JSON file

Overview

The simulation of powder bed/substrate fusion is a typical simulation setup, and such simulation preset is available.

All parameters of the simulation can be specified by the user in the input JSON file. If a parameter is not listed in the JSON file, default values from the default.json are used.

JSON data is written as a comma-separated list of key/value pairs. The list is enclosed in curly brackets. The key and value are separated by a colon(:) in the middle with the key on the left and the value on the right. The key is a string surrounded by double quotation marks. The value can be (1) a number, (2) a string, (3) or JSON data object. With the third option, the JSON data is nested.

Note

The nested field can be referred in the description with dot syntax, i.e. the {ScanStrategy: {Beam:  ... }} field is referred to as ScanStrategy.Beam.

Here are zero level data description. The values of ‘JSON’ data files are detailed in the further sections.

Key	Value type	Default value
outputDir	string	./output/
The directory will be created in the current folder. The output data will appear in it during the simulation
licenseFile	string	end-2022-12-31.lic
Provided with the software
config	JSON data
Computation parameters
sizes	JSON data
Substrate Size
NumericalParams	JSON data
Numerical parameters
PhysicalWorld	JSON data
Gravity and convection cooling model
Powder	JSON data
Powder settings
Substrate	JSON data
Substrate setting
Camera	JSON data
Gas environment of the melting proces
Material	string	CoCr
Material of the substrate and powder. Chosen from the Materials Library. See Materials
Filler	string	null
Material name for the filler particles model
ScanStrategy	JSON data
Energy source (Laser beam / electron beam) configuration
Sensors	JSON data
Sensors setting file
Tprobes	string
Temperature probes file
Visual	JSON data
Visualization parameters
PowderBedGenerator	JSON data
Settings of the internal powder bed generator
G-code-converter	JSON data
Converter settings for scanning path setting
MaterialsLibrary	JSON data
Materials library

For convenience, the provided JSON file is annotated. Some fields are added as comments for the user and are not used in the code. For example, the fields units and comment that can be found in different sections of the default JSON file are only reference.

Computation Parameters

Here the simulation configuration can be controlled with the parameters in the config section. Set the maximal number of steps MaxTimesteps or turn on AutoTermination to set upper limit on the simulation time. If the simulation takes too much disc space, you can increase DumpDataRate, IterationSubstepsRate, turn off DumpVTK, DumpVDB, DumpARR. If more frames per second are required in the rendered images animation, decrease IterationSubstepsRate. Other options are for advanced use of the software.

Key	Value type	Default value
AdaptiveResizePeriod	value	16
Number of time steps between grid resize events
TrMeshCellsMergeRate	value	8
The ratio of Tractile Mesh cells coalescing Rate to the cells splitting Rate
AllowToRunoutXYbox	true/false	false
Set to true to continue simulation even when the Meltpool Grid is outside the simulation region
LinkBeamWithMeltpool	true/false	false
The meltpool window is around the beam incidence spot when the beam is turned on. This options allows to link the meltpool Grid with beam center even if the beam power is 0
MemoryAllocation	string	device
Where to allocate data. Possible types: device, host, managed
StatsCalcRate	value	1
Internal use only. Doesn’t make sense in the release
DiagnosticsRate	value	1000
Number of time steps after which program statistics and diagnostics functions are called
calcCurv	true/false	true
Flag to include the curvature and wetting simulation
calcEvaporation	true/false	true
Flag to include the evaporation process
calcConvection	true/false	true
Flag to include the convection process
rayTracing	true/false	true
Flag to include the ray tracing process
EheatSolver	true/false	true
Flag to include the thermal process
BCFixedTemperatureXY	true/false	false
Flag to setup isothermal Boundary Conditions at x an y boundaries (\(T=\) preheating)
GasSolver	NA
Flag to include gas physics (this solver is supplied separately)
CriticalSpatters	value	10
ClearSpattersRate	value	1000
In the simulation, the high-resolution Meltpool grid follows the melted liquid. Sometimes, small droplets are ejected from the meltpool and fly across the domain; sometimes, some liquid droplet takes too long to cool down and solidify. In these cases, the meltpool grid becomes larger, and time cost for an iteration becomes too large. Check the rendered3D/ images. If this issue is visible, adjust these parameters. CriticalSpatter is the minimal number of cells inside liquid particles that are not deleted during the simulation and ClearSpattersRate is the number of steps between the calls of the procedure of removing the spatters
calcBubbles	true/false	false
Flag to enable the bubble simulation: correct pressure for the gas trapped by liquid and pore formation
calcGrains	true/false	false
Flag to enable the grains growth solidification based on the Cellular Automata model
StopIfGrainsLimitBoxReached	true/false	true
Terminate simulation with error if the meltpool reaches the limit box or if the Bound grains are reached by liquid cells
SolidificationCriterion	string	Temperature
The solidification process criteria besed on the temperature either on the grain growth Cellular Automata model. The possible values are Temperature and GrainsCA.
MaxTimesteps	value	1000000000
The maximal number of the time steps. The required number of the steps can be estimated as, i.e. <track length>/(<laser speed>*<time step>) + <extra> . The extra time must be just enough to observe solidification if only the track geometry is studied, or can be larger to study the cooling process.
AutoTermination	true/false	false
Turn on for automatic termination of simulation when scanning is finished and all liquid cells are solidified
DumpDataRate	value	100000
3D data dump rate (time steps). 3D data files take disc space and writing to disc takes time, so it should not be frequent
IterationSubstepsRate	value	1000
Frequency of all other outputs: images, probes, etc.
DumpVTK	true/false	true
Set false if you do not need to save VTK files with tractile mesh temperature and velocities of meltpool. This can save disk space.
DumpVDB	true/false	true
Set false if you do not need to save OpenVDB file geometry.vdb
DumpARR	true/false	true
Set false if you do not need to save ARR files

Simulation domain and Substrate Sizes

The sizes section defines full simulation domain size. The fluid dynamics simulation takes place only around the meltpool area. The meltpool area is allowed to move inside the bounds that are specified here.

Key	Value type	Default value
FullXapprox	value	0.006
FullYapprox	value	0.005
FullZapprox	value	0.004
An upper estimate of the simulation domain size (m). This is the sizes recorded in the geometry grid, the size of the volume in the geometry.vdb file.
substrate	value	0.0035
Substrate thickness (m). The simulation domain from \(z=0\) to \(z=\) substrate is filled with metal, unless initGeometryVDBfile is specified in the Substrate section.
substrateBase	value	0.0
z-coordinate of the lower boundary of the substrate
GrainsLimitBox	list of values	[[0, 0, 0], [1, 1, 1]]
An array of the two coordinates (m): the two corners of the Limit box where the grains are initialized

Numerical Parameters

The NumericalParams section defines the mesh cell size and units for nondimensionalization of time, mass and temperature.

Key	Value type	Default value
dr	value	3e-06
Mesh cell size (m). Should be much less than the smallest particle in the powder, meltpool depth and height. See recommended values
dt	value	3e-08
Time step size (s). See recommended values
unit_mass	value	1e-14
Mass unit (kg). In the numerical model, if \(m=1\) in the dimensionless units, the physical mass is \(m=\) unit_mass kg.
unit_T	value	1000.0
Temperature unit (K). In the numerical model, if \(T=1\) in the dimensionless units, the physical temperature is \(T=\) unit_T K.

Powder

In the KiSSAM simulation, the geometry of the powder particles is input through a VDB file. If the powder is defined with sphere coordinates and radii, it should be rasterized with the provided script. In the Powder section of the JSON file, the input VDB file is specified, and the wetting angle of powder particles, which is, in general, different from the wetting angle of the substrate.

Key	Value type	Default value
initSpheresVDBfile	string
The name of the VDB file with input solid geometry.
wettingAngle	value	120
Wetting angle of melt contacting with powder particles (degrees).
components	NA
Powder components weight composition with names, eg {“name1”: 0.3, “name2”: “balanced”}, If null than the values from MaterialLibrary will be used
initialNucleiDensity	value	0
Concentration of the initial grains in the substrate (1/m³)
FlecksFile	NA
The file with the initial position and size of the filler particles
FillerPSD	list of values	[[0, 5e-06], [100, 5.001e-06]]
FillerVolumeFrac	value	5
Settings for the initial distribution of the filler particles

Substrate

The substrate settings are in the Substrate section. All other properties of the substrate material are defined through the Material setting.

Key	Value type	Default value
preheating	value	300.0
Preheating temperature of the substrate (K)
wettingAngle	value	0
Wetting angle of the melt contacting with substrate (degrees)
components	NA
dictionary — Substrate components weight composition with names, eg {“name1”: 0.3, “name2”: “balanced”}. If null than the values from MaterialLibrary will be used
initGeometryVDBfile	string
Path to the file with the initial geometry. Leave empty for flat geometry.
initialNucleiDensity	value	100000000000000.0
Concentration of the initial grains in the substrate (1/m³)

Camera

The surrounding gas parameters in the chamber are defined in the Camera section.

Key	Value type	Default value
AmbientGas	string	Ar
The gas material is specified as one of the keywords for the materials in the Materials section.
pressure	value	100000.0
temperature	value	300.0
flowVelocity	value	1.0
Gas fluid parameters: pressure (P), temperature (K) and flow speed (m/s). Flow velocity is used in the Whitaker convection model.
initialVelocityX	value	0.0
initialVelocityY	value	0.0
initialVelocityZ	value	0.0
Initial gas velocity (m/s) is used in the RKDG gas solver if config.GasSolver is not 0.

Scanning Strategy

The scanning strategy is defined in the ScanStrategy. section of the JSON file. There are three presets: single track and square layer, and a manual input for the scan path.

Key	Value type	Default value
Type	string	SingleTrack
Scanning strategy preset. Can be SingleTrack, SquareLayer, or XYpositions.
SingleTrack	JSON data
Description of the Single Track scanning strategy.
SquareLayer	JSON data
Description of the Square Layer scanning strategy.
XYpositions	JSON data
Manual setting of an arbitrary scanning strategy
Beam	JSON data
Description of the energy source: power, shape, type.

Single Track

In this preset, laser beam turns on in the startPosX, startPosY position, travels parallel to the \(x\)-axis with the speed defined in the Beam section, and turns off when the travel distance is over the defined length.

Fig. 5 Single Track Scan Path

Key	Value type	Default value
length	value	0.005
Track length (m)
startPosX	value	0.0005
startPosY	value	0.00116
Starting position (m) of the laser in the simulation domain. It should be inside the domain defined with sizes.FullXapprox, sizes.FullYapprox. If the powder is inside the domain, the starting position of the laser should be in the domain covered by the powder.

Square Layer

The settings of a square layer simulation. In this preset, laser beam turns on in the startPosX, startPosY position. If hatchX (hatchY) is zero, the beam travels parallel to the \(x\)-axis (\(y\)-axis) until the travel distance is over dimX (dimY), then waits for delayBetweenTracks seconds, then it shifts by hatch distance and travels for the same distance in the opposite direction. The scanning speed is defined in the Beam section.

Key	Value type	Default value
startPosX	value	0.0005
startPosY	value	0.00116
Starting position (m) of the laser in the simulation domain. It should be inside the domain defined with sizes.FullXapprox, sizes.FullYapprox. If the powder is inside the domain, the starting position of the laser should be in the domain covered by the powder.
dimX	value	0.003
dimY	value	0.003
Square layer dimensions (m). Can be negative. If the laser position is \(x>\) startposX + dimX, or \(y>\) startposY + dimY, simulation ends
hatchX	value	0
hatchY	value	0.00015
Hatch distance. To set the scanning speed vector parallel to the \(x\)-axis, set hatchX\(=0\) and hatch size in hatchY. If the scan vector is parallel to the \(y\)-axis, set hatchY\(=0\) and hatch size in hatchX. hatchX and hatchY should be negative if dimX or dimY is negative respectively.
delayBetweenTracks	value	0
Delay time between tracks (seconds)

Manual Scan Path

If XYpositions is set as scanning strategy, a set of points is read either from a source file, or from a set of points. Here is an example of an input file. The first column is time (s), the second and third columns are \(x\) and \(y\) positions of the laser at that time. The fourth and fifth columns are optional. They contail laser power (W) and laser spot width (m) at that point correspondingly.

0.00   1e-3  1e-3  300 100e-6
2.e-3  3e-3  1e-3  300 200e-6
3.e-3  3e-3  2e-3  300 200e-6
4.e-3  2e-3  2e-3  300 100e-6
5.e-3  2e-3  1e-3  300 100e-6
6.e-3  1e-3  1e-3  300 100e-6

If the strategy is set with a pointsArray instead of the input file, the array contains the rows of this file.

Key	Value type	Default value
sourceFile	NA
Filename of the input data. Set Null to use pointsArray
pointsArray	list of values	[[0, 0.001, 0.001, 300, 90], [0.001, 0.002, 0.001, 500, 90]]
Defines scanning strategy if sourceFile is set to Null. Each point of the scanning strategy is an an array of 3 (or 5) numbers: \(t\), \(x\), \(y\), and, optionally, power, and width.

Beam Setting

The energy source parameters are set in the ScanStrategy.Beam section.

Key	Value type	Default value
type	string	Laser
Source type: Laser, Ebeam or Unknown
Shape	string	Gauss
Beam shape: Gauss, Tophat, Manual, or Unknown
Power	value	300.0
Laser or Ebeam Power (W)
Width	value	0.0001
The Gaussian pulse D4s parameter (m)
Speed	value	1.0
Scanning Speed (m/s)
ShapeFile	string	beamshape.dat
string — Filename with text lines X-coordinate,Y-coordinate,Power representing the beam shape profile used for “Manual” beam Shape
ElectronsEnergy	value	120000.0
For electron beam, electrons energy (eV)
SuppressBackScattering	value	0
For electron beam, set to 0 if electrons are not tracked in the backwards direction

The shape file format is as follows:

 #Xcoordinate,m       Ycoordinate,m   Power
-0.0002 -0.0002 0
-0.0002 -0.000199 0
-0.0002 -0.000198 0
-0.0002 -0.000197 0
-0.0002 -0.000196 0
-0.0002 -0.000195 0
-0.0002 -0.000194 0
-0.0002 -0.000193 0
-0.0002 -0.000192 0
 ...

Visualization

The image output parameters are set in the Visual section.

Key	Value type	Default value
RenderOnlyMeltpool	true/false	true
Render or not the 3D images of the region beyond the meltpool grid which are saved in ‘rendered3D’ directory
distanceBetweenXsecs	value	0.0005
Distance between \(x=const\) cross-sections (m).
3DrenderedDomainSize	list of values	[0.002, 0.0015, 0.0005]
Box size (m) for 3D renders output. Set larger than the meltpool grid to see the whole meltpool grid. Set smaller for faster rendering.
BeamToBoxMinDistanceX	value	0.0003
BeamToBoxMinDistanceY	value	0.0003
Minimum distance from the beam to the visualization box boundary (m) along X- and Y-axes. If this distance becomes smaller than specified parameter, then the vizualization box will be shifted along X-(Y-)axis.
ComponentWtLimits	list of values	[0, 1]
array of 2 numbers — Minimum and maximum limit of wt.part for component1 at cross-section images

Physical World

The section includes the gravity parameter and the choice of the evaporation model

Key	Value type	Default value
gravity	value	9.8
Gravity acceleration in m/s²
convectionCoolingModel	string	Whitaker
Convection cooling model, possible types are Whitacker and Unknown