CONTROL UNIT FOR PULSED IRRADIATION IN ADDITIVE MANUFACTURE

Abstract

A method for the computer-aided provision of control instructions for pulsed irradiation in the additive production of a component structure includes establishing process parameters, including a pulse frequency, a pulse width, a scan speed, and an irradiation power; defining the pulse frequency and scan speed as process constants; and determining parameter values of the pulse width and of the irradiation power from the process constants which have been defined. A corresponding computer program product, a method for bed-based additive production, and a corresponding control device are adapted for pulsed irradiation in the additive production of a component structure.

Claims

1. A method for computer-aided provision of control instructions (f, τ, v, P) for pulsed irradiation in an additive production of a component structure, comprising: i) establishing process parameters, comprising a pulse frequency (f), a pulse width (τ), a scan speed (v) and an irradiation power (P), ii) defining the pulse frequency (f) and scan speed (v) as process constants, and iii) determining parameter values of the pulse width (τ) and of the irradiation power (P) from the process constants which have been defined.

2. The method as claimed in claim 1, wherein a value of the pulse frequency (f) between 1 kHz and 25 kHz is selected.

3. The method as claimed in claim 1, wherein a value of the irradiation power (P) between 50 W and 300 W is determined.

4. The method as claimed in claim 1, wherein a melt pool overlap (o) is additionally defined as a process constant, and wherein the melt pool overlap (o) is determined from parameter values of the established process parameters.

5. The method as claimed in claim 4, wherein a pathwise melt pool overlap (o) is determined from parameter values of the frequency, pulse width (τ) and scan speed (v), and a layerwise melt pool overlap is determined from a value of the irradiation power (P).

6. The method as claimed in claim 1, wherein the pulse frequency (f) and scan speed (v) are defined only layerwise as process constants.

7. The method as claimed in claim 1, wherein a duty cycle of between 25% and 75% is selected for the pulsed irradiation.

8. The method as claimed in claim 1, wherein a value of the scan speed (v) between 100 mm/s and 3000 mm/s is selected.

9. The method as claimed in claim 1, wherein with an increasing defined pulse frequency (f), a lower irradiation power (P) and a smaller pulse width (τ) are determined.

10. A computer program product stored on a non-transitory computer readable media, comprising: commands which, when executed by a computer cause this computer to carry out the method as claimed in claim 1.

11. A method for powder bed-based additive production of a component structure comprising: executing the control instructions produced by the method as claimed in claim 1.

12. A control device for the additive production of a component structure, wherein the control device is configured to employ the control instructions provided by the method as claimed in claim 1 in order to control an energy beam of an additive production apparatus in the course of the additive production of the component structure.

13. An additive production apparatus, comprising: a control device as claimed in claim 12.

14. The method as claimed in claim 7, wherein a duty cycle of 50% is selected for the pulsed irradiation.

15. The computer program product as claimed in claim 10, wherein the commands control the irradiation in an additive production apparatus.

16. The control device as claimed in claim 12, wherein the energy beam comprises a laser beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 indicates the principle of additive powder bed methods with the aid of a schematic sectional view of a corresponding production apparatus.

[0036] FIG. 2 shows a schematic flow chart indicating method steps according to the invention.

[0037] FIG. 3 indicates a setpoint situation with respect to process parameters determined based on a schematic plan view of an irradiation path.

[0038] FIG. 4 indicates an actual situation with respect to process parameters determined based on a schematic plan view of an irradiation path.

[0039] FIG. 5 shows a diagrammatic overview of the measured profile of the irradiation power, parametrically plotted as a function of the pulse frequency and respectively the duty cycle.

[0040] FIG. 6 shows a diagrammatic overview of the pulse width which is plotted, while being parameterized by the irradiation power, as a function of the pulse frequency and respectively the duty cycle.

DETAILED DESCRIPTION OF INVENTION

[0041] In the exemplary embodiments and figures, elements which are the same or have the same effect may respectively be provided with the same references. The elements represented and their size proportions with respect to one another are not in principle to be regarded as true to scale, and individual elements may instead be represented as being exaggeratedly thick or large for improved representability and/or for improved understanding.

[0042] FIG. 1 shows an additive production apparatus 100. The production apparatus 100 is advantageously configured as an LPBF apparatus and for the additive construction of components or constituent parts from a powder bed. The apparatus 100 may especially also refer to an apparatus for electron beam melting.

[0043] Accordingly, the apparatus comprises a construction platform 1. A component 10 to be additively produced is produced layerwise on the construction platform 1 from a powder bed. The latter is formed by a powder material 5, which may for example be distributed layerwise on the construction platform 1 by means of a cylinder 4 and then a coater 7.

[0044] After the application of each powder layer L, regions of the layer are selectively melted with an energy beam 6, for example a laser or an electron beam, and subsequently solidified, according to the predetermined geometry of the component 10. In this way, the component 10 is constructed layerwise along the construction direction z shown.

[0045] The energy beam 6 advantageously comes from a beam source 2 and is scanned position-selectively over each layer L by means of a controller 3.

[0046] The controller or control device 3 is advantageously configured to employ the control instructions in order to control the energy beam 6 in the course of the additive production of the component structure 10.

[0047] After each layer L, the construction platform 1 is advantageously lowered by an extent corresponding to the layer thickness (cf. arrow directed downward on the right in FIG. 1). A thickness of the layer(s) L is usually only between 20 μm and 40 μm, so that the overall process may easily comprise the selective irradiation of thousands to tens of thousands of layers. High temperature gradients, for example of 10.sup.6 K/s or more, may in this case occur because of the only very locally acting energy input. A stress state of the component is therefore also correspondingly high during the construction and thereafter, which generally makes additive production processes much more complicated.

[0048] The component 10 may be a component of a turbomachine, for example a component for the hot-gas path of a gas turbine. In particular, the component may refer to a rotor blade or guide vane, a ring segment, a combustion chamber part or burner part, such as a burner tip, a shroud, a screen, a heat shield, a nozzle, a seal, a filter, an orifice or lance, a resonator, a piston or a swirler, or a corresponding transition, insert, or a corresponding retrofit part.

[0049] The geometry of the component is conventionally established by a CAD file. After such a file has been read into the production apparatus 100 or the controller 3, the process subsequently requires first the establishment of a suitable irradiation strategy, for example by CAM means, so that the component geometry is also divided into the individual layers. Accordingly, the measures according to the invention as described below in the additive production of material layers may also already be expressed by a computer program product C. The computer program product C to this end advantageously comprises commands which, when a corresponding program or method is run by a computer, or the controller 3, cause it to carry out control instructions according to the invention and/or the selective irradiation accordingly.

[0050] The method steps according to the invention are illustrated with the aid of FIG. 2. The method according to the invention is primarily a method for the computer-aided provision of control instructions for pulsed irradiation in the additive production of the component structure 10.

[0051] The method comprises (i) establishing process parameters, comprising a pulse frequency f, a pulse duration or pulse width τ, a scan speed v and an irradiation power P, as indicated in the left part of FIG. 2. With the aid of the pulse width τ, the pulse frequency f and/or the scan speed v, a melt pool overlap o may in particular also be determined (see below). The arrows and connections in the left part of the representation of FIG. 2 are intended to indicate that the irradiation parameters described are correlated and/or interact with one another.

[0052] The method furthermore comprises (ii) defining a pulse frequency f and a scan speed v as process constants, as indicated in the middle part of FIG. 2. These parameters are in particular kept constant for the irradiation of a layerwise irradiation pattern and/or for the irradiation of individual vectors or paths (as represented in FIGS. 3 and 4 below).

[0053] The method furthermore comprises (cf. (iii) on the right in FIG. 2), determining parameter values of at least the pulse width τ and the irradiation power P from the process constants which have been defined.

[0054] A parameter value of the pulse frequency f may, in particular, be selected from a value range of between 1 kHz and 25 kHz.

[0055] Furthermore, a parameter value of the irradiation power P, which advantageously indicates a peak power or an average power per period, of between 50 W and 300 W may be determined.

[0056] A melt pool overlap o (cf. likewise FIGS. 3 and 4 below) may furthermore be defined as a process constant and additionally be determined from parameter values of the established process parameters. The melt pool overlap mentioned here may furthermore refer to a pathwise melt pool overlap, namely one such as is shown with the aid of the references o1 and o2 in FIGS. 3 and 4 below, respectively; and to a layerwise melt pool overlap (not explicitly denoted here). The pathwise melt pool overlap o may in particular be determined from parameter values of frequency, pulse width τ and scan speed v; while the layerwise melt pool overlap may essentially be defined by the irradiation power P. Under given further parameters, as is known, the irradiation power also determines the extent of a melt pool along the construction direction z and/or along the layer sequence.

[0057] Parameter values of the duty cycle of the pulsed irradiation may for example be selected from a range of between 25% and 75%, for example 50% or more or less.

[0058] A value of the scan speed v may however be selected from a range of between 50 mm/s or 100 mm/s and 3000 mm/s, for example 200 mm/s, 300 mm/s, 500 mm/s, 1000 mm/s, 1500 mm/s, 2000 mm/s, 2500 mm/s or more or less.

[0059] Often, it may be observed that with an increasing defined pulse frequency f, a lower irradiation power P and a shorter pulse width τ must also be selected (see FIGS. 5 and 6 below).

[0060] The algorithm provided by the means according to the invention advantageously—as described above—dimensions the relevant irradiation parameters and matches them to one another in order to obtain an expedient structural outcome of the component structure 10 and/or to counteract control artefacts.

[0061] FIG. 3 shows a schematic plan view of an irradiation path in pulsed irradiation operation for at least a part of each component layer. The irradiation path or vector is denoted by the reference V. Individual pulses and/or melt pools M with the length a of the vector V are intended to be indicated elliptically, the neighboring pulses overlapping (spatially) in a lenticular or circular region o1. Such an overlap o1 may qualitatively refer in the present case to an expedient measure for the production of a coherent structure for the component.

[0062] FIG. 4 shows—in a similar way to FIG. 3—a schematic plan view of an irradiation path V. In contrast to FIG. 3, pulses and/or corresponding melt pools having a length b, with b<a, are respectively shown here. Melt pools M shortened in this way may be produced, for example, by a shorter pulse width τ. It is furthermore shown that the melt pools M overlap only within a very small overlap region o2. Consequently, the overlap o2 is no longer sufficient to bring about a homogeneous or coherent component structure 10.

[0063] Although this is not explicitly denoted here, a person skilled in the art will clearly understand with reference to the representation of FIG. 1 that a corresponding melt pool overlap is necessary not only pathwise but also layerwise in order to produce a continuous component structure 10. This is because with a reduction of the irradiation power, for example, beyond a certain point the overlap of the melt pools along the construction direction z would also be critically reduced.

[0064] Instead of a coherent component structure, with an insufficient overlap at best a porous and unstable component structure would be obtained.

[0065] FIGS. 5 and 6 show (further) correlation effects of irradiation parameters with the aid of exemplary measurement values.

[0066] With the aid of six partial diagrams, FIG. 5 respectively shows measurement values of a pulsewise normalized irradiation power (field variable) in the relevant context. By the partial representation from the top left to the bottom right, the setpoint value of the irradiation power is respectively shown in varying 50 watt steps from 50 to 300 W. A further parameter for which measurement values are respectively shown is the duty cycle (cf. the legend at the top right in FIG. 5). This represents the dimensionless ratio of the pulse width to the period duration of the respective pulse. Here, measurement values are respectively shown for a duty cycle of 25%, 50% and 75%. A further parameter on the X axis is the frequency, to which the normalized power, that is to say a corresponding drop in the measured power, is respectively assigned particularly at 1 kHz, at 2 kHz, at 3 kHz, at 4 kHz, at 5 kHz, at 10 kHz, at 20 kHz and at 25 kHz.

[0067] It may be seen that with an increasing frequency, as well as overall at very low setpoint powers, for example of 50 W and 100 W, there is a smaller actual value, that is to say a greater drop relative to the setpoint value.

[0068] FIG. 6 shows a situation very similar to FIG. 5, merely with the difference that the normalized pulse width τ—instead of the power—is respectively plotted on the Y axis. A profile of the pulse width similar to the behavior of the power is now again to be seen from FIG. 6. With an increasing frequency and at rather low powers (cf. the upper row of the partial representation), there is also a smaller pulse width.

[0069] These deviations or artefacts may be explained in that a laser in conventional production apparatuses (without the control solution according to the invention) is often configured for a high power range, nominally for example about 1000 W, and it cannot therefore be controlled reliably in the low power range.

[0070] For high frequencies, the described deviation may be explained qualitatively in that, with a rising frequency, an inherent response time must also increasingly be taken into account in the control of the laser.

[0071] The described deviations may still be successfully resolved, or compensated for, by the means of the present invention.