Define additive manufacturing?
Mass is added to a workpiece to achieve a desired geometry
Advantages/Disadvantages of additive?
Advantages:
- Optimised geometry
- Doesn’t require dedicated moulds / tools
Disadvantages:
- Much more expensive than other processes
- Can develop porosity, anisotropy and residual stresses
Describe Fused Filament Fabrication? (FFF)
- Extruder moves in 2 directions over a table that can be raised and lowered.
- Filament (usually thermoplastic) is extruded through a small heated die (head)
- Through the controlled movement of the table / extrusion head and the switching on and off the flow of filament, complex geometries are built layer by layer.
- Table lowered after each layer
Describe Stereolithography (SLA)
- Where liquid polymer is selectively cured into a solid by an ultraviolet laser.
1. Platform is put in vat of polymer and raised to highest position so that only a thin layer of polymer covers it
2. Component is cured from bottom up, with platform being lowered after each layer until the top layer is completed.
Describe Selective Laser Sintering (SLS) and Electron Beam Melting (EBM)?
- Metallic / Non-Metallic powder is melted using laser or electron beam to achieve a desired shape.
1. A thin layer of powder is deposited, and the laser/beam traces the desired shape to sinter the powder particles into a solid.
2. Layer is lowered by a platform and a fresh layer of powder is deposited.
3. Process is repeated and the layers stack on top of each other forming the component
Describe Laminated Object Manufacturing (LOM)
- Layers of material (usually vinyl/plastic) are cut using computer-controlled machines (usually lasers/cutters) and stacked to form the component
- Cross hatching is often cut into excess material to simplify its removal.
Describe 3D printing?
- Printing head deposits binder on a layer of polymer, ceramic or metallic powder.
- Bed is lowered and another layer of powder is deposited and fused by the binder
- Continues until all layers have been manufactured.
Define / info about composites?
- Combination of 2 (or more) chemically distinct + insoluble materials with a recognisable interface.
- Properties / structural performance of the composite is better than each individual material
- The dispersed phase (fibres) usually made of glass/carbon
- The continuous phase/matrix usually plastic, metal or ceramic
Describe spray + hand layup
Hand layup - materials are placed by hand in proper order, brushed and shaped in a mould by hand using a roller
Spray layup - Materials are sprayed into the mould rather than placed by hand. Rolling may be necessary
Define Filament Winding
- Resin and fibres are combined at the time of curing
- Reinforcing filament is wrapped around the form on a rotating mandrel
- Reinforcements are impregnated by passing them through a polymer bath
Define welding?
- Joining process where material is melted and then solidified to form a strong joint between the 2 parts
What are the 2 categories of welding?
Fusion - base material heated to melting point
Solid state - parts are joined under pressure and heated below the melting point
What are the 3 types of fusion welding and describe them?
Resistance - combination of heat and pressure where heat is generated through electrical resistance at interface of 2 parts.
Oxyfuel gas - fuels mixed with oxygen are burned to generate heat
Arc - electrical arc (discharge of electrical current across a gap) is used to melt the metal. 5000+ degrees. Filler material is added to increase volume and strength of joint
What are some parameters that can affect magnitude and distribution of residual stresses in SLS (or EBM)?
- Thermal conductivity of powder/solid
- Laser power
- Peak temp @ sintering location
- Geometry of part
