Advanced Topics in Design for Automotive Additive Manufacturing

AutoEPCON 2019Alex JuJames McCutcheonDavid Tucker

Optional subtitle

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Agenda

1. Multi Jet Fusion Overview

2. Texture Design for Additive

– Bump Maps

– 3D Scanning

– Sculpted Textures

– Generative Methods

– Printability Considerations

3. Lattice Structures

– Structure Classification

– Cell Topology and Geometry

– Mechanical Properties

– Lattice Generation

– General Uses

AutoEPCON 2019

Multi Jet Fusion Overview

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HP Jet Fusion 3D Build Unit

Software and PluginsJob preparation and submission

Command CenterPrinter management

HP Jet Fusion 3D Printer

What is Multi Jet Fusion?

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HP Jet Fusion 3D Processing Station

• A powder-based process, where agents are deposited on a bed of powder and then fused with thermal energy

• Platform will allow the use of different agents to control voxel-level properties (such as color, conductivity, translucency)

Fusion

HP Multi Jet Fusion Manufacturing Process

Fused Fused Fused

Fused

Apply energyApply agentsMaterial Spreading

Area based melting throughput

Energy

Pattern

Heat signature

White powder temperature < melt

IR spectrum

Visible spectrum

Part temperature > melt

200

190

180

170

160

150

140

130

120

1 10

100

˚C

Service Parts

/ Development Production Service & Spares

Vo

lum

e

Prototype Low Volume Production

Research

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Service Parts

/ Development Production Service & Spares

Vo

lum

e

Prototype Low Volume Production

High Value Applications

• Lightweight• Personalized

• Fluid Management Systems• Faster Time to Market• Energy Absorption

Research

Texture Design for Additive

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Texture Development in 3DP: Bump Maps

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Bump map applied (using planar wrapping) to a simple curved surface

2D Checker, a provided texture in

Rhinocerous

Bump Maps from Photos

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Original photograph Grayscaled image, for use as a 3D bump map

Photo-generated bump map applied to a simple surface

Seamless Bump Maps for Tiling

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Using the Offset filter & healing brush to create a seamless

texture in Photoshop

Tiled seamless image Tiled bump map applied across a simple surface

CAD-Sculpted Textures

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Textures created in Rhino, then applied to a singly-curved surface.

Use the ShowZBuffer function in Rhino to get a bump map that you can also apply to surfaces instead.

Generative Tools for Randomized Texture

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Randomly attracted barnacles to a spherical surface, flat with

the underlying surface

Randomly attracted heart-shaped molecules on a torus,

randomly oriented

Spherical molecules seeded along a chair-shaped surface

Printability Considerations

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• Tested heights/depths of 0.2mm, 0.5mm, 1mm, 2mm, and 4mm

• Logo line widths shown (outer ring): 0.4mm, 0.5mm, 0.75mm, 1mm

Printability Considerations

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Assorted test plaques, for testing the printed clarity and effectiveness of different depths and widths.

“A lattice material is defined as a spatially periodic network of structural elements.”

A. S. Phani and M. I. Hussein, Dynamics of Lattice Materials, Chichester, West Sussex: John Wiley & Sons, 2017

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Structure Classification

Lattice Structure

Uniform

• Identical unit cells are periodically distributed throughout the structure

• Are the ‘typical’ lattice structure

Random

• Cell topology and sizing are randomly distributed throughout the structure

• Examples include:

– Natural materials like cork and sponge, traditionally manufactured foams, Voronoi lattices

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Structure Classification

Lattice Structure

Pseudo-random

• Cells have the same topology, but vary in shape and size

• Used in conformal lattices to adapt to the external shape of the structure

• Conformal lattices avoid partial cells along their boundaries helping to retain integrity

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Lattice StructureFurther Classification

Homogenous

Heterogenous

Gradient

• Strut or wall thickness is kept constantthroughout the lattice

• Strut or wall thickness variesthroughout the lattice

• Strut or wall thickness varies according to a gradient function/pattern

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Unit CellCell Topology & Geometry

• Lattice materials can be comprised of open or closed cells

• Unit cells can generated from space filling polyhedra or a tessellating combination of polyhedrons

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Cubic Face Centered CubicX-Shaped Octet

Unit CellTriply Periodic Minimal Surface

• Repeat in three dimensions and are locally area minimizing

• Defined mathematically

• Most TPMS are not self intersecting

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Bending vs. Stretch Dominated

Mechanical Properties

Bending Dominated

• Responds to applied loads through the bending of unit cell beams

• Have a stress plateau in the plastic region after an initial stress peak

• Absorb a large amount of energy at lower stresses

Stretch Dominated

• Responds to applied loads through the axial stretching/compression of unit cell beams

• Exhibit higher yield stresses

• Suited to lightweight/stiff applications

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J. Souza, A. Grossmann and C. Mittelstedt, "Micromechanical analysis of the effective properties of lattice structures in additive manufacturing," Additive Manufacturing, vol. 23, pp. 53-69, 2018.

Lattice GenerationGeneralized Workflow

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Space Generation Lattice Generation Lattice Trimming/Integration

Mesh Reduction

Lattice GenerationGeneralized Workflow

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Combine the lattice with solid bodies or generate a lattice skin. Trim the lattice where needed.

Repair and reduce the resultant mesh prior to printing

Generate a closed surface/solid body (a lattice volume) that forms the boundary of the space to be filled with the lattice structure

Fill the lattice volume with the desired lattice. Many tools allow for the selection/generation of different unit cells, beam thicknesses and cell sizes

Lattice ApplicationsGeneral Uses

• Strong lightweight structures

• Auxetic structures

• Structures with low thermal expansion coefficients

• Energy absorbing structures

• ‘Tunable’ structures

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Come see more sample parts at table 18!

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