Method and apparatus for measuring powder mass flow rate for powder jet overlay welding

Abstract

To provide a device and a method for measuring a powder mass flow rate for a powder ejection buildup welding.SOLUTION: Before a powder ejection buildup welding, a powder mass flow rate is set by a powder mass flow rate specification device, and a powder mass flow rate detector is corrected on the basis of the setting. After that, a power switching unit is used to start a powder ejection buildup welding without interrupting transfer of the powder mass, and the powder mass flow rate is monitored by the powder mass flow rate detector during the powder ejection buildup welding.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for measuring powder mass flow rate for powder jet overlay welding. [Background technology]

[0002] Powder cladding has become increasingly important as an additive manufacturing process in recent years. In the case of powder cladding, powder is supplied in a targeted manner to the laser processing area, and the powder composition, in particular the materials used, and the size of the powder particles may be varied. In some manufacturing processes, the powder may be applied in an inert gas atmosphere.

[0003] In order to achieve a uniform application and a qualitatively uniform surface coating, it is necessary to transport the powder to the laser processing area with as constant a powder mass as possible. The powder mass flow rate (Pulvermassenstrom) may vary, for example, depending on the powder composition.

[0004] WO2015 / 155116A1 shows how a powder jet (Pulverstrahl) is passed through various openings in a laser processing area for testing purposes. To determine the powder mass flow rate, the powder jet passes through each opening through the processing area for a predetermined period of time. The powder jet that has passed through the processing area is collected in a measuring cup and the collected powder mass is determined using a balance. Using the collected powder mass, the opening with the associated powder jet is used for laser metal deposition welding.

[0005] EP 1950001 A1 shows a method in which a powder mass is fed into a high-energy beam device (high-energy jet (Hochenergiestrahl)) over a defined period of time. The powder mass is then collected and the position of the powder jet relative to the high-energy beam device is adjusted depending on the collected powder mass and a specified value. In view of this, it is an object of the present invention to provide an apparatus and method for improving the measurement of powder mass flow rate. Summary of the Invention [Problem to be solved by the invention]

[0006] 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 an apparatus and a method for measuring the powder mass flow rate for powder jet welding overlay.

[0007] According to the invention, the apparatus includes at least one powder metering device (Pulverdosierer), a controller, a powder mass flow detector, a powder mass characterization device, and a powder switcher. In an embodiment, the at least one powder metering device may include, for example, one or more conveying belts, one or more pinch valves, one or more conveying disks, and / or one or more rotary conveyors.

[0008] In some embodiments, the controller may be comprised of multiple controllers. The controller may include, for example, one or more analog and / or digital circuits. In some embodiments, the control unit may be configured to control one or more output parameters in response to at least one input parameter.

[0009] The powder mass flow detector may be configured to determine the powder mass flow rate, for example, by gravimetric measurements, radiation attenuation measurements, reflectance measurements, and the like.

[0010] The powder changer may be configured to supply powder mass flows according to the control to different receivers, which may for example be a scale and / or a process head as a powder mass determining device.

[0011] According to the invention, at least one powder quantity delivery device is configured to supply the powder mass to the scale and / or to the processing head via the powder mass flow detector depending on the powder changer. This has the advantage that the powder mass flow rate can be adjusted without the powder mass being supplied to the processing head. On the other hand, once the powder mass flow rate is set (work preparation), switching to powder jet overlay welding is easy because the powder mass flow rate is uninterrupted. Supply interruptions can lead to fluctuations in the supply of the powder mass, especially when switching on.

[0012] According to the invention, the control unit is configured to calibrate the powder mass flow detector based on the powder mass flow measured by the balance. The powder mass flow detector may be used to monitor the powder mass flow during powder mass jet overlay welding. As a result, the calibration of the powder mass flow detector may increase the accuracy in monitoring the powder mass flow, since changes in the powder mass, in particular changes in the material and / or protective gas composition, may affect the detection sensitivity of the powder mass flow detector for the powder mass flow.

[0013] In an embodiment, the control unit may be configured to adjust the powder dispensing device based on the powder mass flow rate measured by the scale and the specified powder mass flow rate, which has the advantage that a precise adjustment of the powder mass flow rate to the specified powder mass flow rate is possible in situ, in particular before powder jet welding overlay.

[0014] In an embodiment, the control unit may be configured to adjust the powder mass discharge device based on the powder mass flow rate detected by the powder mass flow detector and the specified powder mass flow rate. This has the advantage that the powder mass flow rate can be monitored, especially during powder jet overlay welding. Since the powder mass flow detector can be calibrated using a scale before powder jet overlay welding, accurate monitoring of the powder mass flow rate is possible on the spot during powder jet overlay welding.

[0015] In a particularly efficient embodiment, the device includes a centrifuge, a gravitational separator, and / or an inertial separator between the powder changer and the balance to separate the powder mass from the gas or gas mixture. It is also conceivable to use other methods to separate the powder mass from the gas or gas mixture. Separating the powder mass from the gas or gas mixture has the advantage that the measurement of the powder mass flow rate using the balance becomes more accurate. For example, the shielding gas helium is less dense than air and therefore rises in an air-filled environment. As a result, for example, the measurement results of the balance can be distorted due to the buoyancy of the gas or the mass of the gas. Separating the powder mass from the gas or gas mixture prevents this distortion of the measurement results.

[0016] In a particularly stable embodiment, the controller may be configured to control the powder mass flow rate via one or more pinch valves. Pinch valves have the advantage that they are particularly resistant to clogging and reduce pressure spikes compared to other regulating valves. In particular in the case of a control loop, controlling the powder mass flow rate to a target flow rate can reduce oscillations and therefore reduce the time it takes for the oscillations to settle.

[0017] In a particularly cost-effective embodiment, the balance may be configured to measure the powder mass flow rate by measuring the mass of deposited solids at a time interval. Measurements of the mass of solids separated at time intervals may be determined, for example, by forming a difference. In a further embodiment, the balance may be recalibrated for this purpose or the zero point may be adjusted accordingly. For example, the accuracy may be increased by extending the time interval. This has the advantage that the powder mass flow rate may be measured relatively accurately with little effort.

[0018] In a particularly efficient embodiment, the control unit may be configured to perform the steps of: setting the feed rate per unit time of the at least one powder mass dispenser in the work preparation mode according to the specified powder mass flow rate and / or according to the powder mass flow rate measured by the balance; and calibrating the powder mass flow rate detector according to the specified powder mass flow rate and according to the powder mass flow rate measured by the balance. This has the advantage that the powder mass flow rate is accurately set by the powder mass determination device before the powder jet overlay welding and the powder mass flow rate is monitored during the powder jet overlay welding. Since the calibration is performed at the specified powder mass flow rate, the accuracy in monitoring the supplied powder mass flow rate can be increased, as a result of which in particular non-linear errors can be better corrected in the calibration. A powder mass flow rate that differs less from the specified powder mass flow rate leads to a more uniform application of the powder mass and an improved quality of the powder mass application.

[0019] In a particularly efficient embodiment, the control unit may be configured to at least: operate the powder switcher in the working mode to supply the powder mass to the processing head via the powder mass flow detector in order to perform the powder jet overlay welding; and monitor the powder mass flow rate in the working mode with the powder mass flow detector. This has the advantage that it is possible to switch from the work preparation mode to the working mode without having to interrupt the powder mass supply. As a result, it is possible to prevent the powder mass flow rate supplied at the specified powder mass flow rate from settling, especially at the start of the working mode. This leads to an improved quality of the powder mass application, especially when the powder jet overlay welding is started.

[0020] In particular in automated embodiments, the control unit may be configured to switch from the working mode to the working preparation mode if the difference between the powder mass flow rate detected by the powder mass flow detector and the specified powder mass flow rate exceeds a predefined value. This has the advantage that the powder jet build-up welding is interrupted if the build-up of the powder mass deviates too much from the specified powder mass application. This makes it possible to ensure a certain quality of the powder mass application. Furthermore, the powder mass flow rate can be adjusted again and / or the powder mass flow detector can be simultaneously recalibrated using the powder mass determination device. This also has the advantage that errors in the calibration of the powder mass flow detector can be eliminated in a simple manner. In this way, the desired powder mass flow rate during the powder jet build-up welding can be ensured in an automated manner.

[0021] According to the invention, the device may be configured to perform the following method. The method according to the invention may include the steps of supplying a powder mass, determining a powder mass flow rate of the supplied powder mass, calibrating a powder mass flow rate detector according to the determined powder mass flow rate, supplying a powder mass at the specified powder mass flow rate to the processing head via the powder mass flow rate detector, and monitoring the powder mass flow rate with the powder mass flow rate detector. The powder mass flow rate may be determined, for example, with a scale. The scale may be configured to measure the powder mass deposited on the scale over a predefined period of time. This may be done, for example, by setting a suitable zero point or by taking the difference between two measurement results. In an embodiment, the scale may include a powder mass receiver. In an embodiment, the scale may be configured to remove the powder mass of the powder mass receiver.

[0022] Particularly accurate embodiments may include a step of separating the powder mass from the gas or gas mixture before determining the powder mass flow rate. This has the advantage that the powder mass flow rate measured by the balance is not distorted by the gas or gas mixture. For example, helium has a smaller mass than air and therefore creates buoyancy in an air-filled space. If the powder mass is mixed with, for example, helium as a shielding gas, the balance will measure a lower powder mass flow rate if the powder mass is not previously separated from the helium.

[0023] In a particularly cost-effective embodiment, the powder mass flow rate may be measured using a scale.

[0024] A particularly efficient embodiment may comprise the step of activating a powder changer in order to change the feeding direction of the powder mass flow from the specific part to the processing head, which has the advantage that, in particular at the start of the powder jet build-up welding, settling during the powder mass feeding is avoided, since the powder mass is fed to the specific part with a uniform powder mass flow rate before the powder jet build-up welding.

[0025] In a particularly advantageous embodiment, the feed rate per unit time may be controlled as a function of the determined powder mass flow rate of the fed powder mass and as a function of the specified powder mass flow rate. This has the advantage that the powder mass flow rate can be relatively precisely adjusted / controlled prior to the powder jet overlay welding. Depending on the embodiment, the control unit may, for example, comprise a corresponding analog or digital closed loop control.

[0026] In a particularly advantageous embodiment, the supply amount per unit time may be adjusted depending on the detection value of the powder mass flow detector and depending on the specified powder mass flow rate. This has the advantage that the supplied powder mass flow rate during powder jet build-up welding can be controlled / adjusted depending on the powder mass flow rate detected by the powder mass flow detector. Thereby, the supplied powder mass flow rate can not only be monitored but also adjusted during powder jet build-up welding. The corresponding adjustment / control may be performed, for example, by a control unit and / or an analog or digital circuit.

[0027] In particular in an automated embodiment, the method may be performed again if the difference of the powder mass flow rate detected by the powder mass flow detector from the specified powder mass flow rate exceeds a predetermined value. This has the advantage that there is an automated switch between powder jet build-up welding and a precise adjustment of the powder mass flow rate, including the calibration of the powder mass flow detector, if it can be assumed that the delivered powder mass flow rate deviates from the specified powder mass flow rate by more than a limit value. If the difference of the powder mass flow rate from the specified mass flow rate is less than a predetermined value, powder jet build-up welding can be continued. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 shows a schematic diagram of an apparatus for measuring powder mass flow rate for powder jet overlay welding according to an embodiment of the present invention. [Diagram 2] FIG. 2 shows a schematic process flow diagram of a method according to an embodiment of the present invention. [Diagram 3] FIG. 3 shows a schematic process flow diagram of a method for measuring / determining powder mass flow rate according to an embodiment of the invention. [Figure 4] FIG. 4 shows a schematic diagram of an apparatus for measuring powder mass flow rate for powder jet overlay welding according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In some embodiments, components may be combined, split into multiple components, and / or additional components may be added without affecting the functionality of the invention. Steps may be swapped in order, performed in parallel, combined or divided, and / or additional steps may be added.

[0030] Figure 1 shows a schematic diagram of an apparatus 10 according to an embodiment of the invention for measuring the powder mass flow rate for powder jet welding build-up. In Figure 1, the powder mass flow (Pulvermassenstrom) is shown diagrammatically with solid arrows. The dashed lines show connections for signal and / or data exchange between different components. The connections for signal and / or data transmission may be wired and / or wireless.

[0031] In this embodiment, the powder mass is supplied by two powder dosing devices, namely powder dosing devices 11a and 11b. The powder dosing devices are configured to generate powder mass flows. The powder mass flows are combined in a Y-connection 13 to form a common powder mass flow. In an embodiment with a powder dosing device, the Y-connection may be optionally omitted. In an embodiment, particularly if the device includes multiple powder dosing devices, the device may include multiple Y-connections and / or alternatives such as mixers or multiple Y-connections (n-fold Y-connections (n-fache Y-Verbindungen)).

[0032] The common powder mass flow thus generated is sent to the powder switcher 15 via the powder mass flow detector 14. In response to the driving of the powder switcher 15, the powder switcher directs the powder mass flow to the processing head 16 and / or the scale 18. In this embodiment, the powder switcher is controlled by the control unit 20.

[0033] In this embodiment, the powder separator 17 is arranged between the powder changer 15 and the balance 16. It may be configured to separate the powder from the gas or gas mixture, in particular the shielding gas.

[0034] In an embodiment, the control device 20 may consist of a number of partially independent control devices, which are configured to control and / or regulate the powder dispensing devices 11a, 11b in response to detection data from the powder mass flow detector 14 and / or in response to data / signals from the balance 18 and a specified powder mass flow rate.

[0035] In this embodiment, the controller 20 is further configured to calibrate the powder mass flow detector 14 in response to the data / signal from the scale 18 and / or the specified powder mass flow rate. The scale 18 may be configured to measure the powder mass flow rate, for example, by measuring the mass of powder deposited on the scale 18 over a time interval. The powder mass flow rate is then obtained by dividing the measured powder mass by the length of the time interval.

[0036] In this embodiment, the control unit is configured to control the processing head. The processing head may be configured to be moved in one, two, or three directions. In an embodiment, the processing head may include a laser unit configured to introduce a predetermined energy into the laser processing area during powder jet overlay welding.

[0037] In an embodiment, the control unit is configured to direct the powder mass flow from the at least one powder dispensing device 11a, 11b in the work preparation mode by means of a powder switcher via the powder mass flow detector 14 to the scale. The powder mass is separated from the gas and gas mixture in an optional powder mass separator arranged upstream of the scale. In this embodiment, the control unit is configured to adjust and control the at least one powder dispensing device 11a, 11b such that a specified powder mass flow rate is measured by the scale 18. As a result, when the at least one powder dispensing device is adjusted, it is not necessary to calibrate the powder mass flow detector 14. The powder mass flow detector may be configured, for example, optically, by radiation means, or by contact to detect the powder mass flow rate. In an embodiment, the detection data of the powder mass flow detector is simply adjusted according to the calibration.

[0038] After the calibration of the powder mass flow detector, in this embodiment, powder jet build-up welding may be performed. In this embodiment, in order to switch to the working mode, i.e. the mode of powder jet build-up welding, the powder switcher 15 is actuated via a control signal, so that the powder mass flow is supplied to the processing head 16 instead of the balance. This allows switching from the work preparation mode to the working mode without interrupting the supply of the powder mass.

[0039] During powder jet overlay welding, the powder mass flow rate is monitored using a powder mass flow detector, thereby ensuring a constant powder mass flow rate.

[0040] In an embodiment, the control unit may be configured to interrupt or abort the powder jet build-up welding if the difference of the powder mass flow rate detected by the powder mass flow detector from a specified powder mass flow rate exceeds a predetermined limit value. For this purpose, the powder changer 15 may be activated by the control unit 20 such that the powder mass flow is fed from the powder changer 15 to the balance 18. The powder mass flow rate is then adjusted again by means of the balance and, if necessary, the powder mass flow detector may be calibrated.

[0041] In an embodiment, the control unit may be configured to interrupt or stop the powder jet welding build-up based on an external signal, for example a detection signal from a detector for checking the powder mass deposition. In a variant, this may mean that there is a change from a working mode to a working preparation mode, or that the powder jet welding build-up is stopped.

[0042] FIG. 2 shows a schematic flow chart of the process of a method according to an embodiment of the invention. In a first step S11, a powder mass is supplied. The powder mass is preferably suitable as powder for powder jet overlay welding. In a second step S12, the powder mass flow rate of the supplied powder mass is determined. In a next step S13, depending on the determined powder mass flow rate, it is checked whether the powder mass flow rate deviates from the specified powder mass flow rate by more than a predefined tolerance. If the difference is greater than the tolerance, the supply of the powder mass is adjusted via step S14 and the powder mass flow rate is determined again in step S12. If the difference is less than the tolerance, the powder mass flow rate detector is calibrated in step S15 with the determined powder mass flow rate.

[0043] Based on the preparation for powder jet build-up welding in steps S11 to S15, powder jet build-up welding can be performed in step S16. In order to switch from the preparation step to the step of performing powder jet build-up welding S16, for example, a powder switcher may be operated to change the supply direction to the processing head for powder jet build-up welding, instead of the specifying unit that specifies the powder mass flow rate as shown in step S12.

[0044] During powder jet overlay welding S16, the powder mass flow rate is monitored using a powder mass flow detector in steps S16a, S17-S19. In step S16a, the powder mass flow rate is detected by the powder mass flow detector. In step S17, it is checked whether the difference of the powder mass flow rate detected by the powder mass flow detector from a specified powder mass flow rate is greater than a predetermined tolerance. If the difference is greater, the powder jet overlay welding is interrupted and processing continues with step S12 of determining the powder mass flow rate. In some embodiments, when steps S12-S16 are performed again, step S15 of calibrating the powder mass flow detector may be omitted.

[0045] If the difference of the detected powder mass flow rate from the specified powder mass flow rate is within the tolerance, then in step S18 it is checked whether the detected powder mass flow rate corresponds to the specified value. If the detected powder mass flow rate corresponds to the specified powder mass flow rate, then the execution of the powder jet overlay welding continues in step S16. If the values ​​do not match, then the powder mass supply is adjusted in step S19 and the process continues to step S16 where the powder jet overlay welding is also performed.

[0046] In an embodiment, step S16 of performing powder jet overlay welding may be continued after step S18 if the difference of the detected powder mass flow rate from the specified powder mass flow rate is below a further tolerance. Otherwise, processing continues to step S19 of adjusting the powder mass supply. In an embodiment, the tolerance values ​​of steps S17 and S18 may be the same value.

[0047] In an embodiment, steps S16, S16a, S17-S19, particularly including monitoring the powder mass flow rate during powder jet build-up welding using a powder mass flow detector, may, for example, be performed in a different order, may employ additional steps, or may be at least partially combined.

[0048] 3 shows a schematic flow chart of the process of a method for measuring / determining powder mass flow rate according to an embodiment of the present invention. With the start of the method S21, in step S22, the powder mass flow rate i is calculated according to the conveying disk speed n. ist In this embodiment, the powder dispensing device is a conveying disk. In this embodiment, the specified powder mass flow rate i soll are transmitted in parallel. After the start of the method, a measurement cycle S24 begins.

[0049] Depending on whether a cycle has just started with the powder changer to scale activated, step S26 or step S25 is performed. If the cycle started from a stopped state, step S26 causes the powder carrier / powder dispenser to wait for 60 seconds in this exemplary embodiment. If the powder changer to scale has been activated, step S25 causes the powder changer to wait for 30 seconds in this exemplary embodiment. Steps S25 and S26 may be omitted if the powder changer has not been activated or if the powder feeder has not been activated from a stopped state.

[0050] In the next step S27, a first measurement of the powder mass m0 is made on the balance. In a further step S28, a time interval / measurement duration T is waited, in this exemplary embodiment 30 seconds. During the time interval / measurement duration T, the powder mass flow is fed to the balance. Then, in step S29, a second measurement of the powder mass m1 is made. In a next step S30, the equation i ist = (m1-m0) / T to determine the powder mass flow rate.

[0051] In a further step S31, the powder mass flow rate i soll The difference between the specified powder mass flow rates is determined. In this exemplary embodiment, the difference is determined according to the formula |i soll -i ist | / i soll If the difference is less than a predetermined tolerance, in this exemplary embodiment 1%, the specified powder mass flow rate i soll Conveying disk speed for feeding n erfis determined at the conveying disk speed n, and the measurement / determination of the powder mass flow rate i can be completed in step S33.

[0052] If the difference is greater than a predefined tolerance, the speed n of the conveying disk is adjusted in step S34. In some embodiments, the reaction time of the powder dispensing device may be waited for in step S35, in this exemplary embodiment 20 seconds, before the cycle starts again in step S24.

[0053] FIG. 4 illustrates one embodiment of the present invention for measuring powder mass flow rate for powder jet overlay welding. 1 shows a schematic diagram of an apparatus according to the present invention. In this embodiment, pinch valves 11a, 11b meter the powder supplied by powder conveyors 41a, 41b. The resulting powder flows are combined into one flow by a Y-connection 13. In this exemplary embodiment, the pinch valves are controlled via a directional valve for driving one or more dosing devices. The powder mass flow is supplied from the Y-connection 13 to a powder changer 15 via a powder mass flow detector 14.

[0054] As shown in this embodiment, the powder changer 15 may be controlled by a directional control valve for driving the powder changer 43. The powder mass flow can be fed to the processing head 16 via the powder transfer 16a. Furthermore, the powder mass flow can be fed onto the scale 18. The powder separator 17 may be arranged in the conveying path between the scale 18 and the powder changer 15. In an embodiment, the directional control valve for driving the one or more dosing devices 42, the directional control valve for controlling the powder changer, the scale 18, the mass flow detector 14, the powder separator, and / or the processing head may be connected to each other, for example, via one or more controllers.

[0055] The controller may be configured to control / adjust the powder mass flow rate, for example, using a directional control valve for driving one or more dispensing devices 42 based on data / signals provided by the powder mass flow detector 14 and / or the scale 18. In an embodiment, the controller may be configured to control the powder switcher by a directional control valve for driving the powder switcher, thereby switching between a work preparation mode and a work mode of the powder jet overlay welding.

[0056] In the work preparation mode, the specified powder mass flow rate may be adjusted by the balance 18, the directional control valve for driving the one or more constant rate dispensers 42 and the one or more constant rate dispensers 11a, 11b. The powder mass flow detector 14 may preferably be calibrated after the powder mass flow rate is adjusted. After that, in order to switch to the work mode without interruption, the powder mass flow may be supplied to the processing head 16 by activating the directional control valve for driving the powder switcher 43. While the powder is being supplied to the processing head 16, the supplied powder mass flow may be monitored by the powder mass flow detector 14.

[0057] In an embodiment, the control unit may be configured to automatically switch to a work ready mode and adjust the powder mass flow rate again if the powder mass flow detector 14 detects an excessive deviation from the predefined value. This has the advantage that it is ensured that the powder mass flow rate corresponds to the target value, for example when powder from a first batch is used up during powder jet build-up welding and powder from a second batch is supplied. [Explanation of symbols]

[0058] 11a,11b Powder quantitative dispensing device 13 Y connection part 14 Powder mass flow detector 15 Powder Changer 16 Processing head 16a Powder transfer to processing head 16 17 Powder separator 18 Scales 20 Control section 41a, 41b Powder carrier 42 Directional control valve for driving one or more constant rate dispensers 43 Directional control valve for driving the powder changer i ist Measured / specified powder mass flow rate i soll Specified powder mass flow rate T Time interval / measurement duration m0 1st weight measurement m1 2nd weight measurement n Transport disc speed n erf i soll Speed ​​of conveying disc for feeding

Claims

1. 1. An apparatus (10) for measuring a powder mass flow rate for powder jet overlay welding, comprising: At least one powder dispenser (11a, 11b), A control unit (20); Including, The apparatus comprises: A powder mass flow detector (14); A powder mass characterization device (18); A powder changer (15); Including, said at least one powder dispenser (11a, 11b) being adapted to supply a powder mass to a powder mass determining device (18) and / or a processing head (16) via said powder mass flow detector (14) in response to said powder switcher (15); the control unit (20) is configured to calibrate the powder mass flow detector (14) based on the powder mass flow rate measured by the powder mass characterizing device (18); 13. The apparatus according to claim 12, further comprising a centrifuge, gravitational separator and / or inertial separator (17) for separating powder mass from gas or gas mixture between said powder changer (15) and said powder mass determination device (18).

2. 2. The apparatus of claim 1, wherein the control unit (20) is configured to adjust the powder mass flow rate dispenser (11a, 11b) based on the powder mass flow rate measured by the powder mass characterizing device (18) and a specified powder mass flow rate.

3. 3. The apparatus according to claim 1 or 2, wherein the control unit (20) is configured to adjust the powder mass flow rate dispenser (11a, 11b) based on the powder mass flow rate detected by the powder mass flow detector (14) and a specified powder mass flow rate.

4. The control unit (20) controls the powder quality via one or more pinch valves (11a, 11b).

4. An apparatus according to any one of claims 1 to 3, configured to control a volume flow rate.

5. 5. Apparatus according to any one of claims 1 to 4, wherein the powder mass characterisation device (18) is configured to measure the powder mass flow rate by measuring the mass of deposited solids over a time interval.

6. In the work preparation mode, the control unit (20) - adjusting the feed rate of said at least one powder dispenser (11a, 11b) per unit time in response to a specified powder mass flow rate and in response to the powder mass flow rate measured by said powder mass determining device (18); and calibrating the powder mass flow detector (14) in response to a specified powder mass flow rate and / or a powder mass flow rate measured by the powder mass characterizing device (18).

7. In order to perform powder jet build-up welding, the control unit (20) includes at least in an operating mode, activating the powder changer (15) to supply the powder mass to the processing head (16) via the powder mass flow detector (14); monitoring powder mass flow rate with said powder mass flow detector (14) in an operational mode; 7. An apparatus according to claim 1, configured to:

8. 8. The apparatus of claim 7, wherein the control unit (20) is configured to switch from an operating mode to an operating preparation mode when a difference between the powder mass flow rate detected by the powder mass flow detector (14) and a commanded powder mass flow rate exceeds a predetermined value.

9. 1. A method for measuring powder mass flow rate for powder jet overlay welding, comprising: feeding a powder mass to a powder mass characterization device (18) via a powder mass flow detector (14); - separating the delivered powder mass from the gas or gas mixture by means of a centrifuge, gravitational separator and / or inertial separator (17); determining a powder mass flow rate of the delivered powder mass by said powder mass determining device (18); calibrating said powder mass flow detector (14) in response to the determined powder mass flow rate; activating a powder changer (15) to change the feeding direction from the powder mass characterization device (18) to the processing head (16); supplying a powder mass to the processing head (16) via the powder mass flow detector (14) at a specified powder mass flow rate; monitoring powder mass flow rate with said powder mass flow detector; Including, A method wherein the step of determining the powder mass flow rate occurs after the step of separating the delivered powder mass.

10. The method of claim 9 , wherein the powder mass flow rate is measured using a balance.

11. 11. The method according to claim 9 or 10, wherein the amount of powder fed per unit time is controlled in dependence on a specified powder mass flow rate of the fed powder mass and in dependence on a specified powder mass flow rate.

12. 12. The method according to any one of claims 9 to 11, wherein the amount of feed per unit time is adjusted in response to the detection value of the powder mass flow detector (14) and in response to a specified powder mass flow rate.

13. 13. The method according to any one of claims 9 to 12, wherein the method is performed again when the difference of the powder mass flow rate detected by the powder mass flow detector (14) from a designated powder mass flow rate exceeds a predetermined value.

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