Additive manufacturing Flashcards
What are AM/RP technologies ?
- Solid free-form fabrication,
- Direct Digital
- Manufacturing (DDM), or
Layer(ed) manufacturing
Classification of AM/RP processes
Subtractive
Additive
Virtual
7 Categories of Additive Manufacturing
VAT Photopolymerisation
Material Jetting
Binder Jetting
Material Extrusion
Powder Bed Fusion
Sheet Lamination
Direct Energy Deposition (DED)
What is Direct Energy Deposition (DED)?
Nozzle deposits molten material (metal, polymer or ceramics) onto a build platform; molten with laser, plasma arc or electron beam
Process of Material Extrusion?
Material is drawn through a nozzle, where it is heated and is then deposited layer by layer. (FDM)
Process o f Binder Jetting?
A print head deposits a binder adhesive on a bed of powder based material; 3D Powder Printing (3DP)
Process of Material Jetting
?
Material is jetted onto a build platform where it solidifies (curing using UV); 3D Polyjet Printing
Process of VAT Photo polymerisation?
Liquid photopolymer resin is cured with a UV light source
What are some of the Additive technologies?
- Fused Deposition Modelling (FDM)
- Stereolithography (SLA – Stereolithography Apparatus; or SL, STL)
- Selective Laser Sintering (SLS)
- Direct Metal Laser Sintering (DMLS)
- Electron-Beam Melting (EBM)
- 3-Dimensional Printing Technologies
- Solid Ground Curing (SGC)
- Laminated Object Manufacturing (LOM)
What are some of the characteristics of tooling?
- Toughness and wear resistance
- Complex geometries
- Very high dimensionally accuracy (0.01 mm or better)
- Very high surface finish
What are the different types of tooling?
- Indirect tooling:
Prototypes are used as patterns for making moulds and dies - Direct tooling:
Production tools are cast as net shape tools directly from CAD files
Rapid tooling- Indirect tooling prototypes are used in a number of manufacturing processes such as..
- Vacuum Casting – RP pattern is cast into a silicone or other temperature vulcanised rubber (RTV) mould
- Sand Casting – RP pattern made by Laminated Object Manufacturing resembles the traditionally used wooden pattern
- Investment Casting – RP pattern made by Laminated Object Manufacturing from paper are often used as they are dimensionally stable with the paper shell burning out
What are the advantages of rapid tooling?
Less dependent on highly skilled patternmakers
Reduction of high labour costs
Shorter lead-times in the production of patterns and moulds using the concept of net shaped tools
Optimised mould design possible; chill- and cooling-channel placement possibly leading to reduced cycle times
What are the disadvantages of rapid tooling?
Potentially reduced tool life
Limited material range; often only specialised and proprietary materials and processes available
AM/RP applications
- direct production of functional and saleable products
- For short production runs
- Products which cannot be made by subtractive processes.
Advantages of AM/RP
Natural progression to produce functional and saleable products directly from CAD data
Ideal for short production runs as no tooling is required; significant time and cost savings
Ideal for producing custom parts tailored to customer specifications
Ideal for products that cannot be made by using traditional manufacturing processes (subtractive or compressive)
Limitations of AM/RP
Economic reasons due to high raw material costs
Time issue to produce parts quickly for high volume manufacture
Long-term performance characteristics with regards to wear and life cycle compared to well established traditional methods of manufacturing
Basic steps to AM/RP models
- Define what needs building either in a CAD or 3-D solid model software
- Seperate bounding surface of the CAD model into a collection of slices (STL format)
- Analyse each slice separately to set and compile instructions for the AM/RP machine to manufacture the part
- Manufacture the model building one layer at a time
Fused Deposition Modelling (FDM)
Thermoplastic is spool-fed and extruded through a heated die constructing the part layer by layer
FDM – Principle/Method
Filaments of heated thermoplastic or wax are extruded from the tip of an extruder-die that moves in the x-y plane
Lowering the platform which is kept at a lower temperature to apply subsequent layers upon the first; solidification by cooling
Support structures may have to be built along the way, fastened to the part
Desired properties for FDM
Rigid, dimensionally stable
Good strength and toughness
High resistance (chemical, UV, abrasion)
Nontoxic (biocompatible, sterilisable
Applications of FDM
Detailed models for fit & form testing using engineering plastics including patient- and food-contacting applications
Prototypes for higher-temperature applications
Trade show and marketing parts & models
Rapid manufacturing of small detailed parts
Patterns for investment casting
Fabrication of specialised manufacturing tools
Advantages of FDM
Office Friendly
No Fumes
Support structures generated automatically
Prototypes can be drilled, tapped or machined
Tough and durable prototypes with no need for post curing
Wide range of plastics
Disadvantage of FDM
Slow processing time compared to some AM/RP technologies
Accuracy limited by the thickness of the filament
Requires support structure
Limited to plastics
High investment cost
Stereolithography – SLA
Fabricating a solid plastic part out of a photosensitive liquid polymer using a UV laser beam to solidify the polymer
SLA – Principle/Method
- UV light scans the photosensitive polymer resin causing resin to cure in the shape of the part
- Lowering the platform by the layer (slice) thickness after each new layer is formed at the surface
- Final curing cycle in an UV oven to complete photo-polymerisation
Advantages of SLA
Very accurate immediately after completion of the model
Quick Prototyping process for visualisation and verification
purposes
Smooth surface finish
Support structures are generated automatically
Can produce solid and hollow prototyp
Disadvantages of SLA
Support structures need to be broken off (manually)
Some inaccuracy in the z-direction
Limited to photosensitive resins (typically brittle)
Prototypes are generally difficult to machine due to being brittle
Parts are prone to the “trapped volume” problem in which cups
in the structure that hold fluid cause inaccuracies
Materials do not work well with “living hinges”, points, edges
and thread design
Selective Laser Sintering – SLS
A moving laser beam melts and fuses (sinters) a heat-fusible powder one layer at a time to build solid 3D parts
SLS – Principle/Method
- Scanning and sintering metallic and non-metallic, thermoplastic powder using a carbon dioxide laser beam (CO2) that causes the powder to sinter (fuse or melt) and solidify in the shape of a layer of the
prototype - Powder bed moves up and delivers polymer which aroller spreads across the surface of the build area, forming an even layer of powder
- Non-sintered powder forms a ‘cake’ encapsulating and supporting the model as the build progresses
What are the desired material properties?
- Sterilisable, biocompatible, flame-retardant
- High stiffness, toughness, elevated temperature resistance
- Anisotropic mechanical properties (fibre-filled)
What are the two types of 3D Printing technologies?
- Binder Jetting
- Material Jetting
Powder 3DP technology
Ink-jet printing heads move across a powdered material in a scanning pattern, distributing (printing) a liquid inorganic binder to “glue” (fuse) the powder in the shape of each layer
Applications of 3D Printing?
- Concept models
- Parts for limited functional testing
- Colour models for FEA and other engineering related applications
- Architectural & landscape models
- Colour industrial design models, especially consumer goods & packaging
- Castings
3D-Jetted Photopolymer – Principle
Ink-jet printing heads ejects micro-droplets of molten plastic or wax material onto a stationary platform which is cured by UV light(polymer phase change inkjet or jetted photopolymer technology)
3D-Jetted Photopolymer – Applications
- Concept development
- Design validation
- Form and fit analysis
- Moulding and foundry casting patterns
- Pattern for investment casting
Laminated Object Manufacturing – LOM
Solid models are generated by laminating layers of sheet material on top of each other and laser-trim the cross-sectional shape of each layer
LOM – Principle/Method
- Paper or plastic sheet material with a heat-activated glue on one side is bonded to the build platform by applying pressure using a heated roller
- A focused CO2 laser burns the outline of the first layer into the paper and then criss-crosses the excess area
- The platform lowers and a feeder/collector mechanism advances new sheet material onto the build platform
- The platform raises to a height consistent with the sheet/stock thickness ready for laminating the next layer
Solid Ground Curing – SGC
A solid model is created by selectively exposing and curing an entire layer of photosensitive polymer when shining a UV light source through a photo mask that is positioned above the surface of the liquid polymer
SGC – Principle/Method
- A photo mask is printed on a glass plate using an electrostatic process (similar to photocopying and laser printing) charging a negative image of the layer onto the surface
- Thin layer of liquid photopolymer is distributed over the surface of the work platform
- Photo mask is positioned above the polymer surface, exposed to a high powered UV light source which cures the desired cross section of the photopolymer layer
Additive Manufacturing : Limitations
Materials – growing range but will remain limited range with high costs
Accuracy and surface roughness – often tolerance limit +/- 0.01mm
Equipment cost – expensive often with poor output per £ investment
Which of the following are typical problems with the various additive manufacturing technologies? (three best answers)
a) Inability of the designer to design the part
b) Inability to convert a solid part into layers
c) Limited material variety
d) Part accuracy
e) Poor machinability of the starting material
f) Part shrinkage
c) Limited material variety
d) Part accuracy
e) Poor machinability of the starting material
Direct Metal Laser Sintering - Principle/Method
Scanning and sintering metallic powder using a focusedlaser beam (fibre laser) that causes the powder to sinter (fuse or melt) and solidify in the shape of a layer of the prototype
DMLS – Applications
Functional Prototypes
Series-production parts
Tooling
Aerospace, Motorsport, Medical (dental, implants etc.)
DMLS – Advantages
All metals are recyclable; use only what you sinter!
Near net-shape process, producing parts with high accuracy
and detail resolution
Good surface quality and excellent mechanical properties
Constant development and release of new materials onto the
market
DMLS – Limitations
Much more complex process than Selective Laser Sintering
with regards to designing support structure and orientation
Parts need to be cut from the steel plate (usually using WireEDM);
increase to cycle time and labour costs
3D-Jetted Photopolymer – Advantages
Small layer thickness eliminating the stair effect common to
complicated curved surfaces
Quick processing time; adjustable resolution
Coloured printing
Multi-material printing
End-use parts
Office friendly (quiet, safe, odour-free, easy to use)
Living hinges and joints
Plymouth University - School of Marine Science and Engineer
3D-Jetted Photopolymer – Limitations
Limited choice of materials – only polymer and waxes can be
used
Limited opportunity to enhance properties during post
processing – functional and aesthetic qualities of parts are
largely determined during the printing stage
Support structure needed for overhangs, undercuts and fragile
elements
