A method and system for automatic adjustment and control of laser spot pose in laser-assisted milling

Abstract

This invention belongs to the field of laser-assisted machining technology, and discloses an automatic adjustment and control method and system for laser-assisted milling spot pose. The control method, based on the characteristics of laser-assisted machining technology, performs tool path planning to obtain a tool position file, and calculates the spatial pose of the laser spot under the actual tool path using a proposed laser attitude control algorithm, thereby obtaining a tool-laser synchronous CNC program that changes synchronously and in coordination with the machining tool path. A control system is built based on this method, including a machine tool CNC device, a laser revolution unit, and a laser temperature control unit. The CNC device integrates the laser's "on / off," power, and pose control. The laser revolution unit is used to adjust the pose of the laser spot, ensuring it is always positioned directly in front of the tool to preheat a localized area of ​​the workpiece material. This solves the limitations of traditional unidirectional feed machining, enabling continuous laser-assisted machining of complex-shaped workpieces and promoting the industrial application of laser-assisted machining technology.

Description

Technical Field

[0001] This invention belongs to the field of laser-assisted processing technology, and in particular relates to a method and system for automatic adjustment and control of laser spot posture in laser-assisted milling. Background Technology

[0002] Manufacturing is the foundation of a nation's strength and the cornerstone of its power. The upgrading of national defense equipment relies heavily on the rapid development of the manufacturing sector. With the continuous upgrading of weaponry technology, advanced missiles, aircraft, and armored tanks are increasingly demanding new materials, requiring materials and structures to possess both high strength and lightweight characteristics. This necessitates the extensive use of typical difficult-to-machine materials such as titanium alloys, titanium-aluminum alloys, nickel-based superalloys, and ultra-high-strength steel. However, these materials exhibit poor thermal conductivity, high strength, and high brittleness, making them difficult to machine using traditional cutting methods. This results in high cutting forces / heat and severe tool wear, significantly increasing machining costs and reducing efficiency. Laser-assisted machining technology offers a solution for the efficient cutting of these difficult-to-machine materials. It utilizes a high-energy laser beam to locally heat and soften the workpiece material in the area to be cut, thereby improving the machinability of these materials. This method effectively reduces cutting forces and tool wear rates, improving both machining efficiency and workpiece surface quality.

[0003] In actual parts manufacturing, the machining trajectory is not simply a straight line, but a complex trajectory composed of simple machining units such as straight lines and curves. For laser-assisted machining technology with complex trajectories, on the one hand, it is necessary to improve the integration between the laser equipment and the machine tool, enabling real-time adjustment of the laser spot position during machining at the equipment structure level; on the other hand, it is necessary to consider the specific requirements and limitations of laser-assisted machining technology at the control system level, such as… Figure 1 As shown, this enables it to control the laser spot position and orientation in real time during processing, thereby achieving the optimal laser preheating effect.

[0004] However, current laser-assisted machining equipment suffers from insufficient integration and a lack of corresponding control systems. This prevents the achievement of maximum automated laser-assisted machining, hinders continuous machining capabilities, and prevents the full realization of the advantages of laser-assisted machining technology for engineering applications. Furthermore, there are currently no available control methods or systems for the coordinated control of the laser path and milling path during machining, making it impossible to precisely adjust the laser spot's pose. Simultaneously, given a part's geometry, it is impossible to plan a laser-assisted machining path and automatically generate the necessary NC program, thus hindering laser-assisted machining in any direction. Summary of the Invention

[0005] This invention provides an automatic laser spot pose adjustment and control method and system for laser-assisted milling. After comprehensively considering the requirements of laser-assisted machining technology, it proposes an automatic laser spot pose adjustment and control theory and system, overcoming the problem of coordinated control between the laser path and milling path in the prior art, and realizing the coordinated planning of laser trajectory and tool trajectory in the machining of complex-shaped parts. Furthermore, this invention addresses the limitations of laser control technology in laser-assisted machining devices, improves the degree of integration and automation, and provides a theoretical basis for the engineering application of subsequent laser-assisted composite machining processes.

[0006] To achieve the above objectives, the present invention provides a control method for automatic adjustment of laser spot pose in laser-assisted milling, comprising the following steps:

[0007] Step 1: Based on the structural characteristics of the workpiece, set the cutting parameters, plan the tool machining path, and then obtain the tool position source file;

[0008] Step 2: Extract the tool's position and orientation information during the machining process from the tool position source file;

[0009] Step 3: Obtain the optimal laser process parameters based on the tool position source file and the tool's position and attitude information during the machining process;

[0010] Step 4: Based on the position and orientation information of the tool during the machining process, and according to the positional relationship between the laser spot and the tool in laser-assisted machining, calculate the center coordinates of the laser spot under the actual toolpath;

[0011] Step 5: Calculate the vector angle for laser head pose adjustment based on the optimal laser process parameters to obtain the control sequence for laser rotation angle adjustment;

[0012] Step 6: Obtain the tool-laser synchronous CNC code based on the optimal laser process parameters, the coordinates of the laser spot center under the actual toolpath, and the control sequence for adjusting the laser rotation angle;

[0013] Step 7: Turn on the laser shutter and machine tool power. After completing the initial adjustment of tool setting and laser pose, perform laser-assisted machining according to the given tool-laser synchronous CNC code.

[0014] Tool machining path planning aims to minimize the laser pose adjustment time during machining.

[0015] The process of obtaining the optimal laser process parameters is as follows: establish a workpiece temperature field simulation model, load the position and attitude information of the tool during the processing, perform simulation analysis on the internal temperature field of the workpiece, optimize and select the laser process parameters with the ideal preheating temperature field distribution as the target.

[0016] Obtaining the optimal laser process parameters specifically includes the following steps:

[0017] The analytical formula for solving the temperature field distribution of the material workpiece is established as follows:

[0018]

[0019] Where: N s α is the laser order; P is the laser output power; α is the thermal diffusivity of the material; η is the laser energy absorptivity of the material; k is the thermal conductivity of the material; r p r is the radius of the laser spot; r is the distance from the center of the spot. It is an incomplete gamma function; It is a gamma function;

[0020] Based on the material properties and actual processing parameters, a simulation model of the material temperature field is established.

[0021] Through the above simulation analysis, multiple sets of laser parameters and workpiece temperature field distribution data were obtained. Based on the actual machining cutting parameters and temperature boundary conditions, the corresponding laser parameters were optimized to achieve a better laser preheating effect. The laser process parameters include the laser preheating distance D. L Laser power P and laser spot diameter D.

[0022] When calculating the vector angle for laser head pose adjustment based on optimal laser process parameters, the vector coordinates of the tool center and the laser spot center are established. The angle between the laser head reference and the laser head reference is calculated to obtain the vector angle for laser head pose adjustment.

[0023] The tool-laser synchronous CNC code includes tool machining instruction information, synchronously changing laser pose control instruction information, and laser control instruction information.

[0024] Includes the following steps:

[0025] 1) Position the laser beam using the red indicator light and adjust its initial position;

[0026] 2) During processing, according to the laser power setting instruction in the machine tool CNC instruction, the power control signal is output to the laser power control terminal to complete the setting of the laser output power, and the control signal is compensated and corrected in real time within the set tolerance through the feedback signal value of the laser temperature control unit.

[0027] 3) After the laser power setting command, the laser “switch” command in the machine tool CNC command controls the start and stop of laser light output. The “switch” signal is specifically a voltage signal.

[0028] 4) Finally, the laser detects the voltage signal value at the modulation end. If it matches the set value, the laser emits light; otherwise, it does not emit light.

[0029] Simultaneously, a control system for automatically adjusting the laser pose in laser-assisted milling is provided, including a laser orbiting unit and a laser temperature control unit. The laser orbiting unit is used for laser spot pose adjustment, and the laser temperature control unit is used for workpiece surface temperature control. The laser orbiting unit is mounted on the spindle box and controlled by the machine tool CNC device to achieve precise control of the laser pose. The laser temperature control unit includes a non-contact temperature sensor and a data processing unit for real-time measurement of the cutting zone temperature and feedback comparison to ensure that the laser output power is within a predetermined value.

[0030] The machine tool's CNC device is connected to the laser control signal port of the laser and outputs the laser control signal through the machine tool's CNC program instructions, thus completing the high-frequency control of the laser output beam "switching" and power adjustment.

[0031] The infrared temperature sensor is a fiber optic temperature sensor that uses a fiber optic focusing lens arranged parallel to the laser head to achieve high-speed acquisition of the temperature at the laser spot location.

[0032] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0033] (1) This invention solves the technical difficulties of laser integrated control under complex machining trajectories in the field of laser-assisted machining. That is, by using laser attitude control algorithm, the laser attitude control sequence under the actual machining tool path is calculated, and then the numerical control command of the laser spot running trajectory that is synchronized and coordinated with the machining tool path is obtained. The continuous laser-assisted machining numerical control program of the workpiece is automatically generated through post-processing technology, which can realize the continuous laser-assisted machining of complex shaped workpieces and promote the industrial application of laser-assisted machining technology.

[0034] (2) This invention connects the laser control signal to the machine tool CNC system and controls the laser output signal through the machine tool CNC instructions. The control response time is less than 10 milliseconds, which can effectively avoid the laser from irradiating the unprocessed area when adjusting the posture, thus ensuring the safety of equipment and personnel. At the same time, an infrared temperature sensor is used to monitor the temperature during the processing in real time and compare it with the preset temperature, thereby adjusting the laser power control signal output by the CNC system to achieve the optimal laser preheating effect under the setting and improve the processing quality.

[0035] (3) The automatic adjustment and control system for laser spot position in laser-assisted milling proposed in this invention can accurately adjust the spatial position of the laser spot through the laser revolution unit, so that the laser spot can always be in the predetermined position to preheat the workpiece material. Attached Figure Description

[0036] Figure 1This is a schematic diagram illustrating the coordination of tool path and laser path in laser-assisted machining, as shown in the example of this invention.

[0037] Figure 2 This is a flowchart illustrating the implementation of the laser-assisted milling automatic spot pose control method in this invention example.

[0038] Figure 3 This is a simple example diagram of toolpath planning in a planar laser-assisted milling process, as shown in this invention.

[0039] Figure 4 This is a flowchart illustrating the extraction of tool axis pose information from the tool position file in an example of the present invention.

[0040] Figure 5 Figures (a) to (c) show the simulation results of the temperature field of titanium alloy under different velocities, powers, and incident angles, respectively.

[0041] Figure 6 This is a schematic diagram of the algorithm principle used to calculate the laser spot pose under the actual tool path in the example of this invention;

[0042] Figure 7 This is a flowchart illustrating the laser shutter "switch" and power feedback control in an example of the present invention.

[0043] Figure 8 This is a schematic diagram of the principle of the automatic laser spot adjustment control system in this invention example. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0045] like Figure 2 As shown, this invention provides an automatic laser spot pose adjustment and control method for laser-assisted milling. By controlling the laser beam output, including its "on / off" state, power, and spot spatial pose, high-efficiency, high-quality, and high-reliability continuous laser-assisted machining of complex-shaped workpieces can be achieved. For ease of explanation, only the parts relevant to the embodiments of this invention are shown, and are detailed below:

[0046] Step 1: Before machining the part, a 3D model of the part is first created. Then, reasonable process parameters and steps are adopted according to the machining conditions and quality requirements. In laser-assisted machining, when machining to the turning point (inflection point) of the straight trajectory, laser and tool pose adjustment must be performed. The laser is turned off during the repositioning process, and the laser shutter is opened after the repositioning is completed. Based on this, the tool machining trajectory is optimized with the goal of minimizing the laser pose adjustment time.

[0047] Furthermore, the formula for calculating the time required for laser pose adjustment is as follows:

[0048] Where: i is the number of laser pose adjustment inflection points, θ i V represents the laser pose adjustment angle value. i For laser pose adjustment speed;

[0049] like Figure 3 The image shows an example of a tool path in planar laser-assisted milling. Given a fixed machining step size and machining row spacing, the reciprocating (row cutting) tool path has more laser pose inflection points than the helical (circular cutting) tool path, resulting in more frequent laser pose changes. At the same adjustment speed, the helical tool path (circular cutting) is more efficient and safer.

[0050] Step 2: After completing the toolpath optimization, generate the CLSF toolpath file for the part machining path, based on... Figure 4 The illustrated process extracts the actual machining path information of the tool, namely the coordinate data and tool axis direction vector data during the machining process. Specifically:

[0051] 1) Based on the CAD model of the parts, generate the tool position source file (CLSF file) of the machining path using CAM software;

[0052] 2) Import the CLSF file and read the file information line by line;

[0053] 3) When the read signal is a speed command, extract the speed data and keep it unchanged until the next speed command;

[0054] 4) Determine if it is a straight line command. If so, generate straight line motion information; otherwise, determine if it is a circular arc command. If so, generate circular arc motion information.

[0055] 5) Combine speed data to integrate linear or circular motion information into motion control commands to obtain tool motion information at different times;

[0056] 6) Read line by line in a loop until the read information is "END-OF-PATH", which means that the last line of the file has been reached. At this point, the loop ends and the reading is complete.

[0057] Step 3: By establishing a workpiece temperature field simulation model and loading the actual processing path information obtained in Step 2, the internal temperature field of the workpiece under the actual processing path is simulated and analyzed. With the ideal preheating temperature field distribution as the target, laser process parameters, including the laser preheating distance D, are optimized and selected. L Laser power P and laser spot diameter D;

[0058] Furthermore, step 3 includes the following steps:

[0059] Step 3.1: Establish the analytical formula for the temperature field distribution of the material workpiece, the expression is:

[0060]

[0061] Where: N s η is the laser order; P is the laser output power; α is the thermal diffusivity; η is the laser energy absorptivity of the material; k is the thermal conductivity of the material; r p r is the radius of the laser spot; r is the distance from the center of the spot. It is an incomplete gamma function; This is a gamma function.

[0062] Step 3.2: Taking titanium alloy as an example, based on the material properties, mainly including laser absorptivity, thermal conductivity, and effective softening temperature, and combined with actual processing parameters, a material temperature field simulation model is established. The simulation results are as follows: Figure 5 As shown.

[0063] Step 3.3: Through the above simulation analysis, multiple sets of laser parameters and workpiece temperature field distribution data are obtained. Based on the actual machining cutting parameters and temperature boundary conditions, the corresponding laser parameters can be optimized to achieve a better laser preheating effect.

[0064] Step 4: Determine the preferred laser process parameters as shown in Step 3, such as... Figure 6 As shown, based on the spatial coordination relationship between the laser spot and the tool in laser-assisted machining, the distance T from the tool center along the predetermined machining trajectory is calculated at different times k. k For the preheating distance D L The coordinates P of the center of the laser spot k ;

[0065] Step 5: Establish the tool center coordinates and the spot center coordinate vectors. And calculate the angle θ between it and the laser orbital unit reference. k This yields the control sequence for adjusting the laser rotation angle.

[0066] Step 6: After completing steps 3 to 5, according to the CNC code writing method (APT language), write the control sequence for adjusting the laser rotation angle into the CNC code, that is, output the CNC code for laser-assisted processing through post-processing.

[0067] As an embodiment of the present invention, during the processing, as the laser position is adjusted in real time, it may be necessary to close the optical shutter to prevent the laser from irradiating the unprocessed area during rotation. Therefore, in this invention, the laser's optical shutter control and power control are integrated into the CNC device to ensure the synchronous operation of the processing system and the laser system. Figure 7 This is a logic diagram of the laser shutter and power control. Power monitoring and feedback are implemented through the laser temperature control unit in the control system. The "switching" of the laser shutter is controlled by defined numerical control (NC) code instructions, which are generated at the corresponding positions during post-processing output of the NC code. Details are as follows:

[0068] 1) Position the laser beam using the red indicator light and adjust its initial position;

[0069] 2) During processing, according to the laser power setting instruction in the machine tool CNC instruction, the power control signal is output to the laser power control terminal to complete the setting of the laser output power, and the control signal is compensated and corrected in real time within a certain tolerance through the feedback signal value of the laser temperature control unit.

[0070] 3) After the laser power setting command, the laser “switch” command in the machine tool CNC command controls the start and stop of laser light output. The “switch” signal is specifically a voltage signal, with 0V for off and 24V for on.

[0071] 4) Finally, the laser detects the voltage signal value at the modulation (MOD) terminal. If it matches the set value, the laser emits light; otherwise, it does not. This is the emergency stop switch for laser emission. In normal operation, the signal value is normally open, meaning the laser emits light normally after the power and switch settings are set.

[0072] Step 7: Turn on the laser shutter and machine tool power. After completing the initial adjustment of tool setting and laser pose, perform laser-assisted machining according to the given tool-laser synchronous CNC code.

[0073] To achieve the start / stop of the laser beam and real-time adjustment of laser power in the above control method, as well as the coordination and synchronization of the laser path and tool path, this invention also provides a control system for automatic adjustment of the laser spot pose in laser-assisted milling, such as... Figure 8As shown, the core components of the control system include a machine tool CNC device, a laser orbiting unit, and a laser temperature control unit. The CNC device integrates the laser's "switch," power, and pose control. The laser orbiting unit can adjust the relative position between the laser head and the spindle for real-time adjustment of the laser spot pose during processing. The laser temperature control unit monitors the preheating temperature in real time and provides feedback adjustment for the preheating temperature during laser-assisted milling.

[0074] As one embodiment of the present invention, the laser temperature control unit includes an infrared non-contact temperature sensor and a data processing unit. Specifically, the infrared temperature sensor is a fiber optic temperature sensor, which achieves high-speed acquisition of the temperature at the laser spot position through a fiber optic focusing lens arranged parallel to the laser head. It can handle temperature measurement in the processing of workpieces with complex geometries, and its response time is less than 80μs, enabling near-perfect laser power control.

[0075] In summary, this invention provides an automatic laser spot pose adjustment control method and system for laser-assisted milling. The control method, based on the characteristics of laser-assisted machining technology, performs toolpath planning to obtain a tool position file, and calculates the spatial pose of the laser spot under the actual toolpath using a proposed laser attitude control algorithm. This results in a tool-laser synchronous CNC program that changes synchronously and in coordination with the machining toolpath, enabling real-time adjustment of the spot position, power, and start / stop during machining. Under the guidance of this control method, a corresponding control system is built. The core units include a machine tool CNC device, a laser revolution unit, and a laser temperature control unit. The CNC device integrates the laser's "on / off," power, and pose control. The laser revolution unit adjusts the laser spot pose, allowing adjustment of the laser spot position under any toolpath to ensure it is always positioned directly in front of the tool to preheat the local material of the workpiece. The laser temperature control unit monitors the preheating temperature and provides feedback compensation to adjust the laser power signal output by the CNC device. This invention solves the limitations of traditional unidirectional feed machining, enabling continuous laser-assisted machining of complex-shaped workpieces and promoting the industrial application of laser-assisted machining technology.

[0076] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for automatic adjustment of laser spot pose in laser-assisted milling, characterized in that, Includes the following steps: Step 1: Based on the structural characteristics of the workpiece, set the cutting parameters, plan the tool machining path, and then obtain the tool position source file; Step 2: Extract the tool's position and orientation information during the machining process from the tool position source file; Step 3: Obtain the optimal laser process parameters based on the tool position source file and the tool's position and attitude information during the machining process; Step 4: Based on the position and orientation information of the tool during the machining process, and according to the positional relationship between the laser spot and the tool in laser-assisted machining, calculate the center coordinates of the laser spot under the actual toolpath; Step 5: Calculate the vector angle for laser head pose adjustment based on the optimal laser process parameters to obtain the control sequence for laser rotation angle adjustment; Step 6: Obtain the tool-laser synchronous CNC code based on the optimal laser process parameters, the coordinates of the laser spot center under the actual toolpath, and the control sequence for adjusting the laser rotation angle; Step 7: Turn on the laser shutter and machine tool power. After completing the initial adjustment of tool setting and laser pose, perform laser-assisted machining according to the given tool-laser synchronous CNC code.

2. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 1, characterized in that, The tool machining path planning aims to minimize the laser pose adjustment time during the machining process.

3. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 1, characterized in that, The process of obtaining the optimal laser process parameters is as follows: establish a workpiece temperature field simulation model, load the position and attitude information of the tool during the processing, perform simulation analysis on the internal temperature field of the workpiece, optimize and select the laser process parameters with the ideal preheating temperature field distribution as the target.

4. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 3, characterized in that, Obtaining the optimal laser process parameters specifically includes the following steps: The analytical formula for solving the temperature field distribution of the material workpiece is established as follows: in: The laser order; P η is the laser output power; α is the thermal diffusivity of the material; η is the laser energy absorptivity of the material; k The thermal conductivity of the material; The laser spot radius; r The distance from the center of the light spot; It is an incomplete gamma function; It is a gamma function; Based on the material properties and actual processing parameters, a simulation model of the material temperature field is established. Through the above simulation analysis, multiple sets of laser parameters and workpiece temperature field distribution data were obtained. Based on the actual machining cutting parameters and temperature boundary conditions, the corresponding laser parameters were optimized to achieve a better laser preheating effect. The laser process parameters include the laser preheating distance. Laser power P and laser spot diameter D .

5. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 1, characterized in that, When calculating the vector angle for laser head pose adjustment based on optimal laser process parameters, the vector coordinates of the tool center and the laser spot center are established. And calculate the angle between it and the laser head reference, that is, obtain the vector angle for laser head pose adjustment.

6. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 1, characterized in that, The tool-laser synchronous CNC code includes tool machining instruction information, synchronously changing laser pose control instruction information, and laser control instruction information.

7. The control method for automatic adjustment of laser-assisted milling spot pose according to claim 6, characterized in that, Includes the following steps: 1) Position the laser beam using the red indicator light and adjust its initial position; 2) During processing, according to the laser power setting instruction in the machine tool CNC instruction, the power control signal is output to the laser power control terminal to complete the setting of the laser output power, and the control signal is compensated and corrected in real time within the set tolerance through the feedback signal value of the laser temperature control unit. 3) After the laser power setting command, the laser "switch" command in the machine tool CNC command controls the start and stop of laser light output. The "switch" signal is specifically a voltage signal. 4) Finally, the laser detects the voltage signal value at the modulation end. If it matches the set value, the laser emits light; otherwise, it does not emit light.

8. A control system for automatically adjusting the laser pose in laser-assisted milling, characterized in that, The control method for automatically adjusting the laser spot pose in laser-assisted milling as described in any one of claims 1-7 includes a laser revolution unit and a laser temperature control unit. The laser revolution unit is used for adjusting the laser spot pose, and the laser temperature control unit is used for controlling the surface temperature of the workpiece. The laser revolution unit is mounted on the spindle box and controlled by a CNC machine tool to achieve precise control of the laser pose. The laser temperature control unit includes a non-contact temperature sensor and a data processing unit for real-time measurement of the cutting zone temperature and feedback comparison to ensure that the power output by the laser is within a predetermined value.

9. The control system for automatically adjusting laser pose in laser-assisted milling according to claim 8, characterized in that, The machine tool's CNC device is connected to the laser control signal port of the laser and outputs the laser control signal through the machine tool's CNC program instructions, thus completing the "switching" and high-frequency control of the laser output beam and power adjustment.

10. The control system for automatically adjusting laser pose in laser-assisted milling according to claim 8, characterized in that, The infrared temperature sensor is a fiber optic temperature sensor that uses a fiber optic focusing lens arranged parallel to the laser head to achieve high-speed acquisition of the temperature at the laser spot location.

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