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Structural Optimization & MechanicsDelft University of Technology
Topology Optimization for Additive Manufacturing
Matthijs Langelaar
State of the Art and Challenges
Additive World Conference 2016
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Additive manufacturing: focus on design
AM enables the fabricationof “almost any” design.
So.. what design to make?
Topology optimization
Additive manufacturing
Concept geometry
Detailed design
Final component
Post-machining
From functionality to product
Desired functionality
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Aligned advantages
Topology Optimization
• Design freedom: part performance not limited by imagination of designer
• Time to market:fast, nearly automated design process
• Customization:tailored designs for specific requirements
Additive Manufacturing
• Design freedom: relatively few shape restrictions, ‘complexity for free’
• Time to market:no tooling needed, on-demand production
• Customization:produce many different part at once
SLM limitation: critical overhang angle
Clijsters et al, 2012
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Existing solutions to overhang problem
1. Adjust part orientation
2. Adjust part itself
3. Add support structures
Topology optimization
Additive manufacturing
Concept geometry
Detailed design
Final component
Post-machining
Design for manufacturing
Desired functionality
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Structural Optimization & MechanicsDelft University of Technology
Topology Optimization for Additive Manufacturing
Matthijs Langelaar
Additive World Conference 2016
• Aim: include overhang restrictions in topology optimization
• Benefits:
• No need for support structures: less material usage
• Less pre-processing for AM
• Less post-machining: faster production, lower costs
Outline
• Motivation
• Brief introduction to topology optimization
• Print-ready topology optimization
• Approach
• Simplified AM process model
• Examples
• Next steps
• Concluding remarks
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Topology optimization: generating the best material distribution
bracket
What shape to use?
design domaintopology optimization resultpost-processed final design
Where to place material?
Topology optimization process
1. Define problem:
2. Discretize and parameterize material distribution
3. Optimize material distribution forbest performance
- Objective, constraints- Domain, boundary conditions- Loadcases
4. Evaluate / fine-tune result(postprocessing, shape optimization)
Load
Maximize stiffnessUse only 50% material
i
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Topology optimization loop
Values of the density variables
Componentanalysis
(FEA)Values of theobjective and constraints
New
Optimizationalgorithm
Gradient information(design sensitivity)
New
New
Example: compliant mechanism design
• Maximize desired motion
• Sufficient stiffness in other directions
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Outline
• Motivation
• Brief introduction to topology optimization
• Print-ready topology optimization
• Approach
• Simplified AM process model
• Examples
• Next steps
• Concluding remarks
Current practice
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Print-ready topology optimization
Builddirection
Comparison
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Previous approaches
• Automatic post-processing
• Suppressing overhang using filtering techniques
Leary et al., 2014
Gaynor and Guest, 2014
Previous attempts @ TU Delft
• Filter-based approach
• Boundary angle constraints
• Boundary angle constraints with level sets
Serphos, 2014
Driessen, 2015
Van de Ven, 2015
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Topology optimization for print-ready designs
Values of the density variables
Componentanalysis
(FEA)Values of theobjective and constraints
Optimizationalgorithm
Gradient information(design sensitivity)
printed design
Topology optimization for print-ready designs
Componentanalysis
(FEA)Values of theobjective and constraints
Optimizationalgorithm
Gradient information(design sensitivity)
blueprint design
Printingprocess
simulation
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AM process model
F
Builddirection
45 critical overhang angle assumed
AM process model formulation
0.8
0.30.5 0.0
0.5
support 1 2 3max , ,
print blueprint supportmin ,
Builddirection
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AM process model formulation
support 1 2 3max , ,
print blueprint supportmin ,
Langelaar, 2016, in review
printed design
Topology optimization for print-ready designs
Componentanalysis
(FEA)Values of theobjective and constraints
Optimizationalgorithm
Gradient information(design sensitivity)
blueprint design
Printingprocess
simulation
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AM process model: implementation
• min/max operations are not differentiable: replace by smooth approximations
• Layer-by-layer processing:printing simulation in build direction,sensitivity analysis in reverse direction
• Computational cost: very minor (1%)
Outline
• Motivation
• Brief introduction to topology optimization
• Print-ready topology optimization
• Approach
• Simplified AM process model
• Examples
• Next steps
• Concluding remarks
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Examples
• Process simulation test
• 2D validation
• 3D validation
Process simulation test
Blueprint design
Printed design (ideal)
Printed design(smoothed process model)
Builddirection
• Solid parts fully correct
• Light gray parts gradually fade out
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2D validation: test problem
• Maximize stiffness
• 50% material
N
S
W E
2D validation: printability of reference design
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Topology optimization for AM
Printable, self-supporting designsachieving near-ideal performance
94%94% 100.0%100.0% 99%99%90%90%
100%100%
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Higher resolution test
100%100%
93%93% 94%94% 100%100% 98%98%
3D validation
• Maximize stiffness
• 30% material
• 6 orientations
F
Langelaar, 2016, in review
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Reference design
Printability of reference design
Builddirection
As printed
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Topology optimization for AM
Builddirection
100% printable
Different part orientation
F
Builddirection
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Design with ‘support structures’
Different orientations, different designs
100%100%
100%100%
99%99%93%93%
93%93%
101%101%
102%102%
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Beyond beams
Reference PrintablePrintable Builddirection
Outline
• Motivation
• Brief introduction to topology optimization
• Print-ready topology optimization
• Approach
• Simplified AM process model
• Examples
• Next steps
• Concluding remarks
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Limitations
Current approach fast and effective, but:
• Based on structured, regular mesh
• Fixed 45 critical angle
• Limited to 6 main build directions
• Only fully supported designs, no control over
performance vs. support structure cost
• No consideration of stress, distortion, overheating
Current developments
• Formulation that • works on arbitrary meshes• for any critical angle• and any build direction
Emiel van de Ven
• Formulation that allows tradeoff solutions between support structure cost and part performance
• Development of more advanced thermomechanical AM process models
Marius Knol, Can Ayas
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Concluding remarks
• Topology optimization can provide the designs needed to fully benefit from AM freedom
• Topology optimization for AM generates fully printable optimized designs: this eliminates the need and costs of part redesign, supports, postprocessing
• Including AM restrictions can maintain high design performance
• Methods hopefully soon adopted by commercial software companies
Structural Optimization & MechanicsDelft University of Technology
Topology Optimization for Additive Manufacturing
Matthijs Langelaar
Additive World Conference 2016