Thermomechanical Analysis of Powder Bed–Type Additive Manufacturing Processes Using the Pattern-Based Method

The layer-by-layer deposition of raw material from a recoater or roller blade is simulated using progressive element activation in a structural or a thermal analysis. The following steps are required to define the deposition process and scan pattern parameters completely:

• Create a table collection with a name that begins with "ABQ_TMP". The table collection must contain a parameter table of type "ABQ_AM_ThermoMech_PatternBased_Activation" as well as the other parameter tables listed below.
• Define the build parameters (such as slice or layer thickness and build coordinate system) in a parameter table of type "ABQ_AM_ThermoMech_PatternBased_Activation".
• Define the laser power, scan spacing, and speed in a parameter table of type ABQ_AM_ThermoMech_ScanParameter_Define.
• Define parameters of rectangular patches that make up a rectangular unit cell (see Scan Pattern–Mesh Intersection), which is repeated to cover the cutting plane or a layer, in a parameter table of type ABQ_AM_ThermoMech_PatternBased_Define. You can define the following parameters: a local angle, $\phi$; the extents of a patch $(x_{\min },y_{\min })$ and $(x_{\max },y_{\max })$; and a label of the parameter table of type ABQ_AM_ThermoMech_ScanParameter_Define defining laser power and other scan parameters to apply to this patch.
• Define the parameters of the bounding box, inside which a particular scan-pattern strategy is active, in a parameter table of type ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define.
• List the names of all of the parameter tables of type ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define defining all active strategies in a table of type "ABQ_AM_ThermoMech_PatternBased_ScanStrategies".
• As described above, you must define at least one parameter table of each of the following types: "ABQ_AM_ThermoMech_PatternBased_Activation", "ABQ_AM_ThermoMech_PatternBased_Activation", "ABQ_AM_ThermoMech_PatternBased_Define", "ABQ_AM_ThermoMech_PatternBased_ScanStrategies", and "ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define".
• Optionally, define parameter tables of types ABQ_AM_ThermoMech_PatternBased_Advanced and ABQ_AM_ThermoMech_Activation_Advanced to specify advanced options.
• Refer to the table collection when you turn on the progressive element activation feature. You can include only one option to turn on progressive element activation in an analysis.

Abaqus activates elements automatically according to the specified pattern parameters and automatically estimates the printing time of each layer. Abaqus assigns a local orientation for anisotropic materials to elements at the time of activation based on the pattern definition. You must define an initial local orientation and refer to it from the section definition for the elements that use an anisotropic material.

A dedicated collection of parameter table, property table, and event series types is available to include all of the definitions required by special-purpose techniques for additive manufacturing. You can use the abaqus fetch utility to obtain the file containing all of the type definitions of parameter tables, property tables, and event series required by the special-purpose techniques for additive manufacturing as follows:

abaqus fetch job=ABQ_am_special_purpose_types.inp

TABLE COLLECTION, NAME="ABQ_TMP_Activation 1"
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_PatternBased_Activation"
$h$, coordinates defining the build system $I-J-K$,
recoater time, print start time, TOTALTIME / STEPTIME
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_ScanParameter_Define", LABEL = "Island 1"
Power, scan spacing, speed, on time fraction
include as many parameter tables of type ABQ_AM_ThermoMech_ScanParameter_Define as needed
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_PatternBased_Define", LABEL="Pattern 1"
$x_{\min },y_{\min },x_{\max },y_{\max }$, 
label of a table of type ABQ_AM_ThermoMech_ScanParameter_Define such as "Island 1", $\phi$
additional data lines to define more patches
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define", LABEL="Scan region 1"
"label of a table of type ABQ_AM_ThermoMech_PatternBased_Define such as "Pattern 1", $\theta$
$x_{\min },y_{\min },z_{\min },$ $x_{\max },y_{\max },z_{\max }$ 
include as many parameter tables of type 
ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define as needed
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_PatternBased_ScanStrategies"
list of labels of parameter tables of type ABQ_AM_ThermoMech_PatternBased_ScanStrategy_Define
such as "Scan region 1" in the analysis
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_Activation_Advanced"
"Full" or "Partial", min volume fraction threshold for partial activation, 
max volume fraction threshold for partial activation, volume fraction threshold for full activation
...
ELEMENT PROGRESSIVE ACTIVATION, NAME=activation name, ELSET=element set name
...
STEP
STATIC or HEAT TRANSFER
...
ACTIVATE ELEMENTS, ACTIVATION=activation name
 "ABQ_TMP_Activation 1"
...

The following steps are required to define the heat source completely that follow the pattern parameters defined above:

• Create a table collection with a name that begins with "ABQ_TMP". The table collection must contain a parameter table of type ABQ_AM_ThermoMech_PatternParameters and a property table of type ABQ_AM_AbsorptionCoeff.
• In the parameter table, specify the name of the table collection that is referred to when you turn on the progressive element activation feature.
• In the property table, define the absorption coefficient for the material.
• Refer to the table collection in the distributed load definition.

Abaqus computes and applies moving heat fluxes to each element automatically according to the specified scanning trajectory. There may be more than one distributed load definition. Each distributed load definition must refer to a different table collection. Element sets referred to from distributed load definitions must be subsets of the element set referred to when you specify elements that can be activated during an analysis.

TABLE COLLECTION, NAME="ABQ_TMP_Laser 1"
PARAMETER TABLE, TYPE="ABQ_AM_ThermoMech_PatternParameters"
"ABQ_TMP_table collection name" referred from ACTIVATE ELEMENTS, such as "ABQ_TMP_Activation 1"
PROPERTY TABLE, TYPE="ABQ_AM_AbsorptionCoeff"
absorption coefficient
...
STEP
HEAT TRANSFER
...
DFLUX
element set name, MBFNU, ,"ABQ_TMP_Laser 1"
...

For information on specifying free surface radiation and convective heat transfer, see Progressive Cooling via Convection and Radiation.

A scan pattern can be visualized over the part geometry by requesting element solution-dependent field variables for output and plotting them as contours over the finite element mesh. For a pattern-based analysis, the first two element solution-dependent field variables are internally set to the patch ID and scan region ID, respectively (see Figure 1).

SOLID SECTION, ELSET=element set name, MATERIAL=material property name
ELEMENT SOLUTION-DEPENDENT VARIABLES
2
1, RegionID
2, Patch/IslandID
…
OUTPUT, FIELD, FREQUENCY=1
ELEMENT OUTPUT
ESDV