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Introduction&Basic Principles-Additive manufacturing is the formalized term for what used to be called rapid prototyping
(mostly plastics used) and what is popularly called 3D Printing.
-Additive Manufacturing (AM) – a wide range of materials (ca. 20 years). Requiring right
material, right AM process, right printing machine and (and right post-processing)
-Basic Requirement For AM to be useful➔3Fs(Form,Fit, Function)- geometry, accuracy &
mechanical properties
-Generic AM Process Steps:
• CAD (external and internal geometry and sizes)
• conversion to STL
• transfer to AM machine and STL file manipulation (position, orientation)
• machine setup (layer thickness, energy input, speed...)
• build (fully automated)
• cooling and detachment from the build plate
• post-processing (cleaning, support removal, heat treatment, sanding, painting,
assembly...)
• ready for use
,-Important points:
• AM machine maintenance (limited service life of moving mechanisms,
mirror, lens, nozzle, wiper, etc.)
• Machine environment (no electrical noise, no vibrations, low humidity, good ventilation,
safety / hazard concerns)
• Outside common standards for solid materials and subtractive processes (>100 years)
• Part by part variation (low reproducibility)
• Materials storage & handling
• Material degrading over the cycles of re-use
Development of AM
-Computer-Aided Manufacture (CAM) represents a channel for converting the virtual models developed
in CAD into the physical products that we use in our everyday lives.
-Most CAD systems these days utilize Non-Uniform Rational Basis-Splines, or NURBS [6]. NURBS are an
excellent way of precisely defining the curves and surfaces that correspond to the outer shell of a CAD
model.
-STL is now a standard output for nearly all solid modeling CAD systems and has also been adopted by
AM system vendors [8]. STL uses triangles to describe the surfaces to be built. Each triangle is described
as three points and a facet normal vector indicating the outward side of the triangle.Size of triangles
detrmines the smoothness of the surface.
-There are two kinds of laser processing used in AM; curing and heating. With photopolymer resins the
require- ment is for laser energy of a specific frequency that will cause the liquid resin to solidify, or
“cure.” Usually this laser is in the ultraviolet range but other frequencies can be used. For heating, the
requirement is for the laser to carry sufficient thermal energy to cut through a layer of solid material, to
cause powder to melt, or to cause sheets of material to fuse.
-For example, the early photocurable resins resulted in models that were brittle and that warped easily.
Powders used in laser-based powder bed fusion processes degraded quickly within the machine and
many of the materials used resulted in parts that were quite weak. Materials have been tuned to suit
more closely the operating parameters of the different processes and to provide better output parts
-One of the reasons AM technology was originally developed was because CNC technology was not able to
produce satisfactory output within the required time frames. CNC machining was slow, cumbersome, and
difficult to operate. AM technology on the other hand was quite easy to set up with quick results, but had
poor accuracy and limited material capability.
-For geometries that can be machined using a single set-up orientation, CNC machining is often the
fastest, most cost-effective method. For parts with complex geometries or parts which require a large
proportion of the overall material volume to be machined away as scrap, AM can be used to more quickly
and economically produce the part than when using CNC.
,-AM= layer by layer processing to make 3D objects directly from CAD files
-Stereolithography(SLA)=light causes photosensitive liquşd to turn into 3D solid plastics in a layer by
layer fashion
-Why AM come into play now?
Because PC processing power increased as well as PC’s graphics capability.Also, machine control and
integration of process steps increased in time.
-Evoparation mostly occurs with metal in laser printing
-Curing➔ changing a photopolymer from liquid to solid
-Ceramics have very high melting point. To decrease this you mix it with another material. (composite)
-hybrid= AM and NC(numerical control) (only surface modelling instead of 3D modelling) combined
-Ink-jet / droplet printing
- Increasing resolution
- Multiple colours
- Increasing viscosity of “ink”
• Poly-jet printer with photopolymer as ink, cured by a UV lamp
-Liquid polymers➔photopolymers/composites (SLA), hydrogels
-Discrete particles➔Powders(characteristics of them:particle size, size dist.,shape, flowability)
Thermoplastic= softer as T increases, harder as T decreases
Wetting of melt to solid and bonding with solid (without wetting you cant bond it with other
solids good)
Examples
SLS – selective laser sintering (plastic, metal)
Binder jetting/drop on powder – printing a binder/glue onto a powder bed (plastic,
ceramic or metal)
-Molten material➔ material gets melted from solid to liquid and it is extruded from nozzle
Examples:
• FDM - Fused Deposition Modelling (plastic)
• MDDM - Micro Droplet Deposition Manufacturing (metal, droplet size 30 – 100 μm) –
partial re-melting of solidified layer
• Atomic Diffusion Additive Manufacturing
, -Solid sheet systems➔Using laser to cut out profiles from sheet material and layers are bonded using a
heat-activated resin or ultrasonic welding
Examples
• LOM - Laminated Object Manufacturing (paper) – bonding by glue
• UAM – Ultrasonic Additive Manufacturing (UAM) (metal) - solid-state bonding
-ASTM Classification➔ 7 classification
• Vat photopolymerization: processes that utilize a liquid photopolymer that is contained in a vat
and processed by selectively delivering energy to cure specific regions of a part cross-section.
• Powder bed fusion: processes that utilize a container filled with powder that is processed
selectively using an energy source, most commonly a scanning laser or electron beam.
• Material extrusion: processes that deposit a material by extruding it through a nozzle, typically
while scanning the nozzle in a pattern that produces a part cross-section.
• Material jetting: ink-jet printing processes.
• Binder jetting: processes where a binder is printed into a powder bed in order to
form part cross-sections.
• Sheet lamination: processes that deposit a layer of material at a time, where the
material is in sheet form.
• Directed energy deposition: processes that simultaneously deposit a material
(usually powder or wire) and provide energy to process that material through a single deposition
device.v
-Metal systems➔Metal AM is smaller in market share than plastic but the growth rate is higher
•Metal AM is smaller in market share than plastic but the growth rate is higher
DMLS (Direct Metal Laser Sintering - powder bed) / LENS (Laser-Engineering Net Shaping –
powder feed) / SLM / EBM
• Powders of Ti, Ti alloys, Al alloys, Ni-based alloys, Co-Cr alloys, steels UAM – Ultra-sonic
Additive Manufacturing (UAM)
• Sheets of Al, Cu, Stainless Steel and Ti WF-AM (Wire-Feed AM)
• Wires of Ti, Ti alloys, Al alloys, Ni-base alloys, Co-based alloys, stainless steel, W, Ta, Zr, Mo, Nb
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