A powder recycling filtration system and method for laser fusion additive manufacturing

Abstract

The application provides a powder recycling and filtering system and method for laser melting additive manufacturing, the system is a whole-process closed structure, comprising a closed feeding unit, a separation unit connected with the closed feeding unit, the separation unit pre-treats the powder, a vibration unit connected with the separation unit, a dust removal unit connected with the vibration unit, a collecting unit, an inert gas protection unit connected with the closed feeding unit, the separation unit, the vibration unit, the dust removal unit and the collecting unit, and a PLC automatic control unit for controlling the closed feeding unit, the separation unit, the vibration unit, the dust removal unit, the collecting unit and the inert gas protection unit. The application realizes three-stage cooperation of the separation unit pre-treatment, the vibration unit screening and the dust removal unit screening, and finally obtains 15-53 mu m qualified powder with a proportion of greater than or equal to 94%.

Description

Technical Field

[0001] This invention relates to the field of supporting equipment technology for metal additive manufacturing, and more specifically, to a powder recovery and filtration system and method for selective laser melting additive manufacturing of metals. Background Technology

[0002] In the mass production of metal 3D printing, the recycling of unmelted powder is a crucial step in controlling costs and stabilizing molding quality. Existing recycling technologies generally suffer from the following drawbacks:

[0003] 1. Open or semi-open recycling means that the powder comes into direct contact with the air, which makes it easy to oxidize and absorb water, resulting in an increase in oxygen content, which cannot meet the requirements of aerospace-grade printing;

[0004] 2. The use of a single vibrating screen for grading not only results in poor grading accuracy but also makes the screen prone to clogging, making it difficult to stably separate the standard powder particle size of 15-53μm. At the same time, it cannot effectively remove sintered lumps, large particles, and ultrafine powder.

[0005] 3. Some equipment incorporates electrostatic dust removal units, but uses a high-voltage electric field, which can easily generate electric sparks from conductive metal powders, posing a dust explosion hazard.

[0006] 4. The functional units are simply assembled, lacking collaborative design, without full-process inert gas closed-loop protection, low degree of automation, high degree of manual intervention, large powder loss and low recycling rate.

[0007] 5. The recycled powder has uneven particle size distribution and poor flowability, and cannot be directly reused for powder spreading. It requires secondary processing, which greatly increases production costs.

[0008] The prior art disclosed in CN120079890A is a metal powder recovery system for additive manufacturing of rocket engine thrust chambers, including powder collection, sieving and grading, purification, particle size adjustment and intelligent control modules. The powder collection module captures residual metal powder and collects data to generate a dataset; the sieving and grading module uses a joint algorithm to separate particles; the purification module constructs a multi-stage purification model to remove the oxide layer and decompose organic matter; the particle size adjustment module designs a composite control strategy to adjust the particle size distribution; the intelligent control module establishes an optimization model to generate parameter adjustment instructions. In addition, the system also has powder characteristic analysis, circulation monitoring and anomaly handling modules. The prior art has the following problems: (1) Chemical reagents are used in the powder purification stage, which can easily cause environmental pollution; (2) The purity of the powder is poor during recovery. Summary of the Invention

[0009] In view of this, the present invention aims to provide a powder recovery and filtration system and method for selective laser melting additive manufacturing of metals. This addresses the problems of existing technologies that use chemical reagents in the powder purification stage, which easily cause environmental pollution, and the poor purity of the recovered powder.

[0010] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0011] A powder recovery and filtration system for laser melting additive manufacturing, the system being a fully closed-loop structure, including...

[0012] Sealed feeding unit: The sealed feeding unit is used to seal and connect with the powder hopper outlet of the 3D printing equipment to input the metal powder to be recycled into the system.

[0013] Separation unit: The separation unit is connected to the closed feeding unit, and the separation unit pre-treats the powder;

[0014] Vibration unit: The vibration unit is connected to the separation unit. The vibration unit is used to screen out large particles, ultrafine powder and qualified powder, wherein the qualified powder enters the next unit.

[0015] Dust removal unit: The dust removal unit is connected to the vibration unit. The dust removal unit is used to purify qualified powder and improve particle size uniformity and flowability.

[0016] Collection unit: includes a large particle collection chamber, an ultrafine powder recovery chamber, and a qualified powder collection chamber, and the three collection chambers are independently sealed.

[0017] Inert gas protection unit: The inert gas protection unit is connected to the closed feeding unit, separation unit, vibration unit, dust removal unit and collection unit, and the inert gas protection unit is used to achieve a low oxygen or oxygen-free environment throughout the process;

[0018] PLC automatic control unit: controls the sealed feeding unit, separation unit, vibration unit, dust removal unit, collection unit, and inert gas protection unit.

[0019] Furthermore, the pretreatment involves sieving out large particles of powder.

[0020] Furthermore, the sealed feeding unit adopts a quick-connect sealing interface, which can be directly connected to the powder hopper outlet of the SLM equipment. The interface has a built-in sealing airbag and a one-way shut-off valve. The feeding adopts a variable frequency screw conveyor, and the conveying speed is adjustable from 5-15 kg / h.

[0021] Furthermore, the separation unit adopts a horizontal tangential air intake cyclone separator with an air intake angle of 30° and an operating speed of 800-1200 r / min.

[0022] Furthermore, the vibration unit adopts a double-layer vertical ultrasonic vibrating screen, wherein the upper screen mesh has a diameter of 53μm and the lower screen mesh has a diameter of 15μm, and the screen inclination angle is 3-5°; ultrasonic vibration generators are arranged on both sides of the screen, with a working frequency of 20-30kHz and a power of 100-200W; an inert gas online backflushing system is provided at the bottom of the screen, with argon or nitrogen as the backflushing medium, a backflushing pressure of 0.03-0.06MPa, and automatic backflushing for 5 seconds every 30 seconds.

[0023] Furthermore, powder with a particle size > 53 μm is considered large particles, powder with a particle size < 15 μm is considered ultrafine powder, and powder with a particle size of 15–53 μm is considered qualified powder.

[0024] Furthermore, the dust removal unit adopts a low-voltage safety electrostatic dust removal structure with a working voltage of 20-40kV. The cavity is covered with a polytetrafluoroethylene insulation layer and is equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution.

[0025] Furthermore, the inert gas protection unit adopts a closed-loop argon or nitrogen protection system with closed-loop inert gas micro-positive pressure protection and stable oxygen content ≤200ppm.

[0026] Furthermore, the micro-positive pressure is 0.03-0.05 MPa.

[0027] A powder recovery and filtration method for laser melting additive manufacturing, using the system described above, is characterized by comprising the following steps:

[0028] S1. The metal powder to be recycled enters the closed feeding unit and proceeds to step S2.

[0029] S2. The metal powder to be recovered enters the separation unit for pretreatment. The pretreatment is the first screening to remove large particles, and then proceeds to step S3.

[0030] S3. The metal powder to be recovered enters the vibration unit for a second screening, and then proceeds to step S4.

[0031] S4. The metal powder to be recovered enters the dust removal unit for a third screening and then exits the silo.

[0032] Compared with existing technologies, the powder recovery and filtration system and method for selective laser melting additive manufacturing of metals described in this invention have the following advantages:

[0033] 1) The system classification accuracy of the present invention is high: through the pretreatment of the separation unit, the sieving of the vibration unit, and the sieving of the dust removal unit, the three-level synergy results in a final qualified powder of 15-53μm with a proportion of ≥94%, and the particle size distribution meets the requirements of SLM powder spreading.

[0034] 2) The system of the present invention adopts low oxygen anti-oxidation: closed-loop inert gas micro positive pressure protection, oxygen content is stable ≤200ppm, and the oxygen content of the recovered powder meets the requirements of high-end printing.

[0035] 3) The system of this invention is safe and explosion-proof: low-voltage electrostatic field + insulating cavity + spark monitoring + rapid power off multiple protections, completely eliminating the safety hazards of electrostatic purification of metal powder;

[0036] 4) The system of the present invention operates stably and does not clog: ultrasonic vibration + inert gas online backflushing provides dual anti-clogging, extending the screen life by more than 3 times and enabling continuous operation for a long time;

[0037] 5) The invention has a high degree of automation: PLC provides full-process linkage control, eliminating the need for manual operation, increasing recycling efficiency by 120%, and reducing labor costs by 75%;

[0038] 6) The present invention has a high powder recycling rate: the qualified powder recovery rate is ≥92%, which can be directly reused for powdering, significantly reducing the powder procurement cost and making it highly versatile. Attached Figure Description

[0039] Figure 1 This is a diagram of a powder recovery and filtration system for laser melting additive manufacturing according to the present invention;

[0040] Figure 2 This diagram illustrates a powder recovery and filtration method for laser melting additive manufacturing according to the present invention. Detailed Implementation

[0041] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] This invention overcomes the problems of severe oxidation, low grading accuracy, easy screen clogging, poor safety, and low automation in existing recycling equipment. It provides a powder recovery and filtration system for laser melting additive manufacturing that can stably recover metal powder with a standard particle size of 15-53μm, has controllable oxygen content, operates safely and stably, and can be directly reused. The system is a fully closed-loop structure. Figures 1-2 As shown, it includes a closed feeding unit, a separation unit, a vibration unit, a dust removal unit, an inert gas protection unit, a PLC automatic control unit, and a collection unit; each unit is connected in sequence through a closed pipeline and operates in a slightly positive pressure environment of inert gas throughout the process.

[0043] More specifically, the system includes a hermetically sealed feeding unit: the hermetically sealed feeding unit is used to seal and connect with the powder hopper outlet of the 3D printing equipment to input the metal powder to be recycled into the system.

[0044] Specifically, the sealed feeding unit adopts a quick-connect sealing interface, which can be directly connected to the powder hopper outlet of the SLM equipment. The interface has a built-in sealing airbag and a one-way shut-off valve to prevent air infiltration and powder backflow. The feeding adopts a variable frequency screw conveyor with an adjustable speed range of 5-15 kg / h to ensure continuous and stable graded purification.

[0045] Separation unit: The separation unit is connected to the closed feeding unit and performs pretreatment on the powder.

[0046] Specifically, a horizontal tangential air inlet cyclone separator is used with an air inlet angle of 30° and a working speed of 800-1200 r / min. It is used to pre-separate sintered blocks, large particle agglomerates and hard impurities with a particle size >53μm, and directly discharge them into the large particle collection bin to reduce the load on subsequent screening and avoid screen clogging.

[0047] Vibration unit: The vibration unit is connected to the separation unit. The vibration unit is used to screen out large particles, ultrafine powder and qualified powder, wherein the qualified powder enters the next unit.

[0048] Specifically, the vibration unit is the core grading mechanism, employing a double-layer vertical ultrasonic vibrating screen: the upper screen has a mesh size of 53μm, the lower screen has a mesh size of 15μm, and the screen tilt angle is 3° to 5°; ultrasonic vibration generators are configured on both sides, with a working frequency of 20 to 30kHz and a power of 100 to 200W, used to break up powder agglomerates; the bottom of the screen is equipped with an inert gas online backflushing system, with argon or nitrogen as the backflushing medium, a pressure of 0.03 to 0.06MPa, and automatic backflushing for 5 seconds every 30 seconds to achieve online self-cleaning of the screen.

[0049] After sieving: powder >53μm enters the large particle collection bin, ultrafine powder <15μm enters the ultrafine powder recovery bin, and qualified powder of 15~53μm enters the next unit.

[0050] Dust removal unit: The dust removal unit is connected to the vibration unit. The dust removal unit is used to purify qualified powder and improve particle size uniformity and flowability.

[0051] Specifically, the dust removal unit adopts a low-voltage safety electrostatic dust removal structure with a working voltage of 20-40kV. The interior of the chamber is covered with a polytetrafluoroethylene insulation layer and equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution to eliminate the risk of explosion. It mainly adsorbs residual trace ultrafine powder, further purifies qualified powder, and improves particle size uniformity and flowability.

[0052] Collection unit: includes a large particle collection chamber, an ultrafine powder recovery chamber, and a qualified powder collection chamber, and the three collection chambers are independently sealed.

[0053] Specifically, the collection unit is equipped with three independent sealed chambers: a large particle collection chamber, an ultrafine powder recovery chamber, and a qualified powder collection chamber; the qualified powder collection chamber can be directly connected to the powder spreading equipment to achieve direct reuse of the recovered powder without exposure.

[0054] Inert gas protection unit: The inert gas protection unit is connected to the closed feeding unit, separation unit, vibration unit, dust removal unit and collection unit, and the inert gas protection unit is used to achieve a low oxygen or oxygen-free environment throughout the process.

[0055] Specifically, the inert gas protection unit adopts a closed-loop argon / nitrogen protection system. The system maintains a slight positive pressure of 0.03 to 0.05 MPa and has a built-in online oxygen content sensor. The upper limit of oxygen content is set to 200 ppm. When the limit is exceeded, gas is automatically replenished to achieve a low-oxygen or even oxygen-free environment throughout the process, thus inhibiting powder oxidation.

[0056] PLC automatic control unit: controls the sealed feeding unit, separation unit, vibration unit, dust removal unit, collection unit, and inert gas protection unit.

[0057] Specifically, the PLC automatic control unit integrates real-time monitoring and automatic adjustment of parameters such as feed rate, cyclone speed, ultrasonic parameters, backflushing pressure, oxygen content, and electrostatic voltage. All units operate in conjunction with each other, and the unit has abnormal alarm and automatic shutdown protection functions to achieve unmanned continuous operation.

[0058] A powder recovery and filtration method for laser melting additive manufacturing, using the system described above, includes the following steps:

[0059] S1. The metal powder to be recycled enters the closed feeding unit and proceeds to step S2.

[0060] S2. The metal powder to be recovered enters the separation unit for pretreatment. The pretreatment is the first screening to remove large particles, and then proceeds to step S3.

[0061] S3. The metal powder to be recovered enters the vibration unit for a second screening, and then proceeds to step S4.

[0062] S4. The metal powder to be recovered enters the dust removal unit for a third screening and then exits the silo.

[0063] The working principle of this invention is as follows: The powder to be recycled enters the device through a closed feeding unit. Under the protection of a slight positive pressure of inert gas, it first passes through a cyclone separator to remove large particulate impurities; then it enters a double-layer ultrasonic vibrating screen, where, under the synergistic effect of ultrasonic vibration and inert gas backflushing, qualified powder of 15-53μm is accurately separated; subsequently, the qualified powder enters a low-pressure electrostatic dust removal unit to remove residual ultrafine powder and complete deep purification; the oxygen content is automatically controlled throughout the process, and finally, qualified powder with low oxygen, high purity, and uniform particle size is obtained, which can be directly reused for powder spreading and printing in SLM equipment.

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0065] Example 1: Recovery of TC4 Titanium Alloy Powder

[0066] Raw metal powder: particle size 10–70 μm, oxygen content 470 ppm, 15–53 μm particles account for 84%. During the metal powder recovery process, the system maintains a slight positive pressure of 0.04 MPa, with an oxygen content limit of 200 ppm. The specific recovery steps are as follows:

[0067] 1. The metal powder to be recycled enters the closed feeding unit; the feeding adopts a variable frequency screw conveyor with a feeding rate of 10 kg / h;

[0068] 2. The metal powder to be recovered enters the separation unit for pretreatment; a horizontal tangential air inlet cyclone separator is used, with an air inlet angle of 30° and a working speed of 1000 r / min;

[0069] 3. The metal powder to be recovered enters the vibration unit for a second screening; a double-layer vertical ultrasonic vibrating screen is adopted: the upper screen mesh has a diameter of 53μm, the lower screen mesh has a diameter of 15μm, and the screen tilt angle is 3°; ultrasonic vibration generators are configured on both sides, with a working frequency of 25kHz and a power of 120W; the bottom of the screen is equipped with an inert gas online backflushing system, the backflushing medium is argon gas, the pressure is 0.04MPa, and it automatically backflushes for 5 seconds every 30 seconds to achieve online self-cleaning of the screen.

[0070] 4. The metal powder to be recovered enters the dust removal unit for a third screening; a low-pressure safety electrostatic dust removal structure is adopted, with a working voltage of 30kV. The inside of the chamber is covered with a polytetrafluoroethylene insulation layer, equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution to eliminate the risk of explosion; it mainly adsorbs residual trace ultrafine powder, further purifies qualified powder, and improves particle size uniformity and flowability.

[0071] Recovery results: 95.2% of the powder was of acceptable quality in the 15-53μm range, with an oxygen content of 450ppm. The powder had good flowability and could be directly used for aerospace-grade TC4 printing, with an effective recovery rate of 92%.

[0072] Example 2: Recovery of 316L stainless steel powder

[0073] Raw metal powder: particle size 12-65μm, oxygen content 250ppm, 15-53μm accounts for 83.5%.

[0074] During the metal powder recovery process, the system maintains a slight positive pressure of 0.03 MPa and an oxygen content limit of 200 ppm. The specific recovery steps are as follows:

[0075] 1. The metal powder to be recycled enters the closed feeding unit; the feeding adopts a variable frequency screw conveyor with a feeding rate of 12kg / h;

[0076] 2. The metal powder to be recovered enters the separation unit for pretreatment; a horizontal tangential air inlet cyclone separator is used, with an air inlet angle of 30° and a working speed of 1200 r / min;

[0077] 3. The metal powder to be recovered enters the vibration unit for a second screening; a double-layer vertical ultrasonic vibrating screen is adopted: the upper screen mesh has a diameter of 53μm, the lower screen mesh has a diameter of 15μm, and the screen tilt angle is 3°; ultrasonic vibration generators are configured on both sides, with a working frequency of 20kHz and a power of 100W; the bottom of the screen is equipped with an inert gas online backflushing system, the backflushing medium is argon gas, the pressure is 0.045MPa, and it automatically backflushes for 5 seconds every 30 seconds to achieve online self-cleaning of the screen.

[0078] 4. The metal powder to be recovered enters the dust removal unit for a third screening; a low-pressure safety electrostatic dust removal structure is adopted, with a working voltage of 28kV. The inside of the chamber is covered with a polytetrafluoroethylene insulation layer, equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution to eliminate the risk of explosion; it mainly adsorbs residual trace ultrafine powder, further purifies qualified powder, and improves particle size uniformity and flowability.

[0079] Recovery results: 94.8% of the 15-53μm qualified powder was recovered, the oxygen content was 260ppm, the screen did not clog after 8 hours of continuous operation, and the effective recovery rate was 93%.

[0080] Example 3: Recovery of TC4 Titanium Alloy Powder

[0081] Raw metal powder: particle size 10-60μm, oxygen content 400ppm, 15-53μm accounts for 80%.

[0082] During the metal powder recovery process, the system maintains a slight positive pressure of 0.05 MPa and an oxygen content limit of 200 ppm. The specific recovery steps are as follows:

[0083] 1. The metal powder to be recycled enters the closed feeding unit; the feeding adopts a variable frequency screw conveyor with a feeding rate of 15 kg / h;

[0084] 2. The metal powder to be recovered enters the separation unit for pretreatment (first screening); a horizontal tangential air inlet cyclone separator is used, with an air inlet angle of 30° and a working speed of 900 r / min;

[0085] 3. The metal powder to be recovered enters the vibration unit for a second screening; a double-layer vertical ultrasonic vibrating screen is adopted: the upper screen mesh has a diameter of 53μm, the lower screen mesh has a diameter of 15μm, and the screen tilt angle is 3°; ultrasonic vibration generators are configured on both sides, with a working frequency of 30kHz and a power of 200W; the bottom of the screen is equipped with an inert gas online backflushing system, the backflushing medium is argon gas, the pressure is 0.05MPa, and it automatically backflushes for 5 seconds every 30 seconds to achieve online self-cleaning of the screen.

[0086] 4. The metal powder to be recovered enters the dust removal unit for a third screening; a low-pressure safety electrostatic dust removal structure is adopted, with a working voltage of 30kV. The inside of the chamber is covered with a polytetrafluoroethylene insulation layer, equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution to eliminate the risk of explosion; it mainly adsorbs residual trace ultrafine powder, further purifies qualified powder, and improves particle size uniformity and flowability.

[0087] Recovery results: 94% of the 15-53μm qualified powder was found, with an oxygen content of 430ppm. The powder had good flowability and could be directly used for aerospace-grade TC4 printing, with an effective recovery rate of 90%.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that step 1 (the metal powder to be recovered enters the separation unit for pretreatment) is not performed.

[0090] Recovery results: 70% of the powder was of acceptable quality in the 15-53μm range, with an oxygen content of 400ppm. The powder had good flowability and could be directly used for aerospace-grade TC4 printing, with an effective recovery rate of 75%.

[0091] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A powder recovery and filtration system for laser melting additive manufacturing, wherein the system is a fully enclosed structure, characterized in that, include Sealed feeding unit: The sealed feeding unit is used to seal and connect with the powder hopper outlet of the 3D printing equipment to input the metal powder to be recycled into the system. Separation unit: The separation unit is connected to the closed feeding unit, and the separation unit pre-treats the powder; Vibration unit: The vibration unit is connected to the separation unit. The vibration unit is used to screen out large particles, ultrafine powder and qualified powder, wherein the qualified powder enters the next unit. Dust removal unit: The dust removal unit is connected to the vibration unit. The dust removal unit is used to purify qualified powder and improve particle size uniformity and flowability. Collection unit: includes a large particle collection chamber, an ultrafine powder recovery chamber, and a qualified powder collection chamber, and the three collection chambers are independently sealed. Inert gas protection unit: The inert gas protection unit is connected to the closed feeding unit, separation unit, vibration unit, dust removal unit and collection unit, and the inert gas protection unit is used to achieve a low oxygen or oxygen-free environment throughout the process; PLC automatic control unit: controls the sealed feeding unit, separation unit, vibration unit, dust removal unit, collection unit, and inert gas protection unit.

2. The system according to claim 1, characterized in that, The pretreatment involves sieving out large particles of powder.

3. The system according to claim 1, characterized in that, The sealed feeding unit adopts a quick-connect sealing interface, which can be directly connected to the powder hopper outlet of the SLM equipment. The interface has a built-in sealing airbag and a one-way shut-off valve. The feeding adopts a variable frequency screw conveyor, and the conveying speed is adjustable from 5-15 kg / h.

4. The system according to claim 1, characterized in that, The separation unit adopts a horizontal tangential air intake cyclone separator with an air intake angle of 30° and an operating speed of 800-1200 r / min.

5. The system according to claim 1, characterized in that, The vibration unit adopts a double-layer vertical ultrasonic vibrating screen, wherein the upper screen mesh has a diameter of 53μm and the lower screen mesh has a diameter of 15μm, and the screen inclination angle is 3-5°; ultrasonic vibration generators are arranged on both sides of the screen, with a working frequency of 20-30kHz and a power of 100-200W; the bottom of the screen is equipped with an inert gas online backflushing system, the backflushing medium is argon or nitrogen, the backflushing pressure is 0.03-0.06MPa, and it automatically backflushes for 5 seconds every 30 seconds.

6. The system according to claim 1, characterized in that, Powder with a particle size > 53 μm is considered large particle, powder with a particle size < 15 μm is considered ultrafine powder, and powder with a particle size of 15–53 μm is considered qualified powder.

7. The system according to claim 1, characterized in that, The dust removal unit adopts a low-voltage safety electrostatic dust removal structure with a working voltage of 20-40kV. The cavity is covered with a polytetrafluoroethylene insulation layer and is equipped with a spark detection sensor and a fast power-off protection device. In case of abnormal discharge, the high voltage is cut off within 0.1s and inert gas is added for dilution.

8. The system according to claim 1, characterized in that, The inert gas protection unit adopts a closed-loop argon or nitrogen protection system with closed-loop inert gas micro-positive pressure protection and stable oxygen content ≤200ppm.

9. The system according to claim 8, characterized in that, The micro-positive pressure is 0.03-0.05 MPa.

10. A method for recovering and filtering powder used in laser melting additive manufacturing, employing the system described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. The metal powder to be recycled enters the closed feeding unit and proceeds to step S2. S2. The metal powder to be recovered enters the separation unit for pretreatment. The pretreatment is the first screening to remove large particles, and then proceeds to step S3. S3. The metal powder to be recovered enters the vibration unit for a second screening, and then proceeds to step S4. S4. The metal powder to be recovered enters the dust removal unit for a third screening and then exits the silo.

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