Method and device for three-dimensional imaging of a molten pool based on dual-wavelength digital holographic laser 3D printing

Abstract

The application discloses a three-dimensional imaging method and device for a molten pool based on a dual-wavelength digital holographic laser 3D printer, and the method comprises the following steps: S1, combining a first laser beam and a second laser beam with different wavelengths into a synthetic light wave; S2, dividing the synthetic light wave into a reference light wave and a detection light wave through a polarization light splitting module; S3, making the reference light wave incident on an imaging platform of a high-speed camera, and making the detection light wave sequentially irradiate to a molten pool surface through a dichroic plate and a galvanometer module; and after being reflected by the molten pool surface, the detection light beam carrying molten pool surface topography information sequentially passes through a galvanometer system, a dichroic plate and a polarization light splitting module to reach an imaging plane of the high-speed camera, so as to record an interference image of the three-dimensional topography of the molten pool. Furthermore, a device for realizing the method is provided, and the device can realize rapid and accurate three-dimensional topography measurement of a molten pool of a laser 3D printer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser additive manufacturing, and particularly relates to a three-dimensional imaging method and device for a laser 3D printing molten pool based on dual-wavelength digital holography. BACKGROUND

[0002] Laser 3D printing has the characteristics of high energy density, low heat input, and small heat-affected zone, and has significant advantages in manufacturing complex structural parts of aerospace products. With the deep implementation of the lightweight design concept of structural parts of aerospace products, more and more complex structural parts of aluminum alloy laser 3D printing that cannot be measured and inspected have appeared, which has become a weak link in the quality assurance of aerospace products. In order to solve the practical problems faced by the production of aerospace products, an indirect method is commonly used at present, that is, a simulation part is processed before printing, and then X-ray and metallographic sectioning and other destructive methods are used to determine the stability of the equipment and process state before processing of the product, and then laser processing of the product is carried out based on the stability to ensure the quality of the product. With the continuous improvement of the production of aerospace products, the quality control is becoming more and more strict, and the current product quality testing and assurance scheme is becoming more and more unsuitable for the requirements of the construction of a powerful aerospace country, so there is an urgent need for an advanced online testing method to comprehensively, accurately and real-timely master the key quality information such as the three-dimensional morphology of the molten pool in the laser 3D printing process of the product part.

[0003] Digital holographic microscopy technology combines the characteristics of digital holography and microscopic imaging, and is one of the most representative technologies in the field of quantitative phase measurement. With the advantages of non-contact, no marker, high resolution, fast reconstruction and the like, digital holographic microscopy technology plays an important role in the fields of micro-electro-mechanical system (MEMS) measurement, micro-optical element characterization, and biological cell dynamics analysis.

[0004] The molten pool of laser 3D printing belongs to the measurement object of micro-nano size, and the dual-wavelength digital holography technology effectively realizes the measurement and three-dimensional reconstruction of micro-nano size objects, so that good results can be achieved when applied to the measurement of the molten pool of laser 3D printing. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a three-dimensional imaging method and device for a laser 3D printing molten pool based on dual-wavelength digital holography, which aims to realize rapid and accurate three-dimensional morphology measurement of the laser 3D printing molten pool.

[0006] In order to achieve the above-mentioned purpose, the specific scheme of the application is as follows:

[0007] The three-dimensional imaging method for the laser 3D printing molten pool based on dual-wavelength digital holography comprises the following steps:

[0008] S1, combining two first laser beams and second laser beams of different wavelengths into a synthetic light wave;

[0009] S2, the synthetic light wave of step S1 is divided into reference light wave and probe light wave by polarization light splitting module;

[0010] S3, the reference light wave of step S2 is incident on the imaging platform of the high-speed camera, the probe light wave is sequentially irradiated to the surface of the molten pool through the dichroic plate and the galvanometer module, and the probe light beam carrying the surface topography information of the molten pool after being reflected by the surface of the molten pool sequentially passes through the galvanometer system, the dichroic plate and the polarization light splitting module to reach the imaging plane of the high-speed camera to record the interference image of the three-dimensional topography of the molten pool.

[0011] Further, the wavelength setting value of the first laser beam is λ1, the wavelength setting value of the second laser beam is λ2, and the calculation formula of the wavelength λ of the synthetic light wave is:

[0012] Further, the first laser beam, the second laser beam and the synthetic light beam are all collimated and expanded by the collimation and expansion system and then emitted in parallel.

[0013] The device for realizing the laser 3D printing molten pool three-dimensional imaging method based on the dual-wavelength digital holography comprises a light combination module, a third collimation and expansion system, a polarization light splitting module, a high-speed camera, a dichroic plate, a galvanometer module and a molten pool, the light beam emitted by the light combination module sequentially passes through the third collimation and expansion system and the polarization light splitting module to be divided into reference light wave and probe light wave, the reference light wave is incident on the high-speed camera, the probe light wave is sequentially irradiated to the surface of the molten pool through the dichroic plate and the galvanometer module, and the probe light beam carrying the surface topography information of the molten pool after being reflected by the surface of the molten pool sequentially passes through the galvanometer system, the dichroic plate and the polarization light splitting module to reach the imaging plane of the high-speed camera.

[0014] Further, the light combination module comprises a first light emitting unit, a second light emitting unit, a first reflector and a third non-polarization light splitter, the first light emitting unit comprises a first laser, a first collimation and expansion system and a first non-polarization light splitter, the first laser beam emitted by the first laser sequentially passes through the first collimation and expansion system and the first non-polarization light splitter, and the first non-polarization light splitter divides the beam to form a first split beam and a second split beam, the first split beam is incident on the first spectrometer, and the second split beam is reflected by the first reflector to the third non-polarization light splitter; the second light emitting unit comprises a second laser, a second collimation and expansion system and a second non-polarization light splitter, the second laser beam emitted by the second laser sequentially passes through the second collimation and expansion system and the second non-polarization light splitter, and the second non-polarization light splitter divides the beam to form a third split beam and a fourth split beam, the third split beam is incident on the second spectrometer, and the fourth split beam is incident on the third non-polarization light splitter to combine with the second split beam to form a synthetic light wave.

[0015] Further, the polarization beamsplitting module comprises a polarization beamsplitter and a fourth mirror along the propagation direction of the incident light beam, the second mirror is arranged vertically to the polarization beamsplitter, the third mirror is arranged on the light path reflected by the second mirror, the filtering module is arranged on the light path reflected by the third mirror, the filtering module is arranged vertically to the polarization beamsplitter and forms a reflected light path with the second mirror, and the 1 / 4 wave plate is arranged on the reflected light path of the fourth mirror.

[0016] Further, the filtering module comprises a shell, a filter and a focusing lens arranged in the shell, the filter is arranged on the light-in side of the shell, and the focusing lens is arranged on the light-out side of the shell.

[0017] Further, the molten pool is formed by the outgoing light of the manufacturing laser passing through the dichroic mirror and the galvanometer module to the 3D powder bed.

[0018] Advantages of the present application

[0019] 1. The laser 3D printing molten pool three-dimensional imaging method and device based on dual-wavelength digital holography of the present application can realize rapid and accurate three-dimensional topography measurement of the laser 3D printing molten pool by setting two laser beams with different wavelengths to be combined into a combined light wave through a combination module, collimating and expanding the combined light wave through a collimating and expanding system, and splitting the combined light wave into a reference light wave and a probe light wave through a polarization beamsplitting module, and then by sequentially irradiating the probe light wave to the molten pool surface through a dichroic plate and a galvanometer module, and by recording the interference image of the three-dimensional topography of the molten pool through the probe light beam carrying the topography information of the molten pool surface.

[0020] 2. The dual-wavelength digital holography three-dimensional imaging device can reconstruct the three-dimensional topography of the molten pool through single interference imaging.

[0021] 3. The dual-wavelength digital holography three-dimensional imaging device can realize real-time dynamic three-dimensional topography reproduction of the molten pool, and can better measure the molten depth and width of the molten pool, thereby facilitating better observation and judgment of the printing quality.

[0022] 4. The dual-wavelength digital holography three-dimensional imaging device can be connected to the existing laser 3D printing system, and can adjust the processing parameters in real time according to the real-time imaging and feedback and prediction of defects, thereby improving the quality of the processed parts. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a structural schematic diagram of the laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography of the present application.

[0024] Figure 2 The figure is a structural schematic diagram of the polarization beamsplitting module in the laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography of the present application. Figure 1 The figure is a structural schematic diagram of the polarization beamsplitting module in the laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography of the present application.

[0025] Figure 3 For Figure 1 Filter module structure diagram in the figure.

[0026] In the figure:

[0027] 1, the first laser; 2, the second laser; 3, the first collimating beam expander system; 4, the second collimating beam expander system; 5, the first spectrometer; 6, the second spectrometer; 7, the first non-polarizing beam splitter; 8, the second non-polarizing beam splitter; 9, the first mirror; 10, the third non-polarizing beam splitter; 11, the third collimating beam expander system; 12, the high-speed camera; 13, the filter module; 14, the polarizing beam splitter; 15, the second mirror; 16, the third mirror; 17, the fourth mirror; 18, the 1 / 4 wave plate; 19, the dichroic plate; 20, the manufacturing laser; 21, the galvanometer module; 22, the molten pool; 23, the filter; 24, the converging lens. DETAILED DESCRIPTION

[0028] The application will be further explained in connection with the drawings and specific embodiments, and it should be noted that the specific embodiments are not used to limit the scope of the application.

[0029] The specific embodiment provides a laser 3D printing molten pool three-dimensional imaging method based on double-wavelength digital holography, including the following steps:

[0030] S1, two beams of first laser beams and second laser beams with different wavelengths are collimated and expanded by collimating beam expander systems and then emitted in parallel, and then combined into a synthetic light wave by a light combination module; the wavelength setting value of the first laser beam is λ1, the wavelength setting value of the second laser beam is λ2, and the wavelength λ of the synthetic light wave is calculated according to the formula:

[0031] S2, the synthetic light wave of step S1 is collimated and expanded by a collimating beam expander system and then emitted in parallel, and then divided into reflected reference light waves and transmitted probe light waves by a polarizing beam splitter module;

[0032] S3, the reference light wave of step S2 is incident on the imaging platform of the high-speed camera 12, and the probe light wave is sequentially irradiated to the surface of the molten pool 22 through the dichroic plate 19 and the galvanometer module 21, and the probe light beam carrying the surface topography information of the molten pool 22 after being reflected by the surface of the molten pool 22 sequentially passes through the galvanometer system 21, the dichroic plate 19 and the polarizing beam splitter module to reach the imaging plane of the high-speed camera 12, so as to record the interference image of the three-dimensional topography of the molten pool 22.

[0033] As Figure 1As shown, the device for implementing the above-mentioned laser 3D printing molten pool three-dimensional imaging method based on dual-wavelength digital holography includes a light combination module, a third collimating and expanding system 11, a polarization light splitting module, a high-speed camera 12, a dichroic plate 19, a galvanometer module 21, and a molten pool 22. The light beam emitted by the light combination module passes through the third collimating and expanding system 11 and the polarization light splitting module in sequence to be divided into a reference light wave and a probe light wave. Specifically, the light combination module includes a first light emitting unit, a second light emitting unit, a first mirror 9, and a third non-polarized light splitter 10. The first light emitting unit includes a first laser 1, a first collimating and expanding system 3, and a first non-polarized light splitter 7. The first laser 1 emits a first laser beam, which passes through the first collimating and expanding system 3 to form a laser beam with a large diameter and parallel emission, and then passes through the first non-polarized light splitter 7 to be divided into two beams of light beams with equal energy, i.e., a light beam one and a light beam two. The light beam one is incident on a first spectrometer 5, which is mainly used to measure whether the wavelength of the laser emitted by the first laser 1 is a set value.

[0034] The light beam two is reflected by the first mirror 9 to the third non-polarized light splitter 10. The second light emitting unit includes a second laser 2, a second collimating and expanding system 4, and a second non-polarized light splitter 8. The second laser 2 emits a second laser beam, which passes through the second collimating and expanding system 4 to form a laser beam with a large diameter and parallel emission, and then passes through the second non-polarized light splitter 8 to be divided into two beams of light beams with equal energy, i.e., a light beam three and a light beam four. The light beam three is incident on a second spectrometer 6, which is mainly used to measure whether the wavelength of the laser emitted by the second laser 2 is a set value. The light beam four is incident on the third non-polarized light splitter 10, so that the light beam two emitted by the first laser 1 and the light beam four emitted by the second laser 2 form a combined light wave at the third non-polarized light splitter 10. The combined light wave passes through the third collimating and expanding system 11 to form a laser beam with a larger diameter and parallel emission, and then the laser beam is divided into a reference light wave and a probe light wave after passing through the polarization light splitter 14. Among them, Figure 1 The white arrow in the polarization light splitting module indicates the reflected light of the probe light wave.

[0035] The laser wavelengths of the first laser 1 and the second laser 2 are different. The selection of the wavelength λ1 of the first laser beam emitted by the first laser 1 and the wavelength λ2 of the second laser beam emitted by the second laser needs to refer to the size of the measured object. Generally speaking, the smaller the difference between the wavelength λ1 and the wavelength λ2, the larger the measurable range, but the worse the resolution. In this specific implementation, the width and depth of the measured molten pool 22 are about 100-200 um, and the combined wavelength should be greater than the size of the measured object.

[0036] The first collimating beam expanding system 3, the second collimating beam expanding system 4 and the third collimating beam expanding system 11 serve to improve the collimation of the light beam and expand the diameter of the light beam, so that the probe light beam can cover the area of the molten pool 22.

[0037] The reference light wave is incident on the high-speed camera 12, and the probe light wave is sequentially irradiated to the surface of the molten pool 22 through the dichroic plate 19 and the galvanometer module 21. The probe light beam carrying the surface topography information of the molten pool 22 after being reflected by the surface of the molten pool 22 sequentially passes through the galvanometer system 21, the dichroic plate 19 and the polarization light splitting module to reach the imaging plane of the high-speed camera.

[0038] Specifically, as shown in the figure, Figure 2 The polarization light splitting module includes a polarization light splitting mirror 14 and a fourth mirror 17 along the propagation direction of the incident light beam. A second mirror 15 is arranged in the vertical direction of the polarization light splitting mirror 14. A third mirror 16 is arranged on the light path reflected by the second mirror 15. A filtering module 13 is arranged on the light path reflected by the third mirror 16. The filtering module 13 includes a housing and a filter 23 and a focusing lens 24 arranged in the housing. The filter 23 is arranged on the light-in side of the housing, and the focusing lens 24 is arranged on the light-out side of the housing. The filtering module 13 is arranged in the vertical direction of the polarization light splitting mirror 14 and forms a reflected light path with the second mirror 15. A 1 / 4 wave plate 18 is arranged on the reflected light path of the fourth mirror 17. The filter 23 serves to filter the reflected light and scattered light of the interference factors such as splashes and plasma plume, and only allows the light in the wavelength range of λ1 and λ2 to pass through the filter to reach the focusing lens, so as to avoid the influence of the interference light on the interference imaging quality. Then, clear interference imaging is realized by adjusting the distance between the focusing lens 24 and the high-speed camera 12.

[0039] The reference light wave is reflected by the polarization light splitting mirror 14 and sequentially passes through the second mirror 15, the third mirror 16 and the filtering module 13 to reach the imaging plane of the high-speed camera 12.

[0040] The probe light wave is reflected by the fourth mirror 17 and sequentially passes through the 1 / 4 wave plate 18, the dichroic plate 19 and the galvanometer module 21 to irradiate to the surface of the molten pool 22. The molten pool 22 is formed by the emitted light of the manufacturing laser 20 passing through the dichroic mirror 19 and the galvanometer module 21. The probe light wave carrying the surface topography information of the molten pool 22 after being reflected sequentially passes through the galvanometer module 21, the dichroic plate 19, the 1 / 4 wave plate 18, the fourth mirror 17, the polarization light splitting mirror 14 and the filtering module 13 to reach the imaging plane of the high-speed camera 12. At this time, the probe light wave and the reference light wave form interference, and the interference pattern is recorded by the high-speed camera 12.

[0041] The polarization beam splitter module functions to divide the synthetic light wave into a reference light wave and a probe light wave. When the synthetic light wave reaches the polarization beam splitter 14, the s-polarization component of the synthetic light wave is reflected due to the inability to pass through the polarization beam splitter 14, and then passes through the second mirror 15, the third mirror 16, and the filter module 13 in sequence, and finally reaches the imaging plane of the high-speed camera 12. The light beam is the reference light wave. The polarization beam splitter 14, the second mirror 15, and the third mirror 16 are specially angled to avoid the interference of the coaxial virtual image on the interference image. Similarly, when the synthetic light wave reaches the polarization beam splitter 14, the p-polarization component of the synthetic light wave can pass through the beam splitter. The p-polarized light (linearly polarized) is first passed through the 1 / 4 wave plate 18, and the polarization state is converted from linear polarization to circular polarization. When the outgoing circularly polarized light passes through the dichroic plate 19 and the galvanometer module 21 in sequence to reach the molten pool surface 22 and is reflected according to the established route back to the 1 / 4 wave plate 18, the light beam is secondly passed through the 1 / 4 wave plate 18, and the polarization state of the light is converted from circular polarization to linear polarization again, but the polarization direction is changed to s-polarized light. Therefore, the s-polarized light at this time is reflected back to the polarization beam splitter 14 after being reflected by the fourth mirror 17, and then is reflected to the imaging module due to the inability of the s-polarized light to pass through the polarization beam splitter 14, and interference is generated with the reference light wave. The light beam is the probe light wave.

[0042] The dichroic plate 19 is mainly used for transmitting the manufacturing laser and reflecting the probe light, and preventing the reflected light of the manufacturing laser from damaging the corresponding optical elements.

[0043] The frame rate of the high-speed camera 12 is 5000 fps, which is used to record the interference image of the three-dimensional topography of the molten pool. Since the laser 3D printing molten pool is a high dynamic object, a high frame rate camera is required to capture the high-speed changes of the molten pool.

[0044] The device of the above specific embodiment can provide help for in-situ detection of the three-dimensional topography parameters (such as the melt depth and the melt width) of the molten pool of the printed part of the aerospace product.

Claims

1. A laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography, characterized in that, The system includes a beam combining module, a third collimating and expanding system, a polarization beam splitting module, a filtering module, a high-speed camera, a dichroic plate, a galvanometer module, and a molten pool. The beam emitted from the beam combining module is sequentially split into a reference beam and a probe beam by the third collimating and expanding system and the polarization beam splitting module. The reference beam is incident on the high-speed camera, and the probe beam is sequentially irradiated onto the surface of the molten pool by the dichroic plate and the galvanometer module. After being reflected by the surface of the molten pool, the probe beam carrying information about the morphology of the molten pool is sequentially transmitted through the galvanometer system, the dichroic plate, and the polarization beam splitting module to reach the imaging plane of the high-speed camera. The beam combining module includes a first light-emitting unit, a second light-emitting unit, a first reflector, and a third unpolarized beam splitter. The first light-emitting unit includes a first laser, a first collimating and expanding beam system, and a first unpolarized beam splitter. The first laser beam emitted from the first laser passes sequentially through the first collimating and expanding beam system and the first unpolarized beam splitter. After being split by the first unpolarized beam splitter, it forms beam split one and beam split two. Beam split one is incident on a first spectrometer, and beam split two is reflected by the first reflector to the third unpolarized beam splitter. The second light-emitting unit includes a second laser, a second collimating and expanding beam system, and a second unpolarized beam splitter. The second laser beam emitted from the second laser passes sequentially through the second collimating and expanding beam system and the second unpolarized beam splitter. After being split by the second unpolarized beam splitter, it forms beam split three and beam split four. Beam split three is incident on a second spectrometer, and beam split four is incident on the third unpolarized beam splitter and combined with beam split two to form a composite light wave. The polarization beam splitter module includes a polarization beam splitter and a fourth reflecting mirror along the propagation direction of the incident beam. A second reflecting mirror is provided in the direction perpendicular to the polarization beam splitter. A third reflecting mirror is provided in the light path reflected by the second reflecting mirror. A filtering module is provided in the light path reflected by the third reflecting mirror. The filtering module is located in the direction perpendicular to the polarization beam splitter and forms a reflected light path with the second reflecting mirror. A quarter-wave plate is provided in the reflected light path of the fourth reflecting mirror.

2. The laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography according to claim 1, characterized in that, The filtering module includes a housing and a filter and a focusing lens disposed inside the housing. The filter is disposed on the light-inlet side of the housing, and the focusing lens is disposed on the light-outlet side of the housing.

3. The laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography according to claim 1, characterized in that, The molten pool is formed by the output light from the manufacturing laser passing through a dichroic mirror and a galvanometer module to reach the 3D powder bed.

4. An imaging method for a laser 3D printing molten pool three-dimensional imaging device based on dual-wavelength digital holography as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1, the first and second laser beams of different wavelengths are collimated and expanded by the collimation and beam expanding system, and then combined into a composite light wave by the beam module; S2, the synthesized light wave from step S1 is collimated and expanded by the collimation and beam expanding system and then emitted in parallel, and then split into a reflected reference light wave and a transmitted probe light wave by the polarization beam splitting module. S3, the reference light wave from step S2 is incident on the imaging platform of the high-speed camera, and the probe light wave is sequentially irradiated onto the surface of the molten pool through the dichroic plate and the galvanometer module. After being reflected by the surface of the molten pool, the probe beam carrying the surface morphology information of the molten pool passes sequentially through the galvanometer system, the dichroic plate and the polarization beam splitter module to reach the imaging plane of the high-speed camera, so as to record the interference image of the three-dimensional morphology of the molten pool.

5. The laser 3D printing molten pool three-dimensional imaging method based on dual-wavelength digital holography according to claim 4, characterized in that, The wavelength setting value of the first laser beam is The wavelength setting value of the second laser beam is The formula for calculating the wavelength λ of the synthesized light wave is: .

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