Preparation method of coated powder capable of being used for cold metal melting additive manufacturing

Abstract

The invention discloses a preparation method of coated powder capable of being used for cold metal melting additive manufacturing, and belongs to the technical field of additive manufacturing, the preparation method comprises the following steps: S1, metal powder and polymer binder powder are respectively weighed according to a mass ratio by adopting an electronic balance; s2, dissolving polymer binder powder, and adding the metal powder in the S1; S3, coating the polymer binder on the metal powder through a solvent precipitation method to obtain composite powder coated with the polymer binder; according to the method, the blank can be prepared through low-temperature sintering by using laser sintering equipment only by using extremely few low-temperature binders in the preparation of the low-temperature composite powder, and different from forming by adopting high-temperature molten metal powder in conventional metal additive manufacturing, thermal stress deformation caused by high-temperature melting can be effectively reduced; and meanwhile, a complex structure which cannot be manufactured due to the influence of thermal stress deformation can be manufactured, so that the quality problems of buckling deformation and the like caused by the existence of high-temperature melting thermal stress are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a method for preparing coated powder that can be used for cold metal melting additive manufacturing. Background Art

[0002] Additive manufacturing technology is an advanced manufacturing technology that is based on a three-dimensional data model and can form metal parts by stacking discrete materials (such as liquid, powder, wire or block) layer by layer and then undergoing post-processing steps. Compared with traditional metal manufacturing technology, additive manufacturing technology has significant advantages such as short manufacturing cycle, no need for molds, high design freedom, integrated molding of complex structures, and high material utilization. It can greatly improve the structural complexity and specific strength of parts and realize rapid and low-cost production of parts.

[0003] Currently, common metal additive manufacturing technologies mainly include powder bed fusion (PBF) and directed energy deposition (DED), which directly apply energy (laser, electron beam or arc) to the metal material itself, and stack discrete metal materials layer by layer through local melting to form metallurgically bonded metal parts. Metal parts prepared by PBF or DED often need to be melted and solidified at ultra-high temperatures, which may introduce more thermal stresses during the manufacturing process, and are prone to warping, deformation and cracking defects, which seriously limit the application scope and quality of metal additives. The current common method to solve warping is to design a support structure during printing, but for parts with complex internal structures, the support structure cannot completely solve the deformation problem caused by thermal stress. At the same time, wire cutting is required to remove the support after printing.

[0004] In order to avoid the above technical problems, it is necessary to provide a method for preparing coated powder that can be used for cold metal melting additive manufacturing to overcome the above defects in the prior art. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing coated powder that can be used for cold metal melting additive manufacturing, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing coated powder that can be used for cold metal melting additive manufacturing, comprising the following steps:

[0007] S1. Weigh the metal powder and the polymer binder powder respectively according to the mass ratio using an electronic balance;

[0008] S2. Dissolve the polymer binder powder and add the metal powder in S1:

[0009] S3, coating the metal powder with a polymer binder by a solvent precipitation method to obtain a composite powder coated with the polymer binder;

[0010] S4. Obtain a metal part prepared from the powder of S3.

[0011] As a preferred embodiment, the melting point of the polymer binder is 50-100°C.

[0012] As a preferred embodiment, the proportion of the metal powder is 85% to 98%, and the proportion of the polymer binder is 2% to 15%.

[0013] As a preferred embodiment, the metal powder is 316L stainless steel powder, the particle size of the metal powder is 15-80 μm, and the thickness of the binder shell of the composite powder is 5-10 μm.

[0014] As a preferred embodiment, the polymer binder powder is dissolved and the metal powder in S1 is added by adding the weighed polymer binder powder into the solvent, gradually heating to a temperature close to the boiling point of the solvent, stirring continuously until the binder is completely dissolved, and then adding the metal powder in step S1.

[0015] As a preferred embodiment, the method of coating the metal powder with a polymer binder by a solvent precipitation method comprises the following steps:

[0016] Step 1, keep the S2 solvent warm for 0.5-2h, then stop heating and gradually cool it to room temperature;

[0017] Step 2, the solvent in step 1 is continuously stirred, and the adhesive is gradually precipitated on the surface of the metal particles;

[0018] Step 3: Filter, dry, grind and sieve the remaining material in the above step 2, select powder with a particle size less than 80 μm, and obtain a composite powder coated with an adhesive.

[0019] As a preferred embodiment, the step of obtaining a metal part prepared from the powder of S3 comprises the following steps:

[0020] Step 1, sintering the composite powder coated with a polymer binder by selective laser sintering technology to form a preform;

[0021] Step 2: Degreasing and secondary sintering the preform under vacuum or atmosphere protection to obtain a dense metal part.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention only requires a small amount of low-temperature binder to prepare the low-temperature composite powder, and can use the existing common laser sintering equipment to perform low-temperature sintering to prepare the green body. Different from the conventional metal additive manufacturing that uses high-temperature molten metal powder to form, the thermal stress deformation caused by high-temperature melting can be effectively reduced. At the same time, complex structures that cannot be manufactured due to the influence of thermal stress deformation can be prepared, thereby avoiding quality problems such as warping deformation caused by the existence of thermal stress caused by high-temperature melting.

[0024] The present invention uses an electronic balance to accurately weigh metal powder and polymer binder powder, and then obtains coated powder through steps such as dissolution, solvent precipitation coating, and screening. The existing common laser sintering equipment can be used to perform low-temperature sintering to prepare a green body. At the same time, there is a certain flexibility in the selection of binders. One or a mixture of epoxy resin powder, polyethylene glycol, polyaldehyde resin, and polyethylene oxide powder can be used, which can be adjusted according to different needs. Moreover, parameters such as the metal powder ratio of 85%-98% and the binder shell thickness of 5-10μm can also be optimized within a certain range to adapt to different application scenarios and performance requirements. This makes the technology widely applicable in the field of metal additive manufacturing and easy to promote and apply.

[0025] The present invention, by adopting a low-temperature sintering process, does not need to operate at ultra-high temperatures like traditional metal additive manufacturing, so the requirements for the high temperature resistance of the equipment are reduced, and the equipment cost and maintenance cost are also reduced accordingly. At the same time, in the preparation process, dense metal parts with complex shapes can be quickly prepared in batches, which improves production efficiency and the production benefits of the enterprise, and has significant economic advantages in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process of preparing coated powder by cold metal melting additive manufacturing of the present invention;

[0027] Figure 2 This is a scanning electron microscope schematic diagram of epoxy resin coated powder prepared in Example 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of a scanning electron microscope of polyethylene glycol-coated powder prepared in Example 2 of the present invention;

[0029] Figure 4 This is a scanning electron microscope diagram of the polyaldehyde resin coated powder prepared in Example 3 of the present invention;

[0030] Figure 5 This is a schematic diagram of a scanning electron microscope of the epoxy resin and polyethylene glycol composite coated powder prepared in Example 4 of the present invention;

[0031] Figure 6This is a schematic diagram of preparing a sample by low-temperature sintering of the coated powder of the present invention using a laser sintering device. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the embodiments.

[0033] The following examples are used to illustrate the present invention, but they cannot be used to limit the scope of protection of the present invention. The conditions in the examples can be further adjusted according to specific conditions. Simple improvements to the method of the present invention under the premise of the concept of the present invention belong to the scope of protection claimed in the present invention.

[0034] See also Figure 1-6 The present invention provides a method for preparing coated powder that can be used for cold metal melting additive manufacturing, comprising the following steps:

[0035] S1. Weigh the metal powder and the polymer binder powder respectively according to the mass ratio using an electronic balance;

[0036] S2. Dissolve the polymer binder powder and add the metal powder in S1:

[0037] S3, coating the metal powder with a polymer binder by a solvent precipitation method to obtain a composite powder coated with the polymer binder;

[0038] S4. Obtain a metal part prepared from the powder of S3.

[0039] The preparation of low-temperature composite powder only requires a very small amount of low-temperature binder, and the existing common laser sintering equipment can be used to perform low-temperature sintering to prepare the green body. This is different from the high-temperature molten metal powder forming used in conventional metal additive manufacturing. It can effectively reduce the thermal stress deformation caused by high-temperature melting. At the same time, it can prepare complex structures that cannot be manufactured due to the influence of thermal stress deformation, thereby avoiding quality problems such as warping deformation caused by the existence of thermal stress caused by high-temperature melting.

[0040] The melting point of the polymer binder is 50-100° C. The polymer binder is one or a mixture of epoxy resin powder, polyethylene glycol, polyaldehyde resin and polyethylene oxide powder.

[0041] The proportion of metal powder is 85% to 98%, and the proportion of polymer binder is 2% to 15%.

[0042] The metal powder is 316L stainless steel powder, the particle size of the metal powder is 15-80 μm, and the thickness of the binder shell of the composite powder is 5-10 μm.

[0043] The polymer binder powder is dissolved and the metal powder in step S1 is added. The weighed polymer binder powder is added to the solvent, gradually heated to a temperature close to the boiling point of the solvent, and stirred continuously until the binder is completely dissolved, and then the metal powder in step S1 is added.

[0044] The metal powder and the polymer binder powder are accurately weighed by an electronic balance, and then the coated powder is obtained through the steps of dissolution, solvent precipitation coating, screening, etc., and the green body can be prepared by low-temperature sintering using the existing common laser sintering equipment. At the same time, there is a certain flexibility in the selection of the binder, and one or a mixture of epoxy resin powder, polyethylene glycol, polyaldehyde resin, and polyethylene oxide powder can be used, which can be adjusted according to different needs. Moreover, parameters such as the metal powder ratio of 85%-98% and the binder shell thickness of 5-10μm can also be optimized within a certain range to adapt to different application scenarios and performance requirements. This makes the technology widely applicable in the field of metal additive manufacturing and easy to promote and apply.

[0045] The polymer binder is coated on the metal powder by a solvent precipitation method, comprising the following steps:

[0046] Step 1, keep the S2 solvent warm for 0.5-2h, then stop heating and gradually cool it to room temperature;

[0047] Step 2, the solvent in step 1 is continuously stirred, and the adhesive is gradually precipitated on the surface of the metal particles;

[0048] Step 3: Filter, dry, grind and sieve the remaining material in the above step 2, select powder with a particle size less than 80 μm, and obtain a composite powder coated with an adhesive.

[0049] Obtaining a metal part prepared from S3 powder includes the following steps:

[0050] Step 1, sintering the composite powder coated with a polymer binder by selective laser sintering technology to form a preform;

[0051] Step 2: Degreasing and secondary sintering the preform under vacuum or atmosphere protection to obtain a dense metal part.

[0052] By adopting the low-temperature sintering process, there is no need to operate at ultra-high temperatures like traditional metal additive manufacturing, so the requirements for the high temperature resistance of the equipment are reduced, and the equipment cost and maintenance cost are also reduced accordingly. At the same time, during the preparation process, dense metal parts with complex shapes can be prepared in batches quickly, which improves production efficiency and the production benefits of the enterprise, and has significant economic advantages in industrial production.

[0053] Embodiment 1

[0054] S1 Weighing: Use an electronic balance to weigh 316L metal powder and epoxy resin powder according to the mass ratio; the particle size of 316L metal powder is 25-50μm, the softening point of epoxy resin is 85-95℃, the epoxy value equivalent is 714-833e / gp, and the mass ratio of 316L metal powder to epoxy resin is 95:5;

[0055] S2 dissolution: add the weighed epoxy resin into the ethanol solvent, stir the solution and gradually heat it to 80°C. After the epoxy resin is completely dissolved, add 316L powder into the solution;

[0056] S3 coating: After adding 316L metal powder, keep warm for 1 hour, stop heating, and gradually cool to room temperature while stirring continuously during the process;

[0057] S4 screening: filter the remaining solution, dry it at 70-80°C, grind it after drying, and finally screen it with a sieve to obtain epoxy resin-coated 316L "core-shell" structure powder with a particle size of less than 80 μm;

[0058] Embodiment 2

[0059] S1 Weighing: Use an electronic balance to weigh 316L metal powder and polyethylene glycol resin respectively according to the mass ratio; the particle size of 316L metal powder is 25-50μm, the melting point of polyethylene glycol is 60℃, and the mass ratio of 316L metal powder to polyethylene glycol resin is 95:5;

[0060] S2 dissolution: Add the weighed polyethylene glycol into ethyl acetate solvent, stir the solution and gradually heat it to 50°C. After the polyethylene glycol resin is completely dissolved, add 316L powder to the solution;

[0061] S3 coating: After adding 316L metal powder, keep warm for 0.5h, stop heating, and gradually cool to room temperature while stirring continuously during the process;

[0062] S4 screening: filter the remaining solution, dry it at 40-50°C, grind it after drying, and finally screen it with a sieve to obtain polyethylene glycol-coated 316L "core-shell" structure powder with a particle size of less than 80 μm;

[0063] Embodiment 3

[0064] S1 Weighing: Use an electronic balance to weigh 316L metal powder and polyaldehyde resin according to the mass ratio; the particle size of 316L metal powder is 25-50μm, the melting point of polyaldehyde resin is 95℃, and the mass ratio of 316L metal powder to polyaldehyde resin is 92.5:7.5;

[0065] S2 dissolution: add the weighed polyaldehyde resin into ethyl acetate solvent, stir the solution and gradually heat it to 60°C. After the polyaldehyde resin is completely dissolved, add 316L powder into the solution;

[0066] S3 coating: After adding 316L metal powder, keep warm for 1.5h, stop heating, and gradually cool to room temperature while stirring continuously during the process;

[0067] S4 screening: filter the remaining solution, dry it at 80-90°C, grind it after drying, and finally screen it with a sieve to obtain a polyaldehyde resin-coated 316L "core-shell" structure powder with a particle size of less than 80 μm;

[0068] Embodiment 4

[0069] S1 Weighing: Use an electronic balance to weigh 316L metal powder, epoxy resin and polyethylene glycol resin respectively according to the mass ratio; the particle size of 316L metal powder is 25-50μm, the softening point of epoxy resin is 85-95℃, the epoxy value equivalent is 714-833e / gp, the melting point of polyethylene glycol resin is 60℃, and the mass ratio of 316L metal powder, epoxy resin and polyethylene glycol resin is 92.5:2.5:5;

[0070] S2 dissolution: add the weighed polyethylene glycol and epoxy resin into the ethanol solvent, stir the solution and gradually heat it to 50°C. After the polyethylene glycol and epoxy resin are completely dissolved, add 316L powder into the solution;

[0071] S3 coating: After adding 316L metal powder, keep warm for 2 hours, stop heating, and gradually cool to room temperature while stirring continuously during the process;

[0072] S4 screening: filter the remaining solution, dry it at 40-50℃, grind it after drying, and finally screen it with a sieve to obtain epoxy resin and polyethylene glycol-coated 316L "core-shell" structure powder with a particle size of less than 80μm.

[0073] The working principle and use process of the present invention are as follows: first, 316L stainless steel powder with a particle size of 15-80 μm and polymer binder powder are weighed with an electronic balance according to the mass ratio of a specific metal powder to a binder, and then the binder powder is added to a suitable solvent, heated to a point close to the boiling point to dissolve, and then the metal powder is added and mixed, followed by heat preservation, cooling and stirring, so that the binder is precipitated on the surface of the metal powder due to a change in solubility to form a 5-10 μm thick coating layer, and the composite powder is obtained by filtering, drying, grinding and screening. The principle is to use a solvent precipitation method to achieve coating based on the physical properties between the binder, the solvent and the metal powder, and then the composite powder is selectively sintered by laser. Based on the low melting point of the binder, the bonding metal powder is first melted into a preform, and then the binder is degreased to remove the binder under vacuum or atmosphere protection, and the density is increased by secondary sintering, so as to finally obtain a dense metal part with excellent performance, avoiding the thermal stress problem of the traditional high-temperature melting process, and ensuring the tensile strength, elongation at break and dimensional accuracy of the parts.

[0074] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing coated powder that can be used for cold metal melting additive manufacturing, characterized in that: The following steps are involved: S1. Weigh the metal powder and the polymer binder powder respectively according to the mass ratio using an electronic balance; S2. Dissolve the polymer binder powder and add the metal powder in S1: S3, coating the metal powder with a polymer binder by a solvent precipitation method to obtain a composite powder coated with the polymer binder; S4. Obtain a metal part prepared from the powder of S3.

2. A method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The melting point of the polymer binder is 50-100°C.

3. A method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The proportion of the metal powder is 85% to 98%, and the proportion of the polymer adhesive is 2% to 15%.

4. A method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The metal powder is 316L stainless steel powder, the particle size of the metal powder is 15-80 μm, and the thickness of the binder shell of the composite powder is 5-10 μm.

5. The method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The polymer binder powder is dissolved and the metal powder in step S1 is added, by adding the weighed polymer binder powder into the solvent, gradually heating to a temperature close to the boiling point of the solvent, stirring continuously until the binder is completely dissolved, and then adding the metal powder in step S1.

6. The method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The method of coating the metal powder with a polymer binder by a solvent precipitation method comprises the following steps: Step 1, keep the S2 solvent warm for 0.5-2h, then stop heating and gradually cool it to room temperature; Step 2, the solvent in step 1 is continuously stirred, and the adhesive is gradually precipitated on the surface of the metal particles; Step 3: Filter, dry, grind and sieve the remaining material in the above step 2, select powder with a particle size less than 80 μm, and obtain a composite powder coated with an adhesive.

7. A method for preparing coated powder for cold metal melting additive manufacturing according to claim 1, characterized in that: The step of obtaining a metal part prepared from the powder of S3 comprises the following steps: Step 1, sintering the composite powder coated with a polymer binder by selective laser sintering technology to form a preform; Step 2: Degreasing and secondary sintering the preform under vacuum or atmosphere protection to obtain a dense metal part.

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