Abstract
In a method for scanning the surface of metallic workpieces, during scanning, a welding torch with a consumable welding wire is moved over and towards the workpiece surface, until contact of the welding wire with the workpiece is detected, and the welding wire is subsequently moved away from the workpiece. Before scanning, slag-removal is carried out to remove slag at the welding wire end, wherein the welding current is lowered to a minimum, and the welding wire is moved cyclically with a rapid recurrent forward/backward movement over a specified path length toward the workpiece, and by a smaller distance away from the workpiece, until a short circuit between the welding wire and the workpiece is detected, whereupon slag-removal is ended, and upon the detection of no short circuit, slag-removal is repeated, and upon the detection of several short circuits one after the other, slag-removal is ended.
Claims
1-13. (canceled)
14. A method for scanning the surface (O) of metallic workpieces (W), wherein, during a scanning process (AP), a welding torch (1) with a consumable welding wire (2) is moved over the surface (O) of the workpiece (W), and the welding wire (2) is moved towards the surface (O) of the workpiece (W) at specified points in time (t.sub.i) at a forward speed (v.sub.SV), until contact of the welding wire (2) with the workpiece (W) is detected by a welding current source (4), and the welding wire (2) is subsequently moved away from the workpiece (W) again at a backward speed (v.sub.SR), wherein before the scanning process (AP), a slag-removal process (SE) is carried out to remove slag at the end of the welding wire (2), wherein at the start of the slag-removal process (SE), the welding current (I) is lowered to a minimum, and the welding wire (2) is moved cyclically with a rapid recurrent forward/backward movement over a specified path length in the direction of the workpiece (W), and by a smaller distance away from the workpiece (W) again, so that the conveyance of the welding wire (2) to the workpiece (W) prevails, and upon the detection of no short circuit (KS) between the welding wire (2) and the workpiece (W), the slag-removal process (SE) is repeated, and upon the detection of several short circuits (KS) between the welding wire (2) and the workpiece (W) one after the other, the slag-removal process (SE) is ended, wherein the slag-removal process (SE) is started when the wire feed speed (v.sub.d) sinks below a specified threshold value (v.sub.ds) when moving the welding wire (2) at a specified wire feed speed (v.sub.dc) in the direction of the workpiece (W) before the scanning process (AP).
15. The method according to claim 14, wherein the slag-removal process (SE) is ended when detecting five short circuits (KS) between the welding wire (2) and the workpiece (W) one after the other.
16. The method according to claim 14, wherein the slag-removal process (SE) is started when detecting no short circuit (KS) between the welding wire (2) and the workpiece (W) during a defined time span (Δt.sub.KS) before the scanning process (AP).
17. The method according to claim 14, wherein before measuring whether the wire feed speed (v.sub.d) falls below the specified threshold value (v.sub.ds), a specified time period (αt.sub.T) is awaited.
18. The method according to claim 14, wherein the slag-removal process (SE) is started when exceeding a specified maximum value (F.sub.max) of the force (F) on the welding wire (2).
19. The method according to claim 14, wherein the slag-removal process (SE) is started when exceeding a specified threshold value ((dF/dt).sub.max) of the change of the force (dF/dt) over time on the welding wire (2).
20. The method according to claim 14, wherein the slag-removal process (SE) is started when the wire feed speed (v.sub.d) sinks below a specified threshold value during the scanning process (AP).
21. The method according to claim 14, wherein the slag-removal process (SE) is started when exceeding a specified maximum value (F.sub.max) of the force (F) on the welding wire (2) during the scanning process (AP).
22. The method according to claim 14, wherein the slag-removal process (SE) is started when exceeding a specified threshold value ((dF/dt).sub.max) of the change of the force (dF/dt) on the welding wire (2) during the scanning process (AP).
23. The method according to claim 14, wherein the angle of attack (β) of the welding torch (1) to the surface (O) of the workpiece (W) is determined, and the slag-removal process (SE) is deactivated when falling below a specified threshold value of the angle of attack (β.sub.G).
24. The method according to claim 14, wherein an error message is output when detecting no stable short circuit (KS) between welding wire (2) and workpiece (W) after several repetitions of the slag-removal process (SE), in particular after 15 repetitions.
25. The method according to claim 24, wherein the end of the welding wire (2) is cut off in a cutting device (7) after outputting the error message.
Description
[0019] The present invention will be described in more detail on the basis of the enclosed drawings. Shown are:
[0020] FIG. 1 a schematic diagram of a welding device for carrying out a welding process and scanning process;
[0021] FIG. 2 the time courses of the welding voltage, of the welding current, and of the feed speed of the welding wire and of a movement diagram of the welding wire during a slag-removal process in a schematic manner;
[0022] FIG. 3 the time courses of the wire feed speed and of the voltage in a schematic manner in the case of an exemplary embodiment of the slag-removal process;
[0023] FIG. 4 the time courses of the wire feed speed and of the voltage in the case of an alternative triggering condition for the slag-removal process in a schematic manner;
[0024] FIG. 5 the time courses of the wire feed speed, of the force on the welding wire, as well as of the change of the force over time on the welding wire in the case of a further triggering condition for the slag-removal process in a schematic manner;
[0025] FIG. 6 a welding torch in an angular position to the workpiece, which is desired for a slag-removal process; and
[0026] FIG. 7 a welding torch in an angular position to the workpiece, which is unsuitable for the slag-removal process.
[0027] FIG. 1 shows a schematic diagram of a welding device for carrying out a welding process and scanning process AP. A welding torch 1 with a welding wire 2 is connected to a corresponding manipulator 3, for example a welding robot. A welding current source 4 supplies the welding torch 1 or the welding wire 2, respectively, with the welding current I and the welding voltage U. The welding wire 2 is conveyed at a feed speed v.sub.d from a wire roll 6 to the welding torch 1 via a feed device 5. During the scanning process AP, the welding torch 1 with the welding wire 2 is moved along a specified path and at a specified speed over the surface O of the workpiece W with the help of the manipulator 3. At specified points in time, the welding wire 2 is moved at a forward speed v.sub.SV to the surface O of the workpieces W, until the welding current source 4 detects contact of the welding wire 2 with one of the workpieces W. The welding wire 2 is subsequently moved away from the workpieces W again at a backward speed v.sub.SR. The position of the surface O of the workpieces W is determined and stored at each of the points in time in the welding current source 4. To remove possible slag from the free end of the welding wire 2, a slag-removal process SE can be carried out, wherein the welding current I is lowered to a minimum, and the welding wire 2 is moved cyclically with a rapid recurrent forward/backward movement over a specified path length in the direction of the workpiece W, and by a smaller distance away from the workpiece W again, so that the conveyance of the welding wire 2 to the workpiece W prevails, until a short circuit between the welding wire 2 and the workpiece W is detected. If the slag cannot be removed from the welding wire 2 during the slag-removal process SE even after several repetitions, it may be necessary to cut off the end of the welding wire 2 manually or in a cutting device 7, and to thus free it from the slag. The manipulation of the welding torch 1 to the cutting device 7 can also be carried out fully automatically by means of the manipulator 3, in particular welding robot.
[0028] FIG. 2 shows the courses of the welding voltage U, of the welding current I, of the feed speed v.sub.d of the welding wire 2, and of a movement diagram of the welding wire 2 relative to the workpiece W during a slag-removal process SE in a schematic manner. To prevent that a scanning process AP cannot be carried out or cannot be carried out correctly due to a slag adhering to the welding wire 2, a slag-removal process SE takes place beforehand, if necessary. The welding wire 2 is thereby not continuously conveyed to the workpiece W by means of the slag-removal process SE, but is moved forward, thus to the workpiece W, and back again, thus removed from the workpiece W, at a certain frequency. The welding wire 2 is thereby moved forward over a certain distance at a relatively high speed v.sub.d, and is conveyed back again by a distance smaller than forward, so that the conveyance of the welding wire 2 to the workpiece W prevails. The frequency, at which the forward/backward movement of the welding wire 2 is carried out, is thereby preferably between 50 Hz and 150 Hz. It goes without saying that it is also possible to use lower or higher frequencies for the slag-removal process SE. It should thereby generally be ensured that the frequency also defines the duration for the slag-removal process SE. This is why in particular higher frequencies are significant because the duration is thus shortened. The welding wire 2 is conveyed with a rapid recurrent forward/backward movement, for example at a set frequency of 75 Hz, until contact with the workpiece W. If slag is present on the welding wire 2, no short circuit KS between welding wire 2 and workpiece W can be detected or can be detected by a control device of the current source 4 or of a short circuit monitoring, respectively. The welding wire 2 is further moved backward and forward again recurrently according to the set frequency. Finally, the slag is released from the end of the welding wire 2, and the current source 4 can detect a short circuit KS due to an increase of the current I or drop in voltage U, respectively. The slag-removal process SE can subsequently be ended. The current I during the slag-removal process SE is usually limited, for example to maximally 3 A, so that a burning off of the welding wire 2 can be prevented.
[0029] FIG. 3 shows the time courses of the wire feed speed v.sub.d and of the voltage U in a schematic manner in the case of an exemplary embodiment of the slag-removal process SE. Before carrying out a scanning process AP, the welding torch 1 stands in a start position above the workpiece W. The welding wire 2 also stands several mm above the surface O of the workpiece W. Before the scanning process AP is now initiated, the welding wire 2 begins to move in the direction of the workpiece W at a specified feed speed v.sub.dc. Until reaching the specified value of the feed speed v.sub.dc, a transient response of the actual value of the wire feed speed occurs, which is why a certain specified time Δt.sub.T is preferably awaited, before the latest wire feed speed v.sub.d is measured. An unintentional triggering of the slag-removal process SE during these setting processes can thus be prevented. The slag-removal process SE is triggered when the latest wire feed speed v.sub.d has dropped below a specified threshold vas after the time Δt.sub.T has lapsed. This threshold value vas is only valid in the start phase. After activation of the slag-removal process SE, the welding wire 2 is moved with high acceleration and force F to the workpiece W and away from it. The welding wire 2 is initially still in the air, but approaches the surface O of the workpiece W more and more. The welding wire 2 subsequently “hammers” on the surface O of the workpiece W, and the slag adhering to the end of the welding wire 2 is thereby removed or this is at least attempted. To detect as reliably as possible in this way whether the slag was removed from the welding wire 2, the slag-removal process SE is stopped only when a defined number n, for example 5, of cyclical short circuits KS is detected. After this first phase of a slag-removal process SE, a switchover into the scanning phase AP takes place. If no short circuits at all should occur (because the welding wire 2 does in fact insulate), the slag-removal process SE continues to work until a termination is made by the operator or the robot control. However, a time restriction would also be conceivable here.
[0030] If a drop in the wire feed speed v.sub.d below a certain specified threshold occurs again after the slag-removal process SE ended, the slag-removal process SE can be triggered again (not illustrated).
[0031] FIG. 4 shows the time courses of the wire feed speed v.sub.d and of the voltage U in the case of an alternative triggering condition for the slag-removal process SE in a schematic manner. Before the use of a scanning process AP, the welding wire 2 is thereby moved to the workpiece W and away from the workpiece W again, and a slag-removal process SE is then started, when no short circuit KS between the welding wire 2 and the workpiece W is detected during a specified time span Δt.sub.KS. In the illustrated example, no short circuit KS (drop in voltage) is detected during this specified time span Δt.sub.KS, and the slag-removal process SE is thus started.
[0032] FIG. 5 shows the time courses of the wire feed speed v.sub.d, of the force F on the welding wire 2, as well as of the change of the force dF/dt over time on the welding wire 2 in the case of a further triggering condition for the slag-removal process SE in a schematic manner. It is pointed out that the course of the time derivation of the force in the lowermost diagram is illustrated in a highly simplified manner. The slag-removal process SE can then be triggered when the force F on the welding wire 2 increases above a specified maximum value F.sub.max. In the alternative or in addition, the slag-removal process SE can also be started when a certain increase in force dF/dt exceeds a specified threshold (dF/dt).sub.max. These conditions of exceeding a maximum force F.sub.max on the welding wire 2 or of a maximum change in force (dF/dt).sub.max over time on the welding wire can also be determined during the scanning process AP and not before the scanning process AP. The respective threshold values for the maximum force F.sub.max and the maximum force change (dF/dt).sub.max over time are set according to experience, and it goes without saying that they can differ for the condition before the scanning process AP and during the scanning process.
[0033] FIG. 6 shows a welding torch 1 in an angle β of approximately 90° to the surface O of the workpiece W, which is desired for a slag-removal process SE. This is a suitable angle β for the slag-removal process SE, because the welding wire 2 essentially impacts frontally on the surface O of the workpiece W here, and the likelihood of the removal of the slag from the end of the welding wire 2 is thus very high.
[0034] A welding torch 1 in an angular position to the workpiece W, which is unsuitable for the slag-removal process SE, is outlined in FIG. 7. Here, the angle β of the welding torch 1 to the surface O of the workpiece W falls below a specified threshold value β.sub.G of, for example, 45°. In this case, the welding wire 2 or the end thereof, respectively, is bent or deflected, respectively, during the slag-removal process SE, and the removal of the slag cannot be ensured. When falling below the critical angle β.sub.G between welding torch 1 and welding wire 2, the slag-removal process SE can thus also be deactivated automatically because a slag removal cannot be ensured.
[0035] The position of the welding torch 1 could also be detected automatically by means of corresponding sensors, for example gyro sensors and, if need be, by means of a detection of a torch identification BID located in the welding torch 1 for the consideration of the torch geometry, and the angle β of the welding torch 1 or of the welding wire 2, respectively, to the surface O of the workpiece W could be calculated therefrom. The slag-removal process SE can then be detected automatically in the case of very flat attack angles of the welding torch 1, in order to rule out malfunctions and deformations of the welding wire 2. It goes without saying that an error message can thereby be output to the user or welder, respectively.
[0036] In the case of certain geometries of welding torches 1 or specific geometries with high friction, it would frequently be necessary to specifically adapt a plurality of the control parameters for the reliable triggering and functioning of the slag-removal process SE. This could also be carried out automatically by means of a torch identification BID located in the welding torch 1. The optimal control parameters of the slag-removal process SE would thus be available automatically for every type of the welding torch 1.
