Week 4 - Additive Manufacturing 1

Additive manufacturing vs subtractive vs forming

AM Cost Vs Colume and Complexity

• Cost vs Volume

Formative: high upfront, but low after that, wins at high volume

AM: Low upfront, but roughly keeps same and loses after lot of points.

• Cost vs Complexity

Traditional methods: Cost rises significantly with complexity

AM: Complexity and customization are free, no difference in cost.

Build orientation and support structures

Build orientation affects:

• Surface finish (staircases)

• Build time (taller orientation = longer)

• Support requirements

• Mechanical properties (anisotropy)

Supports:

• Typically required over 45 degrees.

• Needed for both mechanical and sometimes thermal management.

• Post processing can be 40-50% of total cost.

• Want to remove as many supports as possible.

Material extrusion + Advantages/Disadvantages

Thermoplastic filament is heated into nozzle and extruded layer by layer. Previous layer is partially remelted by new layer.

Advantages:

• Low capital investment

• wide range of materials available

• Can make objects of varying density

• Can do multi colour or material with different nozzles

• No protective atmosphere required, can be scaled.

Disadvantages:

• Poor dimensional tolerance

• Warping and distortion common.

• Resolution linked to build rate.

• Supports require removal and often post processing.

• Anisotropic parts, stronger in xy plane.

VAT Polymerization + Advantages/Disadvantages

Can be done SLA (laser traced) or DLP (Whole layer at once), but works by using UV light to cure liquid resin thermosets, layer by layer.

Advantages:

• Fine details possible with an accurate smooth finish.

• Complex geometries achievable.

• Build rates commercially are quire fast.

• Least anisotropic of all AM.

• Process is scalable and large prints possible.

Disadvantages:

• Limited range of materials, typically with poorer themomechanical properties.

• Requires wash, rinse and UV cure all post processing.

• Supports materials required, and can’t be a different material.

• No vertical stacking of parts in build chamber.

Binder Jetting + Advantages/Disadvantages

Spread each powdered layer with a roller, a jet binder glues particles at necks, repeated layer by layer.

Advantages:

• No support needed, as powder does so.

• Can stack parts into the build chamber.

• No residual stresses as no heats used.

• No protective atmosphere.

• Can make colours.

• Comparatively fast and cheap.

Disadvantages:

• Parts made are inherently porous, with 50-70% usual density.

• Green parts (pre-processin) are weak and fragile.

• Can postprocess to improve properties, but this leads to stresses.

AM When and when not to use

Use when:

• Low volume

• High complexity

• Mass customization needed

• On demand, with low lead time needed.

Don’t use when:

• High volumes

• High tolerances required

• Material properties need to be strong.

• Part is large and simple.