METHOD FOR DEFINING WELDING PARAMETERS FOR A WELDING PROCESS ON A WORKPIECE AND WELDING DEVICE FOR CARRYING OUT A WELDING PROCESS ON A WORKPIECE WITH DEFINED WELDING PARAMETERS

Abstract

In a method for defining welding parameters for a welding process on a workpiece, a welding torch fastened to a robot is guided over the workpiece along a predetermined welding path and predetermined welding parameters for processing the workpiece are set as a function of the position along the welding path. A welding device carries out a welding process. For the more exact definition of the welding parameters, before the welding process is carried out, at least one parameter representing the cooling is recorded as a function of the position along the welding path, and the at least one parameter representing the cooling along the welding path is considered for the welding process when defining optimized welding parameters as a function of the position along the welding path.

Claims

1. A method for defining welding parameters (P.sub.i(x)) for a welding process on a workpiece (4), in which a welding torch (2) fastened to a robot (11) is guided over the workpiece (4) along a predetermined welding path (3) and predetermined welding parameters (P.sub.i(x)) for processing the workpiece (4) are set as a function of the position (x) along the welding path (3), wherein, before the welding process is carried out, at least one parameter (P.sub.K(x)) representing the cooling is recorded as a function of the position (x) along the welding path (3), and the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3) is considered for the welding process when defining optimized welding parameters (P.sub.i,opt(x)) as a function of the position (x) along the welding path (3).

2. The method according to claim 1, wherein, before the welding process is carried out, the workpiece (4) is heated along the welding path (3) with a heat source (5), and the at least one parameter (P.sub.K(x)) representing the cooling is recorded along the welding path (3) with the aid of at least one detection device (6).

3. The method according to claim 2, wherein the workpiece (4) is heated in a pulsed manner along the welding path (3), preferably to a temperature below the melting temperature (T.sub.s) of the workpiece (4).

4. The method according to claim 2, wherein, in addition to, in particular during, the recording of the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3), the workpiece base temperature (T.sub.u) is recorded.

5. The method according to claim 2, wherein the at least one parameter (P.sub.K(x)) representing the cooling is recorded along the welding path (3) during a cleaning process carried out before the welding process, in particular a surface plasma processing operation.

6. The method according to claim 1, wherein, prior to carrying out the welding process, a virtual replication (4′) of the workpiece (4) is heated along a virtual welding path (3′) corresponding to the welding path (3) with a virtual heat source (5′), and the at least one parameter (P.sub.K(x′)) representing the cooling is recorded along the virtual welding path (3′) with the aid of at least one virtual detection device (6′).

7. The method according to claim 1, wherein, before the welding process is carried out, the at least one parameter (P.sub.K(x′)) representing the cooling along a virtual welding path (3′) corresponding to the welding path (3) is determined from stored properties of the virtual replication (4′) of the workpiece (4) in dependence on the material and the geometric conditions from a virtual replication (4′) of the workpiece (4) with predetermined environmental situations, for example clamping devices (17).

8. The method according to claim 1, wherein the process of recording the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3) is carried out at a speed (v.sub.A) which is higher than or equal to the welding speed (v.sub.s) during the welding process.

9. The method according to claim 1, wherein the average cooling rate (ΔT/Δt) is recorded as a parameter (P.sub.K(x)) representing the cooling.

10. The method according to claim 1, wherein, when exceeding and/or falling below predetermined threshold values (P.sub.KG(x)) for the parameter (P.sub.K(x)) representing the cooling along the welding path (3), a warning is issued and/or a message is stored.

11. A welding device (1) for carrying out a welding process on a workpiece (4) with fixed welding parameters (P.sub.i(x)), having a welding torch (2) which is fastened to a robot (11) and is guidable over the workpiece (4) along a predetermined welding path (3) during the welding process, wherein the welding torch (2) is connected to a welding current source (12), which welding current source (12) has a control device (13) for controlling the welding process with predetermined welding parameters (P.sub.i(x)) as a function of the position (x) along the welding path (3), wherein a recording device (15) is provided for recording at least one parameter (P.sub.K(x)) representing the cooling as a function of the position (x) along the welding path (3) before carrying out the welding process, and wherein the control device (13) is connected to the recording device (15) and configured for controlling the welding process with optimized welding parameters (P.sub.i,opt(x)) as a function of the position (x) along the welding path (3), taking into account the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3).

12. The welding device (1) according to claim 11, wherein the recording device (15) for recording the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3) contains a heat source (5) for heating the workpiece (4) along the welding path (3) and at least one detection device (6) for recording the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3).

13. The welding device (1) according to claim 12, wherein the heat source (5) for heating the workpiece (4) along the welding path (3) is generated by a light source (7), in particular a laser beam source (8).

14. The welding device (1) according to claim 12, wherein at least one detection device (6) is formed by a thermal imaging camera (9), in particular an infrared camera, and/or by at least one temperature sensor (10) for measuring the temperature of the surface of the workpiece (4) along the welding track (3).

15. The welding device (1) according to claim 11, wherein the recording device (15) for recording the at least one parameter (P.sub.K(x)) representing the cooling along the welding path (3) contains a virtual heat source (5′) for heating a replication (4′) of the workpiece (4) along a corresponding virtual welding path (3′) of the welding path (3) and at least one virtual detection device (6′) for recording the at least one parameter (P.sub.K(x′)) representing the cooling along the virtual welding path (3′).

Description

[0033] The present invention is further explained with reference to the appended drawings. In the drawings:

[0034] FIG. 1 is a schematic representation of a welding device configured to receive a parameter representing the cooling along the welding path of a workpiece prior to performing the welding process;

[0035] FIG. 2 is a block diagram of an embodiment of a recording device for recording a parameter representing the cooling along the welding path;

[0036] FIG. 3 is a schematic block diagram of a virtual recording device for recording at least one parameter representing the cooling along the virtual welding path of a virtual workpiece;

[0037] FIG. 4 is a schematic representation of a welding device during the execution of a welding process, taking into account at least one parameter representing the cooling recorded before the welding process in the determination of the welding parameters;

[0038] FIGS. 5A to 5C show various clamping situations of a workpiece to illustrate the resulting different cooling behaviour along the weld path;

[0039] FIGS. 6A and 6B show two temporal cooling curves with different cooling behaviour and different temperature of the workpiece; and

[0040] FIG. 7 shows the course over time of a method carried out before the welding process for recording at least one parameter representing the cooling along the welding path of a workpiece and the subsequent welding process, considering the at least one parameter representing the cooling in the determination of the welding parameters.

[0041] FIG. 1 shows a schematic representation of a welding device 1 configured to record a parameter P.sub.K(x) representing the cooling along the welding path 3 of a workpiece 4 before performing a welding process. The welding device 1 is used to carry out a welding process on a workpiece 4 with fixed welding parameters P.sub.i(x) as a function of the position x along the welding path 3. To that end, a welding torch 2 is fastened to a robot 11 which guides the welding torch 2 over the workpiece 4 along a predetermined welding path 3 during the welding process and produces a welded joint between two or more workpieces 4 or a coating of a workpiece 4. The welding torch 2 is connected to the welding power source 12 whose control device 13 controls or regulates the welding process and the corresponding fixed welding parameters P.sub.i(x). During the processing, the workpiece 4 is held in the desired position by means of clamping devices 17. The arrangement and geometry of the clamping devices 17, the geometry of the workpiece 4 and a number of other factors, such as, for example, the temperature of the workpiece 4, influence the cooling behaviour of the weld seam and thus the quality of the welded joint. Usually, certain welding parameters P.sub.i(x) for the welding process are determined on the basis of experience or previous test welds on test workpieces and the welding process is carried out independently of the respective cooling situation.

[0042] According to the invention, it is now provided that before the welding process is carried out, at least one parameter P.sub.K(x) representing the cooling is recorded depending on the position (x) along the welding path 3, and the at least one parameter P.sub.K(x) representing the cooling along the welding path 3 is considered for the welding process during the definition of optimised welding parameters P.sub.i,opt(x) depending on the position x along the welding path (3). For this purpose, a recording device 15 is located on the robot 11, which heats the workpiece 4 before the welding process and detects the cooling behaviour and derives or calculates therefrom at least one parameter P.sub.K(x) representing the cooling. The cooling behaviour of the workpiece 4 is thus analysed under the real conditions, considering the geometry and arrangements of the clamping devices 17 and taking into consideration the geometry of the workpiece 4 and considering the environmental conditions, in order to be able to incorporate the respective cooling behaviour into the definition of the optimised welding parameters P.sub.i,opt(x). The parameters P.sub.K(x), which are representative of the cooling, can be considered in the definition of the optimised welding parameters P.sub.i,opt(x) for an optimum welding result and maximum welding quality. For example, it is possible to proceed at locations along the welding path 3 of the workpiece 4 with good or rapid cooling behaviour with a lower welding speed or higher welding power than at locations with slower cooling behaviour. The welding quality can also be improved by preheating the workpiece 4 at certain points, taking into account the cooling behaviour of the workpiece 4 at these points.

[0043] During the recording of the parameters P.sub.K(x) representing the cooling, the robot 11 travels with the recording device 15 along the desired welding path 3 and heats the workpiece 4 to a temperature which is preferably below the melting temperature of the material of the workpiece 4 and also below that temperature which could lead to a structural change in the material of the workpiece 4. Following the heating, the surface temperature of the workpiece 4 is detected and evaluated and at least one parameter P.sub.K(x) representing the cooling, for example the cooling rate ΔT/Δt, is calculated therefrom. The parameters P.sub.K(x) representing the cooling are stored in a database 18 or a memory. Thus, in the subsequent welding process, a correction can be made by means of the optimised welding parameters P.sub.i,opt(x), considering the cooling behaviour of the real workpiece 4. The memory 18 can be located at different points of the welding system and can, for example, also be integrated into the welding current source 12.

[0044] The process of recording the at least one parameter P.sub.K(x) representing the cooling along the welding path 3 can be carried out at a speed v.sub.A which is higher than or equal to the welding speed v.sub.s during the welding process. In order to save time, the at least one parameter P.sub.K(x) representing the cooling along the welding path 3 can also be recorded directly preceding the welding process or during a cleaning process to be carried out before the welding process.

[0045] FIG. 2 shows a block diagram of an embodiment of a recording device 15 for recording a parameter P.sub.K(x) representing the cooling along the welding path 3 of a workpiece 4. The recording device 15 contains a heat source 5 with which the workpiece 4 is heated to a temperature which is below the melting temperature of the material of the workpiece 4 and below the temperature at which the structure of the workpiece 4 is changed. The heating of the workpiece 4 along the welding path 3 can take place, for example, in the form of pulses. The heat source 5 may be generated by a light source 7, in particular a laser beam source 8. The at least one parameter P.sub.K(x) representing the cooling along the welding path 3 is recorded in a contactless manner with the aid of at least one detection device 6, which can be formed by a thermal imaging camera 9, in particular an infrared camera. Instead of or in addition to a thermal imaging camera 9, at least one temperature sensor 10 or an array of a plurality of temperature sensors 10 can also be used for detecting the temperature on the surface of the workpiece 4. In addition to recording the at least one parameter P.sub.K(x) representing the cooling along the welding path 3, and in particular during this recording, the basic workpiece temperature Tu can also be recorded with the aid of at least one temperature sensor 14.

[0046] If a parameter P.sub.K(x) representing the cooling exceeds certain threshold values P.sub.KG(x), a warning (for example in acoustic or visual form) could be issued to alert the user to an impermissible or critical cooling situation. The user can then carry out appropriate countermeasures, such as, for example, a displacement of clamping devices or a preheating or cooling of the workpiece 4, in order to again observe the threshold values P.sub.KG(x). In addition to the warning or as an alternative thereto, a corresponding message can also be stored for documentation purposes.

[0047] In FIG. 3, a schematic block diagram of a virtual recording device 15′ for recording at least one parameter P.sub.K(x) representing the cooling along the virtual welding path 3′ of a virtual workpiece 4′ is represented. In this case, the virtual workpiece 4′, together with the virtual clamping devices 17′, is simulated on a computer 16 or a mobile terminal, such as, for example, a smartphone, and, before the welding process is carried out, the virtual replication 4′ of the workpiece 4 is heated along a virtual welding path 3′, corresponding to the welding path 3, with a virtual heat source 5′ or the virtual welding process itself, and the at least one parameter P.sub.K(x) representing the cooling is recorded or calculated or simulated along the virtual welding path 3′ with the aid of at least one virtual detection device 6′. The parameters P.sub.K(x) representing the cooling are stored in a database 18 or a memory. The software required for this purpose makes use of stored information on the heat-conducting properties of various materials for the workpieces 4 and clamping devices 17, which have been determined beforehand. By means of such a simulation, various situations can be tried out before the welding process is carried out without needing to use a real workpiece 4. In this way, welding parameters P.sub.i,opt(x) optimised in a simple and rapid manner can be adapted as a function of the respective prevailing cooling situation of the workpiece 4 in order to achieve the best welding qualities in each case.

[0048] In FIG. 4 a schematic representation of a welding device 1 during the execution of a welding process, considering at least one parameter P.sub.K(x) recorded before the welding process and representing the cooling in the determination of optimised welding parameters P.sub.i,opt(x) is represented. In this case, the parameters P.sub.K(x) determined before the welding process is carried out and stored in a database 18 or the like are taken into account as a function of the point along the welding path 3 for correcting or changing the fixed welding parameters P.sub.i(x), and optimised welding parameters P.sub.i,opt(x) are thus determined with which the welding process is carried out. As a result, an optimum quality of the weld seam along the welding path 3 of the workpiece 4 is achieved, taking into account the cooling behaviour of the workpiece. In addition, external measures, such as, for example, the preheating of the workpiece, can influence the cooling behaviour of the workpiece 4 and a higher welding quality can be achieved.

[0049] FIGS. 5A to 5C represent various clamping situations of a workpiece 4 for illustrating the resulting different cooling behaviour along the welding path 3. In the side view of a workpiece 4 according to FIG. 5A, the clamping devices are arranged very close to the welding path 3. This results in maximum cooling. In the variant according to FIG. 5B, the clamping devices are arranged at a greater distance from the welding path, as a result of which normal cooling of the weld seam results. In the variant according to FIG. 5C, the clamping devices 17 are arranged very far away from the welding path 3 and cover only a very short region of the workpiece 4. In this variant, a minimal cooling effect results due to the clamping devices. These illustrations illustrate the influence of the geometry and arrangement of the clamping devices 17 on the cooling behaviour of the workpiece 4 after a welding process. The cooling situation of a workpiece can thus also be influenced by a corresponding arrangement of the clamping devices 17. In addition to the arrangement of the clamping devices 17, the cooling effect is also dependent on the material of the clamping devices 17 and their thermal conductivity, as well as on the contact surface between the workpiece 4 and the clamping device 17.

[0050] FIGS. 6A and 6B show time cooling curves with different cooling behaviours and different temperatures T of the workpiece 4. FIG. 6A shows the time cooling curve of a workpiece 4 without prior heating (Curve A) and with prior heating (Curve B). FIG. 6B shows the time cooling of a workpiece 4 with normal cooling (Curve A) and strong cooling (Curve B).

[0051] In FIG. 7, the course over time of a method carried out before the welding process for registering at least one parameter P.sub.K(x) representing the cooling along the welding path 3 of a workpiece 4 and the subsequent welding process, considering the at least one parameter P.sub.K(x) representing the cooling, is shown in the definition of the optimised welding parameters P.sub.i,opt(x). As already mentioned above, the Phase I of the recording of the parameters P.sub.K(x) representing the cooling of the workpiece 4 can also take place at a higher speed v.sub.A than the subsequent welding process (Phase II), which takes place at a lower speed v.sub.s.