Laser-assisted ultra-precision machining thermal error pre-compensation method

Abstract

The invention discloses a laser-assisted machining path thermal error pre-compensation method, which comprises the following steps of: establishing a force-thermal coupling analysis model for a laser-assisted machining system, accurately calculating the temperature field change and deformation condition of a tool rest structural part in the laser-assisted machining process, and accurately correcting the parameter precision of the force-thermal coupling analysis model through model calibration. Thermal deformation epsilon t of a system tool nose point, a tool placement pose theta and an uncompensated tool path (xt ', zt') are obtained based on model calculation, and a processing tool path (xt, zt) is obtained through pre-compensation tool nose thermal deformation calculation, so that high-precision laser-assisted ultra-precision processing is realized under the condition that a tool rest has a thermal drift error.

Description

Technical Field

[0001] The invention belongs to the technical field of laser-assisted ultra-precision machining, and in particular relates to a machining path thermal error pre-compensation method. Background Art

[0002] Core devices with ultra-smooth surfaces and high-precision surface features play an important role in consumer electronics, defense industry, and biomedicine. The single-point diamond turning method is an important means to achieve high-precision and efficient processing of such devices. However, for the increasingly widely used hard and brittle material devices, the traditional single-point diamond turning method cannot meet the processing needs of hard and brittle materials due to processing problems such as rapid tool wear and severe surface fragmentation. The laser-assisted ultra-precision machining method uses laser to soften the workpiece material, enhance its machinability, and effectively improve the tool life and the processing quality of hard and brittle materials, thus gaining wide application and attention. However, the laser-assisted ultra-precision machining method also has inherent defects. In the machining system, due to factors such as tool surface reflection, workpiece reflection, and tool holder obstruction, it is inevitable that the laser will be irradiated on the tool holder, thereby introducing additional heat to destroy the balance of the tool holder structure, resulting in thermal drift of the tool holder system, thereby affecting the machining accuracy of the device. At present, there are some ways in engineering to reduce the impact of the above problems. On the one hand, the heat source can be isolated by adding thermal insulation gaskets around the heat source of the tool holder. On the other hand, the heat dissipation of the tool holder can be increased by adding a heat sink. At the same time, the influence of thermal errors can be reduced by tool holder structural design and tool holder material selection. However, no matter which of the above methods is used, the flexibility of structural design adjustment of the tool holder is poor, the implementation difficulty and cost are high, and the final thermal error influence cannot be completely eliminated. In summary, it is urgent to study a high-precision and universal processing method to suppress thermal errors in laser-assisted ultra-precision machining. Summary of the invention

[0003] The purpose of the present invention is to solve the above problems and provide a cutting trajectory thermal error pre-compensation and high-precision machining method for laser-assisted ultra-precision machining scenarios.

[0004] In order to solve the above technical problems, the technical solution of the present invention is: a laser-assisted machining path thermal error pre-compensation method, characterized in that: the method establishes a force-heat coupling analysis model for the laser-assisted machining system, accurately calculates the temperature field change and deformation of the tool holder structure during the laser-assisted machining process, accurately corrects the force-heat coupling analysis model parameter accuracy through model calibration, and obtains the thermal deformation ε of the tool tip point of the system based on the model calculation. t , tool placement θ and uncompensated tool trajectory (x t ',z t '), the pre-compensation tool tip thermal deformation is calculated to obtain the machining tool trajectory (x t ,z t), thereby achieving high-precision laser-assisted ultra-precision machining in the presence of thermal drift errors in the tool holder.

[0005] Furthermore, the mechanical-thermal coupling analysis model is established based on the laser-assisted ultra-precision machining system used in the experiment. The energy density and distribution of the tool holder heat source depend on the actual laser loading form. The energy source is accurately loaded to the corresponding position of the tool holder model based on the laser power reflected to the tool holder in the experiment.

[0006] Furthermore, the mechanical-thermal coupling analysis model is solved and calculated using numerical solution methods such as finite element method and finite difference method.

[0007] Furthermore, the model calibration process is carried out by actually measuring the thermal drift changes of several characteristic points of the tool holder structure and comparing them with the model output values. By correcting the key parameters of the model, the measured values ​​are made as close as possible to the simulated values.

[0008] Furthermore, the uncompensated tool trajectory z t 'Calculated through workpiece geometry and tool nose radius, rake angle and other geometric parameters.

[0009] Furthermore, the tool placement posture θ refers to the angle θ between the tool center axis and the Z axis of the machine tool.

[0010] Furthermore, the machining tool trajectory is calculated by the following formula:

[0011]

[0012] When the thermal deformation of the tool tip is along the positive direction of the X-axis and Z-axis of the machine tool, a "+" sign is indicated in the public display; when the thermal deformation of the tool tip is along the negative direction of the X-axis and Z-axis of the machine tool, a "-" sign is indicated in the public display.

[0013] Furthermore, the tool trajectory calculation formula needs to ensure that the thermal deformation ε t and uncompensated tool path (x t ',z t ') are consistent in timing.

[0014] The beneficial effects of the present invention are:

[0015] 1. The method provided by the present invention does not require any hardware modification and is applicable to most laser-assisted ultra-precision machining systems and their application scenarios.

[0016] 2. The method of the present invention has a model parameter calibration link, and the thermal error compensation accuracy of the laser-assisted ultra-precision machining system is high.

[0017] 3. The method of the present invention can effectively improve the surface accuracy of laser-assisted ultra-precision machining workpieces. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The thermal deformation result diagram of the tool rest in the Y-axis height direction of the machine tool is obtained by the finite element simulation calculation of the present invention;

[0019] Figure 2 The present invention uses finite element simulation to calculate the change in thermal drift of the tool tip in the Z-axis direction of the machine tool and compares the surface error of the workpiece processed using an uncompensated thermal drift tool trajectory;

[0020] Figure 3 This is a comparison diagram of the surface error results of the same workpiece laser-assisted ultra-precision turning using the original tool trajectory and the pre-compensated tool trajectory of the present invention, wherein (a) is the original tool trajectory result, and (b) is the pre-compensated tool trajectory result. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0022] like Figures 1 to 3 As shown, the present invention provides a laser-assisted machining path thermal error pre-compensation method, which establishes a force-heat coupling analysis model for the laser-assisted machining system, accurately calculates the temperature field change and deformation of the tool holder structure during the laser-assisted machining process, accurately corrects the force-heat coupling analysis model parameter accuracy through model calibration, and obtains the thermal deformation ε of the tool tip point of the system based on the model calculation. t , tool placement θ and uncompensated tool trajectory (x t ',z t '), the pre-compensation tool tip thermal deformation is calculated to obtain the machining tool trajectory (x t ,z t ), thereby achieving high-precision laser-assisted ultra-precision machining in the presence of thermal drift errors in the tool holder.

[0023] The mechanical-thermal coupling analysis model is established based on the laser-assisted ultra-precision machining system used in the experiment. The energy density and distribution of the tool holder heat source depend on the actual laser loading form. The energy source is accurately loaded to the corresponding position of the tool holder model based on the laser power reflected to the tool holder in the experiment. The mechanical-thermal coupling analysis model is solved and calculated using numerical solution methods such as the finite element method and the finite difference method.

[0024] The model calibration process is carried out by actually measuring the thermal drift changes of several characteristic points of the tool holder structure and comparing them with the model output values. By correcting the key parameters of the model, the measured values ​​are made as close as possible to the simulation values.

[0025] Uncompensated tool path z t 'Calculated through workpiece geometry and tool nose radius, rake angle and other geometric parameters.

[0026] The tool placement position θ refers to the angle θ between the tool centerline and the machine tool Z axis. The machining tool trajectory is calculated by the following formula:

[0027]

[0028] When the thermal deformation of the tool tip is along the positive direction of the X-axis and Z-axis of the machine tool, a "+" sign is indicated in the public display; when the thermal deformation of the tool tip is along the negative direction of the X-axis and Z-axis of the machine tool, a "-" sign is indicated in the public display.

[0029] The thermal deformation ε must be guaranteed in the tool trajectory calculation formula t and uncompensated tool path (x t ',z t ') are consistent in timing.

[0030] This embodiment is a laser-assisted ultra-precision turning processing scenario, in which the tool holder is placed along the Z-axis direction of the machine tool, and the angle θ between the center axis of the tool and the Z-axis of the machine tool is zero. The workpiece aperture is 10mm, which is a rotationally symmetrical aspherical surface. The laser-assisted ultra-precision turning processing device used includes two structural parts: a tungsten carbide tool holder and a stainless steel tool holder.

[0031] Since part of the laser beam will be reflected and irradiated on the tool holder, thermal expansion of the tool holder and tool holder is inevitable during laser-assisted ultra-precision turning. In order to accurately obtain the thermal expansion trend of laser-assisted ultra-precision turning, the finite element simulation method was used to analyze the three-dimensional thermal-mechanical coupling model of the tool holder. The model package simultaneously considers heat exchange, thermal radiation and natural convection heat transfer, and loads an 18W laser heat source at the same time, and the laser irradiates the local upper surface of the tool holder. The initial temperature and ambient temperature of the model structure are both set to 293K.

[0032] Since the experiment uses a feed speed of 2mm / min and the workpiece aperture is 10mm, the total processing time is 150s. Before laser-assisted ultra-precision turning, a dwell time of 30s is reserved. Therefore, the finite element model is used to accurately calculate and analyze the mechanical deformation of 180s of laser heating. The simulation results show that during laser heating, the tip of the diamond tool will gradually expand in the y-axis and z-axis directions, which will seriously affect the tool setting accuracy of the diamond tool and the shape accuracy of the processed workpiece. And due to the symmetrical structural design, there is no thermal drift of the diamond tool tip along the x-axis direction. Specifically, the vertical height of the diamond tool tip will increase by 10.9μm, such as Figure 1 As shown. The expansion of the tool height needs to be pre-adjusted during the tool fine setting process. In addition, the shape error of the workpiece obtained by laser-assisted ultra-precision turning using a non-compensated tool path is different from the thermal deformation of the tool holder in the z direction ε t There is great consistency, such as Figure 2This shows the accuracy of the finite element simulation calculation and also shows that thermal expansion is the main factor affecting the shape accuracy of the workpiece in laser-assisted ultra-precision turning. Figure 2 The deviation between the experiment and the simulation is mainly caused by the tool setting error, the tool head radius measurement error and the tool waviness.

[0033] After accurately calculating the thermal drift change of the tool holder during laser-assisted ultra-precision turning, the tool trajectory can be pre-compensated. The tool trajectory generation is divided into two steps: the first step is to calculate the original tool trajectory (x) without thermal drift compensation based on the ideal surface shape of the workpiece being processed and taking into account the geometric shape of the diamond tool used (including geometric parameters such as the tool nose radius and negative rake angle). t ',z t '). In the second step, according to the finite element calculation results and the feed rate used in the experiment, the thermal drift of the tool holder over time ε t Transformed into the thermal drift ε along the x-coordinate x Since the angle θ between the tool centerline and the machine tool Z axis is zero, the original tool trajectory (x t ',z t ') minus ε x , we can get the compensation tool path (x t ,z t ).

[0034]

[0035] The original tool path and the pre-compensated tool path were used to machine the unbonded tungsten carbide mold using the laser-assisted ultra-precision turning method. The shape error of the machined workpiece was measured using the UA3P-300 shape measuring instrument. There is a large difference in shape accuracy between the original tool path and the compensated tool path. Figure 3 As shown in (a), when the original tool path is used, a large shape error PV value of 4.015 μm is inevitable. When the compensated tool path is used, the workpiece has better shape accuracy due to pre-compensation of thermal deformation, and the PV value is 0.573 μm. Figure 3 (b) shows that there is no obvious contour fluctuation in the surface shape error of the workpiece center area, indicating that the diamond tool tip is successfully aligned with the workpiece center by pre-adjusting the tool expansion height through fine tool setting.

[0036] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for pre-compensation of thermal errors in laser-assisted machining paths, characterized in that: This method establishes a mechanical-thermal coupling analysis model for the laser-assisted machining system, accurately calculates the temperature field change and deformation of the tool holder structure during laser-assisted machining, accurately corrects the accuracy of the mechanical-thermal coupling analysis model parameters through model calibration, and obtains the thermal deformation ε of the tool tip point based on the model calculation. t , tool placement θ and uncompensated tool trajectory (x t ',z t '), the pre-compensation tool tip thermal deformation is calculated to obtain the machining tool trajectory (x t ,z t ), thereby achieving high-precision laser-assisted ultra-precision machining in the presence of thermal drift errors in the tool holder.

2. A laser-assisted machining path thermal error pre-compensation method according to claim 1, characterized in that: The mechanical-thermal coupling analysis model is established based on the laser-assisted ultra-precision machining system used in the experiment. The energy density and distribution of the tool holder heat source depend on the actual laser loading form. The energy source is accurately loaded to the corresponding position of the tool holder model based on the laser power reflected to the tool holder in the experiment.

3. A laser-assisted machining path thermal error pre-compensation method according to claim 1, characterized in that: The mechanical-thermal coupling analysis model is solved and calculated using numerical solution methods such as finite element method and finite difference method.

4. The method for pre-compensation of thermal errors in laser-assisted machining paths according to claim 1, characterized in that: The model calibration process is carried out by actually measuring the thermal drift changes of several characteristic points of the tool holder structure and comparing them with the model output values. By correcting the key parameters of the model, the measured values ​​are made as close as possible to the simulated values.

5. The method for pre-compensation of thermal errors in laser-assisted machining paths according to claim 1, characterized in that: The uncompensated tool path z t 'Calculated through workpiece geometry and tool nose radius, rake angle and other geometric parameters.

6. The method for pre-compensation of thermal errors in laser-assisted machining paths according to claim 1, characterized in that: The tool placement posture θ refers to the angle θ between the tool center axis and the machine tool Z axis.

7. The method for pre-compensation of thermal errors in laser-assisted machining paths according to claim 1, characterized in that: The machining tool trajectory is calculated by the following formula: When the thermal deformation of the tool tip is along the positive direction of the X-axis and Z-axis of the machine tool, a "+" sign is indicated in the public display; when the thermal deformation of the tool tip is along the negative direction of the X-axis and Z-axis of the machine tool, a "-" sign is indicated in the public display.

8. The method for pre-compensation of thermal errors in laser-assisted machining paths according to claim 1, characterized in that: The tool trajectory calculation formula must ensure that the thermal deformation ε t and uncompensated tool path (x t ',z t ') are consistent in timing.

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