DE102020209386A1 - Process for producing cavities in a layer-wise additively manufactured structure - Google Patents

Abstract

A method for producing cavities (11) in a structure to be produced in layers for a component (11) is specified. The method comprises processing material for the structure (10) during the layer-by-layer construction of the structure with an ultrashort pulse laser (B2), removing material to produce cavities (11) according to a predetermined geometry in the structure. Furthermore, a correspondingly manufactured component and a corresponding device are specified.

Description

The present invention relates to a method for producing cavities, porosity or cooling channels in a layered or additively produced structure for a component. Furthermore, a correspondingly manufactured component and a corresponding device are specified.

The component is preferably intended for use in the hot gas path of a gas turbine, such as a stationary gas turbine. The component structure particularly preferably relates to a component of a combustion chamber, such as a resonator component or another part subjected to hot gas. Alternatively, the component may be another coolable or partially porous component, such as one used for automotive or aerospace applications.

The component is preferably a component to be cooled, for example it can be cooled via fluid cooling. For this purpose, the component preferably has a tailor-made permeability for a corresponding cooling fluid, for example cooling air.

Modern gas turbines are subject to constant improvement in order to increase their efficiency. However, this leads, among other things, to ever higher temperatures in the hot gas path. The metallic materials for rotor blades, especially in the first stages, are constantly being improved in terms of their strength at high temperatures, creep loading and thermomechanical fatigue.

Due to its disruptive potential for the industry, generative or additive manufacturing is becoming increasingly important for the series production of the turbine components mentioned above, such as turbine blades or burner components.

Additive manufacturing processes include, for example, selective laser melting (SLM) or laser sintering (SLS) or electron beam melting (EBM) as powder bed processes.

Other additive processes are, for example, "Directed Energy Deposition (DED)" processes, in particular laser deposition welding, electron beam or plasma powder welding, wire welding, metallic powder injection molding, so-called "sheet lamination" processes, or thermal spraying processes (VPS LPPS, GDCS).

Additive manufacturing processes have generally proven to be particularly advantageous for complex or delicately designed components, for example labyrinth-like structures, cooling structures and/or lightweight structures. In particular, additive manufacturing is advantageous due to a particularly short chain of process steps, since a manufacturing or manufacturing step of a component can be carried out largely on the basis of a corresponding CAD file and the selection of corresponding manufacturing parameters.

A CAD file or a computer program product, for example, as a (volatile or non-volatile) storage medium, such as a memory card, a USB stick, a CD-ROM or DVD, or in the form of a downloadable file from a server and / or provided or comprised in a network.

The production of gas turbine blades using the described powder bed-based process (LPBF for “Laser Powder Bed Fusion”) advantageously enables the implementation of new geometries, concepts, solutions and/or designs that reduce the manufacturing costs or the construction and throughput time, optimize the manufacturing process and, for example, improve a thermo-mechanical design or durability of the components.

Hot gas components manufactured in a conventional way, for example by casting, are significantly inferior to the additive manufacturing route, for example in terms of their design freedom and also in relation to the required throughput time and the associated high costs as well as the manufacturing effort.

In the LPBF processes, it is already fundamentally possible to produce porous structures or cavity structures by irradiation selection and/or parameter variations. However, such pores or cavities are randomly distributed in their size due to a parameter variation and can hardly be influenced.

Furthermore, pores, cavities or channels can be designed in the CAD model and then implemented in terms of printing or production technology. If the pores or channels are provided in the CAD model, however, they must have a minimum size so that they can be realized by the manufacturing facility or the corresponding 3D printer. The material must also have a minimum wall thickness so that it can be generated by the machine. This is why thin-walled structures can only be "printed" up to a minimum size. In addition, generated pores can become clogged directly with new powder when the next layer is covered due to this minimum size. Furthermore, by leaving fusible lines free, open spaces can only be created imprecisely This is because the geometric dimensions of the melt pools can differ significantly despite the same parameters and - depending on the component geometry - can be subject to natural fluctuations in their width and height of at least ± 5 µm.

Currently, the construction process of components with pores, cavities and cooling channels requires complex depowdering.

A method for producing a component by successively solidifying individual layers by irradiation with laser radiation using a laser, wherein at least one edge region surface of the respective layer is irradiated with an ultrashort pulse laser for each layer after irradiation with the laser is known from, for example EP 3 022 008 B1 .

It is an object of the present invention to solve the technical problems described above. In particular, an improved possibility of metered material removal during the additive construction of a component should be specified in order to tailor cavities.

This object is solved by the subject matter of the independent patent claims. Advantageous configurations are the subject matter of the dependent patent claims.

One aspect of the present invention relates to a method for producing cavities, porosity or cooling channels in a structure to be produced in layers or additively for the component. The component structure is preferably produced by means of selective laser melting or electron beam melting.

The method comprises processing material for the structure during the layer-by-layer build-up thereof with a short-pulse laser, preferably ultra-short-pulse laser, whereby material is removed (subtractively) or evaporated, preferably in order to produce the voids or cavities according to a predetermined geometry or porosity in the structure.

According to the additive layered manufacturing process, the removal of powdery material as well as already solidified solid material of the structure of the component can affect. Nevertheless, the removal can refer to both, i.e. solid material coated with a new layer of powder, for example.

In the case of ultra-short-pulse lasers, the pulse operation or a pulsation or pulse duration usually extends into the range of picoseconds or femtoseconds. In contrast, a solid-state or fiber laser used as standard for selective irradiation in additive manufacturing, for example, could in principle also achieve pulse durations close to the femtosecond range in mode-locked or pulsed operation.

The proposed means make it possible, in particular, to produce or process the finest structures with particularly high accuracy. The use of ultra-short laser pulses allows irradiation with laser foci of less than 50 µm in diameter. This has the advantage that the exposed material is heated so quickly and so intensely that it changes into a plasma phase or vaporizes without first changing into a molten bath. A heat-affected zone preferably does not even form around the laser focus. In the absence of measurable heat exchange with the surrounding powder, there are consequently no hot cracks, thermal stresses or any other disadvantageous manufacturing artifacts, such as surface roughness, which conventionally occurs when powder particles are drawn into a melt pool and thus harden. Furthermore, it is advantageously possible to prevent small cavities from having to be freed from powder in a costly manner when powder is applied again.

In one configuration, the structure for the component is built up by a powder bed-based method, in particular selective laser sintering, selective laser melting or electron beam melting.

In one embodiment, the structure for the component is built up by selective laser melting, with the ultrashort pulse laser being different from a melting laser for selective laser melting. The ultra-short pulse laser is preferably set up for the application of even shorter laser pulses, such as femtosecond laser pulses (see above).

In one configuration, an energy input, for example an irradiation power, of the ultrashort pulse laser into the material is selected in such a way that the material is removed by direct or immediate vaporization. As indicated above, this can advantageously prevent the formation of a real molten pool and a heat-affected zone. In this way, the development of excessive surface roughness and hot cracks can also be advantageously prevented.

In one embodiment, the material is processed without a real melt pool, a liquid material phase, or even just a heat-affected zone being created in the material.

In one embodiment, the ablation of material by the ultrashort pulse laser along a layer normal, usually the vertical build-up direction of the process, is dimensioned to be larger than a layer thickness of material or powder to be newly applied. Because if the removal is less than a new layer width, the new layer would completely close the cavity created by the removal. The ablation depth of the ultrashort pulse laser can be set, for example, via an exposure duration or pulse duration or the laser intensity or laser power.

In one embodiment, the cavities or pores are produced with dimensions that are smaller than, for example, the smallest, mean or median diameter of powder particles or a powder fraction of the material. Thus, even when the powder is applied again, it is advantageous that no new particles get into the small cavity that has formed. A complex depowdering of the same can accordingly be advantageously dispensed with.

In one embodiment, the cavities or pores are produced with dimensions in the micrometer range, preferably less than 50 μm, particularly preferably less than 20 μm.

In one embodiment, the material is removed in successive layers at the same or only slightly offset (lateral) layer position in order to form cavities or hollow channels (at least partially or in projection) along a build-up direction of the structure. Advantageously, these channels also do not necessarily have to be subsequently freed of powder if the dimensions are small enough (see above) to prevent powder from being deposited in them at all. As a result of this configuration, cooling cavities can advantageously be configured vertically or also obliquely or diagonally at different angles, passing through the component structure. Accordingly, the mentioned slight misalignment can designate a measure that subsequently still ensures fluidic communication in the individual layers of the structure.

In one embodiment, the material is removed within a layer (to be strengthened) in order to form hollow channels within this layer, for example in the layer plane of the structure. Of course, these hollow channels can also relate to a plurality of fluidically separate or connected channels. According to this embodiment, too, the removal of material is of course preferably predetermined or defined in advance—by a CAD file and/or control instructions of the production plant.

In one configuration, the ultrashort pulse laser is (additionally) used to reduce a surface roughness of the cavities and/or to (specifically) structure a surface of the cavities or cavities.

In one embodiment, only material that has already been solidified is carried out by the ultrashort pulse laser, for example subsequently, after the material has been selectively irradiated, in order to produce the cavities in the structure. According to this configuration, the removal then expediently also takes place before a renewed powder coating.

A further aspect of the present invention relates to a component which is produced or can be produced according to or with the aid of the method described, the cavities in the structure of the component having a dimension along one dimension which is smaller than a smallest or average diameter of powder particles appropriate fraction of the material.

In one configuration, a wall thickness of structures of the component is smaller than a molten pool formed during the production process for building up the corresponding structure, for example in the lateral dimension. According to this refinement, the design of the component can also advantageously be made more filigree.

In one configuration, the component has a lattice structure, for example with lattice struts according to the dimensions of the wall structure described above, it being possible for the cooling channels to run obliquely or diagonally through the component, for example.

A further aspect of the present invention relates to a device for additively manufacturing a component, comprising an irradiation device for selectively solidifying the preferably powdered material for the component, and a controller and a beam source for applying an ultrashort pulse laser to remove the material, as described above. Under certain circumstances, the irradiation device can also be used for the material removal described here, for example via the working laser in the LPBF process, which can also be designed to generate ultra-short laser pulses.

Configurations, features and/or advantages that relate to the method or the component in the present case can also relate to the device, and vice versa.

As used herein, the term "and/or" when used in a series of two or more ele ment means that each of the listed items can be used alone, or any combination of two or more of the listed items can be used.

Further details of the invention are described below with reference to the figures.

1 indicates schematically the working principle of a powder bed-based additive manufacturing process.

the 2 and 3 indicate schematically and qualitatively technical aspects in the formation of cavities during the process.

In the 4 A method according to the invention and a correspondingly manufactured component are described below. In particular shows 4 a schematic sectional view of a component in whose structure material was removed using an ultrashort pulse laser.

5 indicates similar to 4 and then apply a powder coating to the material removal described.

6 indicates further embodiments of the present invention, in particular with regard to the method for producing cavities, as well as to the arrangement of cooling channels in the component structure.

the 7 until 9 indicate further details of the method described and the component obtained in this way.

In the exemplary embodiments and figures, elements that are the same or have the same effect can each be provided with the same reference symbols. The elements shown and their proportions to one another are not to be regarded as true to scale; instead, individual elements may be shown with exaggerated thickness or dimensions for better representation and/or better understanding.

1 shows a schematic sectional view of an additive manufacturing system or device 100, on which the principle of powder bed-based additive manufacturing methods is indicated qualitatively. The system 100 is preferably set up for the layer-by-layer additive construction of a component 10 by selective laser sintering, selective laser melting or electron beam melting.

Accordingly, the system has a construction platform 1 that can be lowered. The construction platform 1 is successively coated in layers with a starting material P, preferably in powder form. This takes place by means of a horizontally movable coating device 3. After a layer with layer thickness L has been selectively exposed by an energy beam, for example a laser or electron beam, according to the desired component geometry, a new layer of powder is preferably applied by means of the coating device 3.

The selective irradiation takes place by means of an irradiation device 2 . The irradiation device 2 also has a controller 4 for controlling the irradiation device 2 . Alternatively, the irradiation device 2 can be connected to and/or coupled to the controller. To melt the powder P, a (liquid) molten pool indicated by the reference M and a heat-affected zone W are created at the point of impact of the laser, in which either partially liquid phases are still present and/or the material is still particularly susceptible to hot cracks or other defects.

The irradiation device 2 is usually equipped with a beam source for emitting an energy beam B1, in particular a working laser, for the selective welding of the structure for the component 10. Conventional laser-based additive manufacturing systems usually work with solid-state or fiber lasers, for example with erbium or ytterbium as a doping element for the laser-active fiber core. Under certain circumstances, such laser sources can also be used to achieve very short or ultra-short laser pulses, in particular with a corresponding device for mode locking (not explicitly identified), or the like. In addition to the laser beam B1, the irradiation device 2 is preferably equipped with a second beam source for emitting ultra-short laser pulses (compare dashed beam B2 in 1 ) equipped. The ultra-short pulsed laser beam B2 is preferably set up to emit pulsed laser radiation with pulse durations in the picosecond and femtosecond range.

According to the present invention, this laser beam B2 is used for material processing, more precisely for the metered or tailored removal of material, in particular in order to generate tailor-made small cavities, pores, cavities or cooling channels in the structure of the component 10 .

Unlike from the 1 suggests that the technical solution of the present invention can also be implemented using a single beam source, namely when one and the same laser is used, for example, in continuous operation as a working laser and in ultra-short pulsed operation for serial material removal.

However, the laser beam B2 is preferably emitted by a beam source (not explicitly identified) that is different from the beam source for emitting the laser beam B1.

The component 10 is preferably a component of the hot gas path of a turbomachine that can be cooled and is to be cooled during operation, such as a turbine blade, heat shield component of a combustion chamber and/or a resonator component, for example a Helmholtz resonator.

Alternatively, the component 10 may be a ring segment, burner part or tip, skirt, shield, heat shield, nozzle, seal, filter, orifice or lance, plunger or swirler, or a corresponding transition, use, or a corresponding retrofit part.

2 shows schematically and only qualitatively a cross-sectional view of a layer stack of an additively constructed structure for the component 10, wherein an (oval) contour of weld beads can still be seen in the uppermost layer or layer of the material; this layer has not yet been remelted by subsequent irradiation over several layer thicknesses.

A gap or a cavity or a corresponding hollow space 11 , created for example by parameter variation, is identified by the reference number 11 .

How based on 3 makes clear, such pores tend to become clogged with new powder P as a result of a subsequent powder coating (inevitably). In other words, powder particles fill up pores that normally have minimum sizes above the usual and average powder diameters. A corresponding layer defect could be partially compensated for in this way. However, it is then inherently impossible to introduce tailor-made pores in a structure for the component 10 that is to be built up additively.

4 indicates similar to the representations of 2 and 3 part of a layered structure for a component 10. As indicated above, the reference character B2 indicates an ultra-short laser pulse which is used for material processing, in particular for the metered removal of material from the layer. In particular, cavities 11 of a specific (tailor-made) geometry can be formed in the structure of the component 10 by this measure according to the invention.

Appropriately, an energy input, for example controlled via the parameters of the exposure and pulse duration, the temporal and spatial radiation or energy density or the laser intensity of the ultrashort pulse laser B2 in the material is chosen such that the material is removed by immediate and direct evaporation. This, preferably without a real molten bath (as indicated by the reference sign M in 1 shown) arises in the material.

Furthermore, in the 4 subsequent to recognizing that the depth t of the material removal (cf. also 5 ) or pore depth of material through the ultrashort pulse laser B2 along a layer normal or vertical build-up direction z (cf 6 further below) is dimensioned larger than a layer or layer thickness L of material to be applied. If, on the other hand, the removal were less than one layer width and the layer thickness L, a new layer to be applied would completely close the resulting cavity again.

5 In cross section, FIG. The raw material powder fractions are of course subject to some variation in powder diameters, which is also reflected in the representation of the 5 is indicated. Furthermore, it can be seen in the upper area of the illustration that the cavities 11 or pores are produced with dimensions d2 that are smaller than a mean and/or smallest diameter d1 of powder particles of the corresponding raw powder fraction of the material. This lateral dimension of the material removal or that of the pores has the advantageous effect that no new powder particles can penetrate into the resulting pore when powder is applied again. A time-consuming depowdering of these cavities is therefore not necessary. For this purpose, the dimension d2 is preferably selected—via the pulsed operation of the laser B2—to be less than 100 μm, particularly preferably less than 50 μm, in particular less than 20 μm.

6 shows in one to the 4 and 5 Similar cross-sectional view shows a component 10 or a part thereof, in which entire hollow channels 11, for example for cooling the component during operation, have been introduced using the method described here. In the upper layers, oval weld beads can again be seen, as well as—over at least three layers—hollow channels according to the invention. Layer by layer, these channels 11 can be provided with an offset v by means of laser pulses introduced in an offset manner, in order, for example, to allow a cooling channel, which would otherwise extend vertically through the component 10, to run slightly obliquely or diagonally.

The cooling channel 11 shown at the top right, on the other hand, has been introduced in layers by the material removal of the ultra-short pulse laser B2 in such a way that it runs vertically and parallel to the direction of construction of the component 10 .

However, if the channels 11 are offset (as can be seen on the left), the free spaces generated by the ultra-short pulse laser B2 are partially sealed again. Because in newly melted layers there is always a molten pool, which is known to be dimensionally unstable and significantly limits the geometric resolution of the structures achieved. For this reason, the offset v mentioned must be designed in such a way that the remaining free spaces remain fluidically connected and form a channel.

According to the present invention, provision can also be made for individual or multiple channels to be introduced partially or completely within a layer L, in that material is correspondingly removed there only in one layer. The situation is shown in the lower part of the illustration 6 indicated by the round circles, which are intended to illustrate that a corresponding cooling channel runs into the plane of representation. At the bottom right of the component 10 shown, the dotted lines also indicate an oblique and diagonal cooling process.

It is obvious to a person skilled in the art that the geometry of the cooling channels 11 formed in this way can of course be tailored in a simple manner by controlling the working laser and the ultra-short pulse laser B2 in accordance with the individual design requirements of the component 10 . In particular, the density of the channels can be adapted to a corresponding cooling capacity, which is required for the component to be operated as intended.

In other words, the channels 11 can be built up in all coordinate or spatial directions. They can be generated in one plane (x, y direction) or across several planes (z direction). It is therefore also possible to generate complex structures, such as lattice structures with very small lattice struts or wall thicknesses. For example, a wall thickness (compare reference symbol b in 7 further below) can be dimensioned smaller by the method described than a melt pool that usually occurs during the manufacturing process or a weld bead resulting therefrom during the construction of the corresponding structure. As described above, the melt pool is the decisive factor in continuous laser operation as far as the wall thickness and the surface roughness of the built-up structures are concerned. With the means presented, among other things, the shaping and the spatial resolution of additive thin wall structures can be significantly improved.

As an alternative or in addition to using the ultrashort pulse laser B2 for material removal, the ultrashort pulse laser B2 can also be used to reduce surface roughness of the cavities 11 and/or to structure a surface 12 of the cavities.

7 also shows a possible comparison between the layer thickness L and the depth t of the material yield, whereby the latter is chosen to be approximately four times greater than the layer thickness L in the present case. Furthermore, in 7 the wall thickness b is drawn on the right edge of the component structure (see above).

the 8th and 9 also show how the dimension or contour k of a corresponding cavity 11 is defined when further component layers are built up after the material has been removed. In the 8th a cavity 11 is shown again, which extends into the structure of the component 10 over several layers.

9 FIG. 1 also indicates further layers L running above the cavity 11 for the structure of the component 10, for example as a result of a progressive build-up process.

Should now - starting from the situation in 8th - A new layer of powder or material closes the resulting cavity 11, the geometry k of the cavity is determined in the lower part by the ultra-short pulse laser B2, and in the upper part by the geometry of the overlying melting path. The initial width of the cavity is therefore also determined by the height at which it is delimited by the overlying melt line. As indicated above, the working laser B1 not only melts the last layer of powder, but also the layers underneath it (again).

The upper end of a cavity contour k created with the USP laser is closed again by overlying layers, which are irradiated and solidified in normal working mode.

This creates, as in 9 (relative to 8th ) can be seen, a reduction in the vertical extent or depth t of the cavity 11.

Conventionally, ie without the described merits of the present invention, cavities or cavities are only generated during the LPBF process when the material is melted. In this case, the affected area is not exposed, the powder is not melted and the material is not cooled and solidified into solid material. However, this only works up to a certain material or wall thickness (see above).

The present invention advantageously overcomes this limitation by using the ultrashort pulse laser B2 exclusively for ablation of already solidified material, for example following selective irradiation of the material to produce the cavities 11 in the structure. In other words, a complete layer structure is preferably first produced with the laser B2, and the cavities 11 are only introduced subtractively afterwards. Therefore - as described - even complex and very fine cavities or pores can be integrated into LPBF-produced components.

The use of laser pulses described above means that significantly finer structures can be generated, since these enable greater accuracy in the material removal than the usual working lasers, and thus fine cavities or filigree lattice structures can also be produced.

Furthermore, no additional and non-uniform heat that could generate internal stresses is thus advantageously introduced into the component. The ultra-short, intensive radiation input leads to direct (plasma) evaporation. As a result, there are advantageously no or no disadvantageous hot micro and/or macro cracks, no material fatigue, no measurable molten pool, not even a measurable heat exchange, no smoke, no laser-induced shock waves, no impaired surface roughness or material defects, stresses or other changes resulting therefrom of the structure, or the surface quality.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 3022008 B1 [0015]

Claims (15)

Method for producing cavities (11) in a structure for a component (11) to be produced layer by layer, comprising processing material for the structure (10) during the layered construction of the structure with an ultrashort pulse laser (B2), material being removed in order to to produce cavities (11) according to a predetermined geometry in the structure. procedure according to claim 1 , wherein the structure for the component (10) is built up by a powder-bed-based method, in particular selective laser sintering, selective laser melting or electron beam melting. procedure according to claim 1 or 2 , wherein the structure for the component (11) is built up by selective laser melting, and wherein the ultrashort pulse laser (B2) is different from a melting laser (B1) for the selective laser melting. Method according to one of the preceding claims, wherein an energy input of the ultrashort pulse laser (B2) into the material is selected in such a way that the material is removed by direct vaporization. Method according to one of the preceding claims, in which the material is processed without creating a veritable molten pool (M) in the material. Method according to one of the preceding claims, wherein the ablation (t) of material by the ultrashort pulse laser (B2) along a layer normal (z) is dimensioned to be greater than a layer thickness (L) of material to be applied. Method according to one of claims 2 until 6 , wherein the cavities (11) or pores are produced with dimensions (d2) that are smaller than a diameter (d1) of powder particles of the material. A method according to any one of the preceding claims, wherein the material is removed in successive layers at the same or a slightly offset (v) layer position to form hollow channels (11) along a build-up direction (z) of the structure. A method according to any one of the preceding claims, wherein the material within a layer (L) is removed to form hollow channels (11) within the layer of the structure. Method according to one of the preceding claims, wherein the ultrashort pulse laser is used to reduce a surface roughness of the cavities (11) and/or to structure a surface (12) of the cavities. Method according to one of the preceding claims, wherein only already solidified material is carried out by the ultrashort pulse laser (B2) following selective irradiation of the material in order to produce the cavities (11) in the structure. A component (10) made according to or by means of the method of any preceding claim, wherein the voids (11) in the structure of the component along one dimension have a dimension (d2) that is smaller than a minimum or median diameter of powder particles (d1) of the material. Component (10) according to claim 12 , wherein a wall thickness (b) of structures of the component is smaller than a melt pool (M) arising during the manufacturing process for building up the corresponding structure. Component (10) according to claim 12 or 13 , wherein the component (10) has a lattice structure with cooling channels (11) running obliquely or diagonally through the component. Device (100) for the additive manufacturing of a component, comprising an irradiation device (2, B1) for selectively solidifying a material for the component (10), and a controller (4) and a beam source for applying an ultrashort pulse laser to remove the material according to a method according to one the Claims 1 until 11 is set up.

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