topology optimization of additive manufactured gps bracket niël...
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Topology Optimization of Additive Manufactured GPS bracket
Niël Agenbag
Date: 10 July 2019
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Introduction
• Using topology optimization to re-design a mounting bracket
from a sheet metal design to a 3D printable design, having
half the original weight
• The original design is sheetmetal
• This work forms part of an AISI project used to develop Design
for Additive Manufacturing (DfAM)
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Introduction
• Intention is to show step by step how to use SOL 200 – make it
accessible to new user
• Illustrate the pitfalls that were encountered
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Introduction
• GPS bracket and antenna location
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Introduction
• GPS existing bracket sheet metal concept
GPS
Mountin
g
fasteners
Bracket
mount
holes
Holes for
looms (should
be left open)
Sheetmetal
mass: 76.6g
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Introduction
• Loads
• Component is subjected to the following inertial loads:
• Mass has to be minimized for these loads.
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Definitions SOL 200
• Topology (layout and load-path study)
• Topometry (element by element sizing optimization)
• Topography (finite element grids are moved as normal vectors
to the shell surface or the user's given direction)
We will use this
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Tools
The following software was chosen to analyze the component:
• MSC.Apex to create the model
• MSC.Patran to set up SOL 200 optimization
• MSC.NASTRAN to run SOL 200 optimization
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MSC.Apex
Apex screenshot of geometry and mesh
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Modelling strategy
• Model the GPS as a point mass
• Connect the point mass to bracket using RBE2
• The dependent nodes of this RBE is connected
to another RBE2 that is connected to the bore of
the fastener
• The mounting hole nodes of the bracket are
connected to a central node using an RBE3.
Central node is constrained using SPC
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Modelling strategy
• Model the elements of the component using
HEX8 elements
• The mount fasteners are constrained using SPC
in local x, y, z as well as the rotational out of
plane moments. It is not constrained in the
moment direction of the rotation of the fastener
(constrained in direction 1,2,3,4,5 of local coord
in picture below)
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MSC.Patran
First perform linear static run (Good practice and shows low stresses)
Unstressed
design region
as expected
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MSC.Patran
Set up optimization
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MSC.Patran
Set up optimization: Groups for design space and non-design
space
Non-design
space:
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MSC.Patran
Set up optimization
Design space (can
be changed by
optimization):
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MSC.Patran
Set up optimization: Get current mass and calculate what it
should be after optimization
• Density specified in [tonnes/m3] for further dynamic analysis
• Design space mass = 494.87g
• Non-design space mass = 2.79g
• GPS mass = 127.6g
• Existing sheetmetal bracket = 76.6g.
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MSC.Patran
Set up optimization: Get current mass and calculate what it
should be after optimization
• Final mass target for design space = 35g
• This is a 50% mass saving
• BUT
• the mass constraint is specified in terms of the total mass of the
model (494.87g + 2.79g + 127.6g = 625g)
• Therefore the mass fraction that the optimizing algorithm must
aim for is: 35g/625g = 0.056 > round down to 0.05.
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MSC.Patran
Set up optimization: Menus
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MSC.Patran
Set up optimization
Starting
volume
fraction
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MSC.Patran
Set up optimization
Goal
function
Mass
constraint
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MSC.Patran
Set up analysis
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MSC.Patran
Set up optimization: Algorithm can be set up here
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MSC.Patran
Set up optimization: Issues
• There were some issues with the native Patran BDF where it
wrote out the DRESP2 card with incorrect parameters. This has
to be manually corrected using a text editor. This is important
to note with Patran 2019. Potentially this will be fixed in later
versions. The DRESP2 card is written out incorrectly by Patran to
be in the long format, but it enters to long integers in the C2
and C3 column of the DRESP2 card. The defaults are
acceptable in the DRESP2 card and the defaults are loaded
whenthe C2 and C3 columns are left blank. The card should
be changed to be as follows for the above example:
DRESP2 1 COMPL AVG
DRESP1 20 30 40 50 60 70
The result was run and imported. The result is shown in the
following picture:
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Baseline results Coarse model RBE2
Results: Elements
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Baseline results Coarse model RBE2
Results (using Patran Insight tool to get surfaces)
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RBE2 results fine model
Now rerun the same model setup with a finer mesh:
This is to check for mesh convergence
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RBE2 results fine model
Splits bracket in 2 parts, but it is not allowed to stress subsystems
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RBE2 results fine model
Issues:
The larger model had memory issues, so the "METHOD" option
needed to be changed to 4 where it was 1 as written out with
Patran in the BDF. It gives the following error in the F06 file:
*** SYSTEM INFORMATION MESSAGE 7603 (DMKCRS)
METHOD I IS SELECTED BY THE PROGRAM TO PERFORM TRIPLE MATRIX PRODUCT
*** SYSTEM INFORMATION MESSAGE 7603 (DMKCRS)
METHOD I IS SELECTED BY THE PROGRAM TO PERFORM TRIPLE MATRIX PRODUCT
*** USER WARNING MESSAGE 7510 (ADS9P4S)
MSCADS DESIRED STORAGE REQUIRES TO INCREASE OPEN CORE BY AT LEAST 136120667358
WORDS
WILL ATTEMPT TO OPTIMIZE WITH AVAILABLE STORAGE
*** USER WARNING MESSAGE 7510 (ADS9P4S)
MSCADS MINIMUM STORAGE REQUIRES TO INCREASE OPEN CORE BY AT LEAST 26591772018
WORDS
WILL ATTEMPT TO OPTIMIZE WITH AVAILABLE STORAGE
*** SYSTEM FATAL MESSAGE 7510 (ADS9P4S)
INSUFFICIENT MEMORY AVAILABLE FOR OPTIMIZER MSCADS
USER ACTION: SWITCH TO METHOD =4 OR REDUCE SIZE OF DESIGN MODEL
0FATAL ERROR
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RBE2 results fine model
Issues:
It can be fixed using the following BDF entry (simply change
METHOD to 4):
$ ...OPTIMIZATION CONTROL
DOPTPRM* DESMAX 50 FSDMAX 0
* P1 0 P2 13
* METHOD 4 OPTCOD MSCADS
* CONV1 .001 CONV2 1.-20
* CONVDV .001 CONVPR .01
* DELP .2 DELX .5
* DPMIN .01 DXMIN .05
* CT -.03 GMAX .005
* CTMIN .003
*
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RBE3 results fine model
Rerun the fine model with RBE3:
This makes the load path go below the whole GPS again:
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RBE3 results redo model
Redo design space and use RBE3 and mass element to model
GPS
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RBE3 results redo model
Redo design space and use RBE3 and mass element to model
GPS
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Important to note
Notes:
• The number of iterations of optimization can easily exceed the
default, so set number of iterations to a high value, typically
50:$ ...OPTIMIZATION CONTROL
DOPTPRM* DESMAX 50 FSDMAX 0
* P1 0 P2 13
* METHOD 4 OPTCOD MSCADS
* CONV1 .001 CONV2 1.-20
* CONVDV .001 CONVPR .01
* DELP .2 DELX .5
* DPMIN .01 DXMIN .05
* CT -.03 GMAX .005
* CTMIN .003
*
• It is noteworthy that *.xdb should be selected as the output
format. Both HDF5 and OP2 files are imported by Patran and
made part of the DB file. This takes an inordinate amount of
time, whereas the XDB immediately attaches immediately. It is
therefore important to choose the XDB output:
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Important to note
Choose XDB:
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Important to note
Notes:
• Additional to the XDB run, the BDF was rerun TOPVAR with the
"STRESS" optional entry of the TOPVAR card set to 5 MPa. This
was done to check if it had an influence on the outcome of
the optimization. This entry will prevent the optimization from
having an element with a stress above 5 MPa.
$ $$ $$ $$ $$ $$ $
TOPVAR* 1 PSOLID PSOLID .7
* .5 2
* STRESS 5.0
• The bracket stresses were all below 5MPa
• This is useful for cases where fatigue endurance limit is
important. Stresses can be kept below endurance limit by the
optimizer.
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Final mass
Before and after
The optimization was run as before and the final iteration
(number 32) showed a bracket with a mass of 19.5g.
This is a significant improvement over the sheetmetal bracket
that was 76g.
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Design Loop
Overlay of exported elements and design in CATIA
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Design Loop
• Exported the elements as IGES from Patran
• Import IGES into CATIA
• Designer uses the IGES element geometry
• Designs a new bracket with the guidelines
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Design Loop
Part design iteration 1 from design:
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Design Loop
Future work as part of design loop:
• Perform a linear static FEA in order to guide the designer as to
where to remove material
• Remove material at low stress regions, typically at center span
of rods
• Perform a final linear static FEA for the stress report
• 3D Print final design
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Conclusions
• NASTRAN SOL 200 is a useful tool for identification of the critical
load path using
• Combinations of load cases
• Frequency response criteria (not covered in this
presentation)
• Stiffness criteria
• It is important to note that the finite element modelling
strategy (eg. RBE2 vs RBE3) can influence the SOL200 outcome
(the load path)
• NASTRAN SOL 200 can be used in the Design for Additive
Manufacturing (DfAM) workflow because it can be used in the
optimization of components
• Significant mass savings are possible using SOL 200
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Conclusion
THE END
QUESTIONS