ISEMP BCCMSChallengeComputing time estimation4Example ALM process: 10cm x 10cm x 10cm cubeCalculation time estimation:• Elements: 2.500.000.000 + base plate• Time increments: 250.000.000 (10.000 increments per layer)Realistic process simulation is impossible!Aim: Prediction of temperature field, distortion and residual stressBase platePart• Layer size: ~40µm• Melt pool diameter: ~100µm• Process time: ~7h (10s per layer)
ISEMP BCCMSChallengeSimplifications5Simplifications must be made in order to enable thermo-mechanical FEMsimulations:Powder MaterialLaser / Heat fluxBase PlateLayer quantitySize reduction- effective heat capacityBoundary Conditions:- fixed displacement- negative heat fluxSummarizationHatch sections Complete layersEffective heat conductivity Isolation / Convection
ISEMP BCCMSChallengeRequirements for thermo-mechanical FEMsimulations of ALM processes6Layer-based mesh• Each layer has the same height• Layers are solid and match the slice contour• Connection of layers at nodesHeatingCooldownNext LayerAdaptive time steps• Small time steps for heating phase• Increasing time steps while powder feedProcess input• Use of real process parameters• Reproduction of hatching strategies
ISEMP BCCMSFEM preprocessingFrom STL to FEA8Preprocessing Software FE Meshing & JobFEM JobCAD / STLFEM-ALM Interface Tool: CAD Import, Slicing, Meshing, Job generation:8CAD Source: BEGO Medical GmbH
ISEMP BCCMSALM FE Meshing9FEM preprocessingMeshing of segments with hex8 elements with connection between layers:Segmentation FE MeshSlice StackActive LayerNodesElements Grid
ISEMP BCCMSFEM preprocessingALM FE MeshingGeneration of meshes of entire components (close to the CAD)Example:Layer thickness: 400 µmLayers: 160Elements: ~26.00010Thermo-mechanical FEA forrealistic layer sizes possibleMapping of the contour withless elements (no „voxels“)FEA- Residual Stress- Distortion
ISEMP BCCMS12Simulation modelsFEM Simulation of ALM processes• Deactivation of all elements of the part atprocess start• Sequential activation of singleelements/layers or material change (powderconsolidation)• Heat flux on activated elements• Calculation of temperature field (and strains)QLayer activationSequential activation
ISEMP BCCMS13Simulation modelsLayer modelthermo-mechanical FEA- Mesh of the geometry- Activation of layers- Simultaneous heat flux perlayerHatching modelThermal / thermo-mechanical FEA- Mesh of the geometry- Sequencially activation ofelements- Usage of real hatchingsPowder modelThermal FEA- Mesh of the completebuilding space (powder)- Consolidation at meltingtemperature- Usage of real hatchingsµm mm cmSimulation models
ISEMP BCCMS14Simulation modelsLayer modelthermo-mechanical FEA- Distortion- Residual stresses- Process stabilityHatching modelThermal / thermo-mechanical FEA- Local temperature field- Residual stresstendencies of differenthatchingsPowder modelThermal FEA- Micro defects (unmoltenpowder)- Powder attachments atsurfaces- Melt pool propagationµm mm cmSimulation models
ISEMP BCCMSConclusionPotential of FEM simulation of ALM processes21Thermo-mechanical FEA• Tendencies for residual stressand deformation during ALM andprocess after post-processingFEM simulations for prediction of residual stresses and for derivation ofstrategies for optimal thermal managementComputer-based process optimizationThermal FEA• Knowledge basics for thermalprocess management• Investigations on critical localenvironmentsSupport structures, orientation, hatching strategies, …
ISEMP BCCMSConclusionConvergence problems by instable process22Thermo-mechanical FEM simulations break by instable ALM processes:Reasons:1. Bad supported overhangs 2. Local overheatings• Too high laser power• Low heat conductivity of support structure• Bad geometry or orientationBreak because of missing mechanical boundary conditionsBreak because of too large strainszpartactivateddeactivated
ISEMP BCCMSConclusionNeed for integration of process constrainsby topology optimization23Support structures• Thermal and mechanical aspects restrict freedom ofdesigns• Stresses after post-processing (milling)Consideration of the manufacturing process for topology optimization oflight weight partsSource: EADS IWIntegration of process related issues to the topologyoptimization process due to advanced guidelinesResidual stresses• Stresses while process hot cracks• Stresses after process lower fracture resistance
www.isemp.deNils KellerGroup Leader Additive Layer Manufacturing and JoiningAirbus endowed Chair for Integrative Simulation andEngineering of Materials and Processes (ISEMP)Faculty 1 / PhysicsUniversity of BremenAm Fallturm 1, Entrance A, Room 3.2828359 BremenTel.: +49-(0)421-218-62325E-Mail: email@example.comContact information
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