Detection device

Abstract

Detection device (1) for a system (2) for the additive manufacturing of three-dimensional objects (3) by means of arc welding, wherein the detection device (1) is connectable to or connected with a welding head (5) of the system (2), wherein the detection device (1) is configured to detect an arc voltage during an additive manufacturing process carried out on the system (2) and to determine a quality parameter describing a quality of the object (3) produced in the manufacturing process based on the detected arc voltage.

Description

[0001] The invention relates to a detection device for a system for the additive manufacturing of three-dimensional objects by means of arc welding, wherein the detection device can be connected to or is connected to a welding head of the system.

[0002] Systems for the additive manufacturing of three-dimensional objects using arc welding, in which building material is melted by means of a welding head of the system and deposited or applied to a build surface or a previously solidified layer of the building material, are generally known from the prior art. To melt the building material, an arc voltage is applied to the welding head so that the building material, for example a metal wire, can be melted.

[0003] Such systems for the additive manufacturing of three-dimensional objects adjust the arc voltage based on a control process executed on the system. The system operator typically receives no information from the system about the currently set arc voltage or whether it is changed during a manufacturing process. Generally, the operator cannot influence the arc voltage. Therefore, process scenarios can occur in which the system, due to its internal control routine or the control process executed on the system, changes the arc voltage during the welding process or during the production of a component, without this being apparent to the operator or identifiable by the operator. Furthermore, the operator cannot prevent such a change in the arc voltage from being made by the system.

[0004] Such fluctuations or changes in the arc voltage can, however, cause geometric properties of the object, such as waviness, and also impair its mechanical properties, for example, by negatively affecting tensile strength, yield strength, and elongation at break. While systems for process monitoring are known to exist in the plant, these typically only monitor the total energy input in the weld or current and voltage peaks, for example, by recording maximum or average values ​​of the arc voltage.

[0005] In the systems described, an arbitrary metric is typically applied to the recorded values, such as the arc voltage, for example, the mean, median, standard deviation, and the like, meaning that individual fluctuations cannot be identified and evaluated. However, such systems are unsuitable or not designed for identifying or verifying whether fluctuations in the arc voltage occurred during the manufacturing of the object that lead to a geometric or mechanical impairment of the object.

[0006] The invention is based on the objective of providing an improved detection device for a system for the additive manufacturing of three-dimensional objects, in which process monitoring is improved.

[0007] The problem is solved by a detection device according to claim 1. The dependent claims relate to possible embodiments.

[0008] As described, the invention relates to a detection device for a system for the additive manufacturing of three-dimensional objects by means of arc welding. Arc welding is understood in particular to mean "wire arc additive manufacturing" (WAAM), i.e., a process in which a building material, in particular a metal wire, is melted and deposited by an electric arc.

[0009] The detection device is, in particular, a separate device that can be connected to the system for detecting the arc voltage. Specifically, the detection device is connected to the welding head of the system. The detection device can, for example, be designed as a separate unit and thus connected to a commercially available arc welding system. Consequently, it is not necessary to rely on the system's monitoring systems; instead, an additional detection device can be connected to the system to perform the specific verification and monitoring described herein.

[0010] The invention is based on the finding that the detection device is designed to detect an arc voltage during an additive manufacturing process carried out on the system and to determine a quality parameter describing the quality of the object produced in the manufacturing process, based on the detected arc voltage. As described, the detection device is connected to the system and, in the connected state, is designed to detect the arc voltage that is set at the welding head during the manufacturing process.

[0011] When the additive manufacturing process is carried out with the system, the sensing device connected to the welding head records the arc voltage throughout the entire manufacturing process. This allows, in particular, fluctuations in the arc voltage that occur during the welding process to be detected and resolved by the sensing device. The sensing device is generally designed to output or display the recorded values, especially the arc voltage recorded during the manufacturing process, to a user. Specifically, the sensing device directly outputs the recorded arc voltage without using a metric.

[0012] Based on the measured arc voltage, the detection device is designed to determine a quality parameter that describes the quality of the object produced in the manufacturing process. In other words, the detection device establishes a relationship between the arc voltage measured during the additive manufacturing process and the quality of the manufactured object. If fluctuations in the arc voltage occur that could impair the geometric or mechanical properties of the object, this is detected by the detection device and therefore leads to the determination of a corresponding quality parameter.

[0013] Depending on the fluctuations in the arc voltage, the quality parameter can describe, in particular, any impairment of the object's quality. The quality parameter can at least indicate whether the quality of the manufactured object meets requirements, for example, whether it is rated as "OK" or "not OK." It is also possible for the quality parameter to indicate the extent of the impairment, for example, through the magnitude of the deviation or fluctuation in the arc voltage in specific areas of the object, or depending on the affected area, especially whether it is a critical area.

[0014] In this application, the term "arc voltage" is used to refer to the quantity detected by the detection device. Since the arc voltage correlates with other electrical quantities via the known electrical relationship, it is also possible, if necessary, to detect an electrical parameter of the arc, such as an arc current, instead of the arc voltage. Therefore, the term "arc voltage" is used synonymously with the term "arc current" in this description, so that the two terms are interchangeable.

[0015] Advantageously, the arc voltage is used by the detection device to assess the quality of the object. Such an assessment of object quality based on the detected arc voltage is not provided for by the system itself or by the system manufacturer. The detection device can therefore be connected to an existing system and record the arc voltage throughout the manufacturing process. Based on the detected arc voltage, the quality of the manufactured object can be evaluated during the manufacturing process itself.

[0016] The detection device can be further developed to determine a voltage deviation between an actual arc voltage and a target arc voltage, particularly above an arc limit value. As described above, the detection device is designed to detect the arc voltage of the system during the manufacturing process of the additively manufactured object. Specifically, in the described configuration, a voltage deviation can be determined by the detection device, namely between an actual arc voltage and a target arc voltage. The voltage deviation can be referenced to an arc limit value, for example, a maximum voltage deviation.

[0017] The actual arc voltage represents the arc voltage recorded during the manufacturing process. The target arc voltage can be specified, determined, or measured. The target arc voltage can, for example, describe an average arc voltage over the entire manufacturing process or a portion thereof, or be determined based on the preceding welding process, such as at least one preceding layer.

[0018] If the actual arc voltage deviates from the target arc voltage by more than the arc limit value, for example, defined by an arc voltage used for a preceding section of the object, particularly an underlying layer, or in a previous welding cycle, this can be determined accordingly via the detection device. It is also possible to determine and output a quality parameter. Specifically, it is determined that if the arc voltage deviates above the arc limit value, an impairment of the geometric and / or mechanical properties of the object is likely or certain. Monitoring the arc voltage, and in particular determining the voltage deviation, is therefore a direct indicator of the quality of the manufactured object.

[0019] In general, the detection device for measuring arc voltage or arc current can include a suitable voltage or current sensor. Such a sensor is connected to the welding head of the system so that the detection device can measure the currently output arc voltage or arc current.

[0020] In a further development of the detection device, it may be provided that the device is configured to output a first or second quality parameter based on the determined voltage deviation. As already described, the detection device is intended to detect or determine whether the currently measured actual arc voltage deviates from the target arc voltage by more than one arc limit value. The arc limit value can, in principle, be defined arbitrarily.

[0021] Specifically, the arc voltage limit can be between 0.1V and 10V, particularly between 0.5V and 5V, for example, 2V. If the voltage deviation between the actual arc voltage and the target arc voltage is below the arc voltage limit, the detection device can output an initial quality parameter, for example, "OK" and / or the voltage deviation at the relevant point on the object.

[0022] If the arc limit is exceeded due to a voltage deviation, the detection device can determine and output a second quality parameter, for example, "not OK" and / or the voltage deviation at the relevant point on the object. Consequently, the user or the detection device can directly determine the extent to which a voltage deviation has occurred in the additive manufacturing process and how it is likely to affect the quality of the manufactured object. This can trigger a follow-up inspection, for example, if the second quality parameter is output or if the output quality parameter gives cause for a follow-up inspection, such as indicating an impairment of a geometric and / or mechanical property of the object.

[0023] In a further embodiment, the detection device can be configured to detect the arc voltage with a defined detection rate of at least 500 Hz, and in particular at least 1 kHz. As already described, it is necessary to achieve the highest possible resolution for detecting the arc voltage with the detection device in order to reliably detect fluctuations or voltage deviations. In particular, this allows for the reliable detection of any changes in the arc voltage and the resulting voltage deviations. If the detection rate is lower, such changes cannot be detected but are at least smoothed out due to the lower detection rate. Specifically, the detection rate can be at least 2 kHz, and it may be advantageous to set the detection rate even higher, for example at least 3 kHz, at least 4 kHz, or at least 5 kHz.In particular, this makes it possible to detect even short-term fluctuations in the arc voltage and to determine the quality of the object based on such a voltage deviation.

[0024] In a further embodiment, the detection device can be configured to detect the arc voltage in a voltage curve describing a welding cycle, particularly in a welding state where the wire is at its greatest distance from the workpiece. The voltage curve describes a welding cycle in which the workpiece material, for example, a wire, is melted. The system executes such welding cycles sequentially to melt the workpiece material. For example, to generate welding cycles, workpiece material is cyclically melted at 70 Hz, or the voltage curve is repeatedly output.

[0025] This means that the voltage curve describing the welding cycle is repeatedly output for the application of the building material, particularly for the melting of the building material in the welding head. During a welding cycle, the voltage thus changes according to the previously described voltage curve. The voltage curve has at least one initial stage or maximum value. Advantageously, the arc voltage is detected by the sensing device at this initial stage or maximum value. This corresponds, in particular, to a welding condition in which the building material, for example, a wire, is at its greatest distance from the workpiece. Specifically, the arc voltage is always detected at the same point on the voltage curve.

[0026] In one embodiment, the detection device can be configured to determine the quality parameter with spatial resolution. As previously described, the detection device can detect the arc voltage during the manufacturing process. The detection device can thus detect the arc voltage at any point during the manufacturing process. This allows the detection device to establish a correlation between the manufactured sections of the object and the arc voltage present at those points.

[0027] This means that the quality parameter, which is determined based on the measured arc voltage, can be determined with spatial resolution. In other words, the arc voltage and / or voltage deviation and / or the quality parameter present during the object's manufacture can be determined at any location, point, or section of the object. Consequently, a quality parameter can be determined and output for each object section or point. This allows, for example, the output to be provided to the user, showing how the quality parameter is distributed across the object or which areas of the object might be critical with regard to quality.

[0028] The detection device can be further developed to output the quality parameter, particularly as a two-dimensional or three-dimensional model. For example, the quality parameter can be determined with spatial resolution, as described above. Subsequently, the quality parameter can be output for individual points or individual welding cycles within the object. Furthermore, it is possible to output a two-dimensional model, for example, for each layer.

[0029] The arc voltage and / or voltage deviation and / or quality parameters can be output at individual points or sections within a layer. The quality parameter can also be output as a three-dimensional model, allowing the entire object to be represented three-dimensionally, with the quality parameter displayed at individual points, for example, in each welding cycle. This simplifies subsequent inspection or rework of the object, for instance, by identifying a specific area based on the quality parameter and directing that area to further inspection or rework. This subsequent inspection and / or rework can be triggered automatically. Similarly, rejects can be identified based on the quality parameter.For example, a defect in the object can be identified during the manufacturing process if a certain voltage deviation occurs, and the manufacturing process can be stopped if necessary, especially if the defect is particularly critical, for example above the arc limit or a second arc limit.

[0030] Further development of the detection device may include the determination of at least one change in a process parameter of the system based on the quality parameter. For example, it may be determined that a regulation of the arc voltage occurs during the operation of the system, triggered, for example, by a process condition and / or environmental condition.

[0031] By changing a process parameter, for example a gas flow, a temperature or the like, the manufacturing process on the plant can be adjusted in such a way that a regulation of the arc voltage, which leads to a voltage deviation that has the previously described effects on the properties of the object, can be reduced or prevented.

[0032] In addition to the detection device, the invention relates to a system for the additive manufacturing of three-dimensional objects by means of arc welding, which includes a previously described detection device. The invention further relates to a method for operating a system for the additive manufacturing of three-dimensional objects by means of arc welding, wherein a detection device, in particular a previously described detection device, is connected to a welding head of the system, wherein, during an additive manufacturing process carried out on the system, an arc voltage is detected by means of the detection device, and a quality parameter describing the quality of the object produced in the manufacturing process is determined based on the detected arc voltage. The method can be carried out, in particular in all details, with or on the previously described detection device.

[0033] All advantages, details, designs and / or features described in relation to the detection device are fully transferable to the plant and the process.

[0034] The invention is explained with reference to exemplary embodiments and the figures. The figures are schematic representations and show: Fig. 1. A schematic representation of a detection device for a system for the additive manufacturing of three-dimensional objects according to an exemplary embodiment; and Fig. 2 A schematic representation of two exemplary diagrams of the arc voltage detected by the detection device according to an embodiment.

[0035] Fig. Figure 1 schematically shows a detection device 1 for a system 2, which is designed for the additive manufacturing of three-dimensional objects 3 by means of arc welding. In other words, the system 2 is designed to melt building material 4, in particular a metal wire, by applying an arc voltage to a welding head 5 and to apply the molten building material 4 layer by layer to form the object 3 or to a build platform 6.

[0036] In the Fig. In the depicted state, the detection device 1 is connected to the system 2, specifically to the welding head 5. The detection device 1 can, in principle, be a separate device that can be provided independently of the system 2 and connected to it. The detection direction 1 has a sensor designed to detect the arc voltage in the system 2. For example, the sensor is a voltage sensor or a current sensor. Generally, the term "arc voltage" can be replaced with "arc current," so that instead of the arc voltage, the arc current or another electrical parameter could also be detected or measured. The description is transferable accordingly.

[0037] The detection device 1 determines a quality parameter based on the detected arc voltage, which describes the quality of object 3. In other words, the detection device 1 monitors the arc voltage during the manufacturing process of object 3. The arc voltage detected by the detection device 1 can also be referred to as the "actual arc voltage." If a voltage deviation from a target arc voltage occurs, for example, an arc voltage present at the beginning of the welding process or in a previous welding cycle, such a voltage deviation is detected and determined by the detection device 1.

[0038] Fig. Figure 2 schematically shows two diagrams 7 and 8, in which the arc voltage in volts is plotted against time. This results in a voltage curve 9 and 10 in diagrams 7 and 8. Each voltage curve 9 and 10 describes one welding cycle. The voltage curve 9 can be captured or fixed. To apply the building material 4, the voltage curve 9 and 10 is repeatedly output to melt the building material 4 and apply it layer by layer. The voltage curve 9 and 10 can, for example, be repeatedly output at 70 Hz. This means that the voltage curves 9 and 10 do not describe an entire layer of object 3, but rather a section of the layer, namely one welding cycle. Each layer of object 3 comprises a multitude of welding cycles, each of which produces a section of the layer.Since the detection device 1 is designed to detect the arc voltage with a defined detection rate of at least 500Hz, in particular at least 1kHz, at least 2kHz, at least 3kHz, at least 4kHz, at least 5kHz, deviations in the arc voltage or the course of the arc voltage can be detected with particularly high resolution.

[0039] For example, diagram 7 shows a target arc voltage curve, meaning that voltage curve 9, for instance, represents or defines a target arc voltage. The target arc voltage can be determined, for example, based on the start of the welding process or at least one preceding welding cycle. The target arc voltage can also be predefined.

[0040] As in Fig. As shown in Figure 2, the arc voltage is recorded in the same state in each voltage curve 9, 10, namely preferably at a maximum value of the voltage curve 9, 10 or at a first stage in the course of the voltage curve 9, 10. This welding state represents, for example, the state in which the building material 4, for example a wire, has the greatest distance from the manufactured object 3.

[0041] As in Fig. As shown in Figure 2, the detection device 1 detects the arc voltage and compares it. A voltage deviation 11 between voltage curve 9 and voltage curve 10 is thus determined. The voltage deviation 11 can be, for example, 2 V. The voltage deviation 11 is compared with an arc limit value. The arc limit value can be, for example, 0.5–5 V, with an arc limit value of 1.5 V being used in this embodiment.

[0042] Since the measured voltage deviation 11 is above the arc limit, the detection device 1 can determine and output a corresponding quality parameter for object 3. This determined quality parameter can, for example, include the arc voltage measured at this location on object 3 or the measured voltage deviation 11. The quality parameter can also classify object 3 or the relevant section of object 3 as "not OK". This can, for example, trigger a follow-up inspection or rework in system 2.

[0043] Alternatively, it is also possible to adjust or change at least one process parameter of system 2 to prevent such fluctuations or voltage deviations 11 in the arc voltage. For example, at least one gas flow and / or at least one temperature in system 2 can be set so that the actual arc voltage corresponds to the target arc voltage, at least within the arc limit value.

[0044] When determining the quality parameters, the detection device 1 can proceed with spatial resolution or determine at least one quality parameter with spatial resolution. Since the detection device 1 records the arc voltage during the process, it can be determined which arc voltage is present at which section of the object 3. This can, for example, be related to the individual welding cycles. Thus, it can be precisely specified in which welding cycle the actual arc voltage corresponds to the target arc voltage, or a voltage deviation 11 can be specified for each welding cycle.

[0045] This further enables the detection device 1 to determine the quality parameter as a model of object 3. For example, the model can be output as a two-dimensional model, for instance for each layer, or as a three-dimensional model of an object section or the entire object 3. This allows a user to directly see in which sections or areas of object 3 which arc voltage or voltage deviation 11 is present, or where the arc voltage has exceeded the arc limit. This simplifies subsequent inspection or rework of object 3.

[0046] The method described herein can be used with the detection device 1, as for example in Fig. As shown in Figure 1, the advantages, details, and features described are therefore also applicable to the process.

[0047] All advantages, details and features described in relation to the embodiments shown in the Fig. can be combined, interchanged and transferred to one another as desired. REFERENCE MARK LIST 1 Detection device 2 Annex 3 objects 4 Building materials 5 welding heads 6 building platforms 7, 8 Diagram 9, 10 Voltage curve 11 Voltage deviation

Claims

[1] Detection device (1) for a system (2) for the additive manufacturing of three-dimensional objects (3) by means of arc welding, wherein the detection device (1) is connectable to or connected with a welding head (5) of the system (2), characterized by , that the detection device (1) is designed to detect an arc voltage during an additive manufacturing process carried out on the system (2) and to determine a quality parameter describing the quality of the object (3) produced in the manufacturing process based on the detected arc voltage. [2] Detection device (1) according to claim 1, characterized by , that the detection device (1) is designed to determine a voltage deviation (11) between an actual arc voltage and a target arc voltage, in particular above an arc limit value. [3] Detection device (1) according to claim 2, characterized by, that the detection device (1) is designed to output a first quality parameter or a second quality parameter based on the determined voltage deviation (11). [4] Detection device (1) according to any one of the preceding claims, characterized by , that the detection device (1) is designed to detect the arc voltage with a defined detection rate of at least 500Hz, in particular at least 1kHz. [5] Detection device (1) according to any one of the preceding claims, characterized by , that the detection device (1) is designed to detect the arc voltage in a voltage curve (9, 10) describing a welding cycle, in particular in a welding state in which a wire has the greatest distance from the manufactured object (3). [6] Detection device (1) according to any one of the preceding claims, characterized by, that the detection device (1) is designed to determine the quality parameter with spatial resolution. [7] Detection device (1) according to any one of the preceding claims, characterized by , that the detection device (1) is designed to output the quality parameter, in particular as a two-dimensional or three-dimensional model. [8] Detection device (1) according to any one of the preceding claims, characterized by , that the detection device (1) is designed to determine at least one change in a process parameter of the plant (2) based on the quality parameter. [9] Apparatus (2) for the additive manufacturing of three-dimensional objects (3) by means of arc welding, comprising a detection device (1) according to one of the preceding claims. [10] Method for operating a system (2) for the additive manufacturing of three-dimensional objects (3) by means of arc welding, wherein a detection device (1), in particular a detection device (1) according to one of claims 1 to 8, is connected to a welding head (5) of the system (2), characterized by , that by means of the detection device (1) an arc voltage is detected during an additive manufacturing process carried out on the system (2) and a quality parameter describing a quality of the object produced in the manufacturing process (3) is determined based on the detected arc voltage.

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