Modern Manufacturing Methods:Additive Manufacturing

Rahul Panat

School of Mechanical and Materials EngineeringWashington State University

1

Outline• What is additive manufacturing?

– Types of equipment/processes– Applications

• Microscale Additive Printing– Processes at microscale– Applications

Newmancraneins.com

What is additive manufacturing?

• Subtractive Manufacturing– Any process of removing material– Milling, Cutting, Drilling, etc…

• Additive Manufacturing– Any process of adding material– Filament, Laminate, Liquid, Powder, etc…

• Rapid Prototyping – Original name• Additive Manufacturing – Best name• 3D Printing – Most common name

Types

4

Filament (FDM, FFF)Stratasys, RepRap, Makerbot†, 3D Systems

Powder (Sintered – SLS or Electron beam)Eos, Arcam

Powder (Inkjet Binder)Z-Corp‡, ExOne

Liquid (SLA, DLP) 3D Systems

Liquid (Inkjet) Objet†, Solidscape†

LaminatedSolido, Mcor

†Owned by Stratasys‡Owned by 3D Systems

Materials

http://www.shapeways.com/materials

RepRap vs Stratasys

~$550 RepRap Prusa ~$15000 uPrint Stratasys

Sept 2011 A 0.254 mm layer is the smallest Stratasys can go.

Reprap vs SLA

3D Systems SLA-7000 @ 0.1mm vs RepRap Mendel Prusa @ 0.15 mm (RepRapBCN version)http://reprapbcn.wordpress.com/2012/05/24/reprap-mendel-prusa-vs-3dsystems-sla-7000-stereolithography/

~$900 RepRap Prusa ~$650,000 3D Systems SLA-7000

Subtractive Processes

• Series of material removal by machining and finishing operations

• Typical Steps– Computer-based drafting packages, which can produce three-

dimensional representations of parts– Interpretation software, which can translate the CAD file into a format

usable by manufacturing software– Manufacturing software, which is capable of planning the operations

required to produce the desired part shape– Computer-numerical-control (CNC) machinery, with capabilities necessary

to produce the parts

• Usually a soft material (usually a polymer or wax) is used as the work-piece

Additive Processes

• Parts are built layer by layer– Stereolithography– Multi Jet/polyJet modeling– Fused-deposition modeling– Ballistic-particle manufacturing– Three-dimensional printing– Selective laser sintering– Electron-beam melting– Laminated object manufacturing

• Differences in the method of producing individual slices – Typically 0.1–0.5 mm (0.004–0.020 in.)

• Operations require dedicated software• Much faster than subtractive processes –

– Few minutes to a few hours

Fused Deposition Modeling (FDM)• Gantry-robot controlled extruder head moves in two principal directions over a table,

which can be raised and lowered as required• Extruder head is heated, and extrudes polymer filament at a constant rate through a

small orifice. – Head follows a predetermined path– Extruded polymer bonds to the previously deposited layer

• Drawbacks– Complex parts may be difficult to build directly because once the part has been constructed up to height

a, the next slice would require the filament to be placed at a location where no material exists underneath to support it

– Needs support material separately extruded

https://www.youtube.com/watch?v=WHO6G67GJbM

Stereolithography• Curing (hardening) of a liquid photopolymer into a specific shape

– Photocurable liquid-acrylate polymer– The liquid is a mixture of acrylic monomers, oligomers (polymer intermediates), and a photoinitiator (a compound that

undergoes a reaction upon absorbing light)

• The platform is lowered sufficiently to cover the cured polymer with another layer of liquid polymer, and the sequence is repeated

• Part is removed from the platform, blotted, and cleaned ultrasonically and with an alcohol bath• Total cycle times in stereolithography range from a few hours to a day, without post-processing

steps such as sanding and painting• Depending on their capacity, the cost of the machines is in the range from $100,000 to $400,000!

https://www.youtube.com/watch?v=NM55ct5KwiI

Multijet/Polyjet Modeling• Print heads deposit the photopolymer on the build tray; UVt bulbs, alongside the jets, instantly

cure and harden each layer• No need for post-modeling curing• Smooth surface of layers as thin as 16 μm• Two different materials are used: one for the actual model, and a second gel-like resin for

support – Each material simultaneously jetted and cured, layer by layer– Support material removed later removed, with an aqueous solution

https://www.youtube.com/watch?v=Som3CddHfZE

Undoprototipos.com

Additive vs Subtractive

Additive Subtractive

Selective Laser Sintering (SLS)• Sintering of non-metallic or, less commonly, metallic powders selectively into an

individual object• Materials: Polymers (such as ABS, PVC, nylon, polyester, polystyrene, and epoxy), wax,

metals, and ceramics, with appropriate binders• With ceramics and metals: common practice to sinter only a polymer binder that has

been blended with the ceramic or metal powders – ceramic/metal sintered in a furnace

Wikipediahttps://www.youtube.com/watch?v=srg6fRtc-oc

Electron Beam Melting• E-beam, melting uses the energy source associated with an electron• beam to melt titanium or cobalt-chrome powder to make metal prototypes. The• workpiece is produced in a vacuum

Fraunhofer. gov

https://www.youtube.com/watch?v=jSH2vrtVNqQ

Hindawi.com

Laminated Object Manufacturing• Roll-to-roll process is applied with heat activated glue or vinyl cutters

https://www.youtube.com/watch?v=4ebj6hH0HnY

Three Dimensional Printing• A print head deposits an inorganic binder material onto a layer of polymer, ceramic, or

metallic powder• Allows considerable flexibility in the materials and binders used• A piston, supporting the powder bed, is lowered incrementally, and with each step, a

layer is deposited and then fused by the binder

Laser Engineered Net-Shaping• Metal powder sprayed on a part• Lasers used to sinter the powder

LENSTM system creates near net shape manufacturing

Turbine blade made by LENS at Sandia National Lab

LENSTM: Laser enabled net-shaping (courtesy Optomec Inc)

https://www.youtube.com/watch?v=SYbw1oSzPVA

Additive Manufacturing at Microscale

At Micro-scale: Additive vs SubtractiveSubtractive Process

Substrate 1 Clean substrate

CuSubstrate

2 Conductive layer

CuSubstrate

Photoresist

3 Photoresist deposition

CuSubstrate

Photoresist

UV light

4 UV Exposer

CuSubstrate

Photoresist

5 Photoresist development

Cu Pattern

Substrate 6 Etching

Direct Write Process

Substrate

Substrate

2

3

Substrate 1Clean substrate

Printing

Sintering

Energy (Thermal, Laser, Photonic) Chemicals

Mask

Advantages of Additive Processes vs Lithography

• Additive methods typically have the below features–Minimal to no harmful chemicals–Fewer Steps–No material waste–Largely independence from the chemical compatibility of the

substrate–Ability to manufacture on curved/vertical surfaces– Require large numbers of print-heads working on several

units to realize large numbers of units/panel to lower cost

Micro-additive MethodsNanoscale ‘Pen’

DPN*

Dip Pen Nanolithography (Science, Vol 283, Jan 1999).Microscale Pen (Advanced Materials 25: 4539-4543)Electric potential driven plating (J. Appl. Phys. 115, 044915 (2014))

Electric Field DrivenAdditive Method

Microscale ‘Pen’

Movie

Micro-Battery

AFM tip for manufacturing

Methods: Inkjet Printing

3-D Antenna: Adv Materials, March 18 2011Printed board: http://dx.doi.org/10.1145/2493432.2493486

Printed Electronics

Printed Antenna

Length scale >~50micronDrop on demand printingLow standoff height of ~2mm

Methods: Inkjet Printing

• Most commonly used method is drop-on demand by– Thermal actuation (e.g. Hewlett-Packard) – Piezo actuation by pressure pulse using PZT (e.g. Epson)– Certain methods may include syringe pressure for larger diameter nozzle

• Ink formulations are the key elements– Viscosity < 10cP– May include various elements like water, glycol– Could be UV curable– Non-Newtonian behavior (e.g. shear thinning) of the ink can influence the printing quality

• Fluid Mechanics models can predict the printing volume per drop, velocity, etc as a function of puse voltage, fluid properties, and nozzle size

Applied Mathematical Modelling, Volume 12, Issue 2, April 1988, Pages 182

Aerosol Jet • Clog resistance nozzle (sheath gas)

• High density micro droplets

• Continuous stream

• Tightly focused (forced)

• Able to print high viscosity ink (< 1000 cP)

• Up to 500nm particles with line resolution 10µm

Methods: Aerosol Jet Printing

Ack: M. J Renn

https://www.youtube.com/watch?v=F6_5L-Vtb0M

• Aerosol particles created by ultrasonic energy or pneumatic pressure

• Particles carried by a gas to deposit on a substrate

Methods: Aerosol Jet Printing

• Mist of ink spheres 1-5µm in diameter, with several nanoparticles per drop• Equipment works to focus & collimate to reduce overspray• Aerosol particles are directed by stream of gas to ‘print’ on the substrate with forces

acting on the particle• Forces on Aerosol Particle:

– FSt + FBa + FVm + FPs + FGr + FMa + Fsa =

FSt is Stokes force (steady viscous drag force)Fba is Basset force (nonsteady viscous drag force), FVm is the virtual mass force (inertia of fluid surrounding particle added to particle), FPs is the pressure gradient force, FGr is the buoyancy force caused by gravity, FMa is the Magnus lift force due to particle rotation, and FSa is the Saffman lift force on a particle with local shear flow

ω is the vorticity of the fluid surrounding the particleand Ω is the angular rate of rotation of the particle

*

Journal of Nanotechnology, Vol 2012, Article ID 324380

Methods: Aerosol Jet Printing

• Stokes and Saffman force are the most important forces indetermining printing quality• Particle size, solvent viscosity etc determining factors for micro-additive printing quality• Overspray an issue, esp with on-equipment laser

100µm Tip

~10µm Beam

Printing quality by Aerosol Jet

Journal of Nanotechnology, Vol 2012, Article ID 324380

Nanoparticle Sintering• Sintering of nanoparticles determines porosity of micro-additive methods• Kinetics of sintering controlled by

– Evaporation and condensation (EC)– Surface diffusion (SD)– Grain boundary diffusion (GDB)– Volume diffusion from the surface of the particle (VDS), – Volume diffusion from the interior of the particle (VDV)– Viscous flow (VF).

Sintered nanoparticles

• Nanoparticles can sinter at much lower temperature compared to bulk counterparts due to their high s-t-v ratio

– e.g. 100nm silver particles can sinter at 200 C, whereas bulk Ag MP is 961 C

• Photonic energy can be used to selectively heat nanoparticles for short durations of time to avoid heating substrates• MP depression given by

Nanoparticle Sintering

Where: TMB=bulk melting temperatureσsl=solid liquid interface energyHf=bulk heat of fusionρs=density of solidd=particle diameter

𝑇𝑇𝑀𝑀 𝑑𝑑 = 𝑇𝑇𝑀𝑀𝑀𝑀 1 −4 𝜎𝜎𝑠𝑠𝑠𝑠𝐻𝐻𝑓𝑓𝜌𝜌𝑠𝑠𝑑𝑑

Thermochimica Acta 463 (2007) 32–40

Gold Nanoparticle DataPhys Rev A, Vol. 13 (6) 1976

• Thermal sintering in an oven• Laser sintering• Photonic sintering by a flash of UV light• Plasma sintering

Sintering Methods

Photonic CuringSinteron S2000On-equipment laser for Aerosol Jet

Highly porousstructure

Highly densestructure

Residual Stresses

• Recent studies using neutron diffraction show significant residual strain/stresses in additively manufactured parts

• Residual stresses can have adverse effect for structural and other applications• Residual stress for micro-additive manufacturing remains relatively unexplored

Metallurgical and Materials Transactions A, 2014, Volume 45, Issue 13, pp 6260-6270

Reliability

• Reliability requirements for micro-additively manufactured parts are same as that made using lithography/MEMS

• Typical issues include– Degradation under thermal cycling– Degradation under cyclic mechanical load– Electro-migration under moisture/temperature conditions– Kirkendall voids under electrical current with dissimilar materials

• Methods to assess reliability for printed electronics for newer applications yet to be standardized in industry

http://reliabilitycalendar.org/blog/event/dfr-wearable-electronics-reliability-issues-and-real-life-solutions-in-printed-electronics/

Applications: 3-D Antennas

• Metal dielectric structures for 3-D antennas

Polymer Pillar (75 µm diameter)

Metal Line(25µm wide)

400 µm

Benefits: Electronic fabrication in 3-D that is difficult/impossible to make by lithography or MEMS Avoids the use of chemicals and results in minimal waste Electronics directly integrated with chips

Journal of Micromechanics and Micro-engineering, Vol. 25 (10), 107002 (2015)

Antenna-like structures fabricated at WSU

Directional antenna simulation

view

Substrate

Solid dielectric pillar micro-manufactured by dispense and cure

Applications: 3-D Dielectrics and Structural Materials

• Metal dielectric structures as antennas

Benefits: High strength to volume ratio structure possible Avoids the use of chemicals and results in minimal waste Electronics on vertical walls possible

Si post (Ack. Dr. M. Renn) Micro Springs (Ack. Dr. M. Renn)

Polymer cones fabricated at WSU

Applications: Transistors and Bio Parts

Thin –film Transistors Biological

Surface Mount Technology Association Pan Pacific Symposium, 2002Nature Biotechnology 32, 773–785 (2014)

• Several applications of direct printing of materials• The field has only been explored superficially