FOR A SURFACE OF A POWDER BED

The present invention relates to additive manufacturing (AM) and in particular to systems and methods of additive manufacturing having heating of a surface of a powder bed by using a hot gas film.

Additive Manufacturing (AM) , also known as Additive Layer Manufacturing (ALM) , 3D printing, rapid prototyping or freeform fabrication, is a group of processes of joining additive materials i.e. plastic, metal or ceramic to make objects from 3D model data, usually building it up layer upon layer .

Additive manufacturing (AM) is a relatively new consolidation process that is able to produce a functional complex part, layer by layer, without moulds or dies. This process uses a powerful heat source such as a laser beam or an electron beam to melt a controlled amount of additive material, for example metal in the form of metallic powder or wire, which is then deposited, initially, on a build platform or a surface of a prefabricated workpiece. Subsequent layers are then built up upon each preceding layer. As opposed to conventional machining processes, this computer-aided manufacturing (CAM) technology builds complete functional parts or, alternatively, builds features on existing components i.e. on a workpiece, by adding material to the workpiece layer by layer rather than by removing it as is done in machining.

Additive manufacturing often starts by slicing a three dimensional representation, for example a CAD model, of a part to be manufactured into very thin layers, thereby creating a two dimensional image of each layer. As aforementioned the part to be manufactured may be a part that is built from beginning or may be a part that is to be built on a workpiece, for example during repairing of a chipped turbine blade the chipped turbine blade is the workpiece and the patch formed to fill or reform the chipped part is the part that is built on the workpiece. The workpiece is positioned on the build platform. To form each layer, popular laser additive manufacturing techniques such as selective laser melting (SLM) and selective laser sintering (SLS) involve mechanical pre-placement of a thin layer of metal powder of precise thickness on a surface of the workpiece and in adjoining horizontal surface above the build platform. Such pre-placement is achieved by using a mechanical wiper or by a powder spreading mechanism to sweep or spread a uniform layer of the powder or to screed the layer, after which an energy beam, such as a laser, is indexed across the powder layer according to the two dimensional pattern of solid material for the respective layer. After the indexing operation is complete for the respective layer, the build platform, and therefore the horizontal plane of deposited material, is lowered and the process is repeated until the three dimensional part is completely built on the workpiece as desired. In order to protect the thin layers of fine metal particles from contaminants and from moisture pickup, the operation is usually performed under gases like nitrogen or an atmosphere of inert gas, e.g. argon.

Alternatively, when manufacturing the part from the beginning, no pre-placement of the workpiece on the build platform is required. A first layer of the part is manufactured by the additive manufacturing process in one of the layers, generally the first layer, of the powdered material spread on the build platform. Subsequent layers of the part are manufactured on top of the first layer of the part by the additive manufacturing process as aforementioned. Nowadays the AM processes are widely used in aerospace and energy industries, medical applications, jewelry, etc. Selective Laser Melting (SLM) and Selective Laser Sintering (SLS) , such as Direct metal laser sintering (DMLS) , Direct metal laser melting (DMLM) , are AM processes that use energy in the form of a high-power laser beam to create three- dimensional metal parts by fusing, or sintering in case of SLS, fine particles of thin powder layer together.

Although the SLM/SLS technologies become widely used in various applications, the SLM/SLS technologies have some limitations such as surface roughness, part accuracy, and the formation of layered residual stresses, which are reinforced by the high thermal gradients due to melting and solidification in a very short time. To control and vary the part properties and quality, the SLM/SLS technologies processing parameters, including laser power, laser scan speed, layer thickness, preheating and post-heating of the powdered bed, need to be varied and controlled.

During the SLM/SLS processes, high thermal gradients are present inside the parts because of the fast heating and cooling of the powdered material forming the part layer by layer. These thermal gradients lead to thermal stresses, which may cause residual stresses or even micro/macro cracks in the part that is built. To resolve these issues, preheating of the powdered bed, particularly of the layer of the powdered material that is to be melted or sintered, may be implemented, and thus during the building up of the part, the temperature differences within the powdered material will be lower, which results in lower thermal gradients. Preheating of the powder bed prior to the laser beam exposure provides beneficial effects during the SLM/SLS processes. Setting the temperature of the powder close to its melting point might save the energy induced by the laser and improve the wettability of the solid by the liquid phase i.e. of the underlying surface of the workpiece or of a layer formed in a previous step. In addition, preheating of the powder material reduces the thermal gradients and slows down the cooling rates within heat affected zone lowering susceptibility for residual stresses formation and cracking during solidification. Additionally, reduction of the thermal gradients and slowing down of the cooling rates within heat affected zone is also achieved by post-heating associated with controlled cooling of the melted or sintered layer thereby also lowering susceptibility for residual stresses formation and cracking during solidification.

One of the existing approaches for preheating the substrate and powder bed during SLM/SLS processes is based on heating build platform by installing a heating element underneath the build platform. In this approach the build platform, and the all the powder stacked on top of it are heated up. In order to prevent the excessive heating of the surrounding structure, for example, walls surrounding the building platform, passive cooling (use of insulation) as well as active cooling are applied. The temperature of the build platform is constantly monitored by a thermocouple probe. The current preheating system can achieve temperatures up to 1000°C for long runs. Moreover, this technique results in undesired heating of the entire powdered bed, and also of the build platform, even though only heating of the surface of the layer of the powdered material to be scanned may be desired .

Another approach is to heat up surface of the powder bed by using Infra-red heating. Infra-red heaters are generally placed above the build platform to maintain a desired temperature (up to 900°C) of the powder bed and the powder in the feed cartridge.

Yet another approach is to use Laser-beam heating. In AM systems equipped with this technique, each powder bed layer is scanned in two stages, the preheating stage and the melting stage. In preheating stage, a high current laser beam with a high scanning speed is used to preheat the powder layer (up to 0.4 - 0.6 of melting temperature) in multiple passes. This technique makes the AM process lengthy as every layer built requires multiple passes.

Yet another approach is to use Induction heating, in which the powder bed along with a workpiece is placed inside an Induction coil surrounding the powder bed and the workpiece placed therein, and thus resulting into heating of the powder bed and the workpiece. This approach is not conveniently usable for AM processes that do not use a workpiece .

Moreover, the aforementioned techniques have other drawbacks as well, for example the maximum pre-heating temperature that can be achieved and uniformity or homogeneity in temperature distribution in heating of the surface of the layer of the powdered material to be scanned. Therefore, there is a requirement for an AM process having a heating technique that ensures heating of the surface of the powdered bed substantially uniformly, that may be used with or without having a workpiece, and that does not involve undesired heating of the other parts of the AM device for example of the entire powdered bed, or of the build platform, etc.

Thus an object of the present invention is to provide an additive manufacturing technique, in particular an additive manufacturing apparatus and an additive manufacturing method for preheating of the surface of the layer of the powdered material to be scanned.

The above object is achieved by an additive manufacturing apparatus according to claim 1 of the present technique, and an additive manufacturing method according to claim 8 of the present technique. Advantageous embodiments of the present technique are provided in dependent claims.

In an aspect of the present technique, an additive manufacturing apparatus is presented. The additive manufacturing apparatus, hereinafter also referred to as the AM apparatus includes a part building module having a build platform, a powder supply module also known as a feed cartridge for storing a powdered material, a spreading mechanism, a hot gas injection module, and an energy beam arrangement. The part building module bounds a bed of powdered material provided by the powder supply module to the part building module layer by layer. The build platform receives and supports the bed of powdered material, and optionally a workpiece embedded within the bed of powdered material when such workpiece is being used. The spreading mechanism spreads powdered material along a direction of spreading of the powdered material to form a layer of powdered material on the build platform and/or on the bed of powdered material in successive build cycles. The hot gas injection module provides a film of a gas over a surface of the bed of powdered material. The gas may be, but not limited to, Argon or Nitrogen or any gas that is being used in the atmosphere of inert gas formed in the part building module for protecting the thin layers of the particles of powdered material from contaminants and from moisture pickup. The gas forming the film is at a predetermined temperature configured to provide heating of the surface of the bed. The hot gas injection module includes a gas supply unit, one or more gas injectors, and a heating element. The gas supply unit stores and provides the gas. The injectors receive the gas from the gas supply unit and inject the gas into the part building module forming the film over the surface of the bed of the powdered material . The heating element heats the gas to the predetermined temperature before being injected by the one or more gas injectors. The energy beam arrangement selectively scans portions of the surface of the bed of powdered material so heated by the film and melts or sinters the selectively scanned portions to form the part by itself or onto the workpiece or onto a previously formed part. The film is formed contiguous with the surface of the bed of powdered material and thus heats up the surface of the bed of powdered material. The phrase 'forming the film' and like phrases as used herein includes injecting the gas on the surface for formation of the film and thereafter further injecting, intermittently or continuously, the gas to maintain the film so formed. The heating via the hot gas film as performed in the present technique heats up the surface of the bed of powdered material directly, without heating the entire powder bed or the build platform as is done in the aforementioned conventional additive manufacturing techniques. The temperature of the gas forming the film and a time duration for which the film is formed or maintained is selected such that a desired heating effect of the surface of the bed of powdered material is achieved. By increasing or decreasing the temperature of the gas forming the film or by altering the time duration for which the film is formed or maintained on a given layer of the powdered material, the amount of heating of the surface of the bed of powdered material can be controlled. Lesser time duration or lower temperature of the gas forming the film results in lesser heating of the surface of the bed of powdered material, and vice versa.

In an embodiment of the AM apparatus, at least one of the one or more gas injectors includes a single elongated slit, as opposed to multiple holes, for releasing the gas to form the film. The slit is elongated parallel to the surface of the bed of the powdered material and to the direction of spreading of the powdered material by the spreading mechanism. Thus the film formed is capable of covering the entire surface of the bed of the powdered material without interfering with operation of the spreading mechanism.

In another embodiment of the AM apparatus, at least one of the one or more gas injectors includes an array of a plurality of openings or holes. Each opening releases the gas independent of the other openings and the gas released from several or all such openings forms the film. The array is arranged parallel to the surface of the bed of the powdered material and to the direction of spreading of the powdered material by the spreading mechanism. Thus the film formed is capable of covering the entire surface of the bed of the powdered material without interfering with operation of the spreading mechanism.

In another embodiment of the AM apparatus, the one or more gas injectors are retractable into a wall of the part building module. Thus the gas injectors can be retracted within the wall when the spreading mechanism is operational to form the layer of powdered material and thereby the gas injectors do not interfere with operation or movement of the spreading mechanism. The gas injectors are exposed or pushed out of the wall of the part building module only when the formation of the film is desired and at all other times during the AM process the gas injectors can be positioned within the wall of the part building module.

In another embodiment of the AM apparatus, at least one of the one or more gas injectors are positioned on a first side of the part building module oriented parallelly to the direction of spreading of the powdered material by the spreading mechanism. Moreover, in another embodiment of the AM apparatus in addition to the aforementioned embodiment, at least one of the one or more gas injectors is positioned on a second side of the part building module oriented parallelly to the direction of spreading of the powdered material by the spreading mechanism. The first side and the second side are opposite to each other or in other words facing each other. Thus, the gas injectors do not interfere with operation or movement of the spreading mechanism.

In another embodiment, the AM apparatus further includes a flow rate regulator. The flow regulator controls a flow rate of the gas injected from one or more gas injectors into the part building module, and thereby controls the formation of film and maintenance of the film. Furthermore, by regulating or controlling the flow rate of the gas injected from one or more gas injectors the flow regulators ensures that the powdered material at the surface of the bed is not disturbed thereby reducing chances of any distortions in the surface of the bed of powdered material.

In another aspect of the present technique an additive manufacturing method, hereinafter also referred to as the AM method or simply as the method, is presented. In the method a layer of powdered material is spread on a build platform of an AM apparatus. Subsequently or simultaneously, a gas is heated to a predetermined temperature. Thereafter, the surface of the bed of powdered material on the build platform is heated by forming a film of the gas so heated over the surface of the bed of powdered material. As aforementioned, the phrase forming the film' and like phrases as used herein for the AM apparatus and the AM method includes injecting the gas on the surface for formation of the film and thereafter further injecting, intermittently or continuously, the gas to maintain the film so formed. Finally in the AM method, one or more portions of a surface of the layer of powdered material are selectively scanned by an energy beam arrangement, thereby melting or sintering the selectively scanned portions to form the part or portions or layers of the part. In the AM method of the present technique, the gas may be, but not limited to, Argon or Nitrogen or any gas that is being used in the atmosphere of inert gas formed in the part building module of the AM apparatus .

In an embodiment of the AM method, the heating of the surface of the bed of powdered material on the build platform by forming the film of the gas is continued after the portions of the surface of the layer of powdered material are selectively scanned. This provides post heating and thermally regulated cooling of the scanned portions.

In another embodiment the method, after a layer of the part is previously formed by melting or sintering the selectively scanned portions as aforementioned, the build platform is lowered along with the layers of the part previously formed and an existing bed of powdered material . The one or more layers of the part previously formed are now workpiece for the further steps of the AM process of the present technique. The lowering of the build platform provides space on top of the existing bed of powdered material to accommodate a new layer, i.e. a subsequent layer or another layer, of powdered material to be subsequently spread. Thereafter, the new layer of powdered material is spread on the existing bed of powdered material, i.e. supported on the build platform, and on a surface of the previously formed layer of the part i.e. on a surface of the workpiece . Therefore, the new layer of powdered material spreads continuously over the existing bed of powdered material and the surface of the workpiece. Thereafter in the method of the present technique, the surface of the bed of powdered material i.e. the surface of the new layer on the build platform is heated by forming another film of the gas over the surface of the bed of powdered material. Finally, in the method of the present technique, one or more portions of the surface of the new layer of powdered material are selectively scanned by the energy beam arrangement to melt or sinter the selectively scanned portions onto the workpiece. Thus the AM method can be repeated in a looped manner and each new layer added to the powder bed may be heated up using the hot gas film heating of the present technique before being melted or sintered, and consequently added, onto the underlying workpiece. Additionally, the heating of the surface of the bed of powdered material on the build platform is continued after the portions of the surface of the new layer of powdered material are selectively scanned. This provides post heating and thermally regulated cooling of the scanned portions of the new layer.

In another embodiment, the method includes controlling a flow rate of the gas while forming the film of the gas over the surface of the bed of powdered material. By controlling or regulating the flow rate of the gas while forming the film the formation of film and maintenance of the film are controllable. Furthermore, by regulating or controlling the flow rate of the gas the film may be formed such that the powdered material at the surface of the bed is not disturbed thereby reducing chances of any distortions in the surface of the bed of powdered material .

In another embodiment of the AM method, the predetermined temperature is between 40 percent and 90 percent of a melting temperature or a sintering temperature of the powdered material. This provides a range for achieving effective preheating, and optionally for achieving effective post-heating, of the surface of the bed of the powdered material.

In another embodiment of the AM method, in forming the film, the gas is injected over the surface of the bed of powdered material perpendicularly to a direction of spreading of the powdered material. Thus gas injectors that are used for injecting the gas to form the film do not interfere with operation or movement of the spreading mechanism.

The present technique is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawing, in which:

FIG 1 schematically illustrates a top

conventionally known additive manufacturing system;

FIG 2 schematically illustrates a side view of the conventionally known additive manufacturing system of FIG 1;

FIG 3 schematically illustrates a top view of an exemplary embodiment of an additive manufacturing apparatus having gas injectors, in accordance with aspects of the present technique;

FIG 4 schematically illustrates a side view of the additive manufacturing apparatus of FIG 3 as viewed along a direction perpendicular to a direction of spreading of the powdered material to form layers ; FIG 5 schematically illustrates another side view of the additive manufacturing apparatus of FIG 3, as viewed along the direction of spreading of the powdered material to form layers ; FIG 6 depicts a flow chart representing an additive manufacturing method in accordance with aspects of the present technique;

FIG 7 schematically illustrates an exemplary embodiment of the AM method of the present technique depicting an initial stage of the AM method wherein no preformed substrate or workpiece is being used in the AM method;

FIG 8 schematically illustrates another exemplary embodiment of the AM method of the present technique also depicting an initial stage of the AM method wherein a pre-formed substrate or a workpiece is being used in the AM method and a part is to be built on top of the workpiece;

FIG 9 schematically illustrates a later stage, subsequent to the stage of FIGs 7 and 8, of the AM method of the present technique;

FIG 10 schematically illustrates an exemplary embodiment of the gas injector of the present technique; and

FIG 11 schematically illustrates another exemplary embodiment of the gas injector of the present technique .

Hereinafter, above-mentioned and other features of the present technique are described in details. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details.

It may be noted that in the present disclosure, the terms "first", "second", etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated.

The basic idea of the present technique is to heat a surface of a powder bed by using a film of hot gas before selectively scanning the surface to sinter or melt the powder material. FIG 1 schematically illustrates a top view of a conventionally known additive manufacturing system 2 and FIG 2 schematically illustrates a side view of the conventionally known additive manufacturing system 1 of FIG 1.

The additive manufacturing system 2, hereinafter also referred to as the AM system 2 or simply as the system 2, generally includes a part building module 10, also known as the build chamber 10, in which a part is build by additive manufacturing (AM) for example by SLM or SLS processes . The part building module 10, hereinafter also referred to as the module 10, is a container for example a box shaped or barrel shaped container and having a top side of the container open. FIG 2 represents such a container having side walls 11,12, 13,14 and a bottom surface 15. The side walls 11,12,13,14 and the bottom surface 15 together define a space in which the part is built. The part may be build with or without a prefabricated workpiece or substrate. The space receives a workpiece 5 when the part is built onto the workpiece 5 for example as a part or integral addition to the workpiece 5. The workpiece 5 is an object that is supposed to be worked on by the AM system and built upon by addition of layer after layer by a suitable AM process by adding layer after layer of powdered material 7. The workpiece 5 may also be understood as portions or layers of the part that is to be built and that are already built by the AM process in previous cycles of layer scanning. The powder material 7 is provided by a powder storage module 20, also known as the feed cartridge 20, that stores the powdered material 7, hereinafter also referred to as the powder 7. The powder 7 in the feed cartridge 20 is stored in an open top container having side walls 21, 22 and a bottom 26. The bottom 26 is placed on top of a piston 28 that makes the bottom 26 slide or move in Z direction, as represented by the coordinate system shown in FIG 2.

When the piston 28 moves upwards in the Z direction, i.e. in a direction 29, the powder 7 from the container 20 is raised above and outside the container 20. The powder 7 is then spread as top surface 9 of a bed 8 of the powder 7 in the module 10 by using a powder spreading mechanism 30, hereinafter also referred to as the spreading mechanism 30 or simply as the mechanism 30, which evenly spreads a thin layer of the powder 7 in the module 10. The layer is spread in a direction 32 shown in FIG 2. Reference numeral 33 in FIG 1 presents an axis along the direction 32. The opposing walls 11, 12 are generally perpendicularly disposed to the axis 33. Usually the layer spread has a thickness of few micrometers, for example between 20 μπι and 100 μτα.

The module 10 or the build chamber 10 binds the bed 8 of powdered material 7 limiting the bed 8 by the side walls 11,12,13,14 and the bottom surface 15. The module 10 also includes a build platform 16. The bottom surface of the container of the module 10 is formed by the build platform 16, hereinafter also referred to as the platform 16. The platform 16 receives and supports the bed 8 of powdered material 7 and also the workpiece 5, if any, that is positioned on the platform 16 embedded within the bed 8. The platform 16 is placed on top of a piston 18 that makes the platform 16 slide or move in Z direction, as represented by the co-ordinate system shown in FIG 2.

When the piston 18 moves downward in the Z direction, i.e. in a direction 19, the bed 8, along with the workpiece 5 when present, is lowered thereby creating a space at surface 9 of the container of the module 10 to accommodate the layer that is spread by the spreading mechanism 30. The layer so spread by the spreading mechanism forms the surface 9 of the bed 8 and also covers a surface 55 of the workpiece 5 when present.

It may be noted that although in FIGs 1 and 2 only one feed cartridge 20 and associated powder spreading mechanism 30 have been depicted, in most of the AM systems 2 there are generally two such feed cartridges 20 and associated powder spreading mechanisms 30, one on each side of the module 10, such as on side of the opposing walls 11 and 12.

The system 2 also includes an energy beam arrangement 40. The energy beam arrangement 40 generally has an energy source 41 from which an energy beam 42 such as a Laser beam 42 or an electron beam 42 is generated, and a scanning mechanism 44 that directs the beam 42 to specific selected parts of the surface 9 of the powder bed 8 to melt or sinter the selectively scanned portions to form the layers of the part 5 or onto the workpiece 5 when present. The specific portions of the surface 9 to which the beam 42 is directed are referred to as scanned. The selections of portions that are to be scanned by the beam 42 by action of scanning mechanism 44 are based on a 3D model, for example a CAD model, of the part that has to be built. When the part is being built on a preformed substrate or on previously scanned and thereby built layers of the part, the portions of the surface 9 that are selectively scanned by the beam 42 are generally limited on top of the surface 55 and thus are able to melt or sinter and be added to the surface 55 of the substrate or on the previously scanned and built layers of the part i.e. on the surface 55 of the workpiece 5. Once added to the workpiece 5, the portions of the layer so added form part of the workpiece 5.

The build chamber 10, the feed cartridge 20, the spreading mechanism 30, and the energy beam arrangement 40 are well known in the art of additive manufacturing thus not described herein in further details for the sake of brevity.

FIGs 3, 4 and 5 schematically illustrates a top view, a side view, and another side view of an exemplary embodiment of an additive manufacturing apparatus 1 in accordance with aspects of the present technique. FIG 4 schematically illustrates the side view of the additive manufacturing apparatus of FIG 3 as viewed along a direction perpendicular to the direction 32 of spreading of the powdered material 7 as shown in FIGs 1 and 2. The direction perpendicular to the direction 32 is along an axis 35 as shown in FIG 3. FIG 5 schematically illustrates the side view of the additive manufacturing apparatus 1 of FIG 3, as viewed along the direction 32 of spreading of the powdered material 7 i.e. along the axis 33.

The additive manufacturing apparatus 1 of the present technique hereinafter also referred to as the AM apparatus 1 or simply as the apparatus 1, includes the build chamber 10, the powder supply module 20 or the feed cartridge 20, the powder spreading mechanism 30, and the energy beam arrangement 40 as explained in reference to FIG 1. Additionally, the apparatus 1 includes a hot gas injection module 60, hereinafter also referred to as the module 60.

The module 60, as shown in FIG 4, includes a gas supply unit 62, one or more gas injectors 64, and a heating element 68.

The gas supply unit 62 stores and provides a gas 99. The gas 99 may be, but not limited to, Argon or Nitrogen or any gas that is being used in an atmosphere of inert gas formed in the part building module 10 for protecting the thin layers of the particles of powdered material 7 from contaminants and from moisture pickup. The one or more gas injectors 64 receive the gas 99 from the gas supply unit 62 and inject the gas 99 into the part building module 10.

FIG 5 schematically shows working of the gas injectors 64, hereinafter also referred to as the injectors 64. Region A in FIG 5 has been depicted in enlarged view in top part of FIG 5. The gas 99 injected into the part building module 10 or in other words released from the injectors 64 is injected or released in such a way that the gas 99 forms a film 90 over the surface 9 of the bed 8 of the powdered material 7 present in the module 10, particularly on top of the platform 16. The heating element 68, for example an electrical heater, heats the gas 99 to a predetermined temperature before the gas 99 is injected or released by the injectors 64. The heating element 68 may heat the gas 99 in the gas supply unit 62, or may heat the gas 99 while the gas 99 is flowing from the gas supply unit 62 to the injectors 64. As shown in FIG 5, the film 90 is formed contiguous with the surface 9 of the bed 8 of powdered material 7, and preferably covers or envelops entire area of the surface 9. The predetermined temperature is higher than an ambient temperature in the module 10, and higher than temperature of the inert gas forming the atmosphere in the module 10. For example, the predetermined temperature of the gas 99 may be between 40% and 90% of a melting temperature or sintering temperature of the powdered material 7. The injectors 64 inject the heated gas 99 onto the surface 9 resulting into formation of the film 90 and thereafter optionally the injectors 64 continue injecting, intermittently or continuously, the heated gas 99 to maintain the film 90 so formed for a desired or predetermined duration of time, i.e. for a given time period.

As a result of the covering of the surface 9 by the film 90 of the heated gas 99, the surface 9 of the bed 8 of powdered material 7 heats up i.e. the powdered material 7 at the surface 9 or forming the surface 9 heat up . The temperature of the gas 99 forming the film 90 and/or the time duration for which the film 90 is maintained is selected such that a desired heating effect of the surface 9 of the bed 8 of powdered material 7 is achieved. Thus, the module 60 provides the film 90 of the gas 99 over the surface 9 of the bed 8 of powdered material 7 before the energy beam arrangement 40 selectively scans each layer during the AM process of the present technique. Hereinafter positioning, orientation and further structural aspects of the injectors 64 have been explained in further details. The injectors 64 may be placed on the walls 11,12,13,14. In an embodiment of the AM apparatus 1, the injectors 64 are retractable into the wall 11,12,13,14 on which the injectors 64 are position. The injectors 64 are retracted within the wall 11,12,13,14 when the spreading mechanism 30 is operated i.e. when the spreading mechanism 30 is spreading the powdered material 7 to form the layer of powdered material 7. The injectors 64 are pop-out or are exposed or pushed out of the wall 11,12,13,14 when the formation of the film 90 is desired. Alternatively, as depicted in FIGs 3 and 5, one, i.e. a first injector 64, of the one or more injectors 64 is positioned on a first side 13' of the part building module 10 i.e. on the side of the module 10 towards the wall 13. In other words, the injector 64 is oriented perpendicularly to the axis 35 and parallelly to the axis 33. The gas 99 is injected onto the surface 9 in a direction 34 along the surface 9 as shown in FIG 3. Additionally, as shown in FIGs 3 and 5, another, i.e. a second injector 64, of the one or more injectors 64 is positioned on a second side 14' of the part building module 10 i.e. on the side of the module 10 towards the wall 14. The gas 99 is injected from the second injector 64 onto the surface 9 in a direction 36 along the surface 9 as shown in FIG 3. In other words, the first and the second injectors 64 are oriented perpendicularly to the axis 35 and parallelly to the axis 33 as shown in FIG 3.

FIGs 10 and 11 schematically illustrate further details of the injectors 64. Although FIGs 10 and 11 show only one injector 64, the one or more of the injectors 64 may be similar to the injector 64 depicted in FIGs 10 and 11. In an embodiment of the AM apparatus 1 as shown in FIG 11, the injector 64 includes a plurality of openings 66 or holes 66 or nozzles 66. The openings 66 are arranged in an array. Each opening 66 releases the gas 99 independent of the other openings 66 and the gas 99 released from several or all such openings 66 forms the film 90. The array is arranged parallel to the surface 9 of the bed 8 of the powdered material 7 and to the direction 32 of spreading of the powdered material 7. In another embodiment of the AM apparatus 1 as shown in FIG 10, the injector 64 includes a single elongated slit 65, as opposed to multiple openings 66 of FIG 11, for releasing the gas 99 to form the film 90. The slit 65 is elongated parallel to the surface 9 of the bed 8 of the powdered material 7 and to the direction 32 of spreading of the powdered material 7.

In another embodiment, the AM apparatus 1 further includes a flow rate regulator 69 as shown in FIG 4. The flow rate regulator 69, also referred hereinafter to as the flow regulator 69, controls a flow rate of the gas 99 injected from the injectors 64 into the part building module 10. The flow regulator 69 may include valves, flow stoppers, etc. Such mechanisms for regulating a flow of gasses out from a nozzle or opening are well known in the art of fluid mechanics and thus not explained herein in further details for the sake of brevity.

Thus in the AM apparatus 1 of the present technique, heating of the powdered material 7 at the surface 9 of the bed 8 of the powdered material 7 is achieved via the hot gas film 90. The hot gas film 90 heats up the powdered material 7 at the surface 9 directly.

The present technique also presents an additive manufacturing method 100, hereinafter also referred to as the AM method 100 or simply as the method 100, as depicted in the flow chart of FIG 6. The method 100 is implemented by the AM apparatus 1 as explained hereinabove with respect to FIGs 1 to 5 and FIGs 10 and 11. The method 100 of the flow chart of FIG 6 is explained hereinafter in combination with FIGs 7, 8 and 9. In explaining the method 100 references have been made to the AM apparatus 1 and its components such as the build platform 16 that may be understood to be same as that explained in reference to FIGs 1 to 5 and FIGs 10 and 11.

FIG 7 schematically illustrates an initial stage of an exemplary embodiment of the AM method 100 of the present technique. The representation of FIG 7 schematically depicts an instance wherein a part is to be manufactured by the AM method 100 of the present technique without using a preformed workpiece or substrate. FIG 8 schematically illustrates another exemplary embodiment of the AM method 100 of the present technique also depicting an initial stage of the AM method 100 wherein a pre-formed substrate 5 or a workpiece 5 is being used in the AM method 100 and a part is to be built on top of the workpiece 5. Therefore, FIGs 7 and 8 present two different scenarios or embodiments of the AM method 100 wherein the AM method 100 is started without the pre-formed workpiece 5 and with the pre-formed workpiece 5.

As shown in FIG 6, the method 100 includes a step 110 in which a layer 70 of powdered material 7 is spread on a build platform 16 of the AM apparatus 1, by using the spreading mechanism 30. As shown in FIG 7 the layer 70 may be a first layer formed on the platform 16 and thus the bed 8 is formed only of the first layer 70 of powdered material 7. Alternatively, as shown in FIG 8, the layer 70 may be a first layer 70 formed on the workpiece 5, particularly on a surface 55 of the workpiece 5, positioned on the platform 16 embedded in a pre-existing bed 8 of powdered material 7. A top part of the layer 70 in for both FIGs 7 and 8, is a surface 9 which forms the surface 9 of the bed 8 of powdered material 7.

Subsequent to or simultaneously with the step 110, in a step 120 in the method 100 a gas 99 is heated to a predetermined temperature, for example between 40% and 90% of a melting temperature or sintering temperature of the powdered material 7. Thereafter, the surface 9 of the bed 8 of powdered material 7 standing on the build platform 16 is heated in a step 130, which is subsequent to step 110 and step 120. The heating 130 of the surface 9 is performed by forming a film 90 of the gas 99 so heated in the step 120. The film 90 is formed over or on the surface 9 and is contiguous or adjacent to the surface 9 i.e. the gas 99 forming the film 90 is in direct physical contact with the surface 9. Finally in the AM method 100 as shown in FIG 6, in a step 140 one or more portions of the surface 9 of the layer 70 of powdered material 7 are selectively scanned by the energy beam arrangement 40 of the AM apparatus 1. As a result of the step 140 the powdered material 7 in the selectively scanned portions of the layer 70 is melted or sintered to form the part or portions or layers of the part. As aforementioned in description for the AM apparatus 1, in the AM method 100 of the present technique, the gas 99 may be, but not limited to, Argon or Nitrogen or any gas that is being used in the atmosphere of inert gas formed in the part building module 10 of the AM apparatus 1.

The film 90 formed in the step 130 may be allowed to disintegrate or dissolve into the part building module 10 of the AM apparatus 1 before the step 140 is performed. Alternatively, in an embodiment of the AM method 1, the heating 130 of the surface 9 of the bed 8 of powdered material 7 is continued during and after the step 140 by maintaining the film 90 over the surface 9 of the layer 70.

Optionally, in addition to the aforementioned steps 110 to 140, the method 100 may be continued further as follows: In a step 150, following the step 140, the platform 16 is lowered in the direction 19 (shown in FIGs 4 and 5) along with portions or layers of the part formed as a result of the previously performed step 140, and along with the workpiece 5 when present, and the existing bed 8 of powdered metal material 7. The layers of the part formed as a result of the previously performed step 140, with or without the pre- formed substrate 5, are referred hereinafter as the workpiece 5 for further steps of the AM method 100.

As a result of the step 150, a space on top of the existing bed 8 is generated. The space so generated is same as the thickness of the next layer that is to be spread on the powder bed 8. Thereafter, a new layer 80 or another layer 80, as shown in FIG 8, is spread in a step 160 by using the spreading mechanism 30 and the powder 7 provided by the feed cartridge 20. The space created in the step 150 accommodates the layer 80 of powdered metal material 7 which now forms the surface 9 of the powder bed 8. As shown in FIG 8, the layer 80 also spreads continuously over a previously formed layer 75 of the workpiece 5. The workpiece 5 at this stage has a surface 56, which includes a surface of the previously formed layer 75. Thereafter, in the AM method 100 of the present technique, in a step 170 the surface 9 of the bed 8 of powdered material 7 i.e. the surface 9 of the layer 80 is heated by forming another film 90 of the gas 99 on top of the surface 9 of the layer 80. Finally, in the AM method 100 of the present technique, in a step 180 one or more portions of the surface 9 of the layer 80 are selectively scanned by the energy beam arrangement 40 to melt or sinter the selectively scanned portions onto the workpiece 5.

In another embodiment, the AM method 100 includes controlling a flow rate of the gas 99 while forming the film 90 of the gas 99 over the surface 9 of the bed 8 of powdered material 7 during the step 130 and/or the step 170. Furthermore, in another embodiment of the AM method 1, in forming the film 90, the gas 99 is injected over the surface 9 of the bed 8 of powdered material 7 perpendicularly to the direction 32 as shown in FIGs 3, 10 and 11.

While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

List of Reference Characters

1 additive manufacturing apparatus

2 conventionally known system

5 work piece/substrate

7 powdered material

8 bed of powdered material

9 surface of the bed

10 part building module

11, 12, 13, 14, 21, 22 wall

13' first side of the part building module

14' second side of the part building module

15 surface of the build platform

16 build platform

18 piston

19 direction of movement of the piston

20 powder supply module

26 powder platform

28 piston

29 direction of movement of the piston

30 spreading mechanism

32 direction of spreading of the powdered material

33 axis along the direction of spreading of the powdered material

34 direction of injecting of gas from the first side

35 axis perpendicular to the direction of spreading of the powdered material

36 direction of injecting of gas from the second side

40 energy beam arrangement

41 energy source

42 power beam

44 scanning mechanism

55 surface of the work piece surface of the workpiece

hot gas injection module

gas supply unit

gas injectors

slit in the gas injector

openings in the gas injector

heating element

flow rate regulator

layer of powdered material

previously formed layer of the workpiece layer of powdered material

film

gas

additive manufacturing method

spreading a layer of powdered material

heating the gas to a predetermined temperature heating the surface of the bed

selectively scanning portions of the surface lowering the build platform

spreading the layer of powdered material heating of the surface of the bed

selectively scanning portions of the surface