A turning device for processing of a tubing joint

Abstract

The present application relates to the field of machining and intelligent manufacturing equipment, in particular to a turning device for oil pipe joint machining, which comprises a spindle drive mechanism, a flexible multi-jaw chuck, an inner support mandrel, an array type electromagnetic induction generator and a hydrostatic pressure compensation ring; the device clamps the outside of the oil pipe through the flexible multi-jaw chuck, the inner support mandrel is coaxially arranged in the inner hole of the oil pipe, and an annular closed chamber filled with magnetorheological fluid is formed between the two; the core is that the flexible outer chuck and the inner support mandrel cooperate and utilize centrifugal radial cutting force to antagonize the hydrostatic pressure compensation ring, so as to convert the fluid pressure into continuous support distribution opposite to the cutting radial force under the rotating working condition; the present application avoids the plastic deformation and oval buckling of the thin-walled oil pipe caused by simply relying on increasing the external clamping force in the traditional way, and effectively improves the basic bending resistance support ability and machining stability when turning the long overhanging pipe.

Description

Technical Field

[0001] This invention relates to the field of machining and intelligent manufacturing equipment, specifically a turning device for machining oil pipe joints. Background Technology

[0002] When oil pipe fittings are being machined, thin-walled cylindrical pipes are prone to insufficient local stiffness due to the overhang ratio during turning, and are frequently disturbed by dynamic radial cutting forces during the machining process. To stably clamp thin-walled pipe fittings and suppress cutting vibration, existing solutions generally adopt the form of increasing the radial clamping force of the chuck or adding a static solid support structure inside the pipe fitting. Although this solution has a certain support capacity in conventional thick-walled parts or short overhang turning scenarios, the critical buckling pressure threshold of thin-walled cylinders under external pressure is low. Over-reliance on external chuck clamping will lead to irreversible plastic deformation and elliptic buckling of the pipe wall. At the same time, the static internal support structure cannot dynamically and adaptively adjust with the high-frequency fluctuations of the tool feed position and cutting load, resulting in limited dynamic damping and stiffness of the inner wall near the cutting zone. This can easily induce chatter and micro-deformation during the machining incubation stage, making it difficult to support the high stability and high precision turning requirements of long overhang oil pipe fittings.

[0003] Therefore, how to improve the dynamic compliance and local vibration-resistant support stiffness of the turning area in real time without destroying the overall posture of the thin-walled tube has become an urgent technical problem to be solved. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a turning apparatus for machining oil pipe joints. Specifically, the technical solution of the present invention includes:

[0005] The lathe includes a bed and a spindle drive motor. A spindle box is fixedly connected to the bed, and the spindle is supported inside the spindle box. The spindle is driven by the spindle drive motor. A flexible multi-jaw chuck is fixedly connected to the front flange of the spindle, and the flexible multi-jaw chuck is used to clamp the oil pipe to be processed. An inner support mandrel is coaxially inserted in the central inner hole of the spindle, and the outer diameter of the inner support mandrel is smaller than the inner diameter of the oil pipe. An annular closed chamber is formed between the inner support mandrel and the oil pipe. An array-type electromagnetic induction generator is fixedly connected to the outer wall of the inner support mandrel, and the annular closed chamber is filled with magnetorheological fluid. A centrifugal radial cutting force antagonistic hydrostatic pressure compensation ring is provided between the front flange of the spindle and the root of the inner support mandrel.

[0006] Optionally: The centrifugal radial cutting force antagonistic hydrostatic compensation ring includes four conical hydrostatic chambers evenly distributed along the circumference, and the large end of each conical hydrostatic chamber is connected to an annular closed chamber.

[0007] Optionally: the small end of the conical hydrostatic chamber is connected to a throttling orifice, and one end of the throttling orifice is connected to a liquid storage chamber, which is located inside the inner support mandrel.

[0008] Optionally: A tool post base is provided on the outer side of the lathe bed, and a cutting tool is fixedly installed on the tool post base. The lathe bed is also equipped with a feed servo system for driving the tool post base to move. An acoustic emission sensor is installed on the tool post base. A control module is installed on the outer side of the lathe bed near the spindle box.

[0009] Optionally: the flexible multi-jaw chuck is fixedly connected to the main shaft by six evenly distributed bolts, and the tail end of the inner support spindle is fixedly connected to the front flange face of the main shaft.

[0010] Optionally, the array-type electromagnetic induction generator consists of 12 independent ring excitation coils equidistantly distributed along the axial direction.

[0011] Optionally: The control module includes a latent feature extraction module and a variable stiffness mapping compensation module, and the output terminal of the latent feature extraction module is electrically connected to the variable stiffness mapping compensation module, and the output terminal of the variable stiffness mapping compensation module is electrically connected to the array-type electromagnetic induction generator.

[0012] Optionally, the control module is configured to perform the following operations:

[0013] Step 1, Initialization and Signal Acquisition: Continuously extract the high-frequency harmonic components of the stator current of the spindle drive motor and the acoustic emission signals collected by the acoustic emission sensor on the tool holder base;

[0014] Step 2, Latent Feature Extraction and Analysis: Perform Fast Fourier Transform on the extracted stator current signal to separate the cutting fundamental frequency and chatter sideband in the current signal;

[0015] Step 3, Stiffness Calculation: Based on the cutting fundamental frequency and chatter sideband in the extracted stator current signal, calculate and output the dynamic stiffness attenuation of the oil pipe wall.

[0016] Step 4, Variable stiffness mapping compensation and execution: Adjust the excitation parameters of the array electromagnetic induction generator according to the calculated dynamic stiffness attenuation.

[0017] Step 5, safety threshold intervention: If the calculated dynamic stiffness attenuation exceeds the preset safety threshold, the feed servo system's scaling factor is reduced simultaneously; if the calculated dynamic stiffness attenuation is less than or equal to the preset safety threshold, the current feed scaling factor remains unchanged.

[0018] Optionally, step four includes the following sub-steps:

[0019] Coordinate tracking and positioning: Using the position of the cutting tool when it is aligned with the workpiece machining start point as the reference zero position, the current axial feed coordinate of the cutting tool is tracked and positioned to a specific independent ring excitation coil in the array electromagnetic induction generator that is directly opposite the cutting tool entry point.

[0020] Dynamic excitation control: When the dynamic stiffness decay increases, the excitation current pulse width and current intensity of a specific independent toroidal excitation coil are increased.

[0021] Flexible compliance: The excitation coil in the non-cutting area remains de-energized.

[0022] The present invention has the following beneficial effects:

[0023] 1. This invention utilizes a flexible multi-jaw chuck in synergy with an inner support mandrel inserted into the inner bore of the oil pipe to be machined, avoiding irreversible plastic deformation and elliptic buckling of thin-walled oil pipes caused by simply increasing the radial clamping force of the external chuck in the traditional method. At the same time, in conjunction with a centrifugal radial cutting force antagonistic hydrostatic compensation ring, the conical hydrostatic chamber, throttling orifice, and liquid storage cavity are connected to convert fluid pressure changes into a continuous fluid support distribution opposite to the radial cutting force under rotational conditions, effectively improving the basic bending support and stability during the turning of long overhanging pipes.

[0024] 2. This invention overcomes the defect that static internal support structures cannot be dynamically and adaptively adjusted; it uses a control module to extract stator current signals and acoustic emission signals to calculate dynamic stiffness attenuation, and tracks the specific independent ring excitation coil in the dynamic control array electromagnetic induction generator of the cutting tool coordinate; it causes the magnetorheological fluid in the area directly opposite the cutting tool to transform into a solid-like elastic body to provide local high-strength stiffness support, while the non-cutting area maintains a flowing state to absorb residual vibration energy, thereby improving compliance in real time and effectively suppressing turning chatter without damaging the overall posture of the pipe. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0026] Figure 1 This is a schematic diagram of the overall structure of the device;

[0027] Figure 2 This is a cross-sectional view of the spindle box of the device;

[0028] Figure 3 This is a schematic diagram of the flexible multi-jaw chuck structure of the device;

[0029] Figure 4 This is a schematic diagram of the centrifugal radial cutting force antagonistic hydrostatic pressure compensation ring structure of the device.

[0030] In the diagram: 1. Lathe bed; 2. Spindle drive motor; 3. Spindle box; 4. Spindle; 5. Flexible multi-jaw chuck; 6. Oil pipe; 7. Internal support mandrel; 8. Annular closed chamber; 9. Array-type electromagnetic induction generator; 10. Magnetorheological fluid; 11. Centrifugal radial cutting force antagonistic hydrostatic compensation ring; 12. Conical hydrostatic chamber; 13. Throttling orifice; 14. Liquid storage chamber; 15. Tool post base; 16. Lathe tool; 17. Acoustic emission sensor; 18. Control module; 19. Bolt; 20. Independent annular excitation coil. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0032] Example 1:

[0033] like Figure 1 As shown, a turning apparatus for machining oil pipe fittings includes:

[0034] The lathe bed 1 and the spindle drive motor 2 are provided. A spindle box 3 is fixedly connected to the lathe bed 1, and a spindle 4 is supported inside the spindle box 3. The spindle 4 is driven by the spindle drive motor 2. A flexible multi-jaw chuck 5 is fixedly connected to the front flange of the spindle 4, and the flexible multi-jaw chuck 5 is used to clamp the oil pipe 6 to be processed. An inner support mandrel 7 is coaxially inserted in the central inner hole of the spindle 4, and the outer diameter of the inner support mandrel 7 is smaller than the inner diameter of the oil pipe 6. An annular closed chamber 8 is formed between the inner support mandrel 7 and the oil pipe 6. An array-type electromagnetic induction generator 9 is fixedly connected to the outer wall of the inner support mandrel 7, and the annular closed chamber 8 is filled with magnetorheological fluid 10. A centrifugal radial cutting force antagonistic hydrostatic pressure compensation ring 11 is provided between the front flange of the spindle 4 and the root of the inner support mandrel 7.

[0035] Combination Figure 2 As shown, in this embodiment, the lathe bed 1 serves as the mounting base for the entire machine, supporting the spindle box 3, the spindle drive motor 2, and the cutting execution components. The spindle box 3 supports the spindle 4 through a bearing assembly, ensuring that the spindle 4 maintains rotational accuracy within a set speed range. The spindle drive motor 2 is connected to the spindle 4 via a transmission connection, satisfying the torque output required for turning the inner and outer diameters and threads of the oil pipe 6 connector.

[0036] refer to Figure 3 A flexible multi-jaw chuck 5 is installed on the front flange face of the spindle 4. The flexible multi-jaw chuck 5 applies a clamping load to the oil pipe 6 that is lower than the elastic instability condition of the pipe wall. Its function is to maintain the overall posture of the oil pipe 6 and limit axial movement, rather than concentrating the anti-cutting main load on the outer surface of the pipe wall.

[0037] The elastic instability condition of the pipe wall refers to the critical instability pressure threshold calculated based on the buckling theory of thin-walled cylinders under external pressure. It is ensured that the maximum radial pressure applied by the chuck is strictly less than the critical instability pressure threshold to prevent irreversible plastic deformation or elliptic buckling of the oil pipe 6 during the clamping stage. The inner support mandrel 7 is coaxially inserted through the central inner hole of the main shaft 4. The inner support mandrel 7 and the inner wall of the oil pipe 6 form an annular closed cavity 8, which is filled with magnetorheological fluid 10.

[0038] The magnetorheological fluid 10 maintains its flowability in the absence of a magnetic field, and its apparent viscosity and shear modulus increase in the energized state, thereby enabling the inner support capacity of the oil pipe 6 to change with the control signal; the array-type electromagnetic induction generator 9 is fixed to the outer wall of the inner support mandrel 7. Its function is not to make the entire section of the oil pipe 6 rigid at the same time, but to apply a magnetic field locally to the annular closed cavity 8 of the corresponding cutting area, so that the local support stiffness and damping are increased synchronously.

[0039] A centrifugal radial cutting force antagonistic hydrostatic compensation ring 11 is set between the front flange of the spindle 4 and the root of the inner support mandrel 7. It is used to establish hydrostatic support related to the radial disturbance of cutting during the rotation of the spindle 4. This structure combines external flexible clamping, internal variable stiffness support and rotation-induced fluid compensation, so that the thin-walled oil pipe 6 can meet the requirements of anti-collapse and vibration resistance under the overhang condition of exceeding the preset length-to-diameter ratio threshold. Compared with the method of relying solely on chuck clamping, it can reduce the ellipticization of the pipe wall and improve the turning stability.

[0040] like Figure 4 As shown, the centrifugal radial cutting force antagonistic hydrostatic pressure compensation ring 11 includes four conical hydrostatic pressure chambers 12 evenly distributed along the circumference, and the large end of the conical hydrostatic pressure chamber 12 is connected to the annular closed chamber 8.

[0041] In this embodiment, the centrifugal radial cutting force antagonistic hydrostatic compensation ring 11 adopts multiple circumferentially distributed conical hydrostatic liquid chambers 12, preferably four, to keep the circumferential support stiffness distribution basically symmetrical and reduce the additional radial runout caused by unilateral pressure bias; the large end of the conical hydrostatic liquid chamber 12 is set towards the annular closed cavity 8, and its design purpose is to increase the communication area with the main area of ​​the magnetorheological fluid 10, so that the pressure-bearing liquid chamber can improve the response rate of local pressure rise when the gap narrows;

[0042] In the conical structure, the large end region bears the main pressure-bearing function, while the small end region regulates the flow rate. The combination of the two allows the liquid chamber to be sensitive to radial displacement changes to meet a preset response threshold. When the oil pipe 6 is subjected to turning load and bends within the elastic deformation range, the conical hydrostatic liquid chamber 12 near the force-bearing side experiences a pressure increase due to the reduction in geometric clearance, while the corresponding liquid chamber on the back side experiences pressure release due to the change in clearance. This results in a support distribution in the circumferential direction opposite to the direction of the radial component of the cutting force. Here, the geometric clearance specifically refers to the radial fluid film thickness formed between the outward-facing large end face of the conical hydrostatic liquid chamber 12 and the inner wall of the clamped oil pipe 6.

[0043] After the conical hydrostatic chamber 12 is directly connected to the annular closed chamber 8, the pressure change in the compensation ring can be transmitted to the area near the inner circumference of the oil pipe 6, so that the basic bending support is not limited to the compensation ring body, but extends to the cutting adjacent area; this structure makes the hydrostatic compensation not only a single-point support, but a fluid support continuously distributed along the circumference, which is suitable for the dynamic turning conditions of thin-walled cylindrical parts.

[0044] The conical hydrostatic chamber 12 has a small end connected to a throttling orifice 13, and one end of the throttling orifice 13 is connected to a liquid storage chamber 14, which is located inside the inner support mandrel 7.

[0045] In this embodiment, the small end of the conical static pressure liquid chamber 12 is connected to the throttling orifice 13, and the throttling orifice 13 is connected to the liquid storage chamber 14 disposed inside the inner support mandrel 7. The liquid storage chamber 14 is used to provide the fluid source required for static pressure compensation and to form a relatively stable liquid supply volume through the internal space of the inner support mandrel 7. The function of the throttling orifice 13 is to establish controlled flow resistance so that when the magnetorheological fluid 10 in the liquid storage chamber 14 enters the conical static pressure liquid chamber 12 under the action of centrifugal pressure induced by the rotation of the main shaft 4, it does not flow in unobstructed, but forms a corresponding relationship between flow rate and pressure.

[0046] Thus, when the liquid film gap decreases due to force on one side of the conical hydrostatic liquid chamber 12, the pressure difference between the two ends of the throttling orifice 13 increases, and the internal pressure of the liquid chamber rises; when the gap is restored or increased, the internal pressure of the liquid chamber decreases and rebalances with the annular closed chamber 8; the orifice diameter of the throttling orifice 13 can be matched according to the viscosity of the selected magnetorheological fluid 10, the operating speed range of the spindle 4, and the target compensation stiffness, so that the liquid chamber provides a damping effect in the stable cutting frequency band and a pressure response effect in the vibration disturbance frequency band;

[0047] The liquid storage chamber 14 is arranged inside the inner support spindle 7, which can avoid the impact of additional external liquid supply pipeline on the rotation accuracy of the spindle 4 and reduce the number of rotary seals, making it easier to manufacture and assemble. This arrangement integrates the liquid supply, throttling and pressure bearing paths of the compensation ring inside the rotating center component, which is beneficial to improving the structural compactness and operational reliability of the rotary system.

[0048] A tool post base 15 is provided on the outer side of the lathe bed 1, and a cutting tool 16 is fixedly installed on the tool post base 15. The lathe bed 1 is also equipped with a feed servo system for driving the tool post base 15 to move. An acoustic emission sensor 17 is installed on the tool post base 15. A control module 18 is installed on the outer side of the lathe bed 1 near the spindle box 3.

[0049] In this embodiment, a tool post base 15 is provided on one side of the lathe bed 1. The tool post base 15 is used to support the cutting tool 16 and ensure that it moves along the set feed direction. When the cutting tool 16 contacts the oil pipe 6 for cutting, it generates cutting force, frictional heat and elastic release wave. The acoustic emission sensor provided on the tool post base 15 is used to collect high-frequency elastic wave signal. The acoustic emission signal here is the propagation response of local microcrack initiation, frictional slip and micro-vibration energy release in the structure. Its frequency is higher than the low-frequency signal that is easy to measure by conventional displacement sensors, which is suitable for identifying early changes in the chatter incubation stage.

[0050] The control module 18 is installed near the spindle box 3 to shorten the signal transmission path and reduce the impact of electromagnetic interference on the sampling results; a high-frequency current sensor for real-time acquisition of stator current and an isolation sampling unit are connected in series on the power supply circuit of the spindle drive motor 2; the lathe bed 1 is also equipped with a feed servo execution unit for driving the tool post base 15 to move axially.

[0051] The control module 18 receives signals from the acoustic emission sensor and related current information from the spindle drive motor 2, and outputs them to the array electromagnetic induction generator 9 and the feed servo execution unit. The combination of the tool holder base 15, the acoustic emission sensor and the control module 18 establishes a correspondence between the mechanical state of the cutting zone, the electrical state of the drive side and the excitation state of the execution side, which facilitates the conversion of the dynamic compliance change of the tube wall into a calculable and controllable physical quantity. By using the tool holder base 15 to install the acoustic emission sensor instead of directly installing it on the rotating workpiece, the rotation lead wire and slip ring structure can be avoided, reducing the complexity of the system layout.

[0052] Example 2:

[0053] The flexible multi-jaw chuck 5 is fixedly connected to the main shaft 4 by six evenly distributed bolts 19, and the tail end of the inner support spindle 7 is fixedly connected to the front flange face of the main shaft 4.

[0054] In this embodiment, the flexible multi-jaw chuck 5 is installed on the front flange face of the spindle 4 through multiple circumferentially distributed connectors, preferably using six bolts 19, so that the chuck installation preload is evenly distributed along the circumference, reducing the end face tilt caused by the connection off-center load after clamping; the body of the flexible multi-jaw chuck 5 can adopt an elastic compensation jaw structure or a clamping jaw structure with a flexible layer, so that each jaw can adapt to the outer diameter error of the oil pipe 6 within the preset compensation tolerance range, reducing the concentration of local contact pressure;

[0055] The tail end of the inner support spindle 7 is fixedly connected to the tail end flange of the main spindle 4, so that the inner support spindle 7 and the main spindle 4 keep coaxial and rotate synchronously, avoiding relative rotation between the two and causing abnormal fluid disturbance in the annular closed chamber 8; the flanges at both ends of the main spindle 4 respectively undertake the installation functions of the external clamping parts and the internal support parts, so that the external clamping center and the internal support center of the workpiece can establish a coaxial relationship through the same rotation reference during assembly;

[0056] This connection method can reduce the unevenness of local cavities caused by the eccentricity of the inner support mandrel 7 and reduce the impact of the thickness difference of the solidification area of ​​the magnetorheological fluid 10 on the uniformity of support. Through uniform connection and coaxial fixation, a stable geometric correspondence is formed between the workpiece clamping system and the internal support system, which makes it easier for the subsequent excitation area to be consistent with the tool cutting area.

[0057] The array-type electromagnetic induction generator 9 consists of 12 independent ring excitation coils 20 that are equidistantly distributed along the axial direction.

[0058] In this embodiment, the array-type electromagnetic induction generator 9 employs multiple independent annular excitation coils 20 distributed equidistantly along the axial direction, preferably 12 in number; here, "independent" means that each annular excitation coil has a power supply channel that can be addressed independently and an excitation parameter that can be adjusted independently, so that the corresponding coil can be selected to work according to the current cutting coordinate of the tool.

[0059] The annular excitation coil is wound around the outer circumference of the inner support mandrel 7 and is insulated and fixed to the outer wall of the inner support mandrel 7, so that the magnetic field mainly acts on the magnetorheological fluid 10 in the corresponding axial region of the annular closed chamber 8; the purpose of the axial equidistant distribution is to divide the effective processing length of the oil pipe 6 into multiple support units, and the effective working width of each support unit is matched with the tool tip influence zone to improve the targeting of local strengthening.

[0060] If a single long coil is used, the entire magnetorheological fluid 10 will simultaneously enter a high viscosity state, reducing the overall compliance of the tubing 6 and hindering the dissipation of residual vibrations in the non-cutting area. By using multiple independent coils, stiffness is increased only in the cutting-related area, while the remaining areas maintain fluid dynamics, achieving a balance between support and compliance. The number of coils can be adjusted according to the machining length of the tubing 6, the inner diameter of the spindle 4, and the predetermined control resolution. Twelve independent annular excitation coils 20 can meet the needs of local excitation and axial following control within the range of common joint machining lengths.

[0061] The control module 18 includes a latent feature extraction module and a variable stiffness mapping compensation module, and the output terminal of the latent feature extraction module is electrically connected to the variable stiffness mapping compensation module, and the output terminal of the variable stiffness mapping compensation module is electrically connected to the array-type electromagnetic induction generator 9.

[0062] In this embodiment, the control module 18 consists of a latent feature extraction module and a variable stiffness mapping compensation module. The latent feature extraction module is used to receive the stator current signal of the spindle drive motor 2 and the output signal of the acoustic emission sensor, and to separate the components related to the dynamic compliance change of the workpiece. Here, latent features refer to state quantities that cannot be directly observed through the shape of the workpiece, but can be indirectly reflected by the driving load fluctuation and the high-frequency response of the structure, including the change of flutter sideband energy, the local stiffness attenuation trend, and the vibration sensitive area information corresponding to the tool position.

[0063] The variable stiffness mapping compensation module receives the output of the latent feature extraction module, converts the feature quantity into a stiffness adjustment command for the magnetorheological fluid 10 support, and outputs the corresponding excitation control signal to the array electromagnetic induction generator 9. The two are electrically connected, so that the feature recognition result can directly participate in the subsequent excitation parameter calculation, avoiding invalid information isolation between sampling, processing and execution.

[0064] This modular setup allows for a clear division of labor in the control logic. The implicit feature extraction module is responsible for obtaining chatter-related indicators from complex signals, while the variable stiffness mapping compensation module is responsible for calculating coil selection and excitation intensity results according to a predetermined mapping relationship. Through this structure, dynamic instability symptoms during turning can be converted into local support adjustment amounts to improve the damping and dynamic stiffness of the inner wall adjacent to the cutting zone.

[0065] The input sources for the latent feature extraction module include the original waveform of the stator current of the spindle drive motor 2 after isolation sampling, the original waveform of acoustic emission after amplification and bandpass processing, and the current axial displacement feedback signal from the feed servo system; wherein, the stator current is used to characterize the modulation result of the cutting load on the drive side, the acoustic emission signal is used to characterize the high-frequency energy release state in the cutting zone, and the axial displacement feedback signal is used to establish the correspondence between the feature quantity and the current cutting section;

[0066] The latent feature extraction module can process the following logic during operation: it segments the original waveform of the stator current and removes the power frequency background component and low frequency drift component to obtain the current analysis signal for frequency domain analysis; it performs envelope extraction or energy statistics on the original waveform of acoustic emission to form a high-frequency activity index for consistency verification.

[0067] The components near the cutting fundamental frequency and the sideband components in the current analysis signal are separated, and it is determined whether the sideband energy rises synchronously with the high-frequency activity of acoustic emission. When the two change synchronously, it is determined that there is an effective disturbance related to the dynamic compliance change of the workpiece in the current analysis window; otherwise, it is suppressed as non-cutting noise or occasional interference.

[0068] The above processing logic actually constructs a latent feature recognition model for cutting state. The purpose of this model is to separate and confirm effective features directly related to flutter in real time from complex electrical and acoustic signals. Logically, the model includes two stages: feature extraction and consistency verification. The current analysis signal is extracted in the frequency domain to output candidate sideband energy. At the same time, the acoustic emission signal is analyzed in the time domain to output high-frequency activity energy.

[0069] In the feature extraction stage, the Hilbert transform is used to extract the signal envelope of the acoustic emission signal, and the root mean square value of the envelope signal within the current time window is calculated as the high-frequency activity energy index. In the verification stage, these two are used as inputs for synchronization comparison. A synchronization time tolerance is set. When the growth rate of the candidate sideband energy of the current analysis signal relative to the previous time window exceeds the set ratio, and the high-frequency activity energy of the acoustic emission increases synchronously within the tolerance window and exceeds the background noise threshold, it is determined to be a valid flutter feature.

[0070] The data flow between the above modules is carried out in real time through a high-speed fieldbus to ensure low latency in feature extraction. The model as a whole represents the physical homology and strong coupling relationship between the micro fractures and friction energy release in the mechanical cutting zone and the load fluctuations of the spindle drive motor 2. The misjudgment caused by a single electromagnetic interference is eliminated through cross-validation of multi-source signals. The output results of the above processing flow include the flutter sideband energy level, the local stiffness attenuation trend level, and the vibration sensitive section number. All of the above results are used as inputs to the variable stiffness mapping compensation module.

[0071] The mapping relationship in the variable stiffness mapping compensation module refers to the corresponding rules for converting the aforementioned characteristic results into excitation section selection, excitation current intensity level and duration level. Essentially, it is a control conversion relationship from state identification quantity to support adjustment quantity, rather than a single empirical judgment. This module can prioritize selecting the corresponding ring excitation coil based on the vibration sensitive section number, then determine the upward, maintenance or downward adjustment of the excitation current based on the local stiffness attenuation trend level, and determine the excitation maintenance time and cancellation conditions based on the flutter sideband energy level.

[0072] After this processing, the output of the control module 18 is no longer a general excitation command, but an executable control result that includes the action position, action intensity and action duration, so that those skilled in the art can complete the control implementation based on the disclosed signal source, processing sequence and output flow.

[0073] Control module 18 is configured to perform the following operations:

[0074] Step 1, Initialization and Signal Acquisition: Continuously extract the high-frequency harmonic components of the stator current of the spindle drive motor 2 and the acoustic emission signals collected by the acoustic emission sensor 17 on the tool holder base 15;

[0075] Step 2, Latent Feature Extraction and Analysis: Perform Fast Fourier Transform on the extracted stator current signal to separate the cutting fundamental frequency and chatter sideband in the current signal;

[0076] Step 3, Stiffness Calculation: Based on the cutting fundamental frequency and chatter sideband in the extracted stator current signal, calculate and output the dynamic stiffness attenuation of the pipe wall of oil pipe 6.

[0077] Step 4, Variable stiffness mapping compensation and execution: Adjust the excitation parameters of the array electromagnetic induction generator 9 according to the calculated dynamic stiffness attenuation.

[0078] Step 5, safety threshold intervention: If the calculated dynamic stiffness attenuation exceeds the preset safety threshold, the feed rate parameter of the tool 16 feed servo system is reduced simultaneously; if the calculated dynamic stiffness attenuation is less than or equal to the preset safety threshold, the current feed rate parameter is kept unchanged.

[0079] In this embodiment, the control module 18 performs multi-source signal acquisition, frequency domain analysis, state calculation, excitation compensation, and safety intervention according to the system cycle. During the initialization and signal acquisition phase, the stator current of the spindle drive motor 2 is input to the control module 18 through the isolation sampling unit, and the high-frequency harmonic components are obtained by filtering. The acoustic emission signal on the tool holder base 15 is amplified and bandpass processed before being input to the same computing platform. The purpose of setting up the acoustic emission channel is to assist in verifying the current signal identification results and avoid non-cutting electromagnetic disturbances being misjudged as flutter symptoms.

[0080] In the latent feature extraction and analysis stage, the stator current data obtained by continuous sampling is divided into analysis windows according to the system period, and a fast Fourier transform is performed on each analysis window to obtain the cutting fundamental frequency and its nearby sideband information; the cutting fundamental frequency represents the dominant frequency component of the current stable cutting load, and the chatter sideband represents the additional frequency component generated in the current spectrum after the workpiece micro-deformation modulates the transient load of the spindle 4;

[0081] In the energy ratio calculation and stiffness estimation stages, the square of the flutter sideband amplitude is compared with the square of the cutting fundamental frequency amplitude to obtain the normalized energy index. After being mapped by a pre-calibrated stiffness conversion coefficient, this index outputs the dynamic stiffness attenuation and radial pose deviation amplitude. The pre-calibration can be obtained through standard specimens, different overhangs, and different combinations of cutting parameters. Essentially, it constructs a joint stiffness and pose estimation model. The purpose of this model is to accurately estimate the real-time stiffness loss and deformation of the cutting zone of the tubing 6 when it is not possible to directly measure the displacement on the rotating workpiece.

[0082] Logically, the model consists of two sub-models: the stiffness attenuation calculation sub-model receives the energy ratio and the oil pipe 6 overhang amount preset by the equipment parameters as input, and calculates the dynamic stiffness attenuation amount by looking up a table or linear interpolation; the pose deviation estimation sub-model receives the dynamic stiffness attenuation amount and the current cutting point coordinates as input, and calculates the radial pose deviation amplitude by combining the force deformation relationship of the cantilever beam.

[0083] Specifically, the oil pipe 6 is equivalent to a cantilever beam with one end fixed to the chuck, and the effective overhang length of the oil pipe 6 is set as follows: The current cutting point is at a distance of [distance] from the fixed end. The equivalent radial cutting force increment derived from the dynamic stiffness attenuation is: Equivalent cutting radial force increment The product of the calculated dynamic stiffness attenuation as a percentage of the initial stable stiffness and the pre-calibrated basic radial cutting force, or obtained by interpolation using a pre-defined stiffness attenuation and radial force fluctuation data mapping table, is used to determine the radial pose deviation amplitude. The theoretical calculation formula is:

[0084]

[0085] in, The elastic modulus of material 6 for tubing. The moment of inertia of section 6 of the tubing; the theoretical analysis formula provides a rigorous mechanical basis for safety threshold intervention; the model as a whole characterizes how the high-frequency energy of chatter caused by cutting load is transformed into local stiffness degradation and overall radial geometric deviation through the structural characteristics of thin-walled pipes, so as to establish a direct causal relationship between the energy ratio and the dynamic compliance of the pipe wall; in the variable stiffness mapping compensation and execution stage, the control module 18 selects the corresponding excitation channel and adjusts its excitation parameters according to the calculation results, so that the magnetorheological fluid 10 locally changes from a low viscosity state to a high viscosity state, thereby improving the inner wall support capacity of the corresponding cutting zone;

[0086] During the safety threshold intervention phase, if the dynamic stiffness attenuation exceeds the preset threshold, the control module 18 sends a rate correction command to the feed servo system to reduce the amount of material removed per unit system cycle so as to keep the dynamic displacement within the allowable error range. This execution process makes the detection quantity, calculation quantity and execution quantity have a clear physical correspondence, which is convenient for those skilled in the art to implement.

[0087] The continuous extraction in step one refers to the control module 18 repeatedly performing sampling, buffering, analysis and output at a fixed control cycle. Each analysis window contains at least one current sample within a complete rotation cycle of the main shaft 4 and stores it corresponding to the acoustic emission sample within the same time period. When the analysis window ends, the control module 18 incorporates the new sampled data into the next analysis window to ensure that the subsequent judgment is based on continuous time-series data rather than discrete isolated points.

[0088] The processing sequence in step two can be refined as follows: First, the current analysis signal is weighted by a window function, then a fast Fourier transform is performed to locate the frequency band where the cutting fundamental frequency is located in the spectrum, and the additional peak values ​​within a predetermined range on both sides of the frequency band are used as candidates for flutter sidebands. The candidate sidebands are then screened in conjunction with the energy rise of the acoustic emission channel within the same time window. If the sideband changes but the acoustic emission does not show a corresponding enhancement, the change is determined to be the noise generated by the drive side and is not included in the subsequent stiffness calculation.

[0089] The energy ratio in step three is used to characterize the relative strength of chatter disturbance relative to the stable cutting load. The larger the value, the higher the proportion of additional dynamic disturbance in the cutting process. The pre-calibrated stiffness conversion factor is a mapping parameter used to convert this relative energy index into the change in the dynamic support capacity of the workpiece. The method for determining it is as follows: first, select a standard oil pipe specimen with known material, wall thickness and overhang, then record the energy ratio and measured radial vibration response simultaneously under different cutting parameters, and establish corresponding conversion tables or segmented mapping rules according to the specimen type.

[0090] For the same type of tubing 6, before actual processing, the corresponding coefficients can be selected based on the outer diameter, wall thickness, processing length, and clamping overhang. It is not required to solve new complex models in real time during processing. The dynamic stiffness attenuation obtained in step three represents the degree of reduction in the current pipe wall's ability to bear radial disturbances relative to the initial stable cutting state. The radial pose deviation amplitude represents the estimated radial offset of the current cutting zone relative to the theoretical rotation center. The former is mainly used as the judgment input for excitation intensity and feed correction, while the latter is mainly used as the auxiliary input for deformation error envelope verification and safety intervention level determination.

[0091] The sub-millisecond delay in step four refers to the control execution delay between the output of the effective characteristic result from the current analysis window and the receipt of the new excitation parameter command by the corresponding excitation coil being less than one control millisecond. Its purpose is to enable the local support adjustment to follow the changes in the cutting state, without requiring the magnetorheological fluid 10 to complete all rheological stabilization at the same time.

[0092] The preset safety threshold in step five is the judgment boundary used by the control module 18 to distinguish between mild dynamic instability that can be suppressed by local excitation and risky states that require synchronous reduction of material removal rate. This threshold can be obtained based on trial cutting calibration: first, gradually increase the cutting load on the target oil pipe type 6, record the dynamic stiffness attenuation corresponding to when the surface rippling begins to deteriorate significantly or the radial pose deviation approaches the finished product tolerance boundary, and then set the value below the safety margin of this state as the safety threshold.

[0093] The preset deformation error envelope refers to the upper limit boundary of the allowable radial pose deviation formed by the change of tool position. It can be preset according to the joint machining accuracy requirements, the dimensional tolerance of the thread or shoulder, and the overhang length. Therefore, the safety threshold is responsible for triggering whether to reduce the feed rate, and the deformation error envelope is responsible for limiting the final allowable dynamic displacement range. The two play independent but complementary roles in the control logic.

[0094] Step four includes the following sub-steps:

[0095] Coordinate tracking and positioning: Using the position of the cutting tool 16 when it is aligned with the workpiece machining start point as the reference zero position, the current axial feed coordinate of the cutting tool 16 is tracked and positioned to the specific independent ring excitation coil in the array electromagnetic induction generator 9 that is directly opposite the cutting point of the cutting tool 16.

[0096] Dynamic excitation control: When the dynamic stiffness decay increases, the excitation current pulse width and current intensity of the specific independent ring excitation coil 20 are increased.

[0097] Flexible compliance: The excitation coil 20 in the non-cutting area remains de-energized;

[0098] In this embodiment, step four is further refined into three execution sub-processes: coordinate tracking and positioning, dynamic excitation control, and flexible compliance maintenance.

[0099] During coordinate tracking and positioning, the control module 18 reads the displacement feedback of the feed servo system of the cutting tool 16, converts the feedback into the axial segment number corresponding to the current cutting point, and then matches the number with the independent ring excitation coil 20 in the array electromagnetic induction generator 9 to determine the specific independent ring excitation coil that should be activated.

[0100] During the dynamic excitation control process, the control module 18 generates excitation current intensity command and pulse width command according to the magnitude of dynamic stiffness attenuation. When the dynamic stiffness attenuation increases, the control module 18 increases the excitation energy of the specific independent ring excitation coil by increasing the pulse width modulation duty cycle of the specific independent ring excitation coil or by directly increasing the driving current amplitude.

[0101] The increased magnetic induction intensity passing through the annular closed chamber 8 due to the enhanced excitation current causes the magnetic particles inside the magnetorheological fluid 10 corresponding to the inner side of the cutting contact area to rapidly arrange themselves into a denser particle chain structure under the action of a strong magnetic field. This chain structure directly resists the externally applied shear force, thereby improving the local apparent viscosity, shear yield stress and equivalent support stiffness.

[0102] This process directly establishes a clear causal relationship from electrical signal regulation to changes in fluid rheological properties, and then to the improvement of overall mechanical support stiffness; here, the transformation from Newtonian fluid to a solid-like elastic body refers to the transformation of magnetorheological fluid 10 from a free-flowing state to a controlled rheological state with significant shear resistance under the action of an external magnetic field, rather than an irreversible change in material composition.

[0103] During the flexible compliance process, the remaining excitation coils that do not correspond to the cutting point do not output excitation current, and the magnetorheological fluid 10 in its coverage area remains in a flowable state so as to release local stress, absorb residual vibration and adapt to the small deformation of the thin-walled tubing 6 in sections that do not bear the main cutting support task; through the above sub-process, the local high stiffness support area and the surrounding compliant area can move along the feed path of the cutting tool 16, so that the support enhancement effect is concentrated in the cutting-related area and the additional stress caused by the excessive rigidity of the whole tube is reduced;

[0104] In coordinate tracking and positioning, "alignment" refers to the process where, after the cutting tool 16 falls into the effective axial segment covered by a certain coil according to its current axial coordinate, the center coil corresponding to that segment is preferentially selected as the main excitation coil. When the cutting tool 16 is located near the boundary of two adjacent coils, the control module 18 can simultaneously output a preset transition excitation to the two adjacent coils, so that the local support area moves smoothly in the axial direction, avoiding sudden changes in support stiffness caused by too fast coil switching. The axial segment number can be established through zero-position calibration after the equipment is assembled. Specifically, the position of the cutting tool 16 when it is aligned with the workpiece machining start point is used as the reference zero position, and the coordinate boundaries of each segment are divided according to the center distance of adjacent annular excitation coils. This allows the displacement feedback to be directly converted into the coil selection result.

[0105] Dynamic excitation control is not simply executed in two general states of increasing or decreasing, but can be switched step by step according to at least three levels of excitation. The control module 18 can first read the dynamic stiffness attenuation level output in step three, and then query the pre-established level correspondence table to obtain the target excitation current intensity range and pulse width range. If the current level is higher than the previous control cycle, the current intensity of the main excitation coil is increased first, and the pulse width is extended as needed.

[0106] If the current level remains stable, the existing excitation parameters are maintained; if the current level decreases, part of the excitation is canceled in the order of first shortening the pulse width and then reducing the current intensity, so as to reduce the unnecessary rigidity range. The purpose of this treatment is to make a monotonic correspondence between the support adjustment amount and the degree of instability, so that those skilled in the art can establish a control parameter table based on the test results without relying on undisclosed internal calculation logic.

[0107] The control parameter table adopts a hierarchical decision logic: for example, when the stiffness attenuation is in the first interval, a pulse width modulation control signal with a basic duty cycle is output; when it is in the second interval, a pulse width modulation control signal with a medium duty cycle is output; when it is in the third interval, a pulse width modulation control signal with the maximum duty cycle is output and the driving current amplitude is increased; the above control commands are sent to the bottom drive board of the array electromagnetic induction generator 9 through the communication interface. After parsing the commands, the drive board generates a pulse width modulation wave with a corresponding duty cycle to control the on and off of the power switch tube, thereby realizing programmable quantitative control of the apparent viscosity and local stiffness of the magnetorheological fluid 10;

[0108] In the flexible compliance holding power outage, the low-level buffer coil here is not a newly added physical entity, but refers to a normal independent ring excitation coil 20 that is spatially adjacent to the main excitation coil before and after; it is not excluded that a low-level buffer coil is retained before and after the main excitation area to form a magnetic field gradient from the high stiffness area to the fluid dynamic area; however, the excitation level of the buffer coil is lower than that of the main excitation coil, and its main function is to weaken the local stiffness change, rather than replace the main support function;

[0109] In terms of the control flow, the final output of step four should include at least the main excitation coil number, the adjacent transition coil number, the excitation level of each coil, and the duration of maintenance. This result is sent to the array-type electromagnetic induction generator 9 for execution, so that there is a clear data flow between coordinate information, state variables, and execution variables.

[0110] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A turning apparatus for machining oil pipe joints, comprising: A lathe bed (1) and a spindle drive motor (2) are characterized in that: a spindle box (3) is fixedly connected to the lathe bed (1), and a spindle (4) is internally supported in the spindle box (3); the spindle (4) is driven by the spindle drive motor (2); a flexible multi-jaw chuck (5) is fixedly connected to the front flange of the spindle (4), and the flexible multi-jaw chuck (5) is used to clamp the oil pipe (6) to be processed; and an inner support core is coaxially inserted in the central inner hole of the spindle (4). The shaft (7) has an outer diameter smaller than the inner diameter of the oil pipe (6). An annular closed chamber (8) is formed between the inner support mandrel (7) and the oil pipe (6). An array-type electromagnetic induction generator (9) is fixedly connected to the outer wall of the inner support mandrel (7). The annular closed chamber (8) is filled with magnetorheological fluid (10). A centrifugal radial cutting force antagonistic hydrostatic pressure compensation ring (11) is provided between the front flange of the main shaft (4) and the root of the inner support mandrel (7).

2. The turning apparatus for machining oil pipe joints according to claim 1, characterized in that: The centrifugal radial cutting force antagonistic hydrostatic compensation ring (11) includes four conical hydrostatic chambers (12) evenly distributed along the circumference, and the large end of the conical hydrostatic chamber (12) is connected to the annular closed chamber (8) outward.

3. A turning apparatus for machining oil pipe joints according to claim 2, characterized in that: The conical hydrostatic chamber (12) has a throttling orifice (13) at its small end, and one end of the throttling orifice (13) is connected to a liquid storage chamber (14), which is located inside the inner support mandrel (7).

4. A turning apparatus for machining oil pipe joints according to claim 3, characterized in that: A tool post base (15) is provided on the outer side of the lathe bed (1), and a cutting tool (16) is fixedly installed on the tool post base (15). The lathe bed (1) is also equipped with a feed servo system for driving the tool post base (15) to move. An acoustic emission sensor (17) is installed on the tool post base (15). A control module (18) is installed on the outer side of the lathe bed (1) near the spindle box (3).

5. A turning apparatus for machining oil pipe joints according to claim 1, characterized in that: The flexible multi-jaw chuck (5) is fixedly connected to the main shaft (4) by six evenly distributed bolts (19), and the tail end of the inner support spindle (7) is fixedly connected to the front flange face of the main shaft (4).

6. A turning apparatus for machining oil pipe joints according to claim 1, characterized in that: The array-type electromagnetic induction generator (9) consists of 12 independent ring excitation coils (20) that are equidistantly distributed along the axial direction.

7. A turning apparatus for machining oil pipe joints according to claim 4, characterized in that: The control module (18) includes a latent feature extraction module and a variable stiffness mapping compensation module, and the output terminal of the latent feature extraction module is electrically connected to the variable stiffness mapping compensation module, and the output terminal of the variable stiffness mapping compensation module is electrically connected to the array electromagnetic induction generator (9).

8. A turning apparatus for machining oil pipe joints according to claim 7, characterized in that: The control module (18) is configured to perform the following operations: Step 1, Initialization and Signal Acquisition: Continuously extract the high-frequency harmonic components of the stator current of the spindle drive motor (2) and the acoustic emission signals collected by the acoustic emission sensor (17) on the tool holder base (15); Step 2, Latent Feature Extraction and Analysis: Perform Fast Fourier Transform on the extracted stator current signal to separate the cutting fundamental frequency and chatter sideband in the current signal; Step 3, stiffness calculation: Based on the cutting fundamental frequency and chatter sideband in the extracted stator current signal, calculate and output the dynamic stiffness attenuation of the pipe wall of the oil pipe (6); Step 4, Variable stiffness mapping compensation and execution: Adjust the excitation parameters of the array electromagnetic induction generator (9) according to the calculated dynamic stiffness attenuation. Step 5, safety threshold intervention: If the calculated dynamic stiffness attenuation exceeds the preset safety threshold, the feed servo system of the cutting tool (16) is reduced synchronously; if the calculated dynamic stiffness attenuation is less than or equal to the preset safety threshold, the current feed servo system is kept unchanged.

9. A turning apparatus for machining oil pipe joints according to claim 8, characterized in that: Step four includes the following sub-steps: Coordinate tracking and positioning: Using the position of the cutting tool (16) when it is aligned with the workpiece machining start point as the reference zero position, the current axial feed coordinate of the cutting tool (16) is tracked and positioned in the array electromagnetic induction generator (9) to a specific independent ring excitation coil (20) that is directly opposite the cutting point of the cutting tool (16). Dynamic excitation control: When the dynamic stiffness decay increases, the excitation current pulse width and current intensity of a specific independent ring excitation coil (20) are increased. Flexible compliance: The excitation coil (20) in the non-cutting area remains de-energized.

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