Materials T9 - Manufacturing

Solidification of Metal

Nucleus forms → dentritic growth → grains form

Dendrites

Tree-shaped formations that occur during crystalisation

Small chill grains form on mold walls

Outer layer

Columnar grains grow towards centre of ingot

Middle layer

Equiax grains

Inner layer

Casting

Molten metal is poured into a cast, used for creating complex shapes

Sand Casting

Sand is used to form the mold used for casting

Wrought Processing

Processes that involve deformation of metal, typically by hand

Increases ductility, lowers strength, prevents permanent strain

Reasons that high temperatures are used during wrought processes

Rolling

Material is squeezed between two rollers, thinning and lengthening the material

Hot Rolling

Rolling that occurs at high temperatures, increases ductility and reduces strength

Cold Rolling

Rolling that occurs at/near room temperature, maintains strength

Drawing

Creates cup-shaped parts by forcing sheet metal into a die using a punch

Extrusion

Billet material forced through a die to produce a shape with the same cross-section as the die - use softer alloys

Forging

Metal is compressed between two dies to impart the shape onto the work, hammering process at high temps

Annealing

Reorganisation of grains to increase ductility/malleability in a cold worked alloy

Recovery

Annihilation and rearrangement of dislocations (stage one of annealing)

Recrystallisation

Nucleation and growth of new grains (stage two of annealing)

Grain Growth

Stage three of annealing

As-rolled, high strength but low ductility

State of aluminium

Partially recrystallised, increasing ductility

State of aluminium

Recrystallised, ductile

State of aluminium

Processing of Thermoplastics

Heat until soft, shape, set via cooling

Processing of Thermosets

Prepolymer is molded, set via cooling

Transfer Molding (polymers)

Material (thermoplastic/set) in bottom heated mold is shaped by compressing top mold

Injection Molding (polymers)

Hydraulic pressure applied to chamber to feed heated thermoplastic pellets into mold

Extrusion (polymers)

Screw feeds heated plastic pellets through shaping die to produce long shape

Blow Molding (polymers)

Creates hollow plastic products by blowing air into plastic blank to fill a mold cavity

Melt Spinning (polymers)

Extrusion-type process where molten material is pulled through fine extrusion dies (spinneret) to form fibres used for fabrics

Glass Forming Processes

Pressing, blowing, drawing, fibre forming

Glass Pressing

Forming glass into the shape of a mold using a ram, for thicker products

Glass Blowing

Using compressed air to force softened glass into the shape of a mold

Sheet Glass

Molten glass is rolled into a sheet and cooled over a pool of liquid tin

Annealing Glass (Heat Treating Glass)

Removes internal stress caused by uneven cooling

Tempering Glass (Heat Treating Glass)

Puts surface of glass part into compression, suppressing surface crack propagation

Clay, filler, fluxing agent

Components of clay mixture

Hydroplasticity

When clay becomes plastic when water is added

Effect of Adding Water to Clay

Material shears easily along weak van der Waals bonds

Drying Clay

Removing excess water causing shrinkage

Firing Clay

Reduces porosity, causes fluxing agents to melt and form glass

Clay Extrusion

Extruding clay into shape for products such as bricks

Slip Casting

Slip (mixture of clay and water) poured into a mold and either drained for hollow product or dried for solid product

Powder Pressing

Forms solid mass of powder which requires sintering

Sintering

High temperature process used to densify and strengthen powder parts, carried out under hot isostatic pressing

Binder Jetting (BJT)

Polymer glue holds power together, used for metals/ceramics/composites

Directed Energy Deposition (DED)

Laser used to set flow of metal powder mixed with inert gas, exceeds 2000^oC and used for metals/composites

Material Extrusion (MEX)

Thermoplastic filament heated and prints layers, also called FDM (filament deposition modelling)

Material Jetting (MJT)

Incoming resin is a liquid which is cured by a UV light - liquids can be mixed during printing and polymer can have range of properties

Powder Bed Fusion (PBF)

Laser/electron beam heats metal powder to form solid, usually in enclosure w/ inert gas, used for polymers/metals

Sheet Lamination (SHL)

Metal sheets bonded w/ polymer, can be welded after stacking - lots of waste material

Vat Polymerisation (VPP)

Starting material is liquid polymer which is set by a laser/UV light - can be rigid or rubbery

Rapid protoyping, quick turnaround, faster design improvements

Advantages of 3D printing

Anisotropy

Strength of 3D printed material is dependent on the direction it was constructed