METHOD AND DEVICE FOR CARRYING OUT AND MONITORING A MACHINING PROCESS OF A FIRST WORKPIECE AND A SECOND WORKPIECE BY MEANS OF A HIGH-ENERGY MACHINING BEAM

Abstract

A welding method and device for joining first and second workpieces using a high-energy machining beam. The method comprising inserting the first workpiece into a workpiece holder; positioning the second workpiece on a top side of the first workpiece at a target position for joining the workpieces; providing a high-energy machining beam, and focusing the machining beam on a current machining area; generating a measuring beam in an optical coherent tomograph, the measuring beam being coupleable into the machining beam; carrying out a process measurement by the measuring beam in the current machining area during machining of the workpieces; carrying out a control measurement by the measuring beam on at least one of the workpieces; and determining a distance between the first and second workpieces for detecting a gap between the workpieces, based on the result of the control measurement.

Claims

1. A method for carrying out and monitoring a machining process of a first workpiece and a second workpiece for joining the first and second workpieces using a high-energy machining beam, wherein the method comprises the steps: inserting the first workpiece into a workpiece holder; positioning the second workpiece on a top side of the first workpiece at a target position for joining the workpieces; providing a high-energy machining beam that has an optical axis, and projecting the machining beam on a current machining area; generating a measuring beam in at least one optical coherent tomograph, the measuring beam being coupleable into the machining beam; carrying out a process measurement using the measuring beam in the current machining area during machining of the workpieces using the machining beam; carrying out a control measurement using the measuring beam on at least a portion of at least one of the workpieces; and determining a distance between the first workpiece and the second workpiece for detecting a gap that is possibly present between the workpieces, based on the result of the control measurement.

2. The method according to claim 1, wherein the process measurement and the control measurement are carried out by the same coherent tomograph.

3. The method according to claim 1, comprising the further step: carrying out the control measurement, using the optical coherent tomograph, at least in part during the machining of the workpieces.

4. The method according to claim 1, wherein a predefined thickness of the first workpiece and a predefined thickness of the second workpiece are used for determining the distance between the first workpiece and the second workpiece.

5. The method according to claim 1, wherein the control measurement includes at least one determination of the position of the workpiece holder, the control measurement being carried out, at least in part, before the first workpiece is inserted.

6. The method according to claim 1, wherein the control measurement includes at least one measurement on the top side of the first workpiece in a state in which the second workpiece is at the target position.

7. The method according to claim 6, wherein for at least a portion of the control measurement, on the top side of the first workpiece a measuring beam is at least partially guided through a hole in the second workpiece that is provided in the second workpiece independently of the machining of the workpieces.

8. The method according to claim 7, wherein the hole in the second workpiece is welded closed on the top side of the first workpiece after the measurement.

9. The method according to claim 1, wherein for the control measurement, at least one test machining of the workpieces that is different from the machining of the workpieces is carried out.

10. The method according to claim 9, wherein the test machining takes place through both workpieces in such a way that a bottom side of the first workpiece is penetrated at certain points.

11. The method according to claim 9, wherein after the test machining, an area in which the test machining has been carried out is welded closed using the machining beam.

12. The method according to claim 9, wherein the machining of the workpieces and the test machining are carried out using machining beams that have different beam diameters.

13. The method according to claim 12, wherein a switchable fiber is used for generating the machining beams for the test machining and for the machining of the workpieces.

14. The method according to claim 1, wherein for the control measurement, at least one measurement is carried out on a bottom side of the first workpiece.

15. The method according to claim 14, wherein for the measurement on the bottom side of the first workpiece, a measuring beam is deflected on at least a portion of the workpiece holder by use of a reflective element.

16. A device for carrying out and monitoring a machining process of a first workpiece and a second workpiece for joining the first and second workpieces using a high-energy machining beam, wherein the device comprises: a workpiece holder into which at least the first workpiece is insertable; a machining unit having a machining beam source for generating the high-energy machining beam, which has an optical axis, and including machining beam optics for projecting the high-energy machining beam on a current machining area, and at least one optical coherent tomograph for generating a measuring beam that is coupleable into the machining beam optics, wherein the device is configured: in an inserted state of the first workpiece in which the second workpiece is positioned on a top side of the first workpiece at a target position for machining the workpieces, to carry out at least one process measurement using the measuring beam during machining of the workpieces using the machining beam; to carry out a control measurement using the measuring beam on at least a portion of at least one of the workpieces; and to determine a distance between the first workpiece and the second workpiece, based on the result of the control measurement, in order to detect a gap that is possibly present between the workpieces.

17. The device according to claim 16, wherein the machining unit has a switchable fiber through which a beam diameter of the machining beam may be changed.

18. The device according to claim 16, further including a control unit that is configured to determine the distance between the first workpiece and the second workpiece based on the result of the control measurement and based on a predefinable thickness of the first workpiece and a predefinable thickness of the second workpiece.

19. The device according to claim 16, wherein the workpiece holder includes at least one reflective element through which the measuring beam may be directed onto a bottom side of the first workpiece.

20. A method for manufacturing a workpiece for use in a method according to claim 1, which is configured to be joined to another workpiece along a joining seam using a high-energy machining beam, comprising the steps: producing a workpiece blank; and providing the workpiece blank with multiple holes along a course that a future joining seam is to follow.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0054] Preferred embodiments of the invention are explained in greater detail below with reference to the appended schematic drawings, which show the following:

[0055] FIG. 1 shows a schematic overall view of a first exemplary embodiment of a device according to the invention for carrying out a machining process of a first workpiece and a second workpiece;

[0056] FIG. 2 shows a schematic sectional illustration of the two workpieces in a joined state, in an area without a gap between the workpieces;

[0057] FIG. 3 shows a schematic sectional illustration of the two workpieces in an area in which a gap is present between the workpieces;

[0058] FIG. 4 shows a schematic top view of the two workpieces during machining, in which a measurement is carried out on a top side of the first workpiece according to one aspect of the invention;

[0059] FIG. 5 shows a schematic top view of the two workpieces during machining, in which a measurement is carried out on a top side of the first workpiece according to a further aspect of the invention;

[0060] FIG. 6 shows a schematic illustration for depicting test machining according to one aspect of the invention;

[0061] FIG. 7 shows a schematic temporal depth profile for the test machining, which results from a measurement of a control measurement during the test machining;

[0062] FIG. 8 shows a workpiece holder according to one aspect of the invention that is provided with reflective elements; and

[0063] FIG. 9 shows a schematic flow chart of one exemplary embodiment of a method according to the invention for carrying out and monitoring a machining process of a first workpiece and a second workpiece.

DETAILED DESCRIPTION OF THE INVENTION

[0064] Multiple aspects of the invention are described below. Different procedures for gap detection, distance determination, and carrying out machining, test machining, process measurements, and control measurements are described. These procedures may be implemented in different embodiments of the invention. Likewise, some or all of these aspects may be implemented in a single embodiment, and may be applied alternatively or in addition to one another, for example for purposes of a plausibility check or for a user selection of the type of gap detection. In particular, a device according to the invention is suitable for implementing multiple aspects of the method.

[0065] FIG. 1 shows a schematic overall view of one embodiment of a device 10 according to the invention for carrying out a machining process of a first workpiece 12 and a second workpiece 14. The machining process is a welding process for joining the first workpiece 12 and the second workpiece 14 by means of a high-energy machining beam 15, in the present case, a laser beam. The workpieces 12, 14 in the present case are sheet metal parts. However, any workpieces that can be joined by means of the machining beam are possible according to the invention.

[0066] The device 10 includes a workpiece holder 16 into which the workpieces 12, 14 are appropriately inserted. The device 10 also includes a machining unit 18 having a machining beam source 20 that generates the high-energy machining beam 15. The machining unit 18 includes machining beam optics 22, only schematically illustrated, by means of which the machining beam 15 may be projected and/or focused on a current machining area 24. A joining seam for joining the workpieces 12, 14 along a predetermined course may be produced in a manner known per se by appropriate relative movement between the machining beam 15 and the workpieces 12, 14, for example by appropriately advancing the workpieces 12, 14 and/or by moving the machining beam optics 22 and/or an optical element of the machining beam optics 22 and/or of the machining unit 18.

[0067] The device 10 also includes an optical coherent tomograph 26 having a known design, by means of which a measuring beam 28, which is coupleable into the machining optics 22 via a deflection unit 30, likewise only schematically illustrated, and guidable onto the workpieces 12, 14, may be generated. In a known manner the coherent tomograph 26 has a suitable light source, for example a superluminescent diode, and a measuring arm and a reference arm. Distances relative to a reference point may be determined by means of an interferometer of the optical coherent tomograph 26.

[0068] The measuring beam 28 and the machining beam 15 may be displaced in such a way that they coincide. However, the measuring beam 28 is displaceable independently of the machining beam 15, so that the machining beam 15 and the measuring beam 28 may meet at different locations on the workpieces 12, 14. This is schematically illustrated by the dotted lines in FIG. 1.

[0069] The device 10 also has a control unit 60 that is configured to automatically control the machining unit 18 and the optical coherent tomograph 26. The device 10 also has a user interface, not illustrated, via which information may be input and output.

[0070] FIG. 2 shows a schematic sectional illustration of the two workpieces 12, 14 in a joined state. The first workpiece 12 is inserted into the workpiece holder 16 prior to machining. The second workpiece 14 is placed at a target position on the first workpiece 12. In the superposed state, machining then takes place by means of the machining beam 15, via which a joining point 62 is produced. The joining point forms a section of a joining seam between the workpieces 12, 14.

[0071] FIG. 2 illustrates an area of the workpieces 12, 14 in which the workpieces 12, 14 lie directly on top of one another, so that no gap is formed between them. This represents the desired case in which the workpieces 12, 14 may be reliably joined. When the machining beam 15 is projected onto the top side 64 of the second workpiece 14, in the machining area 24 (see FIG. 1) first the second workpiece 14 on top melts, followed by the first workpiece 12 situated underneath, wherein a melt is formed that extends in both workpieces 12, 14 and joins them. When the machining beam 15 is advanced or switched off, the molten material of the workpieces 12, 14 solidifies and forms the joining point 62. If the workpieces 12, 14 are superposed in an area of the joining point 62 without a gap, the sum of a thickness 38 of the first workpiece 12 and a thickness 40 of the second workpiece 14 corresponds to a distance between oppositely situated points on the top side 64 of the second workpiece 14 and a bottom side 48 of the first workpiece 12. Such points are marked by crosses in FIG. 2.

[0072] However, due in particular to deformations in the workpieces 12, 14, a gap 34 may form, at least in places, between the workpieces 12, 14, as schematically illustrated in FIG. 3. The workpieces 12, 14 are then situated at a distance 36 from one another that corresponds to a distance between a bottom side 66 of the second workpiece 14 and a top side 32 of the first workpiece 12. Consequently, a distance between the mentioned points on the top side 64 of the second workpiece and the bottom side 48 of the first workpiece 12 is greater, by this distance 36, than the sum of the thicknesses 38, 40 of the workpieces 12, 14.

[0073] The device 10 is configured to carry out a process measurement by means of the measuring beam 28 during the machining of the workpieces 12, 14. This process measurement takes place, for example, by guiding the measuring beam 28 into a keyhole 68 that is formed in the current machining area 24 during the machining (see FIG. 4). The keyhole 68 is typically formed just behind, based on the machining direction, an impingement area 70 of the machining beam 15 in the current machining area 24.

[0074] In addition, the device 10 is configured to carry out a control measurement, which is different from the process measurement, by means of the measuring beam 28. In the present case, the control measurement is carried out by means of the optical coherent tomograph 26. The control measurement is at least partially carried out during the machining of the workpieces 12, 14. In addition, the control unit 60 carries out a control of the control measurement.

[0075] Based on a result of the control measurement, a gap 34 that is possibly present between the workpieces 12, 14 is then detected. In addition, the control measurement encompasses multiple measurements at different locations. The presence of a gap 34 is subsequently carried out for the current machining area 24; i.e., the control measurement is carried out in such a way that for the current machining area 24 it may be determined whether a gap 34 is present between the workpieces 12, 14 in this area, or the workpieces 12, 14 lie directly one on top of the other. In addition, the distance 36 between the workpieces 12, 14 is determined, so that a conclusion may be drawn concerning a dimension of the gap 34 and a likely result of machining in the current machining area 24. The determination of the distance 36 or the presence of a gap 34 is carried out automatically by the control unit 60, based on the control measurement.

[0076] According to one aspect, the control measurement includes a measurement of a distance from a reference point to a point on the top side 64 of the second workpiece 14. This measurement is carried out, for example, by briefly interrupting the process measurement during the machining and moving the measuring beam 28 forward in the machining direction, as indicated by the dotted line in FIG. 1. The measurement then takes place, for example, in the next machining area before the second workpiece 14 is machined in that area.

[0077] Furthermore, the control measurement includes a measurement that allows a conclusion to be drawn concerning a position of the bottom side 48 of the first workpiece 12. According to one aspect, for this purpose a position of the workpiece holder 16 is determined by means of the measuring beam 28 before the workpieces 12, 14 are inserted. In addition, predefined values for the thicknesses 38, 40 of the workpieces 12, 14 are used. Assuming that the first workpiece 12 lies flat on the workpiece holder 16, a distance 36 between a measuring point in question on the workpiece holder 16 and a corresponding measuring point on the top side 64 of the second workpiece 14 corresponds to the distance 36 between the above-mentioned oppositely situated points on the bottom side 48 of the first workpiece 12 and the top side 64 of the second workpiece 14. The measuring points are illustrated by crosses in FIGS. 2 and 3 by way of example. If the distance 36 differs from a sum of the thicknesses 38, 40 of the workpieces 12, 14, the presence of a gap 34 is deduced. In addition, the distance 36 and thus the thickness of the gap 34 may be determined. The measurement on the workpiece holder 16 may include multiple measuring points, for example according to a future and/or planned course of a joining seam.

[0078] According to another aspect, within the scope of the control measurement at least one measurement is additionally or alternatively carried out on the top side 32 of the first workpiece 12 by means of the measuring beam 28. This measurement is carried out after the first workpiece 12 is inserted and before the second workpiece 14 is inserted. In combination with the measurement on the top side of the second workpiece 14, based on a distance between a measuring point on the top side 32 of the first workpiece 12 and a measuring point on the top side 64 of the second workpiece 14, the presence of a gap may be deduced by comparing the stated distance to the known thickness 40 of the second workpiece 14. If the distance is greater than the thickness 40 of the second workpiece 14, on this basis the distance 36 between the workpieces 12, 14 may be determined as the difference between the distance between the measuring points and the thickness 40. In addition, the presence of a gap 34 may be deduced. The measuring points are illustrated by crosses in FIGS. 2 and 3 by way of example. The measurement on the top side 32 of the first workpiece 12 may include multiple measuring points, for example according to a future and/or planned course of a joining seam.

[0079] FIG. 4 illustrates a further aspect of the method according to the invention. Within the scope of the control measurement, a measurement is carried out on the top side 64 of the first workpiece 12 when the second workpiece 14 is already at the target position. In the illustrated case, the second workpiece has multiple notches 72, 74, 76, which due to a geometry of the second workpiece 14 and/or due to a target geometry of the finished component or the finished part are present independently of the control measurement or independently of the machining of the workpieces 12, 14. For the control measurement, the measuring beam 28 is temporarily directed onto at least one of the notches 72, 74, 76 and is guided through same onto the top side 32 of the first workpiece 12. In addition, as described above, a measurement is carried out on the top side 64 of the second workpiece 14. This takes place either during the machining by deflection of the deflection unit 30 (OCT scanner), or with a brief interruption of the machining by deflection of a machining scanner 21 of the machining beam optics 22. Analogously to the aspect described above, a distance between corresponding measuring points may then be compared to a known thickness 40 of the second workpiece 14. A notch 72, 74, 76 is advantageously selected in each case that is closest to the future machining area in which the top side 64 of the second workpiece 14 is measured, in order to form pairs of measuring points.

[0080] According to yet another aspect, for which reference is made to FIG. 5, the second workpiece 14 is provided with multiple holes 42, 44, 46 that are provided in the second workpiece 14 independently of the machining of the workpieces 12, 14. According to the invention, for manufacturing the second workpiece 14, for this purpose a suitable workpiece blank is provided with multiple holes 42, 44, 46 along a course that a future joining seam is to follow.

[0081] Within the scope of the control measurement, in an inserted and positioned state of the workpieces 12, 14 the measuring beam 28 may then be guided through one of the holes 42, 44, 46 in each case in order to once again carry out a measurement on the top side 32 of the first workpiece 12. For this purpose, the measuring beam 28 in each case is advantageously guided through a hole 42 that is closest to the current machining area 24. In addition, the measurement is advantageously carried out on the top side 64 of the second workpiece 14 in the vicinity of the corresponding hole 42, so that paired measuring points are close to one another and close to a gap 34 that may possibly be present.

[0082] The holes 42, 44, 46 may then be welded closed when the current machining area 24 is appropriately advanced. The holes 42, 44, 46 are thus present only for the control measurement, whereas a finished part is provided without the holes 42, 44, 46.

[0083] FIG. 6 illustrates a further aspect, in which test machining of the workpiece 12, 14 that is different from the machining of the workpieces 12, 14 takes place during the control measurement. For this purpose, the machining beam 15 is briefly moved forward, out of the current machining area 24, and thus follows the course illustrated by dash-dotted lines in FIG. 6, and not the course for machining the current machining area 24, which is illustrated by the dotted line. The deflection angle is typically much smaller than schematically illustrated in FIG. 6. By means of the machining beam 15, the test machining takes place in such a way that material is melted through both workpieces 12, 14, and the bottom side 48 of the first workpiece 12 is penetrated at certain points.

[0084] During the control measurement, the measuring beam 28 is displaced in such a way that it coincides with the machining beam 15 and/or enters a keyhole of the test machining. A temporal depth profile 78 for the test machining may thus be created within the scope of the control measurement. Such an OCT depth measurement profile 78 is schematically illustrated in FIG. 7, which depicts the machining depth T, measured by OCT measurement, as a function of the machining time t. The test machining begins at a point in time t.sub.0, at which the machining beam 15 is directed onto the top side 64 of the second workpiece 14, and ends at a point in time t.sub.e. At the start, the material of the second workpiece 14 melts in an impingement area, with the machining depth initially undergoing little or no change. A keyhole then gradually forms in the second workpiece 14, and the machining beam 15 also penetrates into the first workpiece 12. In FIG. 6, characteristic points for the test machining process are marked by crosses situated on the top sides 32, 64 and bottom sides 48, 66 of the workpieces 12, 14. During the machining, a melt forms between the workpieces 12, 14 which may bridge the workpieces 12, 14, even in the presence of a gap 34. At least the point on the bottom side 66 of the second workpiece 14 and the point on the top side 32 of the first workpiece 12 may then possibly not be clearly identifiable in an OCT measurement. In addition, the temporal depth profile 78 in each case follows a different course, depending on the material composition, the thicknesses 38, 40 of the workpieces, the distance 36 between the workpieces 12, 14, parameters of the machining beam 15, and other machining parameters. Under certain circumstances, although this course may have the plateaus and jumps mentioned at the outset, the course often is not visible when the machining depth corresponds to the thickness 40 of the second workpiece 14, a sum of the thickness 40 of the second workpiece 14, and the distance 36 between the workpieces 12, 14, or additionally the thickness 38 of the first workpiece 12, in particular for the case of the mentioned bridging melt.

[0085] In contrast, the overall thickness of the superposed workpieces 12, 14 is apparent from the depth profile 78, since the point on the top side 64 of the second workpiece 14 as well as the point on the bottom side 48 of the first workpiece 12 are clearly represented. Even after a penetration on the bottom side 48 of the first workpiece 12, a portion of the measuring beam 28 is always reflected. However, this reflection takes place solely from areas within the superposed workpieces 12, 14. Therefore, a maximum penetration depth is measured that originates from the point on the bottom side 48 of the first workpiece. The sum of the thicknesses 38, 40 of the workpieces 12, 14 and the distance 36 between the workpieces 12, 14 may thus be reliably determined from the depth profile 78. This sum may in turn be compared to the sum of the known workpiece thicknesses 12, 14 in order to determine the distance 36 between the workpieces 12, 14 and deduce the presence of a gap 34.

[0086] Multiple test machinings may be carried out during the machining, so that the presence or the course of the gap 34 may be determined. In addition, these test machining points may be welded closed during the subsequent machining of the workpieces 12, 14.

[0087] In the case shown, the machining device 18 has a switchable fiber 50 by means of which the diameter of the machining beam 15 may be changed. A large diameter is used for machining the workpieces 12, 14, while a small diameter is used for the test machining. The bottom side 48 of the first workpiece 12 is therefore penetrated only in a small area, and a corrosion protection layer is damaged only to a negligible extent.

[0088] FIG. 8 shows a workpiece holder 16 according to one aspect of the invention, which is provided with reflective elements 52, 54, 56, 58. Within the scope of the control measurement, the measuring beam 28 is directed onto the reflective elements 52, 54, 56, 58 in such a way that a measurement may be carried out on the bottom side 48 of the first workpiece 12. The measurement in question is carried out in an inserted and positioned state of the workpieces 12, 14. This measurement may in turn be combined with a measurement on the top side 64 of the second workpiece 14. This is schematically illustrated by the measuring points marked by crosses in FIG. 8.

[0089] The reflective elements 52, 54, 56, 58 may include polished surfaces, mirrors, or other suitable reflective elements. In addition, at least one of the reflective elements 52, 54, 56, 58 may be movable and/or pivotable, thus allowing deflection of the measuring beam 28 in an adjustable manner.

[0090] Alternatively, a measurement on the bottom side 48 of the first workpiece 12 is carried out by means of a further optical coherent tomograph (not illustrated).

[0091] In addition, it is also possible according to the invention to provide the first workpiece 12 with holes and/or notches through which the measuring beam may be guided onto the bottom side 66 of the second workpiece 14. This may be carried out by means of the workpiece holder 16 with reflective elements 52, 54, 56, 58 and/or by means of a further optical coherent tomograph. The above-described control measurements through the second workpiece 14 onto the top side 32 of the first workpiece 12 may similarly take place on the bottom side 66 of the second workpiece 14. In addition, a measurement is carried out on the bottom side 48 of the first workpiece 12. A distance between corresponding measuring points may then be compared to the known thickness 40 of the first workpiece 12 in order to determine the distance 36 between the workpieces 12, 14 and/or deduce the presence of a gap 34.

[0092] In principle, for the described measuring points it is possible for them to correspond to the points onto which the measuring beam 28 is directed. However, it is also possible to direct the measuring beam 28 onto some other point, wherein this point and the corresponding measuring point lie in a shared plane that is parallel to a main plane of extension of the workpieces 12, 14. It is then possible, for example, to determine a distance along a surface normal of the workpieces 12, 14, even when points that are offset relative to one another perpendicularly with respect to the surface normal are measured.

[0093] FIG. 9 shows a schematic flow chart of a method for carrying out and monitoring a machining process of the workpieces 12, 14. The method is carried out by means of the device 10.

[0094] The first workpiece 12 is inserted into the workpiece holder 16 in a first step S1 of the method.

[0095] The second workpiece 14 is positioned in the target position on the top side 32 of the first workpiece 12 in a second step S2 of the method.

[0096] The high-energy machining beam 15 is provided and projected and/or focused on the current machining area 24 in a third step S3 of the method.

[0097] The measuring beam 28 is generated in the optical coherent tomograph in a fourth step S4 of the method, the measuring beam 28 being deflected via the movable deflection unit and at least temporarily coupled into the machining beam 15.

[0098] A process measurement is carried out in the current machining area 24, during the machining of the workpieces 12, 14, by means of the measuring beam 28 in a fifth step S5 of the method.

[0099] A control measurement is carried out by means of the measuring beam 28 in a sixth step S6.

[0100] The distance 36 between the workpieces 12, 14 is determined in a seventh step S7, based on the result of the control measurement, for detecting a gap 24 that is possibly present between the workpieces 12, 14.

[0101] Different aspects of the method have also been described in conjunction with the device 10. This also results in further steps or substeps of the method.