CN-116558648-B - Temperature measurement system and method for laser melting pool of powder bed

CN116558648BCN 116558648 BCN116558648 BCN 116558648BCN-116558648-B

Abstract

The invention discloses a temperature measurement system and a method for a laser melting pool of a powder bed, and belongs to the technical field of additive manufacturing. The system comprises a powder bed laser melting device, a molten pool temperature measuring device, a data processing device and a temperature control device, wherein the powder bed laser melting device comprises a forming cavity, a forming platform and a continuous fiber laser, the continuous fiber laser is used for generating laser, the laser irradiates metal powder and melts the metal powder to form a molten pool, the molten pool temperature measuring device comprises a dichroic mirror, a spectroscope, a first infrared narrow-band filter, a second infrared narrow-band filter, a first photodiode and a second photodiode, a thermal radiation infrared beam emitted by the molten pool outwards reaches the spectroscope after being reflected by the dichroic mirror, the beam is divided into two paths by the spectroscope, the two paths of beams respectively reach the two photodiodes, and the data processing device is used for calculating and obtaining the temperature of the molten pool according to signals acquired by the two photodiodes. The invention measures the absolute temperature of the molten pool through the two photodiodes, and has the advantages of high sampling frequency, high measurement precision and low cost.

Inventors

YANG YONGQIANG
JIANG RENWU
WANG DI
YAN ZHONGWEI
ZHOU HANXIANG
LIU LINQING
WANG YAN

Assignees

华南理工大学

Dates

Publication Date: 20260512
Application Date: 20230516

Claims (7)

1. A system for measuring the temperature of a powder bed laser melt pool, comprising: The powder bed laser melting device comprises a forming cavity, a forming platform and a continuous fiber laser, wherein a powder spreading unit is arranged in the forming cavity, the forming platform comprises a forming cylinder, the powder spreading unit is used for spreading metal powder on the forming cylinder, and the continuous fiber laser is used for generating laser, irradiating the laser on the metal powder and melting the metal powder to form a molten pool; the molten pool temperature measuring device comprises a dichroic mirror, a spectroscope, a first infrared narrow-band filter, a second infrared narrow-band filter, a first photodiode and a second photodiode; Laser emitted by the continuous fiber laser sequentially passes through the collimator, the dichroic mirror for transmission, the vibrating mirror for position adjustment and the field lens for focusing and then reaches the forming cylinder; the infrared beam of heat radiation emitted outwards by the molten pool sequentially passes through the field lens, the vibrating lens and the dichroic mirror and then reaches the spectroscope; dividing the thermal radiation infrared beam into two paths by a spectroscope, wherein one path of light beam passes through a first infrared narrow-band filter to reach a first photodiode, and the other path of light beam passes through a second infrared narrow-band filter to reach a second photodiode; the center wavelength of the first infrared narrow-band filter is different from the center wavelength of the second infrared narrow-band filter; the wavelength of the laser generated by the continuous fiber laser is 1064nm; The shortest transmission wavelength of the dichroic mirror is more than 1000nm and less than 1064nm, and the shortest reflection wavelength of the dichroic mirror is less than 800nm; The central wavelength of the first infrared narrow-band filter is 800nm, and the central wavelength of the second infrared narrow-band filter is 900nm; The data processing device is connected with the first photodiode and the second photodiode and is used for calculating and obtaining the temperature of the molten pool according to signals acquired by the two photodiodes; The tracing device comprises a blackbody radiation source; The forming platform is arranged in the first unit cavity, and the blackbody radiation source is arranged in the second unit cavity; The first unit cavity and the second unit cavity are integrally formed and movably arranged below the forming cavity, the first unit cavity is moved to the lower part of the forming cavity when a laser selective area is melted, the continuous fiber laser is closed when a temperature measured value is traced, the second unit cavity is moved to the lower part of the forming cavity, and a thermal radiation infrared beam generated by the blackbody radiation source is received by the first photodiode and the second photodiode respectively through the field lens, the galvanometer, the dichroic mirror and the spectroscope optical path which are the same as those of the temperature measurement of a molten pool so as to perform in-situ coaxial calibration.
2. A powder bed laser melt bath temperature measurement system according to claim 1, wherein the data processing means calculates the bath temperature by the formula: Wherein, the For the second radiation constant to be the same, Is the center wavelength of the first infrared narrowband filter, Is the center wavelength of the second infrared narrow-band filter, The output signal of the first photodiode and the actual object are at the wavelength The product of the spectral emissivity, For the output signal of the second photodiode and the actual object at the wavelength The product of the lower spectral emittance.
3. The system for measuring the temperature of a powder bed laser melting bath according to claim 1, wherein the powder laying unit comprises a powder laying vehicle, a powder laying guide rail and an air intake guide rail; the powder spreading vehicle is used for scraping metal powder from a powder cylinder and falling the powder after reaching a preset position along the powder spreading guide rail; The air inlet guide rail is used for inputting protective gas.
4. A powder bed laser melt bath temperature measurement system as described in claim 1, wherein the spectroscopic ratio is 1:1.
5. A method of measuring the temperature of a powder bed laser melt pool for use in a system as claimed in any one of claims 1 to 4, comprising the steps of: irradiating laser light onto the metal powder, melting the metal powder to form a molten pool; The infrared beam of heat radiation emitted outwards by the molten pool reaches the spectroscope after being reflected by the dichroic mirror, and the beam is divided into two paths by the spectroscope, wherein one path of beam reaches the first photodiode through the first infrared narrow-band filter, and the other path of beam reaches the second photodiode through the second infrared narrow-band filter; signals acquired by the two photodiodes are acquired, and the temperature of the molten pool is calculated according to the acquired signals.
6. The method for measuring the temperature of a powder bed laser melting bath according to claim 5, further comprising the step of tracing the temperature measurement value: closing the continuous fiber laser, setting a blackbody radiation source below the forming cavity, and controlling the blackbody radiation source to generate a preset constant temperature; The infrared beam of thermal radiation generated by the blackbody radiation source is reflected by the dichroic mirror and then reaches the spectroscope, and the spectroscope divides the beam into two paths, wherein one path of beam passes through the first infrared narrow-band filter to reach the first photodiode, and the other path of beam passes through the second infrared narrow-band filter to reach the second photodiode; and calculating the temperature value of the blackbody radiation source according to the signals acquired by the two photodiodes, and calibrating the photodiodes according to the calculated temperature value and a preset temperature value so as to realize tracing of the temperature measured value.
7. The method of claim 5, further comprising the step of calibrating temperature measurement components within the temperature measurement system, the temperature measurement components comprising a thermal imager and a pyrometer.

Description

Temperature measurement system and method for laser melting pool of powder bed Technical Field The invention relates to the technical field of additive manufacturing, in particular to a temperature measurement system and a method of a powder bed laser melting molten pool. Background The powder bed laser melting technique (Laser powder bed fusion, LPBF) scans the metal powder on the powder bed according to the planned scanning path of the three-dimensional model, so that the metal powder is selectively melted and solidified, and finally the metal powder is overlapped to form a metal entity. The technology has high molding precision and excellent mechanical property, and is widely used in the fields of aerospace, biomedical treatment, automobile industry and the like. The heat source is LPBF the driving force for forming, and the metal powder is melted-solidified layer by layer to form a part with metallurgical strength. Among them, heat distribution and heat transfer are key factors affecting the quality of the part formation, so that it is necessary to measure the temperature of the molten pool in real time during the formation process, and a non-contact temperature measurement method is generally used to measure the temperature of the molten pool. The conventional instruments comprise an infrared thermal imager, a pyrometer and the like, however, the sampling frequency of the instruments is low, the cost is high, and the instruments are not easy to be used for industrialized production. In addition, because the precision of the instrument is reduced after the instrument is used for a period of time, the temperature measuring instrument is required to be calibrated in order to ensure the measurement precision, and because the powder bed laser melting non-contact temperature measuring instrument is often coaxially installed and is troublesome to detach, the in-situ tracing device is required to be studied. Disclosure of Invention In order to solve at least one of the technical problems existing in the prior art to a certain extent, the invention aims to provide a temperature measurement system and a method for a powder bed laser melting molten pool. The technical scheme adopted by the invention is as follows: a powder bed laser melt bath temperature measurement system comprising: The powder bed laser melting device comprises a forming cavity, a forming platform and a continuous fiber laser, wherein a powder spreading unit is arranged in the forming cavity, the forming platform comprises a forming cylinder, the powder spreading unit is used for spreading metal powder on the forming cylinder, and the continuous fiber laser is used for generating laser, irradiating the laser on the metal powder and melting the metal powder to form a molten pool; The molten pool temperature measuring device comprises a dichroic mirror, a spectroscope, a first infrared narrow-band filter, a second infrared narrow-band filter, a first photodiode and a second photodiode, wherein a thermal radiation infrared beam emitted outwards by a molten pool is reflected by the dichroic mirror and then reaches the spectroscope, and the beam is divided into two paths by the spectroscope; And the data processing device is connected with the first photodiode and the second photodiode and is used for calculating and obtaining the temperature of the molten pool according to signals acquired by the two photodiodes. Further, the temperature measurement system further comprises a tracing device, wherein the tracing device comprises a blackbody radiation source, and the blackbody radiation source is used for generating preset temperature; When tracing the temperature measured value, closing the continuous fiber laser, and setting the tracing device below the forming cavity; The infrared beam of thermal radiation generated by the blackbody radiation source is reflected by the dichroic mirror and then reaches the spectroscope, and the spectroscope divides the beam into two paths, wherein one path of beam passes through the first infrared narrow-band filter to reach the first photodiode, and the other path of beam passes through the second infrared narrow-band filter to reach the second photodiode; and calculating the temperature value of the blackbody radiation source according to the signals acquired by the two photodiodes, and calibrating the photodiodes according to the calculated temperature value and a preset temperature value so as to realize tracing of the temperature measured value. Further, the data processing apparatus calculates the bath temperature by the following formula: Wherein lambda 1 is the center wavelength of the first infrared narrow-band filter, lambda 2 is the center wavelength of the second infrared narrow-band filter, M 1 is the product of the output signal of the first photodiode and the spectral emissivity of the actual object at the wavelength lambda 1, M 2 is the product of the output signal of the second photodiode and the s