Design Workflow for AM: From CAD to PartDesign Workflow for AM: From CAD to Part Sanjay Joshi...

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

1

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

2

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

3

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

4

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

5

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

6

……………

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

7

• 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

8

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

9

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

10

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

11

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

12

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

13

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

14

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)

15

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

16

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

17

• 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

18

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

19

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

20

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

21

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

22

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

23

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

24

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

25

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

26

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

27

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

28

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

29

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

30

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

31

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

32

Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018

Execution and Build

33

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

34

Industry Practicum: Additive Manufacturing with Metallic MaterialsJuly 17-20, 2018, Penn State University – Innovation Park, PA USA © CIMP-3D@PSU 2018

Simulations

35

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

36

SIMULATION