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Copyright© 2017 MSC Software Corporation
Topology Optimization to
Additive Manufacturing
Workflow
Hanson Chang
MSC Software Corporation
May 13, 2017
14th Annual AIAA Southern California Aerospace Systems and
Technology (ASAT) Conference
Copyright© 2017 MSC Software Corporation 2
Presentation Outline
• Additive manufacturing (3D printing) challenges
• Proposed Topology Optimization to Additive Manufacturing
Workflow
• Engine Mount example demonstrating the integrated
workflow
• Metal and Plastic AM
Copyright© 2017 MSC Software Corporation
• Additive Manufacturing (3D printing)
of metallic and plastic parts have
made tremendous progress in the
last few years
• Although complex parts and
assemblies are being printed
regularly in production
environments, several challenges
remain:
– How to get the Right Shape
– How minimize Distortion
– How to minimize Residual Stress
3
Additive Manufacturing Challenges
Distortion plot
Copyright© 2017 MSC Software Corporation4
Proposed Topology Optimization + AM Workflow
Topo Opt
CAD Edit
Additive Manufacturing
Simulation
CAD
Distortion and Residual Stress
Final CAD Design
Stress, Buckling, Fatigue
Assessment
Copyright© 2017 MSC Software Corporation
• The starting point of Additive
Manufacturing is an STL shape file.
There are two ways to arrive at this
design shape:
– Tradition structural design is often
based on the designer’s intuition or
best practices. The purpose is to
design for subtractive manufacturing
(milling, drilling, cutting, grinding, etc.)
– Topology optimization produces a
lightweight organic shape which often
cannot be manufactured by traditional
methods but is ideal for additive
manufacturing
5
Challenge Number 1: Getting the Right Shape
Copyright© 2017 MSC Software Corporation
• Examples of Nastran topology optimization
6
Examples of Topology Optimization
Copyright© 2017 MSC Software Corporation
• Choose a mass target (typically 30% or 40%)
• Topology optimization uses the Density Method to find the load path
in a structure while meeting the mass target
• The Density Method
ρ = ρ0c
E = E0cp
Where c is the normalized density and is the independent design variable
ρ and E are dependent design variables
p is user-selected penalty factor with a default value of 3.0
• As Nastran minimizes compliance (product of displacement times
applied load), it drives the normalized density c to either 0 or 1
• The normalized density c, when plotted in Patran, will help us
determine the optimized shape
7
Math Behind Topology Optimization
Copyright© 2017 MSC Software Corporation
• Engine Mount Redesign
– Modify the existing engine mount design to reduce
weight while meeting stiffness, strength, buckling, and
fatigue requirements for 14 load cases.
8
Engine Mount Example
Engine Mount
Engine Mount
Trunnion
Thrust Strut
Front Mount Ring
Link
Copyright© 2017 MSC Software Corporation
• Setting up the topology optimization– Define design regions by selecting properties
– Set weight goal – final weight as a fraction of
original weight (0.3 in this example)
– Optionally set stress limits
9
Optimization Setup
Design region
Non-Design region
Copyright© 2017 MSC Software Corporation
• Manufacturing constraints
– Minimum member size
– Symmetry
– Extrusion
– Casting
• Typically not necessary for
additive manufacturing
10
Optionally Set up Manufacturing Constraints
Copyright© 2017 MSC Software Corporation
• The optimized shape is smoothed and
plotted
• The model is skinned and saved as an
.STL file
11
The Topology Optimized Shape
Copyright© 2017 MSC Software Corporation
• The .STL file is used as a guide to modify the original CAD part
• The CAD part editing can be done in
– Any CAD package
– MSC Patran or Apex
12
Import STL into CAD and Modify
+
Copyright© 2017 MSC Software Corporation 13
Animation of Optimization History
Optimization History Animation
Copyright© 2017 MSC Software Corporation 14
Perform Stress Analysis
Copyright© 2017 MSC Software Corporation 15
Perform Buckling Analysis
• Perform buckling analysis
• Minimum buckling factor = 8.37
Copyright© 2017 MSC Software Corporation 16
Perform Fatigue Analysis
• Fatigue life required = 200,000 cycles
• Fatigue life computed = 212,000 cycles
Copyright© 2017 MSC Software Corporation
• Determine as-printed distortion and
residual stress
– Actually printing the part is expensive
(material cost and time)
– Advantages of analytical printing (AM
simulation) over actual printing
• Quickly explore different print parameters:
– Material and powder selection
– Speed
– Build path/hatching pattern
– Build-up orientation and support
– Cutting direction and sequences
– Support removal
– Heat treatment
• Redesign shape to compensate for the
distortion
• Reduce the cost of printing the part multiple
times to iteratively arrive at the optimal
design
• Not tying up the machine17
Challenges Number 2 and 3: Minimize Distortion
and Residual Stress
Copyright© 2017 MSC Software Corporation
• A voxel mesh with solid
fraction technique is used
to represent the part
18
How the AM Simulation Works - Meshing
Copyright© 2017 MSC Software Corporation 19
How the AM Simulation Works – Three Approaches
Scalable Analysis Approaches
• Macro Scale– Extremely fast
– Element layer (> powder layer) analyzed in one step
– Inherent Strain Approach - pure mechanical
– Delivers Distortion & Stress
• Meso Scale– Reasonably fast
– Element layer analyzed in one step or by segments
– Thermal, mechanical or thermo-mechanically coupled
– Able to deliver approximate thermal history and derived results
• Micro Scale– High level of Detail
– Moving Heat Source Model
– Full transient thermo-mechanically coupled, i.e. welding
– Delivers exact thermal history and derived results
Available in Version 1.0
Copyright© 2017 MSC Software Corporation 20
How the AM Simulation Works – Inherent Strain
Inherent strains
• Comprises of
– Plastic strains
– Thermal strains
– Creep strains
– Phase transformation strains
• Reflect
– Material
– Manufacturing parameters
– (Individual) machine
• Are orthotropic by nature
• The AM simulation tool
reverse engineers the inherent
strains from test deflection
results
Inherent Strain Definition
Inherent Strains reverse engineered from
measured deflections
Copyright© 2017 MSC Software Corporation 21
How the AM Simulation Works – Calibration
Step 1: User builds 3 test cantilver beams on a specific
machine
Build cantilevers Cut at center Measure tip displacements
Copyright© 2017 MSC Software Corporation 22
How the AM Simulation Works – Calibration
Step 2:
Automatic calibration by the software using
cantilever beam displacements as input Store in database
Copyright© 2017 MSC Software Corporation 23
Additive Manufacturing Simulation
• Once calibrated, we are ready to run simulations
Copyright© 2017 MSC Software Corporation 24
Additive Manufacturing Simulation
• Engine mount distortion results
AM animation
Copyright© 2017 MSC Software Corporation 25
AM animation
Additive Manufacturing Simulation
• Engine mount residual stress results
Copyright© 2017 MSC Software Corporation
• Shown below is a parametric study of various part orientations
and support systems followed by different cutting sequences
and heat treatment
• This helps you determine the optimal set of printing parameters
before you ever physically print the part!
26
Parametric Studies
Copyright© 2017 MSC Software Corporation
• Similar technology is implemented in both metal and
plastic additive manufacturing tools
– Metal AM simulation – Simufact Additive
– Plastic/Composites AM simulation – Digimat-AM
27
Metal and Plastic AM Simulation
Digimat-AMSimufact Additive
Copyright© 2017 MSC Software Corporation
• A topology optimization to additive manufacturing
workflow was presented which met the following
challenges– Getting the Right Shape
– Minimize Distortion
– Minimize Residual Stress
28
Conclusion
Distortion and residual stress
predicted and minimized by
AM Simulation
Right shape produced by
Topology Optimization
Copyright© 2017 MSC Software Corporation 29
Thank you!
14th Annual AIAA Southern California Aerospace Systems and
Technology (ASAT) Conference