MECH2305
Introduction to Engineering Design and Manufacturing
Casting Part II
Dr Michael Bermingham, PhD
School of Mechanical & Mining Engineering, UQ, EAIT
m.bermingham@uq.edu.au
Casting Methods
• Many different casting processes and variants
– Sand casting
We will briefly look at these,
– Die casting read about others in private study
– Investment casting
– Centrifugal casting
– Squeeze casting
– Semisolid casting
– Slush casting
– Directional solidification – e.g single crystal turbine blades
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Sand Casting
• A pattern (of the desired cast product) is made, typically in halves but can be more
complicated. The pattern also contains a feeding system.
• Sand is packed around the pattern.
• The pattern is removed leaving a empty cavity for the liquid metal to fill.
• Sometimes cores are inserted in the sand mould (e.g. if hollow sections are desired)
• The sand mould is assembled and ready for casting
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Sand Casting
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Typical Sand mould
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Typical Sand mould
• Flask – supports & contains mold
• Cope – top part of 2 piece mold
• Drag - bottom part of 2 piece mold
• Parting line – partition between cope
& drag
• Pouring basin - Molten metal is
poured into pouring basin until there
is metal in riser
• Riser – supplies additional molten
metal to the casting as it shrinks
during solidification. Mould cavity
should solidify before the
solidification of risers. Open riser and
blind riser
Typical Sand mould
• Sprue - Molten metal flows down
through sprue & fills mould cavity
• Gate & running system - controls
metal flow into mould cavity
• Cores - are inserts made from sand.
they form hollow regions of final
casting and form the interior surface
of castings
• Vents - carry off gases produced
when molten metal contacts sand.
Much gas permeates out through
sand.
• Fettle – a process to cut off runner &
riser, remove adhering sand, etc.
Types of sand mould
– Green sand mould: sand + clay + water (bonding agent)
• Used as moist (so called “green”) or skin dried in air or oven or furnaces
• The cheapest and easy to recycle
– Cold-box moulds:
• organic or in-organic binder used to bind sand, eg inorganic silicate
binder cured by CO2
• Harder molding surface
• More expensive because sand cannot be recycled
– Baked mould: Oven or furnace dried or baked.
• Stronger than green sand
• Better dimensional accuracy & better surface finish
• Greater mould distortion, greater susceptibility to hot cracking (sand is
less collapsible).
Making a sand mould
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MECH2305
Making a sand mould
• Patterns – parting agent is used
– Form cavity in mould – the shape of the castings
– Can be single piece, split patterns and match-plate patterns.
– Made from wood, plaster, plastic or metal.
– Design should allow for metal shrinkage upon solidification
– ease of removal from sand through proper taper or draft
Steam engines
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Making a sand mould
• Cores
– Cores form hollow region of finished casting.
– Cores are placed in mold cavity before casting to form the interior surface.
– Cores are anchored by core prints and sometime are supported by chaplets.
– Cores are made of sand in the similar way of making moulds.
– Cores are removed during shakeout & fettling
Sand Casting
• Advantages
– Low capital investment means that short production runs are viable.
– Use of sand cores allows fairly complex shapes to be cast.
– Large components can be produced.
• Disadvantages
– The process has a high unit cost, as it is labour intensive and time consuming.
– The sand mould leaves a poor surface finish, which often requires further processing.
– Cannot make thin sections.
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Making engine block
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Die Casting
• Die Casting (also known as permanent mould casting) uses a reusable metal
mould (usually hardened steel)
• Liquid metal can be poured or shot into the mould under gravity or pressure
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High Pressure Die Casting
Hot chamber Die Casting Cold chamber Die Casting
Liquid metal is injected very quickly at high pressures (typically 15-30MPa).
Short cycle times (200-300/hr), thin wall components can be cast. Turbulent
filling which may cause defects. Restricted to low melting point alloys to prevent
die wear. Machines and dies are very expensive, but used for mass production
so individual component cost is low.
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Die Casting
• Moulds are expensive, need large production runs to be
economical
Die Casting
• Highly automated process, can have low costs if have large
production runs
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High Pressure Die Casting
• Advantages:
– Very low unit cost.
– High definition & surface finish.
– Excellent dimensional accuracy.
– Cool metal mould gives fast solidification, leading to a fine grain structure.
– Can produce thin sections.
• Disadvantages:
– A large capital investment is required to set up a die casting process.
– It is difficult to control the microstructure of the solid.
– The alloys used must have a low melting point, often at the expense of other properties, such as strength and
stiffness.
– Cannot be used for complex shapes, as the casting couldn’t be ejected from the mould.
– Cannot be used for large castings.
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Low Pressure die casting
• Used when cast component quality is required
– Low turbulence means less chance of oxide or porosity entrapment
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Investment Casting
• Also known as “lost wax” casting
• Pattern made of wax or plastic through various methods
• Wax patterns are assembled
• Assembly coated with fine ceramic slurry – Repeated until shell has developed desired wall thickness
(approx. 8mm)
• De-waxing - remove wax by heating to 90 ~ 175°C
• Harden mold – fire the moulds at 650 ~ 1050°C to dry the mould, burn off residual max
• Pour in molten metal
• Shakeout & separate parts
• Finishing
• Expensive, but good surface finishing, high dimensional accuracy and suitable for making complicated
shapes.
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Investment Casting
Investment Casting
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Investment Casting
To make small, precise, complex shaped components
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Investment Casting
• Advantages
– Metals with a high melting temperature can be cast due to ceramic mould
– Complex shapes can be formed by using ceramic liners in the original wax patterns
– Good surface finish can be obtained using fine ceramic material
• Disadvantages
– Expensive as mould cannot be reused
– Time consuming (drying times for ceramic range roughly 24 hrs)
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Titanium melted onto copper – how is this possible?
From my video I asked how Ti (Mp 1680˚C) can be melted on Cu (Mp1080˚C)
Solid Ti Liquid Ti
“Skull”
This flash can
be thought of as
the skull
