TWI882588B - Surface profile and temperature monitoring system for laminate manufacturing - Google Patents

Abstract

The present invention provides a surface profile and temperature monitoring system for laminated manufacturing. The surface profile and temperature monitoring system is installed on the laminated manufacturing equipment. A computer unit can choose to use the surface 3D measurement mode or the pyrometer measurement mode. It has both the surface profile image measurement and the molten pool temperature measurement functions, saving hardware construction and manufacturing process costs, and improving the accuracy and efficiency of laminated manufacturing.

Description

Surface profile and temperature monitoring system for laminate manufacturing

This invention is based on layer-by-layer manufacturing with an optical system to set up monitoring technology for surface profile and melt pool temperature, and specifically refers to a powder bed fusion molding technology that utilizes the high power and high energy characteristics of lasers to melt and fuse metal powders laid flat on a powder bed together.

Laser stacking, especially metal powder sintering, is an industrial technology with high development potential. One of the main development technologies in this industry at this stage is the monitoring technology of the processing process. Because in the laser stacking process (Selective Laser Melting), the surface powder coating state in the working area before laser sintering and the monitoring of the molten pool state during the sintering process are the most important conditions for improving processing quality and reducing processing costs. This concept has been valued by many research teams in recent years, and new monitoring methods or highly integrated combined systems have been proposed one after another.

Previous technologies mainly use two methods to achieve the purpose of monitoring the surface powder coating state of the working area of the multilayer manufacturing process: (1) Through a single or multiple CCD or CMOS image detectors, combined with structured light projection technology, the surface contour is calculated and constructed by projecting light deformation. Structured light projection can restore the surface contour with the assistance of computer vision and triangulation. (2) Using optical tomography (OCT), based on the laser scanner in the multilayer manufacturing system, an interferometer system is constructed and low-coherent light sources are used for interference measurement. The contrast generated by interference is used as the basis for determining surface undulation.

There are several related extension problems in the above-mentioned existing technical methods: (1) The method of obtaining multiple stripe images by phase-shift structured light projection technology and then establishing a three-dimensional surface profile by calculation. Because multiple images need to be processed in a time-multiplexed manner and the bright stripes completely cover the entire object to be tested, multiple images need a high-speed and high-resolution camera to speed up the shooting process, and the demodulation time is also one of the factors that must be considered. Although the number of multiple images can improve the image resolution, it requires several times the processing time and captures more information. At the same time, the optical system must be rebuilt based on the phase-shift imaging method. When the laser lamination manufacturing system is the integration target, a larger space needs to be reserved at the machine. In addition, during the laser lamination manufacturing process, the processing chamber is subject to harsh environmental conditions such as high temperature and dust. It is not suitable to directly set the CCD and projector inside the processing chamber. A viewing window must be opened outside the chamber structure for the projector and CCD to capture images, which increases the structural complexity of the processing chamber and the difficulty of system integration. (2) Use optical tomography (OCT) to detect surface morphology. In the layered manufacturing system, an interferometer system is constructed based on a laser scanner. A low-coherent light source is used for interference measurement and the contrast generated by interference is used as the basis for determining surface undulation. The scanning operation method is easier to integrate OCT into the layered manufacturing system. OCT uses interference to achieve excellent resolution under the condition of a large light source bandwidth. However, the interference method requires higher system stability. When the overall scale of the system is larger, it is easy to produce errors due to component and environmental vibration.

Previous technologies mainly use three methods to achieve the purpose of monitoring the temperature state of the molten pool surface: (1) obtain real-time molten pool images through single or multiple CCD or CMOS thermal imaging methods, and estimate the molten pool state through 3D image processing; (2) install a photodetector on the coaxial optical path (laser path) to measure the thermal radiation signal generated in the molten pool during laser sintering during layered manufacturing; (3) use plasma monitoring methods with high-resolution spectrometers to measure the emission spectrum to measure temperature.

There are several related extension problems in the above three methods: (1) Real-time molten pool images can be obtained through single or multiple CCD or CMOS thermal imaging methods, but due to the incoherent images and the resolution of the thermal imager, the molten pool temperature at the hot spot cannot be effectively resolved. In addition, the high-resolution thermal imager is expensive, which increases the system purchase and operation costs. (2) Install a photodetector on the coaxial optical path to measure the thermal radiation emitted by the high-temperature molten pool. The thermal radiation image can be used to generate a temperature image through post-processing. The optical structure of this method needs to be specially designed, and in addition to splitting the high-power infrared laser, it must also reflect the thermal radiation. In addition, the filter used in this structure is quite large and expensive, and the photodiode sensitivity may be insufficient. (3) The method of monitoring the state of the molten pool by plasma spectroscopy is related to the type and density of the gas introduced. Although it has higher intensity and the luminescence wavelength is easier to measure in visible light, plasma luminescence does not directly reflect the state of the molten pool and must be established in a vacuum environment, which may lead to insufficient correlation.

The aforementioned existing technologies are insufficient in the integration requirements of simultaneously constructing surface profile images and melt pool temperature imaging. Therefore, it is necessary to develop a monitoring system for surface profile and temperature of multilayer manufacturing, which has the function of measuring the internal surface profile of the multilayer manufacturing cavity and the temperature of the melt pool, so as to improve the accuracy and efficiency of multilayer manufacturing processing and reduce manufacturing costs.

In order to improve the shortcomings of the previous technology, the present invention provides a surface profile and temperature monitoring system for multi-layer manufacturing. The present invention can use a computer unit to select the surface 3D measurement mode or the pyrometer measurement mode to measure the surface profile and the molten pool temperature, thereby saving the hardware construction and manufacturing process costs and improving the accuracy and efficiency of multi-layer manufacturing processing.

The present invention is a surface profile and temperature monitoring system for multilayer manufacturing, comprising a laser light source, wherein the laser light source generates a laser beam which passes through a scanning galvanometer and then passes through a first focusing lens to a surface to be measured; a first optical lens group, wherein the first optical lens group is composed of a dichroic lens and a beam shrinking lens group, wherein the first optical lens group receives the reflected light and diffused light generated by the laser beam passing to the surface to be measured, and then transmits the reflected light and diffused light to a diffusing grating; a second optical lens group, wherein the second optical lens group is composed of a beam expander group and a polarizing film group, wherein the reflected light and diffused light received by the first optical lens group passes through the diffusing grating and then enters the second optical lens group; and a second focusing lens group is composed of a dichroic lens group and a beam shrinking lens group. A focusing lens, the reflected light and diffuse light received by the first optical lens group passes through the diffraction grating, enters the second focusing lens, and then transmits to an optical fiber array; a photoelectric conversion module, the photoelectric conversion module selectively receives the optical signal of the reflected light and diffuse light transmitted from the second optical lens group or the optical fiber array, and then converts it into an electrical signal; a computer unit, the computer unit controls the form of the laser beam emitted by the laser light source, and selects to use the surface 3D measurement mode or the pyrometer measurement mode, and receives the electrical signal output by the photoelectric conversion module, thereby establishing the surface profile image of the surface to be measured and the information of the molten pool temperature.

In one embodiment of the present invention, the laser beam is a red laser with a wavelength of 630-670nm, or a near-infrared laser with a wavelength of 800-1100nm.

In one embodiment of the present invention, the first optical lens group includes a dichroic lens and a focusing lens group.

In one embodiment of the present invention, the second optical lens group includes a beam expander group and a polarizer group.

In one embodiment of the present invention, the expansion lens assembly is composed of a concave lens and a convex lens.

In one embodiment of the present invention, the polarizer set is composed of four directional polarizers, and the four directional polarizers are 0°, 45°, 90° and 135° respectively.

In one embodiment of the present invention, the photoelectric conversion module has a plurality of photodetectors inside.

In one embodiment of the present invention, the surface to be tested refers to the surface of the area where the material powder to be sintered is laid in the laminate manufacturing chamber.

In one embodiment of the present invention, the process of establishing the surface profile image of the surface 3D measurement mode is as follows: the computer unit controls the laser light source to provide a red laser and selects the surface 3D measurement mode. After the red laser is transmitted to the scanning galvanometer, it is transmitted to the surface to be measured through the first focusing lens. At this time, the reflected light and diffuse light generated by the surface to be measured are transmitted back to the first optical lens group through the original optical path, and then transmitted to the diffraction grating and the second optical lens group after passing through the first optical lens group, and then transmitted to the photoelectric conversion module to be converted into an electrical signal, and then transmitted back to the computer unit, thereby establishing the surface profile image of the surface to be measured.

In one embodiment of the present invention, the process of establishing temperature monitoring information in the pyrometer measurement mode is as follows: the computer unit controls the laser light source to provide a near-infrared laser, and selects the pyrometer measurement mode. The near-infrared laser is transmitted to the scanning galvanometer and then to the surface to be measured through the first focusing lens. At this time, the reflected light and diffused light generated by the surface to be measured are transmitted back to the first optical lens group through the original optical path, and then to the diffraction grating, and to a second focusing lens and an optical fiber array, and then to the photoelectric conversion module to convert into an electrical signal, and then transmitted back to the computer unit, thereby establishing the temperature monitoring information of the surface to be measured.

In one embodiment of the present invention, the computer unit provides coordinate information to calculate the height image or temperature monitoring information of the surface to be measured of the coordinates of the area currently irradiated by the laser beam, and after integrating the height image or temperature monitoring information of all coordinates of the area, the overall surface contour image or overall temperature monitoring information (thermal image) of the surface to be measured is obtained.

In one embodiment of the present invention, the laser beam used in the surface 3D measurement mode is selected to be a red laser with a wavelength of 630-670nm, and the laser beam used in the pyrometer measurement mode is selected to be a near-infrared laser with a wavelength of 800-1100nm.

The above overview and the following detailed description and attached figures are all for the purpose of further explaining the methods, means and effects adopted by the present invention to achieve the intended purpose. Other purposes and advantages of the present invention will be elaborated in the subsequent description and illustrations.

10: Laser light source

10A: Near infrared laser beam

10B: Red laser beam

11: Scanning galvanometer

12: First focusing lens

13: Surface to be tested

14: First optical lens group

14A: Dichroic mirror

14B: Focus lens set

15: Diffused grating

16: Second optical lens group

16A: Beam expander set

16B: Polarizer set

17: Photoelectric conversion module

18:Computer unit

19: Second focusing lens

20: Fiber optic array

Figure 1 is a schematic diagram of the surface profile and temperature monitoring system used for layered manufacturing of the present invention.

Figure 2 is a block diagram of the surface profile image creation process system of the present invention.

Figure 3 is a block diagram of the surface molten pool temperature establishment process system of the present invention.

The following is a specific example to illustrate the implementation of the present invention. People familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this manual.

Photodiode is a sensor that converts light intensity into current. A transimpendence amplifier (TIA) can be used to convert current signals into voltage signals. In the application of high temperature thermometers, the reaction speed and high response intensity must be considered to overcome the problem of insufficient intensity of thermal radiation after spectral analysis. In the current-to-voltage converter part, an operational amplifier with low input current noise is selected to improve the signal-to-noise ratio. The analog signal generated by the current-to-voltage converter needs to be converted into a digital signal through an analog-to-digital converter. The microprocessor reads the voltages of the three analog-to-digital converters in sequence and transmits them to the PC via the USB interface. The pyrometer uses the ratio of light intensities of two different wavelengths to estimate the temperature of the object to be measured. Therefore, the transmittance/reflectivity of the optical system of different wavelengths, the quantum efficiency of the photodetector, and the gain of the current-to-voltage converter will affect the ratio of light intensities. Therefore, each pyrometer hardware needs to be calibrated.

The surface profile and temperature monitoring system for layered manufacturing of the present invention uses optical polarization imaging technology to obtain the surface profile image of the powder bed after the powder laying process in the layered manufacturing process. Optical polarization imaging (OPI) uses the fact that when electromagnetic waves are reflected by the interface, the oscillation and phase of the reflected light are related to the direction of the reflecting surface. Different polarization states have different time responses, so that the polarization characteristics can be used as a tool for measuring the surface normal direction. The surface microstructure can be displayed through polarization processing. The subtraction of different polarization images can highlight the subtle changes in the surface structure and can be used to analyze the surface image.

In recent years, polarization imaging has become one of the most important technologies in the field of machine vision. The main reason is that polarization information is easy to obtain. The intensity information of specific linear polarized light can be obtained through a polarizer, and the reaction of the polarization state to geometric factors is easier in image processing. In 2018, Gary A. Atkinson et al. pointed out that when polarization imaging is applied to surface morphology measurement, when the polarization of the incident light changes, the polarization rate of the reflected light (diffuse reflected light) will also change, and a large change indicates a high response intensity. The surface profile (height) image can be calculated through mathematical models and image processing programs.

The structure diagram of the surface profile and temperature monitoring system for layered manufacturing of the present invention is shown in FIG1 , and includes: a laser light source 10, providing a near-infrared laser beam 10A or a red laser beam 10B, the laser beam passes through a scanning galvanometer 11, and then passes through a first focusing lens 12 to transmit the beam to a surface to be measured 13. After the laser beam irradiates the surface to be measured 13, it will generate reflected light and diffuse light, which will return to the scanning galvanometer 11 along the same optical path, and pass through a first optical lens group 14, the first optical lens group 14 is composed of a dichroic lens 14A and a focusing lens group 14B. The light beam (reflected light and diffuse light) passes through the first optical lens group 14 and is transmitted to a diffraction grating 15. In the surface 3D measurement mode The lower light beam (reflected light and diffused light) passes through the diffraction grating 15 and is transmitted to the second optical lens group 16, which is composed of a beam expander group 16A and a polarizer group 16B, and then is transmitted to the photoelectric conversion module 17, and the light source (reflected light and diffused light) is converted into an electrical signal and then output to the computer unit 18; in the pyrometer measurement mode, the light beam (reflected light and diffused light) passes through the diffraction grating 15 and is transmitted to the second focusing lens 19, and the light beam (reflected light and diffused light) passes through the second focusing lens 19 and is transmitted to the optical fiber array 20, and then passes through the optical fiber array 20, and then is transmitted to the photoelectric conversion module 17, and the light source (reflected light and diffused light) is converted into an electrical signal and then output to the computer unit 18. The computer unit controls the laser light source form emitted by the laser light source and selects the surface 3D measurement mode or the pyrometer measurement mode, receives the electrical signal output by the photoelectric conversion module, and thereby establishes the surface profile image of the surface to be measured and the molten pool temperature and other information.

In one embodiment of the present invention, two measurement modes are switched mutually, and the user can select the surface 3D measurement mode (establishing the profile image of the surface to be measured) or the pyrometer measurement mode (establishing the surface molten pool temperature monitoring status information) by himself, and a multi-layer manufacturing and processing equipment is equipped with the functions of the surface profile image measurement system and the surface temperature thermal imaging system. The block diagram of the surface profile image establishment process system of the present invention is shown in Figure 2. The computer unit 18 controls the laser light source 10 to provide a red laser source (laser beam) 10B with a wavelength of 630~670nm, and selects to use the surface 3D measurement mode. After the red laser 10B is transmitted to the scanning galvanometer 11, it is transmitted to the surface to be measured 13 through the first focusing lens 12. At this time, the reflected light and diffused light generated by the surface to be measured are transmitted back to the first optical lens group 14 through the original optical path, and then transmitted to the diffraction grating 15 and the second optical lens group 16 after passing through the first optical lens group 14, and then transmitted to the photoelectric conversion module 17 to be converted into an electrical signal, and then transmitted back to the computer unit 18, thereby establishing a surface profile image of the entire surface to be measured 13.

The system block diagram of the surface molten pool temperature state information establishment process of the present invention is shown in FIG3. The computer unit 18 controls the laser light source 10 to provide a near-infrared laser source (laser beam) 10A with a wavelength of 800-1100 nm, and selects the high temperature meter measurement mode. The near-infrared laser 10A is transmitted to the scanning galvanometer 11 and then transmitted to the to-be-measured through the first focusing lens 12. Surface 13, at this time, the reflected light and diffuse light generated by the surface 13 to be measured are transmitted back to the first optical lens group 14 through the original optical path, and then to the diffraction grating 15, and then to a second focusing lens 19 and an optical fiber array 20, and then to the photoelectric conversion module 17 to be converted into an electrical signal, and then transmitted back to the computer unit 18, thereby establishing the temperature monitoring information of the entire surface to be measured. The surface molten pool refers to the area of the material powder to be sintered in the lamination manufacturing cavity, and the molten state surface after laser sintering.

In one embodiment of the present invention, the computer unit calculates the height of the surface to be measured of the coordinates of the area currently irradiated by the laser beam based on the coordinate information provided by the scanning galvanometer. When the laser beam completes the scanning of the surface to be measured in the entire working area, the computer unit summarizes the height of all coordinate areas of the working area, combines the calculation to establish the overall surface profile image of the surface to be measured in the working area, and further feeds back the data of the overall surface profile image to the computer unit for fine-tuning the working parameter settings of different working areas, so as to improve the quality and yield of the finished product of the multilayer manufacturing workpiece. The surface height and molten pool temperature measured by the present invention can also be used as feedback indicators, so that users can know the results in real time, which can be used as a reference for subsequent process parameter adjustment and device improvement design.

In one embodiment of the present invention, the laser light source can share the optical path with the sintering laser used in the multilayer manufacturing process. Generally, the laser device for sintering in multilayer manufacturing is installed outside the working chamber to avoid adverse environmental factors such as dust and high temperature in the chamber affecting its working accuracy and efficiency. Therefore, the laser light source required by the present invention only needs to use the laser path design for sintering and install the surface profile and molten pool temperature monitoring equipment, which can reduce the cost of repeated hardware installation.

In one embodiment of the present invention, whether using the surface 3D measurement mode or the pyrometer measurement mode, the temperature of the object to be measured is estimated by comparing the light intensity ratio of several different polarizations or different wavelengths. Therefore, the transmittance/reflectivity of the optical system with different polarizations or wavelengths, the quantum efficiency of the photodetector, and the gain of the current-to-voltage converter will affect the light intensity ratio. Therefore, it is necessary to calibrate the hardware of each pyrometer. The calibrated equivalent parameters are stored in the computer unit. After the computer unit reads the signal and interprets it and performs software post-processing, the surface profile and the molten pool temperature image can be generated.

The surface profile and temperature monitoring system of the present invention converts polarized light intensity data into polarized imaging, and then generates surface profile image information of the layered manufacturing processing area through calculation. There are many ways to choose from in the existing technical literature, and it is not limited to the literature method cited in the present invention.

In one embodiment of the present invention, the optical fiber array is an optical fiber element arranged side by side at equal intervals. Based on the fact that diffracted light with a longer wavelength has a larger diffraction angle, different wavelength components in thermal radiation enter different channels in the optical fiber array respectively. The optical fibers at the rear end of each channel are connected to a photodetector to measure real-time information, forming the basis of a high temperature thermometer. Optical fibers are used instead of free space to guide light to the photodetector in order to increase spatial flexibility and reduce background interference.

The present invention provides a surface profile and temperature monitoring system that can switch between two different measurement modes for different light sources, improve the monitoring accuracy of the surface to be measured, effectively increase the efficiency of multilayer processing and reduce manufacturing costs. Through the design of the second focusing lens and the optical fiber array, the space required for the optical system to set up multiple optical devices on the multilayer manufacturing equipment can be saved, and the stability of the light source collected by the coaxial system can be improved. It is also easier to adjust the radiation characteristics related to the surface to be measured, and increase the adjustability of the system. The surface profile and temperature monitoring system of the present invention can be integrated into the multilayer manufacturing system, and the original laser optical path of the multilayer manufacturing system is used, without adding additional optical path design and hardware costs.

The above embodiments are only for illustrative purposes to illustrate the features and effects of the present invention, and are not intended to limit the scope of the substantial technical content of the present invention. Anyone familiar with this art may modify and change the above embodiments without violating the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be as listed in the scope of the patent application described below.

10: Laser light source

10A: Near infrared laser beam

10B: Red laser beam

11: Scanning galvanometer

12: First focusing lens

13: Surface to be tested

14: First optical lens group

14A: Dichroic mirror

14B: Focus lens set

15: Diffused grating

16: Second optical lens group

16A: Beam expander set

16B: Polarizer set

17: Photoelectric conversion module

18:Computer unit

19: Second focusing lens

20: Fiber optic array

Claims (7)

A surface profile and temperature monitoring system for multilayer manufacturing includes: a laser light source, the laser light source generates a laser beam which passes through a scanning galvanometer and then passes through a first focusing lens to a surface to be measured; a first optical lens group, the first optical lens group is composed of a dichroic lens and a beam shrinking lens group, the first optical lens group receives the reflected light and diffused light generated by the laser beam passing to the surface to be measured, and then transmits it to a diffraction grating; a second optical lens group, the second optical lens group is composed of a beam expander group and a polarizer group, the reflected light and diffused light received by the first optical lens group passes through the diffraction grating and enters the second optical lens group. a second focusing lens, the reflected light and the diffused light received by the first optical lens group enter the second focusing lens after passing through the diffraction grating, and then are transmitted to an optical fiber array; a photoelectric conversion module, the photoelectric conversion module selectively receives the optical signal of the reflected light and the diffused light transmitted from the second optical lens group or the optical fiber array, and then converts it into an electrical signal; a computer unit, the computer unit controls the form of the laser beam emitted by the laser light source, selects to use the surface 3D measurement mode or the pyrometer measurement mode, and receives the electrical signal output by the photoelectric conversion module, thereby establishing a surface profile image of the surface to be measured and the temperature of the molten pool; wherein the process of establishing the surface profile image of the surface 3D measurement mode is as follows: the computer unit controls the laser light source to provide a red laser, and selects the surface 3D measurement mode. After the red laser is transmitted to the scanning galvanometer, it is transmitted to the surface to be measured through the first focusing lens. At this time, the reflected light and diffuse light generated by the surface to be measured are transmitted back to the first optical lens group through the original optical path, and then transmitted to the diffraction grating and the second optical lens group after passing through the first optical lens group, and then transmitted to the photoelectric conversion module to be converted into an electrical signal, and then transmitted back to the computer unit, thereby establishing the surface to be measured. Surface profile image; wherein the process of establishing temperature monitoring information in the pyrometer measurement mode is as follows: the computer unit controls the laser light source to provide a near-infrared laser, and selects the pyrometer measurement mode. The near-infrared laser is transmitted to the scanning galvanometer and then to the surface to be measured through the first focusing lens. At this time, the reflected light and diffuse light generated by the surface to be measured are transmitted back to the first optical lens group through the original optical path, and then to the diffraction grating, and to a second focusing lens and an optical fiber array, and then to the photoelectric conversion module to convert into an electrical signal, and then transmitted back to the computer unit, thereby establishing the temperature monitoring information of the surface to be measured. A surface profile and temperature monitoring system for layered manufacturing as described in claim 1, wherein the laser beam used in the surface 3D measurement mode is a red laser with a wavelength of 630~670nm. A surface profile and temperature monitoring system for layered manufacturing as described in claim 1, wherein the laser beam used in the pyrometer measurement mode is a near-infrared laser with a wavelength of 800-1100nm. A surface profile and temperature monitoring system for multilayer manufacturing as described in claim 1, wherein the polarizer set has polarizers in four directions, and the directions of the four polarizers are 0°, 45°, 90° and 135° respectively. A surface profile and temperature monitoring system for layered manufacturing as described in claim 1, wherein the beam expander assembly is composed of a concave lens and a convex lens. As described in claim 1, the surface profile and temperature monitoring system for laminated manufacturing, wherein the computer unit provides coordinate information, calculates the height image of the surface to be measured of the coordinates of the area currently irradiated by the laser beam, and after integrating the height images of all coordinates of the area, obtains the overall surface profile image of the surface to be measured. A surface profile and temperature monitoring system for multilayer manufacturing as described in claim 1, wherein the photoelectric conversion module has a plurality of photodetectors inside.

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