Method for solving the step of pipe end thread machined by two-inch cutter

Abstract

The present application relates to two feet knife processing technical field, disclose a kind of method for solving two feet knife processing pipe end thread appears step, applied to three-axis numerical control thread cutting machine, comprising: control upper tool rest device and lower tool rest device are respectively carried out reference trial cutting on the outer surface of the pipe blank to be processed, obtain the diameter data of two ends of corresponding reference circle;According to diameter data and processing length, first error slope and second error slope corresponding to upper tool rest device and lower tool rest device are respectively solved independently;Combined with target thread total length, error slope is converted into X axis and Y axis error compensation parameter;Error compensation parameter is respectively superimposed to the preset processing endpoint coordinate, and X axis and Y axis processing endpoint new coordinate are reconstructed and generated;According to new coordinate, machine tool is controlled to carry out thread cutting.The present application converts spindle inclination error into algebraic revision of endpoint coordinate, makes upper and lower station cutting track parallel to each other, eliminates the step misplacement defect of tool connection position, and improves thread forming precision.

Description

Technical Field

[0001] This invention relates to the field of two-foot cutter machining technology, specifically a method for solving the problem of stepped defects in pipe end threads during two-foot cutter machining. Background Technology

[0002] In the production of pipes such as oil casing, the processing quality of the pipe end threads directly affects the connection strength and sealing performance of the pipe string. Currently, such threads are usually processed using a three-axis CNC thread turning machine with a double tool table. The double tool table system is a two-foot tool processing mode, which is equipped with an upper tool table and a lower tool table, which are responsible for rough turning and finish turning of the threads respectively, so as to improve processing efficiency.

[0003] Under ideal cutting conditions, the rotation centerline of the machine tool spindle should be strictly parallel to the guide rail axis along the Z-axis feed of the tool. However, due to long-term wear and tear of the machine tool, guide rail assembly errors, and changes in chuck clamping conditions, the spindle often tilts and eccentricates to a certain extent. When the spindle axis deviates from the set Z-axis direction, the actual rotation axis of the workpiece will form a spatial angle with the theoretical linear feed trajectory of the tool. In a dual-tool table machining scenario, since the upper and lower tool tables are located in different spatial planes, the overall tilt of the spindle will project radial offsets of different values ​​on the X-axis and Y-axis planes.

[0004] This multi-plane spatial offset causes the cutting references of the upper and lower worktables to diverge. The thread generatrices produced by the roughing and finishing operations on the upper and lower worktables cannot coincide. The radial cutting amount of the tool varies unevenly along the axial direction of the pipe end, resulting in shape distortion of the machined pipe end dimensions, such as inverted or normal conical shapes. When the two tools operate consecutively, the cutting trajectory of the finishing tool on the lower worktable cannot completely encompass the cutting surface left by the roughing tool on the upper worktable, ultimately leading to obvious misalignment steps in the finished long thread of the pipe end. This type of step defect disrupts the surface continuity and structural parameters of the thread, making the product unable to meet industry standards, thus causing the pipe fitting to be scrapped or reworked. Existing conventional CNC systems lack independent measurement and coordination compensation mechanisms for multi-worktable spatial offsets, making it difficult to fundamentally eliminate this machining defect caused by hardware deviation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for resolving the issue of stepped defects in pipe end threads during machining with two-foot cutters. This method solves the problem of misaligned steps in the pipe end threads caused by the misalignment of the cutting trajectories of the upper and lower tool tables due to the tilt of the machine tool spindle, which prevents the finishing trajectory from fully encompassing the roughing trajectory.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, applied to a three-axis CNC thread turning machine, wherein the three-axis CNC thread turning machine is equipped with an upper tool table device feeding along the X-axis direction, a lower tool table device feeding along the Y-axis direction, and a guide rail feeding along the Z-axis direction; the method includes: S100, control the upper tool holder device and the lower tool holder device to perform reference trial cutting on the outer surface of the tube blank to be processed, respectively forming the first reference outer circle and the second reference outer circle, and obtain the diameter data of the two ends of the first reference outer circle and the diameter data of the two ends of the second reference outer circle. S200, based on the diameter data of both ends of the first reference outer circle and the machining length, calculate the first error slope corresponding to the upper tool holder device; based on the diameter data of both ends of the second reference outer circle and the machining length, calculate the second error slope corresponding to the lower tool holder device; S300, combined with the target total thread length, the first error slope and the second error slope are respectively converted into the X-axis error compensation parameters corresponding to the upper tool holder device and the Y-axis error compensation parameters corresponding to the lower tool holder device; S400, the X-axis error compensation parameters and the Y-axis error compensation parameters are superimposed on the preset X-axis machining endpoint coordinates and Y-axis machining endpoint coordinates respectively, and new X-axis machining endpoint coordinates and new Y-axis machining endpoint coordinates are reconstructed; S500, the three-axis CNC thread cutting machine is controlled to perform thread cutting based on the new coordinates of the X-axis machining endpoint and the new coordinates of the Y-axis machining endpoint.

[0007] Preferably, before performing S100, the method further includes: Set the center of the chuck end face as the origin of the machining space; The movement path parallel to the rotation axis of the tube blank center is defined as the Z-axis direction; The first path of the upper tool holder device, moving towards the feed guide rail, is defined as the X-axis direction, and the second path of the lower tool holder device, moving towards the feed guide rail, is defined as the Y-axis direction.

[0008] Preferably, S100 specifically includes: The first tool on the upper tool holder is controlled to feed along the X-axis to a first set radial position, and while keeping the X-axis coordinate locked, it feeds along the Z-axis to machine the first reference outer circle. Extract the diameter data of the first segment of the reference outer circle at the end furthest from the chuck and the diameter data at the end closest to the chuck; The second tool on the lower tool holder is controlled to feed along the Y-axis to a second set radial position, and while keeping the Y-axis coordinate locked, it feeds along the Z-axis to machine the second reference outer circle. Extract the diameter data of the second segment of the reference outer circle at the end furthest from the chuck and the diameter data at the end closest to the chuck.

[0009] Preferably, in S100: The cutting depth corresponding to the second set radial position is greater than the cutting depth corresponding to the first set radial position, so that the second tool cuts a brand new complete cylindrical surface on the outer surface of the same tube blank.

[0010] Preferably, S200 specifically includes: Calculate the first absolute difference between the diameter data of the end of the first reference outer circle furthest from the chuck and the diameter data of the end closest to the chuck; The ratio of the first absolute difference to the machining length of the first segment of the reference outer circle is established as the first error slope; Calculate the second absolute difference between the diameter data of the end of the second reference outer circle furthest from the chuck and the diameter data of the end closest to the chuck; The ratio of the second absolute difference to the machining length of the second reference outer circle is established as the second error slope.

[0011] Preferably, S300 specifically includes: The product of the first error slope and the total length of the target thread is calculated to obtain the X-axis error compensation parameter; The product of the second error slope and the total length of the target thread is calculated to obtain the Y-axis error compensation parameter.

[0012] Preferably, S400 specifically includes: Extract the preset X-axis and Y-axis machining endpoint coordinates from the target thread machining program; The preset X-axis machining endpoint coordinates are algebraically added to the X-axis error compensation parameters to generate new X-axis machining endpoint coordinates. The preset Y-axis machining endpoint coordinates are algebraically added to the Y-axis error compensation parameters to generate new Y-axis machining endpoint coordinates.

[0013] Preferably, after generating the new coordinates of the X-axis machining endpoint and the new coordinates of the Y-axis machining endpoint, step S400 further includes: The preset X-axis machining endpoint coordinates in the target thread machining program are overwritten and replaced with the new X-axis machining endpoint coordinates; The preset Y-axis machining endpoint coordinates in the target thread machining program are overwritten and replaced with the new Y-axis machining endpoint coordinates.

[0014] Preferably, S500 specifically includes: Load the overwritten target thread machining program and replace it with a new tube blank to be machined; The upper tool holder is controlled to feed along the Z-axis direction, and dynamically linked feeds are performed in the X-axis direction according to the new coordinates of the X-axis machining endpoint, so that the cutting trajectory slope of the upper tool holder is equal to the first error slope. The lower tool chute is controlled to continue feeding along the Z-axis, and synchronous position intervention is performed in the Y-axis direction according to the new coordinates of the Y-axis machining endpoint, so that the cutting trajectory slope of the lower tool chute is equal to the second error slope.

[0015] Preferably, during the process of controlling the three-axis CNC thread cutting machine to perform thread cutting: The first tool on the upper tool holder performs rough thread turning, and the second tool on the lower tool holder performs finish thread turning. The cutting trajectory of the upper tool holder and the cutting trajectory of the lower tool holder are parallel to each other in three-dimensional space, and both are parallel to the actual central rotation axis of the new tube blank to be processed.

[0016] This invention provides a method for solving the problem of stepped defects appearing when machining pipe end threads with a two-foot cutter. It has the following beneficial effects: 1. This invention controls the upper and lower tool holders to perform benchmark test cutting on the outer surface of the tube blank, extracts the diameter data at both ends, and independently calculates the first and second error slopes. Then, the spatial offset error of the machine tool spindle caused by wear or assembly is projected onto the X-axis and Y-axis planes for independent quantification. This avoids the interference effect of the upper and lower tool holders running simultaneously, and provides an accurate basic reference for subsequent multi-channel data intervention.

[0017] 2. This invention combines the total length of the target thread, converts the calculated error slope into the corresponding error compensation parameter, and directly superimposes it into the preset machining endpoint coordinates to generate new coordinates. It can transform the spindle tilt angle compensation in three-dimensional space into the algebraic offset correction of the endpoint position of the CNC system, so that the slope of the reconstructed tool feed trajectory is equivalent to the actual deflection slope of the spindle, ensuring that the tool spatial motion trajectory can be strictly parallel to the real rotation center line of the tube blank.

[0018] 3. This invention utilizes the reconstructed new coordinates of the machining endpoint to drive a three-axis CNC thread turning machine for cutting, ensuring that the feed paths of tools at different stations follow a unified axis of rotation in space. This allows the tool trajectory of finishing at the lower station to completely cover the tool trajectory of roughing at the upper station, eliminating the step misalignment defect at the junction of the two tools. At the same time, it ensures that the cutting allowance is evenly distributed throughout the axial section, preventing tool breakage caused by sudden changes in local cutting amount, and improving the overall forming accuracy of the pipe end thread. Attached Figure Description

[0019] Figure 1 This is a block diagram illustrating the control logic and architecture of the processing system of the present invention; Figure 2 This is the main flowchart of the method for machining a stepped thread on the end of a pipe using two cutting tools according to the present invention; Figure 3 This is a sub-flowchart of the baseline trial cutting of the present invention; Figure 4 This is a sub-flowchart of the measurement point calibration and position verification steps of the present invention; Figure 5 This is a sub-flowchart of the feature extraction and error model solving steps of the present invention; Figure 6 This is a flowchart of the end-point coordinate compensation and target thread turning of the present invention; Figure 7 This is a partial structural diagram of the present invention; Figure 8 This is a graph comparing the radial dimension deviation of the thread before and after implementing coordinate compensation in this invention.

[0020] Among them, 10 is the chuck; and 20 is the tube blank. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0022] See attached document Figure 1 This invention provides a machining system for solving the problem of stepped threads appearing on the ends of pipes when machining with a two-foot cutter. The system includes a three-axis CNC threading machine and a control system installed in the three-axis CNC threading machine. The three-axis CNC threading machine has an axial feed axis and a radial feed axis. The direction parallel to the central rotation axis of the pipe blank to be machined is defined as the Z-axis, and the two feed directions perpendicular to the central rotation axis are defined as the X-axis and Y-axis, respectively. The end of the three-axis CNC threading machine is equipped with a chuck for clamping the pipe blank to be machined.

[0023] The three-axis CNC thread turning machine is equipped with an upper tool chuck and a lower tool chuck. The upper tool chuck is mounted at the X-axis position and feeds along the X-axis, while the lower tool chuck is mounted at the Y-axis position and feeds along the Y-axis. The control system is internally connected to a reference trial cutting module, a feature extraction module, an error model calculation module, and an endpoint coordinate compensation module. The reference trial cutting module sends running commands to the upper and lower tool chucks to move the tool along the Z-axis to turn the reference outer circle. The feature extraction module receives the diameter data at both ends of the reference outer circle and transmits it to the error model calculation module. The error model calculation module combines the diameter data and the machining length value of the reference outer circle to generate error compensation parameters. The endpoint coordinate compensation module retrieves the error compensation parameters, reconstructs the coordinate values ​​of the X-axis and Y-axis, and directs the three-axis CNC thread turning machine to complete the turning of the target thread.

[0024] See attached document Figure 2 This invention provides a method for solving the problem of stepped defects in pipe end threads processed by two-foot cutters, comprising the following steps: S100, the reference test cutting module adjusts the upper tool holder device to turn the first reference outer circle of the tube blank held by the chuck along the Z-axis. The retraction action is triggered after the first reference outer circle is turned. The system command adjusts the lower tool holder device to turn the second reference outer circle of the tube blank along the Z-axis. S200, the feature extraction module receives the diameter data at both ends of the first reference outer circle and the diameter data at both ends of the second reference outer circle. The system aggregation stage transmits the received diameter values ​​to the error model calculation module. The S300 error model calculation module defines the quotient of the diameter difference between the two ends of the first reference outer circle and the machining length of the first reference outer circle as the first error slope. The internal logic defines the quotient of the diameter difference between the two ends of the second reference outer circle and the machining length of the second reference outer circle as the second error slope. The product of the first error slope and the total length of the target thread is converted into the error compensation parameter corresponding to the upper tool holder device, and the product of the second error slope and the total length of the target thread is converted into the error compensation parameter corresponding to the lower tool holder device.

[0025] The S400 endpoint coordinate compensation module retrieves the generated error compensation parameters. The control system superimposes the error compensation parameters for the upper tool holder into the X-axis machining endpoint coordinates. The coordinate writing program superimposes the error compensation parameters for the lower tool holder into the Y-axis machining endpoint coordinates. The three-axis CNC thread turning machine reads the new coordinates and completes the target thread turning. See attached document Figure 3 Step S100 includes the following sub-steps: S101: The instruction data reads the internal hardware assembly parameters of the three-axis CNC thread turning machine, determines the center position of the chuck end face, and the control system sets the center of the chuck end face as the origin of the machining space.

[0026] S102. The mechanical fixture fixes the tube blank to be processed. The system defines the central rotation axis of the tube blank to be processed. The reference trial cutting module defines the movement path parallel to the central rotation axis of the tube blank to be processed as the Z-axis direction. The Z-axis direction corresponds to the axial feed guide of the three-axis CNC thread turning machine. The tool moves along the Z-axis direction to form the axial cutting span.

[0027] S103. The CNC hardware itself has two feed guideways perpendicular to the central rotation axis. The control logic defines the first path moving towards the feed guideway as the X-axis direction and the second path moving towards the feed guideway as the Y-axis direction. The upper tool turret is mounted at the X-axis position, and the corresponding tool tip moves along the X-axis direction to generate the first radial cutting value. The lower tool turret is mounted at the Y-axis position, and the corresponding tool tip moves along the Y-axis direction to generate the second radial cutting value.

[0028] Ideally, the spindle rotation centerline is strictly parallel to the Z-axis. Long-term wear and tear causes the spindle rotation centerline to deviate from the Z-axis, creating a spatial angle. This spatial arrangement results in the upper tool chute being located in the X-axis plane and the lower tool chute in the Y-axis plane. The spatial angle of the spindle rotation centerline projects different offset errors onto the X-axis and Y-axis planes, respectively.

[0029] To clearly quantify the mapping relationship of multiple tool turrets in three-dimensional space, a basic model of the spatial machining position is defined: ; in, Theoretical machining points representing the surface of the tube blank to be processed; This represents the theoretical feed coordinate value of the upper tool holder in the X-axis direction; This represents the theoretical feed coordinate value of the lower tool turret in the Y-axis direction; This represents the theoretical feed coordinate value along the Z-axis of either the upper or lower tool chute.

[0030] S104. The control system sends a spindle operation command. The blank to be processed rotates synchronously with the chuck and reaches the set speed. The reference trial cutting module activates the machining program of the upper tool holder device, and the internal command retrieves the cutting parameters of the first tool assembled at the X-axis station.

[0031] S105, the three-axis CNC thread turning machine drives the upper tool holder to move towards the outer surface of the tube blank to be processed. The first tool approaches the tube blank to be processed along the X-axis direction. After the feed action reaches the theoretical radial calibration point set by the instruction, the X-axis displacement stops.

[0032] S106. With the X-axis coordinate locked, the first tool performs a linear, uniform cutting motion along the Z-axis. The first segment of the reference outer circle gradually takes shape on the outer surface of the billet as the tool tip moves. The reference trial cutting module defines the coordinates of the starting and ending points of the linear cutting motion. The spatial span between the starting and ending points directly determines the span value measured on the reference surface. To ensure the accuracy of subsequent data extraction, the axial span defined by the endpoint of the cutting motion must encompass the target thread design length.

[0033] ; in, This represents the machining length of the first reference outer circle; This represents the Z-axis coordinate of the test cut and retraction point of the upper tool holder device; The Z-axis coordinate represents the test cut entry point of the upper tool holder device.

[0034] S107. After the first tool reaches the end position set on the Z-axis, a tool retraction signal is triggered. The upper tool holder moves back to the safe avoidance position along the X-axis. The control system marks the completion status of the first segment of the reference outer circle turning and waits for subsequent measurement commands to be received.

[0035] S108: The instruction reads the cutting parameters of the second tool assembled at the Y-axis station, and the three-axis CNC thread turning machine drives the lower tool holder to move towards the outer surface of the tube blank to be processed.

[0036] S109. The second tool approaches the rotation center line of the tube blank along the Y-axis. After the feed action reaches the theoretical radial calibration point set by the internal logic, the Y-axis displacement stops. In order to ensure the complete forming of the cutting surface, the theoretical radial feed depth set by the second tool is greater than that set by the first tool. The extra cutting depth allows the second tool to cut a brand new complete cylindrical surface on the outer surface of the same tube blank.

[0037] S110. The second tool, while locked in the Y-axis coordinate, performs a linear uniform cutting motion along the Z-axis. The second reference outer circle gradually takes shape on the outer surface of the tube blank as the tool tip moves. The reference trial cutting module retrieves the coordinates of the starting point and ending point of the linear tool movement. The spatial span between the starting point and the ending point constitutes the span value of the second reference outer circle. In order to ensure the accuracy of subsequent data extraction, the axial span defined by the tool movement ending point must encompass the target thread design length.

[0038] ; in, This represents the machining length of the second reference outer circle; The z-axis coordinate of the test cut and retraction point of the lower tool table device; The Z-axis coordinate represents the test cut entry point of the lower tool table device.

[0039] S111. After the second tool reaches the Z-axis endpoint, it triggers the tool retraction program. The lower tool turret moves back along the Y-axis to the safe avoidance point. The control system marks the completion status of the second segment of the reference outer circle turning and sends a data reading preparation command to the feature extraction module. After the spindle receives the stop command, it drives the blank to be processed to stop rotating, and the machine tool enters the static measurement waiting stage.

[0040] See attached document Figure 4 Step S200 includes the following sub-steps: S201. The data collection link reads the start and end point information of the upper tool holder device along the Z-axis, defines the forming boundary of the first reference outer circle in the Z-axis direction, and the positioning program marks the edge position of the first reference outer circle away from the chuck as the first measuring point. The system marks the edge position of the first reference outer circle close to the chuck as the second measuring point. The first measuring point is used to extract the diameter data of the end away from the chuck, and the second measuring point is used to extract the diameter data of the end close to the chuck. The line connecting the first measuring point and the second measuring point is parallel to the Z-axis, and the span of the line connecting the two points directly corresponds to the error accumulation range generated by the upper tool holder device.

[0041] S202. The data collection link reads the start and end point information of the tool movement along the Z-axis of the lower tool holder device, defines the forming boundary of the second reference outer circle in the Z-axis direction, and the positioning program marks the edge position of the second reference outer circle away from the chuck as the third measuring point. The internal logic marks the edge position of the second reference outer circle close to the chuck as the fourth measuring point. The third measuring point is used to extract the diameter data of the lower station away from the chuck, and the fourth measuring point is used to extract the diameter data of the lower station close to the chuck. The span of the line connecting the third and fourth measuring points completely covers the error variation range accumulated by the machining of the lower tool holder device.

[0042] S203. In order to ensure the matching degree of the data subsequently transmitted to the error model solution module, the measurement point calibration stage is equipped with a position verification judgment. The internal algorithm judges whether the positioning process has been offset by comparing the coordinate difference of the measurement point on the Z axis.

[0043] ; in, This represents the verification value of the span of the first benchmark outer circle measuring point. This represents the Z-axis coordinate of the second measuring point; This represents the Z-axis coordinate of the first measuring point.

[0044] When the span verification value of the first reference outer circle measuring point is equal to the machining length of the first reference outer circle, the feature extraction module determines that the distribution positions of the first and second measuring points are qualified. The verification mechanism uses the same coordinate difference comparison method to check the distribution status of the third and fourth measuring points. After all measuring points are located, the system opens the data transmission channel.

[0045] S204. The external measuring tool acquires the outer surface dimensions at the first and second measuring points. The outer surface dimension values ​​are input into the control system through the CNC panel. The feature extraction module records the dimension corresponding to the first measuring point as the diameter data of the first segment of the reference outer circle away from the chuck. The internal storage unit records the dimension corresponding to the second measuring point as the diameter data of the first segment of the reference outer circle near the chuck. The feature data associated with the upper tool holder device forms an independent data packet in the storage area.

[0046] S205, The measurement action extends to the third and fourth measuring points. The system control panel receives the dimensional input values ​​for the lower station. The feature extraction module maps the dimension corresponding to the third measuring point to the diameter data of the second reference outer circle away from the chuck. The internal logic maps the dimension corresponding to the fourth measuring point to the diameter data of the second reference outer circle near the chuck. The feature data associated with the lower tool holder is entered into another independent storage area.

[0047] S206. The system summary step reads the values ​​from the two storage areas. The internal calculation logic performs difference operation preprocessing on the extracted raw values. The preprocessing step follows the principle of taking the absolute value of the difference to shield the positive and negative sign interference caused by the tilt direction of the machine tool spindle.

[0048] ; ; in, This represents the diameter difference between the two ends of the first segment's outer circumference. This represents the diameter data of the end of the first reference outer circle furthest from the chuck; This represents the diameter data of the first segment of the reference outer circle near the chuck end; This represents the difference in diameter between the two ends of the second segment's outer circumference. This represents the diameter data of the end of the second reference outer circle furthest from the chuck; This represents the diameter data of the second segment of the reference outer circle near the chuck end.

[0049] S207. The difference calculation result, together with the original diameter data, is connected to the data flow bus of the back-end calculation unit. The system summary stage packages the diameter difference between the two ends of the first reference outer circle and the diameter difference between the two ends of the second reference outer circle and sends them to the error model calculation module. After receiving the instruction signal, the error model calculation module enters the standby state. After the data transmission link is completed, the transmission port is automatically closed to release the system memory.

[0050] See attached document Figure 5 Step S300 includes the following sub-steps: S301. The computation link retrieves the diameter difference between the two ends of the first reference outer circle from the data packet, and the system background synchronously reads the machining length of the first reference outer circle. When the spindle rotation center line deviates from the Z-axis direction, the upper tool chute moves along the Z-axis direction, generating a continuously increasing or decreasing radial offset value. The radial offset value is linearly proportional to the tool travel distance in the Z-axis direction. In order to convert the error under a specific test span into a universal standard, the computation logic needs to solve for the diameter change per unit length.

[0051] S302, The error model calculation module starts the quotient calculation instruction. The internal logic takes the difference in diameter between the two ends of the first reference outer circle as the dividend, and the instruction takes the machining length of the first reference outer circle as the divisor. The result of the division operation reflects the rate of change of the deviation of the upper tool holder station in the X-axis direction. The error model calculation module establishes the quotient of the difference in diameter between the two ends of the first reference outer circle and the machining length of the first reference outer circle as the first error slope.

[0052] ; in, Represents the slope of the first error; This represents the diameter difference between the two ends of the first segment's outer circumference. This represents the machining length of the first reference outer circle.

[0053] S303. After the first error slope is generated, it is stored in the first dedicated cache area of ​​the error model calculation module. The mechanism of extracting the unit length deviation through quotient calculation cuts off the limitation of the specific processing length on error evaluation. The first error slope becomes the exclusive independent intervention benchmark of the upper tool holder device. The independent calculation process eliminates the interference of the spatial position of the lower tool holder device on the X-axis station deviation evaluation.

[0054] S304. The computation link extracts the diameter difference between the two ends of the second reference outer circle in the data packet. The system background synchronously obtains the machining length of the second reference outer circle. The three-dimensional tilt angle generated by the spindle rotation center line deviating from the Z-axis direction forms an independent projection value in the Y-axis plane. The radial offset value of the Y-axis generated by the movement of the lower tool holder along the Z-axis direction is essentially different from the radial offset value of the X-axis generated by the upper tool holder. The system logic needs to solve the change in diameter per unit length of the lower station under a specific test span separately.

[0055] S305, The error model calculation module activates the division operation instruction. The internal logic takes the difference in diameter between the two ends of the second reference outer circle as the dividend, and the control instruction takes the machining length of the second reference outer circle as the divisor. The internal logic establishes the second error slope based on the quotient of the difference in diameter between the two ends of the second reference outer circle and the machining length of the second reference outer circle. The result of the division operation reflects the rate of change of the deviation of the lower tool holder station in the Y-axis direction.

[0056] ; in, This represents the second error slope; This represents the difference in diameter between the two ends of the second segment's outer circumference. This represents the machining length of the second reference outer circle.

[0057] S306. After the second error slope is generated, it is stored in the second dedicated cache area of ​​the error model solution module. The independent solution mechanism eliminates the data limitations caused by the specific machining length. The second error slope serves as an independent intervention benchmark for the lower tool holder. The dual-channel solution process isolates the error derivation interference between different workstations from the calculation level.

[0058] S307, The control system calls the target thread machining program, and the internal instructions extract the total length value of the target thread. The total length of the target thread defines the specific span of the tool moving along the Z-axis during the actual cutting process. The error model calculation module retrieves the first error slope and the second error slope in the buffer area.

[0059] S308, the arithmetic unit executes the multiplication logic instruction, the product of the first error slope and the total length of the target thread is converted into the error compensation parameter corresponding to the upper tool holder device. The multiplication operation projects the unit length deviation change rate onto the actual machining span. The derivation process quantifies the total radial deviation accumulated by the upper tool holder device in the X-axis direction after completing the entire target thread machining.

[0060] S309, The error model calculation module performs parallel calculations for the lower tool holder device. The product of the second error slope and the total length of the target thread is converted into the error compensation parameter corresponding to the lower tool holder device. The error compensation parameter corresponding to the lower tool holder device represents the total radial offset generated by the tool in the second station in the Y-axis direction when completing the target thread turning. The dual-channel independent conversion mechanism ensures that the compensation values ​​of the X-axis and Y-axis do not interfere with each other.

[0061] ; in, This represents the error compensation parameters corresponding to the lower tool holder device; Represents the second error slope; This represents the total length of the target thread.

[0062] S310. The calculated values ​​are entered into the system interaction register to await retrieval. The endpoint coordinate compensation module sends a data retrieval request to the error model solution module. The register is granted read access and is ready to transmit the error compensation parameters corresponding to the upper tool holder and the lower tool holder to the endpoint coordinate compensation module.

[0063] See attached document Figure 6Step S400 includes the following sub-steps: S401, the endpoint coordinate compensation module retrieves the error compensation parameters generated by the error model calculation module, and the data bus transmits the error compensation parameters corresponding to the upper tool holder and the lower tool holder to the coordinate processing unit; the control command synchronously scans the machining program and extracts the X-axis machining endpoint coordinates and Y-axis machining endpoint coordinates. The coordinate values ​​without intervention reflect the tool position endpoint when the spindle rotation center line is not tilted.

[0064] S402, the underlying computing power activates the coordinate system superposition mechanism. The computing unit performs algebraic addition processing on the X-axis channel data. The control system superimposes the error compensation parameters for the upper tool holder into the X-axis machining endpoint coordinates. The data reconstruction process integrates the total X-axis deviation into the original tool path endpoint.

[0065] S403: The new coordinates of the X-axis machining endpoint are generated in the memory area. The machine tool logic reads the newly calculated endpoint value and replaces the original value in the machining program segment, and the tool path is offset accordingly at the endpoint target in the X-axis plane.

[0066] S404: The system instructions process the data of the Y-axis channel where the lower tool holder is located in parallel. The coordinate writing program will add the error compensation parameters for the lower tool holder to the Y-axis machining endpoint coordinates. The new Y-axis machining endpoint coordinates are then generated and enter the waiting-to-write queue.

[0067] S405, the overwrite logic overwrites the new coordinates of the Y-axis machining endpoint into the corresponding position of the machining code of the next workstation, and the dual-channel parallel operation mechanism realizes the correction of the endpoint coordinates of multiple tool turrets.

[0068] ; ; in, Represents the new coordinates of the X-axis machining endpoint; Represents the X-axis machining endpoint coordinates; This represents the error compensation parameters corresponding to the upper tool holder device; Represents the new coordinates of the Y-axis machining endpoint; Represents the coordinates of the Y-axis machining endpoint; This represents the error compensation parameters corresponding to the lower tool holder device.

[0069] S406, the system command activates the thread cutting cycle code. The three-axis CNC thread turning machine reads the new coordinates of the X-axis machining endpoint and the new coordinates of the Y-axis machining endpoint and prepares to execute the turning action. The spindle controller drives the blank to be processed to rotate to the set cutting line speed. The servo drive unit receives the motion interpolation command containing the reconstructed coordinates.

[0070] S407, the two-foot cutting mode enters the first stage of the thread cutting process. The tool on the upper tool holder moves towards the end of the pipe along the Z-axis. The X-axis servo motor performs a small amount of dynamic linkage feed according to the new coordinates of the X-axis machining endpoint. The first tool forms an inclined tool path in the plane formed by the X-axis and Z-axis. The slope of the feed trajectory is equal to the first error slope extracted in the previous step, which cancels the inclined projection of the spindle center line on the X-axis plane, so that the actual spatial movement trajectory of the first tool is strictly parallel to the real rotation center line of the tube blank to be processed.

[0071] S408. The cutting action for the second long thread is completed by the lower station. When the lower tool holder moves along the Z-axis, the Y-axis servo driver performs synchronous position intervention according to the new coordinates of the Y-axis machining endpoint. The feed trajectory slope of the second tool in the Y-axis plane is corrected to be equal to the second error slope. The tool path of the lower station also overcomes the offset caused by the hardware assembly, and its cutting surface always maintains an equidistant distance from the actual rotation center line of the tube blank to be processed.

[0072] The S409 three-axis CNC thread turning machine reads the new coordinates to complete the target thread turning. After the coordinate reconstruction is analyzed, the cutting trajectories of the upper and lower tool turrets are parallel to each other and the step forming principle is eliminated. By linking the change in the endpoint coordinates with the machining length, the reconstructed tool travel rate and the spindle space tilt slope achieve a technical equivalent substitution.

[0073] ; ; in, This represents the slope of the cutting trajectory of the upper tool holder in the X-axis plane; Represents the new coordinates of the X-axis machining endpoint; The X-axis coordinate represents the starting point of the machining process of the upper tool holder. Represents the total length of the target thread; Represents the slope of the first error; This represents the slope of the cutting trajectory of the lower tool table device in the Y-axis plane; Represents the new coordinates of the Y-axis machining endpoint; The Y-axis coordinate represents the starting point of the machining process of the lower tool holder. This represents the second error slope.

[0074] S410 and trajectory correction logic ensure that the cutting paths of different workstations in three-dimensional space follow a unified axis of rotation. The thread segment handled by the first tool and the thread segment handled by the second tool have the same radial cutting depth at the junction. The inner and outer diameter dimensions of the two rudder tools transition smoothly, and the step misalignment defect on the long thread surface of the pipe end is completely eliminated.

[0075] To aid in a deeper understanding of the system and method proposed in this invention, the following specific application examples and experimental verifications are provided, taking into account practical engineering application scenarios and specific numerical calculations.

[0076] See attached document Figure 7 This embodiment is run on a COLINET RPP7-5 three-axis CNC threading machine equipped with a FANUC operating system. The tube blank 20 to be processed is API standard N80Q grade steel pipe, with a nominal outer diameter of 177.8 mm and a wall thickness of 10.36 mm. The target thread type is set as a trapezoidal thread (BC), with a designed taper ratio of 1:16, and the total target thread length defined in the machining program is 124.0 mm. After the chuck 10 clamps the tube blank 20, the length of the pipe end extending out of the chuck 10 is determined to be 215 mm. The cutting tool used for machining is a shaped external cylindrical insert (model C / 26417).

[0077] The benchmark cutting module activates the upper tool chuck to execute the cutting action. The spindle speed is set to 280 rpm. The first tool cuts the first benchmark outer circle on the outer surface of the tube blank 20. The radial cutting target diameter is set to 176.00 mm, and the machining length of the first benchmark outer circle is set to 100.0 mm. The feature extraction module initiates the edge finding and calibration action. The system marks the edge of the first benchmark outer circle near the chuck 10 as point A and the edge away from the chuck 10 as point B. The outside micrometer measures the diameter of the first benchmark outer circle near the chuck 10 at point A as 175.88 mm and the diameter of the first benchmark outer circle away from the chuck 10 at point B as 176.01 mm. The feature data associated with the upper tool chuck is packaged and stored in the memory bus.

[0078] Based on the same test blank 20, the control command drives the lower tool holder to feed, and the second tool turns the second reference outer circle on the surface of the blank 20. To ensure complete coverage of the cutting surface, the radial cutting target diameter set by the command is reduced to 175.00 mm, and the machining length of the second reference outer circle is also set to 100.0 mm. The feature extraction module performs corresponding measurement point mapping on the second reference outer circle, extracting the diameter data of 175.98 mm at point A (closer to chuck 10) and 176.13 mm at point B (away from chuck 10).

[0079] The error model calculation module receives the raw measurement data and performs concurrent calculations of the difference and quotient. The internal calculation logic derives the first error slope corresponding to the upper tool holder and the second error slope corresponding to the lower tool holder: ; ; in, This represents the slope of the first error, in mm / mm; This represents the diameter data of point A in the upper tool holder machining section; This represents the diameter data of point B in the upper tool holder machining section; This represents the machining length of the first reference outer circle; Represents the second error slope; This represents the diameter data of point A in the machining section of the lower tool table; This represents the diameter data of point B in the machining section of the lower tool table; This represents the machining length of the second reference outer circle.

[0080] Calculation results show that the spindle of the three-axis CNC threading machine produces a radial offset of 0.0013 mm for every 1 mm axial movement in the X-axis plane and a radial offset of 0.0015 mm for every 1 mm axial movement in the Y-axis plane.

[0081] The error model calculation module retrieves the total target thread length of 124.0 mm and calculates the error compensation parameters for each tool post over the entire length span through multiplication operations: ; ; in, The error compensation parameter corresponding to the upper tool holder is calculated to be 0.1612 mm. The error compensation parameter corresponding to the lower tool holder is calculated to be 0.1860 mm. This represents the total length of the target thread.

[0082] The endpoint coordinate compensation module overwrites the target program segment based on the spindle deflection direction vector. Based on the increasing relationship between the dimensions of points A and B, the control command determines that the endpoint coordinates of the upper tool chute need to expand outwards, and the endpoint coordinates of the lower tool chute need to contract inwards. Due to the machine tool coordinate system settings, the algebraic addition here is manifested as negative compensation. The arithmetic unit executes an algebraic addition instruction of 0.1612mm for the X-axis endpoint coordinates and an algebraic operation instruction of 0.1860mm for the Y-axis endpoint coordinates. The system loads the reconstructed machining program, replaces the new blank 20 to be processed, and completes the formal thread cutting. The upper and lower tool chute trajectories are highly parallel in three-dimensional space, and both tools perform envelope cutting around the actual deflection axis of the blank 20.

[0083] To further verify the effectiveness and authenticity of the present invention, a comparative test experiment was performed on the threaded products before and after compensation.

[0084] See attached document Figure 8The curve represents the trend of the microscopic distance of the tool cutting trajectory deviating from the standard taper line as a function of the Z-axis feed length. The experiment obtained multiple sets of pipe end thread surface data under the traditional non-intervention machining mode and the coordinate compensation mode of the present invention, and continuously scanned along the thread pitch diameter generatrix by a high-precision coordinate measuring machine.

[0085] In the traditional non-interventional machining mode curve, the upper tool turret performs roughing in the 0-62mm range of the coordinate axis, and the lower tool turret performs finishing in the 62mm-124mm range. Due to the spindle tilt, the reference trajectories of the upper and lower tool turrets do not coincide, and the scanning curve shows a significant abrupt drop at the junction (around Z=62mm). Measurement data shows that the radial cutting depth difference (i.e., step difference) at the junction reaches 0.14mm to 0.16mm, completely exceeding the tolerance zone allowed by the API standard, and the thread morphology exhibits extremely irregular local protrusions.

[0086] After applying the endpoint coordinate compensation logic of this invention, the reconstructed coordinate drives the two rulers to form a mirror envelope trajectory. The scanning curve in the error compensation mode exhibits high smoothness. The upper and lower workstation trajectory segments are completely closed at the beginning and end in the data view. The radial difference jump at the junction position is suppressed to within 0.005mm, which is far below the step threshold that can be seen by the naked eye or measured by conventional measuring tools. The curve closely follows the zero-point tolerance baseline along the entire 124mm span, proving that the cutting allowance is uniformly distributed across the entire axial section. Experimental data clearly show that, through the unit length change rate conversion and endpoint coordinate reconstruction mechanism, the cutting interference problem of the double-tool table is completely eliminated, preventing tool deflection caused by sudden changes in cutting force, and optimizing the overall thread ellipticity index.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for solving the problem of stepped defects appearing when machining pipe end threads with a two-foot cutter, characterized in that, The method is applied to a three-axis CNC threading machine, which includes an upper tool turret for feeding along the X-axis, a lower tool turret for feeding along the Y-axis, and a guide rail for feeding along the Z-axis. S100, control the upper tool holder device and the lower tool holder device to perform reference trial cutting on the outer surface of the tube blank to be processed, respectively forming the first reference outer circle and the second reference outer circle, and obtain the diameter data of the two ends of the first reference outer circle and the diameter data of the two ends of the second reference outer circle. S200, based on the diameter data of both ends of the first reference outer circle and the machining length, calculate the first error slope corresponding to the upper tool holder device; based on the diameter data of both ends of the second reference outer circle and the machining length, calculate the second error slope corresponding to the lower tool holder device; S300, combined with the target total thread length, the first error slope and the second error slope are respectively converted into the X-axis error compensation parameters corresponding to the upper tool holder device and the Y-axis error compensation parameters corresponding to the lower tool holder device; S400, the X-axis error compensation parameters and the Y-axis error compensation parameters are superimposed on the preset X-axis machining endpoint coordinates and Y-axis machining endpoint coordinates respectively, and new X-axis machining endpoint coordinates and new Y-axis machining endpoint coordinates are reconstructed; S500, the three-axis CNC thread cutting machine is controlled to perform thread cutting based on the new coordinates of the X-axis machining endpoint and the new coordinates of the Y-axis machining endpoint.

2. The method for solving the problem of stepped defects in pipe end threads processed by two-foot cutters according to claim 1, characterized in that, Before executing S100, the following is also included: Set the center of the chuck end face as the origin of the machining space; The movement path parallel to the rotation axis of the tube blank center is defined as the Z-axis direction; The first path of the upper tool holder device, moving towards the feed guide rail, is defined as the X-axis direction, and the second path of the lower tool holder device, moving towards the feed guide rail, is defined as the Y-axis direction.

3. The method for solving the problem of stepped defects in pipe end threads processed by two-foot cutters according to claim 1, characterized in that, S100 specifically includes: The first tool on the upper tool holder is controlled to feed along the X-axis to a first set radial position, and while keeping the X-axis coordinate locked, it feeds along the Z-axis to machine the first reference outer circle. Extract the diameter data of the first segment of the reference outer circle at the end furthest from the chuck and the diameter data at the end closest to the chuck; The second tool on the lower tool holder is controlled to feed along the Y-axis to a second set radial position, and while keeping the Y-axis coordinate locked, it feeds along the Z-axis to machine the second reference outer circle. Extract the diameter data of the second segment of the reference outer circle at the end furthest from the chuck and the diameter data at the end closest to the chuck.

4. The method for solving the problem of stepped defects in pipe end threads processed by two-foot cutters according to claim 3, characterized in that, In S100: The cutting depth corresponding to the second set radial position is greater than the cutting depth corresponding to the first set radial position, so that the second tool cuts a brand new complete cylindrical surface on the outer surface of the same tube blank.

5. A method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, as described in claim 4, characterized in that, S200 specifically includes: Calculate the first absolute difference between the diameter data of the end of the first reference outer circle furthest from the chuck and the diameter data of the end closest to the chuck; The ratio of the first absolute difference to the machining length of the first segment of the reference outer circle is established as the first error slope; Calculate the second absolute difference between the diameter data of the end of the second reference outer circle furthest from the chuck and the diameter data of the end closest to the chuck; The ratio of the second absolute difference to the machining length of the second reference outer circle is established as the second error slope.

6. The method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter according to claim 5, characterized in that, The S300 specifically includes: The product of the first error slope and the total length of the target thread is calculated to obtain the X-axis error compensation parameter; The product of the second error slope and the total length of the target thread is calculated to obtain the Y-axis error compensation parameter.

7. A method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, as described in claim 6, characterized in that... The S400 specifically includes: Extract the preset X-axis and Y-axis machining endpoint coordinates from the target thread machining program; The preset X-axis machining endpoint coordinates are algebraically added to the X-axis error compensation parameters to generate new X-axis machining endpoint coordinates. The preset Y-axis machining endpoint coordinates are algebraically added to the Y-axis error compensation parameters to generate new Y-axis machining endpoint coordinates.

8. A method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, as described in claim 7, characterized in that, After generating the new coordinates of the X-axis machining endpoint and the new coordinates of the Y-axis machining endpoint, step S400 further includes: The preset X-axis machining endpoint coordinates in the target thread machining program are overwritten and replaced with the new X-axis machining endpoint coordinates; The preset Y-axis machining endpoint coordinates in the target thread machining program are overwritten and replaced with the new Y-axis machining endpoint coordinates.

9. A method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, as described in claim 8, characterized in that, The S500 specifically includes: Load the overwritten target thread machining program and replace it with a new tube blank to be machined; The upper tool holder is controlled to feed along the Z-axis direction, and dynamically linked feeds are performed in the X-axis direction according to the new coordinates of the X-axis machining endpoint, so that the cutting trajectory slope of the upper tool holder is equal to the first error slope. The lower tool chute is controlled to continue feeding along the Z-axis, and synchronous position intervention is performed in the Y-axis direction according to the new coordinates of the Y-axis machining endpoint, so that the cutting trajectory slope of the lower tool chute is equal to the second error slope.

10. A method for solving the problem of stepped defects in pipe end threads processed by a two-foot cutter, as described in claim 9, characterized in that, During the process of controlling the three-axis CNC thread cutting machine to perform thread cutting: The first tool on the upper tool holder performs rough thread turning, and the second tool on the lower tool holder performs finish thread turning. The cutting trajectory of the upper tool holder and the cutting trajectory of the lower tool holder are parallel to each other in three-dimensional space, and both are parallel to the actual central rotation axis of the new tube blank to be processed.

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