WO2022167408A1

WO2022167408A1 - Irradiation strategy for additive manufacturing with pulsed irradiation

Info

Publication number: WO2022167408A1
Application number: PCT/EP2022/052324
Authority: WO
Inventors: Fabian GÖBEL; Timo HEITMANN; Jan Pascal Bogner
Original assignee: Siemens Energy Global GmbH & Co. KG
Priority date: 2021-02-03
Filing date: 2022-02-01
Publication date: 2022-08-11
Also published as: DE102021200994A1

Abstract

The invention relates to a method for irradiating a material layer (L) during 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), wherein the first energy input (E1) results in a plurality of separate melt pools (S1) in the material layer (L), and defining a second pulsed energy input (E2) into the material layer (L) along the same irradiation vector (V), wherein the second energy input (E2) results in an irradiation of material regions between the separate melt pools (S1) caused by the first pulsed energy input (E1), and wherein layer material is continuously irradiated along the irradiation vector (V) by irradiation with the first and the second pulsed energy inputs (E1, E2). The invention further relates to a corresponding computer program and computer program product.

Description

description

Irradiation strategy for additive manufacturing with pulsed irradiation

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) "methods, in particular laser deposition welding, electron beam or plasma powder welding, wire welding, metallic powder injection molding, so-called "sheet lamination" methods, or thermal spraying methods (VPS LPPS, GDCS).

A method for selective laser melting with pulsed radiation is known, for example, from EP 3 022 008 B1. Additive manufacturing methods have also proven to be particularly advantageous for complex or filigree 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 manufacture 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 assembly 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 far behind 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 detachments, 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 in order to weld thin-walled structures with wall thicknesses or Melting track widths of approx . Produce 100 pm or less . This structural dissolution is limited in particular by the coupling of the solidification process to the discrete solidification of individual melting baths. 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 injections means that there are effectively no more discrete melt pools or these 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 the case of continuous or continuous wave irradiation operation (“cw” for “continuous-wave”). D. H . Wall thicknesses of 100 μm and less cannot be achieved with continuous irradiation under otherwise identical boundary conditions.

Although the pw process means an 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 problem 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, Schmelz zbaden in the material layer causes. There is expediently no overlap between these separate melting baths.

The method also includes specifying a second and/or third or further, in particular offset, pulsed energy input into the material layer along the same irradiation vector, with this second and/or further energy input irradiating material regions between the separate melt baths caused by the first pulsed energy input effected, wherein layer material is uniformly or is continuously irradiated or may be solidified along the irradiation vector.

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 of discrete melting baths. As illustrated by the other exemplary embodiments, the use of an irradiation of the material layer based on the two modes or Energy inputs that individual discrete melting baths of each material layer cool down in parallel (simultaneously) and a melting track, which was interrupted by the first pulsed energy inputs, can advantageously be 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 due to the arrangement or local application of these energy inputs by an energy beam, for example a laser or an electron beam, can be determined 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, which increases productivity or Ef fi ciency 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 determined in such a way that a plurality of separate melt pools is also created in the material layer, with these melt pools being offset along the said irradiation vector, preferably in terms of time and/or space in relation to those brought about by the first pulsed energy input Schmel zbaden are arranged. This embodiment expediently enables the technical improvements described above.

In one embodiment, the second pulsed energy input is applied with a time delay relative 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 melting baths or Traces of melting of the (solidified) layer material, which result from the irradiation with the first pulsed energy input and melting pools, which result from the irradiation with the second pulsed energy input in the material layer, between 30% and 60%, in particular 50%, a melting pool width with overlap the different melting baths in each case in order to achieve continuous material hardening. The mentioned In this case, the melting bath width can measure the melting baths that result from the first energy input and/or those that result from the second energy input.

In one embodiment, a melting trace or a material application or a welding track, which results from the irradiation with the first and/or the second pulsed energy input, a, in particular average, width which corresponds to one to one and a half times the diameter of the energy beam. According to this embodiment, the melt track width can be appropriately dimensioned based on the corresponding beam diameter.

In one embodiment, a melting trace or an application of material or a trace of welding, which results from the irradiation with the first and/or the second pulsed energy input, 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 selective irradiation of the material layer, in particular by selective laser melting, selective laser sintering or electron beam melting, is determined, with the particular aim of increasing or doubling the productivity of the process—compared to conventional irradiation - A two- to ten-fold irradiation speed, in particular four-fold irradiation speed and furthermore a two- to ten-fold irradiation power, in particular four-fold irradiation power, 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 between 50 mm/s and 10, for example. 000 mm/s, in particular between 50 mm/s and 1500 mm/s. In one embodiment - in comparison to conventional pulsed irradiation - a one- to five-fold irradiation frequency or. Pulse frequency for the first pulsed energy input or the second pulsed energy input chosen. With this configuration, the productivity of the irradiation and thus of the entire production process can be correspondingly advantageously improved.

In one embodiment, the first and second pulsed energy inputs 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 terms of the irradiation vector length to be scanned. Because, after a critical cooling time, shrinkage or Solidification effects that 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, further parameters .

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

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

Another 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 the computer to generate irradiation vectors in an additive manufacturing process according to the specified first pulsed energy input and the specified second pulsed energy input as described, to irradiate .

A CAD file or a computer program product can, for example, be used as a (volatile or non-volatile) storage or playback medium, e.g. B. a memory card, a USB stick, a CD-ROM or DVD, or in the form of a downloadable file provided or included by a server and/or 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 can be program code, machine code or include 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 included as CAD data or . include a program or program code for providing this data.

Configurations, features and/or advantages that relate to the irradiation method in the present case can also directly relate to the computer program product or a correspondingly manufactured component, 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.

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

FIG. 1 uses a schematic sectional view to indicate basic process steps of a powder bed-based, additive manufacturing process.

FIG. 2 shows a schematic sketch of a sequence of pulsed energy inputs along an irradiation vector in additive manufacturing.

FIG. 3 compares a sequence of energy inputs similar to FIG. 2 with a corresponding pulse shape of an energy beam.

Similar to FIG. 3, FIG. 4 indicates a sequence of pulsed energy inputs according to the invention 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, rather individual elements may be shown with exaggerated thickness or large dimensions for better representation and/or better understanding.

FIG. 1 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 construction share or components designed from a powder bed.

Alternatively, the system 100 can also be 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 the application of each powder layer L—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 a radiation device 2 and then solidified. The dashed line, which is also marked with the reference sign 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 a continuous irradiation mode (cw), in particular for particularly thin-walled structures for a to realize component 10 .

After each layer L, the construction platform 1 is preferably lowered by an amount corresponding to the layer thickness t (compare the downward-pointing arrow in FIG. 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 also 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. Figure 2 below) should be designed, as the tension can then lead to strong geometric distortion, cracking tendency or even the destruction of the component.

The geometry of the component is usually defined by a CAD file ("Computer-Aided-Design"). After reading such a file 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 the component geometry is 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 bears the basic inventive idea 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 imprinted on the component 10 by the definition of corresponding irradiation parameters. Accordingly, a computer program, computer program product CP or a data carrier comprising such, which already includes the manufacturing instructions that are decisive for the technical success of the component, is 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 moving or guide 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, an orifice or lance, a resonator, a denote stamp or a swirler, or a corresponding transition, insert, or a corresponding aftermarket part.

FIG. 2 schematically shows a sequence of energy inputs, E, along an irradiation vector or irradiation path V, as must be traversed many times over each raw material layer L for the solidification of a component structure. In the illustration in FIG. 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 bath or a coherent, solidified weld track or material track can then 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) melting baths. These overlapping areas are represented by the lens-shaped contours in FIG.

A melting bath width is marked accordingly with the reference character b. In a conventional process, the melting bath width b usually corresponds to a dimension of about 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, the dimension b' (compare the smaller arrow in FIG. 2) is reduced by 10% to 30% compared to the width b.

In addition to FIG. 2, FIG. 3 shows the course of a laser pulse or a corresponding pulse modulation of an energy beam (above). In the middle part of the figure, a melting bath length s _m and an offset so of the melting baths shown resulting from the two energy inputs are drawn in. The dashed vertical lines illustrate the relationship between the melt baths and a corresponding period or period duration T=1/f on the time axis, where f corresponds to the pulse frequency and T _p corresponds to a pulse width.

In particular, as also shown in FIG. An overlap is preferably between 30% and 60% of the width b described above and/or the melting bath length Sm •

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 melting baths is ensured.

The corresponding irradiation vector V is described at the bottom of the illustration in FIG.

FIG. 4 indicates a schematic representation similar to the representation in FIG. 3, which illustrates method 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 includes determining a first pulsed energy input El into the material layer L along an irradiation vector V, the first energy input El causing a plurality of separate melting baths S 1 in the material layer L.

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

As described above, the first and the second pulsed energy input E1, E2 each expediently 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 (here indicated by dashed lines).

The second energy inputs E2 are preferably defined along the irradiation vector V (for the sake of clarity, only one melting bath S2 is marked in intermediate regions between the two energy inputs El in Figure 4) in such a way that a plurality of separate melting baths S2 are also created in the material layer L , which, however, only later lead to a welding track or solidify in a solidified track of material. 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 (re)exposure of the irradiation vector - with spatially offset melting baths (see above). . Advantageously, this strategy allows the process efficiency to be significantly increased (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.

Expediently, 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 by between 30% and 60%, preferably 50% Melting bath width b with the respective different kinds of melting baths in order to achieve continuous material hardening.

The proposed strategy advantageously allows the selection of an irradiation speed v that is two to ten times greater than that of a conventional (pulsed) type of irradiation in an additive manufacturing process, in particular four times the irradiation speed, and/or a two to ten times greater irradiation power P, in particular four times irradiation power . The irradiation power is preferably increased in the same way as the irradiation speed in order to reduce the amount of energy or energy introduced into the material layer over time. to keep the energy density constant.

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 reference symbols S3 and E3 in FIG. the second pulsed energy input El, E2 caused melting baths SI, S2. 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 melting baths. The further pulsed energy input E3 can also preferably be offset or offset along the irradiation vector V. delayed to those of the first or the second pulsed energy input E1, E2 caused melting baths SI, S2 are arranged 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 defined by the ratio of pulse width T _p and period T work cycle or. an exposure speed v is selected or coordinated in such a way that a discrete solidification of the individual melting baths SI, S2 or S3 is enabled. For example, the pulse width T _p can be changed proportionally to the irradiation speed v.

Claims

patent claims

1. A method for irradiating a material layer (L) in the additive manufacturing of a component (10), comprising:

- Defining a first pulsed energy input (El) into the material layer (L) along an irradiation vector (V), the first energy input (El) causing a plurality of separate molten pools (Sl) in the material layer (L), and that

- Defining a second pulsed energy input (E2) in the material layer (L) along the same irradiation vector (V), the second energy input (E2) causing an irradiation of material regions between the first pulsed energy input (El) caused separate molten baths (Sl). , wherein layer material is irradiated continuously along the irradiation vector (V) by irradiation with the first and the second pulsed energy input (E1, E2).

2. The method 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).

3. The method according to claim 1 or 2, wherein the second pulsed energy input (E2) is determined in such a way that a plurality of separate molten pools (S2) also arises in the material layer (L), these molten pools (S2) along the irradiation vector ( L) offset to the first pulsed energy input (E1) caused molten baths (Sl) are arranged.

4. The method according to any one of the preceding claims, wherein the second pulsed energy input (E2) delayed in time to the first pulsed energy input (E1) is applied.

5. The method according to any one of the preceding claims, wherein molten baths (Sl) resulting from the irradiation with the first pulsed energy input (El) 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% of a melt pool width (b) with the respective different melt pools, in order to achieve a continuous solidification of the material.

6. The method according to any 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 that corresponds to one to one and a half times the diameter of a corresponding energy beam .

7. The method as claimed in 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.

8. The method according to any one of the preceding claims, wherein the first and the second pulsed energy input (E2) for a selective irradiation of the material layer (L) are determined, and wherein - in comparison 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.

9. The method according to claim 8, wherein - compared to a conventional pulsed irradiation - a one to five times the frequency (f) is selected.

10. The method according to any 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) an irradiation of material regions between the through the first and the second ge- 19 pulsed energy input (El, E2) caused molten pools (SI, S2), and by the further pulsed energy input caused melt pools along the irradiation vector (V) offset or delayed in time to the first or the second pulsed energy input (El , E2) effected molten pools (SI, S2) are arranged in order to irradiate layer material continuously along the irradiation vector (V).

11. The method according to any one of the preceding claims, wherein the first and the second pulsed energy input (E1, E2) are effected by an energy beam (5) of the same beam source.

12. The method according to any one of claims 1 to 10, wherein the first and the second pulsed energy input (E1, E2) are effected by energy beams (5) from different beam sources.

13. Computer program product (CP), comprising instructions that cause the execution of a corresponding program by a computer (4), for example for controlling the irradiation in an additive manufacturing system (100), this irradiation vectors (V) in an additive manufacturing process according to the to irradiate specified first pulsed energy input (E1) and the specified second pulsed energy input (E2) according to one of the preceding claims.