Abstract
A method for automatically determining optimum welding parameters for carrying out a weld on a workpiece carries out test welds on test workpieces along test welding tracks, and at each test weld a welding parameter is changed automatically along the test welding track from a predefined initial value to a predefined final value. Each resulting test weld seam is measured along the test welding track with a sensor, and a sensor signal is received. A quality parameter characterizing each test weld seam is calculated from the sensor signal. A quality function for characterizing the test weld seam quality in accordance with the changed weld parameters is calculated from the quality parameter. An optimum quality function is ascertained, and the values for the optimum welding parameters are defined based on each quality parameter at this quality function optimum and the corresponding test weld track locations and saved.
Claims
1. A method for automatically determining optimum welding parameters (P.sub.i,opt) for carrying out a weld on a workpiece (4), comprising: carrying out via a welding torch arranged on a process robot actuated by a control device a plurality of test welds on test workpieces (9) along test welding tracks (10), and automatically changing at each test weld at least one welding parameter (P.sub.i(x)) along the test welding track (10) linearly or in specific stages along the test welding track (10) on a predefined length (l) from a predefined initial value (P.sub.i,A) to a predefined final value (P.sub.i,E), depending on the location (x), wherein each test weld is carried out along predefined test welding tracks (10) with a constant tangential vector (t); measuring each resulting test weld seam (11) along the test welding track (10) during or after carrying out the plurality of test welds with at least one sensor (12), and receiving at least one sensor signal (S.sub.j(P.sub.i(x))), depending on the location (x) along the test weld seam (11); processing the at least one sensor signal (S.sub.j(P.sub.i(x))) via the control device and depositing the at least one sensor signal (S.sub.j(P.sub.i(x))) so processed in a database; calculating via the control device at least one quality parameter (Q.sub.k(S.sub.j(P.sub.i(x)))) which characterizes each weld seam (11) from the at least one sensor signal (S.sub.j(P.sub.i(x))); calculating via the control device a quality functional (G(Q.sub.k(S.sub.j(P.sub.i(x))))) for characterizing the quality of the test weld seams (11) in accordance with the changed welding parameters (P.sub.i(x)) from the at least one quality parameter (Q.sub.k(S.sub.j(P.sub.i(x)))); and ascertaining via the control device an optimum of the quality functional (G.sub.opt(Q.sub.k(S.sub.j(P.sub.i(x)))), and determining via the control device from this determined optimum of the quality functional (G.sub.opt(Q.sub.k(S.sub.j(P.sub.i(x)))) the respective optima of the quality parameters (Q.sub.k,opt(S.sub.j(P.sub.i(x))), and from the optima of the quality parameters (Q.sub.k,opt(S.sub.j(P.sub.i(x))) from the sensor signals (S.sub.j(P.sub.i(x))) identifying via the control device those locations (x) as optimum locations (x.sub.opt) along the test weld seam (11) at which the welding result of the test weld is optimum according to the respective quality parameter (Q.sub.k(S.sub.j(P.sub.i(x))), and defining via the control device the welding parameters (P.sub.i(x)) at these locations (x.sub.opt) of the test weld seams (11), identified as optimum, as values for the optimum welding parameters (P.sub.i,opt) for carrying out the welding on the workpiece (4), and saving the values in the database; and carrying out the welding of the workpiece using the values saved in the database.
2. The method according to claim 1, wherein the test welding tracks (10) are measured before carrying out the test welds.
3. The method according to claim 1, wherein at each test weld at least one of the welding parameters (P.sub.i(x)) wire feed speed (v.sub.D(x)) of a welding wire (5) which is to be melted off, welding speed (v.sub.s(x)), free welding wire length, angle of attack (phi_p(x)) of the welding torch (3), working angle (phi_w(x)) of the welding torch (3) and tool center point (TCP(x)) of the welding torch (3) is changed along the test welding track (10), depending on the locations (x).
4. The method according to claim 1, wherein the test welds are carried out on flat test workpieces (9).
5. The method according to claim 1, wherein the test weld seams (11) are measured along the test welding track (10) by non-destructive measurement methods.
6. The method according to claim 1, wherein the test weld seams (11) are processed along the test welding track (10) by destructive measurement methods.
7. The method according to claim 1, wherein the test welds are carried out under various welding conditions (B.sub.l), and the optimum welding parameters (P.sub.i,opt) for the welding under a predefined welding condition (B.sub.v) is carried out by interpolation of the optimum welding parameters (P.sub.i,opt) which were determined at test welds under the bordering welding conditions (B.sub.u, B.sub.o) for the predefined welding condition (B.sub.v).
8. The method according to claim 7, wherein the test welds are carried out under at least two different welding conditions (B.sub.l) respectively of the workpiece temperature, position of the test workpiece (9), opening angle of the test workpieces (9) around the test welding track (10) or the gap width of the test welding track (10).
9. The method according to claim 7, wherein before the carrying out of the interpolation, the quality functional G(Q.sub.k(S.sub.j(P.sub.i(x)))) is determined at the predefined welding condition (B.sub.v) and, when the quality functional G(Q.sub.k(S.sub.j(P.sub.i(x)))) deviates from a threshold value, at least one further test weld is carried out at a further test welding condition (B.sub.z).
10. The method according to claim 1, wherein the width, height, superelevation, under-curvature, seam filling volume and/or the transition angle of the test weld seam (11) is scanned and from these sensor signals (S.sub.j(P.sub.i(x)) the quality parameter (Q.sub.k(S.sub.j(P.sub.i(x)) is calculated along the test welding track (10).
11. The method according to claim 1, wherein the optimum of the quality functional (G.sub.opt(Q.sub.k(S.sub.j(P.sub.i(x))) is determined by successive changing respectively of a welding parameter (P.sub.i(x)) for influencing respectively a quality parameter (Q.sub.k(S.sub.j(P.sub.i(x)))).
12. The method according to claim 1, wherein the optimum of the quality functional (G.sub.opt(Q.sub.k(S.sub.j(P.sub.i(x))) is determined by changing in terms of gradient several welding parameters (P.sub.i(x)) for influencing several quality parameters (Q.sub.k(S.sub.j(P.sub.i(x)))).
Description
(1) The invention is explained further with the aid of the enclosed drawings.
(2) There are shown therein:
(3) FIG. 1 a diagrammatic overview illustration of a welding process;
(4) FIG. 2 a functional sketch of the method according to the invention for the automatic determining of optimum welding parameters for carrying out a weld on a workpiece;
(5) FIG. 3 an illustration of a system for carrying out the method according to the invention;
(6) FIG. 4 a block diagram to illustrate the carrying out of the method according to the invention;
(7) FIGS. 5a-5c various methods for the measuring of test weld seams on test workpieces;
(8) FIG. 6 a sectional image through a welded workpiece in the form of a fillet weld; and
(9) FIGS. 7a-7c the profiles of some characteristics of the resulting weld seam, to illustrate the finding of the optimum welding parameters with the aid of an example.
(10) FIG. 1 shows a diagrammatic overview illustration of a welding process, wherein a welding system, which comprises a welding apparatus 1, a process robot 2 and a welding torch 3, which solves accordingly a welding problem on a workpiece 4. Accordingly, the welding torch 3 is guided along a predefined welding track 7 on the workpiece 4 and burns an arc 6 between the contact nozzle of the welding torch 3 or respectively the end of the welding wire 5 and the workpiece 4. Through the fusing of the material of the workpieces 4 and the melting off of the welding wire 5, a weld seam 8 is produced. Alternatively or additionally to the movement of the welding torch 3 in relation to the workpiece 4, the workpiece 4 can also be moved with respect to the welding torch 3. A relative movement between welding torch 3 and workpiece 4 along the welding track 7 is crucial. Various welding processes are carried out for the welding and depending on the respective position and arrangement of the workpiece 4 and the direction of the welding track 7, which corresponds to the tangential vector t of the welding track 7, specific welding parameters P.sub.i(x) are set. By means of these welding parameters P.sub.i(x), the welding processes or respectively the welding and thereby the weld seam 8 are substantially influenced. Depending on the respective welding task, different requirements are set for the weld seam 8. For example, the welding can be optimized via the setting of the welding parameters P.sub.i(x) for welding speed, secure penetration depth, vibration dynamics requirements, but also a visually pleasing weld seam 8. Therefore, for carrying out a weld on a workpiece 4, taking into account the respective welding task, there is always a set of optimum welding parameters P.sub.i,opt(x), which lead to optimum welding results. The finding of such optimum welding parameters P.sub.i,opt(x) is a very complex method, which is usually reserved for experts or respectively specialists in the field of welding technology. The process of finding optimum welding parameters P.sub.i,opt(X) can last for an accordingly long time, which can lead to long waiting times and in some cases high costs. Furthermore, it can occur that to bridge such waiting times up to the finding of optimum welding parameters P.sub.i,opt(x), compromises are made, which are characterized by insufficient welding quality. It is therefore a matter of great concern to be able to undertake the finding of optimum welding parameters P.sub.i,opt(x) for specific welding tasks in the carrying out of welds on workpieces 4 as quickly as possible and also without the direct involvement of corresponding experts or respectively specialists.
(11) FIG. 2 shows a functional sketch of the method according to the invention for automatically determining optimum welding parameters P.sub.i,opt(x) for carrying out a weld on a workpiece 4. Accordingly, several test welds are carried out on test workpieces 9 along the test welding tracks 10, and at each test weld at least one welding parameter P.sub.i(x) is automatically changed from a predefined initial value P.sub.i,A to a predefined final value P.sub.i,E along the test welding track 10. The change between the initial value P.sub.i,A and the final value P.sub.i,E of the respective welding parameter P.sub.i(x) can take place for example linearly or else in specific stages, wherein the correlation between the welding parameter P.sub.i(x) and the path x covered along the test welding track 10 is always predefined so that, vice versa, at each location x of the test welding track 10, a conclusion can be made regarding the welding parameter P.sub.i(x) which is set there. In particular with the use of very simple test workpieces 9 with preferably straight test welding tracks 10 or respectively test welding tracks 10 with constant tangential vector and an application-oriented arrangement of the test workpieces 9, test welds result which are able to be carried out very easily and quickly, and it is not necessary to weld complete workpieces or respectively components for test purposes, which would lead to great expense and waste.
(12) The resulting test weld seams 11 along the test welding tracks 10 of the test workpieces 9 are measured by corresponding sensors 12, wherein this measuring can be carried out directly during the carrying out of the test weld or else later. In addition to sensors 12, which scan the test weld seam 11 in a contactless manner, or internal sensors which record parameters of the welding current source during the carrying out of the test weld, methods also come into consideration in which the test weld seam 11 is analyzed with destruction of the test workpiece 9. For example, micrographs of the test weld seam 11 can be made at several locations along the test welding track 10 and can be processed for example by means of image processing.
(13) The sensors 12 deliver various sensor signals S.sub.j(P.sub.i(x)), which are processed to at least one quality parameter Q.sub.k(S.sub.j(P.sub.i(x))) characterizing the respective test weld seam 11 of the test workpieces 9. The type of calculation of the quality parameters Q.sub.k(S.sub.j(P.sub.i(x))) from the sensor signals S.sub.j(P.sub.i(x)) depends on the respective welding task and on the criterion which is characteristic for the completion of the respective welding task.
(14) For easier processing of the quality parameters Q.sub.k(S.sub.j(P.sub.i(x))), a quality functional G(Q.sub.k(S.sub.j(P.sub.i(x)))) is calculated for characterizing the quality of the test weld seams 11 as a function of the changed welding parameters P.sub.i(x). Therefore, with the quality functional, a real number results in multi-dimensional space, which has at least one optimum, in particular maximum or minimum, which is able to be found in a manner which is able to be automated relatively easily. As sketched in FIG. 2, the optimum G.sub.opt of the quality functional G can be a maximum of the area dependent on the welding parameters P.sub.1 and P.sub.2. Through corresponding calculation, this optimum of the quality functional G.sub.opt can be found quickly within specific limits in the parameter space. From this optimum of the quality functional G.sub.opt(Q.sub.k(S.sub.j(P.sub.i(x)))) the respective optima of the quality parameters Q.sub.k,opt(S.sub.j(P.sub.i(x))) and from the corresponding locations x.sub.opt of the test welding tracks 10 finally the values are defined and saved for the respective optimum welding parameters P.sub.i,opt. With these optimum welding parameters P.sub.i,opt the welding is carried out on the workpiece 4, resulting in an optimum welding quality corresponding to the welding task.
(15) In contrast to known methods hitherto, the direct deployment of experts or respectively specialists in welding technology is not necessary here. Of course, however, such experts and specialists in welding technology must be used for the defining of the quality parameters Q.sub.k(S.sub.j(P.sub.i(x))) and of the quality functional G(Q.sub.k(S.sub.j(P.sub.i(x))). For specific welding tasks on specific workpieces with specific workpiece geometries, however, numerous test welds on test workpieces 9 and numerous variants of quality parameters and quality functionals can be defined and saved in corresponding data bases and, with access thereto, optimum welding parameters P.sub.i,opt can be automatically defined quickly for individual welding tasks.
(16) FIG. 3 shows an illustration of a welding system for carrying out the method according to the invention. By means of the welding apparatus 1, the welding torch 3, arranged on the process robot 2, for carrying out test welds on test workpieces 9 is controlled accordingly. The welding apparatus 1 and the process robot 2 are actuated accordingly via a control device 17 or respectively a computer, so that the test welds can be carried out on corresponding test workpieces 9 along predefined test welding tracks 10. By means of suitable sensors 12, the weld seam 11 can be measured along the test welding track 10 during the carrying out of the test weld or else after the carrying out of the test weld. For example, optical sensors 13, X-ray sensors 14, temperature sensors 15 or else eddy current sensors 16 come into consideration as sensors 12. Internal sensors can also record parameters of the welding current source during the carrying out of the test weld. The sensor signals S.sub.j(P.sub.i(x)) received by the sensors 12 are processed via the control device 17 and are deposited in corresponding memories or respectively data bases 18. Furthermore, according to the respective welding task, quality parameters Q.sub.k(S.sub.j(P.sub.i(x))) are calculated from the sensor signals S.sub.j(P.sub.i(x)), which characterized the individual test weld seams 11 accordingly. Since along a test weld seam respectively at least one welding parameter P.sub.i(x) is changed from an initial value P.sub.i,A to a final value P.sub.i,E, a point or respectively region which has optimum characteristics exists along the test weld seam 11. These optimum characteristics of the test weld seam 11 are detected accordingly by means of the sensors 12 and are processed accordingly in the control device 17. At the location along the test weld seam 11 at which optimum characteristics of the test weld seam are defined, a back calculation can be carried out to the parameter P.sub.i(x) which is valid there, and this can be defined as optimum and saved accordingly. From the plurality of test workpieces 9 and their test weld seams 11 and the sensor signals S.sub.j(P.sub.i(x)), a plurality of data results, which are deposited in the memories or respectively data bases 18. The data base 18 represents quasi a knowledge data base, in which the expert knowledge of the experts and specialists who are knowledgeable in welding technology is present in a structured manner and can be accessed for the defining of optimum welding parameters P.sub.i,opt.
(17) FIG. 4 shows the principle of finding the optimum welding parameters P.sub.i,opt from this information which is saved in the data bases 18. Accordingly, the control device 17 or respectively the computer is loaded with specific data by which a specific welding task is characterized for carrying out a weld on a workpiece 4. In particular, the specific quality parameter Q.sub.k and the quality functional G will be as a function of the quality parameters Q.sub.k, or from a plurality of such quality parameters Q.sub.k or quality functionals G at least one specific quality parameter Q.sub.k or respectively a specific quality functional G is selected. From the available information of the sensor signals S.sub.j(P.sub.i(x)) obtained from the test welds, a back-calculation can be carried out to the respective optimum welding parameters P.sub.i,opt via the procedure, described above, of finding the optimum of the quality functional G.sub.opt. These optimum welding parameters P.sub.i,opt are then passed on to the welding apparatus 1 and the process robot 2 of the welding system, and the welding is carried out on the workpiece 4 along the welding track 7 with these optimum welding parameters P.sub.i,opt, resulting in a weld seam 8 with optimum characteristics for the respective welding problem which is to be solved.
(18) FIGS. 5a to 5c show various sketches to illustrate the measuring of test weld seams 11 on test workpieces 9. FIG. 5a shows a method for measuring the test weld seam 11 during the carrying out of the test weld, by for example optical sensors 13 or temperature sensors 15 being arranged downstream of the welding torch 3, which sensors scan the weld seam 11 accordingly and receive and pass on the obtained sensor signals S (x) depending on the location along the test welding track 10.
(19) Alternatively or additionally to the above method illustrated in FIG. 5a, also subsequently in accordance with FIG. 5b the test workpiece 9 or respectively the test weld seam 11 can be measured along the test welding track 10, by means of various sensors, such as e.g. optical sensors 13, X-ray sensors 14 or else eddy current sensors 16, which can lead to various quality parameters over the weld seam 11.
(20) In FIG. 5c a method is sketched in which the test workpiece 9 is destroyed for the analysis of the test weld seam 11, by micrographs of the test weld seam 11 and of the surrounding test workpiece 9 being produced at various locations along the test welding track 10. These micrographs can be measured by corresponding sensors and image-processing methods and can provide information concerning the quality of the test weld seam 11. When, with regard to the fulfilling of a specific welding task, a specific micrograph has optimum characteristics, for example optimum penetration depth or suchlike, the respective welding parameter P.sub.i(x) which is used at this location of the test weld seam 11 can be identified and defined and saved as optimum welding parameter P.sub.i,opt.
(21) The automatic methods for measuring the test weld seams 11 along the test welding tracks 10 of the test workpieces 9 can be automated with the use of corresponding devices, so that the plurality of data which can assess the test weld seams 11 can be quickly found and saved.
(22) FIG. 6 shows a sectional view through a welded workpiece with corresponding parameters, which characterize the workpieces and the weld seam accordingly. Included in these parameters are for example: t thickness of the workpieces g gap width between the workpieces a weld seam thickness h seam superelevation t_p penetration depth t_k depth of the undercut phi_ü seam transition angle phi_p angle of attack between welding torch and workpiece in the direction of the weld seam (not illustrated in FIG. 6) phi_w working angle between welding torch and workpiece in the direction transversely to the weld seam
(23) In addition to these parameters for characterization of a weld seam, which are cited by way of example, several further other parameters exist, which can likewise be drawn upon for carrying out the represented method and can be received by corresponding sensors. For example, the amount of spatter, fusion faults, the number of pores in the weld seam and the reproducibility can be named as welding parameters which can characterize the welding.
(24) FIGS. 7a-7c show now with the aid of an example the finding of optimum welding parameters for a specific welding task. In this example, the task consists of keeping the seam superelevation h of a weld seam as small as possible, by the angle of attack ph_p of the welding torch with respect to the workpiece and the working angle phi_w of the welding torch being varied accordingly, and the optimum parameters being selected therefrom. Accordingly, in this example test welds are carried out in which the angle of attack phi_p is changed from an initial value to a final value along the test weld seam of a test workpiece, and in a further test weld the working angle phi_w is changed from an initial value to a final value along the test welding track. The resulting test weld seams on these test workpieces are measured and a sensor signal corresponding to the seam superelevation h is recorded. Therefore, profiles of the seam superelevation h result as a function of the angle of attack phi_p (FIG. 7a) and h as a function of the working angle phi_w (FIG. 7b).
(25) After definition of a quality functional G dependent on the seam superelevation h, an area profile results for the seam superelevation h as a function of the angle of attack phi_p and of the working angle phi_w, as sketched in the diagram of FIG. 7c. The quality functional G has at least one optimum, in the represented example at least one minimum, which is able to be determined easily, and permit a back-calculation to the optimum values for the angle of attack phi_p,.sub.opt and the working angle phi_w,.sub.opt.
(26) In real welds, more than two welding parameters are varied, resulting in a multi-dimensional function of the quality functional G dependent on the respective variable welding parameters P.sub.i(x).
(27) The represented method permits a rapid finding of ideal welding parameters P.sub.i,opt from a plurality of collected data with the aid of test welds which were carried out with the aid of test workpieces, without corresponding experts or specialists in the field of welding technology having to be directly involved.
