METHOD FOR THE ADDITIVE MANUFACTURE OF COMPONENTS, DEVICE, CONTROL METHOD, AND STORAGE MEDIUM

Abstract

The present invention relates to a method for the additive manufacture of components (2), wherein a pulverulent or wire-shaped metal construction material is deposited on a platform (4) in layers, melted using a primary heating device (7), in particular using a laser or electron beam (14), and is heated using an induction heating device (8), which has an alternating voltage supply device (9) with an induction generator (16) and at least one induction coil (10) which can be moved above the platform (4). The induction generator (16) is controlled such that the induction generator is driven with a different output at different specified positions of the at least one induction coil (10). The invention additionally relates to a device, to a control method, and to a storage medium.

Claims

1. Method for the additive manufacture of components (2), wherein a pulverulent or wire-shaped metal construction material is deposited on a platform (4) in layers, melted using a primary heating device (7), in particular using a laser or electron beam (14), and is heated using an induction heating device (8), which has an alternating voltage supply device (9) with an induction generator (16) and at least one induction coil (10) which can be moved above the platform (4), wherein the induction generator (16) is controlled such that the induction generator (16) is driven with a different output at different specified positions of the at least one induction coil (10).

2. The method according to claim 1, wherein for each specified position of the at least one induction coil (10) a maximum output of the induction generator (16) that is retrievable at the respective specified position is determined and preferably stored in a storage device (29), in particular in a way that can be overwritten, and either directly following the determination of the retrievable maximum output or as soon as a specified position is again approached by the induction coil (10), the induction generator (16) is controlled in such a way that it is operated with an output which is a predefined amount below the retrievable maximum output determined for the respective specified position.

3. Method according to claim 2, wherein the at least one induction coil (10) is arranged to be movable above the platform (4) via a traversing unit (11), and the traversing unit (11) is electrically connected to the alternating voltage supply device (9) via a supply line (18), the supply line (18) comprising two electrical conductors (19, 20), in each of which at least one capacitor (21, 22) is arranged, so that the induction coil (10) forms an oscillating circuit with the capacitors (19, 20), and wherein a retrievable maximum output of the induction generator (16) is determined for any specified position of the at least one induction coil (10), in that a) the output of the induction generator (16) is varied, preferably increased, within a predetermined output range between a lower output limit and an upper output limit, and measuring values of the output and measuring values of the frequency are detected during this process, the measuring values of the output being detected in particular indirectly by means of a detection of measuring values of the voltage and the current, b) optionally, each output measuring value is stored with a frequency measuring value assigned to it, c) a curve fitting of a predetermined frequency-dependent output model function to the detected output and frequency measuring values is carried out, wherein at least one value of the total ohmic resistance, which in particular comprises the ohmic resistances of the at least one induction coil (10), of the traversing unit (11) and of the feed line (18) and a value of the insulation resistance (34) between the two electrical conductors (19, 20) of the feed line (18), in particular additionally a value of the inductance of the at least one induction coil (10) are determined as free parameters of the output model function, whereby a resonance curve with a resonance peak is obtained; and d) from the resonance curve, a value of the maximum output of the induction generator (16) which can be retrieved at the respective specified position of the induction coil (10) is determined.

4. Method according to claim 3, wherein the retrievable maximum output of the induction generator (16), in particular additionally the resonance curve, is stored with a specified position of the induction coil (10) assigned to it.

5. Method according to claim 3, wherein in step a) the output of the induction generator (16) is varied continuously and/or stepwise, preferably at predetermined, particularly preferably at uniformly spaced points in time, from the lower output limit to the upper output limit, the output preferably being increased from the lower output limit to the upper output limit in the form of a ramp, in particular with a ramp time in the range from 50 ms to 10 s, preferably in the range from 1 s to 2 s.

6. Method according to claim 4, wherein a specified position is approached by the induction coil (10) and, at the specified position, the output of the induction generator (16) is increased from the lower output limit to a general upper output limit for which it is known that the induction generator (16) can be reliably operated at any predeterminable position of the induction coil (10), and the maximum output of the induction generator (16) which can be retrieved at the specified position is determined and preferably stored with the specified position of the induction coil (10) associated therewith, and after a renewed approach to the specified position, the output of the induction generator (16) is increased from the lower output limit to the retrievable maximum output of the induction generator (16) determined during the previous approach to the specified position, and a new retrievable maximum output of the induction generator (16) is determined for the specified position and is preferably stored with the specified position of the induction coil (10) assigned to it, in particular the retrievable maximum output previously stored for the specified position being overwritten with the new retrievable maximum output.

7. Method according to 6 claim 3, wherein in step c) in the curve fitting the formula: $\left(\omega \right)=\frac{U^2}{Z_{Total}\left(\omega \right)}\mathrm{or}P\left(\omega \right)=I^2.Math.Z_{\mathrm{Total}}\left(\omega \right)\mathrm{where}{Z}_{\mathrm{Total}}\left(\omega \right)=\frac{i}{C_1\omega }-\frac{i}{C_2\omega }+\frac{1}{\frac{1}{R_{\mathrm{ISO}}}+\frac{1}{R_{Total}+iL\omega }}\mathrm{and}\omega =2\pi f$ is used as the frequency-dependent output model function, where U is the voltage measured in particular at the output of the alternating voltage supply device (9), I is the current measured in particular downstream of the output of the alternating voltage supply device (9), preferably in the feed line (18), preferably between one of the capacitors (21, 22) and the alternating voltage supply device (9), Z.sub.Total(ω) is the total impedance of the arrangement of at least the induction coil (10), the traversing unit (11), the supply line (18) and the capacitors (21, 22), R.sub.Total is the total ohmic resistance, R.sub.ISO is the insulation resistance, L is the inductance of the induction coil (10), C1 and C2 are the capacitances of the capacitors (21, 22), and wherein U and I are assumed to be constant.

8. Method according to claim 3, wherein in step c) typical value ranges for the free parameters or a prefabricated curve similar to the resonance curve to be determined are taken into account in the curve fitting in order to reduce the time and resources required for the curve fitting, the typical value ranges and/or the prefabricated curve being stored in a look-up table.

9. Method according to claim 3, wherein in step d) the retrievable maximum output P.sub.MAX is determined from the resonance curve P.sub.Resonance(ω) by algebraically and/or numerically determining the height of the resonance peak as the maximum of the resonance curve P.sub.Resonance(ω).

10. Method according to claim 3, wherein, using the retrievable maximum output determined in step d), an active and/or reactive output prevailing at the respective specified position of the induction coil (10) is determined, wherein, in step d), using the determined total impedance Z.sub.Total at a resonance frequency, an active and/or reactive output prevailing at the respective specified position of the induction coil (10) is determined.

11. Device (1) for the additive manufacture of components (2), having a platform (4) which is provided in order to apply a pulverulent or wire-shaped metal construction material thereon in layers, a primary heating device (7), in particular a laser beam source (7) or electron beam source, which is designed in order to melt a pulverulent or wire-shaped metal construction material preferably applied to the platform (4), an induction heating device (8), which has an alternating voltage supply device (9) with an induction generator (16) and at least one induction coil (10) which can be moved above the platform (4) and is designed to heat a pulverulent or wire-shaped metal construction material preferably applied to the platform (4), and a controller (27), wherein the controller (27) is designed and/or set up to control the induction generator (16) in such a way that it is operated at different specified positions of the at least one induction coil (10) with a different output.

12. Control method for controlling a device (1) according to claim 11, wherein the device (1) is controlled to perform a method according to claim 1.

13. Storage medium comprising a program code which, when executed by a computing device, is designed and/or arranged to control a device according to claim 11 and to perform a method according to claim 1.

14. Method according to claim 4, wherein in step a) the output of the induction generator (16) is varied continuously and/or stepwise, preferably at predetermined, particularly preferably at uniformly spaced points in time, from the lower output limit to the upper output limit, the output preferably being increased from the lower output limit to the upper output limit in the form of a ramp, in particular with a ramp time in the range from 50 ms to 10 s, preferably in the range from 1 s to 2 s.

15. Method according to claim 5, wherein a specified position is approached by the induction coil (10) and, at the specified position, the output of the induction generator (16) is increased from the lower output limit to a general upper output limit for which it is known that the induction generator (16) can be reliably operated at any predeterminable position of the induction coil (10), and the maximum output of the induction generator (16) which can be retrieved at the specified position is determined and preferably stored with the specified position of the induction coil (10) associated therewith, and after a renewed approach to the specified position, the output of the induction generator (16) is increased from the lower output limit to the retrievable maximum output of the induction generator (16) determined during the previous approach to the specified position, and a new retrievable maximum output of the induction generator (16) is determined for the specified position and is preferably stored with the specified position of the induction coil (10) assigned to it, in particular the retrievable maximum output previously stored for the specified position being overwritten with the new retrievable maximum output.

16. Method according to claim 4, wherein in step c) in the curve fitting the formula: $\left(\omega \right)=\frac{U^2}{Z_{Total}\left(\omega \right)}\mathrm{or}P\left(\omega \right)=I^2.Math.Z_{\mathrm{Total}}\left(\omega \right)\mathrm{where}{Z}_{\mathrm{Total}}\left(\omega \right)=\frac{i}{C_1\omega }-\frac{i}{C_2\omega }+\frac{1}{\frac{1}{R_{\mathrm{ISO}}}+\frac{1}{R_{Total}+iL\omega }}\mathrm{and}\omega =2\mathrm{\pi f}$ is used as the frequency-dependent output model function, where U is the voltage measured in particular at the output of the alternating voltage supply device (9), I is the current measured in particular downstream of the output of the alternating voltage supply device (9), preferably in the feed line (18), preferably between one of the capacitors (21, 22) and the alternating voltage supply device (9), Z.sub.Total(ω) is the total impedance of the arrangement of at least the induction coil (10), the traversing unit (11), the supply line (18) and the capacitors (21, 22), R.sub.Total is the total ohmic resistance, R.sub.ISO is the insulation resistance, L is the inductance of the induction coil (10), C1 and C2 are the capacitances of the capacitors (21, 22), and wherein U and I are assumed to be constant.

17. Method according to claim 5, wherein in step c) in the curve fitting the formula: $\left(\omega \right)=\frac{U^2}{Z_{Total}\left(\omega \right)}\mathrm{or}P\left(\omega \right)=I^2.Math.Z_{\mathrm{Total}}\left(\omega \right)\mathrm{where}{Z}_{\mathrm{Total}}\left(\omega \right)=\frac{i}{C_1\omega }-\frac{i}{C_2\omega }+\frac{1}{\frac{1}{R_{\mathrm{ISO}}}+\frac{1}{R_{Total}+iL\omega }}\mathrm{and}\omega =2\mathrm{\pi f}$ is used as the frequency-dependent output model function, where U is the voltage measured in particular at the output of the alternating voltage supply device (9), I is the current measured in particular downstream of the output of the alternating voltage supply device (9), preferably in the feed line (18), preferably between one of the capacitors (21, 22) and the alternating voltage supply device (9), Z.sub.Total(ω) is the total impedance of the arrangement of at least the induction coil (10), the traversing unit (11), the supply line (18) and the capacitors (21, 22), R.sub.Total is the total ohmic resistance, R.sub.ISO is the insulation resistance, L is the inductance of the induction coil (10), C1 and C2 are the capacitances of the capacitors (21, 22), and wherein U and I are assumed to be constant.

18. Method according to claim 6, wherein in step c) in the curve fitting the formula: $\left(\omega \right)=\frac{U^2}{Z_{Total}\left(\omega \right)}\mathrm{or}P\left(\omega \right)=I^2.Math.Z_{\mathrm{Total}}\left(\omega \right)\mathrm{where}{Z}_{\mathrm{Total}}\left(\omega \right)=\frac{i}{C_1\omega }-\frac{i}{C_2\omega }+\frac{1}{\frac{1}{R_{\mathrm{ISO}}}+\frac{1}{R_{Total}+iL\omega }}\mathrm{and}\omega =2\mathrm{\pi f}$ is used as the frequency-dependent output model function, where U is the voltage measured in particular at the output of the alternating voltage supply device (9), I is the current measured in particular downstream of the output of the alternating voltage supply device (9), preferably in the feed line (18), preferably between one of the capacitors (21, 22) and the alternating voltage supply device (9), Z.sub.Total(ω) is the total impedance of the arrangement of at least the induction coil (10), the traversing unit (11), the supply line (18) and the capacitors (21, 22), R.sub.Total is the total ohmic resistance, R.sub.ISO is the insulation resistance, L is the inductance of the induction coil (10), C1 and C2 are the capacitances of the capacitors (21, 22), and wherein U and I are assumed to be constant.

Description

[0057] In the following, the same reference numbers refer to similar components or sections of components.

[0058] A process according to one embodiment of the present invention is explained below with reference to an exemplary device 1 shown in FIGS. 1 to 3 for the additive manufacture of components 2 from a pulverulent metal construction material.

[0059] The device 1 comprises a powder bed space 3 in which a platform 4 is arranged, which extends within a plane spanned by the X-direction and the Y-direction and can be moved up and down in a Z-direction within the powder bed space 3. A powder supply device of the device 1, which is adapted to supply powder to the powder bed space 3 and to apply the supplied powder in a uniform powder layer, is formed in the present case by a powder delivery device 5 and a coating knife 6, which can be moved back and forth in the X-direction over the entire platform 4.

[0060] The device 1 further comprises a primary heating device, in this case a laser beam source 7, which can be a CO2 laser, an Nd:Yag laser, a Yb fiber laser or a diode laser. Furthermore, an induction heating device 8 is provided, which in the present case comprises an alternating voltage supply device 9 and an induction coil 10. The induction coil 10 and the laser beam source 7 are arranged to be movable together above the platform 4. For this purpose, a traversing unit 11 having a first guide 12 and a second guide 13 is provided, wherein the induction coil 10 and the laser beam source 7 are movable back and forth together in the X direction along the first guide 12 and in the Y direction along the second guide 13. The induction coil 10 and the laser beam source 7 are arranged relative to each other such that, during operation of the device 1, a laser beam 14 emerging from the laser beam source 7 can pass through a central opening 15 of the induction coil 10.

[0061] The alternating voltage supply device 9 comprises an induction generator 16 and a transformer 17. In the present case, the distance between the transformer 17 and the induction coil 10 is smaller than the distance between the induction generator 16 and the transformer 17. For reasons of space, this relationship cannot be taken from the figures. The transformer 17 thus serves to bring the output of the induction generator 16 to the induction coil 10 with as little loss as possible. The alternating voltage supply device 9 is electrically connected to the traversing unit 11 via a supply line 18. The traversing unit 11 is arranged to transmit the electrical energy supplied via the supply line 18 to the induction coil 10. For this purpose, the guides 12, 13 of the traversing unit 11 themselves serve as electrical conductors or electrical conductors are provided on the guides 12, 13. Similar electrical conductors of different guides 12, 13 are here electrically connected to each other via sliding contacts. For the sake of clarity, neither the electrical conductors of the guides 12, 13 nor the sliding contacts are shown in the figures. The feed line 18 comprises two electrical conductors 19, 20. A capacitor 21 is arranged in the electrical conductor 19 and a capacitor 22 is arranged in the electrical conductor 20. An ammeter 23 for measuring a current is located between the capacitor 21 and the alternating voltage supply device 9. In addition, a voltmeter 24 for tapping a voltage is disposed between the two electrical conductors 19, 20 in an area between the capacitors 21, 22 and the alternating voltage supply device not shown here, the voltmeter 24 and the ammeter 23 may alternatively be located between the transformer 17 and the induction generator 16.

[0062] The induction coil 10, the electrical conductors of the traversing unit 11, the supply line 18 with the capacitors 21, 22 and the alternating voltage supply device 9 form a so-called resonant outer circuit. More specifically, the capacitors 21, 22 and the induction coil 10 form a series resonant circuit.

[0063] Furthermore, the device 1 is provided with a control and processing unit 26 comprising a controller 27 and a processing device 28, and a storage device 29. The measuring unit 25 is connected to both the processing device 28 and the storage device 29. The storage device 29 is connected to both the controller 27 and the processing device 28. Further, the processing device 28 is connected to the controller 27. In addition, the controller 27 is arranged to control the movements of the platform 4, the powder delivery device 5, the coating knife 6 and the traversing unit 11. Corresponding connecting lines are omitted in the figures for clarity.

[0064] FIG. 3 shows an equivalent circuit diagram of the resonant outer circuit of the device 1. In contrast to FIGS. 1 and 2, the control and processing unit 26 and the storage device 29 in particular are not shown. The induction coil 10 is represented by its ohmic resistance 30 and its inductance 31. The component 2 is indicated by a dashed box and has an ohmic resistance 32. The fact that the eddy currents induced in the component 2 by the induction coil 10 and causing the desired heating of the component 2 are in self-excitation with the inductance 31 of the induction coil 10 is taken into account by the element 33 connected in parallel with the ohmic resistance 32 of the component 2. In parallel with the transformer 17, an insulation resistor 34 is drawn between the electrical conductors 19, 20 of the feed line 18, across which a leakage current I.sub.L flows. In addition, between the induction coil 10 and the insulation resistor 34 is a hatched box 35, which is intended to indicate the variable ohmic resistance when the induction coil 10 is repositioned and/or when the sliding contacts of the traversing unit 11 are in contact with different strengths.

[0065] FIG. 4 shows the equivalent circuit of FIG. 3 in simplified form. Instead of element 30, which represents the ohmic resistance of the coil, element 36 is used, which represents the total ohmic resistance R.sub.Total (including eddy currents in the component). The following relationship holds for the total impedance Z.sub.Total(ω) of the arrangement consisting of the induction coil 10, the traversing unit 11, the feed line 18 and the capacitors 21, 22:

[00002]$Z_{Gesamt}\left(\omega \right)=\frac{i}{C_1\omega }-\frac{i}{C_2\omega }+\frac{1}{\frac{1}{R_{\mathrm{ISO}}}+\frac{1}{R_{Total}+\mathrm{iL}\omega }}$

where ω=2πf and where C.sub.1 represents the capacitance of capacitor 21, C.sub.2 represents the capacitance of capacitor 22, R.sub.ISO represents the insulation resistance 34, L represents the inductance of the coil, R.sub.Total represents the total ohmic resistance represented by element 36, which includes the ohmic resistances of inductor 10, traversing unit 11, and feed line 18, ω represents the angular frequency, and f represents the frequency.

[0066] For the frequency-dependent output model function, the formula is:

[00003]$P\left(\omega \right)=\frac{U^2}{Z_{Total}\left(\omega \right)}\mathrm{or}P\left(\omega \right)=I^2.Math.Z_{Total}\left(\omega \right)$

where U represents the voltage measured by means of the voltmeter 24 and I represents the current measured by means of the ammeter 23. In the present case, U and I are assumed to be constant.

[0067] To generate a component 2, a first powder bed, i.e. a first powder layer of a pulverulent metal material, of uniform thickness is applied to the platform 4 using the powder delivery device 5 and the coating knife 6 in a first step. In a next step, the arrangement consisting of the laser beam source 7 and the induction coil 10 is moved to a first specified position by means of the traversing unit 11 and controlled by the controller 27. The laser beam 14 generated by the laser beam source 7 is now directed through the opening 15 of the induction coil 10 onto a point of the surface of the powder bed to be processed and melts it. Subsequently, the melted powder material is heated by means of the induction heating device 8, whereby no or at least no substantial heating of the unprocessed powder material takes place. For this purpose, the output of the induction generator 16 is first increased in the form of a ramp from a lower output limit of presently about 0.5 kW to a general upper output limit of presently about 6.25 kW, for which it is known that the induction generator 16 can be reliably operated at any predeterminable position of the induction coil 10. As the output is increased, the induction generator 16 continuously shifts the frequency f toward the resonant frequency f.sub.Res. (ω.sub.Res=2πf.sub.Res). Here, measuring values of output P and measuring values of frequency f are determined by means of the measuring unit 25. Each output measuring value is stored with an associated frequency measuring value in the storage device 29. The measuring values of the retrieved output are plotted against the measuring values of the frequency in a curve diagram by means of the processing device 28, see FIG. 5.

[0068] In a next step, a curve fitting of the above described frequency-dependent output model function P(ω) to the acquired output and frequency measuring values is performed by means of the processing device 28. Here, the value L of the inductance 31 is assumed to be constant for simplification. The value R.sub.Total of the total ohmic resistance 36 and the value R.sub.ISO of the insulation resistance 34 are determined as free parameters of the output model function P(ω) during curve fitting. By inserting the determined free parameters into the output model function P(ω), a function for a resonance curve P.sub.Resonance(ω) is obtained. The resonance curve P.sub.Resonance(ω) is superimposed on the measuring points of the curve diagram, see FIG. 5. A so-called resonance peak is clearly visible. From the resonance curve P.sub.Resonance(ω), the value of the maximum output P.sub.Max of the induction generator 16 that can be retrieved at the first specified position of the induction coil 10 is now determined as the height of the resonance peak. More precisely, the height of the resonance peak is determined as the maximum of the resonance curve P.sub.Resonance(ω) by solving P.sub.Resonance(ω) for ω, setting the derivative equal to zero and solving the resulting equation for ω, yielding ω.sub.Res. which is presently about 260000 Hz. inserting ω.sub.Res. into P.sub.Resonance(ω) yields a value for the maximum output P.sub.Max that can be retrieved at the first specified position, which in the present case is about 7.75 kW. P.sub.Max is stored in the storage device together with the first specified position.

[0069] In a next step, the arrangement consisting of the laser beam source 7 and the induction coil 10 is moved to a second specified position by means of the traversing unit 11 and controlled by the control 27. Here, melting of a further area of the surface of the powder bed to be processed takes place by means of the laser beam 14 of the laser beam source 7. Subsequently, the melted powder material is heated by means of the induction heating device 8. Here again, a measuring value determination and processing of the measuring values take place as already described in detail before in connection with the first position. In this way, the arrangement consisting of the laser beam source 7 and the induction coil 10 is moved from position to position by means of the traversing unit 11 in order to selectively melt the powder of the first powder layer according to a desired component structure.

[0070] Subsequently, the platform 4 is lowered in the Z-direction by the amount of a powder layer thickness. Using the powder delivery device 5 and the coating knife 6, a second powder bed, i.e. a second powder layer of the pulverulent metal construction material, of uniform thickness is now applied to the platform 4.

[0071] The arrangement consisting of the laser beam source 7 and the induction coil 10 is moved a second time to the first specified position by means of the traversing unit 11 and controlled by the control 27. First of all, a spot of the surface of the second powder layer to be processed is melted by means of the laser beam 14 of the laser beam source 7. Subsequently, the melted powder material is heated by means of the induction heating device 8. For this purpose, the output of the induction generator 16 is increased in the form of a ramp from the lower output limit to the retrievable maximum output P.sub.Max of the induction generator 16 determined during the last approach to the first position. Again, a measuring value determination and processing of the measuring values take place as described in detail before. In particular, a new retrievable maximum output P.sub.Max of the induction generator 16 for the first position is determined and stored with the first position of the induction coil 10 in the storage device 29. The previously stored retrievable maximum output is overwritten with the newly determined retrievable maximum output. This process is continued until the component 2 is fully generated.

[0072] In summary, the induction generator 16 is controlled by means of the controller 27 in such a way that it is operated at different specified positions of the induction coil 10 during the generation of the component 2 with different outputs. More specifically, at each specified position approached by the induction coil 10, the maximum output of the induction generator 16 that can be retrieved at that position is determined and stored in the storage device 29. As soon as this specified position is again approached by the induction coil 10, the induction generator 16 is controlled by means of the controller 27 in such a way that it is operated with an output which is a predefined amount below the retrievable maximum output determined for this specified position.

[0073] Although the invention has been further illustrated and described in detail by the preferred example embodiment, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of protection of the invention.