Topology Optimization to Additive Manufacturing Workflow Conference... · • Topology optimization uses the Density Method to find the load path ... cantilever beam displacements

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


• 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


• 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


• Examples of Nastran topology optimization

6

Examples of Topology Optimization


• 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


• 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


• 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


• Manufacturing constraints

– Minimum member size

– Symmetry

– Extrusion

– Casting

• Typically not necessary for

additive manufacturing

10

Optionally Set up Manufacturing Constraints


• The optimized shape is smoothed and

plotted

• The model is skinned and saved as an

.STL file

11

The Topology Optimized Shape


• 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

+


Animation of Optimization History

Optimization History Animation


Perform Stress Analysis


Perform Buckling Analysis

• Perform buckling analysis

• Minimum buckling factor = 8.37


Perform Fatigue Analysis

• Fatigue life required = 200,000 cycles

• Fatigue life computed = 212,000 cycles


• 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


• A voxel mesh with solid

fraction technique is used

to represent the part

18

How the AM Simulation Works - Meshing


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


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


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


How the AM Simulation Works – Calibration

Step 2:

Automatic calibration by the software using

cantilever beam displacements as input Store in database


Additive Manufacturing Simulation

• Once calibrated, we are ready to run simulations



• Engine mount distortion results

AM animation


AM animation


• Engine mount residual stress results


• 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


• 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


• 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


Thank you!

14th Annual AIAA Southern California Aerospace Systems and

Technology (ASAT) Conference

Documents

Topology Optimization to Additive Manufacturing Workflow Conference... · • Topology optimization uses the Density Method to find the load path ... cantilever beam displacements