ENG 165-265Spring 2015, Class 5 Additive Manufacturing Techniques

Advanced Manufacturing Choices

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Table of Contents1. Introduction: What is Additive Manufacturing

2. Historical development

3. From Rapid Prototyping to Additive Manufacturing (AM) – Where are we today?

4. Overview of current AM technologies

1. Laminated Object Manufacturing (LOM)

2. Fused Deposition Modeling (FDM)

3. 3D Printing (3DP)

4. Selected Laser Sintering (SLS)

5. Electron Beam Melting (EBM)

6. Multijet Modeling (MJM)

7. Stereolithography (SLA)

5. Modeling challenges in AM

6. Additive manufacturing of architected materials

7. Conclusions

From Rapid Prototyping to Additive Manufacturing

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What is Rapid Prototyping

- From 3D model to physical object, with a “click” - The part is produced by “printing” multiple slices (cross

sections) of the object and fusing them together in situ- A variety of technologies exists, employing different

physical principles and working on different materials- The object is manufactured in its final shape, with no

need for subtractive processing

How is Rapid Prototyping different from Additive Manufacturing?

The difference is in the use and scalability, not in the technology itself:

Rapid Prototyping: used to generate non-structural and non-functional demo pieces or

batch-of-one components for proof of concept.

Additive Manufacturing: used as a real, scalable manufacturing process, to generate fully

functional final components in high-tech materials for low-batch, high-value manufacturing.

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Why is Additive Manufacturing the Next Frontier?

EBF3 = Electron Beam Freeform Fabrication (Developed by NASA LaRC)

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Rapid Prototyping vs Additive Manufacturing today

AM breakdown by industry today

Wohlers Report 2011 ~ ISBN 0-9754429-6-1

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From Rapid Prototyping to Additive Manufacturing

Rapid Prototyping in a nutshell1. 3D CAD model of the desired object is generated2. The CAD file is typically translated into STL* format3. The object described by the STL file is sliced along

one direction (the ‘z’ or ‘printing’ direction)4. Each slice is manufactured and layers are fused

together (a variety of techniques exist). The material can be deposited by dots (0D), lines (1D) or sheets (2D)

A voxel (volumetric pixel or, more correctly, Volumetric Picture Element) is a volume element, representing a value on a regular grid in three dimensional space. This is analogous to a pixel, which represents 2D image data in a bitmap.

*The STL (stereo lithography) file format is supported by most CAD packages, and is is widely used in most rapid prototyping / additive manufacturing technologies. STL files describe only the surface geometry of a three dimensional object without any representation of color, texture or other common CAD model attributes. The STL file describes a discretized triangulated surface by the unit normal and vertices coordinates for each triangle (ordered by the right-hand rule).

A limitation or an opportunity?

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Compromises in Additive ManufacturingAnother key compromise is among process speed, volume and tolerances.

• Laminated Object Modeling (LOM)

• Fused Deposition Modeling (FDM)

• 3D Printing (3DP)

• Selective Laser Sintering (SLS)

• Electron Beam Melting (EBM)

• Multijet Modeling (MJM)

• Stereolithography (SLA, STL)

• Micro-stereolithography (serial and projected)

• Two photon lithography

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Laminated Object Manufacturing (LOM)1. Sheets of material (paper, plastic,

ceramic, or composite) are either precut or rolled.

2. A new sheet is loaded on the build platform and glued to the layer underneath.

3. A laser beam is used to cut the desired contour on the top layer.

4. The sections to be removed are diced in cross-hatched squares; the diced scrap remains in place to support the build.

5. The platform is lowered and another sheet is loaded. The process is repeated.

6. The product comes out as a rectangular block of laminated material containing the prototype and the scrap cubes. The scrap/support material is separated from the prototype part.

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Laminated Object Manufacturing (LOM)

Laminated Object Manufacturing (LOM) was developed by Helisys of Torrance, CA, in the 1990s. Helisys went out of business in 2000 and their LOM equipment is now serviced by Cubic Technologies.

Equipment picture

Current market leaders- Mcor Technologies (Ireland)- Solido (Israel)- Strataconception (France)- Kira Corporation (Japan)

Mcor Technologies Matrix 300+ (uses A4 paper and water-based adhesive)

Courtesy, Cubic Technologies

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Laminated Object Manufacturing (LOM)

KEY APPLICATION AREAS

Maximum build size 40in x 40in x 20in

Resolution in (x,y) +/- .004 in

Resolution in z Variable

Speed Medium

Cost Low

Available materials Paper, Plastic Sheet

KEY METRICS ADVANTAGES

DISADVANTAGES

• Relatively high-speed process• Low cost (readily available materials)• Large builds possible (no chemical

reactions)• Parts can be used immediately after the

process (no need for post-curing)• No additional support structure is

required (the part is self-supported)

• Removal of the scrap material is laborious• The ‘z’ resolution is not as high as for other

technologies• Limited material set • Need for sealing step to keep moisture out

• Pattern Making• Decorative Objects

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Fused Deposition Modeling (FDM)1. A spool of themoplastic wire (typically

acrylonitrile butadiene styrene (ABS)) with a 0.012 in (300 μm) diameter is continuously supplied to a nozzle

2. The nozzle heats up the wire and extrudes a hot, viscos strand (like squeezing toothpaste of of a tube).

3. A computer controls the nozzle movement along the x- and y-axes, and each cross-section of the prototype is produced by melting the plastic wire that solidifies on cooling.

4. In the newest models, a second nozzle carries a support wax that can easily be removed afterward, allowing construction of more complex parts. The most common support material is marketed by Stratasys under the name WaterWorks

5. The sacrificial support material (if available) is dissolved in a heated sodium hydroxide (NaOH) solution with the assistance of ultrasonic agitation.

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Fused Deposition Modeling (FDM)

The fused deposition modeling (FDM) technology was developed by S. Scott Crump in the late 1980s and was commercialized in 1990. The double material approach was developed by Stratasys in 1999.

Current market leaders- Stratasys, Inc.

Stratasys Dimension SST 1200

"Ribbon Tetrus" (Carlo Séquin)

Courtesy, Dr. Robin Richards, University College London, UK

www.nybro.com.au

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Fused Deposition Modeling (FDM)

KEY APPLICATION AREAS

Maximum build size 20” x 20” x 20”

Resolution in (x,y) +/- (0.002” - 0.005”)

Resolution in z +/- (0.002” - 0.01”)

Speed Slow

Cost Medium

Available materials Thermoplastics (ABS, PC, ULTEM…)

KEY METRICS ADVANTAGES

DISADVANTAGES

• Economical (inexpensive materials)• Enables multiple colors• Easy to build DIY kits (one of the most

common technologies for home 3D printing)

• A wide range of materials possible by loading the polymer

• Materials suite currently limited to thermoplastics (may be resolved by loading)

• Conceptual Models• Engineering Models• Functional Testing Prototypes

www.redeyeondemand.com

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Fused Deposition Modeling (FDM)

FAB@Home• First multi-material printer available to the public• Open-source system• Project goal: open-source mass-collaboration developing

personal fabrication technology aimed at bringing personal fabrication to your home (project started by H. Lipson and E. Malone at Cornell in 2006).

• Popular Mechanics Breakthrough Award 2007

RepRap• Open-source system• Founded in 2005 by Dr. A. Bowyer

at the University of Bath (UK)• Project goal: Deliver a 3D printer

that can print itself!• 1st machine in 2007 (Darwin)• Replication achieved in 2008

Do it Yourself FDM rapid prototyping systems

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Fused Deposition Modeling (FDM)Do it Yourself FDM rapid prototyping systems

Cubify Cube• Commercially available fully built for $1,200• Resolution 0.2mm• 16 colors• Prints in ABS and PLA• Awarded 2012 Popular Mechanics Breakthrough Award

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3D Printing (3DP)

1. A layer of powder (plaster, ceramic) is spread across the build area

2. Inkjet-like printing of binder over the top layer densifies and compacts the powder locally

3. The platform is lowered and the next layer of dry powder is spread on top of the previous layer

4. Upon extraction from the machine, the dry powder is brushed off and recycled

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3D Printing (3DP)

Z Corporation first introduced high-resolution, 24-color, 3DP (HD3DP™) in 2005 (600 dpi). Z Corp was later bought by 3D Systems.

Current market leaders- Z Corporation- Exone- Voxeljet

Zcorp Z510

Olaf Diegel Atom 3D printed guitar

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3D Printing (3DP)

KEY APPLICATION AREAS

• Widely used to print colorful and complex parts for demonstration purposes

• Molds for sand casting of metals

Maximum build size 14 in x 10 in x 8 in

Resolution in (x,y) 640 dpi

Resolution in z Variable

Speed Fast

Cost Low

Available materials Plaster, sand, oxide ceramics, sugar and starch for food printing

KEY METRICS ADVANTAGES

DISADVANTAGES

• Can create extremely realistic multi-color parts (24-bit color) using inkjet technology

• Can generate complex components with internal degrees of freedom

• Economical• Versatile

• Very limited materials suite• Low resolution (lowest of all AM technologies)• Negligible mechanical properties (unusable

for any structural application)

Printed with Z Corp 650

3D Printing (3DP)

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Selective Laser Sintering (SLS)1. A continuous layer of powder is

deposited on the fabrication platform

2. A focused laser beam is used to fuse/sinter powder particles in a small volume within the layer

3. The laser beam is scanned to define a 2D slice of the object within the layer

4. The fabrication piston is lowered, the powder delivery piston is raised and a new layer is deposited

5. After removal from the machine, the unsintered dry powder is brushed off and recycled

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Selective Laser Sintering (SLS)

• SLS technology invented at UT Austin in the ‘80s by Joe Beaman, Carl Deckard and Dave Bourell.

• First successful machine: DTM Sinterstation 2000, in late 1990s

• DTM later acquired by 3D Systems

Current market leaders- 3D Systems

3D Systems Sinterstation

Important note: SLS patent runs out in Feb 2014! A huge influx of players and technologies is anticipated. Metal Technology Co.

3D Systems

Bulatov Abstract Creations

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Selective Laser Sintering (SLS)

KEY APPLICATION AREAS

• Structural components

Maximum build size 700 mm x 380 mm x 560 mm

Resolution in (x,y) High (Spot Dependant)

Resolution in z 0.005”

Speed Medium

Cost Medium

Available materials Powdered plastics (nylon), metals (steel, titanium, tungsten), ceramics (silicon carbide) and fiber-reinforced PMCs

KEY METRICS ADVANTAGES

DISADVANTAGES

• Wide array of structural materials beyond polymers

• No need for support materials• Cheaper than EBM• One of two technologies that allow

complex parts in metals

• Expensive relative to FDM, 3DP• The quality of metal parts is not as high as

with EBM

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Electron Beam Melting (EBM)1. The fabrication chamber is

maintained at high vacuum and high temperature

2. A layer of metal powder is deposited on the fabrication platform

3. A focused electron beam is used to melt the powder particles in a small volume within the layer

4. The electron beam is scanned to define a 2D slice of the object within the layer

5. The build table is lowered, and a new layer of dry powder is deposited on top of the previous layer

6. After removal from the machine, the unmelted powder is brushed off and recycled

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Electron Beam Melting (EBM)Current market leaders- Arcam AB (Sweden)

Arcam A2 machine

EBM process developed by Arcam AB (Sweden) in 1997

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Electron Beam Melting (EBM)

KEY APPLICATION AREAS

• Structural components for aerospace (Ti6Al4V, gammaTiAl, Ni superalloys)

• Custom-made bio-implants (Ti6Al4V)

Maximum build size

200mm x 200mm x 350mm

Resolution in (x,y) +/- 0.2mm

Resolution in z 0.002” (0.05 mm)

Speed Medium

Cost High

Available materials Metals: titanium, tungsten, stainless steel, cobalt chrome, Ni-based superalloys.

KEY METRICS ADVANTAGES

DISADVANTAGES

• Method of choice for high-quality metal parts• Wide range of metals• Fully dense parts with very homogeneous

microstructures • Vacuum operation allows building of highly

reactive metals (e.g., Titanium)• High temperature operation (700-1000C)

results in structures free of internal stresses• EBM allows even better microstructural

control than many conventional processes.

• Extremely expensive (more than SLS)• Conventional machining may be required

to finish the goods (rough surface)• Requires vacuum operation

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Multijet Modeling (MJM)1. A piezoelectric print head with

thousands of nozzles is used to jet 16 micron droplets of photopolymer on the printing structure. An additional set of nozzles deposits a sacrificial support material to fill the rest of the layer.

2. A UV curing lamp is scanned across the build to immediately cross-link the photopolymer droplets.

3. The elevator is lowered by one layer thickness and the process is repeated layer-by-layer until the model is built.

4. The sacrificial material is removed:▫ The Objet system uses a photopolymer as

support material; the support material is designed to crosslink less than the model material and is washed away with pressurized water.

▫ The 3D Systems InVision uses wax as support material, which can be melted away.

The method of building each layer is similar to Inkjet Printing, in that it uses an array of inkjet print heads to deposit tiny drops of build material and support material to form each layer of a part.

However, as in Stereolithography (see following slides), the build material is a liquid acrylate-based photopolymer that is cured by a UV lamp after each layer is deposited.

For this reason, Multijet Modeling is sometimes referred to as Photopolymer Inkjet Printing.

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Multijet Modeling (MJM)Current market leaders- Objet- 3D Systems

Multijet modeling (MJM) was introduced by 3D Systems in 1996 as a cheaper alternative to industrial-grade Stereolithography machines.

Objet Desktop 30 Pro

3D SystemsThermojet

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Multijet Modeling (MJM)

KEY APPLICATION AREAS

• Automotive• Defense• Aerospace• Consumer goods• Household appliances• Medical applications

Maximum build size 1000mm x 800mm x 500mm

Resolution in (x,y) 450 dpi

Resolution in z 16 microns

Speed Fast

Cost High

Available materials Acrylate-based photopolymer

KEY METRICS

ADVANTAGES

DISADVANTAGES

• Fast process• Complex parts via sacrificial support

materials

• Accuracy is not as good as SLA

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Stereolithography (SLA)

1. A structure support base is positioned on an elevator structure and immersed in a tank of liquid photosensitive monomer, with only a thin liquid film above it

2. A UV laser locally cross-links the monomer on the thin liquid film above the structure support base

3. The elevator plate is lowered by a small prescribed step, exposing a fresh layer of liquid monomer, and the process is repeated

4. At the end of the job, the whole part is cured once more after excess resin and support structures are removed

A suitable photosensitive polymer must be very transparent to UV light in uncured liquid form and very absorbent in cured solid form, to avoid bleeding solid features into the layers underneath the current one being printed.

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Stereolithography (SLA)Solidification of the monomer can occur in two different modalities:

Free surface mode: Solidification occurs at the resin/air interface. In this mode, care must be taken to avoid waves or a slant of the liquid surface, which would compromise the final dimensional resolution. The elevator moves down at each step (top-down build).

Fixed surface mode: The resin is stored in a container with a transparent window plate for exposure, and solidification occurs at the stable window/resin interface. In this mode, the elevator moves up at each step (bottom-up build).

H-W Kang et al 2012 J. Micromech. Microeng. 22 115021

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Stereolithography (SLA)Two fundamental process variations exist:

▫ Scanning stereolithography. The laser beam is rastered onto the surface. Parts are constructed in a point-by-point and line-by-line fashion, with the sliced shapes written directly from a computerized design of the cross-sectional shapes.

▫ Projection stereolithography. A parallel fabrication process in which all the voxels in a layer are exposed at the same time; the topology to be printed on each layer is defined by 2D shapes (masks). These 2D shapes are either a set of real photomasks or digital masks defined on a DLP projector.

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Stereolithography (SLA)SLA was pioneered by Chuck Hull in the mid-1980s (see picture below). Hull founded 3D Systems to commercialize its new manufacturing process.

Current market leaders- 3D Systems- Sony

3D Systems iPro 9000 XL

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Stereolithography (SLA)

KEY APPLICATION AREAS

• Patterns for metal processing (e.g., molding)

• Prototypes for demonstrational purposes

Maximum build size 1500mm x 750mm x 550mm

Resolution in (x,y) Spot Dependent

Resolution in z 0.004”

Speed Medium

Cost High

Available materials Thermoset polymers: photosensitive resins

KEY METRICS

ADVANTAGES

DISADVANTAGES

• Fast• Good resolution• No need for support material• Photosensitive polymers have acceptable

mechanical properties

• Expensive equipment ($100-$500K)• Expensive materials (photosensitive resins

are ~$100-200 /kg)• Material suite limited to resins

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Stereolithography (SLA)

• The application of rapid prototyping (RP) techniques to MEMS and NEMS requires higher accuracy than what is normally achievable with commercial RP equipment.

• Laminated object manufacturing (LOM), fused deposition modeling (FDM), and selective laser sintering (SLS) all must be excluded as microfabrication candidates on that basis.

• Only stereolithography has the potential to achieve the fabrication tolerances required to qualify as a MEMS or NEMS tool.

• Latest enhancements that have made it an attractive option are high-resolution micro- and nanofabrication methods.

APPLICATION TO MEMS AND NEMS

EPFL, Lausanne, Switzerland

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Stereolithography (SLA)

• Microstereolithography, derived from conventional stereolithography, was introduced by Ikuta in 1993.

• Whereas in conventional stereolithography the laser spot size and layer thickness are both in the 100-μm range, in microstereolithography a UV laser beam is focused to a 1–2-μm spot size to solidify material in a thin layer of 1–10 μm.

• The monomers used in RP and micro-stereolithography are both UV-curable systems, but the viscosity in the latter case is much lower (e.g., 6 cPs vs. 2000 cPs), because high surface tension hinders both efficient crevice filling and flat surface formation at the microscale.

• In microstereolithography the solidified polymer is light enough so that it does not require a support as is required for the heavier pieces made in RP.

MICROSTEREOLITHOGRAPHY

www.miicraft.com

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Stereolithography (SLA)

• Two-photon lithography provides a further enhancement of the SLA resolution.

• Special initiator molecules in the monomer only start the polymerization reactions if activated by two photons simultaneously. The laser intensity field can be tuned so that this event only happens in a very small region near the focus. The result is extremely local polymerization, with resolutions in the tens of nanometers range.

• Two-photon polymerization can occur everywhere in the monomer bath, as opposed to only at the top layer, simplifying the hardware requirements considerably.

TWO-PHOTON LITHOGRAPHY

www.laser-zentrum-hannover.de

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Current materials in Additive Manufacturing

Materials in AM today- Thermoplastics (FDM, SLS)- Thermosets (SLA)- Powder based composites (3DP)- Metals (EBM, SLS) - Sealant tapes, paper (LOM)- Starch and sugar (3DP)• Functional/structural parts

▫ FDM (ABS and Nylon)▫ SLS (thermoplastics, metals)▫ EBM (high strength alloys, Ti, stainless steel, CoCr)

• Non-functional/structural parts▫ SLA (resins): smoothest surface, good for casting▫ LOM (paper), 3D Printing (plaster, sand): marketing and concept prototypes, sand casting molds

• As new materials are introduced, more functional components will be manufactured (perhaps 30-40% by 2020).

• Importantly AM is one of the best approaches for complex architected materials.

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Challenges in AM materials properties predictions

• Most AM processes introduce anisotropy in mechanical properties (z different from x,y)• Local differences in laser/EB power (e.g., perimeter vs center) introduce heterogeneity in

mechanical properties• Laser fluctuations might result in embedded defects that are difficult to identify• All existing machines are open-loop: temperature sensors have been introduced in some

processes, but the readings are not used to optimize the processing parameters on the fly.

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Micro-Architected MaterialsOverarching vision

How can we fill unclaimed regions?- Optimal topology- Optimal geometry- Base material optimization (nm-features)- Hierarchical design

What do we need?- Understand multi-scale mechanical behavior (deformation and failure modes) - Understand processing -> microstructure -> mechanical properties (including size effects)- Developing new models for FE analysis and optimal design

Superior Macroscale Behavior by Topological

Control of the Microstructure

IMPROVED STRENGTHAT THE FILM LEVEL

SIZE EFFECTSIN PLASTICITY

AND FRACTURE

UNIQUE DEFORMATIONMECHANISMS

IMPROVED STRENGTHAT THE MACROSCALE

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A word of caution

Tech Consultancy Puts 3D Printing at Peak of "Hype Cycle"