DE102021200994A1 - Irradiation strategy for additive manufacturing with pulsed irradiation - Google Patents

Abstract

A method for irradiating a material layer (L) in the additive manufacturing of a component (10) is specified. The method comprises determining a first pulsed energy input (E1) into the material layer (L) along an irradiation vector (V), the first energy input (E1) causing a plurality of separate molten pools (S1) in the material layer (L), and that Determination of a second pulsed energy input (E2) into the material layer (L) along the same irradiation vector (V), the second energy input (E2) causing an irradiation of material regions between the separate melt pools (S1) caused by the first pulsed energy input (E1), wherein layer material is irradiated continuously along the irradiation vector (V) by irradiation with the first and the second pulsed energy input (E1, E2). A corresponding computer program or computer program product is also specified.

Description

The present invention relates to a method for irradiating a material layer in the additive manufacturing of a component, and a corresponding computer program or computer program product.

Said component is preferably provided for use in the hot gas path of a gas turbine. For example, the component relates to a component to be cooled with a thin-walled or filigree design. Alternatively or additionally, the component can be a component for use in automobiles or in the aviation sector. Such components are the subject of constant improvement, in particular to increase their efficiency in use.

Due to its disruptive potential for industry, generative or additive manufacturing is also becoming increasingly interesting for the series production of these components.

Additive manufacturing processes (AM: "additive manufacturing"), colloquially also referred to as 3D printing, include, for example, powder bed processes such as selective laser melting (SLM) or laser sintering (SLS), or electron beam melting (EBM). 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).

A method for selective laser melting with pulsed radiation is known, for example, from EP 3 022 008 B1 .

Additive manufacturing processes have also 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. The production of gas turbine blades using the described powder bed-based process (LPBF for “Laser Powder Bed Fusion”) enables in particular 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.

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

However, the powder bed process inherently creates high thermal stresses in the component structure. In particular, irradiation paths or vectors that are too short lead to severe overheating, which in turn often leads to distortion of the structure. Severe warping during the build process easily leads to structural delamination, thermal distortion, or geometric deviations outside of an allowable tolerance.

New LPBF process developments or related methods sometimes use a pulse-modulated ("pw" for "pulsed-wave") laser for welding processing, in particular to weld thin-walled structures with wall thicknesses or

To produce melt track widths of about 100 microns or less. This structural dissolution is limited in particular by the coupling of the hardening process to the discrete solidification of individual molten pools. Currently, pw processes for thin-walled structures, as well as for other applications, are only possible in comparatively low-frequency pulse ranges anyway. From a pulse frequency of around 4000 Hz upwards, the high temporal (and spatial) energy introduced by conventional pulsed energy inputs means that there are effectively no longer any discrete molten pools or they can no longer solidify discretely.

This in turn causes the same limitations and implications for the spatial resolution, which is known to be significantly poorer in continuous wave (“cw” for “continuous wave”) irradiation. This means that wall thicknesses of 100 µm and less cannot be achieved with continuous irradiation under otherwise identical boundary conditions.

It is true that the pw process means improved spatial resolution of the structures to be built; but also significant limitations in process efficiency.

It is therefore an object of the present invention to improve the process efficiency of pulsed or pulse-modulated energy inputs for selective irradiation in the AM range, while at the same time preferably particularly good structural imaging of thin-walled structures is made possible.

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 irradiating a material layer in the additive, in particular powder-bed-based, production of a component, comprising determining a first pulsed energy input into the material layer along an irradiation vector, the first energy input having a plurality of separate, in particular discrete or spaced apart, melt pools in the material layer causes. Expediently, there is no overlap between these separate molten baths.

The method also includes specifying a second and/or third or additional, in particular offset, pulsed energy input into the material layer along the same irradiation vector, with this second and/or additional energy input causing an irradiation of material regions between the separate molten pools caused by the first pulsed energy input , wherein layer material is irradiated or can be solidified uniformly or continuously along the irradiation vector by irradiation with the first and the second pulsed energy input.

In contrast to conventional methods, which also use pulsed irradiation of such material layers, this procedure can be used to decouple the process from the necessary cooling time for discrete molten baths. As illustrated by the further exemplary embodiments, the use of irradiation of the material layer using the two described modes or energy inputs allows individual discrete molten pools of each material layer to cool down in parallel (simultaneously) and a melting track, which was still interrupted by the first pulsed energy inputs, can be advantageously completed by the second or further pulsed energy inputs to form a continuous melting track. In this context, the pulsed energy inputs described are advantageously, but not necessarily, of the same species or uniform. A difference in these energy inputs may only be determined by the arrangement or local application of these energy inputs by an energy beam, for example a laser or an electron beam, in the powder bed.

In other words, the approach described increases a maximum possible frequency in the pulsed irradiation by decoupling it from the cooling time, as a result of which the productivity or efficiency of selective additive manufacturing processes, as a significant limitation, can be significantly increased or improved.

In one configuration, the first and the second pulsed energy input each bring about a discrete solidification of material in the layer.

In one embodiment, the second pulsed energy input is defined in such a way that a plurality of separate melt pools is also formed in the material layer, these melt pools being offset along said irradiation vector, preferably in terms of time and/or space in relation to the melt pools caused by the first pulsed energy input will. This embodiment expediently enables the technical improvements described above.

In one embodiment, the second pulsed energy input is applied with a time delay in relation to the first pulsed energy input, in particular in order to achieve the discrete solidification of the molten baths resulting therefrom.

In one embodiment, the energy inputs mentioned are defined in such a way that molten pools or traces of melting of the (solidified) layer material, which result from the irradiation with the first pulsed energy input and molten pools, which result from the irradiation with the second pulsed energy input in the material layer, are between 30% and 60%, in particular 50%, of a melt pool width overlap with the respective different melt pools in order to bring about a continuous material hardening. The stated melt pool width can measure the melt pools that result from the first energy input and/or those that result from the second energy input.

In one embodiment, a melting track or an application of material or a welding track, which results from the irradiation with the first and/or the second pulsed energy input, has a particularly average width that corresponds to one to one and a half times the diameter of the energy beam. According to this configuration, the melting track width can expediently start out be dimensioned from the corresponding beam diameter.

In one embodiment, a melting track or an application of material or a welding track, which results from the irradiation with the first and/or the second pulsed energy input, has a, in particular average, width of, for example, less than 100 μm, preferably between 80 μm and 100 μm .

In one embodiment, the first and/or the second pulsed energy input for a selective irradiation of the material layer, in particular by selective laser melting, selective laser sintering or electron beam melting, is determined, with in particular to increase or double the productivity of the process - compared to conventional irradiation - a two to tenfold irradiation speed, in particular fourfold the irradiation speed and furthermore a two to tenfold irradiation power, in particular fourfold the irradiation power, are selected for the process.

In one configuration, an absolute irradiation speed, which is used for irradiation according to the first and/or the second energy input, is for example between 50 mm/s and 10,000 mm/s, in particular between 50 mm/s and 1500 mm/s.

In one embodiment—compared to conventional pulsed irradiation—a one to five-fold irradiation frequency or pulse frequency is selected for the first pulsed energy input or the second pulsed energy input. With this configuration, the productivity of the irradiation and thus of the entire production process can be correspondingly advantageously improved.

In one configuration, the first and the second pulsed energy input are brought about by an energy beam from the same beam source, for example a laser or electron source. According to this configuration, the advantages according to the invention can even be used in simple additive manufacturing systems that do not include a plurality of radiation sources. However, this configuration is inherently limited by the singular beam source in the irradiation vector length to be scanned. This is because, after a critical cooling time, shrinkage or hardening effects set in, which lead to a disadvantageous structural result of the weld track and possibly to a loss of homogeneity and resolution of the material application. The critical dimension of the irradiation vector length is defined by an interaction of the raw material used, the set irradiation speed, the heat input and, if necessary, other parameters.

In an alternative embodiment, the first and the second pulsed energy input are brought about by energy beams from different beam sources. This configuration can advantageously and in contrast to the irradiation with only a single energy beam, the limitation of this irradiation strategy to a critical vector length can be circumvented. Energy beams, or the first and second pulsed energy inputs, can be coordinated or used here in such a way that, on the one hand, discrete solidification is still ensured, but, on the other hand, no shrinkage or hardening effects occur.

In one configuration, the irradiation method is a computer-implemented method.

A further aspect of the present invention relates to a computer program or computer program product, comprising instructions which, when a corresponding program is executed by a computer, for example for controlling the irradiation in an additive manufacturing system, cause this to pulse irradiation vectors in an additive manufacturing process according to the specified first To irradiate energy input and the specified second pulsed energy input as described.

A CAD file or a computer program product can, for example, be in the form of a storage or playback medium (volatile or non-volatile), such as a memory card, USB stick, CD-ROM or DVD, or in the form of a downloadable file from a server and/or provided or comprised in a network. The provision can also be made, for example, in a wireless communication network by transferring a corresponding file with the computer program product. A computer program product may include program code, machine code or numerical control instructions, such as G-code, and/or other executable program instructions in general.

The computer program product can also contain geometry data or design data in a three-dimensional format or as CAD data or include a program or program code for providing this data.

Refinements, features and/or advantages that relate to the irradiation method in the present case can also be the computer pro gram product or a correspondingly manufactured component directly, and vice versa.

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

• 1 deutet anhand einer schematischen Schnittansicht grundlegende Verfahrensschritte eines pulverbettbasierten, additiven Herstellungsverfahrens an.
• 2 zeigt eine schematische Skizze einer Abfolge von gepulsten Energieeinträgen entlang eines Bestrahlungsvektors in der additiven Herstellung.
• 3 stellt eine Abfolge von Energieeinträgen ähnlich zur 2 mit einer entsprechenden Pulsform eines Energiestrahls gegenüber.
• 4 deutet ähnlich zur 3 eine erfindungsgemäße Abfolge gepulster Energieeinträge für die additive Herstellung an.

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

• 1 indicates the basic process steps of a powder bed-based, additive manufacturing process using a schematic sectional view.
• 2 shows a schematic sketch of a sequence of pulsed energy inputs along an irradiation vector in additive manufacturing.
• 3 provides a sequence of energy inputs similar to 2 with a corresponding pulse shape of an energy beam.
• 4 indicates similar to 3 an inventive sequence of pulsed energy inputs for additive manufacturing.

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 12 shows an additive manufacturing system 100. The manufacturing system 100 is preferably designed as an LPBF system (selective laser melting) and for the additive construction of parts or components from a powder bed. Alternatively, the system 100 can also relate to a system for electron beam melting or selective laser sintering.

Accordingly, the system has a construction platform 1 . A component 10 to be produced additively is produced in layers on the construction platform 1 . The powder bed is formed by a powder 6 which can be distributed in layers on the construction platform 1 by a coating device 3 .

After each powder layer L has been applied—usually with a preset layer thickness t—areas of the layer L are selectively melted according to the predetermined geometry of the component 10 with an energy beam 5, preferably a laser beam, from an irradiation device 2 and then solidified. The dashed line, which is also marked with the reference number 5, is intended to indicate that the laser can also be operated in a pulsed irradiation mode (pw) in addition or as an alternative to continuous irradiation mode (cw), in particular for particularly thin-walled structures for a component 10 to realize.

After each layer L, the construction platform 1 is preferably lowered by an amount corresponding to the layer thickness t (compare the arrow pointing downwards in 1 ). The thickness t is usually only between 20 μm and 80 μm, preferably 40 μm, so that the entire process can easily involve irradiating tens of thousands of layers.

High temperature gradients of, for example, 10 ⁶ K/s or more can still occur as a result of the only very locally acting energy input. Of course, there is a correspondingly large amount of stress in the component during assembly and afterwards, which considerably complicates the additive manufacturing processes. Such states of stress are all the more critical, the more filigree or thin-walled a component area (cf. 2 further below) should be designed, since the tension can then lead to severe geometric distortion, a tendency to crack or even to the destruction of the component.

The geometry of the component is usually defined by a CAD file (“computer-aided design”). After such a file has been read into the manufacturing system 100, the process then first requires the definition of a suitable irradiation strategy, for example by means of the CAM, which also results in the component geometry being divided into the individual layers.

It can be seen that the choice of a preferred irradiation strategy, including the determination of essential irradiation parameters for the additive manufacturing process of the component 10, already carries the inventive basic ideas and with a simple execution of a corresponding irradiation process the component is inevitably equipped with advantageous structural properties. In other words, the advantageous technical properties are already impressed on the component 10 by the definition of corresponding irradiation parameters. Accordingly, a computer program, computer program product CP or such a comprehensive data carrier, which is already necessary for the technical success of the Component relevant manufacturing instructions includes, part of the present invention. As indicated, the computer program CP can be executed accordingly via a processor or a data processing device or a control unit for the irradiation device 2 .

The component 10 can be a component of a turbomachine, for example a component for the hot gas path of a gas turbine. In particular, the component can be a blade or vane, a ring segment, a combustion chamber or burner part, such as a burner tip, a skirt, a shield, a heat shield, a nozzle, a seal, a filter, a mouth or lance, a resonator, a denote punch or a swirler, or equivalent transition, insert, or equivalent aftermarket item.

2 shows schematically a sequence of energy inputs, E, along an irradiation vector or irradiation path V, as it often has to be traversed over each raw material layer L for the solidification of a component structure. In the representation of 2 , which preferably corresponds to a top view of a component layer, the irradiation takes place in a pulsed manner via a plurality of individual energy inputs in such a way that a coherent molten pool or subsequently a coherent, solidified weld track or material track can be produced. For this purpose, the individual energy inputs E are expediently defined, arranged or selected in such a way that an overlap occurs between adjacent individual (discrete) molten pools. These overlapping areas are indicated by the lens-shaped contours in the 2 shown.

A melt pool width is indicated correspondingly with the reference symbol b. In a conventional process, the melt pool width b usually corresponds to a dimension of around 200 μm or more. Only after a cooling time and a solidification of this molten bath does the molten material shrink slightly, as a result of which the width b' for the solidified material track is slightly reduced. For example, dimension b' (compare smaller arrow in 2 ) reduced by 10% to 30% compared to the width b.

3 shows in addition to 2 and compared to two overlapping discrete molten pools (below) the course of a laser pulse or a corresponding pulse modulation of an energy beam (above). In particular, a melt pool length s _m and an offset s ₀ of the melt pools shown resulting from the two energy inputs are shown in the middle part of the figure.

The dashed vertical lines illustrate the connection between the molten pools and a corresponding period or period length T=1/f on the time axis, where f corresponds to the pulse frequency and T _p corresponds to a pulse width.

as well as in 2 In particular, as shown, the two melt pools E overlap to provide a uniform continuous track of material along the exposure vector V. An overlap is preferably between 30% and 60% of the width b described above and/or the melt pool length S _m •

In order for discrete solidification to actually take place and to prevent a continuous melt pool from forming along vector V, a cooling time must be allowed to elapse after the first energy input (left), for example. Only then can the advantages of pulsed irradiation, in particular the possibility of producing particularly thin-walled structures, be achieved.

In particular, the combination of the frequency f and the exposure speed v must preferably be selected in such a way that discrete solidification is made possible and at the same time an overlapping of the molten pools is ensured.

Below in the representation of 3 the corresponding irradiation vector V is described, with the parameters v and P being intended to indicate a correspondingly selected or fixed irradiation speed.

4 indicates a to the representation of 3 similar schematic representation, which illustrates process steps according to the invention.

The method according to the invention is a method for irradiating a material layer L in the additive manufacturing of a component 10. The method comprises defining a first pulsed energy input E1 into the material layer L along an irradiation vector V, the first energy input E1 having a plurality of separate melt pools S1 in the material layer L causes.

The method also includes specifying a second pulsed energy input E2 into the material layer L along the same irradiation vector V, the second energy input E2 irradiating (melting and solidifying) material regions between the first pulsed energy input E1 caused separate molten baths S1, layer material being irradiated uniformly or continuously along the irradiation vector V by irradiation with the first and the second pulsed energy input E1, E2.

As described above, the first and the second pulsed energy input E1, E2 expediently each bring about a discrete solidification of material in the layer L. This is preferably achieved by a spatial and temporal offset of the energy inputs E2 relative to the energy inputs E2 (presently indicated by dashed lines), reached.

The second energy inputs E2 are along the irradiation vector V (for the sake of clarity in 4 only one molten pool S2 in intermediate areas between the two energy inputs E1) preferably defined in such a way that a plurality of separate molten pools S2 are also formed in the material layer L, which, however, solidify later to form a weld track or a solidified material track due to a time delay. In other words, the second pulsed energy input, which can be formulated similarly or identically to the first pulsed energy input, can only be used in a second step for a (renewed) exposure of the irradiation vector - with spatially offset molten pools (cf. S ₀ above). .

Advantageously, this strategy can significantly increase the process efficiency (see below). At the same time, this type of energy input during the irradiation allows the formation of an advantageously small or thin material track or weld bead, which preferably corresponds to a dimension b' of less than 100 μm, for example between 80 μm and 100 μm, or less.

Appropriately, melt pools S1, which result from the irradiation with the first pulsed energy input E1 and melt pools S2, which result from the irradiation with the second pulsed energy input E2 in the material layer L, overlap between 30% and 60%, preferably 50%, of the melt pool width b the different types of molten baths in each case in order to achieve continuous material hardening.

The proposed strategy advantageously allows the selection of a two to tenfold increased irradiation speed v, in particular fourfold the irradiation speed, and/or a twofold to tenfold increased irradiation power P, in particular fourfold, compared to a conventional (pulsed) mode of irradiation in an additive manufacturing process irradiation power. The irradiation power is preferably increased in the same way as the irradiation speed in order to keep the energy or energy density introduced into the material layer constant over time.

Furthermore - in comparison to conventional (pulsed) irradiation - a pulse frequency f that is one to five times higher can be selected, and the process efficiency can thus also be significantly increased.

The first and the second pulsed energy input E1, E2 can be brought about by an energy beam 5 from the same beam source. This brings about the advantages described above.

As indicated by the references S3 and E3 in 4 is indicated, the method can also include the specification of a third or further pulsed energy input E3 along the irradiation vector V, with the further energy input E3 also irradiating material regions between the melt pools S1 caused by the first or the second pulsed energy input E1, E2, S2 causes. The third pulsed energy input E3 can be similar to the first and/or the second pulsed energy input E1, E2. The same applies analogously to the correspondingly generated melt pools. The further pulsed energy input E3 can also be arranged along the irradiation vector V, preferably offset or delayed in relation to the melt pools S1, S2 caused by the first or the second pulsed energy input E1, E2, in order to irradiate layer material continuously along the irradiation vector V.

Alternatively, the first and the second pulsed energy input E1, E2 can be brought about by energy beams 5 from different beam sources. This brings about the advantages also described above. In particular, as explained, the cooling time can be adjusted as desired depending on the material and process parameters due to the variable time offset of the two lasers or electron beams, so that the limitation of the critical vector length of the irradiation vector V mentioned can be advantageously circumvented. In particular, the frequency f, a work cycle defined by the ratio of pulse width T _p and period T or an exposure speed v are selected or matched to one another such that discrete solidification of the individual molten pools S1, S2 or S3 is made possible. For example, the pulse width T _p can be changed proportionally to the irradiation speed v.

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 [0005]

Claims (13)

Method for irradiating a material layer (L) in the additive manufacturing of a component (10), comprising: - Determination of a first pulsed energy input (E1) into the material layer (L) along an irradiation vector (V), wherein the first energy input (E1) causes a plurality of separate molten pools (S1) in the material layer (L), and that - Determination of a second pulsed energy input (E2) into the material layer (L) along the same irradiation vector (V), the second energy input (E2) causing an irradiation of material regions between the separate melt pools (S1) caused by the first pulsed energy input (E1). , wherein layer material is irradiated continuously along the irradiation vector (V) by irradiation with the first and the second pulsed energy input (E1, E2). procedure according to claim 1 , wherein the first and the second pulsed energy input (E1, E2) each bring about a discrete solidification of material in the layer (L). procedure according to claim 1 or 2 , the second pulsed energy input (E2) being defined in such a way that a plurality of separate molten pools (S2) is also formed in the material layer (L), these molten pools (S2) being offset along the irradiation vector (L) in relation to those of the first pulsed energy input (E1) caused molten pools (S1) are arranged. Method according to one of the preceding claims, wherein the second pulsed energy input (E2) is applied with a time delay in relation to the first pulsed energy input (E1). Method according to one of the preceding claims, wherein molten pools (S1) resulting from the irradiation with the first pulsed energy input (E1) and molten pools (S2) resulting from the irradiation with the second pulsed energy input (E2) in the material layer (L). , between 30% and 60% of a melt pool width (b) overlap with the respective different melt pools in order to bring about a continuous material hardening. Method according to one of the preceding claims, wherein a melting track, which results from the irradiation with the first and/or the second pulsed energy input (E1, E2), has a width which corresponds to one to one and a half times a diameter of a corresponding energy beam. Method according to one of the preceding claims, in which a melting track which results from the irradiation with the first and the second pulsed energy input (E1, E2) has a width (b') of less than 100 µm. Method according to one of the preceding claims, wherein the first and the second pulsed energy input (E2) are set for selective irradiation of the material layer (L), and wherein - compared to conventional irradiation, a two- to ten-fold irradiation speed (v), in particular four times the irradiation speed, and furthermore a two to ten times the irradiation power (P), in particular four times the irradiation power, can be selected. procedure according to claim 8 , where - in comparison to conventional pulsed radiation - a frequency (f) that is one to five times higher is chosen. Method according to one of the preceding claims, comprising the determination of a further pulsed energy input (E3) along the irradiation vector (V), wherein the further energy input (E3) involves an irradiation of material regions between the energy inputs (E1, E2 ). , S2) to irradiate layered material continuously along the irradiation vector (V). Method according to one of the preceding claims, in which the first and the second pulsed energy input (E1, E2) are brought about by an energy beam (5) from the same beam source. Method according to one of Claims 1 until 10 , wherein the first and the second pulsed energy input (E1, E2) are effected by energy beams (5) from different beam sources. Computer program product (CP), comprising instructions which, when a corresponding program is executed by a computer (4), for example for controlling the irradiation in an additive manufacturing system (100), cause this to irradiate vectors (V) in an additive manufacturing process according to the first specified pulsed energy input (E1) and the specified second pulsed energy input (E2) according to any one of the preceding claims.

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