CN112756777B - Laser blackening treatment method for metal surface - Google Patents

Abstract

The invention belongs to the field of laser special processing, and particularly relates to a laser blackening treatment method for a metal surface. The treatment method comprises the following steps: (1) Calculating a surface microstructure through a numerical calculation model according to a preset reflectivity index, wherein the surface microstructure is in a blackened state when meeting the reflectivity index; (2) Calculating laser printing parameters through a numerical calculation model according to the surface microstructure, and carrying out simulation calculation according to the laser printing parameters to obtain a structure consistent with the surface microstructure; (3) And placing the metal surface in a working area of a laser processing system, and carrying out laser processing according to the laser printing parameters to obtain a surface blackening layer. The invention can design and set indexes according to the printing result, calculate the processing technological parameters required by simulation, rapidly process and form, has stable result, can keep stable high extinction performance for a long time under extremely severe environment, and has great application value for a plurality of military optical equipment.

Description

Laser blackening treatment method for metal surface

technical field

The invention belongs to the field of laser special processing, and in particular relates to a laser blackening treatment method for metal surfaces.

Background technique

Stray light is other non-imaging light that diffuses on the image plane in addition to the imaging light in the optical system. It includes non-imaging light energy from radiation sources external to the system and internal radiation sources as well as scattering surfaces. The stray light in the optical system is an important factor affecting the imaging observation accuracy of the system. In order to improve the imaging detection quality, it is necessary to blacken the surface of some components in the optical system to suppress the interference of stray light. Blackening inside the component is an effective method to eliminate stray light. At present, there are two main types of blackening methods: chemical blackening or electroplating blackening. However, with the miniaturization of detectors and the improvement of integration requirements, it is more and more hoped to reduce the detector components and reduce the weight of the detector. The overall blackening treatment method is difficult to meet the demand, and the blackening treatment can be controlled by laser technology. The black area provides a new technical option for metal blackening.

CN102242334A discloses a processing method for partial laser blackening of coated metal parts, comprising the following steps: preparing the coated metal parts, conventional machining and overall electroplating treatment of the metal parts; laser treatment, first fixing the coated metal parts on the laser workbench , the blackened area is set by CAD graphics processing software, and then the appropriate laser parameters are selected for blackening treatment. The infrared laser with a wavelength of 1064nm and a spot diameter of 0.05mm is selected, the laser energy is 3-10W, and the defocus is 2-5mm , the laser scanning speed is 10-600mm/s, the laser frequency is 2000-50000Hz, and the pulse width is 4-40μs. When the blackening effect is not good, the number of blackening treatments can be increased to improve the blackening effect; cleaning, metal Alcohol wiping or alcohol ultrasonic cleaning is required after parts are partially blackened. This technical solution provides a feasible path for laser blackening, but the effect after laser blackening is uncontrollable, the entire process design may not be able to achieve good results, and there is still room for improvement.

To sum up, the prior art still lacks a laser blackening treatment method with high processing efficiency, controllable blackening result and stable generation.

Contents of the invention

Aiming at the improvement needs of the prior art, the present invention provides a laser blackening treatment method on the metal surface, which can design and set indicators according to the printing results, calculate and simulate the processing parameters required for simulation, rapid processing and stable results, and finally obtain A processing method with high processing efficiency and controllable blackening result, the obtained product has stable processing quality and can meet various process requirements, thus solving technical problems such as difficulty in controlling the blackening processing result in the prior art.

In order to achieve the above object, the invention provides a method for laser blackening treatment of metal surfaces, comprising the following steps:

(1) Calculate the surface microstructure through a numerical calculation model according to a preset reflectivity index, and the surface microstructure is in a blackened state when meeting the reflectivity index;

(2) Calculate the laser printing parameters through a numerical calculation model according to the surface microstructure, and the structure obtained by simulation calculation according to the laser printing parameters is consistent with the surface microstructure;

(3) Place the metal surface in the working area of the laser processing system, perform laser processing according to the laser printing parameters, and obtain a blackened layer on the surface.

Preferably, the preset reflectance index is 10% or less, and the surface microstructure is in a blackened state when the reflectance is 10% or less.

Preferably, the numerical calculation model in step (1) and step (2) is time-domain finite element difference method FDTD, and the calculation method is parameter sweep.

Preferably, the parameters of the surface microstructure include height, lateral size and duty cycle, and the parameter scanning calculation method of the surface microstructure is as follows:

(a1) Set the lateral size and duty cycle to remain unchanged, only change the height, and perform wide spectrum simulation calculation through FDTD, the wide spectrum refers to the wavelength of light is 400nm-15um, and the height satisfying the reflectance value is obtained;

(a2) The setting height and duty cycle remain unchanged, only the lateral dimension is changed, and the wide-spectrum simulation calculation is carried out through FDTD to obtain the lateral dimension satisfying the reflectance value;

(a3) Set the horizontal size value and height to remain unchanged, only change the duty cycle, and perform wide-spectrum simulation calculations through FDTD to obtain a duty cycle that satisfies the reflectance value;

(a4) Combining the results of (a1), (a2), and (a3) to iterate to obtain a combined value of height, lateral size, and duty cycle.

As a preference, the value range of the height in (a1) is 1-40 μm;

The value range of the lateral dimension in (a2) is 5-50 μm;

The value range of the duty ratio in (a3) is 0.6-1, wherein, duty ratio=lateral dimension/center-to-center distance of adjacent microstructures.

Preferably, the laser processing parameters include laser energy density, laser frequency, pulse width, laser scanning speed, scanning interval, and scanning mode, and the parameter scanning calculation method of the laser processing parameters is as follows:

(b1) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning interval to remain unchanged, only change the scanning method, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning method that the simulation calculation structure is consistent with the surface microstructure ;

(b2) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the scanning interval, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning interval consistent with the simulation calculation structure and the surface microstructure ;

(b3) Set the laser energy density, scanning interval, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser frequency, simulate laser processing to obtain the simulation calculation structure, and obtain the laser frequency that the simulation calculation structure is consistent with the surface microstructure ;

(b4) Set the laser energy density, laser frequency, scanning interval, laser scanning speed, and scanning mode to remain unchanged, only change the pulse width, simulate laser processing to obtain the simulation calculation structure, and obtain the pulse width consistent with the simulation calculation structure and the surface microstructure ;

(b5) Set the laser energy density, laser frequency, pulse width, scanning interval, and scanning mode to remain unchanged, only change the laser scanning speed, simulate laser processing to obtain a simulated calculation structure, and obtain a laser scan in which the simulation calculation structure is consistent with the surface microstructure speed;

(b6) Set the scanning interval, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser energy density, simulate laser processing to obtain the simulation calculation structure, and obtain the energy density consistent with the simulation calculation structure and the surface microstructure ;

(b7) Iterate the results of (b1), (b2), (b3), (b4), (b5), (b6) to obtain laser energy density, laser frequency, pulse width, laser scanning speed, scanning interval, Combined value for scan mode.

Preferably, the scanning mode in (b1) is set as one of single pulse dot matrix scanning, multi-point parallel scanning, galvanometer scanning, linear scanning after shaping, and linear compound raster scanning after shaping;

The distance of the scanning interval in (b2) ranges from 0.05 μm to 500 μm;

The value range of the laser frequency mentioned in (b3) is 10Hz-100MHz;

The value range of the pulse width described in (b4) is 10fs-5ns;

The laser scanning speed described in (b5) ranges from 1 μm/s to 5000 mm/s;

The laser energy density in (b5) ranges from 0.01J/cm ² to 50J/cm ² .

Preferably, the laser light source is one of femtosecond laser light source, picosecond laser light source and nanosecond laser light source, and the working wavelength of the laser light source is 0.3 μm-5 μm.

As preferably, the metal surface is pre-treated in the step (3), the pre-treatment is to use mechanical processing or chemical treatment to carry out ultra-precision machining and polishing on the surface of the metal material, so that the roughness level of the surface to be processed is less than Ra 6.3.

The beneficial effects of the present invention have:

(1) The present invention can design and set indicators according to the printing results, calculate and simulate the required processing parameters, quickly process and form and the results are stable, and finally obtain a processing method with high processing efficiency and controllable blackening results, and the obtained products The processing quality is stable and meets various process requirements.

(2) The metal surface laser blackening treatment method provided by the present invention can realize the blackening treatment on the surface of different metal materials, and the blackened area has excellent anti-reflection performance, which can meet the needs of high-precision optical imaging systems for high-performance extinction components , the use of laser processing can achieve stable process control and high-consistency manufacturing.

(3) The micro-nano structure with extinction performance prepared by laser on the surface of the metal material body in the present invention has excellent stability and reliability, and can maintain stable high extinction performance for a long time in extremely harsh environments. For many military optics The equipment has great application value.

Description of drawings

Fig. 1 is the aluminum alloy blackening surface of the embodiment of the present invention;

Fig. 2 is a test result of the visible light band reflectance of the aluminum alloy of the embodiment of the present invention after being blackened.

Fig. 3 is the test result of the mid-far infrared reflectance of the aluminum alloy of the embodiment of the present invention after being blackened.

FIG. 4 is a test result of reflectance in the infrared band after the aluminum alloy of the embodiment of the present invention is blackened.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Example

A laser blackening treatment method for a metal surface and a treated blackened layer, which are obtained after treatment by the following method:

(1) Aluminum alloy is selected as the processing metal, the selected laser is a titanium-doped sapphire femtosecond laser, and the center wavelength generated by the laser is 800nm. The size of the aluminum alloy is 60mm×60mm, and the thickness is 2mm. Before the test, the surface of the aluminum alloy sample is polished with sandpaper, and the surface is dark and glossy. After that, the metal substrate is placed in a cleaning solution prepared by acetone and ethanol at a ratio of 1:1. In the process, the ultrasonic cleaning agent was used to clean twice, each time for 20 minutes, to fully remove the pollutants on the surface of the sample, and to perform ultra-precision machining and polishing on the surface of the metal material, so that the roughness level of the surface to be processed was Ra 6.0.

(2) Set the reflectivity to 10%, and the parameters of the microstructure model are determined by the height, lateral size and duty cycle. When the lateral size and duty cycle remain unchanged, only the height is changed, and FDTD can perform wide-spectrum simulation calculations. The reflectivity of normal incidence wide band can be obtained through one simulation calculation. Accordingly, we get the range of model heights that satisfy the condition that the reflectivity is lower than 10%. In the same way, keep the height and lateral dimensions unchanged, only change the duty cycle, and determine the duty cycle range that satisfies the condition that the reflectivity is lower than 10%: keep the height and duty cycle unchanged, only change the lateral size, and determine that the reflectance is satisfied rate below 10% of the lateral dimension range. Specifically as follows:

(a1) Set the horizontal size and duty cycle to remain unchanged, only change the height, and perform wide-spectrum simulation calculations through FDTD to obtain the height that meets the reflectance value; (a2) Set the height and duty cycle to remain unchanged, only change the lateral direction Size, through FDTD for wide-spectrum simulation calculation, get the lateral size value that satisfies the reflectance value; (a3) set the lateral size value and height to remain unchanged, only change the duty cycle, and perform wide-spectrum simulation calculation through FDTD, get the reflectance value that satisfies The duty cycle of the rate value; (a4) Iterated the results of (a1), (a2) and (a3), and determined the height of 30 μm, the lateral dimension of 12 μm and the duty cycle of 0.9 as the structural parameters.

(3) The laser processing parameters are obtained after scanning the processing parameters according to the surface microstructure. The laser processing parameters include laser energy density, laser frequency, pulse width, laser scanning speed, scanning interval, scanning mode, and the parameter scanning calculation method of the laser processing parameters is as follows:

(b1) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning interval to remain unchanged, only change the scanning method, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning method that the simulation calculation structure is consistent with the surface microstructure ;

(b2) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the scanning interval, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning interval consistent with the simulation calculation structure and the surface microstructure ;

(b3) Set the laser energy density, scanning interval, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser frequency, simulate laser processing to obtain the simulation calculation structure, and obtain the laser frequency that the simulation calculation structure is consistent with the surface microstructure ;

(b4) Set the laser energy density, laser frequency, scanning interval, laser scanning speed, and scanning mode to remain unchanged, only change the pulse width, simulate laser processing to obtain the simulation calculation structure, and obtain the pulse width consistent with the simulation calculation structure and the surface microstructure ;

(b5) Set the laser energy density, laser frequency, pulse width, scanning interval, and scanning mode to remain unchanged, only change the laser scanning speed, simulate laser processing to obtain a simulated calculation structure, and obtain a laser scan in which the simulation calculation structure is consistent with the surface microstructure speed;

(b6) Set the scanning interval, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser energy density, simulate laser processing to obtain the simulation calculation structure, and obtain the energy density consistent with the simulation calculation structure and the surface microstructure ;

(b7) Based on (b1), (b2), (b3), (b4), (b5), (b6) univariate scanning test results, determine the laser processing parameters as follows: laser scanning speed 100mm/s, scanning interval 10μm; The laser energy density is 13.5J/cm ² , the laser frequency is 200kHz, the pulse width is 120fs, and the scanning method is single-pulse lattice scanning.

(4) Place the cleaned aluminum alloy sample on the displacement platform of the laser processing system. According to the calculation results, by controlling the movement parameters of the displacement platform and the laser process parameters, the laser scans the aluminum alloy surface to obtain Blackened layer with target microstructure. The product obtained after the processing of this embodiment is shown in Figure 1.

Test Example

The surface reflectance test, the test method is: use the visible-near infrared spectrophotometer to test the reflectance in the visible and middle and far infrared bands, and use the Fourier transform infrared spectrometer to test the reflectance in the far infrared band.

The test results are shown in Figure 2-Figure 4. Figure 2 is the reflectance of the visible light band tested by the visible-near-infrared spectrophotometer, Figure 3 is the reflectance of the mid- and far-infrared light band tested by the visible-near-infrared spectrophotometer, and Figure 4 is the infrared reflectance tested by the Fourier transform infrared spectrometer band reflectivity.

Results and discussion.

From the test result of reflectivity, the reflectivity prepared in embodiment 1 has achieved a reflectivity lower than 10% in the visible-near-infrared-far-infrared band, and has achieved a good anti-reflection effect. The reflectivity of some bands is higher than 10%, reaching 20%, but overall, the design goal has been achieved.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (5)

1. a laser blackening treatment method on metal surface, is characterized in that, comprises the following steps: (1) Calculate the surface microstructure through a numerical calculation model according to a preset reflectivity index, and the surface microstructure is in a blackened state when meeting the reflectivity index; (2) Calculate the laser printing parameters through a numerical calculation model according to the surface microstructure, and the structure obtained by simulation calculation according to the laser printing parameters is consistent with the surface microstructure; (3) placing the metal surface in the working area of the laser processing system, and performing laser processing according to the laser printing parameters to obtain a blackened layer on the surface; The preset reflectivity index is that the reflectivity is less than 10%, and the surface microstructure is in a blackened state when the reflectivity is less than 10%; Wherein, the numerical calculation model described in the step (1) and the step (2) is the time-domain finite element difference method FDTD, and the calculation method is parameter scanning; In step (1), the parameters of the surface microstructure include height, lateral dimension and duty cycle, and the parameter scanning calculation method of the surface microstructure is as follows: (a1) Set the lateral size and duty cycle to remain unchanged, only change the height, and perform wide spectrum simulation calculation through FDTD, the wide spectrum refers to the wavelength of light is 400nm-15um, and the height satisfying the reflectance value is obtained; (a2) The setting height and duty cycle remain unchanged, only the lateral dimension is changed, and the wide-spectrum simulation calculation is carried out through FDTD to obtain the lateral dimension satisfying the reflectance value; (a3) Set the horizontal size value and height to remain unchanged, only change the duty cycle, and perform wide-spectrum simulation calculations through FDTD to obtain a duty cycle that satisfies the reflectance value; (a4) Iterating the results of (a1), (a2) and (a3) to obtain the combined value of height, lateral size and duty cycle; In step (2), the laser processing parameters include laser energy density, laser frequency, pulse width, laser scanning speed, scanning interval, scanning mode, and the parameter scanning calculation method of the laser processing parameters is as follows: (b1) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning interval to remain unchanged, only change the scanning method, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning method that the simulation calculation structure is consistent with the surface microstructure ; (b2) Set the laser energy density, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the scanning interval, simulate laser processing to obtain the simulation calculation structure, and obtain the scanning interval consistent with the simulation calculation structure and the surface microstructure ; (b3) Set the laser energy density, scanning interval, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser frequency, simulate laser processing to obtain the simulation calculation structure, and obtain the laser frequency that the simulation calculation structure is consistent with the surface microstructure ; (b4) Set the laser energy density, laser frequency, scanning interval, laser scanning speed, and scanning mode to remain unchanged, only change the pulse width, simulate laser processing to obtain the simulation calculation structure, and obtain the pulse width consistent with the simulation calculation structure and the surface microstructure ; (b5) Set the laser energy density, laser frequency, pulse width, scanning interval, and scanning mode to remain unchanged, only change the laser scanning speed, simulate laser processing to obtain a simulated calculation structure, and obtain a laser scan in which the simulation calculation structure is consistent with the surface microstructure speed; (b6) Set the scanning interval, laser frequency, pulse width, laser scanning speed, and scanning mode to remain unchanged, only change the laser energy density, simulate laser processing to obtain the simulation calculation structure, and obtain the energy density consistent with the simulation calculation structure and the surface microstructure ; (b7) Iterate the results of (b1), (b2), (b3), (b4), (b5), (b6) to obtain laser energy density, laser frequency, pulse width, laser scanning speed, scanning interval, Combined value for scan mode. 2. The processing method according to claim 1, characterized in that, the value range of the height in (a1) is 1-40 μm; The value range of the lateral dimension in (a2) is 5-50 μm; The value range of the duty ratio in (a3) is 0.6-1. 3. The processing method according to claim 1, characterized in that, the scanning mode described in (b1) is set to single-pulse lattice scanning, multi-point parallel mode scanning, vibrating mirror scanning, linear scanning after shaping, One of the shaped linear compound raster scans; The distance of the scanning interval in (b2) ranges from 0.05 μm to 500 μm; The value range of the laser frequency mentioned in (b3) is 10Hz-100MHz; The value range of the pulse width described in (b4) is 10fs-5ns; The laser scanning speed described in (b5) ranges from 1 μm/s to 5000 mm/s; The laser energy density in (b5) ranges from 0.01J/cm ² to 50J/cm ² . 4. The processing method according to claim 1, wherein the laser light source is one of a femtosecond laser light source, a picosecond laser light source and a nanosecond laser light source, and the operating wavelength of the laser light source is 0.3 μm -5 μm. 5. The processing method according to claim 1, characterized in that, in the step (3), the metal surface has been pre-treated, and the pre-treatment is to carry out ultra-precision machining or chemical treatment on the surface of the metal material. Processing and polishing treatment, so that the roughness level of the surface to be processed is less than Ra6.3.

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