DEVICE AND METHOD FOR MEASURING A POWDER MASS FLOW FOR POWDER NOZZLE DEPOSIT WELDING

Description

Technical field

[0001] The innovation relates to a device and a method for measuring a powder mass flow for powder nozzle deposition welding. Technical background

[0002] Powder jet cladding has gained increasing importance as an additive manufacturing process in recent years. In powder jet cladding, powder is selectively fed into a laser processing area, whereby the powder composition, particularly the materials used and the powder particle size, can vary. In some manufacturing processes, powder deposition can be carried out under a protective gas atmosphere.

[0003] To achieve uniform application and a qualitatively consistent surface coverage, it is necessary that the powder is conveyed into the laser processing area with as constant a powder mass as possible. The powder mass flow can vary depending, for example, on the powder composition.

[0004] WO 2015 / 155116 A1 describes a method in which a powder jet is conveyed through various apertures in a laser processing area for testing purposes. To determine the powder mass flow, a powder jet is conveyed through each aperture into a processing area for a predetermined period of time. The powder jet conveyed into the processing area is collected in a measuring cup, and the collected powder mass is determined using a scale. Using the collected powder mass, an aperture with an associated powder jet is used for laser cladding.

[0005] US 6 940 037 B1 shows a method for laser cladding in which a powder stream is fed from powder reservoirs to a process head, whereby a calibrated optical sensor is used to measure a volume flow of the conveyed powder quantity.

[0006] EP 1 950 001 A1 discloses a method in which a powder mass is conveyed into a high-energy jet over a predetermined period of time. The powder mass is then collected, and a relative position of the powder jet to the high-energy jet is adjusted depending on the collected powder mass and a predetermined value. Against this background, it is an object of the invention to provide a device and a method that improves the measurement of the powder mass flow. Description of the invention

[0007] The object of the invention is achieved by the features of independent claim 1 and by the features of independent claim 10. The dependent claims relate to particular embodiments of the invention. The invention relates to a device and a method for measuring the powder mass flow for powder nozzle deposition welding.

[0008] According to the invention, the device comprises at least one powder dosing device, a control unit, a powder mass flow sensor, a powder mass determination device, and a powder switch. In some embodiments, the at least one powder dosing device can comprise, for example, one or more conveyor belts, one or more pinch valves, one or more conveyor discs, and / or one or more screw conveyors.

[0009] In some embodiments, the control unit may consist of multiple control units. A control unit may, for example, comprise one or more analog and / or digital circuits. In some embodiments, the control unit may be configured to control one or more output parameters depending on at least one input parameter.

[0010] The powder mass flow sensor can be configured to determine a powder mass flow, for example, using weight measurements, beam attenuation measurements, reflection measurements, etc.

[0011] The powder switch can be configured to convey a powder mass flow to various receivers depending on a control system. Receivers can be, for example, a scale as a powder mass determination device and / or a process head.

[0012] According to the invention, the at least one powder dosing device is configured to convey a powder mass via the powder mass flow sensor, depending on the powder switch, to a scale and / or to a process head. This has the advantage that a powder mass flow can be set without the powder mass being conveyed to the process head. Furthermore, after the powder mass flow has been set (work preparation), it is easy to transition to powder nozzle deposition welding, since the conveyance of the powder mass flow is not interrupted. An interruption in the conveyance can lead to fluctuations in the conveyance of the powder mass, particularly during startup.

[0013] According to the invention, the control unit is configured to calibrate the powder mass flow sensor based on a powder mass flow measured by the scale. The powder mass flow sensor can be used to monitor the powder mass flow during powder mass buildup welding. Calibrating the powder mass flow sensor can lead to increased accuracy in monitoring the powder mass flow, since changes in the powder mass, in particular in the material and / or shielding gas composition, can influence the sensory detection of the powder mass flow by the powder mass flow sensor.

[0014] In some embodiments, the control unit can be configured to adjust the powder dosing device based on the powder mass flow measured by the scale and a predetermined powder mass flow. This has the advantage that an exact adjustment of the powder mass flow to a predetermined powder mass flow, especially before powder nozzle deposition welding, is possible. ex situ is possible.

[0015] In some embodiments, the control unit can be configured to adjust the powder dosing device based on the powder mass flow detected by the powder mass flow sensor and a predetermined powder mass flow. This has the advantage that monitoring of the powder mass flow is possible, particularly during powder nozzle build-up welding. Since the powder mass flow sensor can be calibrated using the scale before powder nozzle build-up welding, precise monitoring of the powder mass flow is possible. in situpossible during powder mass buildup welding.

[0016] In a particularly efficient embodiment, the device comprises a centrifugal separator, a gravity separator and / or an inertial separator between the powder switch and the scale for separating the powder mass from a gas or gas mixture. Separating the powder mass from a gas or gas mixture is also conceivable using other methods. Separating the powder mass from a gas or gas mixture has the advantage that measuring the powder mass flow using the scale becomes more accurate. For example, the protective gas helium has a lower density than air, which means that it rises in an air-filled environment. This can, for example, falsify a measurement result from the scale due to the buoyancy of the gas or a mass of the gas. Separating the powder mass from a gas or gas mixture prevents this measurement from being falsified.

[0017] In a particularly robust embodiment, the control unit can be configured to control the powder mass flow via one or more pinch valves. Pinch valves have the advantage of being particularly resistant to blockages and reducing pressure surges compared to other regulating valves. Especially in a control loop, controlling the powder mass flow to a target flow, oscillation can be suppressed and the settling time shortened.

[0018] In a particularly cost-effective embodiment, the scale can be configured to measure the powder mass flow by measuring the solid mass deposited over a time interval. The measurement of the solid mass deposited over a time interval can be determined, for example, by calculating a difference. In further embodiments, the scale can be recalibrated for this purpose, or a zero value can be adjusted accordingly. The accuracy can be increased, for example, by increasing the time interval. This has the advantage that a relatively accurate measurement of the powder mass flow is achieved with little effort.

[0019] In a particularly efficient embodiment, the control unit can be configured, in a work preparation mode, to perform the steps of adjusting a feed rate of the at least one powder dosing device per unit of time as a function of a predetermined powder mass flow and as a function of the powder mass flow measured by the scale, and calibrating the powder mass flow sensor as a function of the predetermined powder mass flow and / or the powder mass flow measured by the scale. This has the advantage that the powder mass flow is precisely adjusted using the powder mass determination device before powder nozzle deposition welding, and the powder mass flow is monitored during powder nozzle deposition welding.Since calibration is performed with the specified powder mass flow, the accuracy of monitoring the conveyed powder mass flow can be increased. In particular, non-linear errors can be better compensated for during calibration. A powder mass flow that exhibits a smaller deviation from a specified powder mass flow leads to a more uniform application of the powder mass and improved powder mass application quality.

[0020] In a particularly efficient embodiment, the control unit can be configured to perform at least the following steps to carry out powder nozzle deposition welding: actuating the powder switch to convey the powder mass to the process head via the powder mass flow sensor in a working mode, and monitoring the powder mass flow using the powder mass flow sensor in the working mode. This has the advantage that it is possible to switch from a work preparation mode to a working mode without having to interrupt the powder mass conveyance. This can prevent the conveyed powder mass flow from fluctuating to the predetermined powder mass flow, particularly at the start of the working mode. This leads to increased quality of the powder mass deposition, especially when powder nozzle deposition welding is started.

[0021] In a particularly automated embodiment, the control unit can be configured to switch from work mode to work preparation mode if a deviation between the powder mass flow detected by the powder mass flow sensor and the specified powder mass flow exceeds a specified value. This has the advantage that the powder nozzle deposition welding is interrupted if the powder mass deposition deviates too significantly from a specified powder mass deposition. This ensures a specified quality of the powder mass deposition. Furthermore, the powder mass flow can be readjusted using the powder mass determination device and / or the powder mass flow sensor can be recalibrated at the same time. This also has the advantage that an error in the calibration of the powder mass flow sensor can be easily eliminated.In this way, a desired powder mass flow can be ensured in an automated manner during powder nozzle deposition welding.

[0022] The device can be arranged according to the invention to carry out the following method.

[0023] A method according to the invention comprises the steps of: conveying a powder mass, determining the powder mass flow of the conveyed powder mass, calibrating a powder mass flow sensor as a function of the determined powder mass flow, actuating a powder switch to change the conveying direction from a powder mass flow determination unit to the process head, conveying the powder mass with a predetermined powder mass flow via the powder mass flow sensor to the process head, and monitoring the powder mass flow by means of the powder mass flow sensor.

[0024] A powder mass flow can be determined, for example, using a scale. The scale can be configured to measure a powder mass applied to the scale over a predetermined time interval. This can be done, for example, by setting the zero point accordingly or by calculating the difference between two measurement results. In some embodiments, the scale can include a powder mass receiver. In some embodiments, the scale can be configured to correct the powder mass receiver for a powder mass.

[0025] In particularly precise embodiments, the method can include the step of separating the powder mass from a gas or gas mixture before determining the powder mass flow. This has the advantage that the powder mass flow measured by the balance is not distorted by a gas or gas mixture. For example, helium has a lower mass than air and therefore creates buoyancy in an air-filled space. If a powder mass is mixed with helium, for example, as a protective gas, the balance will measure a lower powder mass flow if the powder mass is not previously separated from the helium.

[0026] In particularly cost-effective embodiments, the powder mass flow can be measured using a scale.

[0027] Actuating the powder switch to change the conveying direction from the powder mass flow detection unit to the process head has the advantage that, particularly at the beginning of the powder nozzle build-up welding, a oscillation in the powder mass feed is avoided, since the powder mass is conveyed with a uniform powder mass flow to the detection unit before the powder nozzle build-up welding.

[0028] In a particularly advantageous embodiment, the feed rate per unit of time can be controlled depending on the determined powder mass flow of the conveyed powder mass and depending on a predetermined powder mass flow. This has the advantage that the powder mass flow can be set / controlled relatively precisely before the powder nozzle deposition welding process. Depending on the embodiment, a control unit can comprise, for example, a corresponding analog or digital control system.

[0029] In a particularly advantageous embodiment, the feed rate per unit of time can be adjusted depending on the sensor values ​​of the powder mass flow sensor and depending on a predetermined powder mass flow. This has the advantage that the delivered powder mass flow during powder buildup welding can be regulated / adjusted according to a powder mass flow detected by the powder mass flow sensor. Thus, the delivered powder mass flow during powder buildup welding can not only be monitored but also adjusted. Such regulation / control can be implemented, for example, using a control unit and / or an analog or digital circuit.

[0030] In a particularly automated embodiment, the method can be executed again if a deviation of the powder mass flow detected by the powder mass flow sensor from a predetermined powder mass flow exceeds a predetermined value. This has the advantage of automatically switching between the powder nozzle deposition welding and the precise adjustment of the powder mass flow, including calibration of the powder mass flow sensor, if it is assumed that the conveyed powder mass flow deviates from the predetermined powder mass flow by more than a limit value. If the deviation of the powder mass flow from the predetermined powder mass flow is smaller than a predetermined value, the powder nozzle deposition welding can continue. Description of the drawing

[0031] Figure 1shows schematically a device for measuring a powder mass flow for powder nozzle deposition welding according to an embodiment of the invention. Figure 2 shows schematically a process flow diagram of a method according to an embodiment of the invention. Figure 3 shows schematically a process flow plan of a method for measuring / determining the powder mass flow according to an embodiment of the invention. Figure 4 shows schematically a device for measuring a powder mass flow for powder nozzle deposition welding according to an embodiment of the invention.

[0032] In some embodiments, components can be combined, divided into multiple components, and / or additional components can be added without affecting the functionality of the invention. In some embodiments, method steps can be swapped in order, executed in parallel, combined or divided, and / or additional steps can be added without affecting the functionality of the method according to the invention.

[0033] Figure 1 shows schematically a device 10 for measuring a powder mass flow for powder nozzle deposition welding according to an embodiment of the invention. In Figure 1 The powder mass flow is shown schematically with solid arrows. Dashed lines indicate connections for signal and / or data exchange between different components. The connections for signal and / or data transmission can be wired and / or wireless.

[0034] In this embodiment, the powder mass is conveyed by means of two powder dosing devices, the powder dosing devices 11a and 11b. The powder dosing devices are configured to generate a powder mass flow. The powder mass flows are combined into a common powder mass flow in a Y-connection 13. In an embodiment with one powder dosing device, the Y-connection can optionally be omitted. In some embodiments, particularly when the device comprises multiple powder dosing devices, the device can comprise multiple Y-connections and / or alternatives such as mixers or n-fold Y-connections.

[0035] The resulting combined powder mass flow is transmitted via a powder mass flow sensor 14 to a powder switch 15. Depending on the control of the powder switch 15, the latter transmits the powder mass flow to a process head 16 and / or a scale 18. In this embodiment, the powder switch is controlled by the control unit 20.

[0036] In this embodiment, a powder separator 17 is mounted between the powder switch 15 and the scale 16. This can be configured to separate the powder from a gas or gas mixture, in particular a protective gas.

[0037] In some embodiments, the control device 20 may consist of several, partially independent, control devices. In this embodiment, the control device is configured to control and / or regulate the powder dosing devices 11a, 11b depending on sensor data from the powder mass flow sensor 14 and / or depending on data / signals from the scale 18 and a predetermined powder mass flow.

[0038] In this embodiment, the control unit 20 is also configured to calibrate the powder mass flow sensor 14 as a function of data / signals from the scale 18 and / or a predetermined powder mass flow. The scale 18 can, for example, be configured to measure a powder mass flow by measuring a powder mass applied to the scale 18 within a time interval. The powder mass flow is then determined by dividing the measured powder mass by the length of the time interval.

[0039] In this embodiment, the control unit is configured to control the process head. The process head can be configured to be moved in one, two, or three directions. In some embodiments, the process head can include a laser unit configured to deliver a predetermined energy to a laser processing area during powder jet deposition welding.

[0040] In some embodiments, the control unit is configured, in a work preparation mode, to direct the powder mass flow from the at least one powder dosing device 11a, 11b via the powder mass flow sensors 14 to the scale by means of the powder switch. In the optional powder mass separator, which is connected upstream of the scale, the powder mass is separated from gases and gas mixtures. In this embodiment, the control unit is configured to regulate and control the at least one powder dosing device 11a, 11b such that a predetermined powder mass flow is measured by the scale 18. Once the at least one powder dosing device is adjusted accordingly, the powder mass flow sensor 14 can be calibrated. The powder mass flow sensor can be configured, for example, to detect a powder mass flow optically, by means of radiation, or by contact.In some embodiments, the sensor data of the powder mass flow sensor are simply adjusted according to a calibration.

[0041] After calibrating the powder mass flow sensor, powder jet deposition welding can be performed in this embodiment. In this embodiment, to switch to the working mode, powder jet deposition welding, the powder switch 15 is actuated via a control signal, so that the powder mass flow is conveyed to the process head 16 instead of to the scale. This allows switching from a work preparation mode to the working mode without interrupting the powder mass conveyance.

[0042] During powder nozzle cladding, the powder mass flow is monitored using a powder mass flow sensor. This ensures a constant powder mass flow.

[0043] In some embodiments, the control unit can be configured to interrupt or abort the powder nozzle buildup welding if a deviation of the powder mass flow detected by the powder mass flow sensor from a predetermined powder mass flow exceeds a predetermined limit. For this purpose, the powder switch 15 can be actuated by the control unit 20, so that the powder mass flow is conveyed from the powder switch 15 to the scale 18. The powder mass flow can then be readjusted using the scale, and the powder mass flow sensor can be calibrated if necessary.

[0044] In some embodiments, the control unit can be configured to interrupt or abort the powder nozzle deposition welding process based on an external signal, for example, a sensor signal from a sensor for monitoring the powder mass deposition. In some embodiments, this can mean switching from the work mode to the work preparation mode or aborting the powder nozzle deposition welding process.

[0045] Figure 2shows a schematic process flow plan of a method according to an embodiment of the invention. In a first step S11, a powder mass is conveyed. The powder mass is preferably suitable as a powder for powder nozzle deposition welding. In a second step S12, a powder mass flow of the conveyed powder mass is determined. In a next step S13, depending on the determined powder mass flow, it is checked whether the powder mass flow deviates from a predetermined powder mass flow by more than a predetermined tolerance. If the deviation is greater than the tolerance, the conveyance of the powder mass is adjusted in step S14 and the powder mass flow is determined again in step S12. If the deviation is smaller than the tolerance, a powder mass flow sensor is calibrated in a step S15 using the determined powder mass flow.

[0046] Based on the preparations for powder nozzle cladding in steps S11 to S15, the powder nozzle cladding can be performed in a step S16. To switch from the preparation steps to the execution of the powder nozzle cladding S16, a powder switch is actuated to change the conveying direction instead of to a powder mass flow detection unit (see step S12) to a process head of a powder cladding unit.

[0047] During powder nozzle deposition welding S16, the powder mass flow is monitored by the powder mass flow sensor in steps S16a, S17-S19. In step S16a, the powder mass flow is detected by the powder mass flow sensor. In step S17, a check is made to determine whether a deviation of the powder mass flow, detected by the powder mass flow sensor, from a predetermined powder mass flow is greater than a predetermined tolerance value. If the deviation is greater, powder nozzle deposition welding is interrupted and continued with step S12, determining the powder mass flow. Depending on the embodiment, step S15, calibrating the powder mass flow sensor, can be skipped when repeating steps S12 to S16.

[0048] If the deviation of the detected powder mass flow from the specified powder mass flow is within the tolerance range, a check is performed in step S18 to determine whether the detected powder mass flow matches the specified value. If the detected powder mass flow matches the specified powder mass flow, the system proceeds to step S16, where the powder nozzle buildup welding is performed. If the values ​​do not match, the powder mass feed is adjusted in step S19, and the system also proceeds to step S16, where the powder nozzle buildup welding is performed.

[0049] In some embodiments, after step S18, the execution of the powder mass deposition welding (step S16) can continue if the deviation of the detected powder mass flow from the predetermined powder mass flow is below a further tolerance value. Otherwise, the process continues with step S19, adjusting the powder mass feed. In some embodiments, the tolerance values ​​of step S17 and step S18 can have the same value.

[0050] In some embodiments, among other things, steps S16, S16a, S17-S19, which comprise monitoring the powder mass flow during the powder mass deposition welding with the powder mass flow sensor, may be performed in a different order, with additional steps, at least partially combined, etc.

[0051] Figure 3shows a schematic process flow diagram of a method for measuring / determining the powder mass flow according to one embodiment of the invention. At the start S21 of the method, a powder mass flow i actual is generated in a step S22 using a conveyor disk speed n. In this exemplary embodiment, the powder dosing device is a conveyor disk. In this embodiment, a predetermined powder mass flow i target is transferred in parallel. After the start of the method, the measuring cycle S24 begins.

[0052] Depending on whether the cycle has just begun, which includes the powder switch for the scale being actuated, step S26 or step S25 is executed. If the cycle has begun from standstill, the system waits in step S26 for the powder feeder / powder dosing device to settle, in this embodiment 60 seconds. If the powder switch for the scale is actuated, the system waits in step S25 for the powder switch to settle, in this embodiment 30 seconds. If neither the powder switch has been actuated nor the powder feeder has been activated from standstill, steps S25 and S26 can be skipped.

[0053] In a next step S27, a first measurement of a powder mass m0 is taken on a scale. In a further step S28, a time interval / measurement duration T, in this embodiment 30 seconds, is waited for. During the time interval / measurement duration T, the powder mass flow is conveyed onto the scale. A second measurement of the powder mass m1 is then taken in a step S29. In the next step S30, the powder mass flow is determined using the equation i ist = (m1 - m0) / T.

[0054] In a further step S31, a deviation of the powder mass flow i actual from the predefined powder mass flow is determined. In this exemplary embodiment, the deviation is determined using the formula | i target - i actual | / i target . If the deviation is below a predefined tolerance, in this exemplary embodiment 1%, the conveyor disk speed n erf is specified to convey the predefined powder mass flow i target at the conveyor disk speed n , and the measurement / determination of the powder mass flow i can be completed in step S33.

[0055] If the deviation is greater than the specified tolerance, the speed of the conveyor disk n is adjusted in step S34. Depending on the embodiment, a reaction time of the powder dosing device, in this embodiment 20 seconds, can be waited for in step S35 before the cycle is restarted with step S24.

[0056] Figure 4schematically shows a device for measuring a powder mass flow for powder nozzle deposition welding according to one embodiment of the invention. In this embodiment, pinch valves 11a, 11b meter the powder conveyed by powder conveyors 41a, 41b. The resulting powder flows are combined into a single flow by means of the Y-connection 13. In this exemplary embodiment, the pinch valves are controlled via the directional control valve for controlling one or more metering devices. The powder mass flow is conveyed from the Y-connection 13 via the powder mass flow sensor 14 to the powder switch 15.

[0057] As shown in this embodiment, the powder switch 15 can be controlled by means of the directional control valve for controlling the powder switch 43. One possible position is that the powder mass flow is conveyed to the process head 16 via the powder transport 16a. In another possible position, the powder mass flow is conveyed to a scale 18. A powder separator 17 can be arranged on the conveying path between the scale 18 and the powder switch 15. In some embodiments, the directional control valve for controlling one or more dosing devices 42, the directional control valve for controlling the powder switch, the scale 18, the mass flow sensor 14, the powder separator, and / or the process head can be connected to one another, for example, via one or more control units.

[0058] The control unit can, for example, be configured to control / regulate the powder mass flow using the directional control valve for controlling one or more dosing devices 42 based on data / signals provided by the powder mass flow sensor 14 and / or the scale 18. In some embodiments, the control unit can be configured to control the powder switch using the directional control valve for controlling the powder switch and thus to switch between a work preparation mode and a powder nozzle deposition welding working mode.

[0059] In work preparation mode, a predetermined powder mass flow can be set using the scale 18, the directional valve for controlling one or more dosing devices 42, and one or more dosing devices 11a, 11b. Preferably, after setting the powder mass flow, the powder mass flow sensor 14 can be calibrated. To then switch to work mode without interruption, the powder mass flow can be conveyed to the process head 16 by actuating the directional valve for controlling the powder switch 43. While the powder is being conveyed to the process head 16, the conveyed powder mass flow can be monitored using the powder mass flow sensor 14.

[0060] In some embodiments, the control unit can be configured to automatically switch to work preparation mode and readjust the powder mass flow if the powder mass flow sensor 14 detects an excessive deviation from a predetermined value. This has the advantage that, for example, if powder from a first batch runs out during powder nozzle buildup welding and powder from a second batch is conveyed, it is ensured that the powder mass flow corresponds to a target value. REFERENCE SYMBOL LIST

[0061] 11a, 11b Powder dosing device 13 Y-connection 14 Powder mass flow sensor 15 Powder switch 16 Process head 16a Powder transport to process head 16 17 Powder separator 18 Scale 20 Control unit 41a, 41b Powder conveyor 42 Directional valve for controlling one or more dosing devices 43 Directional valve for controlling the powder switch i actual measured / detected powder mass flow i target predetermined powder mass flow T Time interval / measurement duration m0 first weight measurement m1 second weight measurement n Speed ​​of the conveyor disc n required Conveyor disc speed to convey i target

Claims

1. Device (10) for measuring a powder mass flow for powder cladding, comprising: - at least one powder metering device (11a, 11b), - a control unit (20), - a powder mass flow sensor (14), - a powder mass determination device (18), and - a powder switch (15), wherein the at least one powder metering device (11a, 11b) is configured to convey a powder mass via the powder mass flow sensor (14) as a function of the powder switch (15) to a powder mass determination device (18) and / or to a process head (16), and wherein the control unit (20) is configured to calibrate the powder mass flow sensor (14) on the basis of a powder mass flow measured by the powder mass determination device (18).

2. Device according to Claim 1, wherein the control unit (20) is configured to set the powder metering device (11a, 11b) on the basis of the powder mass flow measured by the powder mass determination device (18) and a predefined powder mass flow.

3. Device according to either of Claims 1 and 2, wherein the control unit (20) is configured to set the powder metering device (11a, 11b) on the basis of the powder mass flow detected by the powder mass flow sensor (14) and a predefined powder mass flow.

4. Device according to one of Claims 1 to 3, comprising a centrifugal separator, a gravity separator and / or an inertial separator (17) between the powder switch (15) and the powder mass determination device (18), for separating the powder mass from a gas or gas mixture.

5. Device according to one of Claims 1 to 4, wherein the control unit (20) is configured to control the powder mass flow via one or more pinch valves (11a, 11b).

6. Device according to one of Claims 1 to 5, wherein the powder mass determination device (18) is configured to measure the powder mass flow by measuring a solid mass deposited in a time interval.

7. Device according to one of Claims 1 to 6, wherein the control unit (20) is configured to carry out the following steps in a working preparation mode: - setting a conveyed quantity of the at least one powder metering device (11a, 11b) per unit of time as a function of a predefined powder mass flow and as a function of the powder mass flow measured by the powder mass determination device (18), and - calibrating the powder mass flow sensor (14) as a function of the predefined powder mass flow and / or of the powder mass flow measured by the powder mass determination device (18).

8. Device according to one of Claims 1 to 7, wherein the control unit (20) is configured to carry out at least the following steps in order to carry out the powder cladding: - actuating the powder switch (15) in order, in a working mode, to convey the powder mass via the powder mass flow sensor (14) to the process head (16), and - monitoring the powder mass flow by means of the powder mass flow sensor (14) in the working mode.

9. Device according to Claim 8, wherein the control unit (20) is configured to change from the working mode to the working preparation mode if a deviation between the powder mass flow detected by the powder mass flow sensor (14) and the predefined powder mass flow exceeds a predefined value.

10. Method for measuring a powder mass flow for powder cladding, comprising the steps of: conveying a powder mass, determining the powder mass flow of the conveyed powder mass, calibrating a powder mass flow sensor as a function of the determined powder mass flow, actuating a powder switch for changing the conveying direction from a determination unit of the powder mass flow to the process head, conveying the powder mass with a predefined powder mass flow via the powder mass flow sensor to the process head, and monitoring the powder mass flow by means of the powder mass flow sensor.

11. Method according to Claim 10, comprising the step of: separating the powder mass from a gas or a gas mixture before determining the powder mass flow.

12. Method according to either of Claims 10 and 11, wherein the powder mass flow is measured by means of a balance.

13. Method according to one of Claims 10 to 12, wherein the conveyed quantity per unit of time is regulated as a function of the determined powder mass flow of the conveyed powder mass and as a function of a predefined powder mass flow, and / or wherein the conveyed quantity per unit of time is set as a function of the sensor values of the powder mass flow sensor and as a function of a predefined powder mass flow.

14. Method according to one of Claims 10 to 13, wherein the method is carried out again if a deviation of the powder mass flow detected by means of the powder mass flow sensor from a predefined powder mass flow exceeds a predefined value.