DE102019206451A1 - Process for 3D printing in a protective gas atmosphere and 3D printing device - Google Patents

Abstract

A 3D printing method has the following steps: providing (M11) a melt component, which is selected from the group of metallic materials, metallic material combinations and metallic alloys, in a powder mixture (P); Generating (M12) a protective gas atmosphere in a 3D printing device (10), the protective gas of the protective gas atmosphere having a protective gas of the protective gas atmosphere having at least one portion selected from the group of noble gases and preferably neon and / or having at least one inert gas portion ; and laser melting (M13) the powder mixture (P) in a selective laser melting process, in a work area of the 3D printing device (10), the powder mixture (P) having a melting component selected from the third main group of the periodic table.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a 3D printing device and a method for 3D printing, in particular for the production of components with improved material properties in the aerospace sector.

TECHNICAL BACKGROUND

Stereolithography ("stereolithography", SLA), selective laser sintering ("selective laser sintering", SLS) and selective laser melting ("selective laser melting", SLM) belong to the group of generative manufacturing processes and are commonly referred to as "3D printing processes". On the basis of geometric models, data sets are generated that are used in a special generative manufacturing system for the production of objects of a predefined shape from shapeless materials such as liquids and powders with shape-neutral semi-finished products such as strip, wire or web-shaped material using chemical and / or physical processes be used. 3D printing processes use additive processes in which the starting material is built up sequentially in predetermined shapes.

In the case of selective laser melting (SLM), 3D printing is also referred to by the term laser powder bed melting (LPB-S), which is a so-called additive component (& material) production / manufacturing method can also be used for metallic materials (powder), which for certain materials is viewed as a technology with some potential, also from an economic point of view.

3D printing processes are currently widespread in the production of prototypes or in rapid product development (RPD), in which a resource-efficient process chain is used for the needs-based small and large series production of individualized components. 3D printing processes are widely used in civil engineering, architecture, dental technology, tool making, implantology, industrial design, the automotive industry and the aerospace industry.

3D printers use a computer-aided design system ("computer-aided design", CAD) on the one hand and a blasting system on the other hand, which carries out the generative layer structure of the object to be printed on the basis of the digital production model provided by the CAD system. A three-dimensional CAD model of the object to be printed is subjected to a preparation procedure, known as “slicing”, to generate the control data required for the blasting system. The CAD model is digitally broken down into layers of predetermined uniform thickness with layer normals along the direction of construction of the blasting system, which then form the basis for controlling the energy beam on the starting material surface in the blasting system. A conventional layer decomposition algorithm maps the CAD model onto a tiled surface model, which creates a number of closed curves or surface polygons that define the so-called "slices" between two model sections that follow each other vertically due to the direction in which the blasting system is built.

Such surface models can be stored, for example, in the STL format common for stereolithography, which describes the surface geometry of the three-dimensional object to be printed as raw data of unstructured triangular textures. The blasting system reads in the surface model data and converts it into a corresponding control pattern for the laser beam in an SLA, SLS or SLM production process.

3D printing processes such as SLA, SLS or SLM create a lot of design freedom in the manufacture of complex three-dimensional construction elements and components with regard to their geometric shape and structure. A similar freedom would be desirable in the design of specific material properties of the printed parts and components.

SUMMARY OF THE INVENTION

One of the objects of the invention is therefore to find solutions for objects produced in generative manufacturing processes with improved material properties, in particular with the aid of selective laser melting processes.

These and other objects are achieved by a 3D printing method having the features of claim 1 and a powder mixture having the features of claim 9.

According to a first aspect of the invention, the first 3D printing method therefore comprises the steps of providing a melt component, which is selected from the group of metallic materials, metallic material combinations and metallic alloys, in a powder mixture; generating a protective gas atmosphere in a 3D printing device, the protective gas of the protective gas atmosphere having at least one portion selected from the group of noble gases and / or having a nitrogen portion, and the laser melting of the Powder mixture in a selective laser melting process, in a work area of the 3D printing device, the powder mixture having a melt component selected from the third main group of the periodic table.

According to a second aspect of the invention, a powder mixture for use in a 3D printing process comprises a melt component which is selected from the group of metallic materials, metallic material combinations and metallic alloys; and at least one further component which is selected from the group of semimetals, alkaline earth metals and transition metals.

An essential idea of the invention is to modify a conventional 3D printing process by adding reactants that improve or change the material properties of the finished printed object to the printing process and to carry out the printing process itself under a protective gas atmosphere that makes the reaction that takes place easily controllable. This causes a local change in the material properties of the starting material of the 3D printing process during the printing process, in particular the improvement and stabilization of the alloys produced in the printing process and formed in the melt, the qualification of which in turn also benefits the production process itself.

Laser powder bed melting (LPB-S) for materials of the third main group (so-called earth metals), especially aluminum, is usually carried out in a process chamber flooded with protective gas in order to prevent or reduce an undesirable excessive reaction of the material melt with the ambient air or to be able to minimize. Protective gases of choice can be argon, nitrogen or also helium or mixtures thereof. The protective gases in question are also process gases here, because they have an influence on the melt pool dynamics and material production, i.e. in particular on the generated material density and the quality of the product, although there seems to be a need for improvement at these points.

The 3D printing processes mentioned, and of course laser powder bed melting among them, are particularly advantageous because they enable the production of three-dimensional components in primary molding processes without the need for special production tools that are tailored to the external shape of the components. This enables highly efficient, material-saving and time-saving manufacturing processes for parts and components. Such 3D printing processes are particularly advantageous for structural components in the aerospace sector, since there a large number of different components are used that are tailored to special purposes and that are used in such 3D printing processes with low costs, short production lead times and with low complexity in the Production required manufacturing equipment can be manufactured.

Advantageous refinements and developments emerge from the further subclaims and from the description with reference to the figures.

The laser powder bed melting as a 3D printing process according to the invention can, as mentioned, be carried out under a protective gas atmosphere. In one embodiment, the protective gas of the protective gas atmosphere can have at least a portion of neon. In preferred embodiments, the proportion of neon is 50% or more of the protective gas, particularly preferably the protective gas can also consist exclusively of neon. If there is a remaining portion of the protective gas of the protective gas atmosphere that does not consist of neon, this remaining portion of the protective gas can be replaced by at least one further noble gas, at least one against melting of alloys with a melting component from the third main group, in particular aluminum, inert gas and / or at least one gas that reacts with the melt.

According to the invention, a conventionally provided protective gas is therefore used in the 3D printing device, i.e. the LPB-S system, by neon (Ne) or a rich mixed gas, i.e. with at least 50% Ne content. In this way, the material quality and reproducibility that can be achieved in the LPB-S process can be significantly improved through positive manipulation of the melt pool dynamics and the laser-assisted energy transfer. This in turn also has great positive effects on the usability and economy of the LPB-S process for materials with melt constituent (s) from the third main group, in particular for aluminum materials.

According to one embodiment of the powder mixture according to the invention, the melt component can be selected from the group of metallic materials, metallic material combinations and metallic alloys and at least one further component can be selected from the group of semimetals, alkaline earth metals and transition metals.

In preferred embodiments of the powder mixture according to the invention, the melt component can be selected from the group of aluminum or an alloy thereof, the at least one further constituent can particularly preferably be selected from the group consisting of silicon, magnesium, titanium, zirconium, scandium and vanadium. Of course, several of these options can also be selected as additional components.

With the powder mixtures mentioned, the 3D printing process according to the invention can be used to additively produce an alloy of AISi7Mg0.6, for example, an alloy of AISi7Mg0.6, an aluminum material which, in addition to good corrosion resistance, also has very good properties in terms of Combined durability, strength and ductility. With the 3D printing method according to the invention, the strength of the alloy can be strengthened in the powder bed of laser melting during the layer-by-layer structure of the product through a type of particle reinforcement in such a way that its properties in terms of quality and material density can be further improved according to the invention. In this context, nanoscale silicon composites are primarily strengthened in combination with classic precipitation hardening via coherent phases of Mg ₂ Si.

With the 3D printing process according to the invention, alloys made of aluminum-magnesium-scandium can also be produced additively, with these alloys again being able to convince with excellent values in terms of strength and ductility. The microstructure responsible for this is achieved through high cooling rates and rapid solidification, which can more than keep up with the performance of high-quality cast products. By combining the properties of the material with the freedom of design inherent in additive manufacturing, components with a currently unattainable range of functions are possible. The alloys in question can be welded very well, are very corrosion-resistant, have a low coefficient of thermal expansion, a microstructure that is stable over a wide temperature range, can be easily machined with conventional machining methods and their surfaces can be treated using suitable processes. What is particularly striking here is the high strength and low weight, which can be used profitably for reducing the weight of components.

The above configurations and developments can be combined with one another as desired, provided that it makes sense. Further possible configurations, developments and implementations of the invention also include combinations, not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

Figure list

• 1 eine schematische Illustration einer 3D-Druckvorrichtung gemäß einer Ausführungsform der Erfindung;
• 2 eine schematische Illustration von beispielhaften Details einer 3D-Druckvorrichtung der 1, durch welche in der 3D-Druckvorrichtung eine geeignete Schutzgasatmosphäre erzeugt wird, gemäß einer weiteren Ausführungsform der Erfindung;
• 3 ein Blockdiagramm eines 3D-Druckverfahrens gemäß einer Ausführungsform der Erfindung;
• 4 eine Darstellung einer Oberfläche eines Druckobjekts, das mit einem Verfahren nach dem Stand der Technik gefertigt wurde; und
• 5 eine Darstellung einer Oberfläche eines Druckobjekts, das mit dem erfindungsgemäßen Verfahren gefertigt wurde

The present invention is explained in more detail below with reference to the exemplary embodiments indicated in the schematic figures. The show:

• 1 a schematic illustration of a 3D printing device according to an embodiment of the invention;
• 2 a schematic illustration of exemplary details of a 3D printing device of FIG 1 , by means of which a suitable protective gas atmosphere is generated in the 3D printing device, according to a further embodiment of the invention;
• 3 a block diagram of a 3D printing process according to an embodiment of the invention;
• 4th a representation of a surface of a print object that was produced with a method according to the prior art; and
• 5 a representation of a surface of a print object that was manufactured with the method according to the invention

The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the advantages mentioned emerge with a view to the drawings. The elements of the drawings are not necessarily shown to scale with one another. Directional terminology such as "above", "below", "left", "right", "above", "below", "horizontal", "vertical", "front", "rear" and similar information are only used for explanatory purposes Used for purposes and not to limit the generality to specific configurations as shown in the figures.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The 3D printing process in the sense of the present application comprises a generative manufacturing process in which, on the basis of geometric models, objects of a predefined shape are made from a shapeless powdery material in shape-neutral semi-finished products such as strip, wire or web-shaped material by means of chemical and / or physical processes are manufactured in a special generative manufacturing system. 3D printing process within the meaning of the present application use additive processes in which the starting material is sequentially built up layer by layer in predetermined shapes. The 3D printing process used is selective laser melting (“selective laser melting”, SLM), which is also known as laser powder bed melting (LPB-S or LPB-F (laser powderbed - fusion).

1 shows a schematic illustration of a 3D printing device 10. The 3D printing device 10 is a system for selective laser melting, during the operation of which a laser powder bed melting process takes place. In the following, the 3D printing device 10 will be explained by way of example in connection with SLS or LPB-S.

A laser 1 as an energy source sends an energy beam selectively to a certain part of a powder surface of powdery material Ps , which in a working chamber 3 on a work platform 3a rests. An optical deflection device or scanner module can be used for this purpose 2 such as a movable or tiltable mirror can be provided, which the laser beam L. depending on its tilted position on a certain part of the powder surface of the powder Ps distracts.

At the point of impact of the laser beam L. becomes the powder Ps heated so that the powder particles are melted locally and form an agglomerate when cooled. The laser beam scans as a function of a digital production model provided and possibly processed by a CAD system L. the powder surface. After the selective melting and local agglomeration of the powder particles in the surface layer of the powder Ps can be excess, non-agglomerated powder Pd into a waste container 5 be transmitted. Then the work platform 3a lowered and with the help of a leveling roller 6th or another suitable doctor blade or roller device for new powder Pr from a powder reservoir 4th with a reservoir platform 4a in the working chamber 3 convicted. The powder Pr from the powder reservoir 4th can be preheated to a working temperature just below the melting temperature of the powder using infrared light to accelerate the melting process.

In this way, a three-dimensional "printed" object is created in an iterative, generative building process B. made of agglomerated powder. The surrounding powder serves to support the part of the object that has been built up until then B. so that no external support structure is necessary. Due to the continuous downward movement of the work platform 3a the object is created B. in layered model generation.

The entire 3D printing device 10 can be in one housing 7th be housed, in which by a suitable feeder 8th an atmosphere conducive to the laser melting process can be generated. For example, in the housing 7th a vacuum can be created. Alternatively, through the feeding device 8th a passivating atmosphere with an inert gas mixture such as argon and / or nitrogen, and in particular at least partially neon, can also be generated.

The 2 shows the working chamber 3 , in which about the feeder 8th a protective gas in the housing 7th for generating a protective gas atmosphere A. can be introduced into the 3D printing device 10 in the vicinity of the laser melting process. Neon, which is used in the representation of the 2 is used exclusively as a protective gas, serves for more efficient melting while at the same time quieter melt pool dynamics, which ultimately serves to improve the material properties of the component material already produced from powder during the 3D printing process.

The 3 FIG. 3 shows a block diagram of a schematic sequence of a 3D printing method M which is used in a 3D printing device such as that in connection with 1 and 2 illustrated and discussed 3D printing device 10 can be implemented.

In a 3D printing process M, a step is first carried out M11 , in which a melt component, which is selected from the group of metallic materials, metallic material combinations and metallic alloys, in a powder mixture P is made available or made available. During the subsequent creation M12 a protective gas atmosphere A. In the 3D printing device 10, the protective gas has the protective gas atmosphere A. at least one portion which is selected from the group of noble gases and / or an inert gas portion. Then the powder mixture mentioned P in one step M13 subjected to laser melting in a selective laser melting process which is a laser powder bed melting process. The laser melting M13 is according to the previous generation under the protective gas atmosphere A. carried out, for example, a protective gas atmosphere A. , in which the protective gas used consists of at least one further noble gas, at least one gas which is inert towards melting of alloys with a melting component from the third main group and / or at least one gas which reacts with the melt.

In a 3D printing process M, the melting process takes place in the step M13 initially in one step M12 the creation of a protective gas atmosphere A. in a 3D printing device 10. Here, the protective gas displaces the ambient gas still present in the chamber until a previously defined cleanliness value (for example 1000 ppm residual oxygen contamination) is reached. It is more efficient because it is more economical to vacuum seal the chamber in the first step and then fill in the desired protective gas. The protective gas of the protective gas atmosphere A. is provided with a predominant proportion, for example at least 50%, of neon, while the remaining proportion is formed from the inert gas nitrogen. Finally, under this protective gas atmosphere A. a step M13 be carried out in which a powder mixture Ps or is subjected to a selective laser melting process.

The powder mix Ps can have a melt component selected from the group of metallic materials, metallic material combinations and metallic alloys.

In the 3D printing process M, the melt component can be selected from the third main group of the periodic table or an alloy thereof, for example. The selection of aluminum or an aluminum alloy as the melting component can be particularly advantageous, since aluminum has a very easy tendency to undesired oxidation in conventional 3D printing processes due to its high reactivity with the environment.

In addition, the addition of further surface treatment materials, not shown here, can also result in lubricating properties or electrical conductivity properties of the printed object during the 3D printing process B. be improved. For example, lubricating particles such as graphene, graphite, carbides or sulfides can contribute to this. The electrical conductivity can generally improve conductive additional particles, which can decisively improve their contact conductivity, especially on the surface of printed objects.

The methods described can be used in all areas of the transport industry, for example for aircraft, road vehicles, for rail vehicles or for watercraft, but also in general in engineering and mechanical engineering.

Now the 4th and 5 a comparison explains why an LPB-S process control under a neon-rich protective gas leads to better process results with more uniform remelting behavior.

First shows the 4th the product of the processing of an AlMgSc powder (type Scalmalloy®) in a laser powder bed melting plant from SLM Solutions SLM125H according to the prior art, the printed object here B. was made under an argon protective gas atmosphere. The Al alloy powder was drawn up with a layer thickness of approx. 60 µm, which results in a structural layer thickness of approx. 30 µm. A Yb-YAG laser beam focused on the surface was operated with a diameter of approx. 85 μm with a laser power of 370 watts, resulting in a laser light intensity of more than 10 ⁶ watts / cm ² . The laser beam scans the surface of a component at approx. 800 mm / sec, with the individual melting lines overlapping each other by 100 µm. The process was carried out in a 3D printing device under argon, with a max. Residual oxygen gas contamination of 1000 ppm was present (measured with a so-called lambda probe). As a rule, in the course of the production process, which generally takes several hours, the residual oxygen contamination is steadily reduced. The supplied argon protective gas has a nominal quality of 4.8 (= 98.998%).

The result can be seen in the 4th that the surface of the printed object is very uneven, and splashes (balls) and dark deposits are always recognizable as signs of molten bath eruptions xx.

In contrast, the 5 the surface of a printed object produced by the method according to the invention B. , wherein in the method according to the invention the protective gas argon was replaced by the protective gas neon. It can be seen that the generated surface of the printed object has far fewer process imperfections or adhering spatter, it has a uniform surface finish with easily recognizable melt lines. This makes it obvious that Al materials such as the AlMgSc alloy used here can be processed much better with neon as protective & process gas. That in the 5 The result shown was also achieved without any additional possible optimization of the melting process parameters relating to neon.

In the preceding detailed description, various features have been summarized in one or more examples in order to improve the stringency of the presentation. It should be clear, however, that the above description is merely illustrative and in no way restrictive in nature. It serves to cover all alternatives, modifications, and equivalents of the various features and exemplary embodiments. Many other examples will be immediately and immediately apparent to those skilled in the art on the basis of their technical knowledge in view of the above description.

The exemplary embodiments were selected and described in order to be able to present the principles on which the invention is based and their possible applications in practice as well as possible. As a result, those skilled in the art can optimally modify and use the invention and its various exemplary embodiments with regard to the intended use. In the claims and the description, the terms “including” and “having” are used as neutral terms for the corresponding terms “comprising”. Furthermore, the use of the terms “a”, “an” and “an” should not fundamentally exclude a plurality of features and components described in this way.

List of reference symbols

1

laser

2

Optical deflector

3

Labor Chamber

3a

Work platform

4th

Powder reservoir

4a

Reservoir platform

5

Surplus container

6th

Leveling roller

7th

casing

8th

Feeding device

10

3D printing device

A.

Protective gas atmosphere

B.

Print object

L.

laser beam

M.

3D printing process

M11

Process step

M12

Process step

M13

Process step

P

Powder mix

Pd

Excess powder

Pr

Reservoir powder

Ps

Work powder

SE

Molten pool eruption

Claims (11)

3D printing process (M) with the steps: Providing (M11) a melt component, which is selected from the group of metallic materials, metallic material combinations and metallic alloys, in a powder mixture (P); Generating (M12) a protective gas atmosphere (A) in a 3D printing device (10), the protective gas of the protective gas atmosphere (A) having at least one portion selected from the group of noble gases and / or having at least one inert gas portion, and laser melting ( M13) of the powder mixture (P) in a selective laser melting process, in a work area of the 3D printing device (10), the powder mixture (P) having a melt component selected from the third main group of the periodic table. 3D printing process (M) according to Claim 1 , wherein the protective gas of the protective gas atmosphere (A) has at least a portion of neon. 3D printing process (M) according to Claim 2 , the protective gas proportion of neon in the protective gas atmosphere (A) being at least 50%. 3D printing process (M) according to Claim 2 , whereby the protective gas in the protective gas atmosphere (A) consists exclusively of neon. 3D printing process (M) according to one of the Claims 2 and 3 , wherein a remaining portion of the protective gas in the protective gas atmosphere (A) consists of at least one further noble gas, at least one gas which is inert to the melting of alloys with a melting component from the third main group and / or at least one gas that reacts with the melt. 3-D printing method (M) according to one of the preceding claims, wherein a vacuum is generated in the 3-D printing device before the protective gas atmosphere is produced. 3D printing process (M) according to one of the Claims 1 to 5 , the melt component of the third main group being formed by aluminum. 3-D printing method (M) according to one of the preceding claims, wherein an aluminum alloy with at least the components aluminum, magnesium and scandium or an aluminum alloy with at least the components aluminum, magnesium and silicon is formed in the melt. Powder mixture (P) for use in a 3D printing process (M), in particular a 3D printing process (M) according to one of the Claims 1 to 7th , with: a melt component which is selected from the group of metallic materials, metallic material combinations and metallic alloys; and at least one further component which is selected from the group of semimetals, alkaline earth metals and transition metals. Powder mixture (P) after Claim 9 wherein the melt component is selected from the group of aluminum or an alloy thereof. Powder mixture (P) after Claim 9 or 10 , the at least one further constituent being selected from the group consisting of silicon, magnesium, titanium, zirconium, scandium and vanadium.

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