BME 301 Exam 1

3D printing

additive manufacturing technique that is the process of making 3D objects from digital file with x,y,z axis, layer by layer, and rapid prototyping

Formative manufacturing

mold to object

need a lot of pieces and high starting cost per part, but the more parts the lower the cost

Subtractive manufacturing

chisel or CNC

can start with low numbers, but high cost for few parts and reduces the more parts you get

Additive manufacturing

layer by layer for rapid prototyping of 3D objects

flat line constant cost for few to a lot of parts

Components of 3D printer

Hardware (3D printer itself), Software and Imaging, and Material

3D printing process non-tiles

3D CAD file to STL File to Slicing Software to AM Process to Final Model

STL file

converts mask to Standard tesselation (triangle) language
Describes surface geometry of 3D object using series of linked triangles

Angle control

STL term meaning angle between arc and triangle point is 15 degrees or smaller

Chordial Deviation

Stl term meaning height between arc and flat point is 0.01 to 0.001

Slicer Software

printer specific software which takes STL file and determines where material needs to be deposited layer by layer and optimizes path for extruder to travel and turns that info into G-code

Slicer to Printer

Prusa = prusaslicer

Ultimaker = cura

Bamboo = bamboo studio

Formlabs = preform

3D printing history

1984 - 3D systems invents first SLA printer

1986 - patented, also selective laser sintering invented

1988 - Stratasys invents FDM

1993 - MIT invents and patents inkjet 3D printing sells to Z corporation

1996 - 3D systems sells first inkjet Acrua

2001 - First desktop printer based on plastic sheet lamination developed by solid dimension

2002 - First functional 3D printed Kidney by Wake Forest

2007 - FDM patents expired and prices dropped

2008 = RepRAm self replicating 3D printers using FFF technology

2009 - ASTM published document containing standard terminology on Additive Manufacturing

Benefits of 3D printing

Geometric complexity at no extra cost

Very low start up costs

Customization of every part

Low cost prototyping

Quick turnaround

Materials

Limitations

Lower strength and anisotropic materials

Not cost competitive at higher volumes

Limited accuracy and tolerances

Post processing requirements

Applications of 3D printing

Medical products and equipment - quickly create for patient demand (development, protoypes, active devices)

Prosthetics and Implants - fast and affordable (dental, patient matched, sterilized)

Anatomical models for surgical planning and education - reduction in operative time and planning

Tissue and Biomaterials - more precise

Personalized Drugs - more effective dosages

Vat photopolymerization

category for all 3D printing processes that build objects layer by layer by curing liquid photopolymer resin inside a vat using a light source

Vat polymerization details

first 3D printing system created

expensive compared to FDM

liquid photopolymer in vat is selectively cured by light activated polymerization in X and Y axis

Stereolithography

light source: laser with X,Y movement and galvanometer (mirror)

Lowest resolution: 25- 140 microns (slower due to X,Y sweeps)

Curing: along path of laser travel

Other: expensive optics, good surface finish and sharp and curved parts

Digital Light Processing (DLP)

Light source: projector equipped with Digital micromirror device

Lowest resolution: 20 to 65 microns (determed by DMD and lens)

Curing: entire layer cures at once

Other: faster than SLA, no sweeping motion, pixels from DMD cause artifacts

Masked Lithography

Light source: LCDs and light source (or just LCD)

Lowest Resolution: 15-50 microns (LCD pixels)

Curing: cures in X and Y always

Other: Faster than DLP, no sweeping motion, pixels from LCD cause artifacts

Two-Photon Polymerization

Light Source: Laser with 2PP which is near infarred

Lowest resolution: 15-30nm (optical defraction limits)

Curing: after each particle

Other: extremely slow and expensive

Wavelength equation

Wavelength is proportional to 1/Energy

Top down SLA

parts oriented flat to minimize support layer and layer count

supports similar to FDM

supports for overhang and bridges

build platform starts on top of resin and keeps moving down

Large cross-sectional area

Bottom Up SLA

parts oriented at angle prioritizing print stability (10-15 degrees)

More complex support structures

Build platform sits in resin

Small cross sectional area

Isotropy

SLA printers are close to isotropic because the photopolymers are chemically cross-linked between layers and watertight

SLA printing steps (blocks)

Prepare 3D model

Import model into 3D printing software

Orient and Add supports

Slice Model and generate supports

Prepare/check printer

Fill vat with resin (don’t need to do here)

Start print

Printing process

Monitor print

Post-processing

Remove supports and fine tune

Inspect and Evaluate

Vat Polymerization Materials

Methacrylate and acrylic based resin (photocrosslinkable)

Polyethylene glycol diacrylate (photocrosslinkable)

Poly(TMC)

Poly e-caprolactone

Acrylamide

Epoxy-based photocurable resin

Applications of SLA

Sustainability - ecofriendly materials, low energy required, low carbon footprint

Interdisipline - machine learning and AI, algorithms to improve printing parameters

Biomed - prosthetics, organs, regenerative scaffolds, drug delivery, biocompatible actuators

Micro/nano structures - functional, cellular, biomimetic, ultra-light, durable, porous, etc.

Extrusion Based System

category of processes that builds objects layer by layer by extruding polymer using pneumatic, piston, roller, or screw driven systems

Classified under broader process category of material extrusion

Most commonly used and most cost effective technique

Extrusion types for extrusion based system

Piston - filament

Pneumatic - melted pellet

Screw driven - melted pellet

Other names for extrusion based system

fused filament fabrication - filament material

precision extruding deposition - pellet material

multiphase Jet solidification - powder material

EBS Pellet

most affordable, higher printing speed, larger nozzles, better for larger parts

EBS Filament

convienience and availability, handle and store, high details and clean surface finish

PLA

Good: implants and modeling, ease of printing, stress, most isotropic

Bad: impact resistance

ABS

Good: prosthetic and structural use, heat resistance, relatively good impact/stress

Bad: Ease of printing

PET

Good: Ease of printing and prototyping

Bad: Heat resistance and impact resistance/stress

Nylon

Good: shock absorption with prosthetics, impact resistance

Bad: Isotropy, and heat resistance

TPU

Good: prosthetic linings, impact resistance

Bad: ease of printing, quality, stress, heat resistance

PC

Good: Fluid systems(clear), max stress, heat resistance

Bad: Breakage, ease of printing

Issues with EBS

First layer calibration

Poor print bed adhesion

Warping

Anisotropy

Lack of adequate support material

Filament jamming

EBS Supports

Greater than or equal to 45 degrees and can help warping

EBS print structure

Outer shell

Middle fill - typically 15-20 percent (increase in percent = increase in strength)

Top Layer

Bottom Layer (adhesion layer)

Rectangular Infill (EBS)

standard infill for FDM with strength in all directions and reasonably fast to print but requires printer to do least amount of bridging across infill pattern

Triangular

strength needed in direction of walls but longer print time

Wiggle

allows model to be soft, twist, or compress and good for soft rubbery material or softer nylon

Honeycomb

popular infill because quick to print and very strong providing strength in all directions

Post Processing EBS

support removal - pliers or water soluble PVA,

gap filling, cold welding, aesthetic

Powder based systems

category of 3D printing process that uses a laser of electron beam to melt and fuse material powder

Types of Powder Based System

Selective Laser Sintering

Direct Metal Laser Sinterin

Selective Laser Melting

Electron Beam Melting

SLS

uses fine powder of metals and high power CO2 laser beam scans surface of powder bed to sinter powder particles with no solvents being needed

Electron Beam Melting

same concept as SLS CO2 but electron beam used to melt SLS particles

SLS Parameters

layer spot size, height, thickness, laser energy density, powder bed temp, powder type

Powder bin packing

efficient stacking of parts in build volume, height of bin determines print time, most cost effective to fill bin to maximum capacity

Common SLS materials

Nylon 12 - inexpensive, good mechanical properties, malte rough surface

Alumide - metallic appearance, temperature, resistance

SLS advantages

no support material

complex geometries

relatively strong fundamental parts

high level of accuracy

SLS Drawbacks

shrinkage of parts, surface qualities, and low mechanical strength or properties

SLS post processing

depowdering, polishing, heat treatment

SLS applications

dental implants, bone scaffolding, orthopedics

Droplet Based Systems

category of 3D printing techniques where liquid material is deposited in droplet form by continuous flow where material often turns solid after depostion via cooling of solvent-evaporation

Material Jetting, Binder Jetting

Material Jetting

Additive Manufacturing process in which droplets of material are selectively deposited and cured on a build plate

Binder Jetting

Additive manufacturing process in which a liquid bonding agent selectively binds regions of a powder bed

Mechanisms of inkjet bioprinting

Continuous inkjet bioprinting

thermal drop-on-demand bioprinting

piezoelectric drop-on-demand bioprinting