Conductance-based control system for additive manufacturing

Abstract

A control system for adjusting an additive manufacturing process of an additive manufacturing device configured to add metal to a substrate by metal deposition. The additive manufacturing device includes a nozzle for outputting a metal strip, the nozzle positioned at a distance from the substrate and configured to move in X, Y, and Z axes relative to the substrate via a position actuator. The device further includes a heat source configured to melt the metal strip into a molten pool on the substrate, and a power source configured to supply current to the substrate through the metal strip. The control system determines an electrical conductance between the metal strip and the substrate by measuring at least one electrical property of the supplied current, determines a difference between the determined electrical conductance and a desired electrical conductance, and adjusts at least one of the distance from the substrate to the nozzle, the speed of movement of the nozzle relative to the substrate, the amount of current supplied, the heat supplied by the heat source, and / or the output speed of the metal strip based on the difference to maintain process stability during deposition of the metal layer.

Description

Technical Field

[0001] The inventive concept described in this specification generally relates to a control system for controlling an additive manufacturing process. The control system determines (judges) and controls based on the difference between the measured conductance and a desired nominal conductance.

Background Art

[0002] The process of metal additive manufacturing is a technique of melting a metal wire by using a heat source, such as a laser, to form a metal deposit. Therefore, this process can be described as a metal printer. That is, other terms used in this technology are laser metal deposition and directed energy deposition. This technology is advantageous in many industries, such as the aerospace industry, because it can provide high-throughput manufacturing of complex-shaped products while minimizing waste of expensive raw materials.

[0003] Generally, the principle of this process can be described as a high-power laser that creates a pool of molten metal on a workpiece or substrate to which a wire is supplied. The high temperature of the molten pool and the laser radiation heats and melts the wire. The wire feeder is attached to a processing tool that is moved along a deposition path by an industrial robot together with the laser optics. Thereby, the molten wire solidifies along this deposition path and beads are formed. These beads are arranged side by side and stacked in several layers to form a 3D structure on the substrate using appropriate robot movements. However, this process is very susceptible to disturbances and exhibits non-linear behavior with respect to the shape of the deposit and the input parameters. The positioning of the tool relative to the substrate and the wire feed rate are essential for maintaining a stable deposition process. If the distance between the tool and the workpiece is appropriate, a continuous transfer of material from the solid wire to the molten pool takes place. If the distance is too large, a neck is formed in the material transfer, which is essentially a weak link. If the distance further increases, this neck may break, in which case the wire is melted independently of the substrate. Droplets accumulate at the wire tip before growing too large to be finally maintained by surface tension and falling onto the substrate. The movement of these droplets gives an uneven surface and is not very suitable for further deposition. If the distance is too small, the wire protrudes through the molten pool to the solid substrate, which is called "stubbing". Thereby, the wire vibrates rapidly from side to side, rubbing the unmelted part of the substrate, thereby causing a lack of fusion defect in the deposited material. The disturbance of the distance can be caused by process variations resulting from the geometric shape of the deposit, temperature accumulation, or inadequate planning of the deposition path.

[0004] Furthermore, additional output parameters in the deposition process may cause disturbances in the process, resulting in a decrease in the stability or performance of the process.

[0005] In any case, it is essential to well control the distance between the wire tip and the molten pool on the substrate. In this regard, Patent Document 1 (GB2551163A) discloses laser metal deposition using a laser configured to melt a wire, a nozzle configured to extrude the wire, a DC current source configured to supply a current to the substrate through the extruded wire, and a wire device with a Wheatstone bridge and related processes. Here, the resistance between the nozzle and the substrate forms one resistance Rx of the Wheatstone bridge, and the remaining part of the Wheatstone bridge is powered by an AC voltage source insulated from the DC current source by a capacitor C and / or a bandpass filter F. The device enables a combination of thermoelectric resistance heating and in-situ measurement of the resistance of the nozzle from the substrate to the molten pool to determine the distance between the tool and the substrate surface.

[0006] Non-Patent Document 1 describes an iterative feedforward control process and system for an additive manufacturing process. The feedforward control process uses measured resistance data collected during the deposition of a single layer, after the deposition of a layer, and before the deposition of subsequent layers. The measured resistance data is filtered and supplied to a resistance-distance regression model. The system is purely feedforward in terms of distance and cannot be used for feedback control during layer deposition. According to the system of Non-Patent Document 1, the measured resistance data is not very suitable for feedback control, at least in part, due to "noisy resistance signals that cause operating errors or require low-pass filtering, thus increasing the time lag or resulting in insufficient high-frequency response of the control loop".

[0007] Non-Patent Document 2 describes a method for online control (during single-layer deposition) of laser metal wire deposition based on a resistance model for determining the distance of the chip from the workpiece based on resistance. In contrast to Non-Patent Document 1, the feedback system of Non-Patent Document 2 is a feedback controller, but filtering of the resistance signal is essential, so the processing requirements necessary for the system increase. Also, since the controller is based only on determining the distance from the wire tip to the workpiece, it only controls this distance and other process parameters remain uncontrollable.

[0008] The relationship between resistance and distance is quite complex and depends on many parameters such as the position, temperature, and area of the wire tip. Furthermore, high requirements for both speed and accuracy often exist to meet the requirements imposed on manufacturing. Additionally, the process has additional parameters other than distance that can affect the stability and performance of the process. Therefore, better control of the manufacturing process is needed.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Non-Patent Documents

[0010]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

[0011] Accordingly, the present invention preferably seeks to reduce, alleviate or eliminate one or more of the previously identified drawbacks and disadvantages in the art, either alone or in any combination, and solves at least the aforementioned problems by providing a control system for adjusting the additive manufacturing process of an additive manufacturing apparatus, the apparatus being configured to add metal to a substrate by metal deposition. The apparatus of the present invention comprises a nozzle for outputting a metal strip, the nozzle being configured to be disposed at a distance from the substrate and to move relative to the substrate in the XYZ axes via a position actuator. The apparatus further comprises a heat source configured to melt the metal strip into a molten pool state on the substrate and a power source configured to supply an electric current to the substrate via the metal strip. The control system determines (or judges) the electrical conductance between the metal strip and the substrate by measuring at least one electrical characteristic of the supplied current, determines (or judges) the difference between the determined electrical conductance and a desired electrical conductance, and based on the difference between the determined conductance and the desired conductance, adjusts at least one of the distance from the substrate to the nozzle, the moving speed of the nozzle relative to the substrate, the amount of current supplied, the heat supplied by the heat source, and / or the output speed of the metal strip during the deposition of the metal layer so as to maintain process stability.

[0012] The process has the advantage that control of a number of process parameters is possible. Further, a computationally complex empirical regression model from resistance-to-distance is not required.

[0013] A process for controlling the additive manufacturing process is also provided.

[0014] An additive manufacturing apparatus provided with a control system is provided.

[0015] Further advantageous embodiments are disclosed in the dependent claims of the appended patent claims.

[0016] These and other aspects, features and advantages of the present invention will become apparent and be elucidated from the following description of embodiments of the present invention with reference to the accompanying drawings below.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2a-c

Figure 3a-g

Figure 4a-g

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0018] The following description of the present invention relates to a control system 500 for an additive manufacturing process, an additive manufacturing system, and a method for controlling the additive manufacturing system. The control system 500 maintains system performance by maintaining a nominal conductance. An additive manufacturing apparatus controllable via the control system 500 is configured to add metal to a substrate 30 by metal deposition. The apparatus includes a nozzle 10 for outputting a metal strip 20, a heat source 300 configured to melt the metal strip 20 by supplying heat 301, and a power source 400 configured to supply an electric current to the substrate 30 via the metal strip 20. The control system 500 determines (judges) the electrical conductance between the metal strip 20 and the substrate 30, determines the difference between the determined conductance and a desired nominal electrical conductance, and maintains process stability by adjusting output process parameters so that the nominal electrical conductance is maintained. The apparatus is preferably a laser metal wire deposition (LMD-w) apparatus. The output parameters are at least one of the distance from the substrate 30 to the nozzle 10, the moving speed of the nozzle 10 relative to the substrate 30, the amount of current supplied, the heat 301 supplied by the heat source 300, and / or the output speed of the metal strip 20.

[0019] The inventors have confirmed that general process stability has a linear relationship with conductance. As used herein, general process stability refers to the general performance and robustness of the additive manufacturing process. A stable process is a process that avoids the molten wire forming at the distal end of the substrate 30 (a process that avoids), i.e., potentially causing a catastrophic process failure when melting occurs at a location other than the melt pool 35 and the nozzle 10 becomes filled with molten metal, the aforementioned "stabbing", overheating of the substrate 30, and other critical process conditions.

[0020] The linear relationship between general process stability and conductance enables the use of relatively simple controllers. For example, a conventional proportional, integral, derivative (P, PI, or PID) feedback controller can be used to control an additive manufacturing process via a control system 500. The conductance-based control system 500 does not have to be based solely on a P, PI, or PID control system. For example, the control system 500 can use one or several other control techniques to implement conductance-based control. For example, bang-bang control can be used to control an output parameter or several parameters. Bang-bang control may be particularly suitable for controlling the heat 301 supplied by a heat source. For example, the heat 301 supplied by a heat source can be controlled by turning the heat source 300 on / off to adjust the supplied heat. The control system 500 can be based on sliding mode control. The control system 500 can combine several known control techniques to control several output parameters. The control system 500 can control each of the output parameters by different control techniques. Although different specific control implementations have been described, the control system 500 described herein is a conductance feedback control system 500 that can control an additive manufacturing process during layer deposition to maintain a nominal conductance.

[0021] The control system 500 is an online feedback system in which the measurement of conductance and the determination (judgment) of the difference between the measured conductance and the desired nominal conductance are performed at high speed. The high speed depends on the specific implementation devices used in the system, but can range from several times per second to several hundred times per second or more. Therefore, the system can be considered continuous, without the need to scan the workpiece surface and without checking for errors or disturbances after the layer has been deposited, in contrast to previous systems.

[0022] Figure 1 shows a schematic diagram of a deposition system showing a substrate 30 and a metal strip 20 extending from a nozzle 10. The tip (front end) 25 of the metal strip 20 is heated by heat 301 from a heat source 300 to form a molten pool 35 on the surface of the substrate 30. The distance from the nozzle 10 to the substrate 30 is defined as d, and the length of the strip 20 extending from the nozzle 10 is defined as l.

[0023] Figures 2a - 2c show schematic diagrams of the deposition system where the nozzle 10, the metal strip 20, and the metal strip tip 25 are at different heights d from the surface of the substrate 30. Figure 2a shows a nominally stable system where the height of the tip 25 is at the optimal distance d from the substrate 30. nom Figure 2a represents an ideal state where the molten pool 35 forms as desired on the surface of the substrate 30. In Figure 2b, the distance is less than the optimal distance and stubbing occurs (as described in the background art section). In Figure 2c, since the distance is greater than the optimal distance d, a weak link W is formed. nom

[0024] This control system 500 is designed to adjust process parameters based on the measured conductance so as to avoid the adverse conditions shown in Figures 2b and 2c.

[0025] As described in the background art section, previous control systems were both (i.e.) feed - forward control systems and feedback control systems, based on providing a resistance model for the distance and then controlling the distance of the nozzle 10 from the substrate 30 based on the measured resistance.

[0026] ​The distance of the metal strip chip 25 from the molten pool 35 or the substrate 30 is not specifically modeled and does not necessarily have to be the output of the control system 500. That is, the controller can control other process parameters based on the measured conductance in addition to or instead of the distance of the wire chip from the molten pool 35 to maintain process stability. The control system 500 can control, for example, the moving speed of the nozzle 10 relative to the substrate 30, the amount of current supplied to the metal strip 20, the heat 301 supplied by the heat source 300, and / or the output speed of the metal strip 20. Each or a combination of the above process parameters may be maintained via a conductance-based feedback control system 500.

[0027] To further explain FIG. 1, the nozzle 10 is held at a distance d from the nozzle 10 above the substrate 30 to the substrate 30, and the distance from the nozzle 10 to the substrate 30 is perpendicular to the deposition direction indicated by the arrow in FIG. 1. The wire strip 20 is supplied to the nozzle 10, and the tip 25 of the metal strip 20 is extruded from the end so as to be close to or in physical contact with the substrate 30. In the embodiment shown in FIG. 1, the heat source 300 is a laser, and a laser beam 301 is directed from this laser toward the protruding tip 25 of the metal strip 20 and the substrate 30. The laser beam 301 melts the metal strip 20 into a molten pool 35 state on the substrate 30. The nozzle 10 and simultaneously the laser beam 301 are moved in the deposition direction at a controllable speed. In addition to moving in the deposition direction, the nozzle 10 is moved up and down along the axial direction to adjust the distance d of the wire tip 25 from the nozzle 10 to the substrate 30 according to the measured conductance input given by the control system. The power supply 400 establishes a current flowing from the metal strip 20 toward the substrate 30. In the above description, the distance d is the distance of the wire tip 25 from the substrate 30. Since the length of the wire extending from the nozzle 10 is generally known, in some aspects, d can also be considered as the distance of the nozzle 10 from the substrate 30.

[0028] The inventors have confirmed that a control system 500 is provided that can control additional output parameters in addition to the parameter of the distance from the wire tip 25 to the base material 30 by controlling the conductance and maintaining the nominal conductance, thereby maintaining process stability.

[0029] A control system 500, which can be described as a multi-output parameter conductance-based feedback control system, includes an additive manufacturing apparatus configured to add metal to a base material 30 by metal deposition. The apparatus includes a nozzle 10 for outputting a metal strip 20, a heat source 300 configured to melt the metal strip 20 into a molten pool 35 on the base material 30, and a power source configured to supply an electric current to the base material 30 through the metal strip 20. The control system 500 determines (judges) the electrical conductance between the metal strip 20 and the base material 30. Thereafter, the control system 500 compares the conductance with the nominal conductance. Thereafter, the control system 500 adjusts at least one of the distance from the base material 30 to the nozzle 10, the moving speed of the nozzle 10 relative to the base material 30, the amount of the supplied electric current, the heat supplied by the heat source 300, and the output speed of the metal strip 20 based on the difference between the determined conductance and the nominal conductance. Thereby, the system is controlled by maintaining the nominal conductance during the additive manufacturing process. The control system 500 does not need to determine the distance of the metal strip 20 from the base material 30, and thus does not need to implement a complex regression model within the control system 500.

[0030] The multi-output parameter feedback control system 500 based on conductance can control a plurality of process parameters based only on conductance and does not require modeling of the distance as a function of electrical characteristics. Therefore, it is an improved system compared to the control system based on resistance to distance as described above.

[0031] As described above, the additive manufacturing apparatus includes a nozzle 10 for outputting a metal strip 20 and at least one position actuator 200 for moving the nozzle 10 relative to a substrate 30. The nozzle 10 may be moved relative to the substrate 30 along the XYZ axes via the position actuator 200. That is, the position actuator 200 can move the nozzle 10 along the XY axes along the length and width of the substrate 30. The position actuator 200 controls the position of the nozzle 10 on the Z axis, which is the height axis, toward and away from the substrate 30. The Z axis is generally an axis perpendicular to the deposition direction.

[0032] The position actuator 200 may be any one or a combination of a single-axis linear actuator, an industrial robot, a gantry system, an orbital welding system, a Stewart platform, or a custom-made position actuator 200. The position actuator 200 preferably comprises a combination of a low-resolution actuating component capable of multi-axis movement such as a robot and a high-resolution single-axis actuating component such as a linear actuator. Such a position actuator enables both rapid and accurate movement of the nozzle 10 relative to the substrate 30.

[0033] The position actuator 200 adjusts the position of the nozzle 10, including the protruding tip of the metal strip 20 relative to the substrate 30. The bandwidth of the actuator may preferably be significantly larger than the variation in the surface profile of the substrate 30. Thereby, the position actuator 200 can preferably adjust the axial position of the nozzle 10 or alternatively the feedstock material tip 25 with an amplitude larger than the topological variations of the surface of the substrate 30 in order to avoid physical encounter between the nozzle 10 and the surface of the substrate 30. Thus, the tip of the metal strip 20 can move up and down axially at high speed and follow the profile of the substrate 30. Also, the aforementioned bandwidth of the actuator 200 includes the lateral XY-axis speed of the actuator 200 and thus the lateral XY-axis speed of the nozzle 10 relative to the substrate 30.

[0034] The position actuator 200 may be a robotic arm. For example, the position actuator may be a six-axis robotic arm. The nozzle 10 is positioned at the distal end of the robotic arm.

[0035] The heat source 300 supplies the heat 301 necessary to melt the metal strip 20. The heat source 300 may be, for example, an electric arc, plasma, resistance heating, induction heating, flame, laser, or alternatively an electron beam. The latter two examples, i.e., an electron beam or a laser beam, may be directed towards the substrate 30 and the extruded wire strip to melt them into a molten pool state on the substrate 30. In the following experimental examples, the heat source 300 is a laser beam.

[0036] The power for establishing a current between the metal strip 20 and the substrate 30 may be supplied by a battery source or a welding source. Alternatively, other power sources such as an AC voltage source, a DC voltage source, a voltage regulating source, a current regulating source, or any other different power source may supply the required power.

[0037] The control system 500 determines the conductance between the substrate 30 and the metal strip 20.

[0038] The conductance may be determined by measuring the potential at a first position such as the nozzle 10, the supply material actuator 200, and / or a contact point on the metal strip 20 spaced from the substrate 30, and the potential at a second point such as the substrate 30 or ground. There may be a potential difference between the non-molten wire strip and the substrate 30. In this case, the measurement may be performed between any conductive object in contact with one point of the metal strip 20.

[0039] The control system 500 can determine (judge) the conductance by measuring the current between the power supply and at least one of the wire strip 20, the base material 30, and / or the ground. The current sensor may be a Rogowski coil, a current transformer, a Hall effect sensor, a fluxgate sensor, a magnetoresistive sensor, and a shunt resistor, or a combination thereof.

[0040] In the control system 500 where a shunt resistor is used to measure the current, the shunt resistor is arranged in series with the process, that is, in series with the metal strip 20 and the base material 30. By measuring the voltage across the clearly defined resistance of the shunt resistor, the current passing through the process, that is, the current between the base material 30 and the metal strip 20, can be determined (judged).

[0041] In some embodiments, the measured current can be filtered or (processed). This makes the processing of the system complex, but in some embodiments, the control can be improved by the increased complexity. The signal processing can include filtering, and the filtering can include low-pass filtering, band-pass filtering, notch filtering, or non-linear filtering, or a combination of these filtering processes.

[0042] The signal filtering may be performed by averaging. In addition to or instead of this, the signal processing may be performed by artificial intelligence signal processing. The signal processing may be implemented, for example, by at least one DSP, FPGA, microcontroller, SoC, single-board computer, PLC, or PC, or a combination thereof. The filtering of the signal may be performed by one or more analog components.

[0043] The control system may include a measurement module. The control system may include a processing module.

[0044] The measurement of electrical characteristics may be performed by a measurement module. That is, the measurement of conductance may be performed by a measurement module including, for example, a current sensor. The measurement module can distribute the measured conductance to a controller of the control system 500.

[0045] The filtering of the conductance signal may be performed by a processing module. That is, the above-described filtering may be performed by a processing module.

[0046] The advantage of having a separate measurement module and / or a separate processing module is that it enables the addition of processing capabilities to the system when they are implemented in separate modules. Measurement and / or filtering do not have to be performed by the same processor that outputs processing parameters to the controlled device of the system 500.

[0047] However, the control system 500 or the additive manufacturing system can be described as including means for measuring the electrical characteristics themselves. That is, the measurement module and the processing module are terms used to describe the implementation and architecture of current measurement and filtering within the system, but the architecture does not necessarily affect the performance of the control system.

[0048] The feedstock material, which is the metal strip 20, may be a solid wire or alternatively a metal wire such as a core wire. Or, the metal strip 20 may be a metal band, or any other metal shape having a high aspect ratio, that is, having an end diameter smaller compared to its length.

[0049] In this case, the feedstock actuator may be a wire feeder, or alternatively a band feeder in the case of a metal band.

[0050] The nominal desired conductance value may be determined experimentally. That is, a process may be performed in which the conductance is continuously measured or sampled, and then the process is analyzed to determine the conductance when the process was optimal. For example, a trial layer may be deposited. During deposition of the trial layer, the conductance is measured. The measured conductance is compared to process stability. The nominal conductance may be the measured conductance value when the process is determined (judged) to be stable, ideal, etc. The nominal desired conductance may be determined by simulation. The control system 500 and the additive manufacturing system may be modeled, and a simulation may be performed that defines the nominal desired conductance. Also, the nominal conductance may be regarded as the target conductance. The term nominal as used herein refers to the fact that a particular conductance value can be determined for each particular system and process and can depend on parameters such as the heat source 300, the material of the substrate 30, the desired deposition rate, etc.

[0051] The control system 500 may comprise a known controller implementation such as a P, PI, or PID, bang-bang, sliding mode, excitation signal, etc. controller. The controller may be implemented by various devices known in the art. The controller may be implemented via an FPGA, a microcontroller, an SoC, a single board computer, a PLC or a PC, or a combination thereof. The control system 500 receives an input signal that includes at least the measured conductance.

[0052] Figure 6 is a schematic diagram of the main steps for performing an additive manufacturing process using the conductance-based control system 500 of the present invention. In step 501, a substrate 30 is provided (supplied). The substrate 30 is the surface on which the additive manufacturing process is to be performed, as described above. In step 502, a nozzle 10 for outputting a wire strip is provided above the substrate 30. As described above, the nozzle 10 can be positioned by a robotic actuator such as a standard six-axis robotic arm. The nozzle 10 may be positioned by a robotic actuator via a linear actuator at the end of the robotic arm. The linear actuator can be used for more accurate positioning of the nozzle 10 relative to the substrate 30 than is possible with a robotic actuator. In step 503, a metal strip 20 is supplied to the nozzle 10. In step 504, the metal strip 20 is output from the nozzle 10, i.e., a stock of material is supplied from within the nozzle 10 through the nozzle 10 to the outside of the nozzle 10. Thereafter, a deposition process is started at 505, where the metal strip 20 is melted to form a melt pool or is melted into a melt pool state after the process has started. Melting of the metal strip 20 is performed via a laser heat source 300 in the LMD-w system and process. In some cases, additional or alternative heating may be performed by supplying an electric current through the metal wire such that the metal wire is melted. In step 506, the conductance between the molten metal strip 20 and the substrate 30 is determined (judged). The conductance may be determined (judged) by measuring the electric current passing through the metal strip 20 and the substrate 30 and the voltage difference between the metal strip 20 and the substrate 30. To determine the conductance, a power supply is configured to supply an electric current to the substrate 30 via the metal strip 20. Thereafter, the process parameters can be controlled in 507 using the measured conductance determined (judged) in 506.Process parameters that can be controlled by maintaining the nominal conductance may be the distance from the nozzle 10 to the substrate 30, i.e., the position of the robotic arm, the linear actuator, or both, the speed of movement of the nozzle 10 relative to the substrate 30, i.e., the speed of movement of the robotic arm relative to the substrate 30, the amount of current supplied to the metal strip 20 via the power supply, the heat supplied by the heat source 300, i.e., in the case of an LMD-w system, the laser output power, and / or the rate of output of the metal strip 20 from the nozzle 10.

[0053] Figure 7 is a block diagram showing different components of an additive manufacturing system. Block 10 is a nozzle 10 equipped with a feedstock actuator for supplying the metal strip 20. Block 200 is a position actuator 200 for moving the nozzle 10, including the feedstock actuator. As described above, the position actuator 200 may comprise a robotic arm and a linear actuator. Block 300 is a heat source 300, which in an LMD-w system is a laser heat source 300 for melting the metal strip 20 supplied from the feedstock actuator. Block 400 is a power supply that supplies a current between the metal strip 20 and the substrate 30 and enables measurement of the conductance between the metal strip 20 and the substrate 30. Block 500 is a control system 500 or a controller. The control system 500 may receive input signals from each component, or may receive only an input signal from the power supply, i.e., the measured conductance. Optional signals are indicated by dashed lines. The control system 500 determines (judges) the difference between the measured conductance and the nominal desired conductance and outputs a signal to the system components. The control system 500 may receive input signals, i.e., the measured conductance, from all or some subset of the system components, or from the power supply only. The control system may output control signals to all or some subset of the system components.

[0054] To determine the conductance, at least one electrical property of the additive manufacturing process is determined, for example, by measuring the potential difference across the metal strip 20, and the electrical property (e.g., voltage difference) is processed by a control unit, such as a controller.

[0055] Preferably, as described above, the system is designed to control some aspects of the additive manufacturing process. In such a control system, the controller does not need to convert the conductance to the distance d calc Rather, it is necessary to execute control based on the difference between the measured conductance and the desired nominal conductance. The control system 500 delivers an input based on at least one electrical property (e.g., conductance for a power source, heat source 300, feedstock actuator, linear actuator, and / or robotic arm), and these properties are then adjusted based on this input to obtain optimal metal deposition.

[0056] According to one exemplary embodiment, the control system 500 measures one or more electrical properties of the additive manufacturing process, calculates the conductance based on the measured one or more electrical properties, and adjusts the conductance via an input to the corresponding component of the additive manufacturing apparatus.

[0057] More specifically, when calculating the conductance, the voltage and / or current are measured while the additive manufacturing process is being performed. The conductance may first be calculated via the measured voltage and current signals and then processed, or the measured current and voltage signals may be processed before calculating the conductance. Since the conductance has a linear relationship with the process stability, this linear approximation enables control of the distance, the applied heat, the current passing through the metal strip 20, the moving speed of the nozzle 10 relative to the substrate 30, and the output speed of the metal strip 20, or a combination thereof, based on the measured conductance.

[0058] <Experimental Section>

[0059] [Experiment 1]: LMD-w with a nominal conductance-based control system to avoid droplet formation at nozzle 10 The LMD-w apparatus, i.e., the CoaxPrinter manufactured by Precitec GmbH & Co, was configured to deposit two layers of material on the substrate 30. The deposition process was carried out twice, firstly without any conductance control and secondly with conductance control according to the control system 500 described herein. A typical problem associated with LMD-w is, as described above, droplet formation and wire tip breakage from the substrate 30. This problem is schematically shown in FIG. 5. This problem occurs because the droplet, due to its large size, absorbs the laser light (heat 301) and causes further growth of the droplet.

[0060] Results: Figures 3a - 3g show a series of images taken from a video of an LMD-w process without the conductance-based control system described herein. As seen in FIGS. 3d and 3e, droplets are formed at the tip of the wire, the tip of the wire is detached from the substrate 30, and then melts onto the tip of the nozzle 10 due to surface tension. Such droplet formation causes defects in the deposition process and the process has to be stopped.

[0061] Figures 4a - 4g show a series of images taken from a video of an LMD-w process with the conductance-based control system 500 described herein. As can be seen from these figures, droplet formation is avoided by controlling the nominal conductance. In particular, in the process shown in FIGS. 4a - 4g, the laser output (heat 301) was the main parameter controlled by the conductance-based control system 500. The control of the laser output 301, i.e., the heat source 300, based on the measured conductance resulted in an improved process without droplet formation and without disruptions.

[0062] [Experiment 2]: Deposition System with Nominal Conductance-based Control of Some Process Parameters A deposition system consisting of an industrial 6-axis robot, a high-power YAG fiber laser, a wire feeder, a linear actuator for positioning the wire tip, and a control system 500 implemented in a PLC was used to deposit a cuboid shape (25×25×150 mm). The material used was Alloy 718, which requires special consideration in terms of temperature history to achieve the required material properties. These temperature considerations are addressed by running the process with relatively low heat input. The drawback of this is that process stability is adversely affected by relatively cold processing conditions, resulting in a small process window for maintaining a sound process. Generally, the distance between the wire tip and the substrate 30 must be kept within 0.2 mm of the nominal value to avoid drop material transfer or plunging (stubbing) of the solid wire onto the solid substrate 30 that causes defects. The control system 500 was configured to adjust each of the wire tip position, wire feed rate, and laser output to maintain the nominal conductance.

[0063] Results: The control system 500 was able to mitigate disturbances and varying conditions, such as warping and heat accumulation of the substrate 30, in a way that was not possible for the operator. Measurement and control were performed at a frequency of 100 Hz, which is a speed at which a human cannot simultaneously control the three actuators (linear actuator, wire feed rate, and laser output). The linear actuator feedback control based on a constant conductance conformed to the profile of the substrate 30, and the wire feed control equalized any deviation from the nominal height. The laser control prevented droplet accumulation by reducing the laser output when a decrease in conductance was detected.

[0064] Without a control system, considering the narrow process window and difficult process parameters, it is impossible to avoid the transfer of droplet material and the plunge / stubbing of the wire. The resulting geometry is very poor in terms of both geometry and internal defects.

[0065] [Connection] The present disclosure has described a control system 500 for an additive manufacturing apparatus and a process for controlling the additive manufacturing apparatus. In some aspects, the control system 500 can form components of the additive manufacturing system, that is, the additive manufacturing system can include the control system 500 described herein. The additive manufacturing apparatus may be provided separately from the control system 500, in which case the control system 500 may form a separate component connectable to an existing additive manufacturing apparatus. Alternatively, the additive manufacturing apparatus may be provided with the control system 500 built therein.

[0066] Although the present invention has been described in connection with specific embodiments above, the present invention is not limited to the specific forms described herein. Rather, the present invention is limited only by the appended claims.

[0067] In the claims, the terms "comprises / comprising" do not exclude the presence of other elements or steps. Further, although a plurality of means, elements, or method steps are recited individually, they may be implemented, for example, by a single unit or processor. Additionally, individual features may be included in different claims, and these may optionally be advantageously combined, and being included in different claims does not mean that a combination of features is not feasible and / or advantageous. In addition, singular designations do not exclude a plurality. Terms such as "a", "an", "first", "second", etc. do not exclude a plurality. The reference signs in the claims are given only by way of example and should in no way be construed as limiting the claims.

Description of Symbols

[0068] 10 Nozzle 20 Metal Strip 30 Substrate 35 Molten Pool 200 Position Actuator 300 Heat Source 400 Power Supply 500 Control System

Claims

1. A control system (500) for adjusting an additive manufacturing process of an additive manufacturing apparatus, wherein the additive manufacturing apparatus is configured to add metal to a substrate (30) by metal deposition, and the additive manufacturing apparatus includes: a nozzle (10) for outputting a metal strip (20), which is configured to be disposed at a distance from the substrate (30) and to move relative to the substrate (30) in the XYZ axes via a position actuator (200); a heat source (300) configured to melt the metal strip (20) into a state of a molten pool (35) on the substrate (30); a power source (400) configured to supply an electric current to the substrate (30) via the metal strip (20); and the control system (500) determines, by way of example, i.e., determines the electrical conductance between the metal strip (20) and the substrate (30) by measuring at least one electrical characteristic of the supplied electric current; determines the difference between the determined electrical conductance and a desired electrical conductance; and adjusts at least one of the distance from the substrate (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the substrate (30), the amount of the supplied electric current, the heat (301) supplied by the heat source (300), and / or the output speed of the metal strip (20) based on the difference between the determined conductance and the desired conductance, so as to maintain process stability during the deposition of a metal layer. A control system characterized by this.

2. The control system (500) according to claim 1, wherein the control system (500) is configured to adjust at least one of the moving speed of the nozzle (10) relative to the substrate (30), the amount of the supplied electric current, and / or the heat (301) supplied by the heat source (300).

3. The control system (500) includes at least one controller implementation such as P, PI, or PID; bang-bang; sliding mode; excitation signal; a control system configured to maintain the desired conductance based on the measured conductance; The control system according to claim 1 or 2.

4. The control system (500) is configured to adjust at least two of the distance from the substrate (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the substrate (30), the amount of current supplied, the heat (301) supplied by the heat source (300), and / or the output speed of the metal strip (20) based on the difference between the determined conductance and the desired conductance. The control system according to any one of claims 1 to 3.

5. The control system (500) is configured to adjust the heat (301) supplied by the heat source (300) based on the difference between the determined conductance and the desired conductance, and optionally, further adjust one of the distance from the substrate (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the substrate (30), the amount of current supplied, and the output speed of the metal strip (20). The control system according to any one of claims 1 to 4.

6. The heat source (300) of the additive manufacturing apparatus is a laser, an electric arc, a plasma, a resistance heater, an induction heater, a flame, or an electron beam. The control system according to any one of claims 1 to 5.

7. The control system (500) includes a measurement module configured to measure at least one electrical characteristic and determine conductance based on at least one measured electrical characteristic. The control system according to any one of claims 1 to 6.

8. The electrical characteristics include the potential at a first position and the potential at a second position. The first position is the nozzle (10) or a position on the metal strip (20) spaced apart from the substrate (30), and the second position is one of the substrate (30) or ground. The control system according to any one of claims 1 to 7.

9. The measurement module includes a current sensor configured to measure current. The control system according to claim 7.

10. A method for maintaining the process stability of an additive manufacturing apparatus, The additive manufacturing apparatus is configured to add metal to a substrate (30) by metal deposition, and the additive manufacturing apparatus A nozzle (10) for outputting a metal strip (20), which is configured to be disposed at a distance from the base material (30) and to move relative to the base material (30) in the XYZ axes. A heat source (300) configured to melt the metal strip (20) into a molten pool (35) state on the base material (30). A power source (400) configured to supply an electric current to the base material (30) via the metal strip (20). It is provided with. When depositing a metal layer, the method Determining the electrical conductance between the metal strip (20) and the base material (30) by measuring at least one electrical characteristic of the supplied current. Determining the difference between the determined electrical conductance and the desired electrical conductance, and Based on the difference between the determined conductance and the desired conductance, the distance from the base material (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, Adjusting at least one of the heat (301) supplied by the heat source (300) and / or the output speed of the metal strip (20). A method characterized by comprising the above.

11. The method according to claim 10, comprising adjusting at least one of the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, and / or the heat (301) supplied by the heat source (300).

12. The method according to claim 10 or 11, comprising adjusting at least two of the distance from the base material (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, the heat (301) supplied by the heat source (300), and / or the output speed of the metal strip (20) based on the difference between the determined conductance and the desired conductance.

13. The method includes adjusting the heat (301) supplied by the heat source (300) based on the difference between the determined conductance and the desired conductance, and optionally further adjusting one of the distance from the substrate (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the substrate (30), the amount of current supplied, and the output speed of the metal strip (20). The method according to any one of claims 10 to 12.

14. The method according to any one of claims 10 to 13 includes depositing metal on the substrate (30) by melting.

15. The method determines a desired nominal conductance based on the deposition of a trial layer, compares the conductance measured during the deposition of the trial layer with the process stability, and then selects the desired nominal conductance based on the measured conductance when the process is observed to be stable or ideal. The method according to any one of claims 10 to 14.

16. An additive manufacturing apparatus for adding metal to a substrate (30) by metal deposition, The additive manufacturing apparatus is A nozzle (10) for outputting a metal strip (20), configured to be disposed at a distance from the substrate (30) and configured to move in the XYZ axes relative to the substrate (30); A heat source (300) configured to melt the metal strip (20) into the state of a molten pool (35) on the substrate (30); A power source (400) configured to supply current to the substrate (30) through the metal strip (20); Comprising The additive manufacturing apparatus includes a control system (500) configured to maintain process stability during the deposition of a metal layer. The control system (500) Determines the electrical conductance between the metal strip (20) and the substrate (30) by measuring at least one electrical characteristic of the supplied current; Determines the difference between the determined electrical conductance and the desired electrical conductance; configured to adjust at least one of the distance from the base material (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, the heat (301) supplied by the heat source (300), and / or the output speed of the metal strip (20) based on the difference between the determined conductance and the desired conductance. An additive manufacturing apparatus characterized by the above. **Claim 17** The control system (500) of the additive manufacturing apparatus is configured to adjust at least one of the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, and / or the heat (301) supplied by the heat source (300). The additive manufacturing apparatus according to claim 16. **Claim 18** The control system (500) of the additive manufacturing apparatus is configured to adjust at least two of the distance from the base material (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, the heat (301) supplied by the heat source (300), and / or the output speed of the metal strip (20) based on the difference between the determined conductance and the desired conductance. The additive manufacturing apparatus according to claim 16 or 17. **Claim 19** The control system (500) is configured to adjust the heat (301) supplied by the heat source (300) based on the difference between the determined conductance and the desired conductance, and optionally further adjust one of the distance from the base material (30) to the nozzle (10), the moving speed of the nozzle (10) relative to the base material (30), the amount of current supplied, and the output speed of the metal strip (20). The additive manufacturing apparatus according to any one of claims 16 to 18. **Claim 20** The additive manufacturing apparatus includes a measurement module configured to measure the at least one electrical characteristic and determine the conductance based on the at least one measured electrical characteristic. The additive manufacturing apparatus according to any one of claims 16 to 19.

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