Abstract
In a method for regulating or controlling the conveyance speed of a wire composed of consumable material during a laser soldering or welding method, the wire is melted by a laser beam from a laser unit and is conveyed at a mean conveyance speed toward a workpiece to be processed, wherein a voltage between the wire and the workpiece is measured. A laser soldering or laser welding device carries out this method. In order to avoid at least relatively lengthy short-circuit breaking between the end of the wire and the workpiece, the conveyance speed of the wire, as a function of the measured voltage, is temporarily increased to a predetermined boost speed by increasing the conveyance speed to the predetermined boost speed when a defined voltage limit value is exceeded, and the conveyance speed is reduced again at the latest when the voltage limit value falls below.
Claims
1: A method for regulating or controlling the conveyance speed (v.sub.D) of a wire (4) composed of consumable material during a laser soldering or laser welding method, wherein the wire (4) is melted by a laser beam (L) from a laser unit (2) and is conveyed at a mean conveyance speed (v.sub.D,M) in the direction of a workpiece (5) to be processed, wherein a voltage (U) between the wire (4) and the workpiece (5) is measured, wherein, as a function of the measured voltage (U), the conveyance speed (v.sub.D) of the wire (4) is temporarily increased to a predetermined boost speed (v.sub.D,Boost), which is on average at least 50% above the mean conveyance speed (v.sub.D,M) before the increase, by increasing the conveyance speed (v.sub.D) to the predetermined boost speed (v.sub.D,Boost) when a defined voltage limit value (U.sub.G) is exceeded, and reducing the conveyance speed (v.sub.D) again at the latest when the voltage limit value (U.sub.G) falls below.
2: The method according to claim 1, wherein the conveyance speed (v.sub.D) is increased to a predetermined boost speed (v.sub.D,Boost) which is at least 10 m/min, the conveyance speed (v.sub.D) preferably being increased with a speed change (v.sub.D/t) of at least 2000 m/min/s.
3: The method according to claim 12, wherein, in order to preheat the wire (4), a current (I) is supplied to the wire (4), and a resulting voltage (U.sub.M) is measured, and the conveyance speed (v.sub.D) is temporarily increased to the predetermined boost speed (v.sub.D,Boost) as a function of this measured voltage (U.sub.M).
4: The method according to claim 3, wherein the current (I) through the wire (4) is additionally measured, and a resistance (R) is determined from the measured voltage (U.sub.M) and the measured current (I), and, if a resistance limit value (R.sub.G) is exceeded, the conveyance speed (v.sub.D) is increased to the predetermined boost speed (v.sub.D,Boost), and that wherein the conveyance speed (v.sub.D) is reduced again at the latest when the resistance limit value (R.sub.G) falls below.
5: The method according to claim 1, wherein the conveyance speed (v.sub.D) is reduced at least once by a predetermined conveyance speed amount (v.sub.D1) for a predetermined period of time (t.sub.1) after the increase to the boost speed (v.sub.D,Boost).
6: The method according to claim 1, wherein the conveyance speed (v.sub.D) is again reduced to the mean conveyance speed (v.sub.D,M) before the increase when the voltage limit value (U.sub.G) or the resistance limit value (R.sub.G) falls below.
7: The method according to claim 1, wherein the conveyance speed (v.sub.D) is reduced to a mean conveyance speed (v.sub.D,M) increased by a predetermined conveyance speed amount (v.sub.D2) when the voltage limit value (U.sub.G) or the resistance limit value (R.sub.G) falls below.
8: The method according to claim 7, wherein the mean conveyance speed (v.sub.D,M) increased by the conveyance speed amount (v.sub.D2) is reduced at least once after a defined period of time (t.sub.2) has elapsed by a predetermined conveyance speed amount (v.sub.D3), until the mean conveyance speed (v.sub.D,M) is reached again.
9: The method according to claim 1, wherein the current (I) is regulated or controlled by the wire (4) by reducing the current (I), after increasing the wire conveyance speed (v.sub.D), to the boost speed (v.sub.D,Boost), preferably by a predetermined current amount (I).
10: Method according to claim 1, wherein the conveyance speed (v.sub.D) of the wire (4) is detected and a noise signal (v.sub.D,noise) is generated therefrom, and, if a noise signal threshold (v.sub.D,noise,S) is exceeded, the regulation or control of the conveyance speed (v.sub.D) is deactivated.
11: The method according to claim 10, wherein a warning is issued when the noise signal threshold (v.sub.D,noise,S) is exceeded.
12: A laser soldering or laser welding device (1), comprising a laser unit (2) for melting a wire (4) of consumable material, a wire conveyance device (3) for conveying the wire (4) at a conveyance speed (v.sub.D) in the direction of a workpiece (5) to be processed, and a circuit for measuring the voltage (U) between the wire (4) and the workpiece (5), wherein the laser soldering or laser welding device (1) comprises a regulating or control device (6) which is designed to carry out the method according to claim 1.
13: The laser soldering or laser welding device (1) according to claim 12, wherein the wire conveyance device (3) is formed by a gearless direct drive.
14: The laser soldering or laser welding device (1) according to claim 12, wherein the wire conveyance device (3) for conveying the wire (4) is designed with a conveyance speed of at least 10 m/min, preferably with a speed change (v.sub.D/t) of at least 2000 m/min/s.
Description
[0029] The present invention is further explained with reference to the appended drawings. In the drawings:
[0030] FIG. 1 shows a schematic block diagram of a laser soldering or laser welding device with a regulation or control of the conveyance speed of the wire of consumable material;
[0031] FIG. 2 shows the time profiles of the voltage, the conveyance speed and the current on the wire according to a first embodiment of the invention;
[0032] FIG. 3 shows the time profiles of the voltage, the conveyance speed and the current on the wire according to a second embodiment of the invention;
[0033] FIG. 4 shows the time profiles of the voltage, the conveyance speed and the current on the wire according to a third embodiment of the invention;
[0034] FIG. 5 shows the time profiles of the voltage, the conveyance speed and the current on the wire according to a fourth embodiment of the invention;
[0035] FIG. 6 shows the time profiles of the voltage, the conveyance speed and the current on the wire according to a fifth embodiment of the invention;
[0036] FIG. 7 shows the time profiles of the position of the soldering or welding head in z-direction, the voltage, the conveyance speed and the current on the wire according to a sixth embodiment of the invention;
[0037] FIG. 8 shows the time profiles of the voltage, the conveyance speed, the resistance, and the current on the wire according to a further embodiment of the invention;
[0038] FIG. 9 shows the time profiles of the position of the soldering or welding head in the z-direction, the voltage, the conveyance speed, the resistance and the current on the wire according to a further embodiment of the invention; and
[0039] FIG. 10 shows the time profiles of the position of the soldering or welding head in the z-direction, the voltage, the conveyance speed, the resistance, the current on the wire, a determined noise signal and a warning signal when a certain noise signal threshold is exceeded, according to a further embodiment of the invention.
[0040] In FIG. 1, a schematic block diagram of a laser soldering or laser welding device 1 with a regulation or control of the conveyance speed v.sub.D of the wire 4 of consumable material is represented. The wire 4 of consumable material is melted by the laser beam L of a laser unit 2 in order to connect at least two workpieces 5 to one another or to produce a coating on a workpiece 5 or to use it for the additive finish of a workpiece 5. To this end, the wire 4 is conveyed by a wire drum 7 via a wire conveyance device 3 at a predetermined conveyance speed v.sub.D into the focal point or point of incidence of the laser beam L on the workpiece 5, where it is melted by the energy of the laser beam L. During laser welding, melting of the material of the at least one workpiece 5 also occurs, while during laser soldering, no substantial melting of the material of the workpiece 5 occurs. In addition, the wire 4 can be preheated by a current I, which is applied to the wire 4 in the wire conveyance device 7 (hot wire soldering or hot wire welding). In laser soldering and laser welding, it is very important for the process stability to keep the conveyance speed v.sub.D of the wire 4 constant and to keep the wire 4 always in contact with the fluid molten bath. According to the invention, the conveyance speed v.sub.D of the wire 4 is temporarily increased to a predetermined boost speed v.sub.D,Boost in a regulating or control device 6 as a function of the measured voltage U between the wire 4 and the workpiece 5. Advantageously, when a defined voltage limit value U.sub.G of the voltage U between the wire 4 and the workpiece 5 is exceeded, the conveyance speed v.sub.D of the wire 4 is increased to the predetermined boost speed v.sub.D,Boost, and at the latest when the voltage limit value U.sub.G falls below, the conveyance speed v.sub.D of the wire 4 is again reduced. By also taking into account the current I through the wire 4, a resistance R can also be determined and, when a resistance limit value R.sub.G is exceeded, the conveyance speed v.sub.D can be increased to the predetermined boost speed v.sub.D,Boost and the boost process can be carried out.
[0041] FIG. 2 shows the time profiles of the voltage U, the conveyance speed v.sub.D and the current I on the wire 4 according to a first embodiment of the invention. By measuring the voltage U between the wire 4 and the workpiece 5, an undesired short-circuiting can be detected. For example, the short-circuiting can be determined when a defined voltage limit value U.sub.G is exceeded. The short-circuiting is also evident from a drop of the current I through the wire 4 shown here. However, the measurement of the current I is not absolutely necessary. Depending on the measured voltage U and here with the defined voltage limit value U.sub.G being exceeded, the conveyance speed v.sub.D of the wire 4 is temporarily increased to a predetermined boost speed v.sub.D,Boost, wherein the boost speed v.sub.D,Boost is at least 50% above the mean conveyance speed v.sub.D,M before the increase, in particular is at least 10 m/min. In the example shown, the boost speed v.sub.D,Boost is many times higher than the mean conveyance speed v.sub.D,M before the increase, which, however, requires a corresponding wire conveyance device. The increase of the conveyance speed v.sub.D to the boost speed v.sub.D,Boost preferably takes place as quickly as possible, i.e. with the highest possible acceleration, preferably with a speed change v.sub.D/t of at least 2000 m/min/s. As a result, the short-circuiting is effectively counteracted, as a result of which it can be terminated again after a duration t.sub.KSA, which was shown disproportionately long in the exemplary embodiment. The recurrence of the short circuit is identified by a collapse of the measured voltage U and a drop below the defined voltage limit value U.sub.G, whereupon the conveyance speed v.sub.D is reduced again. Here, after the short-circuiting and the boost process, the conveyance speed v.sub.D is again reduced to that mean conveyance speed v.sub.D,M of the wire 4 which was set before the short-circuiting. As a result of various events, such as, for example, an external disturbance of the laser soldering or laser welding process (e.g., a fluctuation in the height position, a current I set too high for preheating the wire 4, fluctuations in the soldering or welding speed, etc.), a short-circuiting can again occur, as can be seen in the time diagrams. As soon as a further short-circuiting is detected, a boosting process and an increase of the conveyance speed v.sub.D of the wire to the boost speed v.sub.D,Boost takes place again, as a result of which the duration t.sub.KSA of the short-circuiting can be kept very short.
[0042] FIG. 3 shows the time profiles of the voltage U, the conveyance speed v.sub.D and the current I on the wire 4 according to a second embodiment of the invention. In this case, in contrast to the first embodiment according to FIG. 2, in the case of a short-circuiting, the conveyance speed v.sub.D is reduced by a predetermined conveyance speed amount v.sub.D1 a predetermined period of time t.sub.1 after the increase to the boost speed v.sub.D,Boost. By such a stepwise reduction of the conveyance speed v.sub.D, a smoother speed reduction and a reduction of overshoot or undershoot can be achieved.
[0043] FIG. 4 shows the time profiles of the voltage U, of the conveyance speed v.sub.D and of the current I on the wire 4 according to a third embodiment of the invention, the conveyance speed v.sub.D being reduced in a plurality of stages until the short-circuiting can be terminated after the duration t.sub.KSA has elapsed. In contrast to the exemplary embodiment according to FIG. 3, this exemplary embodiment shows a multi-stage method for reducing the conveyance speed v.sub.D. The second short-circuiting shown is shorter, which is why here the boost speed v.sub.D,Boost is reduced only once by the predetermined conveyance speed amount v.sub.D1 before the short-circuiting after the duration t.sub.KSA is ended.
[0044] In FIG. 5, the time profiles of the voltage U, the conveyance speed v.sub.D and the current I on the wire 4 according to a fourth embodiment of the invention are represented. According to a variant, the conveyance speed v.sub.D is reduced here to a mean conveyance speed v.sub.D,M increased by a predetermined conveyance speed amount v.sub.D2 after the short-circuit has been restored after the duration t.sub.KSA has fallen below the voltage limit value U.sub.G. Through this up-regulation of the mean conveyance speed v.sub.D,M after the short-circuiting, an adaptation of the process can be achieved, as a result of which future short-circuiting can be better prevented.
[0045] In FIG. 6, the time profiles of the voltage U, the conveyance speed v.sub.D and the current I on the wire 4 according to a fifth embodiment of the invention with a preheating of the wire 4 are represented. Here, the current I is regulated or controlled by the wire 4 in such a way that the current I is reduced, for example, by a predetermined current amount I after the short-circuiting, that is to say after the increase of the conveyance speed v.sub.D to the boost speed v.sub.D,Boost. This measure, which can also be combined with the embodiment variant shown in FIG. 5, also achieves a corresponding adaptation of the process and prevents future short-circuiting.
[0046] FIG. 7 shows the time profiles of the z-position of the soldering or welding head in vertical direction with respect to the workpiece 5, the voltage U, the conveyance speed v.sub.D and the current I on the wire 4 according to a sixth embodiment of the invention. As can be seen from the course of the uppermost time diagram of the z-position, the position is changed by the height z and subsequently the z-position is reduced again. Upon detection of a short-circuiting, as already described with reference to the exemplary embodiment according to FIG. 5, after a restoration of the short-circuit after the duration t.sub.KSA, the conveyance speed v.sub.D is reduced to a mean conveyance speed v.sub.D,M increased by a predetermined conveyance speed amount v.sub.D2. In addition, after a defined period of time t.sub.2 has elapsed, the mean conveyance speed v.sub.D,M after the short-circuiting is reduced at least once by a predetermined conveyance speed amount v.sub.D3, until the mean conveyance speed v.sub.D,M is reached again. Due to the stepwise increase in the mean conveyance speed v.sub.D,M after each boost process, the probability of new short-circuiting can be reduced. After a certain period of time t.sub.2, the mean conveyance speed v.sub.D,M is again successively lowered to the originally set value. If the disturbance of the z-position is still present at the time of reaching the original mean conveyance speed v.sub.D,M, a short-circuiting occurs again with a boost process followed by a further increase in the mean conveyance speed v.sub.D,M.
[0047] FIG. 8 shows the time profiles of the voltage U, the conveyance speed v.sub.D, the resistance R and the current I on the wire 4 according to a further embodiment of the invention. In this case, in addition to the voltage U, the current I is also detected and the resistance R is calculated therefrom, and this is evaluated in real time. Since, before the actual short-circuiting, a firstly slow and then steeply rising resistance R occurs, this rise or else the rate of change of the resistance R can also be monitored. If the resistance R exceeds a predetermined resistance limit value R.sub.G, the boost process can likewise be triggered with the increased boost speed v.sub.D,Boost. The advantage of this regulation or control variant is that, in the ideal case, the short-circuiting can be completely prevented here. Thus, at no time does the melting bath bridge or the short circuit between the wire 4 and the workpiece 5 break open. The influence on the soldering process or welding process and on the finished soldering or welding seam is the lowest here. FIG. 9 shows the time profiles of the z-position of the soldering or welding head in vertical direction, the voltage U, the conveyance speed v.sub.D, the resistance R, and the current I on the wire 4 according to a further embodiment of the invention. At the beginning, the laser soldering or laser welding process proceeds in a stable manner and without disturbances with a defined conveyance speed v.sub.D and a defined current I for preheating the wire 4. The voltage U is approximately zero. If the z-position is increased by a change in the height z, short-circuiting would occur at a still constant conveyance speed v.sub.D. By measuring the voltage and the current I, calculating a resistance R and observing the exceeding of a resistance limit value R.sub.G, the short-circuiting can be effectively prevented according to the method described in FIG. 8. After the return of the laser or welding head to the original z-position, there are no increases in the voltage U or the resistance R and thus no boosting processes, and the laser soldering or laser welding process runs stably again.
[0048] Finally, FIG. 10 shows the time profiles of the z-position, of the voltage U, the conveyance speed v.sub.D, the resistance R, the current I on the wire 4, of a determined noise signal v.sub.D,noise and of a warning signal when a certain noise signal threshold v.sub.D,noise,S is exceeded, according to another embodiment of the invention. In this case, the current conveyance speed v.sub.D is additionally monitored for disturbances or signal noise. By means of a preferably highly dynamic conveyance device for the wire 4, which is preferably coupled directly to the wire 4 without a transmission, it becomes possible to detect even the slightest disturbances in the conveyance speed v.sub.D and then to evaluate them accordingly. On the one hand, monitoring such short interference peaks also makes sense in principle without the use of the short-circuit stabiliser according to the invention, since the noise signal v.sub.D,noise generated therefrom provides information about the general quality of the conveyance of the wire 4, and accordingly a warning signal W for a possible process stop can also be generated. On the other hand, for a stable function of the boost process in the variant with the evaluation of the resistance R, it is expedient or even necessary also to evaluate and take into account the noise signal v.sub.D,noise. Due to certain disturbances in the conveying path of the wire 4 or incorrect settings, similar courses of the voltage U or of the resistance R can occur as in the case of an imminent short-circuiting. This would falsely trigger a boost process. This can be prevented by an additional evaluation of the noise signal v.sub.D,noise, and only actual short-circuit occurrences are identified. If the noise signal v.sub.D,noise exceeds a noise signal threshold v.sub.D,noise,S, a warning signal W can be output. This error makes it possible to draw conclusions about the quality of the conveyance of the wire 4 and, if necessary, the process can also be stopped. A further function of this warning signal W would be the automatic switching of the triggering algorithm for the short-circuit stabiliser. If the warning signal W stands for FALSE at F, the faster and more effective algorithm can be used by evaluating the course of the resistance R. If the warning signal is set to T for TRUE, the evaluation of the course of the resistance R does not work or does not work optimally, and the triggering algorithm is used via the detection of the actual short-circuiting via the voltage U. By changing the z-position of the workpiece 5 or robot, the melting bath bridges between the wire 4 and the workpiece 5 or melting bath can be torn open. The warning signal W is set to T for TRUE, thus the boost process is triggered by the measurement of the voltage U. The generation of the noise signal v.sub.D,noise is preferably deactivated for the duration of the boost processes and restarted only after a certain waiting time t.sub.min has elapsed for settling of all signal progressions.
