Irradiating a machining field

Abstract

An irradiating device for irradiating a machining field with a machining beam, in particular with a laser beam, for carrying out a welding process, is provided. The irradiating device includes a beam scanner for aligning the machining beam to a machining position in the machining field. The irradiating device has an imaging device for imaging a part-region of the machining field on a pyrometer which has at least two pyrometer segments. The imaging device images thermal radiation which emanates from the machining position in the machining field on a first pyrometer segment, and images thermal radiation which emanates from a position in the machining field being situated ahead of or behind the machining position along an advancing direction of the machining beam in the machining field on at least one second pyrometer segment. A machine tool having such an irradiating device is also provided.

Claims

1. An irradiating device for irradiating a machining field with a machining beam for carrying out a welding process, the irradiation device comprising: a beam scanner configured to align the machining beam along a machining beam path to a machining position in the machining field; and an imaging device configured to image a part-region of the machining field on a pyrometer having at least two pyrometer segments, wherein the imaging device is configured to image thermal radiation emanating from the machining position in the machining field and being aligned by the beam scanner along an observation beam path on a first pyrometer segment of the pyrometer, and image thermal radiation emanating from at least one position in the machining field situated ahead of or behind the machining position along an advancing direction of the machining beam in the machining field and being aligned by the beam scanner along the observation beam path on at least one second pyrometer segment of the pyrometer, wherein the observation beam path is at least partially coaxial with the machining beam path in an opposing direction, and wherein the first pyrometer segment and the at least one second pyrometer segment are associated with different responsive characteristics in relation to the thermal radiation emanating from the machining field.

2. The irradiating device of claim 1, wherein the first pyrometer segment and the at least one second pyrometer segment are formed on a surface of a structured diode.

3. The irradiating device of claim 2, wherein at least two of the pyrometer segments on the surface of the structured diode have different wavelength-dependent sensitivities in relation to the thermal radiation emanating from the machining field.

4. The irradiating device of claim 3, wherein the first pyrometer segment of the structured diode has a maximum sensitivity at a first maximum wavelength that is less than a second maximum wavelength of the at least one second pyrometer segment of the structured diode.

5. The irradiating device of claim 1, wherein each of the first pyrometer segment and the at least one second pyrometer segment is connected to a respective detector by a respective radiation transporter.

6. The irradiating device of claim 5, wherein at least two of the detectors have different wavelength-dependent sensitivities in relation to the thermal radiation emanating from the machining field.

7. The irradiating device of claim 6, wherein a first detector connected to the first pyrometer segment has a maximum sensitivity at a first maximum wavelength that is less than a second maximum wavelength of at least one second detector connected to the at least second pyrometer segment.

8. The irradiating device of claim 1, further comprising a filter disposed between the machining field and at least one of the first pyrometer segment or the at least one second pyrometer segment, wherein the filter is configured for wavelength-dependent attenuation of the thermal radiation emanating from the machining field.

9. The irradiating device of claim 1, wherein at least one of the first pyrometer segment or the at least one second pyrometer segment has at least one curved external edge.

10. The irradiating device of claim 1, wherein the first pyrometer segment is circular.

11. The irradiating device of claim 1, which the pyrometer has at least two second pyrometer segments configured as annular segments.

12. The irradiating device of claim 11, wherein the at least two second pyrometer segments are disposed to be rotationally symmetrical about the first pyrometer segment.

13. The irradiating device of claim 11, wherein the at least two second pyrometer segments are disposed in a plurality of concentric rings.

14. The irradiating device of claim 1, wherein the pyrometer is disposed in an observation beam path running coaxially with the machining beam.

15. The irradiating device of claim 1, further comprising: a loop controller configured to predefine the advancing direction in a movement of the machining beam across the machining field.

16. The irradiating device of claim 15, further comprising: an evaluator configured to identify at least one of second pyrometer segments disposed ahead of the machining position in the advancing direction or second pyrometer segments disposed behind the machining position in the advancing direction.

17. The irradiating device of claim 16, wherein the evaluator is configured to: determine a temperature at the machining position and at least one of a temperature at a position in the machining field ahead of the machining position or a temperature at a position in the machining field behind the machining position; and determine at least one temperature gradient by at least two of the temperatures.

18. The irradiating device of claim 17, wherein the loop controller is configured to regulate, based on at least one of the determined temperature gradient or at least one of the determined temperatures, at least one of an output of the machining beam in the machining field or an advancing speed.

19. A machine tool for producing three-dimensional components by irradiating powder layers by a machining beam, comprising: a machining chamber having a support for applying the powder layers; and an irradiating device configured to irradiate the powder layers in the machining chamber with the machining beam, the irradiating device comprising: a beam scanner configured to align the machining beam to a machining position in a machining field in the machining chamber; an imaging device configured to image a part-region of the machining field on a pyrometer having at least two pyrometer segments, wherein the imaging device is configured to image thermal radiation emanating from the machining position in the machining field on a first pyrometer segment of the pyrometer, and image thermal radiation emanating from at least one position in the machining field situated ahead of or behind the machining position along an advancing direction of the machining beam in the machining field on at least one second pyrometer segment of the pyrometer; a loop controller configured to predefine the advancing direction in a movement of the machining beam across the machining field; and an evaluator configured to identify at least one of second pyrometer segments disposed ahead of the machining position in the advancing direction or second pyrometer segments disposed behind the machining position in the advancing direction.

20. The machine tool of claim 19, wherein the irradiating device is disposed in relation to the machining chamber such that the machining field of the beam scanner in which the machining beam is focused is congruent with a position of one of the powder layers to be irradiated by the machining beam.

21. An irradiating device for irradiating a machining field with a machining beam for carrying out a welding process, the irradiation device comprising: a beam scanner configured to align the machining beam to a machining position in the machining field; an imaging device configured to image a part-region of the machining field on a pyrometer having at least two pyrometer segments, wherein the imaging device is configured to image thermal radiation emanating from the machining position in the machining field on a first pyrometer segment of the pyrometer, and image thermal radiation emanating from at least one position in the machining field situated ahead of or behind the machining position along an advancing direction of the machining beam in the machining field on at least one second pyrometer segment of the pyrometer; a loop controller configured to predefine the advancing direction in a movement of the machining beam across the machining field; and an evaluator configured to identify at least one of second pyrometer segments disposed ahead of the machining position in the advancing direction or second pyrometer segments disposed behind the machining position in the advancing direction.

22. The irradiating device of claim 21, wherein the evaluator is configured to: determine a temperature at the machining position and at least one of a temperature at a position in the machining field ahead of the machining position or a temperature at a position in the machining field behind the machining position; and determine at least one temperature gradient by at least two of the temperatures.

23. The irradiating device of claim 22, wherein the loop controller is configured to regulate, based on at least one of the determined temperature gradient or at least one of the determined temperatures, at least one of an output of the machining beam in the machining field and an advancing speed.

24. An irradiating device for irradiating a machining field with a machining beam for carrying out a welding process, the irradiation device comprising: a beam scanner configured to align the machining beam to a machining position in the machining field; and an imaging device configured to image a part-region of the machining field on a pyrometer having at least two pyrometer segments, wherein the imaging device is configured to image thermal radiation emanating from the machining position in the machining field on a first pyrometer segment of the pyrometer, and image thermal radiation emanating from at least one position in the machining field situated ahead of or behind the machining position along an advancing direction of the machining beam in the machining field on at least one second pyrometer segment of the pyrometer, and wherein the first pyrometer segment and the at least one second pyrometer segment are formed on a surface of a structured diode.

25. The irradiating device of claim 24, wherein the beam scanner is configured to: align the machining beam along a machining beam path to the machining position in the machining field, align the thermal radiation emanating from the machining position in the machining field along an observation beam path on the first pyrometer segment of the pyrometer, and align the thermal radiation emanating from the at least one position in the machining field along the observation beam path on the at least one second pyrometer segment of the pyrometer, and wherein the observation beam path is at least partially coaxial with the machining beam path in an opposing direction.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a schematic illustration of an exemplary embodiment of a machine tool having an irradiating device for irradiating a machining field;

(2) FIG. 2 shows an illustration of a part-region of the machining field having a melt pool and having a focal spot where a machining position is formed;

(3) FIGS. 3A and 3B show illustrations of a pyrometer having a first, central, pyrometer segment and having 16, or having 199, respectively, second pyrometer segments which surround the first, central, pyrometer segment, wherein the pyrometer segments are formed on the surface of a segmented diode; and

(4) FIG. 4 shows an illustration of a pyrometer having a base plate which has a plurality of pyrometer segments, as well as having a radiation transportation device for transporting thermal radiation to a diode.

DETAILED DESCRIPTION

(5) In the following description of the drawings, identical reference signs are used for the same or functionally equivalent components.

(6) FIG. 1 shows an exemplary construction of an irradiating device 1 which has a radiation source 2 in the form of a laser source, for example in the form of a Nd:YAG laser or a fiber laser, for generating a machining beam in the form of a laser beam 3. A scanner device (or a beam scanner) 4 has a first and a second scanner mirror 5a, 5b which by means of associated rotary drives 6a, 6b are rotatable about two rotation axes which in the example shown coincide with the X-direction and with the Y-direction, respectively, of an XYZ coordinate system. An (adaptive) focusing device 7 is disposed in the beam path ahead of the scanner device 4, said focusing device 7 carrying out focusing of the laser beam 3 so as to focus the laser beam 3 that is deflected by the scanner device 4 in a machining field 8, as well as to align the laser beam 3 at a desired machining position XP, YP on the machining field 8.

(7) The irradiating device 1 is part of a machine tool 10 which is used for producing three-dimensional components 11. The machining field 8 corresponds to an XY plane in which a topmost powder layer 12, shown in FIG. 1, is disposed on a powder bed that is applied to a support 13, more specifically to a support plate. The support 13 is disposed in a machining chamber 14 which has a viewing window 15 for the passage of the laser beam 3.

(8) The (adaptive) focusing device 7 serves inter alia for aligning the beam axis Z of the laser beam 3 exiting the focusing device 7 so as to be substantially perpendicular to the XY plane or to the powder layer 12, respectively, independently of the machining position XP, YP on the machining field 8 which in the case of a suitable positioning of the irradiating device 1 coincides with the XY plane of the powder layer 12 that is disposed at a predefined height H above the support 13. It is understood that the powder layer 12, other than is shown in FIG. 1, is not limited only to the upper side of the already completed part of the three-dimensional component 11, but rather forms the topmost layer of a powder bed which extends across the entire upper side of the support 13 up to the height H. Alternatively or additionally to the focusing device 7, an F/theta lens assembly can also be used for aligning the laser beam 3 so as to be substantially perpendicular to the XY plane.

(9) The powder layer 12, more specifically the region of the powder layer 12 that is shown in FIG. 1, which for the production of an additional layer of the three-dimensional component 11 is to be irradiated and which therefore coincides with the geometry of the component 11 to be produced, in the case of the example shown in FIG. 1 is divided by the machine tool 10, for example by an open-loop and/or closed-loop control device (or controller) 29 of the irradiating device 1, into four planar part-regions shown in FIG. 1 and into a further part-region which includes substantially the internal and external contour lines of the component 11 at the respective height H as well as further inward contour lines which mutually separate the four planar part-regions at the respective height H.

(10) As is indicated in FIG. 1, the laser beam 3 in the machining field 8 is moved along an advancing direction V.sub.R, or a scanning direction, respectively, which in the example shown corresponds to the negative X-direction. Thermal radiation 19 which emanates from a circular part-region 16 of the machining field 8, said part-region 16 being illustrated in FIG. 2, is imaged on a pyrometer 17 shown in FIG. 1 by an imaging device in the form of a relay optical system 9, for example in the form of a lens assembly which for simplification is illustrated as a lens in FIG. 1. The beam path of the laser beam 3 is passed by the thermal radiation 19 in the opposite direction along an observation beam path 3a, and the thermal radiation 19 is coupled out from the beam path of the laser beam 3 at a beam splitter mirror 18. The pyrometer 17 is disposed so as to be centric in the observation beam path 3a of the thermal radiation 19 such that the imaging device 9 images thermal radiation 19, which emanates from the machining position XP, YP in the part-region 16, on a first, circular, pyrometer segment 20 of the pyrometer 17 shown in a plan view in FIG. 3A.

(11) The first pyrometer segment 20 is surrounded by a plurality of second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d which are disposed in four concentric rings R1 to R4 about the first pyrometer segment 20. The part-region 16 of the machining field 8 shown in FIG. 2 is imaged with the aid of the imaging device on the circular area that is covered by the first and the second pyrometer segments 20, 21a-d, 22a-d, 23a-d, 24a-d of the pyrometer 17. The imaging scale herein is chosen in such a manner that the diameter of the focal spot B substantially coincides with the diameter of the first pyrometer segment 20.

(12) The second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d are in each case configured as annular segments and extend in each case across an angle of 90° in the circumferential direction, that is to say in each case across a quadrant. The second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d are disposed so as to be rotationally symmetrical about the first pyrometer segment 20.

(13) As is shown in an exemplary manner for the second pyrometer segment 21a (illustrated on the left in FIG. 3A) of the first annular region R1, the second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d that are configured as annular segments have in each case an external contour having a radially inward arcuate external edge 27a as well as a radially outward arcuate external edge 27b, said external edges 27a, 27b being connected to one another by two rectilinear external edges which extend in the radial direction.

(14) In of the example shown in FIG. 3A, the pyrometer is configured as a segmented diode 17, and the pyrometer segments 20, 21a-d, 22a-d, 23a-d, 24a-d are formed on the surface of said diode 17 (cf. FIG. 1). In the case of a pyrometer in the form of a segmented diode 17, the circular first pyrometer segment 20 as well as the second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d can be generated with the aid of micro-structuring surface 17a of the diode 17 such that said pyrometer segments can be contacted in an electrically isolated manner. It is understood that first and second pyrometer segments 20, 21a-d, 22a-d, 23a-d, 24a-d which are also shaped differently than in FIG. 3 can be produced by micro-structured diode 17.

(15) The monitored region 16 shown in FIG. 2 includes the focal spot B where the laser beam 3 meets the powder layer 12, the machining position X.sub.P, Y.sub.P being formed in the center of said focal spot B, as well as a front portion of the melt pool S in which melted powder has formed. The thermal track having the cooled powder material adjoins the melt pool S counter to the advancing direction V.sub.R, that is to say on the right in FIG. 2; said thermal track in the example shown not being situated within the part-region 16 of the machining field 8.

(16) The temperature T.sub.P at the machining position X.sub.P, Y.sub.P is typically in the magnitude of approx. 2000° C. and represents the maximum temperature of the welding process, while the temperature in the environment of the focal spot B is significantly lower, which is why the intensity of the thermal radiation 19 meeting the pyrometer 17 is also significantly lower than at the focal spot B. It can be favorable for a filter device for attenuating the thermal radiation 19 that emanates from the part-region 16, or from the machining field 8, respectively, to be disposed in the beam path between the machining field 8 and the first pyrometer segment 20 and/or at least one of the second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d.

(17) In the case of the pyrometer in the form of the structured diode 17, filter devices of this type can be applied in the form of a coating to a few of the pyrometer segments 20, 21a-d, 22a-d, 23a-d, 24a-d. Such a filter device 26 which in the form of a coating is applied to the first, central, pyrometer segment 20 is indicated by a hatched area in FIGS. 3A and 3B. The filter device 26 serves for attenuating the thermal radiation 19 which emanates from the machining position X.sub.P, Y.sub.P, or the focal spot B, respectively, where the maximum intensity of the thermal radiation 19 is emitted. For this purpose, the filter device 26 can be configured as a bandpass filter which has only a small transmission for a wavelength which corresponds to the maximum emission of a black or grey body at the temperature T.sub.P of approx. 2000° C.

(18) Filtering can accordingly also be optionally performed at the second pyrometer segments 21a-d, 22a-d, 23a-d, 24a-d. For the determination of the temperature T.sub.P at the machining position X.sub.P, Y.sub.P as well as at further positions (see below) in the illustrated part-region 16 of the machining field 8 it can be favorable for the filter device 26 to be configured as a bandpass filter which is designed such that the latter transmits thermal radiation 19 at two different wavelengths which are detected separately for a respective pyrometer segment 20, 21a-d, 22a-d, 23a-d, 24a-d so as to make a direct conclusion, that is to say without any knowledge of the emissivity, pertaining to the temperature T.sub.P at the machining position X.sub.P, Y.sub.P or at other positions.

(19) Alternatively or additionally to the use of filter devices 26, the pyrometer segments 20, 21a-d, 22a-d, 23a-d, 24a-d of the structured diode 17 can also be produced from different materials, more specifically from materials which have a different wavelength-dependent sensitivity in relation to the thermal radiation 19 which emanates from the part-region 16 of the machining field 8. In the example shown in FIG. 3A, the first pyrometer segment 20 has a maximum sensitivity at a maximum wavelength λ.sub.1MAX which is adapted to the wavelength of the maximum emission of thermal radiation 19 of a black or grey body, respectively, having a temperature of approx. 2000° C. By contrast, the second pyrometer segments 21a-d in the first annular region R1 have a maximum sensitivity at a (larger) maximum wavelength λ.sub.2MAX which is adapted to the correspondingly lower temperatures of the thermal radiation 19 which meets the second pyrometer segments 21a-d in the first annular region R1. The maximum wavelength λ.sub.1MAX of the first pyrometer segment 20 is smaller than the maximum wavelength λ.sub.2MAX of the second pyrometer segments 20 in the first annular region R1. Accordingly, the pyrometer segments 22a-d in the second annual region R2 can have a maximum sensitivity, or a maximum wavelength, respectively, which is larger than the maximum wavelength λ.sub.2MAX of the second pyrometer segments 20 in the first annular region R1, etc.

(20) Four positions X.sub.P+4, Y.sub.P, X.sub.P+3, Y.sub.P, X.sub.P+2, Y.sub.P, X.sub.P+1, Y.sub.P which in the advancing direction V.sub.R are situated ahead of the machining position X.sub.P, Y.sub.P, as well as four positions X.sub.P−1, Y.sub.P, X.sub.P−2, Y.sub.P, X.sub.P−3, Y.sub.P, X.sub.P−4, Y.sub.P which along the advancing direction (corresponding to the scanning direction) V.sub.R are situated behind the machining position X.sub.P, Y.sub.P, are illustrated in FIG. 2. The positions X.sub.P+4, Y.sub.P, X.sub.P+3, Y.sub.P, X.sub.P+2, Y.sub.P; X.sub.P+1, Y.sub.P or X.sub.P−1, Y.sub.P; X.sub.P−2, Y.sub.P, X.sub.P−3, Y.sub.P, X.sub.P−4, Y.sub.P, respectively, shown in FIG. 2, more specifically the respective spacing of said positions from the machining position X.sub.P, Y.sub.P, in the example shown are chosen in such a manner that said positions are situated approximately in the center of the second pyrometer segments 21a, 22a, 23a, 24a (illustrated on the left in FIG. 3A), or approximately in the center of the second pyrometer segments 21c, 22c, 23c, 24c (illustrated on the right in FIG. 3A). The associated temperature T.sub.P+4, T.sub.P+3, T.sub.P+2, T.sub.P+1 for the respective position X.sub.P+4, X.sub.P+3, X.sub.P+2, X.sub.P+1, Y.sub.P ahead of the machining position X.sub.P, Y.sub.P in the advancing direction V.sub.R can be determined by means of the thermal radiation 19 impinging upon the respective second pyrometer segment 21a, 22a, 23a, 34a in an evaluation device (or evaluator) 28 (cf. FIG. 1) of the irradiating device 1. The evaluator 28 includes a computing unit (e.g., one or more processors) coupled with a non-transitory computer-readable medium encoding instructions that cause the computing unit to execute the instructions, e.g., to determine the associated temperature T.sub.P+4, T.sub.P+3, T.sub.P+2, T.sub.P+1 for the respective position X.sub.P+4, X.sub.P+3, X.sub.P+2, X.sub.P+1, Y.sub.P ahead of the machining position X.sub.P, Y.sub.P. Accordingly, the associated temperature T.sub.P−1, T.sub.P−2, T.sub.P−3, T.sub.P−4 for a respective position X.sub.P−1, X.sub.P−2, X.sub.P−3, X.sub.P−4, Y.sub.P behind the machining position X.sub.P, Y.sub.P in the advancing direction V.sub.R can also be determined by means of the thermal radiation 19 impinging upon the respective second pyrometer segment 21c, 22c, 23c, 24c in the evaluation device 28.

(21) The evaluation device 28, based on the advancing direction V.sub.R which is predefined by the open-loop and/or closed-loop control device 29, is configured to identify those second pyrometer segments 21a, 22a, 23a, 24a which in the momentary advancing direction V.sub.R are positioned ahead of the machining position X.sub.P, Y.sub.P, as well as those second pyrometer segments 21c, 22c, 23c, 24c which in the momentary advancing direction V.sub.R are disposed behind the machining position X.sub.P, Y.sub.P. It is understood that, for example, in a rotation of the advancing direction V.sub.R by 90° in relation to the advancing direction V.sub.R shown in FIG. 3A, the second pyrometer segments 21b, 22b, 23b, 24b which are disposed above in FIG. 3A, or the second pyrometer segments 21d, 22d, 23d, 24d which are disposed below in FIG. 3A, respectively, are in each case used for the determination of the respective temperatures. Even in the case of the advancing direction V.sub.R running as illustrated in FIG. 3A, the second pyrometer segments 21b, 22b, 23b, 24b which are disposed above in FIG. 3A, or the second pyrometer segments 21d, 22d, 23d, 24d which are disposed below in FIG. 3A, respectively, can be used for the determination of temperatures, or of temperature gradients ΔT transverse, or substantially transverse in relation to the advancing direction V.sub.R. This is favorable in particular in the case of a planar melting of the powder bed in which a plurality of thermal tracks are generated, said thermal tracks running so as to be mutually neighboring and parallel such that the not yet completely cooled neighboring thermal tracks can be evaluated by the evaluation device 28 in this way.

(22) The evaluation device 28 can also be used for determining temperature gradients ΔT by means of the respective temperatures T.sub.P+4, T.sub.P+3, T.sub.P+2, T.sub.P+1, T.sub.P, T.sub.P−1, T.sub.P−2, T.sub.P−3, T.sub.P−4, for example in that the difference between two of the temperatures, for example T.sub.P+4-T.sub.P+3, is formed and said difference is divided by the spacing A (known by virtue of the imaging scale of the imaging device 9) between the two associated positions X.sub.P+4, X.sub.P+3 in the machining field 8: ΔT=(T.sub.P+4−T.sub.P+3)/A.

(23) With the aid of the open-loop and/or closed-loop control device 29, the welding process can be controlled in a closed-loop manner by means of the at least one temperature T.sub.P+4, T.sub.P+3, T.sub.P+2, T.sub.P+1, T.sub.P, T.sub.P−1, T.sub.P−2, T.sub.P−3, T.sub.P−4 determined by the evaluation unit 28 and/or of a respective temperature gradient ΔT, for example in that the output P of the laser beam 3 and/or the advancing speed V.sub.R are/is set such that one or a plurality of the temperatures T.sub.P+4, T.sub.P+3, T.sub.P+2, T.sub.P+1, T.sub.P, T.sub.P−1, T.sub.P−2, T.sub.P−3, T.sub.P−4, or one or a plurality of temperature gradients ΔT, respectively, are in a predefined value range. The determination of temperature gradients ΔT in particular in the region of the thermal track has proven favorable in order for the thermal history and thus the microstructure of the material structure of the three-dimensional workpiece to be determined. The closed-loop control of the welding process with the aid of the open-loop and/or closed-loop control device 29 can be performed in real time; however, it is also possible for the closed-loop control to be performed layer-by-layer, that is to say that the temperature gradient ΔT, for example in the form of the cooling rate, is determined for an entire applied powder layer 12 so as to determine how much heat is stored in the component, or in the powder bed, when melting a powder layer 12 of the powder bed. Other machining parameters can be used for melting the following powder layer 12, that is to say that the laser output P and/or the advancing speed V.sub.R can be suitably adapted, for example.

(24) In particular in the case of the pyrometer 17 having a multiplicity of second pyrometer segments 25, the open-loop and/or closed-loop control device 29 can also serve for using the pieces of information which are delivered by the evaluation device 28 and pertain to the not yet completely cooled neighboring thermal tracks, in order for the closed-loop control of machining parameters, for example the powder P of the machining laser beam 3 and/or the advancing speed V.sub.R, to be used when generating the momentary thermal track. Such a closed-loop control is not performed in real time and can therefore be easily implemented.

(25) It is understood that the part-region 16 of the irradiating region 8 which is imaged on the pyrometer 17 by the imaging device 9 can also be larger than that is illustrated in FIG. 2 such that the thermal track situated to the right of the melt pool S in FIG. 2 is also imaged on the pyrometer 17. The diameter of the part-region 16 can vary, for example between approx. 2 mm and approx. 10 mm. The imaging device 9 can optionally be configured as a zoom lens assembly so as to implement different imaging scales.

(26) FIG. 3B shows a further example for a pyrometer 17 in the form of a segmented diode which differs from the example shown in FIG. 3A in that the second pyrometer segments 25 are disposed in five annular regions R1 to R5 about the central first pyrometer segment 20. One hundred ninety nine second pyrometer segments 25 are disposed about the first pyrometer segment 20 the example shown in FIG. 3B, the surface areas of said second pyrometer segments 25 being in each case identical in the example shown. Subdividing the segmented diode 17 into a larger number of pyrometer segments 20, 25, in particular in the circumferential direction, is advantageous in order for the spatial resolution to be increased and for in this way avoiding that thermal radiation 19 of not yet completely cooled workpiece material or powder which has been generated in a previous welding process, respectively, influences the temperature measurement along the advancing direction V.sub.R.

(27) The segmented diode 17 shown in FIGS. 3A and 3B is distinguished by a high filling factor, a high stability by virtue of the monolithic design, as well as by the potential for implementing a multiplicity of pyrometer segments in an economical manner. Additionally to the segmented diode 17 shown in FIG. 3A, or in FIG. 3B, respectively, the pyrometer can optionally have further diodes or heat-sensitive sensors, respectively, which serve for detecting thermal radiation 19 from regions of the machining field 8 that are more remote from the machining position X.sub.P, Y.sub.P.

(28) FIG. 4 shows an example of a pyrometer 17 which first differs from the pyrometer 17 shown in FIGS. 3A and 3B in that the first pyrometer segment 20 and the second pyrometer segments 21a, 21b, 22a, 22b, 23a, 23b are disposed on a common surface 30 in three annular regions R1 to R3. Moreover, the second pyrometer segments 21a, 21b, 22a, 22b, 23a, 23b extend in each case across an angular range of 180° which is sufficient for assigning the second pyrometer segments 21a, 21b, 22a, 22b, 23a, 23b to positions (not shown) ahead of or behind, respectively, the machining position X.sub.P, Y.sub.P, as long as the advancing direction V.sub.R does not run exactly along the border between neighboring pyrometer segments 21a, 21b, 22a, 22b, 23a, 23b. The first pyrometer segment 20 and the second pyrometer segments 21a, 21b, 22a, 22b, 23a, 23b are in each case connected to a detector in the form of a conventional diode 32, 32a, 32b, . . . by way of a radiation transporting device (or radiation transporter) 31, 31a, 31b, . . . , as this is illustrated in an exemplary manner in FIG. 4 for the first pyrometer segment 20 as well as for the two pyrometer segments 21a, 21b of the first annual region R1. The radiation transporting devices 31, 31a, 31b, . . . enable a spatially separated collection of the thermal radiation 19 that impinges upon a respective pyrometer segment 20, 21a, 21b, 22a, 22b, 23a, 23b.

(29) The radiation transporting devices 31, 31a, 31b, . . . are suitably disposed in geometric terms so as to form light-guiding cones, or a light conductor, respectively, to the respective diode 32, 32a, 32b, . . . and can be based, for example, on reflection, total reflection, refraction, or on diffractive optics. In the example shown, optical waveguides in the form of fibers are used as radiation transporting devices 31, 31a, 31b, . . . which serve for the spatially separated collection and relaying of the thermal radiation 19 from the surface 32 to the, in this case, fiber-coupled standard diodes 32, 32a, 32b, . . . . The surface 30 on which the imaging device 9 images the thermal radiation 19 can, for example, form the end side of a multicore optical waveguide, for example in the form of a fiber bundle, the cores thereof at the end side of said cores being disposed in an annular manner about a center, as is shown in FIG. 4. The cross section shown in FIG. 4, or the end sides of the pyrometer segments 20, 21a, 21b, 22a, 22b, 23a, 23b, respectively, can be guided to the respective diode 32, 32a, 32b, . . . by way of different optical waveguides 31, 31a, 32b, . . . of the multicore optical waveguide in the form of fibers having a circular cross section, for example. The thermal radiation 19 can be directed onto the respective standard diodes 32, 32a, 32b, . . . through the optical waveguides 31, 31a, 31b, . . . .

(30) As has been described further above in the context of FIG. 3A, the diodes 32, 32a, 32b, . . . can be formed from different materials which are adapted to the wavelength of maximum emission in the temperature range of the thermal radiation 19 that is in each case to be expected to impinge upon the respective pyrometer segments 20, 21a, 21b, 22a, 22b, 23a, 23b. For example, the diode 32 which is assigned to the first pyrometer segment 20 can have a smaller maximum wavelength λ.sub.1MAX than the maximum wavelength λ.sub.2MAX of the two diodes 32a, 32b which are assigned to the second pyrometer segments 21a, 21b which are disposed in the first annular region R1. In the example shown in FIG. 4, a higher filling factor is implemented in comparison to the use of a plurality of diodes which are disposed beside one another and which, by virtue of connectors etc., cannot be disposed so as to be directly neighboring.