Laser additive manufacturing control system and method

A computational method for controlling a powder particle uptake by a shielding gas in a laser additive manufacturing system. The computational method includes receiving a gas fluid domain, a powder bed domain, and an inlet shielding gas flow velocity of the laser additive manufacturing system. The method further includes determining a maximum gas flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the gas fluid domain. The method also includes determining a threshold uptake flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the powder bed domain. The method also includes controlling the powder particle uptake of the shielding gas in the laser additive manufacturing system in response to the maximum gas flow velocity and the threshold uptake flow velocity.

TECHNICAL FIELD

The present disclosure relates to a laser additive manufacturing control system and method.

BACKGROUND

Selective laser melting (SLM) is a laser additive manufacturing system and process that has attracted significant interest due to its potential to produce high-resolution and high-density parts from a variety of different metals and alloys. In an SLM process, a high-energy laser beam is utilized to melt and fuse metallic powder particles into a melt pool. Often, high local temperatures associated with the SLM process exceed the material evaporation point and cause evaporation. This vaporization process can cause a vapor-jet effect, which leads to the generation of emissions from the melt pool. Such emissions can include powder particles within the vapor jet and liquid droplets ejected from the melt pool as a result of strong surface tension effects. These ejected particles are commonly referred to as spatter. Such spatter may be redeposited on the powder particles and melt pool, thereby containing the build area and adversely affecting the build quality of the resulting part.

SUMMARY

According to one embodiment, a laser additive manufacturing system for controlling a powder particle uptake by a shielding gas is disclosed. The system includes an inlet configured to inlet a shielding gas flow, a main chamber configured to receive the shielding gas flow, an outlet configured to outlet the shielding gas flow, a substrate situated between the inlet and the outlet and configured to support a powder bed having a number of particles, a laser configured to melt pre-defined regions of the powder bed to form a melt pool and a controller having non-transitory memory for storing machine instructions that are to be executed by the controller and operatively connected to the inlet. The machine instructions when executed by the controller implement the following functions: receiving a gas fluid domain of the main chamber, a powder bed domain of the powder bed, and an inlet shielding gas flow velocity; determining a maximum gas flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the gas fluid domain; determining a threshold uptake flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the powder bed domain; and controlling the powder particle uptake of the shielding gas in the laser additive manufacturing system in response to the maximum gas flow velocity and the threshold uptake flow velocity.

According to another embodiment, a computational method for controlling a powder particle uptake by a shielding gas in a laser additive manufacturing system is disclosed. The method includes receiving a gas fluid domain, a powder bed domain, and an inlet shielding gas flow velocity of the laser additive manufacturing system; determining a maximum gas flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the gas fluid domain; determining a threshold uptake flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the powder bed domain; and controlling the powder particle uptake of the shielding gas in the laser additive manufacturing system in response to the maximum gas flow velocity and the threshold uptake flow velocity.

According to yet another embodiment, a computer readable medium is disclosed. The computer readable medium includes a non-transitory memory for storing machine instructions that are to be executed by a computer. The machine instructions when executed by the computer implement the following functions: receiving a gas fluid domain, a powder bed domain, and an inlet shielding gas flow velocity of a laser additive manufacturing system; determining a maximum gas flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the gas fluid domain; determining a threshold uptake flow velocity within the gas fluid domain based on the inlet shielding gas flow velocity and the powder bed domain; and controlling a powder particle uptake of a shielding gas in the laser additive manufacturing system in response to the maximum gas flow velocity and the threshold uptake flow velocity.

DETAILED DESCRIPTION

The description of a group or class of materials as suitable for a given purpose in connection with one or more embodiments implies that mixtures of any two or more of the members of the group or class are suitable. Description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description and does not necessarily preclude chemical interactions among constituents of the mixture once mixed.

Except where expressly indicated, all numerical quantities in this description indicating dimensions or material properties are to be understood as modified by the word “about” in describing the broadest scope of the present disclosure.

The first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.

Reference is being made in detail to compositions, embodiments, and methods of embodiments known to the inventors. However, it should be understood that disclosed embodiments are merely exemplary of the present invention which may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, rather merely as representative bases for teaching one skilled in the art to variously employ the present invention.

The term “substantially” or “about” may be used herein to describe disclosed or claimed embodiments. The term “substantially” or “about” may modify a value or relative characteristic disclosed or claimed in the present disclosure. In such instances, “substantially” or “about” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 10% of the value or relative characteristic.

Selective laser melting (SLM) is a non-limited example of a powder bed-based additive manufacturing process. In an SLM process, complex-shaped metal components are manufactured in a layer-by-layer fashion. In one example, one relatively thin layer of a metallic powder particle material is deposited upon a solid substrate or previously solidified material. Subsequently, a laser beam may be used to scan and melt one or more pre-defined regions of the relatively thin layer of the metallic powder particle material. Repeating the steps of melting and solidification of the layered metallic powder particle material generates a part, e.g., complex-shaped metal components.

One common issue to SLM and other powder bed-based laser additive manufacturing processes is the ejection of metallic powder particles from and around a melt pool forming during the melting steps. During an SLM process, a large number of ejected particles (otherwise known as spatter) can fall back to the powder bed or on already scanned and solidified regions of the particle due to gravity and/or the particle-gas flow interaction. The redeposited spatters may contaminate the surface of each layer and negatively affect the part quality, e.g., introducing porosity due to insufficient melting of the relatively large sized spatter. A shielding gas flow with an inlet flow rate may be used to remove spatter inside the SLM build chamber. The shielding gas flow attempts to entrain the spatter and move it away from the main build region (e.g., the powder bed) before the spatter falls back onto the build area (e.g., the powder bed and/or the melt pool).

While a shielding gas may be utilized to remove spatter from the build area of a powder bed-based additive manufacturing system, determining an appropriate flow rate or range of flow rates to achieve requisite spatter removal without causing other negative effects may be difficult. For instance, a shielding gas flow rate should be carefully decided because a relatively low shielding gas flow rate may not effectively remove spatter while a relatively high shielding gas flow rate may uptake metal powder particles from the powder bed. The uptake of metal powder particles may adversely affect the quality of the resulting part by redistributing the metal powder particles in the melt pool or an unwanted region of the powder bed. Moreover, the laser beam may directly irradiate a resulting thinner powder bed or a substrate supporting the powder bed once the powder particles are blown up from the substrate.

What is needed are a powder bed-based laser additive manufacturing control system, computational methods and computer readable storage medium having computer readable instruction thereon for causing a processor to carry out the computational methods, to effectively mitigate powder bed particle uptake. The present disclosure, in one or more embodiments, discloses computational methods to determine a threshold gas flow velocity based on a powder uptake phenomenon such that an inlet gas flow rate of an additive manufacturing build chamber is determined. In one or more embodiments, the powder bed-based laser additive manufacturing system may be controlled using the inlet gas flow rate determined using the computational methods of one or more embodiments. The computational methods may be implemented using a computer readable storage medium having computer readable program instructions thereon for causing a processor to carry out the computational methods.

As stated above, an SLM process is a non-limiting example of a powder bed-based additive manufacturing process.FIGS.1A and1Bdepict schematic, side views of SLM build chamber10showing an ideal shielding gas flow and a non-ideal shielding gas flow, respectively. SLM build chamber10includes laser assembly12and build platform14. Powder bed16is supported on build platform14. During the SLM process, laser assembly12scans a pre-defined region of powder bed16in scan direction18to form melt pool20. The scanning may proceed on a layer-by-layer basis of powder bed16.

SLM build chamber10also includes gas flow inlet channel22and gas flow outlet24. Gas flow inlet channel22may include one or more gas flow inlet nozzles for a shielding gas to flow through. The shielding gas may be an inert gas, such as Argon. As depicted by arrows26, the shielding gas flows from gas flow inlet channel22toward gas flow outlet24. As depicted by arrows28, the shielding gas up takes spatter30to remove it from powder bed16and melt pool20. According to the embodiment shown inFIG.1A, this uptake is a result of an ideal shielding gas flow because the removal of spatter30does not affect powder bed16. On the other hand, as depicted by arrows32onFIG.1b, the shielding gas additionally up takes metallic powder particles34of powder bed16. According to the embodiment shown inFIG.1B, this uptake is a result of a non-ideal shielding gas flow because the removal of spatter30also uptakes metallic powder particles34, thereby moving them to other regions of powder bed16and/or melt pool20. In one or more embodiments, computational methods are utilized to determine a threshold gas velocity above powder bed16and an inlet gas flow rate related thereto.

In one embodiment, a computational method is configured to determine an inlet gas flow rate to achieve an efficient rate of spatter removal while preventing and/or minimizing metallic powder particle uptake. The efficient rate of spatter removal may be any of the following values or in a range of any two of the following values: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% and 100%. The minimized metallic powder particle uptake rate may be any of the following values or in a range of any two of the following values: 0%, 0.01%, 0.1%, 0.5%, 1% and 2%. As part of the computational method, the interaction between the shielding gas fluid and the metallic powder particles is examined, and a threshold velocity of the shielding gas flow above powder bed16is determined to prevent or minimize metallic powder particle uptake during the spatter removal process.

In one embodiment, a computational method includes first and second computational steps. The first computational step may be a full-scale computational fluid dynamics (CFD) method configured to simulate gas flow characteristics in SLM build chamber10. The full-scale CFD method may model a domain of a relatively large size, e.g., 100 to 900 millimeters in the X, Y and Z directions. In one or more embodiments, the full-scale CFD method of the first computational step does not model metallic powder particles because the metallic powder particles may be less than 100 micrometers. This significant size difference may make the full-scale CFD method unsuitable to model the metallic powder particles. In these circumstances, the full-size CFD method does not model the metallic powder particles. Rather, a second computational step of a reduced scale may be utilized.

The second computational step may be a reduced scale CFD method integrated with a fully coupled discrete element method (DEM) (CFD-DEM method) configured to simulate the effect of the gas flow characteristics on metallic powder particle motion. The reduced scale CFD-DEM method may model a domain of a relatively reduced size, e.g., 1 to 3 millimeters in the X, Y and Z directions. In one or more embodiments, metallic powder particle motion may be modelled using the reduced scale CFD-DEM method. The second computational step may be configured to determine maximum gas flow velocity at a pre-determined height above powder bed16based on different inlet flow rates in SLM build chamber10. The pre-determined location above powder bed16may be any of the following values or in a range of any two of the following values: 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mm. The second computational step may be configured to determine a metallic powder particle uptake threshold velocity at the pre-determined height above the powder bed. Based on the output of the first and second steps of the computational method, the computational method is configured to determine the relationship between the metallic powder particle uptake threshold velocity and the inlet gas flow rate of the SLM build chamber.

The computational methods and steps, including, but not limited to, the CFD computational methods and the CFD-DEM computational methods, of one or more embodiments are implemented using a computing platform, such as computing platform50illustrated inFIG.2. The computing platform50may include a processor52, memory54, and non-volatile storage56. The processor52may include one or more devices selected from high-performance computing (HPC) systems including high-performance cores, microprocessors, micro-controllers, digital signal processors, microcomputers, central processing units, field programmable gate arrays, programmable logic devices, state machines, logic circuits, analog circuits, digital circuits, or any other devices that manipulate signals (analog or digital) based on computer-executable instructions residing in memory54. The memory54may include a single memory device or a number of memory devices including, but not limited to, random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, or any other device capable of storing information. The non-volatile storage56may include one or more persistent data storage devices such as a hard drive, optical drive, tape drive, non-volatile solid state device, cloud storage or any other device capable of persistently storing information.

Processor52may be configured to read into memory54and execute computer-executable instructions residing in CFD software module58and/or CFD-DEM software module60of the non-volatile storage56and embodying computational methodologies of one or more embodiments. Software modules58and/or60may include operating systems and applications. Software modules58and/or60may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java, C, C++, C#, Objective C, Fortran, Pascal, Java Script, Python, Perl, and PL/SQL.

Upon execution by the processor52, the computer-executable instructions of CFD software module58and/or CFD-DEM software module60may cause the computing platform50to implement one or more of the computing methodologies disclosed herein. Non-volatile storage56may also include CFD data62and CFD-DEM data64supporting the functions, features, calculations, and processes of the one or more embodiments described herein.

The program code embodying the algorithms and/or methodologies described herein is capable of being individually or collectively distributed as a program product in a variety of different forms. The program code may be distributed using a computer readable storage medium having computer readable program instructions thereon for causing a processor to carry out aspects of one or more embodiments. Computer readable storage media, which is inherently non-transitory, may include volatile and non-volatile, and removable and non-removable tangible media implemented in any method or technology for storage of information, such as computer-readable instructions, data structures, program modules, or other data. Computer readable storage media may further include RAM, ROM, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other solid state memory technology, portable compact disc read-only memory (CD-ROM), or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and which can be read by a computer. Computer readable program instructions may be downloaded to a computer, another type of programmable data processing apparatus, or another device from a computer readable storage medium or to an external computer or external storage device via a network.

Computer readable program instructions stored in a computer readable medium may be used to direct a computer, other types of programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions that implement the functions, acts, and/or operations specified in the flowcharts or diagrams. In certain alternative embodiments, the functions, acts, and/or operations specified in the flowcharts and diagrams may be re-ordered, processed serially, and/or processed concurrently consistent with one or more embodiments. Moreover, any of the flowcharts and/or diagrams may include more or fewer nodes or blocks than those illustrated consistent with one or more embodiments.

FIG.3Adepicts a schematic, perspective view of SLM build chamber100configured for use with computational methods of one or more embodiments. SLM build chamber100has a width (W), length (L) and height (H). In one embodiment, W, L and H are 450 mm, 450 mm and 400 mm, respectively, but these dimensions may very significantly based on the design of the SLM build chamber. W may be any of the following values or in a range of any two of the following values: 100, 200, 300, 400, 500, 600, 700, 800 and 900 mm. L may be any of the following values or in a range of any two of the following values: 100, 200, 300, 400, 500, 600, 700, 800 and 900 mm. H may be any of the following values or in a range of any two of the following values: 100, 200, 300, 400, 500, 600, 700, 800 and 900 mm. W, L and H may be independently selected based on these values and ranges.

SLM build chamber100includes inlet rail102configured to receive a shielding gas flow and to direct the shielding gas flow through cylindrical nozzles104. The diameter of inlet rail102may be any of the following values or in a range of any two of the following values: 35, 36, 37, 38, 39, 40, 41, 42, 43 and 44 mm. The axial centerline of inlet rail102may situated about 50 mm above the bottom of SLM build chamber100. The axial length of inlet rail102may be any of the following values or in a range of any two of the following values: 320, 330, 340, 342, 350, 360 and 370 mm. Cylindrical nozzles104are configured to direct the shielding gas flow into main chamber106of SLM build chamber100over powder bed108and toward outlet110. In the embodiment shown inFIG.3A, the number of cylindrical nozzles104is 13. The number of cylindrical nozzles104may be any of the following values or in a range of any two of the following values: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20. In the embodiment shown inFIG.3A, the diameter of each nozzle is 12 mm. The diameter of each cylindrical nozzle104may be any of the following values or in a range of any two of the following values: 10, 11, 12, 13, 14 and 15 mm. In the embodiment shown inFIG.3A, the center to center distance is 18 mm. The center to center distance of adjacent cylindrical nozzles104may be any of the following values or in a range of any two of the following values: 15, 16, 17, 18, 19 and 20 mm.

Outlet110is partially surrounded by outlet housing112. The width (W) of outlet housing may be any of the following values or in a range of any two of the following values: 45, 50, 55, 60, 65, 70 and 75 mm. The length (L) of outlet housing may be any of the following values or in a range of any two of the following values: 280, 290, 300, 310, 320, 330 and 340 mm. The shielding gas flow exits main chamber106through outlet110.

In one or more embodiments, the computational methods simulate a shielding gas flow in main chamber106by assuming the shielding gas is transient, incompressible and/or turbulent. In one or more embodiments, the turbulent flow behavior may be modeled using a k-e turbulent flow model. According to one or more computational methods disclosed herein, an inlet boundary condition for the shielding gas flow through inlet rail102may be referred to as a volume flow rate and an outlet boundary condition for the shielding gas flow exiting through outlet110may be referred to as an outflow. A CFD method may be utilized to simulate the shielding gas flow in main chamber106.

The simulated shielding gas flow is subsequently utilized to simulate shielding gas flow and metallic powder particle interaction. A reduced scale fluid-particle (e.g., a CFD-DEM method) may be used to simulate shielding gas flow and metallic powder particle interaction.FIG.3Bdepicts a schematic, side view of SLM build chamber100shown inFIG.3A. As shown inFIG.3B, the shielding gas starts to flow from inlet rail102within a pre-determined value for an inlet boundary condition as signified by arrows114. The shielding gas flows over powder bed108. The shielding gas flows toward outlet110as signified by arrows116. The metallic powder particles of powder bed108are initially settled in powder bed108, as shown inFIG.3B.

FIG.3Cdepicts a schematic, side view of SLM build chamber150showing gas fluid domain152and powder bed domain154configured for use with one or more steps of a computational method to simulate interactions between a shielding gas flow and metallic powder particles. Powder bed domain154is situated at the bottom of gas fluid domain152, as shown inFIG.3C. The length (L) of gas fluid domain152may be about 30 mm. The height (H) of gas fluid domain152may be about 30 mm. The width (W) of gas fluid domain may be about 0.4 mm. The length (L) of powder bed domain154may be about 4 mm. The height (H) of powder bed domain154may be about 0.2 mm. The depth (D) of powder bed domain154may be about 0.4 mm. In one or more embodiments, the volume of gas fluid domain152is relatively much larger (e.g., 90, 92, 94 or 96%) than powder bed domain154to ensure the shielding gas flow maintains a steady flow stream upon the powder bed.

The computational method to simulate shielding gas flow and metallic powder particle interaction may include first and second steps. The first step may include generating a powder bed. One method of generating the powder may include a rain-drop method, where a pre-determined number of different sized metallic powder particles fall freely within a container under the effects of gravity.FIG.4Adepicts a schematic, perspective view of different sized metallic powder particles200falling within container202under the force of gravity (g), signified by downward arrow204. As depicted by legend206, the different sizes of metallic powder particles200may have a diameter of about 2.000e-03 to 6.000e-03.FIG.4Bdepicts a schematic, perspective view of settled powder bed208after different sized metallic powder particles200have fallen within container202under the force of gravity (g). In one embodiment, settled powder bed208is imported into powder bed108ofFIG.3Aas the initial state for determining an interaction between a shielding gas flow and metallic powder particles. The shielding gas is assigned pre-determined flow properties. Based on these pre-determined flow properties, the shielding gas enters an inlet and exits from an outlet. This flow of shielding gas may cause metallic powder particles to be removed from the powder bed if the flow velocity exceeds a threshold flow velocity.

In one or more embodiments, different sized metallic powder particles are treated as perfect spheres with different diameters. According to the computation methods disclosed herein, the X, Y and Z directional velocities of individual metallic powder particles (including without limitation translational and rotational components) may be determined using Newton's second law of motion. The computational methods disclosed herein may also determine and account for the drag force due to the volume fraction of powder particles and particle-fluid interaction.

In one embodiment, the density and viscosity of the shielding gas for use with one or more computational methods is about 1.225 kg/m3and about 0.00001781 kg/m-s, respectively. In certain embodiments, the shielding gas density may be any of the following values or in a range of any two of the following values: 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 kg/m3. In certain embodiments, the shielding gas viscosity may be any of the following values or in a range of any two of the following values: 0.00001700, 0.00001800, 0.00001900, 0.00002000, 0.00002100 and 0.00002200 kg/m-s. In one embodiment, the density of the metallic powder particles for use with one or more computational methods is about 7,710 kg/m3. In certain embodiments, the density of the metallic powder particles may be any of the following values or in a range of any two of the following values: 2,000, 4,000, 6,000, 8,000, 10,000 and 12,000 kg/m3. In one embodiment, the size distribution of the metallic powder particles is in a range of about 18.8 μm (D10) to about 60.3 μm (D90), with a mean diameter of 36.7 μm.

FIG.5Adepicts a schematic, perspective view of SLM build chamber100showing vertical flow velocity plane118and horizontal flow velocity plane120of a shielding gas flow within main chamber106of SLM build chamber100using a pre-determined inlet shielding gas flow rate and a CFD computational method according to one embodiment.FIG.5Bdepicts a schematic, plan view of horizontal flow velocity plane120.FIG.5Cdepicts a schematic, plan view of vertical flow velocity plane118. The regions of different shading in velocity planes118and120represent different velocities in m/s. Legend122shows the different shading correlated to the velocity in the range of 0.000e+00 and 1.300e+00. As shown inFIG.5A, horizontal flow velocity plane120is taken at a pre-determined distance above powder bed108. According to the computational method shown inFIG.5A, the pre-determined distance is about 1 mm. In certain embodiments, the pre-determined distance may be any of the following values or in a range of any two of the following values: 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mm.

The velocity planes118and120ofFIG.5Aare generated using an inlet shielding gas flow rate of 250 liter/minute. In other embodiments, the pre-determined inlet shielding gas flow rate may be any of the following values or in a range of any two of the following values: 10, 100, 1,000 and 10,000 liter/minute. As can be seen byFIG.5A, the flow velocity of the inlet shielding gas is not evenly distributed within main chamber106. In one embodiment, the computational method determines the interaction between the metallic powder particles in powder bed108at regions in which the flow velocity is within a relatively high range (e.g., 1, 2, 3, 4, 5, 10 or 20% of the maximum flow velocity). If the metallic powder particles in powder bed108are not affected by gas flow at the high velocity regions, the metallic powder particles at low velocity regions are also not affected by gas flow.

As shown inFIG.5B, the maximum flow velocity above powder bed108is about 1.3 m/s. The metallic powder particles in a maximum velocity region may be subject to uptake due to gas flow-particle interaction when the maximum gas flow rate reaches a threshold value. The maximum flow velocity at the pre-determined distance above powder bed108determines a powder particle uptake condition. If the maximum flow velocity at the pre-determined distance above powder bed108is less than the threshold velocity for powder particle uptake, then none of powder bed108is subject to the powder uptake condition.

FIG.6is graph250depicting a functional relationship between maximum velocity (meter/second or m/s) based on an inlet gas flow rate (Liter/minute or L/m) at a pre-determined distance of 1 mm above powder bed108. Data points252are determined using the computational method of one or more embodiments. Dotted line254is a fitted line through data points252. As can be seen inFIG.6, the maximum velocity increases linearly with the increase of inlet flow rate. The linear relationship shown inFIG.6is y(maximum velocity in m/s) equals 0.0055x(inlet gas flow rate (L/m) minus 0.0925. The functional relationship shown inFIG.6may be used to correlate gas flow velocities that do not create the powder particle uptake condition to the inlet flow rate in response to an identified threshold velocity.

FIG.7Ais an image of velocity contour156within gas fluid domain152taken in a vertical velocity plane in response to a pre-determined inlet flow velocity. In the computational method used forFIG.7A, the inlet flow velocity is 9 m/s. As shown inFIG.7A, steady flow stream158is formed over powder bed domain154. Legend160indicates that the velocity of steady flow stream158of about is less than the inlet flow velocity of 9 m/s due to turbulence and other factors.FIG.7Bis an image of velocity contour160taken in a vertical velocity plane in a region between powder bed domain154and pre-determined distance162above powder bed domain154. As shown inFIG.7B, the pre-determined distance162is 1 mm.FIG.7Cis an image of particles164up taken from particles of powder bed domain154. As shown in legend163ofFIG.7B, the maximum gas velocity at the pre-determined distance is 7.34 m/s, and at this maximum gas velocity, particles164are up taken from particles of powder bed domain154. Legend166shows shading for different particle sizes. According to the computational methods of one or more embodiments, this particle uptake condition is controlled.

Different maximum velocities at the pre-determined distance may be obtained by varying the inlet gas velocity of the computational methods of one or more embodiments.FIGS.8A,8B and8Cdepicts images of powder bed300at different inlet gas velocities of 6.53 m/s, 7.34 m/s and 8.19 m/s.FIGS.8A,8B and8Cinclude legend302showing shading for different particle sizes. As shown inFIG.8A, no particles in powder bed300are up taken by the inlet gas flow. As shown inFIG.8B, particles304are up taken from powder bed300. As shown inFIG.8C, particles306are up taken from powder bed300and region308is almost exposed in the underlying substrate. Accordingly, with increased gas velocity, individual powder particles may be gradually blown away from their initial locations, and the powder bed becomes thinner and the surface morphology of powder bed300changes significantly. Moreover, some regions (e.g., region308) may have no powder particles on the underlying substrate. As shown inFIGS.8A,8B and8Cvia the computational methods of one or more embodiments, the maximum velocity of 7.34 m/s at the pre-determined distance of 1 mm shows an early stage of the powder particle uptake condition. According to the computational methods of one or more embodiments, this maximum velocity may be used as a threshold velocity for the powder particle uptake condition in response to the specific powder material and shielding gas parameters used.

The computational methods can be applied to varied powder and gas parameters.FIG.9Ashows an image of velocity contour350within gas fluid domain152and above powder bed domain154taken in a vertical velocity plane in response to a pre-determined inlet flow velocity based on certain powder particle and gas parameters. In this embodiment, the shielding gas has a density of 1.6228 kg/m3and a viscosity of 0.00002125 kg/m-s. In this embodiment, the powder particles have a density of 4,420 kg/m3and the size distribution of the powder particles are between 25 μm (D10) and 53 μm (D90) with a mean diameter of 38 μm. Legend352shows different shading for different velocities within velocity contour350.FIG.9Bshows an image of powder particle bed354within powder bed domain154upon application of velocity contour350. As shown inFIG.9B, particles356are up taken from powder particle bed354at a maximum velocity of 6.523 m/s from an inlet volume flow rate of about 1,000 to 1,500 Liter/minute. According to the computational methods of one or more embodiments, the input velocity may be reduced to determine a threshold velocity for a powder particle uptake condition, such that the condition may be controlled.

The following application is related to the present application: U.S. patent application Ser. No. 16/592,250, filed on Oct. 3, 2019, and issued as U.S. Pat. No. 11,584,079 on Feb. 21, 2023. The identified application is incorporated by reference herein in its entirety.