CN112620655B - Laser coaxial melting and detection feedback control additive manufacturing system - Google Patents

Abstract

The present invention discloses an additive manufacturing system for laser coaxial melting and detection feedback control, including a laser forming system, a LIBS system, a two-color pyrometer system, and a control system. The laser forming system, the LIBS system, and the two-color pyrometer system, through the series connection of a first beam splitter, a second beam splitter, and a third beam splitter, constitute a system for simultaneous laser coaxial melting and detection feedback control. The present invention utilizes a laser induced breakdown spectroscopy (LIBS) device and a two-color pyrometer to perform real-time online detection of the local metal powder mixing ratio and the molten pool temperature in the additive manufacturing process of functional gradient materials, and performs feedback control on the laser power according to the local metal powder mixing ratio and the molten pool temperature, thereby realizing real-time adjustment of the forming parameters in the forming process of functional gradient materials and improving the forming quality of functional gradient materials.

Description

An additive manufacturing system with laser coaxial melting and detection feedback control

Technical Field

The invention belongs to the technical field of additive manufacturing, and relates to an additive manufacturing system with laser coaxial melting and detection feedback control.

Background Art

Laser additive manufacturing technology is a new manufacturing method that realizes the rapid prototyping of three-dimensional parts. Through laser additive manufacturing, the goal of manufacturing three-dimensional parts can be achieved by stacking and welding metal material powder layer by layer.

Functional gradient materials refer to a new type of composite material that is composed of two or more materials and whose composition and structure show a continuous gradient change. In simple terms, the composition of the material changes continuously from one side to the other along the thickness direction, so that the properties and functions of the material also change continuously. Laser additive manufacturing technology can be used to manufacture functional gradient materials. Among them, using mixed powders of metal materials to manufacture functional gradient materials is one of the important applications in the field of laser additive manufacturing.

In the process of laser additive manufacturing, in order to control the forming quality, the molten pool temperature of the forming material should be controlled within a reasonable range. During the forming process, drastic changes in the molten pool temperature may cause unpredictable defects such as cracks and bubbles inside the formed parts. For the forming of functional gradient materials, the metal powder mixing ratios in different gradient areas are different, which corresponds to different forming temperature requirements. Therefore, it is more necessary to realize feedback control of the forming laser power through real-time online monitoring of the metal powder mixing ratio and forming temperature. Furthermore, through real-time online monitoring of the metal powder mixing ratio and forming temperature, real-time optimization of important forming parameters such as laser power, scanning spacing, scanning speed, and substrate powder thickness can be achieved.

Laser induced breakdown spectroscopy (LIBS) is a material composition detection technology that uses high-energy laser pulses to focus on the sample surface. When the high-energy laser is focused on the material surface and reaches the optical breakdown threshold, part of the material at the focused point of the sample will be converted into a plasma state. Then, a signal acquisition instrument is used to collect the spectrum from the plasma, and a spectrometer is used to analyze the collected spectral information, so that the composition and composition ratio of the sample under test can be accurately determined. The two-color radiation pyrometer is also called a colorimetric pyrometer. It uses the wavelengths of two different bands emitted by the same object. The radiation brightness of its spectrum is determined by the single-value relationship between the ratio of the two output signals of the photoelectric conversion and the temperature. It is a non-contact temperature measurement, and its theory is derived from Planck's theorem of blackbody radiation energy distribution. The temperature detection of the two-color radiation pyrometer is less affected by smoke, impurities, protective gas, etc. between the probe and the detection object, and can accurately detect the high-temperature molten pool temperature of the material in the laser additive manufacturing process. Using the temperature monitoring of the two-color radiation pyrometer and the composition detection of the LIBS device, real-time monitoring and feedback control of the laser additive manufacturing process of functional gradient materials can be achieved.

Summary of the invention

The purpose of the present invention is to provide an additive manufacturing system that realizes laser coaxial melting and detection feedback control of functional gradient materials. The device shares a set of optical systems and has the advantages of small size, compact structure, and real-time detection feedback control of the forming and manufacturing process of functional gradient materials.

The technical solution adopted by the present invention is:

A functional gradient material laser coaxial melting and detection feedback control additive manufacturing system, comprising a forming chamber, wherein a fiber laser is arranged in the forming chamber, and the fiber laser generates a forming laser beam; the forming laser beam sequentially passes through a beam isolator, a beam expander, a first beam splitter, a scanning galvanometer, and an F-θ mirror, and is focused on the surface of a mixed powder in a forming cylinder at the bottom of the forming chamber to melt the mixed powder; when the forming laser beam leaves the powder surface, the melted powder solidifies to form a formed part;

A powder spreading roller is provided at the bottom of the forming chamber, which evenly spreads the powder to be processed on the upper surface of the existing powder in the forming cylinder. The excess powder enters the powder recovery cylinder under the action of the powder spreading roller. A first lifting platform is provided at the bottom of the forming cylinder, and a second lifting platform is provided at the bottom of the recovery cylinder.

The additive manufacturing system comprises a LIBS laser, which generates a LIBS pulse laser, and the LIBS pulse laser forms plasma on the forming surface of the powder to be processed after being reflected by the second beam splitter, transmitted by the first beam splitter, reflected by the scanning galvanometer and converged by the F-θ mirror;

The additive manufacturing system also includes a spectrometer and a two-color pyrometer;

After the shaped laser beam melts the powder to be processed, a composite spectrum is emitted; the composite spectrum is received by the two-color pyrometer after passing through the F-θ mirror, the scanning galvanometer, the first beam splitter, the second beam splitter, the third beam splitter, and the second lens group;

The plasma radiates a plasma composite spectrum, and the plasma composite spectrum is received by the spectrometer after passing through the F-θ mirror, the scanning galvanometer, the first beam splitter, the second beam splitter, the third beam splitter, and the first lens group;

The fiber laser, LIBS laser, spectrometer and two-color pyrometer are all connected to a computer. After the laser beam is formed to melt the powder to be processed, the computer controls the two-color pyrometer to collect the composite spectrum emitted by the melted powder to be processed. After the two-color pyrometer has collected the spectrum information of the composite spectrum, the computer controls the LIBS laser to generate a LIBS pulse laser. After a certain delay, the computer control system controls the spectrometer to collect the plasma composite spectrum radiated by the plasma.

The computer performs feedback adjustment on the laser power of the shaped laser beam generated by the fiber laser according to the temperature information of the melted powder to be processed collected by the two-color pyrometer and the composition information of the powder to be processed collected by the spectrometer;

The forming chamber is also provided with a powder mixing system for producing powder, and the powder mixing system includes at least two powder storage tanks, each of which is provided with a powder outlet at the bottom, and the powder outlet is provided with a valve controlled by a computer; the powder from each powder outlet falls into a powder pre-mixing device; the powder mixing device mixes powders of different materials to form functional gradient material powder, and falls onto the bottom surface of the forming chamber.

Furthermore, the first lens group includes at least one lens with positive refractive power; the second lens group includes at least one lens with positive refractive power. The beneficial effects of the present invention are:

(1) The present invention provides an additive manufacturing system for realizing coaxial laser melting and detection feedback control of functional gradient materials: the laser melting forming system, LIBS (laser induced breakdown spectroscopy) system, and two-color pyrometer system of the present invention share a set of optical systems, which belong to the coaxial optical path, and can comprehensively collect the composition information and temperature information of the laser melting point in situ, and the system structure is compact.

(2) The two-color pyrometer detects temperature by using the ratio of the spectral radiation energy of an object at two wavelengths. It can compensate for the measurement error caused by the protective atmosphere and local smoke in the additive manufacturing chamber, and effectively reduce the measurement error of the molten pool temperature caused by the protective atmosphere and local smoke.

(3) The device of the present invention is mainly used in the forming and manufacturing process of functional gradient materials. It monitors the powder ratio and molten pool temperature of the functional gradient materials in real time during the forming process, and adjusts the forming laser power and other forming parameters according to the powder ratio to achieve the purpose of reducing defects such as cracks and bubbles in the formed parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of the present invention.

In the figure: 1. forming chamber, 2. protective gas chamber, 3. fiber laser, 3a. first optical fiber, 4. forming laser beam, 5. beam isolator, 6. beam expander, 7. first beam splitter, 8. scanning galvanometer, 9. F-θ mirror, 10. powder to be processed, 11. formed part, 12. LIBS laser, 12a. second optical fiber, 13. LIBS pulse laser, 14. second beam splitter, 15. plasma composite spectrum, 16. third beam splitter, 17. first lens group, 18. spectrometer, 18a. third optical fiber, 19. composite spectrum, 20. second lens group, 21. two-color pyrometer, 21a. fourth optical fiber, 22. computer control system, 23. first powder storage tank, 24. second powder storage tank, 25. powder mixing device, 26. powder spreading roller, 27. functional gradient material powder, 28. forming cylinder, 29. first lifting platform, 30. powder recovery cylinder, 31. second lifting platform.

DETAILED DESCRIPTION

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in FIG1 , an additive manufacturing system for realizing laser coaxial melting and detection feedback control of functional gradient materials includes a laser forming system, a LIBS system, a two-color pyrometer system, and a control system.

The device can use 1064nm laser as LIBS laser source.

The workflow of the present invention is as follows:

The first powder storage tank 23 and the second powder storage tank 24 store different material powders respectively. After the different material powders fall into the powder mixing device 25, the powder mixing device 25 mixes the different material powders to form functional gradient material powder 27, and falls on the bottom surface of the forming chamber 1. The powder spreading roller 26 evenly spreads the functional gradient material powder 27 on the upper surface of the powder to be processed 10 in the forming cylinder 28, and the excess powder to be processed 10 enters the powder recovery cylinder 30 under the action of the powder spreading roller 26. The computer control system 22 controls the fiber laser 3 to generate a forming laser beam 4. The forming laser beam 4 passes through the beam isolator 5, the beam expander 6, the first beam splitter 7, the scanning galvanometer 8, and the F-θ mirror 9, and is focused on the surface of the powder to be processed 10 to melt the powder to be processed 10. When the forming laser beam 4 leaves the surface of the powder to be processed 10, the melted powder to be processed 10 solidifies to form a formed part 11. The beam isolator 5 is used to block the reflected laser, and the beam expander 6 is used to expand the beam to improve the collimation characteristics of the beam. The first beam splitter 7 and the scanning galvanometer 8 are used to change the path of the shaped laser beam 4. The F-θ mirror 9 is used to form a focused spot of uniform size on the shaped surface of the powder 10 to be processed with the shaped laser beam 4.

After the shaped laser beam 4 melts the powder 10 to be processed, the molten material will emit a composite spectrum 19. After the composite spectrum 19 is diffused by the F-θ mirror 9, reflected by the scanning galvanometer 8, transmitted by the first beam splitter 7, transmitted by the second beam splitter 14, transmitted by the third beam splitter 16, and converged by the second lens group 20, the computer control system 22 controls the two-color pyrometer 21 to receive the composite spectrum 19, and further measures the temperature of the melted powder 10 to be processed.

After waiting for the two-color pyrometer 21 to collect the spectrum information of the composite spectrum 19, the computer control system 22 controls the LIBS laser 12 to generate the LIBS pulse laser 13. After the LIBS pulse laser 13 is reflected by the second beam splitter 14, transmitted by the first beam splitter 7, reflected by the scanning galvanometer 8, and converged by the F-θ mirror 9, a plasma is formed on the forming surface of the powder to be processed 10, and the plasma radiates a plasma composite spectrum 15. After being diffused by the F-θ mirror 9, reflected by the scanning galvanometer 8, transmitted by the first beam splitter 7, transmitted by the second beam splitter 14, reflected by the third beam splitter 16, and converged by the first lens group 17, the plasma composite spectrum 15 is received by the spectrometer 18. After waiting for a certain delay, the computer control system 22 controls the spectrometer 18 to collect the plasma radiation to generate the plasma composite spectrum 15. The two-color pyrometer 21 collects the composite spectrum 19 earlier than the spectrometer 18 collects the plasma radiation to generate the plasma composite spectrum 15, which effectively avoids the influence of the high temperature of the plasma caused by the LIBS pulse laser 13 on the actual temperature measurement of the melted powder to be processed 10.

The computer control system 22 can feedback and adjust the laser power of the forming laser beam 4 generated by the fiber laser 3 based on the temperature information of the melted powder to be processed 10 collected by the two-color pyrometer 21 and the composition information of the powder to be processed 10 collected by the spectrometer 18, so as to achieve different laser powers corresponding to functional gradient material powders with different material ratios, thereby improving the forming quality of the functional gradient material.

When a layer of the powder 10 to be processed is melted and formed, the first lifting platform 29 is lowered by one layer, and the powder spreading roller 26 starts spreading powder again to start printing a new layer. The second lifting platform 31 adjusts the height of the powder stored in the powder recovery cylinder 30 by descending so that the powder height is not higher than the bottom surface of the forming chamber 1.

In the present invention, the first lens group 17 includes at least one lens with positive refractive power, and the second lens group 20 includes at least one lens with positive refractive power.

The laser forming system, the LIBS system, and the two-color pyrometer system are connected in series through the first beam splitter 7, the second beam splitter 14, and the third beam splitter 16 to form a system in which laser coaxial melting and detection feedback control are performed simultaneously.

The number of the first powder storage tanks 23 or the second powder storage tanks 24 is not limited, and the number of the powder storage tanks can be increased as the types of powder materials increase.

The protective gas chamber 2 is connected to the forming chamber 1. The protective gas chamber 2 provides protective gas to prevent the powder from being oxidized and to protect the powder during the testing process and the forming process.

The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims (2)

1. The additive manufacturing system for laser coaxial melting and detection feedback control comprises a forming chamber, and is characterized in that an optical fiber laser is arranged in the forming chamber, and the optical fiber laser generates a forming laser beam; the forming laser beam sequentially passes through a beam isolator, a beam expander, a first beam splitter, a scanning galvanometer and an F-theta lens, and is focused on the surface of mixed powder in a forming cylinder at the bottom of a forming chamber, so that the mixed powder is melted; after the shaping laser beam leaves the powder surface, the melted powder solidifies to form a shaped piece;

The bottom of the forming chamber is provided with a powder spreading roller which uniformly spreads the powder to be treated on the upper surface of the existing powder of the forming cylinder, the redundant powder enters the powder recovery cylinder under the action of the powder spreading roller, the bottom of the forming cylinder is provided with a first lifting table, and the bottom of the powder recovery cylinder is provided with a second lifting table;

The additive manufacturing system comprises an LIBS laser, wherein the LIBS laser generates LIBS pulse laser, and plasma is formed on the forming surface of powder to be processed after the LIBS pulse laser is reflected by a second beam splitter, transmitted by a first beam splitter, reflected by a scanning galvanometer and converged by an F-theta mirror;

the additive manufacturing system further comprises a spectrometer and a bicolor pyrometer;

shaping the laser beam to enable the powder to be processed to be melted, and then emitting a composite spectrum; the composite spectrum is received by a bicolor pyrometer after passing through an F-theta lens, a scanning galvanometer, a first beam splitter, a second beam splitter, a third beam splitter and a second lens group;

the plasma radiates a plasma composite spectrum, and the plasma composite spectrum is received by a spectrometer after passing through an F-theta lens, a scanning galvanometer, a first beam splitter, a second beam splitter, a third beam splitter and a first lens group;

The optical fiber laser, the LIBS laser, the spectrometer and the bicolor pyrometer are all connected with a computer, after the powder to be treated is melted by forming laser beams, the computer controls the bicolor high Wen Jishou to collect the composite spectrum emitted by the powder to be treated after melting, after the bicolor pyrometer collects the spectrum information of the composite spectrum, the computer controls the LIBS laser to generate LIBS pulse laser, and after waiting for a certain time delay, the computer control system controls the spectrometer to collect plasma to radiate the plasma composite spectrum;

The computer feeds back and adjusts the laser power of the forming laser beam generated by the fiber laser according to the temperature information of the melted powder to be processed collected by the bicolor pyrometer and the component information of the powder to be processed collected by the spectrometer;

the forming chamber is also internally provided with a powder mixing system for generating powder, the powder mixing system comprises at least 2 powder storage tanks, the bottom of each powder storage tank is provided with a powder outlet, and the powder outlet is provided with a valve controlled by a computer; the powder of each powder outlet falls into the powder premixing device; the powder mixing device mixes the different material powders into functionally graded material powders and falls onto the bottom surface of the forming chamber.

2. The laser in-line melting and detection feedback controlled additive manufacturing system of claim 1 wherein: the first lens group at least comprises a lens with positive diopter; the second lens group at least comprises a lens with positive diopter.