Powder insert and thermal spray or laser additive manufacturing system for high powder feed rates

Abstract

The present invention relates to a powder insert for a thermal spray or laser additive manufacturing (AM) system and / or a thermal spray or laser additive manufacturing (AM) system enabling feeding powder in high quantities to injectors attached to a thermal spray gun or a laser processing head (LPH) without generating pulsations of the powder feed flow at the outlet of the injectors.

Description

[0001] Powder Insert and Thermal Spray or Laser Additive Manufacturing System for High Powder Feed Rates

[0002] The present invention relates to a powder insert for a thermal spray or laser additive manufacturing (AM) system and / or a thermal spray or laser additive manufacturing (AM) system enabling feeding powder in high quantities to injectors attached to a thermal spray gun or a laser processing head (LPH) without generating pulsations of the powder feed flow at the outlet of the injectors.

[0003] Background

[0004] Thermally sprayed coatings are widely used in different industries to improve wear, friction, heat resistance or abradability of the parts being coated. Depending on the purpose to be achieved with the coating, a wide range of possible coating material feedstock in the form of wire or powder can be used.

[0005] In recent years, the use of Additive Manufacturing (AM) methods has increased for manufacturing complex geometries made from metals, alloys or ceramics or mixtures thereof. One of the advantages of these AM methods is that prototypes and functional models can be manufactured rapidly from metal, ceramics or other materials without preparing dedicated tooling and fixtures first. Another advantage of using AM methods is that internal geometries, e.g. complex tubes, that could not be manufactured using conventional material removing technologies can be manufactured using AM methods. In addition to this, some AM processes allow to repair complex geometries using a material identical or similar to the original material of which the part was manufactured.

[0006] For AM methods using metals, alloys, ceramics or mixtures thereof powders or foils are being used as feedstock for the process. In powder feed AM systems, such as directed energy deposition processes (DED), the powder is fed to one or more injectors attached to the laser processing head. Thermal spray processes use powder, wire or suspensions to feed the coating material to the injectors attached to the thermal spray gun. The process of feeding the feedstock material to the spray gun or laser processing head is critical, especially for processes using powder as feedstock, as pulsations of the material at the point where the material is being melted leads to a variation of the characteristics of the material being deposited. In addition to this, pulsations of the powder flow lead to a variation in the thickness of the material applied or to a lower efficiency of the process in terms of material consumption.

[0007] In order to understand the solution according to the present invention, it is helpful to roughly describe the principles of feeding powder in a thermal spray system or laser AM system and to describe the principles of a powder feeder used in such a system.

[0008] In a thermal spray a spray plume or laser beam is created by a thermal spray gun whereas in a laser AM system a laser beam is created by a laser processing head (LPH). The thermal spray gun or LPH is attached to a robot or NC axis allowing the head to be positioned in a certain distance and angle to the part. The part to which the coating or layer will be applied to, usually called a substrate, is mounted on a parthandling in the form of a rotating and tilting table or a lathe. A booth with an air in- and outlet for removing powder dust created during the thermal spray or laser AM process and one or more loading and service doors encloses the part and thermal spray gun or LPH. The size of the booth is mainly determined by the size of the parts to be coated using the system. In powder-based processes, powder is transported using a carrier gas from powder feeders, more precisely from powder inserts, through powder hoses to injectors attached to the thermal spray gun or LPH. A powder hose will be referred to as a powder feedline in the following. The one or more injectors, having an outlet opening usually being smaller than the inside diameter of the powder hose, are adjusted such that the powder-gas beam created at the outlet of the injectors is injected into the thermal spray plume or laser beam where the powder is molten and deposited on the part. The powder feeders are located outside the booth to enable refilling of the powder inserts without entering the booth or to enable refilling one powder insert while the process is running using another powder insert. During the engineering phase of the thermal spray or laser AM system, the location of the powder feeders is chosen such that the distance to the thermal spray gun or LPH is minimized and the path of the powder feedlines is designed to have as little bends and turns as possible while still allowing the thermal spray gun or LPH to move within the complete working range. For a conventional thermal spray or laser AM system the total length of the powder feedlines varies between 3 and 15 meters. Keeping the total length of the powder feedlines as short as possible and with as little bends and turns as possible allows to minimize the pressure drop within the powder feedlines. This allows to feed powder with a low amount of carrier gas to the injectors. A low amount of carrier gas used to feed the powder to the injectors is particularly important for laser AM systems where a low speed of the powder particles in the powder-gas beam injected into the laser beam is targeted.

[0009] The powder feeders used for a thermal spray or laser AM system schematically consist of two main assemblies: A control unit and a powder insert. The control unit contains a controller for the powder dosing unit and, if present, for the stirrer of the powder insert, a carrier gas supply to the powder insert and a carrier gas supply control unit. The powder insert, as referred to in the present invention, consists of at least a powder container, a dosing unit to transport powder from the powder container to a powdergas outlet, a carrier gas inlet and a powder-gas outlet. With the exception of the carrier gas inlet and the powder-gas outlet, the powder insert is sealed gas-tight. In the powder container, powder is stored. The powder container is usually rotational symmetric and has an outlet opening for the powder on one end and a detachable lid on the other end. For some powder feeder types, a motor driving a stirrer located on the inside of the powder container is attached to the detachable lid to improve flowability of the powder within the powder container. A pressure equalization tube within the container ensures that the pressure within the whole powder insert is the same. Powder flowing through the outlet of the powder container is transported using a dosing unit to a powder-gas outlet. In the following, the powder-gas outlet of the powder insert is referred to using the term suction unit. The suction unit of the prior art powder hopper assemblies has one powder-gas inlet channel and one powder-gas outlet channel, the powder-gas outlet channel being connected to a powder hose. The powder from the dosing unit is transported using a carrier gas through the suction unit to the powder feedline.

[0010] Various types of powder feeders such as vibratory feeders, screw feeders, rotary disc or pneumatic feeders can be used for thermal spray or laser AM systems. However, the disc type powder feeder is the most commonly used form of powder feeder for these applications as it allows for an accurate, efficient and uniform feeding of powder. Disc type powder feeders to feed powder to injectors attached to a thermal spray gun or laser processing head are known. A disc type powder feeder or rotary disc type feeder, such as the TWIN 150 powder feeder as offered by Oerlikon Metco, is a type of powder feeder that utilizes a rotating disc as a powder dosing unit to feed powder from the powder container to the suction unit. The disc is rotated to release the powder in a controlled manner and has one or multiple compartments, pockets or annular grooves that are filled up with powder. In order to control the amount of powder fed to the powder hose, the rotational speed of the disc is adjusted. At the release point of the powder insert powder is transported using a carrier gas from the rotating disc through a suction unit to a powder hose connected to an injector attached to a thermal spray gun or laser processing head.

[0011] Even though rotary disc type powder feeders offer a precise and controlled way of feeding powder to the injector, pulsation of the powder transported to the spray gun or laser processing head in terms of variation of powder feed rate in grams per minute may occur at higher feed rates at the outlet of the injector. The pulsation at high feed rates is mainly caused by variations of the backpressure and / or powder particles blocking the powder hose or injector. This pulsation may lead to non-uniform coating thickness, high coating roughness, a change in characteristics of the coating or to a lower degree of efficiency in terms of powder consumption. In addition to this, in order to ensure a high process efficiency in terms of powder consumption, it is required that the area where the powder injected into the spray plume or laser beam is as narrow as possible. If the powder-gas beam created at the outlet of the injector is wider than the thermal spray plume or laser beam, a higher portion of the powder will not be injected into the spray plume or laser beam and therefore will not be molten and thus not be added as a coating to the substrate. Thus this portion of the powder fed to the injectors is wasted. Ensuring a stable powder flow with low pulsations in a narrow area at a high feed rate is thus a requirement to industrialize thermal spray and laser AM processes.

[0012] According to a prior art approach, higher feed rates with low pulsations are achieved by connecting two or more powder inserts in parallel to one thermal spray gun or laser processing head. Each of the powder inserts being connected with a powder hose to an injector attached to the thermal spray gun or laser processing head. This setup using several powder inserts in parallel to feed powder to injectors attached to a single thermal spray gun or laser processing head has the advantage that feed rates can be increased compared to a setup connecting a single powder insert by a single powder hose to one injector. However, this approach has economical drawbacks due to the investment in several powder feeders to operate the several powder inserts, the cost of maintenance for operating several powder feeders and increased operating cost due to a multiplication of gas consumption for the carrier gas. In addition to this, it is difficult to align the feed rates of the different powder inserts and the injection of several powder feedlines into the same spray plume or laser beam. A misalignment in terms of powder feed rate per injection or particle speed of the different injections using this setup might lead to negative impacts on the coating or layer quality.

[0013] According to another prior art approach, the deficiencies of the prior art approach described above are overcome by applying a powder hose and / or injector with bigger diameter whilst at the same time increasing the carrier gas flow. This reduces the cost of commissioning compared to the prior art approach of using several powder feeders for a single thermal spray gun or processing head. At the same time, this prior art approach increases operating cost by multiplying the carrier gas use. In addition to this, using this prior art approach reduces the deposition efficiency of the feedstock material as the powder jet widens and some particles are not injected into the spray plume or laser beam and thus not deposited on the substrate. Particularly for powder feed laser AM processes, the diameter of the powder-gas beam at the injection into the laser beam needs to be smaller than the diameter of the laser beam in order to ensure that most of the powder being transported to the injector is being deposited on the part.

[0014] In still another prior art approach, in order to increase the feed rate to the injectors the carrier gas flow for each powder feeder is increased without changing the powder hose or injector diameter. This prior art approach leads to increased speed of the powder particles being injected into the spray plume or laser beam. Particularly for powder feed laser AM processes like for example DED, an increased speed of the powder particles being injected into the laser beam can lead to particles ricocheting from the substrate back to the injectors or laser processing head. These ricocheting particles may lead to caking of particles on the injectors or laser lens. Caking of powder onto the injectors influences the powder-gas beam characteristics and thus the coating or layer quality and leads to a reduced lifetime of the gun head. A higher speed of the powder particles at the injection into the laser beam also prevents that powder particles are melted thoroughly. This effect may lead to unmolten powder particles embedded in the coating and thus to a deterioration of the coating quality.

[0015] According to yet another prior art approach, the powder feed rates in a thermal spray or laser AM system are increased by splitting the powder flow from a single powder feedline connected to one powder insert into more than one powder feedlines using a powder feedline splitter attached to the spray gun or laser processing head. In this approach, the distance from the injectors to the splitting point of the powder flow is within the range of less than 50 cm as the powder-gas splitting device is attached to the thermal spray gun or LPH. Using this approach, the deficiencies of the above mentioned prior art approaches in terms of investment and operating cost are overcome. However, the powder feed rates achieved with this prior art approach are still limited because the backpressure downstream of the powder feedline splitter towards the injector leads to pulsations of the powder flow.

[0016] Taking the above said into account it becomes clear that the possibilities provided by the prior art approaches to increase the powder feed rates in a thermal spray or laser AM system are limited.

[0017] Objective of the invention

[0018] The main objective of the present invention therefore is to increase powder feed rates to injectors attached to a thermal spray gun or laser processing head without inducing pulsations of the powder flow at the outlet of the injector and to overcome the technical and economical deficiencies of the prior art approaches.

[0019] Summary of the invention

[0020] According to the invention, this objective is met by splitting the powder-gas flow from one powder feedline into preferably at least two or even more preferably at least three powder feedlines each connected to an injector attached to the thermal spray gun or laser processing head with the splitting point being closer to the powder insert than to the injector or even more preferably with the splitting point being integrated in the suction unit of the powder insert.

[0021] The inventors have detected that, surprisingly, pulsations of the powder flow rate at high powder feed rates can effectively be prevented by increasing the distance between the splitting point of the powder-gas flow and the injectors whilst keeping the total length of the feedline between the powder insert and the injectors constant. According to a prior art approach, the powder feed rate to a thermal spray gun or laser processing head is increased by using a powder-gas splitting device attached to the thermal spray gun or LPH, thus located close to the injectors. Using this prior art approach, the increase in powder feed rate is limited as pulsations tend to occur at higher powder feed rates. By increasing the distance between the powder-gas splitting point and the injectors, oscillations of the backpressure are damped along the powder feedline and the frequency of oscillations is reduced. These effects effectively reduce pulsations of the powder flow at the outlet of the injectors at high powder feed rates. As outlined in the description of the background, increasing the total length of the powder feedlines between the powder insert and the injectors compared to a prior art thermal spray or laser AM system to achieve the same effect is not an alternative solution. Increasing the total length of the powder feedlines would lead to an increased carrier gas flow to overcome the pressure drop within the powder feedlines, the increased carrier gas flow would lead to increased turbulences and an increased speed of the powder particles at the injection of the powder-gas beam into the laser beam.

[0022] According to a preferred embodiment of the present invention, the distance between the powder-gas flow splitting point and the injectors is increased by integrating the powder-gas flow splitting function into the inventive powder insert comprising at least a powder, a suction unit and a powder dosing unit to transport powder from the powder container to the suction unit, wherein the suction unit comprises at least one powdergas inlet channel and preferably at least two or even more preferably at least three powder-gas outlets.

[0023] Tests performed using said inventive powder insert showed that for an iron-based powder the powder feed rate per injector can be increased to approximately 25 g / min without inducing pulsations compared to a powder feed rate per injector of approximately 13 g / min using the prior art approach where the splitting point of the powder-gas flow is at the thermal spray gun or LPH.

[0024] In one embodiment of the powder insert according to the invention, which may be combined with the preaddressed embodiment and any of the embodiments still to be addressed unless in contradiction, the powder is transported from the hopper to the suction unit using a rotating disc.

[0025] In another exemplary embodiment, the objective of the invention is accomplished by a thermal spray or laser additive manufacturing (AM) system according to independent claim 5 wherein the powder-gas flow splitting device, distributing the powder-gas flow to at least two or even more preferably at least three powder feedlines, each connected to an injector, is located along the powder feedline from the powder inserts to the injectors closer to the powder insert than to the injector or by combining one or more powder inserts according to claim 1 with a thermal spray or laser AM system according to claim 5.

[0026] In another embodiment of the present invention, which may be combined with any of the preaddressed embodiments unless in contradiction, the powder feed rate can even further be increased without inducing pulsations of the powder flow at the outlet of the injectors by connecting at least two powder-gas flow splitting devices in series, each of the powder-gas flow splitting devices splitting a powder-gas flow into preferably at least two or even more preferably at least three powder feedlines.

[0027] Said powder insert and / or thermal spray or laser AM system prevent pulsations of the powder feed rate at the outlet of the injector by preventing oscillations of the back pressure in the powder insert and feeding path to further enhance the overall efficiency.

[0028] According to another aspect of the invention a method for feeding powder to a thermal spray gun or laser processing head is proposed. The method comprising the following steps. Powder stored in a container is fed to powder-gas outlets using a dosing unit and subsequently transported using a carrier gas through powder-gas outlets of a suction unit, a powder-gas flow splitting device and powder hoses to injectors. The powder-gas flow is split into preferably at least two or even more preferably at least three powder feedlines closer to the powder insert than to the injectors attached to the thermal spray gun or laser processing head by a powder-gas flow splitting device.

[0029] According to a preferred embodiment of the method the powder-gas flow splitting function is integrated in the suction unit of the powder insert.

[0030] According to a further embodiment of the method, at least two powder-gas splitting devices are connected in series, each of the powder-gas splitting devices splitting the powder-gas from one inlet into preferably at least two or even more preferably at least three powder feedlines.

[0031] In accordance with embodiments it has been found that powders having a density range of 2-15 g / cm3and a particle distribution with preferably at least 95% or even more preferably at least 90% of the particles having a particle size of not more than 60 pm can be fed to the injectors attached to a thermal spray gun or laser processing head with feed rates exceeding 13 g / min per injector for iron or nickel-based alloys, exceeding 16 g / min per injector for metal powders with ceramics added and exceeding 8 g / min per injector for powders having a density lower than 5 g / cm3without inducing pulsations of the powder flow at the outlet of the injectors.

[0032] The invention shall now be further exemplified with the help of figures.

[0033] Description of figures

[0034] Figure 1 illustrates a prior art approach of feeding powder to a thermal spray gun or laser processing head.

[0035] Figure 2 shows a schematic side-view cross-section of a prior art disc powder insert

[0036] Figure 3 illustrates the dependency of the deposition time of the powder feed rate and the limitations in terms of powder feed rates of the prior art approach of using two powder inserts in parallel, each connected with a single powder feedline to a splitting device attached to the thermal spray gun or LPH, with each of the splitting devices splitting the powder-gas flow to 3 powder feedlines.

[0037] Figure 4 shows an exemplary powder insert according to the invention.

[0038] Figure 5 shows an exemplary illustration of the inventive thermal spray or laser AM system wherein a powder-gas flow splitting device is located further away from the injector than from the powder insert.

[0039] Figure 6 shows an exemplary illustration of the inventive thermal spray or laser AM system wherein the powder-gas flow splitting function is integrated in the powder insert

[0040] Detailed description

[0041] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0042] Fig. 1 illustrates a prior art system for feeding powder to a thermal spray gun and / or laser processing head. A booth (101) encloses a thermal spray gun or laser processing head (115) generating a spray plume or laser beam (117). The processing head can be mounted on a robot or NC-axis. Powder inserts (127 and 133) as shown in Fig. 1 are mounted on top of a powder feeders (103 and 105). A powder insert, the details of which are shown in Fig. 2, comprises at least a powder container (107), a dosing unit and a suction unit. Powder stored in one or more powder containers (107 and 109) is transported by a dosing unit, preferably a rotating disc, to a suction unit (129 and 131). The powder feeders (103 and 105) for a rotary disc feeder enclose a drive for the rotating disc, the carrier gas supply and a gas massflow and rotation control unit for the rotating disc not shown in Fig. 1. The powder hoses (111 and 113) constituting the powder feedlines are each connected on one side to the suction unit of the powder inserts (129 and 131) and on the other side to an injector (125) attached to the thermal spray gun and / or laser processing head. The total length of the powder feedlines (111 and 113) between the powder inserts (127 and 133) is determined by the size of the booth (101) and the working range of the thermal spray gun or laser processing head. In prior art thermal spray or laser AM systems the total length of the powder feedlines varies between 3 and 15 meters. The carrier gas transporting the powder to the injectors creates powder-gas beams (119) at the outlet of the injector. The powder-gas beams are injected into the spray plume or laser beam (117) and the powder is molten by the spray plume or laser beam. The injection of the powder into the spray plume or laser beam is crucial for achieving a constant layer thickness and constant coating characteristics. The molten powder is then deposited on the part (121) which is mounted on a turntable (123).

[0043] In Fig. 2 a schematic cross-section of the side view of a prior art disc feeding powder insert is shown. Powder is stored in a rotational symmetric container (201) with a detachable lid. A stirrer (203) driven by a motor (205) improves the flowability of the powder within the powder container. Powder stored within the powder container (201) flows to a spreader piece (207) and subsequently to the groove (209) of the rotating disc (211). The spreader piece ensures that the groove is evenly filled and that the powder does not overflow. The rotating disc (211), rotating around its centerline axis (213) in a counterclockwise direction in Fig. 2 transports the powder from the spreader piece (207) to the suction unit (217) which extends to the bottom of the groove after the powder-gas outlet (221) in the direction of the rotation. Carrier gas (215) inserted into the enclosure of the rotating disc (223) carries the powder through the powder-gas inlet channel (225) of the suction unit (217) to the powder-gas outlet in the form of an aerosol (221). A pressure equalization tube (227) ensures that the pressure within the powder container equals to the pressure within the casing of the rotating disc. The carrier gas mass flow controller and the motor driving the rotating disc not shown in Fig. 2 are integrated within the powder feeder.

[0044] The limitations of the prior art approach of feeding an iron-based powder to a thermal spray gun or laser processing head are shown in Fig. 3. The pulsation threshold (31) for a prior art laser AM system setup comprising two powder inserts each connected to a splitting device attached to the thermal spray gun or laser processing head splitting the powder flow from each powder hose to three injectors, thus with a total of 6 injectors attached to the LPH. With this prior art setup, feed rates of up to 80 g / min are feasible for an iron-based powder, having a density of 7.6 to 8 g / cm3and a particle size distribution with the majority of the particles having sizes between 15 pm and 60 pm without inducing pulsations of the powder injected. Thus by using the prior art setup and the powder described above, pulsation-free injection is possible up to approximately 13 g / min per injector. For feeding metal powders with ceramic contents added, the threshold above which pulsations occur using a prior art setup as described above was found to be at 16 g / min per injector and 8 g / min per injector for powders with a density lower than 5 g / cm3. Above this threshold (31) pulsations with a negative influence on the coating or layer quality occur. If the total feed rate to the thermal spray gun or laser processing feeding iron-based powder using the same prior art approach as described above exceeds 100 g / min (approximately 16 g / min per injector), the thermal spray process or laser AM process becomes even more unstable due to particles blocking the powder hoses.

[0045] In Fig. 4 an exemplary embodiment of a powder insert according to the present invention is shown. Powder is transported from a powder container (401) to an annular groove (409) in a rotating disc (411). The rotating disc (411) transports the powder within the groove to a suction unit (417). Powder transported to the suction unit (417) is carried by a carrier gas supplied through a carrier gas inlet (415) through a powdergas inlet channel (425) of the suction unit (417) to preferably at least two or even more preferably at least three powder-gas outlets (419). By integrating the powder-gas splitting function into the powder insert, the distance of the powder-gas splitting point to the injectors is maximized and pulsations at the outlet of the injectors are effectively prevented at higher powder feed rates. The powder-gas outlets (419) of the suction unit (417) may be round with their centerlines preferably being on a circle concentric to the centerline of the powder-gas inlet channel (425) or with their centerlines being on a line originating from the centerline of the rotating disc.

[0046] Fig. 5 illustrates an exemplary embodiment of the present invention of feeding powder to a thermal spray gun or laser processing head. The illustrative example in Fig. 5 shows the preferred system thermal spray or laser AM system setup with two powder feeders (501 and 525) feeding powder to injectors attached to one thermal spray gun or laser processing head. A thermal spray or laser AM system with only one powder feeder or three or more powder feeders could be conceived without departing from the spirit of the invention. As shown in Fig. 5, powder is transported using a carrier gas through a suction unit (535 and 537) of a powder insert comprising a powder container (503 and 523), a powder stirrer mounted within the powder hopper, a dosing unit (531 and 533) to transport the powder from the hopper to a suction unit, a suction unit (535 and 537) and a carrier gas inlet. The powder-gas mixture flows from the suction unit (535 and 537) through powder hoses (521 and 527) to powder-gas flow splitting devices (505 and 529). The powder-gas flow splitting devices (505 and 529) comprise at least one powder-gas flow inlet and at least two or preferably at least three or more powder-gas flow outlets. The powder-gas flow splitting devices (505 and 529) distribute the powder-gas mixture form the at least one powder-gas flow inlet to at least two or even more preferably at least three separate powder hoses (507) each connected to an injector (509).

[0047] The total distance between the suction unit (535 and 537) and the thermal spray gun or laser processing head (511) and thus the total length of the powder hoses and powder feedlines from the suction piece to the injectors is determined by the size of the booth enclosing the thermal spray gun or laser processing head (511) and the part handling (519). By way of non-limiting example shown in Fig. 5, the powder-gas flow splitting devices (505 and 529) defining the powder-gas flow splitting location along the powder feedlines are located along the powder feedline between the suction unit and the injector such that the spreading points (505 and 529) are closer to the suction unit (503 and 523) than to the injectors (509). Surprisingly, the inventive thermal spray or laser AM system shown in Fig. 5 allows higher powder feed rates than by using the prior art approach of splitting the powder flow from a single powder feedline to two or more powder feedlines directly at or close to the thermal spray gun or laser processing head without inducing pulsations of the powder flow at the outlet of the injector.

[0048] In Fig. 6 another exemplary embodiment of the present invention of feeding powder to a thermal spray gun or laser processing head is illustrated. In order to optimize the back pressure in the feeding path it is proposed to maximize the distance between the injectors and the powder-gas splitting point by using an inventive powder insert according to Fig. 2 with preferably at least two or even more preferably at least three powder-gas outlets. In the example shown in Fig. 6, powder stored in a powder containers (603 and 625) is transported preferably using a rotating disc to at least two or even more preferably at least three separate powder-gas outlets (605 and 623), each of the powder outlets connected to a powder hose constituting a separate powder feedline with each powder feedline connected to a single injector. In this case, the powder is fed from a single powder dosing unit to preferably at least two or even more preferably at least three powder-gas outlets. A carrier gas transports the powder from the powder outlets (605 and 623) to the powder hoses (607). In the example shown, a setup with two powder feeders (601 and 621) and three powder-gas outlets (605 and 622) per powder feeding device is illustrated but it would also possible to use a setup with more than two powder feeders and two or four or more powder outlets per powder insert. The powder-gas flow is distributed between preferably at least two or even more preferably at least three separate powder feedlines (607), each of the powder feedlines connected to an injector (609) attached to the thermal spray gun or laser processing head (611). At the outlet of the injectors, a powder-gas beam (615) is formed each which is being injected into the spray plume or laser beam (613).

[0049] In another embodiment not shown in Fig. 6, a powder-gas flow splitting device located closer to the suction piece than to the injector is added for each powder feedline.

[0050] Powder feeding tests were carried out using the inventive powder insert shown in Fig. 2 in a laser AM system according to Fig. 6. The tests showed that by using the inventive powder insert with three powder-gas outlets per powder insert and using two powder inserts in parallel, a feed rate of at least 25 g / min per injector and thus a total feed rate for 6 injectors together of at least 150 g / min to the laser processing head is possible for iron-based powders without inducing pulsations of the powder flow at the injector outlet can be achieved. This shows that the inventive powder insert allows to almost double the feed rate per injector compared to the prior art approach without inducing pulsations at the injector outlet. Fig. 3 illustrates that by increasing the feed rate to the laser processing head, the deposition time and thus the processing time per part are reduced proportionally. This shows that the inventive powder insert and the inventive thermal spray or laser AM system have a considerable economic benefit.

[0051] The tests performed surprisingly also showed that if using the inventive powder insert, the carrier gas flow had to be increased by 1 / 3 only in order to achieve the increased total powder feed rate. Using a prior art approach of doubling the total feed rate to the laser processing head by doubling the amount of powder inserts used, the total carrier gas flow to the laser processing head would also be doubled. This shows that the inventive powder insert and the inventive thermal spray or laser AM system has not only technical benefits in terms of increased feed rates without compromising the coating or layer quality by pulsations of the powder flow but also considerable economic benefits in terms of reduced investment and operating cost.

[0052] It is preferred that the inventive solutions shown in Fig 5. and Fig. 6 are further improved by a mounting pressure gauge located downstream of the powder insert or downstream of the powder-gas flow splitting device in order to monitor and identify pulsations of the backpressure within the powder feedlines indicating pulsations of the powder-gas flow. In order to further optimize the backpressure and to allow for even higher powder feed rates, carrier gas can be injected downstream of the of the powder insert or powder-gas splitting device.

[0053] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

[0054] List of reference signs

[0055] AM Additive Manufacturing

[0056] DED Directed Energy Deposition LPH Laser Processing Head

[0057] NC Numerical Control

Claims

Claims1 . Powder insert for feeding powder to a thermal spray gun or laser processing head comprising- a powder container (401);- a suction unit (417);- a carrier gas inlet (415);- and a powder dosing unit (411 ) to transport powder from the powder container to a suction unit (417) characterized in that the suction unit (417) comprises at least one powdergas inlet channel (425) and preferably at least two or even more preferably at least three powder-gas outlets (419).

2. Powder insert according to claim 1 characterized in that the powder is transported from the powder container (401 ) to the suction unit (417) by a rotating disc.

3. Powder insert according to claims 1 and 2 characterized in that the centerlines of the powder-gas outlets (419) are located on a circle concentric to the powder-gas inlet channel (425).

4. Powder insert according to claims 1 and 2 characterized in that the centerlines of the powder-gas outlets (419) are located on a line originating from the centerline of the rotating disc.

5. Thermal spray or laser AM system comprising- one or more powder feeders (501);- one or more powder inserts, each comprising at least one powder container (503), at least one powder dosing unit (533), at least one suction unit (535) and a carrier gas inlet;- one or more powder-gas flow splitting devices (505);- preferably at least two or even more preferably at least three injectors (509)attached to a thermal spray gun or laser processing head (511 );- powder hoses (507) and- a thermal spray gun and / or laser processing head (511 ) characterized in that the powder-gas flow splitting device distributing the powder-gas flow to preferably at least two or even more preferably at least three powder feedlines, with each of the powder feedlines connected to a separate injector, is located closer to the powder insert than to the thermal spray gun or laser processing head.

6. Thermal spray or AM system according to claim 5 characterized in that the at least one suction unit comprises at least one powder-gas inlet channel and preferably at least two or even more preferably at least three powder-gas outlets.

7. Thermal spray or AM system according to claims 5 characterized in that at least two powder-gas flow splitting devices are connected in series, each of the powder-gas flow splitting devices splitting a powder-gas flow into preferably at least two or even more preferably at least three powder feedlines.

8. Method to feed powder to a thermal spray gun or laser processing head, the method comprising the steps of:- storing powder in a container;- feeding powder to powder-gas outlets and- transporting the powder using carrier gas through the powder-gas outlets, at least one powder-gas flow splitting device and powder hoses to injectors characterized in that the powder-gas flow is split into preferably at least two or even more preferably at least three powder feedlines closer to the powder insert than to the thermal spray gun and / or laser processing head by the powder-gas flow splitting device.

9. Method according to claim 8 characterized in that the powder-gas flow splitting is performed within the suction unit.

10. Method according to claims 8 and 9 characterized in that at least two powder-gas splitting devices are connected in series, each of the powder-gas splitting devices splitting the powder-gas from one inlet into preferably at least two or even more preferably at least three powder feedlines.11 . Method according to the preceding claims 8 to 10 characterized in that the powder fed to the injectors has a density range of 2-15 g / cm3.

12. Method according to anyone of the preceding claims 8 to 11 characterized in that the powder fed to the injectors has a particle distribution with preferably at least 95% or even more preferably at least 90% of the particles having a particle size of not more than 60 pm.

13. Method according to the preceding claims 8 to 12 characterized in that the powder feed rate to the thermal spray gun or laser processing head for iron or nickel-based alloys exceeds 13 g / min per injector.

14. Method according to the preceding claims 8 to 12 characterized in that the powder feed rate to the thermal spray gun or laser processing head for metal powders with ceramics added exceeds 16 g / min per injector.

15. Method according to the preceding claims 8 to 12 characterized in that the powder feed rate to the thermal spray gun or laser processing head for powders having a density lower than 5 g / cm3exceeds 8 g / min per injector

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