WO2015131989A1

WO2015131989A1 - Method for producing a metal workpiece in layers by means of laser-assisted additive manufacturing

Info

Publication number: WO2015131989A1
Application number: PCT/EP2015/000453
Authority: WO
Inventors: Ernst Miklos; Jim Fieret
Original assignee: Linde Aktiengesellschaft
Priority date: 2014-03-05
Filing date: 2015-02-26
Publication date: 2015-09-11
Also published as: DE102014015039A1

Abstract

The invention relates to a method for producing a metal workpiece in layers by means of additive manufacturing, wherein metallurgical layers of the workpiece are produced by providing a particular metal material in a production chamber for each metallurgical layer and applying a laser beam to said metal material and providing a gas atmosphere in the production chamber during the application of the laser beam to the metal material. According to the invention, the gas atmosphere is provided with different gas composition for different metallurgical layers of the workpiece and, for adjacent metallurgical layers for which the additional gas is provided with different gas composition, the gas composition is selected in such a way that metallurgical properties of the adjacent metallurgical layers influenced by the gas composition have specified differences and a change of the metallurgical properties of the metallurgical layers in a direction of extent of the workpiece perpendicular to a direction of extent of the metallurgical layers follows a specified gradient, a specified profile, and/or a specified distribution.

Description

description

Process for the layered production of a metallic workpiece by laser-assisted additive manufacturing

The invention relates to a method for the layered production of a metallic workpiece by laser-assisted additive manufacturing, in particular by

Laser melting in a production chamber, and a usable for this purpose

Gas mixture.

State of the art

In the course of generative or additive manufacturing processes, a three-dimensional object or a workpiece can be produced in layers from a metallic material. The produced workpiece is composed of different metallurgical layers, which are produced one after the other in the course of the additive manufacturing process. For each of these metallurgical layers of the workpiece, the metallic material may for example be applied in powder form and solidified. For this purpose, the applied material

For example, be acted upon with a laser and / or electron beam. The material can be subjected in this way, for example, a sintering or melting process, whereby the material is solidified. After producing a metallurgical layer, the next layer can be produced in an analogous manner.

Depending on the field of application, additive manufacturing processes are also referred to as rapid prototyping. In the course of a rapid prototyping, for example, tools, workpieces or components can be produced for different purposes. Additive manufacturing processes can work in different areas

Applicable, for example in architecture, mechanical engineering, in the aerospace industry, in medical technology or in the automotive industry. A well-known additive manufacturing process is the so-called laser melting (laser melting or laser sintering, LS). A carrier plate on which a workpiece to be produced is formed layer by layer is in this case usually arranged in a production chamber. The entire manufacturing process takes place in this Production chamber instead. Laser melting is therefore also referred to as chamber technology.

The production chamber is usually closed in itself. In the production chamber, a gas atmosphere can be introduced with a specific composition. Depending on the selected composition of the gas atmosphere in the production chamber, the metallic material can be influenced.

If inert gases (argon, helium) are chosen for the gas atmosphere, no reaction takes place with the metallic material. However, reactive gases which can react with the metallic material can also be used for the gas atmosphere. By choosing the gas atmosphere thus metallurgical properties of the workpiece can be changed. Such methods are known for example from WO 2012/055398 A1 and the

WO 2009/156316 A1. WO 2012/055398 A1 describes laser melting of materials with refractory metals, ie with refractory metals. The gas atmosphere in the production chamber is changed in order to change, for example, a creep resistance of the workpiece or hard phases in the

To produce a workpiece.

According to WO 2009/156316 A1, during laser melting, an inert gas or, temporarily, an active gas can be supplied to specific points of the melting material in order to locally change compositions in the workpiece.

In additive manufacturing processes of the type explained, there is often the risk that so-called metallurgical notches will be created in the workpiece. A metallurgical notch is a sudden, hard transition between regions or layers with different metallurgical properties. The metallurgical properties of the workpiece change abruptly in such metallurgical notches accordingly. These areas of the workpiece may possibly behave very differently under load, resulting in high mechanical

Can lead to stresses or irregularities in the workpiece. At such metallurgical notches can therefore very quickly fractures or defects of the workpiece arise. It is therefore desirable to improve a corresponding method in that a workpiece can be produced without metallurgical notches. Disclosure of the invention

This object is achieved by a method for producing a layer by layer

Workpiece by laser-assisted additive manufacturing, in particular laser melting, solved with the features of claim 1. The invention further relates to a gas mixture with the features of claim 10. Advantageous

Embodiments are the subject of the respective subclaims and the following description.

The laser melting is carried out in a production chamber. The manufactured workpiece is composed of different metallurgical layers, which are produced one after the other. The individual metallurgical layers of the workpiece are each produced by providing a metallic material for each metallurgical layer and applying a laser beam to it. This is done under a gas atmosphere in the production chamber.

The inventive method is thus based on a known method in which metallurgical layers of a workpiece are produced by each provided in a production chamber for each metallurgical layer, a metallic material and is acted upon by a laser beam and in the loading of the layers of the metallic material in the Production chamber one

Gas atmosphere is provided.

The individual metallurgical layers have, in particular, a thickness in the range from 20 μm to 100 μm. The metallic material can be applied, for example, in powder form or in the form of a rod or a belt. The workpiece to be produced is arranged in particular on a carrier plate. After producing a metallurgical layer, the support plate is lowered, in particular, by the thickness of this generated layer, and the next layer is produced in an analogous manner. The support plate is arranged in particular in the production chamber. The laser beam can for example be radiated from the outside into the production chamber or a corresponding laser head can be arranged in the production chamber. The laser beam can be controlled in particular by a control unit. In this control unit data such as CAD data can be stored, which characterize the workpiece to be produced. The control unit can control the laser beam based on these data and move over the carrier plate.

The invention provides that the gas atmosphere for different metallurgical layers of the workpiece is provided with different gas composition, and that for each adjacent metallurgical layers, for which the additional gas is provided with different gas composition, the

Gas composition is chosen in each case such that by the

Gas composition influenced metallurgical properties of each adjacent metallurgical layers have predetermined differences and a change in the metallurgical properties of the metallurgical layers along a direction of extension of the workpiece perpendicular to a

Extension direction of the metallurgical layers a predetermined gradient, a predetermined profile and / or a predetermined distribution follows. One or more of the metallurgical layers of the workpiece may each use a gas composition of a gas atmosphere in the production chamber, but the gas composition is changed after the production of one or more metallurgical layers. By the respective

Gas composition of the gas atmosphere in the production chamber are also metallurgical properties of the respective metallurgical layers of the

Workpiece changed. The gas composition for the metallurgical layers is selected in each case such that metallurgical properties in each case

Change each adjacent metallurgical layers of the workpiece according to predetermined criteria.

The gas composition is selected in each case in particular such that metallurgical properties of respectively adjacent metallurgical layers of the workpiece in particular do not abruptly change, in particular further

continuously or gradually change and that in particular no "jumps" or no sudden changes in the metallurgical properties of each adjacent metallurgical layers occur.

Advantages of the invention

Without limiting the generality, the direction of extension of corresponding (flat) layers as "transverse dimension" of the workpiece and the direction perpendicular thereto, ie the direction in which layer by layer is applied, are referred to below as "longitudinal extent" of the workpiece.

The invention enables no metallurgical notches to be created in the workpiece. Along the entire longitudinal extent of the workpiece, the metallurgical properties change according to the predetermined criteria. Thus, in particular, a smooth, flowing transition between the metallurgical

Ensures properties of each adjacent metallurgical layers. The metallurgical properties of respectively adjacent metallurgical layers are thus matched to one another or adapted to one another, in particular over the complete longitudinal extent of the workpiece. The finished workpiece thus has an anisotropic distribution of metallurgical properties. Although each metallurgical layer per se has constant, isotropic metallurgical properties in each case, so that the manufactured workpiece also has a constant, also constant, width along its transverse extent. has isotropic metallurgical properties. Along its longitudinal extent change the

metallurgical properties, however, and have an anisotropic distribution.

Nevertheless, the invention ensures that the metallurgical

Properties along the longitudinal extent of the workpiece predetermined

Regularities follow and are not distributed arbitrarily. In particular, it is ensured by the invention that no cracks or abrupt changes in the metallurgical properties occur along the longitudinal extent.

In the course of the production of each metallurgical layer, an isotropic homogeneous gas atmosphere with the respective gas composition prevails, in particular in the entire production chamber. Through this each isotropic gas atmosphere The metallurgical properties of the respective complete metallurgical layer can be changed accordingly in a simple, low-cost and cost-effective manner. Thus, it is not necessary to selectively supply certain gases to certain areas of the reflowing material.

Preferably, the gas composition for each or more of the

metallurgical layers each chosen such that the metallurgical

Properties of the respective metallurgical layer (s) are each set to predetermined values. By choosing the gas composition, the metallurgical properties of each metallurgical layer are thus selectively influenced. Thus, the metallurgical properties of adjacent metallurgical layers can be particularly easily matched or matched.

In particular, the set value of a metallurgical property of a specific metallurgical layer depends on the set value of this metallurgical property of the respectively adjacent metallurgical layer.

Preferably, the gas composition for each or more of the metallurgical layer (s) is in each case selected such that the values of the metallurgical properties of respectively adjacent metallurgical layers each have a maximum of one

predetermined threshold differ from each other. This threshold value is chosen in particular such that no metallurgical notch is formed between the respectively adjacent metallurgical layers. Preferably, this is

Threshold 5%, more particularly 2.5%, more particularly 1% of one or more metallurgical properties (see metallurgical properties usable herein below).

By suitably selecting the threshold value, in particular a smooth, flowing transition between the metallurgical properties of respectively adjacent metallurgical layers can be ensured. Furthermore, it is ensured by appropriate choice of the threshold that the change of the metallurgical

Properties along the propagation direction or longitudinal extent of

Workpiece the corresponding gradient, profile or the corresponding

Distribution follows. According to an advantageous embodiment of the invention, the gas atmosphere is provided with different gas composition in the production chamber, that it is completely renewed. Before a new metallurgical layer is produced with altered gas composition of the gas atmosphere is

In particular, the currently existing in the production chamber gas atmosphere removed from the production chamber. The gas atmosphere can be pumped off, for example, and the production chamber can in particular be evacuated. Subsequently, a new gas atmosphere with the respective composition for the respective metallurgical layer is introduced into the production chamber. Thus, it can be ensured that the gas atmosphere with the desired gas composition is actually present in the production chamber and that the metallurgical property of the respective metallurgical layer can be changed or adjusted as desired. Alternatively or additionally, i. in certain, especially minor,

Changes in the gas atmosphere, the gas atmosphere can also be provided by different gas composition in the production chamber, that a predetermined amount of the gas atmosphere from the

Removed manufacturing chamber and / or one or more gases in the

Manufacturing chamber are fed. In this case, in particular, it is not necessary to completely remove the gas atmosphere currently present in the production chamber from the production chamber before producing a new metallurgical layer. By removing the appropriate amount of gas and by supplying a convenient amount of individual gases, the gas composition of the gas atmosphere is adjusted in particular to the desired value for each metallurgical layer. This can save gas.

These two ways of adjusting the gas composition can be conveniently combined. For example, for some metallurgical

Layers of the gas atmosphere are completely renewed, for other metallurgical layers can be added to or removed from certain amounts of gas.

Creep resistance, hardness, rigidity, thermal conductivity, electrical conductivity, a melting point, are preferred by the respective gas composition of the gas atmosphere in the production chamber Corrosion resistance, wear resistance, a

Ductility, electromagnetic properties and / or porosity as metallurgical properties of the respective metallurgical layers of the workpiece changed. Preferably, the workpiece is made of a low-melting metal. For this purpose, the low-melting metal is provided as a metallic material for each metallurgical layer. As low-melting metals here metals are considered, which have a melting point of at most 1500 ° C, preferably of at most 1200 ° C, more preferably of at most 1000 ° C and at least 500 ° C. For example, aluminum, tin, lead, zinc and / or silver or corresponding mixtures or alloys are used as low-melting metals. Corresponding alloys can also be produced from different metallic materials by different

Component mixtures are introduced.

More preferably, the workpiece is not made of a refractory metal or a refractory metal. Accordingly, preferably no refractory metal or high-melting metal is melted as a metallic material.

Refractory metals or high-melting metals have in particular one

Melting point of at least 1500 ° C on. At such high temperatures, gases behave differently than at comparatively low temperatures, in particular at most 1500 ° C. Properties of gases as well as expiring

Reactions are significantly different at such high and low temperatures. In particular, other laws of thermodynamics apply at high temperatures than at such low temperatures. In particular, at high temperatures it is much more expensive to produce special metallurgical properties of the metallurgical layers than at low temperatures. However, it is possible to embed refractory metals or other components, for example for the production of particularly abrasion-resistant workpieces, in a matrix of low-melting metals, for example in order to create composite materials.

Overall, however, the workpiece thus preferably comprises a low-melting metal and the laser melting is preferably carried out at low temperatures of at most 1500 ° C., more preferably of at most 1200 ° C., more preferably of maximum 1000 ° C, carried out. At such low temperatures, the

Workpiece simple, low-effort and inexpensive to manufacture.

Preferably, for the metallurgical layers, a gas composition is used as the gas atmosphere in each case from a pure reactive gas or from a gas mixture with at least one reactive gas as the gas component. In particular, a gas mixture is used, the only different reactive gases than

Has gas components. Due to the concentration of the individual reactive gases of the gas atmosphere, in particular the desired metallurgical properties of the respective metallurgical layer are produced. Preferably, the gas atmosphere is supplied with a gas composition of hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide and / or hydrocarbons as the reactive gas (e).

For example, by using nitrogen in the

Gas composition creep resistance, hardness and / or rigidity than

metallurgical properties of the respective metallurgical layers of the

Workpiece to be changed. In particular, nitrides are produced in the respective metallurgical layers by the nitrogen, which are too high

Creep resistance, hardness and / or stiffness lead.

By using carbon dioxide in the gas composition for the

Gas atmosphere can be produced in the respective metallurgical layers, for example carbides. By carbon dioxide in the gas composition can hardness and / or wear or wear resistance as metallurgical

Properties of the metallurgical layers of the workpiece are changed.

By using oxygen in the gas composition, oxides, in particular metal oxides, can be produced in the respective metallurgical layers. In this way, in particular the ductility or ductility and deformability as metallurgical properties of the respective metallurgical layers of the

Workpiece to be changed.

For example, by using hydrogen in the

Gas composition brittle, brittle layers of the workpiece are generated. In this way, predetermined breaking points can be generated in the workpiece. Advantageously, a gas composition is used for the gas atmosphere containing less oxygen than air under normal conditions. Preferably, the proportion of oxygen in the gas composition is between 0.01% and 21%. Such a gas composition enables different components of the manufacturing chamber (eg, valves, gaskets, hoses, etc.) made of inexpensive materials suitable for compressed air to be used. Thus, it is not necessary to use expensive materials that are explicitly certified for use in oxygen-rich atmospheres. Gas compositions with such an oxygen content are particularly suitable for allowing controlled oxidation or controlled reactions in the production chamber. Thus, desired metallurgical properties of the respective metallurgical layers can be adjusted. Preferably, a gas composition is used for the gas atmosphere, wherein a proportion of combustible or explosive gases is lower than the lower

Ignition limit of the respective gas in the gas composition, more preferably less than the lower ignition limit of the respective gas in air. In particular, hydrogen and / or hydrocarbons are used as combustible or explosive gases.

If a comparatively low oxygen content is chosen for the gas composition or if the gas composition contains no oxygen, the ignition limit of combustible or explosive gases in the gas composition is usually greater than in air. In such low-oxygen gas compositions, in particular a comparatively high proportion of combustible or explosive gases can be selected. During the manufacturing process exists in such an oxygen-poor gas atmosphere despite increased proportion of combustible or explosive gases no or at least hardly explosion or fire hazard. In particular, such a gas atmosphere is completely removed from the same before opening the production chamber to an increased risk of explosion or fire when opening the

Prevent manufacturing chamber by penetration of oxygen.

More preferably, the maximum proportion of combustible or explosive gases in the gas composition is 10% less than the ignition limit of the respective gas in the gas Gas composition or in air. This ensures that the proportion of gases at no time exceeds the respective ignition limit, even if the proportion of the respective gas changes, for example due to reactions of the gas atmosphere with the workpiece.

Preferably, a gas composition having a maximum carbon monoxide content of 30 ppm and / or a maximum carbon dioxide content of 5000 ppm is used for the gas atmosphere. Such a gas composition is particularly useful if there is no safety precaution which prevents the production chamber from being opened before the gas atmosphere has been completely removed. This gas composition can be prevented in such a case that a user or employee suffers health damage. If such a safety precaution is present, the proportion of carbon monoxide and / or carbon dioxide may be selected to be preferably higher than 30 ppm or 5000 ppm.

Claims

claims

Anspruch [en] A method of producing a metallic workpiece by additive manufacturing, in which metallurgical layers of the workpiece are produced by providing a metallic material and a laser beam to each of the metallurgical layers in a manufacturing chamber, and applying them to the layers of the metallic one

Material in the production chamber, a gas atmosphere is provided, characterized in that the gas atmosphere for different metallurgical layers of the workpiece with different

Gas composition is provided and that for each adjacent metallurgical layers, for which the gas atmosphere is provided with a different gas composition, the gas composition is in each case chosen such that influenced by the gas composition

Metallurgical properties of the respective adjacent metallurgical layers have predetermined differences and a change in the metallurgical properties of the metallurgical layers along an extension direction of the workpiece perpendicular to a direction of extension of the metallurgical layers a predetermined gradient, a predetermined profile and / or a predetermined distribution follows.

2. The method of claim 1, wherein the gas composition of the gas atmosphere is selected in each case such that the values of the metallurgical properties of the adjacent metallurgical layers, for the gas atmosphere with

different gas composition is provided, in each case deviate from each other by a predetermined threshold at most.

A method according to any one of the preceding claims, wherein the gas atmosphere is provided with different gas composition in the manufacturing chamber, that it is completely renewed.

4. The method according to any one of the preceding claims, wherein the gas atmosphere is thereby provided with different gas composition in the production chamber that a predetermined amount of the gas atmosphere from the Removed manufacturing chamber and / or one or more gases in the

Manufacturing chamber are fed.

5. The method according to any one of the preceding claims, wherein by the respective gas composition of the gas atmosphere in the production chamber a

Creep resistance, hardness, rigidity, thermal conductivity, electrical conductivity, melting point, corrosion resistance, wear resistance, wear resistance, ductility,

Electromagnetic properties and / or porosity as metallurgical properties of the respective metallurgical layers of the workpiece to be changed.

6. The method according to any one of the preceding claims, wherein in each case a pure reactive gas is used for the gas atmosphere for the metallurgical layers or a gas mixture with at least one reactive gas as the gas component.

7. The method according to claim 6, wherein the gas atmosphere is hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide and / or hydrocarbons as

Has reactive gas.

8. The method according to any one of the preceding claims, wherein each low

melting metal is provided as a metallic material.

9. The method of claim 8, wherein the low melting point metal

Melting point of a maximum of 1500 ° C, in particular of at most 1200 ° C, more particularly of at most 1000 ° C.

A gas composition for use in a method according to any one of

preceding claims, wherein the gas composition contains a pure reactive gas or a gas mixture with at least one reactive gas as the gas component.

1 1. A gas composition according to claim 10, comprising hydrogen, oxygen, nitrogen, carbon dioxide and / or hydrocarbons as a reactive gas.

12. A gas composition according to claim 10 or 1 1, with a proportion of oxygen between 0.01% and 21%.

13. A gas composition according to any one of claims 10 to 12, wherein a proportion of combustible or explosive gases, in particular of hydrogen and / or hydrocarbons, is less than the lower ignition limit of the respective gas in the gas composition or less than the lower ignition limit of the respective Gas in air.

14. A gas composition according to claim 13, wherein a maximum proportion of

flammable or explosive gases, in particular of hydrogen and / or hydrocarbons, by 10% less than the lower limit of ignition of the respective gas in the gas composition or by 10% less than the lower limit of ignition of the respective gas in air.

A gas composition according to any one of claims 10 to 14, having a

maximum content of carbon monoxide of 30 ppm and / or with a maximum content of carbon dioxide of 5000 ppm.