DE102021130258A1 - Process for the production of mechanically prepared flowable iron-based powders for additive manufacturing - Google Patents

Abstract

The object of the invention is to produce an easily flowable metal powder with a high bulk density for additive manufacturing from iron-based scrap, which consists of a simplified combined manufacturing process of mechanical crushing and mechanical shaping and can be manufactured without the use of components that are harmful to health. The aim is to improve the flowability and bulk density of the metal powder and thus the efficiency of the additive manufacturing process. In addition, the use of scrap as the starting material and a non-melting-based process route are intended to improve the economics and ecological footprint of the metal powder.

Description

The invention relates to a process for the production of mechanically prepared metal powders with particularly good flow properties for additive manufacturing, produced from iron-based scrap, in particular high-quality steels (e.g. 1.2316, 1.2343, 1.2367, 1.2709, 1.2714, 1.4404, 1.4542; according to EN 10027-1 and 10027-2), a process for its production and its use.

Additive manufacturing (AM) is a manufacturing process that is characterized by the fact that the components are built up layer by layer. The resulting components can be designed flexibly. This can include, for example, complex geometric shapes, variable material property profiles, but also combinations of different materials (multi-material design).

Additive manufacturing of metal components is becoming increasingly important. In the period from 2010 to 2020, component production in metal AM increased tenfold. An increase by a factor of 10 is also forecast for the period from 2020 to 2030. (It. Wohlers Report 2017; Strategy & Analysis)

• Pulverbett-Verfahren wie z.B. Selektives Laserschmelzen (Selective Laser Melting (SLM)),
• Selektives Lasersintern (Selective Laser Sintering (SLS));
• Metallabscheidung (Directed Energy Deposition (DED));
• Binderstrahlverfahren (Binder Jetting)

Current manufacturing processes of powder-based metallic AM are divided into the following three basic techniques:

• Powder bed processes such as Selective Laser Melting (SLM)
• Selective Laser Sintering (SLS));
• metal deposition (Directed Energy Deposition (DED));
• Binder Jetting

All of the above-mentioned techniques require a material in fine-grained powder form for the layered construction of metallic materials in order to be able to apply a thin layer to the construction platform and thus achieve a precise component construction.

The iron-based powder required for the AM manufacturing process is usually produced using an atomization process (gas or liquid-based). The metallic powder is produced from the melt by atomization (also called atomization). The aim is to generate spherical metal particles. Requirements for the iron base powder produced in this way can include, for example, low oxygen content, no satellites or porosity, and small deviations from the spherical shape and desired particle size.

The object of the invention is to produce an easily flowable metal powder with a high bulk density for additive manufacturing from iron-based scrap, which consists of a simplified combined manufacturing process of mechanical crushing and mechanical shaping and can be manufactured without the use of components that are harmful to health. The aim is to improve the flowability and bulk density of the powder and thus the efficiency of the additive manufacturing process. In addition, the use of scrap as the starting material and a non-melting-based process route are intended to improve the economics and ecological footprint of the metal powder.

The object described above is achieved by a method according to the invention of simplified combined mechanical comminution and mechanical shaping for metallic powders according to patent claim 1. Further advantageous configurations can be found in the dependent claims.

Mechanically processed metal powder for AM production is produced according to the invention from iron-based materials, in particular high-quality steels (e.g. 1.2316, 1.2343, 1.2367, 1.2709, 1.2714, 1.4404, 1.4542 according to EN 10027-1 and 10027-2), particularly preferably from scrap, mechanically crushed and brought into a form that is very convenient for the AM manufacturing process. The resulting very favorable form of the metal powder is characterized by particularly good flowability and high bulk density, which increases the efficiency and cost-effectiveness of the AM manufacturing process.

A well-flowing metal powder results in a stable AM manufacturing process and consistently high quality. Thanks to a plannable, consistently good flowability, the metal powder can be supplied very precisely within the process, which significantly reduces the production time and the material loss that occurs.

Although atomized spherical metal powder is suitable for large-scale technical applications, it is very expensive compared to semi-finished products due to the production process. According to the invention, it has been found that the positive conveying and processing properties of grains that are shaped as spherically as possible for AM powder processing can be achieved more efficiently by other methods. This means that on an elaborate and resource-intensive production of water-atomized or gas-atomized powders can be dispensed with in favor of mechanically crushed powders. The starting material according to the invention can be taken directly from the processing cycle for single-variety iron-based materials. On the one hand, this approach enables an economical and resource-saving end product, and on the other hand, the supply of raw materials is also largely secured. This includes, for example, crushed steel granules with particle sizes of around 1mm to 5mm and waste from machining (steel shavings). Both are typical standard products of the processing industry.

Another positive effect of the mechanically comminuted iron-base powders produced according to the invention, compared to water-atomized or gas-atomized iron-base powders, is the absence of oxygen and the absence of gas inclusions or porosity. Furthermore, the bulk density in the AM process increases due to the rounded, plate-shaped particle shape, which is characterized by a uniform particle thickness of the powder. The particle length or width are independent of this and can vary. This leads to a number of advantages in the AM process, e.g. lower shrinkage, less gas inclusions or porosity.

The metal powder described is produced according to the invention by mechanically comminuting iron-based scrap, particularly preferably pure steel, and forming it into a particularly free-flowing powder.

• Prozessstufe 1: Zerkleinerung des Ausgangsmaterials auf Eisenbasisschrotten (Granulat, Späne) In Prozessstufe 1 wird das Ausgangsmaterial, auf Eisenbasisschrotten, mechanisch zerkleinert, ausgehend von einer Granulat-Körnung zwischen beispielsweise 1 mm bis 5mm (1, a) oder Spänen (1, b) in vergleichbarer Größe zu einem Zwischenprodukt in Form eines feinkörnigen Pulvers mit einer mittleren Partikelgröße von beispielsweise 50µm.
• Prozessstufe 2: Formung eines besonders fließfähigen metallischen Pulvers

According to the invention, the production processes can particularly preferably take place in two process stages:

• Process stage 1: comminution of the starting material, iron-based scrap (granules, chips) In process stage 1, the starting material, iron-based scrap, is mechanically comminuted, starting with a granulate grain size between 1 mm and 5 mm ( 1, a ) or chips ( 1, b ) of a comparable size to an intermediate product in the form of a fine-grained powder with an average particle size of, for example, 50 µm.
• Process stage 2: Formation of a particularly free-flowing metallic powder

In process stage 2, the crushed intermediate product from process stage 1 is turned into a particularly free-flowing metallic powder ( 2 ) with high bulk density ( 3 ) by adjusting the grinding parameters, temperature, duration and speed, preferably adjusted in such a way that a final contour powder shaping proceeds reliably without smearing the material. The formation of the plate-shaped particles is characterized by a uniform particle thickness of the powder of, for example, 10 μm.

According to the invention, high-energy mills such as eccentric vibratory mills are suitable devices for large-scale comminution tasks.

According to the invention, process stages 1 and 2 can be combined within one operation of a high-energy mill. The input material in the form of iron-based granules (particle size e.g. 1mm to 5mm) or chips of a comparable size can be crushed into a well-flowing, rounded plate-shaped powder form (e.g. particle plate thickness of 10µm) in an eccentric vibratory mill in particular.

Claims (7)

Process for the production of a mechanically processed iron-based powder, preferably as pure steel scrap, in any bulk form, for additive manufacturing, in the same device, a high-energy mill, in one operation, characterized by the combination of the process stages: - Crushing of the iron-based scrap starting material and - formation of a particularly flowable plate-shaped iron base powder procedure after claim 1 , characterized in that the plate-shaped iron base powder has a high bulk density after production. Procedure according to claims 1 and 2 , characterized in that there are no changes in the physical material properties between the introduced iron base material and the metal powder produced. Procedure according to one of Claims 1 until 3 , characterized in that the iron base powder has a very low to no oxygen content after production. Procedure according to one of Claims 1 until 3 , characterized in that the iron base powder has very little to no gas inclusions after production. Procedure according to one of Claims 1 until 3 characterized in that the iron base powder has very low to no porosity after manufacture. Procedure according to one of Claims 1 until 6 characterized in that the use of the iron-based powder leads to very low or no porosity in additively manufactured components.

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