Some common Casting Processes used for aluminium are listed below.
Sand casting is the simplest method of casting aluminium. Sand is
made into a mould by forming around a wooden "pattern". The
pattern is removed, the sand mould assembled and molten metal pored in.
The process is chosen for small production runs, for complex shape
castings requiring intricate cores or for very large castings.
Low equipment costs
Largest size of castings possible by any casting method
suited to complex shapes and cores
Very low gas porosity is possible
It is a versatile casting process
Low casting rate
3-5mm minimum wall thickness
Poor linear dimensional tolerances e.g. 4mm / m
Rough surface finish
Coarse grain size compared to diecasting
Casting weights in the range of 0.1 Kg - 100,000 Kg
Approximate economical quantity range 1 - 1000 castings.
Castings are produced by poring molten metal into permanent metal
moulds. (Generally made from Cast Iron).
This process produces 'Chill Castings'
Lower set up cost than Pressure Diecasting
Higher casting rate than sand casting
Low gas porosity levels are possible
Fine grain sizes may be obtained
The highest quality castings with regards to mechanical integrity can be
produced by this method
Less finishing is required than for sand castings.
Minimum wall thickness 3-5mm
Linear tolerance is approximately 3 mm/m
Surface finish better than sand casting
The complexity of possible casting shapes is limited
Casting weight range 0.1 Kg - 70 Kg
Approximate economical quantity range 500 - 2500 (This may increase
where sand cores are used to produce shapes impossible with pressure
Low Pressure Diecasting
This is a repetitive process where identical parts are cast by
injecting molten metal under low pressure into metal dies. This process
requires complex machinery and is similar to high pressure diecasting.
Fair production rates up to 30 / Hr
Thin wall thickness possible ( 2-3mm)
Better linear tolerances than gravity casting
surface finish improved on gravity casting, but not up to pressure
High Yields possible as runners and risers not required
Reduced finishing ir required
Pore free castings are obtainable
Sand cores may still be used to allow complex castings
die costs far lower than for pressure diecasting
Castings are heat treatable
Size of casting limited by machine size
Production rates not up to pressure diecasting
Feeding thin sections through thick sections is not recommended
casting weight range 5 Kg - 25 Kg
Approximate economical quantity range >1000
High Pressure Diecasting
Pressure diecasting is a repetitive process casting identical parts
by injecting Aluminium into metal moulds at pressures in the order of
1000psi. Complex machinery and expensive tooling is required for this
Production rates may be in the order of 200 / Hr
Thin wall thickness at 1 - 2.5mm
The best surface finish is produced by this method
Very fine grain structure is obtained
The castings have high strength in the as-cast condition
Good linear tolerances and repeatable properties are obtained
Size of castings limited by the machine
Sound, thick sections are difficult to cast
Core configuration may be complex to enable disassembly
Porosity may become a concern
High start up costs require long production runs to reduce the overall
Castings cannot be heat treated
casting weight range 0.01 Kg - 25 Kg
Approximate economical quantity range > 10,000 per annum.
A shell mould consists of a sand shell, varying in thickness between 4-10 mm. The
sand particles are bonded together with phenolic resins giving a
The production of shell moulds may be automated which lends itself to medium
to high production runs. The resin coated sand is placed on a hot metal
pattern; this is fired in an oven to harden the shell. After cooling,
the shell is removed from the pattern and is ready for use. Molten metal
is then poured into the shell mould cavity and allowed to cool. The
mould material is broken off the casting. Better dimensioned tolerances
are possible than with sand moulding, which reduces machining costs.
Fine surface finishes equal to that of permanent moulds (12~130 rms) may
be obtained. and consistently reproducible thin castings with fine detail
may be made. The process is more costly than sand, permanent mould or
Plaster Mould Casting
Permeable plaster moulds give a smooth surface finish (80~125 rms) with a finer
surface detail than is obtainable with shell moulds. Castings as thin as
0.5 mm are possible. Slow solidification rates reduce internal stresses
so that any casting distortion is negligible.
Machining and finishing operations may be eliminated by the use of plaster moulds.
Small holes may be cast to size ready for tapping. Surface finish and
dimensional accuracy equates to die casting qualities. LM25 alloys are commonly cast by this process.
This casting method involves producing a "wax
pattern" by injecting wax or plastic into a pattern die. The
pattern is attached to gating and runner systems and this assembly is
dipped in a hard setting refractory slurry, which is then cured. The
pattern is melted out of the mould to leave an exact cavity. The mould
is heated to cure the refractory and to volatolize the remaining wax
pattern material. The moulds are baked and molten metal is poured into
the mould cavity. On solidification of the casting, the mould material
is broken away from the castings.