Method and apparatus for carrying out an arc welding process

Abstract

Method for carrying out an arc welding process in which a welding wire (15) is guided through a contact tube (23), wherein a welding current is transferred to the welding wire (15) through the contact tube (23) to generate the arc (25), wherein the welding current is measured during the arc welding process and the measured current signal (I) is monitored, wherein temporal changes in the measured current signal (I) that exceed at least a limit value in magnitude are detected as an indicator (A) for wear of the contact tube (23), characterized in that the measured current signal (I) is filtered by means of a high-pass filter (40) and the indicator (A) for wear of the contact tube (23) is determined on the basis of the filtered signal.

Description

[0001] The invention relates to a method for carrying out an arc welding process in which a welding wire is guided through a contact tube, wherein a welding current is transferred to the welding wire through the contact tube to generate the arc, wherein the welding current is measured during the arc welding process and the measured current signal is monitored, according to claim 1.

[0002] The invention further relates to an arc welding system for carrying out an arc welding process according to claim 7, comprising: a) a contact tube through which a welding wire is passed, wherein a welding current can be transferred to the welding wire through the contact tube to generate the arc, b) a current measuring device for measuring the welding current during the arc welding process, c) a monitoring device for monitoring the current signal measured by means of the current measuring device.

[0003] Arc welding processes are widely used in practice, for example in conjunction with a shielding gas as metal inert gas welding, such as MIG welding or MAG welding. Arc welding processes can be automated, e.g., using a welding robot. However, arc welding processes can also be carried out manually, i.e., by hand welding.

[0004] The fundamental problem with such welding processes is the wear of the contact tip, which expands during the welding process, negatively impacting the reproducibility of the weld result. A worn contact tip has a particularly negative effect on spatter formation during the welding process. Especially in pressure vessels, weld spatter can reduce fatigue strength and thus lead to premature failure.

[0005] EP 2 199 005 B1 discloses a proposal for the automatic determination of the wear of a power supply section of a contact tip in an arc welding torch. DE 602 03 970 T2 discloses a device and a method for evaluating the degree of wear of an electrode nozzle in gas metal arc welding with a consumable electrode. JP 2000-24779 A discloses a method and a device for determining the service life of a welding tip.

[0006] The invention is based on the objective of providing an improved method and an improved device for carrying out an arc welding process.

[0007] This problem is solved by a method according to claim 1. This involves detecting temporal changes in the measured current signal that exceed at least a certain limit value as an indicator of wear of the contact tube. In this way, the rate of change of the welding current can be used as a reliable indicator of the wear of the contact tube. This enables true in-situ quality control and, if necessary, the correction of a defective welding process.

[0008] Compared to the wear detection described in the prior art, the detection of wear on the contact tube can be carried out significantly faster; that is, the indicator can be determined virtually in real time during the welding process. Consequently, the method according to the invention makes it possible to carry out the welding process with higher quality and, in particular, with a lower frequency of unwanted weld spatter generation.

[0009] The welding current is the quantity that triggers the welding process via an electric arc.

[0010] The indicator can be a binary value that simply indicates the states "not worn" and "worn" with respect to the contact tube. For example, the indicator can be defined as changing from "not worn" to "worn" after a predetermined number of events in which the magnitude of the change over time in the measured current signal exceeds at least a certain threshold.

[0011] The indicator can also include a numerical indication of the contact tube's wear, for example, by acting as a counter for events where the change in the measured current signal over time exceeds a certain threshold. This allows the degree of contact tube wear to be quantitatively recorded and displayed, for example, on a display device.

[0012] Advantageously, the current measuring device for measuring the welding current can be designed such that the welding current can be detected at a high sampling rate, making it possible, for example, to detect a welding current change rate of at least 200 A / ms. For example, the measuring frequency of the current measuring device, i.e., the sampling rate, can be greater than 1 kHz or greater than 5 kHz. A measuring frequency in the range of 10 kHz is advantageous, for example.

[0013] According to an advantageous embodiment of the invention, it is provided that, depending on the indicator, at least one of the following steps is carried out: a) automatic output of a wear warning signal, b) automatic adjustment of at least one parameter of the arc welding process, c) automatic termination of the arc welding process.

[0014] This has the advantage that, depending on how the indicator is used, the user can be warned early of increased wear on the contact tube. Such a signal can, of course, also automatically influence the further course of the arc welding process.

[0015] The wear warning signal can be output as a visual, audible, and / or haptic signal. Adjusting at least one parameter of the arc welding process can, for example, involve regulating the welding current and / or voltage to keep the transferred electrical power or energy constant.

[0016] In the case of feature b), for example, the welding current, welding voltage, and / or the distance between the contact tip and the metal part to be welded can be automatically adjusted as parameters of the arc welding process. For example, as the contact tip wears down, the distance can be reduced, i.e., the contact tip is automatically moved closer to the metal part to be welded or to the weld seam.

[0017] According to an advantageous embodiment of the invention, the temporal changes of the measured current signal, which exceed at least a certain limit value in magnitude, are monitored with respect to their frequency per unit of time, whereby exceeding a certain frequency per unit of time can be detected as an indicator of wear of the contact tube. This allows for a particularly reliable yet very fast detection of wear of the contact tube.

[0018] The temporal change of the measured current signal can be captured, for example, by differentiating the current signal with respect to time. This differentiated current signal can then be categorized into classes based on its magnitude. The values ​​of the differentiated current signal falling into these classes can be processed, for example, by a neural network. An output neuron can then represent an indicator of contact tube wear, for example, by predicting the contact tube diameter beyond which the wear becomes too high for the arc welding process to function effectively. This allows, in particular, real-time control or other manipulation of the welding process. Neural networks are well-suited for controlling industrial processes because they can react quickly to changing input variables.

[0019] According to the invention, the measured current signal is filtered using a high-pass filter, and the indicator for contact tube wear is determined based on the filtered signal. The output signal of the high-pass filter can be integrated, for example, using an integrator. The integrated signal can be monitored for exceeding a threshold value, for example, using a comparator. If the threshold value is exceeded, this is detected as an indicator of contact tube wear. Due to its high stability, the output signal of the high-pass filter or the output signal of the comparator is particularly well-suited for controlling industrial processes, especially welding processes. The output signal of the high-pass filter can be amplified by a signal amplifier before being fed to the integrator.The output signal of the integrator is in an exponential relationship with the contact tube diameter.

[0020] The invention is suitable for all the aforementioned types of arc welding. It is well-suited for integration into a welding power source, as current sensors are often already present in these sources. For example, the invention can be integrated into the welding power source in the form of an additional monitoring module. In the case of a welding power source controlled by a computer program, it is sometimes possible to integrate the invention by extending the computer program. In particular, it is possible to retrofit existing welding power sources with the functionality of the invention at a comparatively low cost. This also applies especially to mobile handheld welding systems, enabling such systems to be used in an improved manner for welding work in offshore environments.

[0021] According to an advantageous embodiment of the invention, the method is designed to carry out a short-arc welding process. Short-arc welding primarily uses wires with a diameter between 0.8 and 1.2 mm, and less frequently wires with a diameter of 1.6 mm. Depending on the wire diameter, the arc voltage ranges, for example, between 14 and 22 volts at a current between, for example, 60 and 200 amperes. Heat input is low during short-arc welding, and the deposition rate is also limited. For this reason, the method is frequently used when welding thin sheets with a thickness of 0.8 mm or more. Short-arc welding is also often employed when working in constrained positions or when performing root welds on thicker surfaces.The main reasons for this are the excellent bridging ability of gaps and the smooth, flat formation of the root back surface. However, this is offset by the high tendency to spatter formation. Advantageously, the inventive method can counteract this spatter formation, so that good quality results can also be achieved in short-arc welding.

[0022] According to an advantageous embodiment of the invention, the process is carried out using an arc welding system which maintains a constant welding voltage by means of a control device or its internal structure. The process according to the invention thus additionally incorporates the control and / or maintenance of a constant welding voltage.

[0023] According to an advantageous embodiment of the invention, the process is carried out without system-specific and / or material-specific reference data. Thus, no reference data for the arc welding system is required, and / or no reference data for the welding wire used or the metal part to be welded. In this way, the process according to the invention can be used directly without prior training processes. Furthermore, no effort is required for storing reference data.

[0024] The aforementioned task is also solved by an arc welding system for carrying out an arc welding process, comprising: a) a contact tube through which a welding wire is passed, wherein a welding current can be transferred to the welding wire through the contact tube to generate the arc, b) a current measuring device for measuring the welding current during the arc welding process, c) a monitoring device for monitoring the measured current signal, wherein d) the monitoring device or an additional detection device is configured to detect temporal changes in the measured current signal which exceed at least a limit value in magnitude as an indicator of wear of the contact tube, characterized in that the arc welding system is configured to carry out a method according to one of claims 1 to 6.

[0025] Here too, the temporal changes of the measured current signal, which exceed at least a limit value in magnitude, can be monitored with regard to their frequency per unit of time, whereby an exceedance of a certain frequency per unit of time is detected as an indicator of wear of the contact tube.

[0026] This also allows the previously explained advantages to be realized. For example, the monitoring device can have a time differentiation device to determine a time-differentiated signal from the measured current signal, which can then be used to detect temporal changes in the measured current signal that exceed a threshold value.

[0027] According to the invention, the arc welding system is configured to carry out a process of the type described above. In particular, the process steps described above can be implemented in the monitoring device and / or an additional detection device. The monitoring device can also be configured to automatically adjust at least one parameter of the arc welding process and / or to automatically terminate the arc welding process.

[0028] The invention is explained in more detail below with reference to exemplary embodiments and drawings.

[0029] They show Fig. 1. A schematic representation of an arc welding system, Fig. 2 an enlarged detail view of part of the arc welding system, Fig. 3 exemplary measurement results of the rate of change of current over time, Fig. 4 an embodiment of a monitoring device.

[0030] The in Fig. The arc welding system shown in Figure 1 has a monitoring device 1, a welding power source 2, a voltage measuring device 3, a current measuring device 4 and an arc welding torch 11. The arc welding system is intended to produce a weld seam on a metal component 10 that is fixed to a holder 8.

[0031] The arc welding torch 11 has a housing 12 through which a welding wire 15 is fed. The welding wire 15 is, for example, on a spool 14 and is fed into the housing 12 via a feeder 13. The welding wire 15 is used as the material for creating the weld and is liquefied by the arc of the arc welding system. The liquefied material of the welding wire 15 is deposited on the metal component 10 as a weld.

[0032] The welding power source 2 is electrically connected via a line 5, e.g., the positive voltage supply line, to the housing 12 or to a component of the arc welding torch 11 located in the housing 12. The other supply line 6 of the welding power source 2, e.g., the negative line, is electrically connected to the metal component 10, e.g., by connecting line 6 to an electrical terminal 9 of an electrically conductive holder 8. The voltage measuring device 3 is connected to lines 5 and 6. In this way, the current welding voltage can be determined by the voltage measuring device 3. A current sensor 7, e.g., a Hall sensor or similar non-contact sensor, or a shunt resistor, is located in line 5. The current measuring device 4 measures the electric current flowing through line 5 via the current sensor 7, i.e., the welding current.The welding voltage measured by the voltage measuring device 3 and the welding current measured by the current measuring device 4 are supplied to the monitoring device 1.

[0033] The monitoring device 1 is configured to perform one or more of the process steps according to the invention, e.g., monitoring the measured current signal I of the welding current for changes over time that exceed at least one limit value in magnitude. For this purpose, the monitoring device 1 can, for example, include hardware components and / or software components (computer programs). If the indicator it determines signals excessive wear of the contact tube of the arc welding torch 11, the monitoring device 1 can, for example, activate a signal transmitter 16 to signal to the user that the contact tube is excessively worn. The user can then interrupt the welding process and replace the contact tube. Alternatively or additionally, the monitoring device 1 can also directly influence at least one parameter of the arc welding process, e.g.,by enabling the monitoring device 1 to control functions of the welding power source 2, such as the welding voltage provided by the welding power source 2 and / or the welding current delivered by the welding power source 2.

[0034] The Fig. Figure 2 shows a cross-sectional view of the front area of ​​the arc welding torch 11 facing the metal component 10. It can be seen that the welding wire 15 is guided within the housing 12 through a wire guide 20 to a front through-opening 24 of a contact tube 23. The contact tube 23 is electrically connected to the conductor 5. The welding current is transmitted to the welding wire 15 via the contact tube 23 in the area of ​​the through-opening 24. For this purpose, the through-opening 24 has an inner diameter D adapted to the diameter of the welding wire 15, e.g., in the form of a low-friction fit, so that the welding wire 15 can be pushed through the through-opening 24 without significant resistance, while also ensuring sufficient electrical contact.

[0035] Shielding gas can also be passed through channels 22 in the housing 12 and exit at the front end of the arc welding torch 11, thus shielding the area surrounding the arc 25 from the environment. In this way, a weld seam 26 can be produced on the metal part 10 by the liquefaction of the welding wire 15 in the area of ​​the arc 25.

[0036] The Fig. Figure 2 shows the contact tube 23 in a new, unworn condition. In this case, the inner diameter D of the through-hole 24 is only slightly larger than the outer diameter of the welding wire 15, e.g., in a range below 0.1 mm. If the inner diameter D of the through-hole 24 increases significantly due to wear of the contact tube, e.g., due to burn-off, friction on the welding wire 15, and / or thermal expansion, the welding wire 15 is guided less precisely. Furthermore, electrical contact is no longer guaranteed, i.e., contact interruptions occur. As a result, unwanted weld spatter is generated on the metal part 10 to a greater extent.

[0037] The Fig. Figure 3 shows exemplary measurement results of the rate of change of the welding current dl / dt over the inner diameter D of the contact tube 23. This illustrates the relationship, recognized by the inventors, between the increase in the diameter D of the contact tube, i.e., the inner diameter of the through-hole 24, and the rate of change of the welding current dl / dt, measured by the current measuring device 4. The diameter D in millimeters is shown on the abscissa axis, and the rate of change of the welding current dl / dt in A / ms is shown on the ordinate axis.

[0038] In the left-hand section, at D = 1.35, it can be seen that most current rate measurements are close to zero, with current rates reaching up to approximately 1,250 A / ms only in isolated cases. Increasing the diameter D to values ​​of 1.5 to 1.6 yields similar results, although at D = 1.6, slightly more measurements close to 1,300 A / ms are observed. At D = 1.65, some current rate measurements up to 1,500 A / ms are detected. At D = 1.75, current rates up to 2,000 A / ms and above are detected. In the latter two sets of measurements, it is particularly noticeable that the frequency of current rates near zero has decreased significantly compared to the measurements at D ≤ 1.6 mm.

[0039] At the in Fig. In the embodiment shown in Figure 3, excessive wear of the contact tube 23 can be detected, for example, at D ≥ 1.65, or at the latest at D ≥ 1.75. This can be done by evaluating the very large current change rates, for example, values ​​above 1,300 A / ms or values ​​above 2,000 A / ms. For example, the frequency of such high current change rates per unit of time can be monitored and, if a limit value is exceeded, used as an indicator of wear of the contact tube 23.

[0040] Based on the Fig. Section 4 describes an advantageous method for evaluating the measured current signal I of the welding current using electronic circuit components. Fig. Figure 4 shows a circuit arrangement in which a high-pass filter 40, an integrator 41, and a comparator 42 are connected in series. The current signal I is fed to an input terminal of the high-pass filter 40. The high-pass filter 40 can, for example, be tuned to a cutoff frequency > 1,000 Hz or a cutoff frequency > 5,000 Hz. A cutoff frequency of 10 kHz is advantageous, for example. Fig. Figure 4 shows the high-pass filter 40 in the form of an active high-pass filter. The invention can also be implemented with a passive high-pass filter. However, an active high-pass filter allows for even more precise filtering of the desired signal components of the current signal I.

[0041] The output signal of the high-pass filter 40 is fed to the integrator 41 as an input. The integrator 41 integrates the input signal and provides it as an output signal. The output signal of the integrator 41 is fed to the comparator 42 as an input signal. The comparator 42 is set to detect a specific threshold value of the input signal. If this threshold value is exceeded by the input signal, the comparator 42 outputs a modified signal, which can be used as an indicator A for wear of the contact tube 23.

Claims

[1] Method for carrying out an arc welding process in which a welding wire (15) is guided through a contact tube (23), wherein a welding current is transferred through the contact tube (23) to the welding wire (15) to generate the arc (25), wherein the welding current is measured during the arc welding process and the measured current signal (I) is monitored, wherein temporal changes in the measured current signal (I) which exceed at least a limit value in magnitude are detected as an indicator (A) of wear of the contact tube (23), characterized by , that the measured current signal (I) is filtered by means of a high-pass filter (40) and the indicator (A) for wear of the contact tube (23) is determined on the basis of the filtered signal. [2] Method according to claim 1, characterized by , that depending on the indicator (A), at least one of the following steps is performed: a) automatic output of a wear warning signal, b) automatic adjustment of at least one parameter of the arc welding process, c) automatic termination of the arc welding process. [3] Method according to any one of the preceding claims, characterized by , that the temporal changes of the measured current signal (I), which exceed at least a limit value in magnitude, are monitored with respect to their frequency per unit of time, whereby an exceedance of a certain frequency per unit of time is detected as an indicator (A) of wear of the contact tube (23). [4] Method according to any one of the preceding claims, characterized by that the procedure for carrying out a short arc welding process is designed. [5] Method according to any one of the preceding claims, characterized bythat the process is carried out using an arc welding system which keeps the welding voltage constant by means of a control device or by its internal structure. [6] Method according to any one of the preceding claims, characterized by that the procedure is carried out without plant-specific and / or material-specific reference data. [7] Arc welding system for carrying out an arc welding process, comprising: a) a contact tube (23) through which a welding wire (15) is guided, wherein a welding current can be transmitted through the contact tube (23) to the welding wire (15) to generate the arc (25), b) a current measuring device (4) for measuring the welding current during the arc welding process, c) a monitoring device (1) for monitoring the current signal (I) measured by means of the current measuring device (4), d) wherein the monitoring device (1) or an additional detection device is configured to detect temporal changes in the measured current signal (I) which exceed at least a limit value in magnitude as an indicator (A) of wear of the contact tube (23), characterized by that the arc welding system is set up to carry out a method according to one of claims 1 to 6.

Images