the measured strain data is cleared to zero, and the deflection adjustment rod is used to give the catheter 4 a certain offset. The catheter 4 obtains a flexural displacement through the offset, and the speed is set to 100r / min to start the device to rotate. At this time, the strain gauge degree is the bending strain. When the bending strain reaches the required value, stop adjusting the offset, and record the offset position and bending strain value of the catheter 4 as shown in Table 4.

[0052] Table 4 Bending fatigue data record

[0053]

[0054] From Figure 4, it can be found that the offset of the test piece without adjusting the outer diameter fixture is much larger than that after adjustment, indicating that the adjustment of the outer diameter fixture structure has a significant impact on the residual stress at the connection position. According to the given a and b dimensions in the scheme, greater residual stress will be introduced into the connector itself. The rotary bending fatigue test found that without controlling the dimensions of the clamping die and the positioning sleeve a and b, the fatigue performance of the connector was unstable. It could not be guaranteed that all three test pieces in a batch passed the fatigue test. The 16-specification conduit 4 did not even reach the fatigue test requirement once. After the size control, the 16-specification connector passed the fatigue test smoothly, and there was no failure in the three pieces in a batch.

[0055] Since the offset only causes the specimen to produce a certain flexural displacement to obtain bending stress, in order to prove that the offset is not a critical influencing factor in this scheme, a control test was conducted, in which the connectors with controlled tooling a and b and the connectors with uncontrolled a and b sizes were installed on the equipment, adjusted to the same offset, and tested, the results are shown in 5.

[0056] Table 5 16×1.4 specification connector control test record

[0057]

[0058] As can be seen from the table, in this test method, the offset is only a means of artificially applying working conditions, and is not a key factor that directly affects fatigue performance. What really affects the fatigue performance of the connector is the stress concentration problem. The fatigue life of the catheter 4 without restrictions on the tooling can only reach 6 to 7 million times, while the catheter 4 component after the control tooling can withstand 10 million stress cycles. This shows that the reasonable size structure of the outer diameter tooling will produce beneficial residual stress on the connector, thereby improving the fatigue performance of the catheter 4.

[0059] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A tooling structure for improving the fatigue life of a 35MPa non-flaring rolled connector, characterized in that: It comprises a clamping mold assembly (1), a positioning sleeve (2) assembled in the clamping mold assembly (1), and a pipe sleeve (3) assembled in the positioning sleeve (2), wherein a guide tube (4) is assembled in the pipe sleeve (3); The clamping mold assembly (1) comprises a first clamping mold body (10) and a second clamping mold body (11) corresponding to the first clamping mold body (10), and a limiting cavity for assembling the positioning sleeve (2) is formed in the first clamping mold body (10) and the second clamping mold body (11).

2. The tooling structure for improving the fatigue life of 35MPa non-flaring rolled connector according to claim 1 is characterized in that: The positioning sleeve (2) comprises a positioning column (20) and a positioning ring (21) arranged on the outer surface of the positioning column (20), the positioning ring (21) and the positioning column (20) form a step-shaped structure, the positioning ring (21) is assembled in the limiting cavity, the positioning column (20) is assembled in the step groove of the first clamping body (10) and the second clamping body (11), and the catheter (4) is assembled in the positioning column (20).

3. The tooling structure for improving the fatigue life of 35MPa non-flaring rolled connector according to claim 1, characterized in that: The end surface of the positioning column (20) is flush with the end surface of the clamping mold assembly (1).

4. A method for improving the fatigue life of a 35MPa non-flaring rolled connector, characterized in that: The operation using the tooling structure according to any one of claims 1 to 3 comprises the following steps: S1: preparing the pipe sleeve (3) and the conduit (4) required for the rolling connection process, and measuring the outer diameter of the conduit (4), the length of the conduit (4), the inner diameter and the outer diameter of the pipe sleeve (3) to ensure that the dimensions of the parts are within the tolerance range; S2: According to the size of the catheter (4), a tooling structure of corresponding size is selected, including a clamping mold assembly (1) and a positioning sleeve (2); S3: Clean the tooling structure, pre-install the catheter (4) and the pipe sleeve (3), put them into the positioning sleeve (2) after assembly, press down the clamping mold assembly (1) to fix the end of the catheter (4), and complete the installation of the tooling structure; S4: Debugging the rolling equipment and completing the permanent connection between the casing and the conduit (4) through the rolling equipment operation; S5: For the combined conduit (4) connected in S4, use a special measuring tool to measure the dimensional parameters of the diameter of the rolled portion at the root of the sleeve (3), the inner diameter of the conduit (4) after rolling, the elongation of the conduit (4) after rolling, and the extension of the end of the conduit (4); S6: measuring the bending strain of the conduit (4) at the rear end of the sleeve (3); when the strain reaches the required value, the conduit (4) is pressurized to 35 MPa and a fatigue test is performed according to the strain value.

5. The method for improving the fatigue life of a 35MPa non-flaring rolled connector according to claim 4, characterized in that: Step S4 specifically includes the following steps: S4.1: Determine rolling parameters according to the specifications of the catheter (4); S4.2: According to the rolling parameters, the rolling device is pressed against the end of the catheter (4) to start the rolling operation, thereby completing the permanent connection between the casing and the catheter (4).

6. The method for improving the fatigue life of a 35MPa non-flaring rolled connector according to claim 4, characterized in that: In step S6, a strain gauge is arranged on the outer wall of the catheter (4) at a distance of 5 mm to 7 mm from the rear end of the sleeve (3), and a strain gauge is also arranged in the vertical direction, and then the combined catheter (4) is installed in the rotary bending fatigue test equipment.

7. The method for improving the fatigue life of a 35MPa non-flaring rolled connector according to claim 6, characterized in that: When measuring strain, first adjust the positions of the headstock and tailstock to ensure that the test piece catheter (4) is coaxial, and use the micrometer to determine the coaxiality. The asymmetric offset indicated by the micrometer should not be greater than 0.08 mm. After determining the coaxiality, the measured strain data is cleared to zero, and the catheter (4) is given a certain offset using the deflection adjustment rod. The catheter (4) obtains a deflection displacement through the offset. Set the speed of 100 r / min to start the device rotating. At this time, the strain gauge degree is the bending strain. When the bending strain reaches the required value, stop adjusting the offset.

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