Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Offered by:
Center for Innovative Materials Processing through Direct Digital Deposition (CIMP-3D)
The Pennsylvania State University & Applied Research Laboratory
July 17-20, 2018 University Park, PA
Design Workflow for AM:From CAD to Part
Sanjay JoshiProfessor of Industrial and Manufacturing Engineering
Penn State University
Industry Practicum: Additive Manufacturing with Metallic Materials
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Input to AM Systems
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3D Part Design as Solid Model -CAD
3-D Scan Data (Point Cloud, Polygonal Mesh)
2-D Slice Data (MRI, CAT Scan)
STL File
Convert(Export)
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Other Types of Data
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Point Cloud Data
MRI - Magnetic Resonance Imaging. Uses magnetism, radio waves and a computer to produce detailed images of your body's organs, tissues and structures.
• Different Formats• DICOM, Nifti, Minc
CT Scan Data
http://www.libe57.org/data.html
https://blog.nikonmetrology.com/wp‐content/uploads/2016/07/Additive‐Manufactured‐metal‐parts‐for‐CT‐inspection‐1024x576.jpg
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
A faceted representation of the boundary, where each facet is a triangle
The facets are created using a process called “tessellation”, which generates triangles that approximate the object boundary
STL File
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
STL File – ASCII Format Example
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……………
Model Name
One triangle
(1,0,0)
(1,1,0)
(0,0,0)
(0,0,‐1)
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
STL Example
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• Units (request a 2D drawing)• Binary vs ASCII• Resolution & File Size
• Deviation Tolerance• Angle Tolerance
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Process of tessellation into triangles creates an approximation
Approximation Errors
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Trade off Size andNumber of facetsError
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Generating STL files from SolidWorks
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2 variables control the generation of triangles
• Deviation– Controls whole-part
tessellation– Small numbers generate
files with greater whole-part accuracy
• Angle– The angle setting refers to
the angular deviation allowed between adjacent triangles
– Controls smaller detail tessellation (0~30 deg)
– Small numbers generate files with greater small-detail accuracy, but they take longer to generate
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Impact of Chordal Tolerance
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Errors of approximation
Much larger than original CAD file for a given accuracy parameter
CAD STL conversion provided by vendor as part of CAD system• CAD model may not be mathematically correct• Tessellation algorithms are not robust• Challenges controlling numerical errors• Difficulty tessellating curved surfaces
Problems with STL files
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364kb 2.19 MB‐70 MB
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Gaps & Missing Triangles
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Tessellation of surfaces with large curvature can result in errors at the intersections of such surfaces leaving gaps or holes along edges of the part model
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Overlapping & Intersecting Triangles
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Facets may sometimes intersect at locations other than their edges resulting in overlapping facets
Overlapping facets may result from numerical round off errors
during tessellation, since floating point numbers are used
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
When the normal to the triangle facets points in the wrong direction (flipped normal)
Confusion caused if specified normal is opposite to that implied by vertex ordering
Mis-Oriented (Flipped) Triangles
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1
2 3
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
• A violation of the vertex to vertex rule
• Triangles whose vertices touch the sides of adjacent triangles
Unmatched Triangle Sides (Bad Edges)
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
• Shell – connected grouping of triangles• A single part must have one single shell• Noise shells caused by extraneous triangles• Overlapping shells – may cause the overlapping material to be printed
twice
Multiple Shells
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Dealing with Defective STL Files
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• STL files must be checked for validity and repaired before the slicing process
• Automatic repair of STL files is often performed by software supplied along with AM machine (or special repair programs)
• Examples include:- MAGICS, NETFABB, POLYGONICA (3rd party software)- INSIGHT, 3-D Sprint (supplied by machine vendors)- MeshLab (open source)
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Fixing with Magics
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Data Redundancies
Unit Ambiguities
Scale Poorly with complex geometry (highly curved surfaces)
Cannot accommodate Colors, Multiple Materials, Texture
Growing gap between what machines can make vs. what STL can represent
NEW Specifications: - ISO / ASTM 52915 AMF specification
- 3MF ( Consortium of companies, Autodesk, 3D
systems, Dassault, EOS, FIR, GE, HO, Microsoft, Materialise, PTC, Siemens, Stratsys, etc.)
Other Probles/issues with STL Files
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Build orientation impacts:• Build time• Requirements for support structures• Thermal behavior• Internal stress buildup• Part properties
Process Planning – Build Orientation
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Build Orientation – Multiple Objectives
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
• Support overhangs during build
• Base supports facilitate removal from build platform
• Anchor part to prevent distortion
• Different designs of supports
Process Planning – Support Structures
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Process Planning – Support Structures
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Source: http://utwired.engr.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/2012/2012-53-Krol.pdf
Supportoptions
Supportfailures
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Generate the layer information
Slicing
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Input TrianglesSort Trianglesin Z Direction
Intersectwith Z plane
Create BoundaryPolylines
SmoothBoundary
OutputBoundary Data
Sliced Files
Increment Z
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
• Material between slicing planes is called “Layer”
• Part is built by sequentially building and stacking layers, resulting in a “quantized” part along the build axis in steps equal to the layer thickness
• Layer thickness depends on machine, material, and process parameters
Layers
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Staircase effect
Surface roughness of surfaces not orthogonal to build direction
Errors related to Slicing
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Dimensions in plane of the layer may be created oversized or undersized
Features along building axis may be moved up or down one layer, and features smaller than the layer thickness may disappear
Errors related to Slicing
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
“Tool path” planning and process parameters determine how each layer will be built:
• Laser power/energy density• Scan speed• Hatch spacing• Hatch orientation• Boundaries/contours• Internal filling (sparse/dense)
• Nearly all of these are determined once a material is selected• Each material has unique
“recipe” for making parts
Process Planning – Tool Path
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Execution and Build
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Performed on the AM machine
Consolidation of multiple parts into single build platform
Machine Set up- Control Software- Hardware setup- Parameter settings on the machine
• Gas Flow rates• Chamber temperatures• Other process variables not set in
programs
Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Cleaning & Removal from machine
Stress relief and heat treatment
Part and support removal
Secondary operations: Hot isostatic pressing (HIP) Improving surface finish (e.g., shot peening) Machining (e.g., threading, tolerances) Assembly (e.g., mating surfaces/interfaces)
Inspection and verification
Post Processing Considerations
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Simulations
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Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018
Digital Workflow: CAD to Part
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SIMULATION