Additive Manufacturing Flashcards
1
Q
Additive Manufacturing/ Rapid Prototyping (AM/RP) technologies
A
Referred to as:
- Solid free-form fabrication
- Direct Digital Manufacturing (DDM)
- Layer(ed) manufacturing
2
Q
What is AM/RP?
A
-Technology that quickly transforms a CAD model into a physical part directly using the computer description of the part shape (integration of CAD with CAM).
3
Q
Method
A
-Fabrication of completely arbitrary 3-dimensional geometries without the constraints from traditional manufacturing techniques.
- Dramatic impact to industry by helping to speed up the product development cycle:
- Rapid evaluation of the design’s manufacturability.
- Concept models used in design reviews to establish design effectiveness & for visualisation purposes in client presentations.
- Working prototypes communicated to suppliers for quotes.
- Reducing high capital costs with production tooling being one of the longest process in the manufacturing process
4
Q
Classification AM/RP processes
A
-Subtractive:
With traditional prototyping processes material is removed from a workpiece.
-Additive:
Build up of a part by adding material incrementally.
-Virtual:
Use of adavanced computer-based visualisation.
5
Q
7 Categories of Additive Manufacturing
A
-Standards to classify the range of AM processes by the Maerican Society for Testing Materials (ASTM) group ASTM F42 - Additive Manufacturing:
- VAT Photopolymerisation (e.g. stereolithorgaphy)
- Liquid photopolymer resin is cured with a UV light source.
- Material Jetting
- Material is jetted onto a build platform where it solidifies (curing using UV); 3D Polyjet Printing
- Binder Jetting
- A print head deposits a binder adhesive on a bed of powder based material; 3D Powder Printing (3DP)
- Material Extrusion
- Material is drawn through a nozzle, where it is heated and is then deposited layer by layer. (FDM)
6
Q
Classification of RP processes
A
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 (3DP)
- Laminated Object Manufacturing (LOM)
7
Q
AM/RP Applications
A
- Prototyping:
- The primary use of rapid prototyping is to quickly make prototypes for communication & testing purposes.
- Very useful for testing a design to evaluate it’s performance.
- Allows to evaluate functionality not possible without RP, e.g. transparent prototype parts
8
Q
AM/RP applications - Rapid Tooling
A
-Tooling is traditionally the most expensive & time consuming of all manufacturing processes. Some characteristics are:
- Toughness & wear resistance
- Complex geometries
- Very high dimensionally accuracy (0.01mm or better)
- Very high surface finish
9
Q
Rapid Tooling - Indirect Tooling
A
- Prototypes are used as patterns for making moulds & dies; used in a number of manufacturing processes e.g.
- 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 paper shell burning out.
10
Q
Rapid Tooling - Investment Casting
A
-Patterns made by stereolithography
11
Q
Rapid Tooling - Direct Tooling
A
- Hard tooling is made directly from CAD data without fabricating a pattern first
- Selectively sintering of polymer-coated steel pellets together to produce a metal mould, burn off the polymer binder & infiltrate with copper.
- Development of ceramic composite materials using Direct Shell Production Casting techniques
- Construct of sand moulds directly from CAD data using sand-like material (foundry-type sand) that is sintered into moulds
12
Q
Rapid Tooling - Facts
A
- Advantages:
- Less dependant on highly skilled patternmakers
- Reduction of high labour costs
- Shorter lead-times in the production of patterns & moulds using the concept of net shaped tools.
- Optimised mould design possible: chill- and cooling-channel placement possibly leading to reduced cycle times.
- Limitations:
- Potentially reduced tool life
- Limited material range; often only specialised and proprietary materials and processes available.
13
Q
AM/RP Applications
A
- Rapid Manufacturing:
- Direct production of functional and saleable products directly from CAD data.
- For short production runs
- Products which cannot be made by subtractive processes
14
Q
AM/RP Applications - Rapid Manufacturing
A
- Advantages
- Natural progression to produce functional and saleable products directly from CAD data.
- Ideal for short production runs as no tooling is required; significant time & 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).
15
Q
AM/RP Applications - Rapid Manufacturing - Limitations
A
- 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.
16
Q
Basic Steps in create AM/RP models
A
- Define the part to be built a CAD environment as a surface or 3D solid model
- Separate bounding surfaces of the CAD model into a collection of slices (triangle facets) and write on a file using STL-format (STL - Stereolithography Tessellation Language).
- Analyse each slice separately to set & compile instructions for the AM/RP machine to manufacture the part.
- Manufacture the model building up one layer at a time driving a laser or modelling head (depending on the type of process) along a path.
17
Q
Basic Steps in creating AM/RP models
A
- Three-dimensional description of each part.
- The part is divided into slices
- Support material is planned.
- A set of tool directions is determined to manufacture each slice
- Extruder path at section A-A for a Fused Deposition Modelling operation.
18
Q
STL File
A
- Link between 3-D CAD design & the 3-D printer hardware
- File format contains design data.
- Modern CAD systems include STL output feature:
- files suitable for rapid prototyping
- requires solid-modellers rather than surface modellers.
19
Q
STL Format
A
- CAD system settings with regards to STL mesh:
- Triangles that are too large, small file size, prototyping with visible facets often calling “facets.”
- Very small triangle mesh, big file size, long processing time, prototype accuracy or resolution not necessarily better.
- For best fidelity a mesh approximately the size of the layers is used by the Additive Manufacturing / Rapid Prototyping system.
20
Q
Fused Deposition Modelling -FDM
A
-Thermoplastic is spool-fed & extruded through a heated die constructing the part layer by layer.
21
Q
FDM - Method
A
- 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 to subsequent layers upon the first; solidification by cooling.
- Support structures may have to be built along the way, fastened to the part.
22
Q
FDM - Process Characteristics
A
- Layer thickness is determined by extruder-die diameter (0.13mm - 0.33mm)
- Extrusion detail of material (flat ribbon 0.08mm - 0.97mm)
- Stepped surface finish on oblique surfaces.
- Surface finish & accuracy:
- Dimensional accuracy in x-y plane between 0.13mm-0.241mm
- Fair to good surface finish
23
Q
FDM - Materials
A
- Polymers - production-grad thermoplastics
- Wax
- Desired properties:
- Rigid, dimensionally stable
- Good strength & toughness
- High resistance (chemical, UV, abrasion).
- Nontoxic (biocompatible, sterilisable).
24
Q
FDM - Applications
A
- Detailed models for fit form testing using engineering plastics including patient - and food - contacting applications.
- Prototypes for higher-temperature applications
- Trade show & marketing parts & models.
- Rapid manufacturing of small detailed parts.
- Patterns for investment casting
- fabrication of specialised manufacturing tools.
25
Stereolithography - SLA
-Fabricating a solid plastic part out of a photsensistive liquid polymer using a UV laser beam to solidify the polymer.
26
SLA - Method
- Scanning the liquid surface of a bath of phot-sensitive polymer resin with a ultraviolet (UV) laser beam that causes the resin to cure in the shape of a layer of the part.
- Lowering the platform by the slice of thickness after each new layer is formed at the surface.
- Final curing cycle in a UV oven to complete photo-polymerisation
27
SLA - Process characteristics
- Layer thickness 0.05mm -0.5mm
- Capable of producing hollow & solid prototypes.
- Prototype must start to be built on the tray for support structure
- Surface finish & accuracy:
* Smooth surface finish
* Stair stepping & faceting depending on layer thickness
* 0.025mm-0.05mm per 25.4mm of part dimension.
28
SLA - Materials
- Photo-sensitive polymers (resins)
* Versatile in allowing to mimic a wide variety of engineering plastics.
* Material spectrum to address requirements such as accuracy, durability, rigidity, flexibility, transparency, colour, temperature or moisture resistance, etc.
29
Special applications resins
-Resins filled with non-crystalline nano-particles for improved strength or detail resolution.
30
SLA - Applications
- Functional prototypes - mimic production parts, used for functional testing & evaluation.
- Presentation models - for design reviews, presentation, sales or marketing purposes.
- Casting pattern for investment casting of a metal part, also used for sand or plaster casting.
- End use production parts, even assemblies.
- Rapid Tooling used to create limited-run tooling.
- Architectural
- Packaging
- Electronics Applications
- Automotive Applications
31
SLA - Variation
- Micro-stereolithography:
* More highly focused laser (as small as 1micrometer)
* Layer thickness ~ 10 micrometers
* Photopolymers with much lower viscosity to ensure uniform layers.
