Additive Manufacturing - Fused Deposition Modelling & Stereolithography Flashcards
Additive Manufacturing/ Rapid Prototyping technologies are referred to as
- Solid free-form fabrication
- Direct Digital Manufacturing (DDM)
- Layered manufacturing
What is AM/RP?
Technology that quickly transforms a CAD model into a physical part using the computer description of the part shape.
Principles of AM
- Fabrication of complicated 3D geometry without the constraints of traditional manufacturing techniques
- Reduce high capital costs with production tooling being the longest process in the manufacturing cycle
- Greatly impacts industry speeding product development cycle
How does AM/RP speed development?
- Rapid evaluation of design’s manufacturability
- Used in design reviews to establish design effectiveness
- Visualise purposes in client presentations
- Working prototypes communicated to suppliers for quotas
Classification of AM/RP processes
Subtractive- With traditional prototyping processes material is removed
Additive- Build up of a part adding material incrementally
Virtual- Use of advance computer-based visualisation
7 Categories of AM
Standards to classify the range of AM processes by the ASTM group
VAT Photopolymerisation- Liquid photopolymer resin is cured with a UV light source
Material Jetting- Material jetted onto a build platform where it solidified (cured using UV) 3D Polyjet Printing
Binder Jetting- A print head deposits a binder adhesive on a bed of powder based material; 3D Power Printing (3DP)
Material Extrusion- Material is drawn through a nozzle, where it is heated and is then deposited layer by later (FDM)
Powder Bed Fusion- Laser of electron beam melt and fuse material powder (SLS, DMLS, EBM, SLM)
Sheet Lamination- Sheet or ribbons of metal bound together using US welding followed by CNC milling; also LOM (paper with adhesive and cut by blades)
Direct Energy Deposition (DED)- Nozzle deposits molten material(metal, polymer, ceramics) onto build platform; molten with laser,plasma arc or electron beam)
Classification of RP process
Additive technologies
- Fused Deposition Modelling (FDM)
- Stereolithography (SLA)
- Selective Laser Sintering (SLS)
- Direct Metal Laser Sintering (DMLS)
- Electron Beam Melting (EBM)
- 3 Dimensional Printing Technologies (3DP)
- Solid Ground Curing (SGC)
- Laminated Object Manufacturing (LOM)
AM/RP Applications
Prototyping
- Primary use of RP is to quickly make prototypes for communication and testing purposes
- Very useful for testing a design to evaluate its performance
- Allows to evaluate funcitonality not possible without RP e.g. transparent prototype parts
AM/RP Applications
Rapid tooling
Traditionally the most expensive and time consuming of all manufacturing processes
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
Characteristics of Tooling
- Toughness and wear resistance
- Complex geometries
- Very high dimensional accuracy (0.01 mm or better)
- Very high surface finish
What manufacturing processes are Prototypes used?
Vacuum casting
Sand Casting
Investment Casting
Rapid Tooling- Direct tooling
Hard tooling is made directly from CAD without fabricating a pattern first:
- Selectively sintering of polymer-coated steel pellets together to produce a metal mould, burn off the polymer binder and 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 that is sintered into moulds
Pros of Rapid Tooling
Pros
-Less dependant on highly skilled pattern makers
-Reduction of high labour costs
-Shorter lead-times in the production of patterns and moulds using the concept of net shaped tools
ld design possible; chill and cooling channel placement possibly leading to reduced cycle times
Cons of Rapid Tooling
- Potentially reduced tool life
- Limited material range; often only specialised and propriety materials and processes available
Rapid Manufacturing applications
- Direct production of functional and saleable products direct from CAD data
- For short production runs
- Products which cannot be made by subtractive processes
Pros of Rapid Manufacturing
- 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 using traditional manufacturing processes (subtractive or compressive)
Cons of Rapid Manufacturing
- 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
Steps to creating AM/RP models
- Define the part to be built in a CAD environment as a surface or 3D solid model (SolidWorks etc..)
- Separate bounding surfaces of the CAD model into a collection of slices (triangular facets) and write on a file using STL-format
- Analyse each slice separately to set and 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
What is STL?
Stereolithography Tesselation Language
What is a STL file?
- It is the link between 3D CAD design and the 3D printer hardware
- The file format contains design data (3D surface as an assembly of planar triangles) to allow deciding object designs into slices (this is a mesh of triangles wrapped around the CAD model)
- Modern CAD systems include STL output feature
- Files suitable for rapid prototyping
- Requires solid-modellers rather than surface-modellers
STL format
CAD system settings with regards to STL mesh:
- Triangles that are too large, small file size, prototype with visible facets.
- Very small triangle mesh, big file size, long processing time, prototype accuracy or resolution not necessarily better
- Best fidelity a mesh approximately the size of the layers is used by the AM/RP system
What is FDM
Fused Deposition Modelling- Thermoplastic is spooled and extruded through a heated die constructing the part layer by layer
FDM Method
- Filaments of heated thermoplastic or wax are extruded from the tip of an extruder die
- 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 and fastened to part
FDM Process characteristics
- Layer thickness is determined by extruder-die diameter (0.13 -0.33mm)
- Extrusion detail of material (flat ribbon 0.08-0.97mm)
- Stepped surface finish on oblique surfaces
- dimensional accuracy between 0.13-0.241mm
- fair to good surface finish
What materials are used for FDM
-Polymers- production grade thermoplastics
-Wax
-Desired properties are:
Rigid, dimensionally stable
Good Strength and toughness
High resistance (chemical, UV, abrasion)
Nontoxic (bio-compatible, sterilisable)
FDM- Applications
- Detailed models for fit&form testing
- Prototypes for higher temperature applications
- Trade show and marketing parts & models
- Patterns for investment casting
- Fabrication of specialised manufacturing tools
SLA
Stereolithography, involves fabricating a solid plastic part out of a photosensitive liquid polymer using a UV laser beam to solidify the polymer.
SLA- Method
- Scanning the liquid surface of a bath of photo-sensitive polymer resin with an ultraviolet laser beam that causes the resin to cure in the shape of a layer of the part
- Lowering the platform by the slice thickness after each new layer is formed at the surface
- Final curing cycle in a UV oven to complete photo-polymerisation
SLA- Process Characteristics
- Layer thickness 0.05-0.5mm
- Capable of producing hollow and solid prototypes
- Prototype must be built on a tray for support structure
- Smooth surface finish
- Stair stepping and faceting depending on layer thickness
- 0.025-0.05mm per 25.4mm of part dimension
SLA- Materials
Photo-sensitive polymers
- 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.
Special application resins
-Resins filled with non-crystalline nano-particle for improved strength or detail resolution
SLA- Applications
- Functional prototypes- mimic production parts for testing
- Presentation models- design reviews, presentation, sales, marketing
- 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
SLA- Variation
Micro-sterolithography
- more highly focused laser (as small as 1 micrometer)
- layer thickness roughly 10 micrometers
- photo-polymers with a much lower viscosity to ensure uniform layers
