Process for the additive manufacturing of a shaped body from a metallic material mixture

Abstract

Method for the additive production of a shaped body (1) from a metallic material mixture (7) by layer-by-layer deposition of the material mixture (7) in individual, successive layers (1.1) using at least two separately present, sheet-, wire- or powder-shaped starting materials (2, 3), of which at least one is meltable, wherein - for each region of the shaped body (1), a material composition and a microstructure of the material mixture (7) intended for this region are specified by material description data; - the starting materials (2, 3) are mixed in a quantity ratio corresponding to their composition specified locally in the molded body (1) to be built up by the material description data, while melting the fusible starting materials (2, 3) to form a molten material mixture (7) - the molten material mixture (7) is deposited at a processing point within the layer (1.1) to be produced, and - by supplying a coolant to the processing point, a microstructure formation of the starting materials (2, 3) is controlled with the respective formation of the metallic material mixture (7) specified for this area by the material description data in the shaped body (1), characterized in that the build-up of the individual layers (1.1) is carried out discontinuously by alternately depositing one or more layers (1.1) at at least two spatially separate positions of the shaped body (1).

Description

[0001] The invention relates to a method for producing complex components from a metallic material mixture, in particular an alloy or an intermetallic phase, by means of additive manufacturing, wherein sheet, wire or powdered metal-containing material is melted and applied in layers.

[0002] The production of complex components from customized materials, such as alloys or metallic mixtures, where – due to their specific properties (e.g., the mass of the individual alloy components) – homogeneous alloy formation is not possible due to segregation, i.e., demixing in the melt during metal production, poses complex challenges to manufacturing processes. The production of such components is usually carried out using vacuum casting or other primary forming processes. Tools, contour freedom, and temperature control are strongly influenced by this and require costly measures to manage them.

[0003] Additive processes allow the production of molded bodies with complex component geometries from individual layers. Using conventional processes, metallic components are predominantly manufactured using a single material. This material can be elemental, i.e., consisting of a single element, or a prefabricated alloy, as described, for example, in DE 10 2013 226 664 A1 for the production of a turbine rotor from a high-temperature metal alloy or in US 2015 / 0135897 A1 for the production of components from a bismuth-containing alloy.

[0004] The additive manufacturing of parts and components has so far been carried out using a pre-finished alloy or material system. The disadvantage here is that certain material systems, such as certain alloys, are difficult to produce in the desired composition on a large scale due to specific effects, such as the influence of gravity or the introduction of specific alloying elements.

[0005] Processes for generative manufacturing using several metallic starting materials, which are only mixed during layer-by-layer application by the 3D printer, have only recently come into focus.

[0006] US 2014 / 0295087 A1 discloses the production of metallic molded bodies using 3D printing processes. In these processes, the poorly weldable material intended for production and a second starting material, e.g., in powder form, are applied in layers to improve weldability. The second material is a readily weldable derivative of the first. The alloy formation under the influence of an energy beam during 3D printing thus creates a component consisting essentially of the first (poorly weldable) material with improved mechanical properties, particularly with regard to its weldability.

[0007] WO 2015 / 094720 A1 describes the production of a circular-cylindrical semi-finished product consisting of two different alloys that gradually merge into one another in a locally defined transition zone of the semi-finished product. For this purpose, two metallic powders are deposited using a single nozzle in proportions corresponding to the required, locally varying composition of the semi-finished layer to be built up. The powders are mixed immediately before their layer-by-layer application. The powder mixture is then melted by an energy beam to form alloys, forming a gradual transition zone from one alloy to the other in the semi-finished product. However, this manufacturing process only works with powdered starting materials, where both starting materials are already present as alloys.In addition, the use of only one nozzle for powder deposition results in a time delay between the mixing process and the deposition process, which makes it almost impossible to precisely adjust a layer composition that needs to be varied in narrowly defined local areas.

[0008] US 2015 / 044084 A1 describes an additive manufacturing process in which different metallic powders are deposited and melted by means of energy input to produce components with variable compositions. The materials are mixed prior to deposition, which makes precise local control of the composition and microstructure in the melting zone difficult.

[0009] DE 10 2011 003 610 A1 discloses a method for additive manufacturing in which at least two different metallic materials are provided, mixed, and then melted layer by layer to form a component. However, the mixing takes place outside the actual melting process, which imposes limitations regarding the homogeneity of the composition and the targeted local control of the microstructure.

[0010] US 2005 / 0133527 A1 describes an additive manufacturing process in which metallic powder materials are melted and built up layer by layer using a directed energy input. The materials used are already available as finished alloys.

[0011] DE 103 42 880 A1 discloses a method for producing metallic workpieces by applying and fusing metallic powder layer by layer with a laser. A homogeneous powder mixture is used in each case, which is prepared prior to deposition.

[0012] DE 10 2006 030 350 A1 describes an additive manufacturing process in which metallic powder materials are applied layer by layer and fused by laser radiation. The powders used are predefined alloys.

[0013] The object of the invention is to produce metallic shaped bodies by layering in the sense of generative manufacturing from several sheet, wire or powder materials, wherein the shaped body should be producible not only according to a predetermined geometric shape, but in particular with an alloy, intermetallic phase or other metallic mixtures of these materials that can be predetermined as desired in terms of material composition and / or microstructure (e.g. grain size), which is homogeneous or locally varying according to specifications, while avoiding segregation effects.

[0014] According to the invention, the above-mentioned object is achieved by a method according to claim 1; expedient embodiments of the invention can be found in the subclaims.

[0015] In the following, the term “material mixture” is used generally for an alloy, intermetallic phase or other metallic mixture formed from a combination of several metallic or metal-containing starting materials.

[0016] According to the invention, for the additive production of the shaped body consisting of a given metallic material mixture, at least two meltable materials in the form of wire, strip, powder or sheet (elementary, i.e. consisting of only one chemical element, or in the form of an alloy) are used, of which at least one is melted by means of an energy supply (e.g. by means of an arc or laser beam). After melting (of one, several or all of the starting materials), the starting materials to be melted to form the material mixture are mixed with one another in corresponding volume proportions to form the material mixture in the molten phase and in a processing point (processing point is the position, i.e.a locally limited area on the surface of the already finished part of the shaped body, where the molten starting materials are applied to the surface) is deposited on the already finished part of the shaped body to be produced, whereby the molten material mixture solidifies after deposition through targeted cooling to form the solid metallic material mixture, i.e. alloy, intermetallic phase or other metallic mixture of substances, with a predetermined composition and microstructure. In this way, each layer of the shaped body, which is to be built up layer by layer, is built up in repeating steps of the process, whereby the composition and microstructure of the metallic material mixture can be specifically adjusted (locally or globally) in the shaped body.

[0017] In the following, microstructure formation is understood to mean the formation of a solid material mixture, i.e. an alloy or another metallic mixture, from a metal-containing melt which was formed from several (elementarily metallic or metal-containing) materials, whereby the (solidified) metallic material mixture is characterized after microstructure formation by a microstructure (i.e. the microstructure, for example a grain size distribution) and a chemical composition which may also be locally inhomogeneous due to the microstructure formed.

[0018] The microstructure formation occurs during the solidification of the molten (e.g., elemental) starting materials mixed together in the desired concentration or volume ratio. This means that the respective materials are immediately remelted locally by the application of energy. Active cooling allows the microstructure formation to be carried out in a controlled manner, for example, by specifically controlling the solidification behavior of the starting materials already mixed in the melt through temperature control during the cooling and solidification of the melt (e.g., forming the alloy). Thus, the formation of the microstructure of the metallic material mixture can be influenced in a controlled manner through targeted temperature control of the melt.

[0019] Preferably, the targeted cooling during the microstructure formation takes place locally, i.e. limited to the area of ​​the processing point, for example by process gas supplied locally via a nozzle.

[0020] What is essential to the invention is that the starting materials intended for the microstructure formation of the metallic material mixture (i.e. the formation of the alloy or the intermetallic phase) are mixed in the molten phase and fed to the processing point in the layers of the shaped body to be produced that are currently being built up, whereby the microstructure formation only takes place at the processing point on or in the layers of the shaped body, i.e. the formation of the metallic material mixture only takes place after the melting and mixing of the individually fed materials, whereby the microstructure formation, i.e. the formation of a microstructure in the metallic material mixture, is significantly influenced by the targeted cooling of the molten material mixture at the processing point.

[0021] According to the invention, the mixing ratio of the individual materials can be varied, i.e., the material composition after microstructure formation can be adjusted within wide limits by the individual volumes of the respective molten starting materials combined and applied. In particular, the composition of the material mixture within the molded body can be varied locally, i.e., by region.

[0022] The additive process according to the invention therefore makes it possible to produce components from tailor-made metallic structures consisting of several materials / elements, such as alloys, by repeatedly depositing a molten material mixture of only droplet size and subjecting it to a targeted solidification (of these droplets).

[0023] This allows, for example, the melt volumes to be significantly reduced compared to state-of-the-art alloying processes, thus avoiding, for example, segregation effects. This process thus allows the production of metallic molded bodies from material mixtures that could only be produced homogeneously and with the desired material composition with considerable technical effort using known methods, e.g., due to segregation effects of the material already alloyed before additive manufacturing.

[0024] The invention is applicable to known additive processes (such as laser sintering, laser melting, form welding, ultrasonic welding, etc.), by means of which individual layers can be produced in different thicknesses from a few micrometers up to several millimeters.

[0025] By creating the desired material composition and structure directly during the "printing" of the component, a very precise adaptation and variation of the respective material composition and structure in the layers or local areas of the molded body is possible, allowing the production of a solid component that, for example, is temperature-resistant on one side, corrosion-resistant on another, and particularly strong in the center due to the selected alloy composition. The possibilities resulting from the invention are - as fundamentally stated - very diverse, since, for example, in a multi-torch system, the most diverse wire materials can be mixed locally and in different ratios.

[0026] Another advantage of the invention is that the desired material system (alloy, intermetallic phase, etc.) is first produced locally. This makes it possible to circumvent previously existing production-related restrictions both in the production of pre-alloyed starting materials (e.g., drawing the wire) and in the component production process (e.g., casting). The layer-by-layer structure in the sense of generative manufacturing makes it possible to create a specific material system with locally defined and locally variable properties. This means that the specific material properties within a solid component can be changed (due to the locally variable composition), or completely new metallic material mixtures, i.e., material systems, can be produced using the method according to the invention.

[0027] Advantageously, the thickness of the deposited layers can be adjusted according to the extent of the locally varying composition and / or structure of the material mixture in the molded body. Thus, the deposited layers can each have a different thickness compared to neighboring layers.

[0028] According to one design variant, the entire molded body, which is built up layer by layer, is tempered—i.e., cooled or heated—during production. Through defined heat control, the material composition can be advantageously influenced, i.e., in addition to targeted cooling of the processing point.

[0029] It can also be provided that the layer-by-layer build-up is carried out under a process gas atmosphere, whereby the formation of the metallic material mixture in the desired composition can be influenced by changing the composition of the process gas during the solidification of the melt.

[0030] The invention can be designed such that a gaseous coolant, e.g., a process gas, a liquid coolant, e.g., a corrosion-inhibiting liquid, or a powdered coolant, e.g., carbon dioxide snow, is used for the targeted cooling of the deposited molten material mixture.

[0031] According to one embodiment of the invention, a liquid heat transfer fluid can be introduced into a construction space in which the molded body is produced. In this case, provision can be made for the construction space to be partially or completely flooded with heat transfer fluid.

[0032] For this purpose, the liquid heat transfer fluid can flow through the installation space. For this purpose, the walls of the installation space have, for example, heat transfer fluid inlet openings through which the heat transfer fluid enters the installation space, and heat transfer fluid outlet openings through which the heat transfer fluid exits the installation space. However, it can also be provided to carry out the layered buildup in stagnant liquid. Thus, only heat transfer fluid is introduced into the installation space until a predetermined liquid level is reached.

[0033] By enclosing the already finished parts of the molded body in a liquid heat transfer fluid, these areas are also externally protected, e.g., from adhering splashes, which can significantly minimize the required post-processing effort. Furthermore, the heat transfer fluid surrounding the molded body, i.e., covering its entire surface (along with any process gas atmosphere prevailing in the build space), can act as oxidation protection. This is particularly the case when, for example, a corrosion-inhibiting fluid is used as the heat transfer fluid.

[0034] It may be provided that the same heat transfer fluid is used as a coolant for targeted cooling at the processing point.

[0035] To ensure continuous production without loss of time (e.g., due to cooling times that cannot be minimized), the individual layers are designed to be deposited discontinuously. While a molten droplet of the material mixture that has just been deposited is still cooling, another molten droplet of the material mixture is already being deposited at a spatially separate location. This allows, for example, multiple layers to be produced simultaneously.

[0036] According to one embodiment, additives can be added to the molten material for grain refinement, e.g., titanium powder into an aluminum-containing melt, in order to specifically influence the microstructure in the solidified material mixture.

[0037] The device for carrying out the method comprises a construction space that can be hermetically sealed from the environment, a printing platform, at least one energy source that is suitable for selectively melting (one or more) metal-containing starting materials, at least two material feed units that are designed in such a way that the starting materials respectively fed to the manufacturing process can be mixed (e.g. melted simultaneously) in a molten phase at a common point immediately above the processing point, and a coolant supply that can supply coolant (liquid, gaseous or powdery) in a targeted manner to the area of ​​the processing position.

[0038] In addition, the device comprises a control unit connected to the above-mentioned components, controlling the additive manufacturing.

[0039] Preferably, the coolant is supplied during the process in the region of the machining point. It can also be provided that the coolant supply can be positioned at a position on the mold surface independently of the machining point, so that targeted cooling can be carried out at a first position where the molten material mixture was previously deposited, while simultaneously depositing the molten material mixture at a second position spatially separate from the first.

[0040] It can be provided that the printing platform can be tempered, in particular cooled.

[0041] The invention is explained in more detail below using an exemplary embodiment. The figure shows a schematic cross-sectional view of an apparatus for carrying out the method.

[0042] The molded body 1 is built up layer by layer in the build space 4 on the printing platform 5 by melting individual metal droplets from the first starting material 2, here a metal wire made of titanium, and the second starting material 3, here in the form of a metal wire made of aluminum, by means of the laser 6 in the quantity ratio of the intermetallic phase to be formed and immediately mixing them to form the molten material mixture 7 (here shown as drops).

[0043] By means of the coolant supply line 8, coolant is selectively supplied via a nozzle (running downstream of the machining point in the feed direction) to the still-molten droplet of the material mixture 7 deposited within layer 1.1, so that it solidifies as part of layer 1.1 into the intermetallic phase titanium aluminide γ-TiAl (with 50 to 55% aluminum) with the desired microstructure. In this example, the layer thicknesses are shown greatly enlarged.

[0044] A heat transfer fluid for tempering the molded body 1 is introduced into the build space 4 via the heat transfer fluid inlet 9.

[0045] The control unit 10 enables the control of the manufacturing process and in particular the microstructure formation. List of reference symbols 1 molded body 1.1 Layer 2 first starting material / titanium-containing wire 3 second starting material / aluminum wire 4 Installation space 5 printing platform 6 lasers 7 metallic material mixture 8 Coolant supply 9 Heat transfer fluid inlet 10 Control unit

Claims

[1] Method for the additive production of a shaped body (1) from a metallic material mixture (7) by layer-by-layer deposition of the material mixture (7) in individual, successive layers (1.1) using at least two separate, sheet-, wire- or powder-shaped starting materials (2, 3), of which at least one is meltable, wherein - for each region of the shaped body (1), a material composition and a microstructure of the material mixture (7) intended for this region are specified by material description data; - the starting materials (2, 3) are mixed in a quantity ratio corresponding to their composition specified locally in the molded body (1) to be built up by the material description data, while melting the fusible starting materials (2, 3) to form a molten material mixture (7) - the molten material mixture (7) is deposited at a processing point within the layer (1.1) to be produced, and - by supplying a coolant to the machining point, a microstructure formation of the starting materials (2, 3) is controlled with the respective formation of the metallic material mixture (7) specified for this area by the material description data in the molded body (1), characterized by that the build-up of the individual layers (1.1) is carried out discontinuously by depositing one or more layers (1.1) alternately at at least two spatially separated positions of the shaped body (1). [2] Method according to claim 1, characterized by that the melting of the fusible starting materials (2, 3) takes place by means of arc, laser (6) or resistance heating. [3] Method according to one of the preceding claims, characterized bythat the layer thickness of the layers (1.1) is selected according to the composition and / or microstructure of the material mixture (7) specified for this area. [4] Method according to one of the preceding claims, characterized by that the temperature of the already solidified areas of the layers (1.1) is varied during the construction of the shaped body (1). [5] Method according to one of the preceding claims, characterized by that a process gas is used as a coolant. [6] Method according to one of claims 1 to 4, characterized by that a corrosion-inhibiting fluid is used as a coolant. [7] Method according to one of claims 1 to 4, characterized by that carbon dioxide snow is used as a coolant. [8] Method according to one of claims 1 to 6, characterized by that the shaped body (1) is completely enclosed by the coolant.

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