A cutting device for external threads

Abstract

This application discloses a cutting device for external threads, relating to the field of turning technology, including a machine tool body; a spindle system for driving workpiece rotation; a feed system including a radial feed axis driven by a linear motor; a tool system mounted on the feed system, including cutting tools; a temperature sensing device for real-time acquisition of the temperature field distribution in the cutting zone; and a control system electrically connected to the spindle system, the feed system, and the temperature sensing device. This application achieves real-time, cycle-by-cycle advance compensation for the coupling error between transient uneven temperature rise at the tool tip and cutting force fluctuation during external thread cutting through strict synchronization of infrared thermal imaging sampling and CNC system control cycles, a layered compensation architecture for thermo-mechanical decoupling, and a heat conduction model correction driven by the rate of change of cutting force.

Description

Technical Field

[0001] This application relates to the field of turning technology, and in particular to a cutting device for external threads. Background Technology

[0002] External threads are indispensable connection and transmission components in mechanical equipment, and are widely used in aerospace, petrochemical, energy equipment and other fields. Their machining accuracy and consistency directly affect the reliability and service life of the whole machine. Turning is the mainstream process for external thread machining. During the machining process, the dynamic offset of the tool tip is the core factor affecting the thread accuracy, which is mainly caused by the fluctuation of cutting force and the transient uneven temperature rise in the cutting zone.

[0003] Currently, most external thread cutting equipment uses a screw-driven feed system, which suffers from backlash and elastic deformation, making it difficult to achieve high-precision dynamic feed. In terms of error compensation, existing technologies mostly use thermocouples and other point temperature measurement methods to compensate for the steady-state thermal error of machine tool components, or estimate the cutting force through motor current to compensate for force error. Some studies have attempted to use infrared thermal imaging technology to monitor cutting temperature, but the sampling frame rate is not synchronized with the control cycle of the CNC system, making it impossible to accurately capture the transient thermal deformation of the tool tip.

[0004] Existing compensation methods mostly handle thermal or force errors separately, failing to effectively address the coupling effect between the two; black-box compensation models based on machine learning lack physical interpretability and have poor adaptability across working conditions; and existing compensation methods do not directly address the dynamic offset of the tool tip position for real-time advance compensation on a cycle-by-cycle basis, making it difficult to meet the machining requirements of high-precision external threads for large pitch and high-strength materials. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a cutting device for external threads.

[0006] This application provides a cutting device for external threads, which adopts the following technical solution:

[0007] A cutting device for external threads, comprising:

[0008] Machine tool body;

[0009] Spindle system, the spindle system being used to drive the workpiece to rotate;

[0010] A feeding system, the feeding system including a radial feed axis, the radial feed axis being driven by a linear motor;

[0011] A tooling system, which is mounted on the feed system, includes cutting tools;

[0012] A temperature sensing device, wherein the temperature sensing device is used to acquire the temperature field distribution of the cutting zone in real time;

[0013] A control system, which is electrically connected to the spindle system, the feed system and the temperature sensing device;

[0014] The temperature sensing device is configured to acquire two-dimensional temperature field distribution images of the cutting tool tip region and the machined thread surface region;

[0015] The control system is configured as follows:

[0016] The temperature gradient value along the cutting edge direction of the cutting tool is extracted in real time from the two-dimensional temperature field distribution image.

[0017] Based on a pre-built thermo-mechanical-geometric coupling compensation model, the dynamic offset of the cutting tool tip position caused by the transient uneven temperature rise and cutting force fluctuation is calculated by taking the temperature gradient value and the cutting force estimate corresponding to the current signal collected in real time from the linear motor as input.

[0018] The dynamic offset of the tool tip position is used as a compensation amount to perform real-time feedforward correction on the feed command of the radial feed axis.

[0019] As a preferred technical solution of this application, the thermo-mechanical-geometric coupling compensation model includes a decoupling layer and a prediction layer;

[0020] The decoupling layer is used to decompose the dynamic offset of the tool tip position into the current thermal offset component and force offset component according to the preset material thermal expansion coefficient and stiffness matrix of the cutting tool.

[0021] The prediction layer is used to use a simplified difference model based on the partial differential equation of heat conduction. According to the current temperature gradient value, temperature change rate and historical temperature gradient sequence of the cutting zone, it predicts the thermally induced offset increment in the next control cycle, and superimposes the thermally induced offset increment with the current thermally induced offset component and force-induced offset component to obtain the dynamic offset of the tool tip position.

[0022] As a preferred technical solution of this application, the prediction layer is further configured to: when predicting the thermally induced offset increment for a future control cycle, introduce the first-order difference of the current signal of the linear motor as the cutting force change rate input, so as to correct the influence of the change in the rate of frictional heat generation caused by the cutting force fluctuation on the thermally induced offset increment.

[0023] As a preferred technical solution of this application, the simplified difference model of the heat conduction partial differential equation is a one-dimensional explicit difference model. The spatial nodes of the one-dimensional explicit difference model are discrete along the direction from the tip to the shank of the cutting tool. The time step is equal to one control cycle of the control system. The boundary conditions of the one-dimensional explicit difference model are updated in real time by the current temperature gradient value.

[0024] As a preferred technical solution of this application, the initial temperature field of the one-dimensional explicit difference model is determined by integrating and averaging the two-dimensional temperature field distribution image acquired by the temperature sensing device at the start of cutting along the cutting edge direction.

[0025] As a preferred technical solution of this application, when the control system calculates the dynamic offset of the tool tip position, it treats the cutting tool as a cantilever beam model, uses the estimated cutting force and the overhang length of the cutting tool as inputs to calculate the force-induced offset component, and uses the average temperature value of the tool holder along the axial direction and the temperature gradient value along the cutting edge direction extracted from the two-dimensional temperature field distribution image, as well as the material thermal expansion coefficient and overhang length of the cutting tool as inputs to calculate the thermally induced offset component.

[0026] As a preferred technical solution of this application, the temperature sensing device is an infrared thermal imager. The sampling frame rate of the infrared thermal imager is synchronized with the control cycle of the control system. The control system acquires a two-dimensional temperature field distribution image in each control cycle and extracts the corresponding temperature gradient value.

[0027] As a preferred technical solution of this application, the thermo-mechanical-geometric coupling compensation model is pre-constructed in the following manner:

[0028] During the calibration phase, a test piece made of the same material as the workpiece to be processed is used to conduct cutting experiments under different combinations of cutting parameters. The temperature field data of the temperature sensing device, the current signal of the linear motor, and the actual offset of the tool tip measured by an external precision displacement sensor are recorded simultaneously. The temperature field data and current signal are used as inputs, and the actual offset of the tool tip is used as the output. A thermo-mechanical-geometric coupling compensation model is established through a system identification method.

[0029] In summary, this application includes the following beneficial technical effects:

[0030] This application achieves real-time advance compensation for the coupling error between transient uneven temperature rise at the tool tip and cutting force fluctuation during external thread cutting by strictly synchronizing infrared thermal imaging sampling with the control cycle of the CNC system, using a hierarchical compensation architecture that decouples thermo-mechanical physics, and correcting the heat conduction model driven by the rate of change of cutting force. Attached Figure Description

[0031] Figure 1 This is a system architecture diagram of the cutting equipment for the external thread of this application. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0033] See Figure 1 A cutting device for external threads, comprising:

[0034] Machine tool body;

[0035] The machine tool body serves as the basic load-bearing structure of the equipment, providing installation reference and rigid support for various systems.

[0036] Spindle system, the spindle system is used to drive the workpiece to rotate;

[0037] The spindle system is installed in the spindle box of the machine tool body. The output end clamps the workpiece to be processed and is used to drive the workpiece to rotate at a constant speed around its own axis, providing the main motion required for thread cutting.

[0038] The feed system includes a radial feed axis, which is driven by a linear motor.

[0039] The feed system includes an X-axis (radial feed axis) and a Z-axis (axial feed axis). The radial feed axis is directly driven by a linear motor, eliminating the backlash and elastic deformation of traditional lead screw drives, and achieving high-response and high-precision radial feed. The entire feed system is mounted on the guide rail of the machine tool body.

[0040] The tool system is mounted on the feed system and includes cutting tools.

[0041] The tool system is fixedly mounted on the radial feed axis slide of the feed system and moves synchronously with the radial feed axis. The tool system includes a tool holder and a cutting tool. The cutting tool is a carbide external thread turning tool, and the overhang length L can be adjusted according to the machining requirements.

[0042] Temperature sensing device, used to acquire the temperature field distribution in the cutting zone in real time;

[0043] The temperature sensing device uses an infrared thermal imager, which is fixedly installed on the machine tool bed near the cutting area via an adjustable bracket. The lens optical axis is aligned with the cutting tool tip area and the machined thread surface area, and the field of view completely covers the cutting area. The trigger input terminal of the infrared thermal imager is electrically connected to the synchronous output terminal of the control system.

[0044] The control system is electrically connected to the spindle system, feed system, and temperature sensing device.

[0045] The control system adopts an industrial-grade CNC system, which is electrically connected to the servo driver of the spindle system, the linear motor driver of the feed system, and the signal output terminal of the temperature sensor.

[0046] The temperature sensing device is configured to acquire two-dimensional temperature field distribution images of the cutting tool tip region and the machined thread surface region; the temperature sensing device is an infrared thermal imager, the sampling frame rate of the infrared thermal imager is synchronized with the control cycle of the control system, the control system acquires one frame of two-dimensional temperature field distribution image in each control cycle, and extracts the corresponding temperature gradient value.

[0047] The control system is configured as follows:

[0048] The temperature gradient value along the cutting edge direction of the cutting tool is extracted in real time from the two-dimensional temperature field distribution image.

[0049] Based on a pre-constructed thermo-mechanical-geometric coupling compensation model, the dynamic offset of the cutting tool tip position caused by transient uneven temperature rise and cutting force fluctuation is calculated using the temperature gradient value and the cutting force estimate corresponding to the current signal collected in real time from the linear motor as inputs. When calculating the dynamic offset of the cutting tool tip position, the control system treats the cutting tool as a cantilever beam model, uses the cutting force estimate and the overhang length of the cutting tool as inputs to calculate the force-induced offset component. At the same time, the average temperature value of the tool holder along the axial direction and the temperature gradient value along the cutting edge direction are extracted from the two-dimensional temperature field distribution image. Combined with the material thermal expansion coefficient and overhang length of the cutting tool, the thermally induced offset component is calculated.

[0050] The thermo-mechanical-geometric coupling compensation model is pre-built in the following way: During the calibration stage, a test piece made of the same material as the workpiece to be processed is used to carry out cutting experiments under different combinations of cutting parameters. The temperature field data of the temperature sensing device, the current signal of the linear motor, and the actual tool tip offset measured by the external precision displacement sensor are recorded simultaneously. The temperature field data and current signal are used as inputs, and the actual tool tip offset is used as output. The thermo-mechanical-geometric coupling compensation model is established through system identification methods.

[0051] The dynamic offset of the tool tip position is used as a compensation amount to perform real-time feedforward correction of the feed command of the radial feed axis.

[0052] The thermo-mechanical-geometry coupling compensation model includes a decoupling layer and a prediction layer;

[0053] The decoupling layer is used to decompose the dynamic offset of the tool tip position into the current thermal offset component and force offset component based on the preset material thermal expansion coefficient and stiffness matrix of the cutting tool.

[0054] The prediction layer uses a simplified difference model based on the partial differential equation of heat conduction. Based on the current temperature gradient value, temperature change rate, and historical temperature gradient sequence of the cutting zone, it predicts the thermally induced offset increment for the next control cycle. This thermally induced offset increment is then superimposed with the current thermally induced offset component and the force-induced offset component to obtain the dynamic offset of the tool tip position. The prediction layer is also configured to introduce the first-order difference of the linear motor's current signal as the cutting force change rate input when predicting the thermally induced offset increment for the next control cycle, in order to correct the impact of changes in the rate of frictional heat generation caused by cutting force fluctuations on the thermally induced offset increment.

[0055] The simplified difference model of the heat conduction partial differential equation is a one-dimensional explicit difference model. The spatial nodes of the one-dimensional explicit difference model are discretized along the cutting tool tip to the tool holder direction. The time step is equal to one control cycle of the control system. The boundary conditions of the one-dimensional explicit difference model are updated in real time by the current temperature gradient value. The initial temperature field of the one-dimensional explicit difference model is determined by integrating and averaging the two-dimensional temperature field distribution image acquired by the temperature sensing device at the start of cutting along the cutting edge direction.

[0056] The control system operates with a fixed control cycle T, and within each control cycle, the following data acquisition and feature extraction operations are performed sequentially:

[0057] The control system sends a synchronization trigger signal to the infrared thermal imager to make the sampling frame rate of the infrared thermal imager completely synchronized with the control cycle of the control system. In each control cycle, the infrared thermal imager acquires a two-dimensional temperature field distribution image T(x, y, k) containing the cutting tool tip area and the machined thread surface area, and transmits it to the control system. Here, the x-axis is the axial direction from the cutting tool tip to the tool holder, the y-axis is the cutting edge extension direction of the cutting tool, and k is the current control cycle number.

[0058] After preprocessing the acquired two-dimensional temperature field distribution image (including noise filtering and background removal), the control system extracts the following two core temperature features:

[0059] Average temperature of the tool holder along the axial direction during the kth control cycle: ;

[0060] Temperature gradient value G(k) along the cutting edge direction: M equally spaced discrete points are selected along the cutting edge direction (y-axis). (j=1, 2, ..., M), the x-coordinate of each point is fixed as the position of the tool tip. Calculate the temperature gradient in the y-direction at each point and then take the average value. The formula is: ,

[0061] in, The discrete step length along the cutting edge direction is determined by the spatial resolution of the infrared thermal imager.

[0062] The control system acquires the q-axis current signal of the linear motor in real time. By utilizing the linear relationship between the linear motor thrust and the q-axis current, the cutting force at the current moment can be estimated. :

[0063] ,in, Let be the thrust constant of the linear motor. This represents the q-axis current of the linear motor under no-load conditions.

[0064] Simultaneously, the first-order difference of the current signal is calculated to obtain the rate of change of cutting force. : .

[0066] Before the equipment is put into formal processing, a thermo-mechanical-geometric coupling compensation model needs to be constructed through calibration experiments. The specific steps are as follows:

[0067] Calibration test preparation: Use a standard test piece made of the same material as the workpiece to be processed and install it on the spindle system; install an external precision displacement sensor (such as a laser displacement sensor) at the tip of the cutting tool to measure the actual offset of the tool tip.

[0068] Multi-condition cutting experiment: Set multiple different combinations of cutting parameters (including spindle speed, feed rate, and depth of cut), and conduct cutting experiments under each set of parameters; during the experiment, simultaneously record the temperature field data of the infrared thermal imager, the current signal of the linear motor, and the actual offset of the tool tip measured by the precision displacement sensor.

[0069] Model parameter identification: based on experimentally collected temperature field data ( , ) and current signal ( , Using the measured actual offset of the tool tip as the output, the system identification method (such as BP neural network, least squares method) is used to determine all unknown parameters (including the distribution of heat sources in the foundation, thermal correction coefficient, stiffness matrix coefficient, etc.) in the thermo-mechanical-geometry coupling compensation model.

[0070] In this application, the decoupling layer operation process is as follows:

[0071] The decoupling layer is used to achieve thermal-mechanical decoupling calculation of the dynamic offset of the tool tip position. Based on the preset thermal expansion coefficient α and stiffness matrix of the cutting tool, the thermally induced offset component and the force-induced offset component at the current moment are calculated independently, thereby decomposing the total dynamic offset of the tool tip position into two independent physical effect components:

[0072] Force-induced offset component calculation: The cutting tool is considered as a cantilever beam model with one end fixed (tool holder end) and the other end free (tool tip end), using the estimated cutting force at the current moment. Using the overhang length L of the cutting tool as input, calculate the force-induced offset component. : Where E is the elastic modulus of the cutting tool material and I is the moment of inertia of the cutting tool cross section.

[0073] Calculation of thermally induced offset component: Based on the average temperature of the tool holder along the axial direction extracted during the k-th control cycle at the current moment. and temperature gradient value along the cutting edge direction Combining the thermal expansion coefficient α of the cutting tool material and Calculate the thermally induced migration component : ,

[0074] in, ,in, .

[0075] In this application, the prediction layer is used to predict the thermally induced offset increment in the next control cycle in advance to compensate for the hysteresis effect of the control system. The specific process is as follows:

[0076] One-dimensional explicit difference model construction: A one-dimensional explicit difference model is established based on the partial differential equation of heat conduction. The spatial nodes of the model are discretized into N nodes along the direction from the tip of the cutting tool to the tool holder (x-axis). The time step is equal to one control cycle T of the control system.

[0077] Initial temperature field determination: At the start of cutting (k=0), the first frame of the two-dimensional temperature field distribution image acquired by the infrared thermal imager is integrated and averaged along the cutting edge direction (y-axis) to obtain the initial temperature field of the one-dimensional explicit difference model. : ,in, Let be the coordinates of the i-th spatial node in the one-dimensional model.

[0078] Real-time boundary condition updates: Within each control cycle, the temperature gradient value along the x-axis from the tool tip to the tool holder is extracted from the two-dimensional temperature field distribution image. Combined with the thermal conductivity of the cutting tool Calculate the heat flux density at the tip of the knife: As the tool tip boundary condition for the one-dimensional explicit difference model, the tool holder end boundary condition is set to a constant machine tool spindle temperature.

[0079] Force-thermal coupling internal heat source correction: When calculating the internal heat source term of the one-dimensional model, the rate of change of cutting force at the current moment is introduced. As a correction term, the change in the rate of frictional heat generation caused by cutting force fluctuations is corrected: ,in, To calibrate the basic internal heat source distribution, This is the thermal correction factor. This is the nominal cutting force under the current cutting parameters.

[0080] Thermally induced migration increment prediction: Based on the updated boundary conditions and internal heat source terms, the temperature field distribution for the next control cycle (time k+1) is solved using a one-dimensional explicit difference equation, and then the thermally induced migration increment within the next control cycle is calculated. .

[0081] Finally, the current thermally induced offset component and the current force-induced offset component calculated by the decoupling layer are superimposed with the future thermally induced offset increment obtained by the prediction layer to obtain the final dynamic offset of the tool tip position:

[0082] ,in, This represents the radial dynamic offset compensation amount of the tool tip in the kth control cycle. For force-induced offset components, This is the predicted thermally induced offset component for the (k+1)th control cycle.

[0083] Using the dynamic offset of the tool tip position as a compensation amount, the original radial feed command is corrected in real time by feedforward correction to obtain the corrected radial feed command. And send it to the linear motor driver: .

[0085] This application achieves real-time advance compensation for the coupling error between transient uneven temperature rise at the tool tip and cutting force fluctuation during external thread cutting by strictly synchronizing infrared thermal imaging sampling with the control cycle of the CNC system, using a hierarchical compensation architecture that decouples thermo-mechanical physics, and correcting the heat conduction model driven by the rate of change of cutting force.

[0086] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A cutting device for external threads, characterized in that, include: Machine tool body; Spindle system, the spindle system being used to drive the workpiece to rotate; A feeding system, the feeding system including a radial feed axis, the radial feed axis being driven by a linear motor; A tooling system, which is mounted on the feed system, includes cutting tools; A temperature sensing device, wherein the temperature sensing device is used to acquire the temperature field distribution of the cutting zone in real time; A control system, which is electrically connected to the spindle system, the feed system and the temperature sensing device; The temperature sensing device is configured to acquire two-dimensional temperature field distribution images of the cutting tool tip region and the machined thread surface region; The control system is configured as follows: The temperature gradient value along the cutting edge direction of the cutting tool is extracted in real time from the two-dimensional temperature field distribution image. Based on a pre-built thermo-mechanical-geometric coupling compensation model, the dynamic offset of the cutting tool tip position caused by the transient uneven temperature rise and cutting force fluctuation is calculated by taking the temperature gradient value and the cutting force estimate corresponding to the current signal collected in real time from the linear motor as input. The dynamic offset of the tool tip position is used as a compensation amount to perform real-time feedforward correction on the feed command of the radial feed axis.

2. The external thread cutting device according to claim 1, characterized in that, The thermo-mechanical-geometry coupling compensation model includes a decoupling layer and a prediction layer; The decoupling layer is used to decompose the dynamic offset of the tool tip position into the current thermal offset component and force offset component according to the preset material thermal expansion coefficient and stiffness matrix of the cutting tool. The prediction layer is used to use a simplified difference model based on the partial differential equation of heat conduction. According to the current temperature gradient value, temperature change rate and historical temperature gradient sequence of the cutting zone, it predicts the thermally induced offset increment in the next control cycle, and superimposes the thermally induced offset increment with the current thermally induced offset component and force-induced offset component to obtain the dynamic offset of the tool tip position.

3. The external thread cutting device according to claim 2, characterized in that, The prediction layer is also configured to: when predicting the thermally induced offset increment for a future control cycle, introduce the first-order difference of the current signal of the linear motor as the cutting force change rate input, so as to correct the influence of the change in the rate of frictional heat generation caused by the cutting force fluctuation on the thermally induced offset increment.

4. The external thread cutting device according to claim 2, characterized in that, The simplified difference model of the heat conduction partial differential equation is a one-dimensional explicit difference model. The spatial nodes of the one-dimensional explicit difference model are discrete along the direction from the tip to the shank of the cutting tool. The time step is equal to one control cycle of the control system. The boundary conditions of the one-dimensional explicit difference model are updated in real time by the current temperature gradient value.

5. The external thread cutting device according to claim 4, characterized in that, The initial temperature field of the one-dimensional explicit difference model is determined by integrating and averaging the two-dimensional temperature field distribution image acquired by the temperature sensing device at the start of cutting along the cutting edge direction.

6. The external thread cutting device according to claim 1, characterized in that, When calculating the dynamic offset of the tool tip position, the control system treats the cutting tool as a cantilever beam model, and uses the estimated cutting force and the overhang length of the cutting tool as inputs to calculate the force-induced offset component. At the same time, it uses the average temperature value of the tool holder along the axial direction and the temperature gradient value along the cutting edge direction extracted from the two-dimensional temperature field distribution image, as well as the material thermal expansion coefficient and overhang length of the cutting tool as inputs to calculate the thermally induced offset component.

7. The external thread cutting device according to claim 1, characterized in that, The temperature sensing device is an infrared thermal imager. The sampling frame rate of the infrared thermal imager is synchronized with the control cycle of the control system. The control system acquires a two-dimensional temperature field distribution image in each control cycle and extracts the corresponding temperature gradient value.

8. The external thread cutting device according to claim 1, characterized in that, The thermo-mechanical-geometry coupling compensation model is pre-built in the following manner: During the calibration phase, a test piece made of the same material as the workpiece to be processed is used to conduct cutting experiments under different combinations of cutting parameters. The temperature field data of the temperature sensing device, the current signal of the linear motor, and the actual offset of the tool tip measured by an external precision displacement sensor are recorded simultaneously. The temperature field data and current signal are used as inputs, and the actual offset of the tool tip is used as the output. A thermo-mechanical-geometric coupling compensation model is established through a system identification method.

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