Multi-nozzle multi-field assisted selective laser melting forming method and device

Abstract

The application provides a multi-nozzle multi-field assisted selective laser melting forming method, which comprises a laser generating system, a control system, an electromagnetic energy field device, an ultrasonic energy field device, a heating device, a forming cavity, an oxygen detection system and a multi-nozzle powder feeding device. The method is characterized in that the selective laser melting requires less powder, thereby reducing the cost, the powder is preheated by the heating device, the existence time of the molten pool is increased, the thermal stress in the forming of the workpiece is eliminated, the ultrasonic energy field device and the electromagnetic energy field device are turned on to act on the molten pool, which is beneficial to the spreading and directional flow of the molten pool, enhances the particle rearrangement process and eliminates defects such as cracks and pores. The purpose is to improve the density of the formed workpiece and improve the use performance of the workpiece. The application also provides a multi-nozzle multi-field assisted selective laser melting forming device.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing of materials, and specifically relates to a multi-nozzle type multi-field assisted selective laser melting forming method and apparatus. Background Technology

[0002] Selective laser melting (SLM) is a type of additive manufacturing technology. Based on a digital model, this technology uses a computer-controlled laser beam to melt pre-laid metal powder and build up the workpiece layer by layer. It has advantages such as rapidly manufacturing workpieces of arbitrary shapes, shortening product manufacturing cycles, and having a wide variety of available materials.

[0003] This invention primarily addresses the following two problems. Problem 1: Currently, in selective laser melting (SLM) technology for printing alloys, to reduce segregation, two or more metal powders are typically ball-milled to achieve uniform powder mixing and pre-alloying, or pre-alloyed powder is used directly as the raw material. However, ball milling deforms spherical powders, which is detrimental to powder spreading and printing. If pre-alloyed powder is used directly, the initial powder processing is extensive, the process is complex, and the cost is high. Furthermore, simply using a doctor blade for powder spreading requires precise control over the powder's shape and particle size distribution. Under certain layer thickness requirements, if the powder is non-spherical or has a wide particle size distribution, the doctor blade is easily damaged. Therefore, if it is possible to directly use multi-component powders to print alloys without ball milling, achieving both cost reduction and uniform powder mixing while minimizing doctor blade damage, this can be achieved by adding a new powder feeding method—a multi-nozzle system. Question 2: In the process of printing alloys using selective laser melting (SLM), because metal powder has a certain reflectivity to laser light, if the laser energy density is too high, the reflected laser light can easily damage the equipment. Therefore, during printing, the laser energy density should be reduced as much as possible while still reaching the alloy's melting point to prevent equipment damage and increase its lifespan. However, at low laser energy, the time from melting to solidification of metal powder is shortened, and the temperature also decreases. This results in poor molten pool flow, making it difficult for the molten pool to spread out. Poor particle rearrangement is accompanied by spheroidization, ultimately leading to reduced alloy density and defects such as cracks and porosity, severely affecting the performance of the formed workpiece. Therefore, how to enhance molten pool flow and make it easier to spread out the molten pool at low laser energy densities is of great significance for selective laser melting forming.

[0004] To address the aforementioned issues, relevant scholars have proposed process improvements. Currently, a domestic patent application (patent number 202110349624.4) describes an apparatus and method for preparing pure tungsten parts by selective laser sintering with ultrasonic-assisted powder spreading. However, while applying ultrasonic vibration to a scraper homogenizes the powder spreading, it does not affect the molten pool during forming, resulting in only a limited improvement in the final product quality. An invention patent (application number 202210170587.5) introduces air-gap ultrasonic vibration technology into laser cladding, applying ultrasound to the molten pool to address issues such as porosity defects caused by insufficient gas escape during melting. However, relying solely on a single energy field for assistance is not ideal.

[0005] Therefore, reducing printing costs, homogenizing the composition of selective laser melting alloys, and controlling the microstructure during the solidification process of molten metal to reduce internal defects in the formed workpiece and improve workpiece quality have become urgent problems to be solved in the process of industrial application and promotion. Summary of the Invention

[0006] To address the problems of existing methods, this invention proposes a method for selective laser melting using a multi-nozzle feeding device and three external energy fields: heat, magnetism, and ultrasound. The multi-nozzle feeding device eliminates the need for pre-alloyed powder. During the process, the metal powder to be melted is digitally positioned to achieve powder mixing. The substrate is preheated by a heating device, and after reaching a predetermined temperature, the ultrasonic and electromagnetic energy fields are sequentially activated to assist the entire metal printing process. This enhances molten pool fluidity, improves particle rearrangement, reduces spheroidization, and minimizes porosity and cracks, thereby achieving the goal of preparing high-performance alloy workpieces. This invention also provides a multi-nozzle, multi-field assisted selective laser melting and forming device.

[0007] This invention is achieved through the following technical solution:

[0008] A multi-nozzle, multi-field assisted selective laser melting forming method includes the following steps:

[0009] Step 1: Polish, clean and dry the substrate, and place it in the molding cylinder;

[0010] Step 2: Place the high-melting-point metal in the powder supply cylinder and the low-melting-point metal in the nozzle;

[0011] Step 3: Adjust the powder spreading shaft to pre-spread the high melting point metal powder onto the substrate with a suitable layer thickness, and use a heating device to adjust to the preset temperature to preheat the substrate.

[0012] Step 4: When the temperature of the metal powder reaches the preset temperature, the corresponding frequency and intensity are preset in the ultrasonic energy field device according to the different inherent frequencies of substances in different states.

[0013] Step 5: Turn on the laser, and simultaneously eject low-melting-point metal from the nozzle to a preset position for melting under the control of the control system. Simultaneously, activate the ultrasonic energy field device and the electromagnetic energy field device for auxiliary printing.

[0014] Step 6: After the first layer melts and solidifies, use a file to smooth the first layer before applying the second layer of powder, and then repeat step 5.

[0015] Step 7: Repeat steps 5 and 6 until the workpiece is formed.

[0016] Preferably, the heating device in step 3 heats the substrate and remains on throughout the melting process;

[0017] Preferably, the ultrasonic energy field device and the electromagnetic energy field device described in step 5 are turned on during the melting process and turned off during the powder spreading process;

[0018] Preferably, in step 6, the file and the powder spreader can operate simultaneously or separately, but the file goes first and the powder spreader goes later.

[0019] The present invention also provides a multi-nozzle type multi-field assisted selective laser melting and forming device, including a laser generating system, a control system, an electromagnetic energy field device, an ultrasonic energy field device, a heating device, a forming cavity, an oxygen detection system, and a multi-nozzle powder feeding device.

[0020] Preferably, the laser generating system can be composed of a CO2 laser, an Nd:YAG laser, or a fiber laser to meet the needs of printing various materials, and finally, an XY scanner and a computer are added.

[0021] Preferably, the control system coordinates the operation of other working devices in the selective laser melting process.

[0022] Preferably, the electromagnetic energy field device is used to generate an electromagnetic field, the ultrasonic energy field device is used to emit ultrasonic vibrations, and the heating device is used to heat the substrate. The three devices work simultaneously in the laser melting process.

[0023] Preferably, the molding cavity consists of a powder supply cylinder, a molding cylinder, a powder recovery cylinder, and a transmission device at the bottom of each cylinder, with the transmission device controlling the up-and-down movement of the molding platform.

[0024] Preferably, the oxygen detection system is used to detect the oxygen content in the molding cavity. During the molding process, the molding cavity is filled with protective gases such as nitrogen or argon to prevent the workpiece from oxidizing.

[0025] Preferably, the multi-nozzle powder feeding device includes a control platform, several nozzles, and a nozzle rotation shaft, used to spray low-melting-point metal powder during laser melting.

[0026] The present invention has the following beneficial effects:

[0027] 1. This invention uses a multi-nozzle powder feeding device to place two or more powders in the powder feeding nozzle, enabling mixed printing of multiple metals. When printing multi-component alloys, there is no need to use pre-alloyed powder, which can reduce costs. During the printing process, there is no need to be limited by the metal powder in the powder supply cylinder, which can achieve flexible powder changing. There is also no need to be limited by the poor powder spreading effect caused by the size and shape of powder particles, which reduces the requirements for powder use.

[0028] 2. This invention controls different ultrasonic frequencies, intensities, and wavelengths through an ultrasonic energy field device, which is beneficial to the flow of metal powder in the molten pool, enhances particle rearrangement, improves grain refinement, thereby increasing workpiece density and performance.

[0029] 3. This invention uses an electromagnetic energy field device to control different voltages to generate magnetic fields of different intensities, which can cause the molten pool to flow in a directional manner, which is beneficial to the refinement and homogenization of the microstructure, reduce defects, and improve the performance of the workpiece.

[0030] 4. The heating device of the present invention preheats the metal powder, which is beneficial to the heat conduction between particles and prolongs the existence time of the molten pool.

[0031] 5. This invention is a selective laser melting method that is easy to operate, highly versatile, flexible in control, digitalized, industrialized, and commercially viable. Attached Figure Description

[0032] Figure 1 This is a structural diagram of a multi-nozzle type multi-field assisted selective laser melting and forming device according to the present invention.

[0033] Figure 2 This is a top view of the molding cavity.

[0034] Explanation of the component labels in the diagram:

[0035] 1: Laser; 2: XY scanner; 3: Computer; 4: Electromagnetic generator; 5: Electromagnetic energy field control console; 6: File; 7: Powder spreading scraper; 8: Multiple nozzles; 9: Inert gas outlet; 10: Multi-nozzle control console; 11: Forming cylinder; 12: Powder supply cylinder; 13: Powder recovery cylinder; 14: Oxygen detection device; 15: Heating device; 16: Ultrasonic energy field device; 17: Transmission plate; 18: Substrate Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example 1:

[0038] like Figure 1 The image shows a multi-nozzle, multi-field assisted selective laser melting and forming device. The following section combines... Figure 1 Detailed explanation of the specific steps of the method described in this invention:

[0039] 1) First, place the polished, cleaned and dried substrate 18 onto the molding cylinder 11;

[0040] 2) Place spherical tungsten powder with D50 = 40μm in the powder supply cylinder 12, and use the computer 3 to control the powder spreading scraper 7 to spread tungsten powder with a layer thickness of 50μm onto the substrate 18.

[0041] 3) Place the spherical copper powder into the nozzle 8, and set the powder feeding rate, powder feeding interval, and powder feeding positioning in the multi-nozzle control console 10;

[0042] 4) Turn on the heating device 15 and set it to 200°C. Preheat the tungsten powder through the heating substrate 18 and monitor the temperature of the tungsten powder on the surface in real time.

[0043] 5) Set the parameters of laser 1 through computer 3. The parameters are: laser power 300W~500W, spot diameter 60μm~100μm, scanning speed 300mm / s~1000mm / s, scanning interval 30μm~50μm. Turn on laser 1. The laser is reflected by the mirror in XY scanner 2, and after being focused by the focusing lens, it is irradiated onto the tungsten powder.

[0044] 6) While turning on the laser 1, turn on the nozzle 8 to position and transport the copper powder. At the same time, adjust the voltage through the electromagnetic energy field control console 5, turn on the electromagnetic generator 4, and turn on the ultrasonic energy field device 16 to apply ultrasonic waves with a frequency of 10-100kHz to assist the melting process.

[0045] 7) After one layer of powder melts and solidifies, use a file to flatten the first layer, then apply and spray the second layer of powder in preparation for printing the next layer. Then repeat step 6).

[0046] 8) After the molding part has been printed layer by layer, turn off the heating device 15, the ultrasonic energy field device 16, and the electromagnetic generator 4, and wait for them to cool down.

[0047] 9) Remove the molded part and use wire cutting to remove it.

[0048] The above description is merely a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment and the accompanying drawings. Therefore, any equivalent or modified versions made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A multi-nozzle, multi-field assisted selective laser melting and forming method, characterized in that, Includes the following steps: (a) First, place the polished, cleaned and dried substrate (18) on the molding cylinder (11); (ii) Place the high melting point tungsten powder in the powder supply cylinder (12), and use the computer (3) to control the powder spreading scraper (7) to spread the high melting point tungsten powder onto the substrate (18); (iii) Place the low-melting-point metal powder in the multi-nozzle (8) and set the powder feeding rate, powder feeding interval and powder feeding positioning in the multi-nozzle control platform (10); (iv) Turn on the heating device (15) and set it to the preset temperature. Preheat the tungsten powder through the heating substrate (18) and monitor the temperature of the tungsten powder on the surface in real time. (v) Set the parameters of the laser (1) through the computer (3). The parameters include laser power, spot diameter, scanning speed and scanning distance. Turn on the laser (1). The laser is reflected by the mirror in the XY scanner (2). After being focused by the focusing lens, it is irradiated onto the high melting point tungsten powder. (vi) While turning on the laser (1), turn on the multi-nozzle (8) to position and transport the low melting point metal powder. At the same time, adjust the voltage through the electromagnetic energy field control console (5), turn on the electromagnetic generator (4), and turn on the ultrasonic energy field device (16) to apply ultrasonic waves to assist the melting process. (vii) After the first layer of powder melts and solidifies, use a file to flatten the first layer, then spread and spray the second layer of powder in preparation for the next layer of printing, and then repeat step (vi). (viii) After the molding part is printed layer by layer, turn off the heating device (15), ultrasonic energy field device (16) and electromagnetic generator (4) and wait for it to cool down; In step (six), the multi-nozzle (8) is opened synchronously with the laser, electromagnetic energy field device and ultrasonic energy field device, and during the melting process, laser irradiation and nozzle powder feeding are carried out simultaneously. In step (seven), the file (6) and the scraper (7) operate simultaneously or in stages. After one layer of printing is completed, the file always goes first and the scraper goes last. In step (seven), the file (6) is set to be parallel or perpendicular to the scraper (7), that is, it moves left and right or back and forth on the substrate.

2. The multi-nozzle multi-field assisted selective laser melting forming method according to claim 1, characterized in that, The powder loading categories for the multi-nozzle (8) in step (iii) are single-component powder, mixed powder, and pre-alloyed powder.

3. A multi-nozzle multi-field assisted selective laser melting and forming apparatus for performing the multi-nozzle multi-field assisted selective laser melting and forming method according to any one of claims 1-2, comprising a laser, a control system, an electromagnetic energy field device, an ultrasonic energy field device, a heating device, a forming cavity, an oxygen detection system, and a multi-nozzle powder feeding device.

4. The multi-nozzle type multi-field assisted selective laser melting and forming device according to claim 3, characterized in that, The multi-nozzle powder feeding device includes a multi-nozzle control platform (10), several nozzles (8), and a nozzle rotation shaft. The multi-nozzle control platform controls the powder feeding rate, powder feeding interval, and powder feeding positioning.

5. The multi-nozzle type multi-field assisted selective laser melting and forming device according to claim 3, characterized in that, When the ultrasonic energy field device (16) acts on the molten pool, it acts on a local area or the entire area.

6. The multi-nozzle type multi-field assisted selective laser melting and forming device according to claim 3, characterized in that, The electromagnetic energy field device includes an electromagnetic energy field control console (5) and an electromagnetic generator (4). The electromagnetic energy field control console (5) is set with different frequencies, voltages, and intensities. The electromagnetic generator (4) controls the direction of the flow of the molten pool by setting different regions acting on the molten pool.

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