METHOD OF PROCESSING AN OBJECT WITH A LIGHT BEAM, AND PROCESSING SYSTEM

Abstract

A method of processing an object with a light beam includes the following steps: projecting a light beam onto the object via a first scanner so as to produce a heated area by locally heating the object; displacing the heated area along a track on the object; capturing images of a first portion of the object with a first camera, via the first scanner; and capturing images of a second portion of the object with a second camera, via a second scanner.

The first scanner and the second scanner are operated so that the first camera captures images of the heated area, whereas the second camera captures images of portions of the object behind and/or ahead of the heated area.

Claims

1. A method of processing an object with a light beam, the method including the following steps: projecting a light beam onto an object using a first scanner for processing the object, said light beam projecting a light spot on the object for producing a heated area by locally heating the object; displacing the heated area along a track on the object; capturing images of a first portion of the object with a first camera, using the first scanner; and capturing images of a second portion of the object with a second camera, using a second scanner; wherein the method further includes the step of operating the first scanner and the second scanner so that the first camera captures images of the heated area, whereas the second camera captures images of portions of the object trailing behind the heated area and/or ahead of the heated area.

2. The method according to claim 1, further including the step of repetitively scanning the light beam in two dimensions with the first scanner so that the light beam follows a two-dimensional scanning pattern and establishes an effective spot having a two-dimensional energy distribution determined by at least the scanning pattern followed by the light beam, a scanning speed and a light beam power, and wherein the two-dimensional energy distribution is dynamically adapted while the heated area is displaced along the track.

3. The method according to claim 1, wherein the first scanner is used to displace the heated area along the track and wherein the first scanner and the second scanner are operated in synchronization so that the second camera captures images of the object having a pre-determined spatial and/or temporal relation to the heated area.

4. The method according to claim 1, further comprising the step of repetitively scanning in two dimensions with the second scanner and operating the second camera in synchronization with the second scanner so as to repetitively obtain a sequence of images of different subareas of the object behind and/or ahead of the heated area.

5. The method according to claim 4, wherein the different subareas are arranged adjacent to each other.

6. The method according to claim 5, wherein the different subareas are arranged in rows and columns forming a matrix.

7. The method according to claim 1, wherein the second camera captures images of portions of the object trailing behind the heated area.

8. The method according to claim 7, wherein images of portions from the second camera are used for determining a cooling rate.

9. The method according to claim 1, wherein the cameras are infrared cameras.

10. The method according to claim 1, wherein both the first scanner and the second scanner are arranged in a processing head.

11. The method according to claim 1, for additive manufacturing.

12. The method according to claim 1, for joining at least two workpieces by welding them together.

13. The method according to claim 1, for laser cladding or laser hardening.

14. The method according to claim 1, wherein the light beam is a laser beam.

15. A processing system comprising: a processing head for projecting a light beam onto an object for processing the object, the processing head including a first scanner for controlled displacement of the light beam in relation to the object; a first camera associated to the first scanner for capturing images of a portion of the object via the first scanner; and a second camera and a second scanner, the second camera being associated to the second scanner for capturing images of a portion of the object via the second scanner, the system being programmed for operating the first scanner and the second scanner so that during processing of the object with the light beam the first camera captures images of a heated area produced by the light beam, whereas the second camera captures images of portions ahead of the heated area and/or trailing behind the heated area.

16. The processing system according to claim 13, wherein the processing head includes the first scanner, the second scanner, the first camera and the second camera.

17. The processing system according to claim 15, programmed for operating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as an example of how the disclosure can be carried out. The drawings comprise the following figures:

[0037] FIGS. 1A and 1B are schematic side elevation views of prior art camera arrangements in relation to a laser processing head;

[0038] FIG. 2 is a schematic side elevation view of a laser processing system in accordance with an embodiment of the disclosure; and

[0039] FIGS. 3-5 are schematic top views of an object subjected to laser processing, schematically indicating the relation between images captured by the first and second cameras in accordance with three alternative embodiments of the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0040] FIG. 2 schematically illustrates a laser processing head 1 in accordance with one possible embodiment of the disclosure. The laser processing head includes a beam splitter 12, a first scanner 13 and an F-theta lens 14, for example, as those of the prior art laser processing head described in relation to FIG. 1B. These components are used to direct a laser beam 11A from a laser source 11 onto an object 1000, for processing of the object, for example, for welding, cladding, additive manufacturing, laser hardening, laser softening, etc. Similarly to what has been discussed in relation to FIG. 1B, a first camera 15, such as a thermal camera, is provided for capturing images of a portion of the object via the first scanner 13. Due to this co-axial arrangement, the first camera 15 will capture images in correspondence with the point where the laser beam is projected onto the object, that is, images will be captured of the laser spot projected onto the surface and the immediately surrounding area. Thus, the first camera is suitably arranged for continuously capturing images of, for example, a melt pool produced by the laser beam when locally heating the object, or of the part of the melt pool that is currently being heated by the laser beam. As the laser spot is displaced along a track on the object (for example, by using the first scanner and/or other means, such as by displacing the entire processing head in relation to the object or vice-versa), the first camera will continue to receive images from the melt pool. The same is applicable to heated areas other than melt pools, for example, to an area being heated without melting in contexts such as laser hardening or laser softening.

[0041] In addition, a second camera 25 is provided, in this embodiment likewise associated to the laser processing head. The second camera 25 is associated to a second scanner, so that the second camera 25 can capture images of portions of the object 1000 via the second scanner 23. Thus, the way in which the second scanner 23 is operated determines the portions of the object of which, at each specific moment, an image can be captured by the second camera 25.

[0042] Thus, by means of this arrangement involving two cameras, images with high resolution can be obtained both of the heated area (such as a melt pool or part thereof) and of a portion behind the heated area and/or ahead of the heated area, that is, for example, a trailing portion where cooling and solidification are taking place. Also, images can be obtained repetitively with high frequency, that is, with a high frame rate. The second camera can thus be used to obtain information, such as in the form of pixelized thermal images, useful for determining factors such as cooling rate, which in turn can be useful for quality control. It can also be used for obtaining images of the area of the workpiece ahead of the laser spot, for example, in order to detect features of the workpiece such as openings, irregularities, etc., that may require adaptation of the path to be followed by the laser spot, and/or of the shape and/or energy distribution of the laser spot.

[0043] FIG. 3 is a top view showing an embodiment applied to laser welding of two workpieces 1001 and 1002 which, in this case, form the object 1000 subjected to laser processing. The workpieces, such as two metal objects, are arranged to mate along an interface area 1003, where the laser beam is applied to produce a weld seam 1005 while being displaced along a track 1004 aligned with the interface area 1003. The laser welding can be produced with a laser processing head 1 as shown in FIG. 2. In FIG. 3 it is schematically illustrated how the laser beam 11A produces a laser spot 11B in correspondence with the interface area 1003, so that a melt pool 11C is established, which travels with the laser spot 11B along the track 1004. In some embodiments, the laser spot is a primary laser spot obtained by the mere projection of the laser beam onto the interface area. In other embodiments, the laser spot is an effective spot obtained by relatively rapid repetitive scanning of the laser beam in two dimensions, following a scanning pattern. As explained above, this can facilitate a dynamic adaptation of the two-dimensional energy distribution while the effective spot is travelling along the track 1004.

[0044] The first camera is arranged to capture an image of a portion 151 of the object in correspondence with the laser spot 11B and including the melt pool 11C or part thereof. Thus, thermal information provided to the system by the first camera 15 can be used to determine parameters such as the maximum temperature of the melt pool 11C, the shape and/or size of the melt pool, the temperature distribution within the melt pool, the temperature of the part of the melt pool that is currently being heated by the laser beam, etc.

[0045] The second camera is arranged to capture images behind the melt pool, that is, in this case, in correspondence with the weld seam 1005 that is being formed by cooling and solidification in the area behind the melt pool, that is, in the area trailing behind the melt pool 11C. Thus, the second camera is arranged to capture images of a portion 251 trailing behind the melt pool. For example, in the illustrated embodiment the first and the second scanners are synchronized and operate with a delay Δt in what regards the movement along the track 1004 so that the respective cameras capture images of the same portion of the object but with a time difference Δt. Thus, and whereas the first camera captures images of the melt pool, the second camera captures images of a portion trailing behind the melt pool, so that the second camera can capture images of a portion suitable for determining parameters such as cooling rate.

[0046] Sometimes it can be of interest to expand the area from which images are being captured by the second camera, for example, to obtain high-resolution images including points at substantial distances from each other, for example, along the track or at the sides of the track followed by the melt pool. This can sometimes be achieved by using a camera with higher resolution, and/or several cameras. However, in an alternative embodiment illustrated in FIG. 4, the second scanner is operated not only to make the second camera track the first camera with the delay mentioned above, but additionally to direct the second camera to different subareas trailing behind the melt pool, so as to obtain images corresponding to, for example, subareas arranged in rows and columns as in the 2×2 matrix formed by subareas 251A, 251B, 251C and 251D, as schematically illustrated in FIG. 4. This can be achieved by operating the second scanner 231 for two-dimensional scanning in accordance with a scanning pattern 231 schematically illustrated in FIG. 4, overlaid on the basic scanning movement that in some embodiments is used to make the second camera 25 track the first camera 15 along the track, as described above.

[0047] FIG. 5 illustrates an embodiment where instead of capturing images of a portion trailing behind the melt pool, the second camera is arranged to capture images of a portion 252 ahead of the melt pool. In other embodiments, images ahead of the melt pool can be obtained using the principles shown in FIG. 4. Capturing images ahead of the melt pool can be useful to, for example, detect irregularities in the interface area, defects in a previously established weld seam, or any other aspects that can be relevant for how the laser heating should be performed. In FIG. 5 it has additionally been schematically illustrated how the laser spot 11B is an effective spot established by rapid two-dimensional scanning of the laser beam along a scanning pattern 11B′ (schematically illustrated as a meander) which, together with features such as the velocity of the laser beam along the different portions of the scanning pattern and the power of the laser beam in correspondence with the different portions of the scanning pattern, determines the two-dimensional energy distribution within the effective spot 11B. Information provided by the second camera can be used to correctly adapt the two-dimensional energy distribution while the effective spot is advancing along the track 1004, taking into account aspects such as irregularities in the track, holes in the workpiece, etc. In this sense, the principles for dynamic adaptation of the two-dimensional energy distribution of an effective spot laid down in WO-2014/037281-A2 and WO-2015/135715-A1 can be used, and the information provided by one or both of the first and second cameras can be used to trigger the adaptation of the two-dimensional energy distribution. In some embodiments, the first scanner can carry out the scanning of the laser beam in accordance with the scanning pattern 11B′, and also the scanning of the effective spot 11B along the track 1004.

[0048] In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0049] The disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the disclosure as defined in the claims.