Type Of Casting Process
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Sand Casting
Plaster Mould Casting
Investment Casting
Shell Molding
Die Casting
Sand Casting
Sand casting is the simplest method of casting aluminum. 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.
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Advantages
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
Limitations
Low casting rate
3-5mm minimum wall thickness
Poor linear dimensional tolerances e.g. 4mm / m
Rough surface finish
Coarse grain size compared to die casting
Casting weights in the range of 0.1 Kg - 100,000 Kg
Approximate economical quantity range 1 - 1000 castings.
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.
Investment Casting
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.
Shell Moulding
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 permeable mould. 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 die casting.
Die Casting
Liquid metal is introduced in metallic molds!
The injection of metal could be:
1. Under influence of high hydraulic pressure with the
die loaded on machine (HPDC).
2. Under influence of low pneumatic pressure with the
die loaded on machine (LPDC).
3. Under influence of Gravity (Poured by hand) in a
stationary mold, called GDC.
4. Under influence of Gravity (Poured by hopper) in a
tilted mold and subsequently straightened, called
‘Durville Process’
Why Pressure Die casting ?
• The decision to choose Pressure Diecasting as the
preferred production method is generally driven by a
requirement for high annual volume. As the annual
demand increases, the lower piece part price offered
by the pressure diecasting route results in a far
cheaper "Total Project Cost" than other methods of
casting Aluminium.
• The diagram below indicates that should the volumes
required be low, then the case for gravity diecasting
or sand casting becomes increasingly strong, due to
the low start up costs.
Types Of Die Casting
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High Pressure Die Casting ( HPDC)
Low Pressure Die Casting (LPDC)
Gravity Die Casting (GDC)
Vacuum / high Vacuum Die Casting
High Pressure Die Casting
Pressure die casting is a repetitive process casting identical parts by injecting
Aluminum into metal moulds at pressures in the order of 1000psi. Complex
machinery and expensive tooling is required for this process.
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Advantages
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
Limitations
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 cost
Castings cannot be heat treated
casting weight range 0.01 Kg - 25 Kg
Approximate economical quantity range > 10,000 per annum.
Low Pressure Die Casting
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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 die casting.
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Advantages
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 die casting
standards
High Yields possible as runners and risers not required
Reduced finishing is required
Pore free castings are obtainable
Sand cores may still be used to allow complex castings
die costs far lower than for pressure die casting
Castings are heat treatable
Limitations
Size of casting limited by machine size
Production rates not up to pressure die casting
Feeding thin sections through thick sections is not recommended
casting weight range 5 Kg - 25 Kg
Approximate economical quantity range >1000
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Gravity Die Casting
Castings are produced by poring molten metal into permanent metal moulds.
(Generally made from Cast Iron).
This process produces 'Chill Castings‘
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Advantages
Lower set up cost than Pressure Die casting
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.
Limitations
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 die casting.)
Vacuum and high Vacuum Die casting
The porosity sets the limit
to
the conventional casting
 Limited heat treatable
 Limited weldable
The die can be vented with
the support of a vacuum
The Quality is increased
with a moderate vacuum
between 200 and 500 mbar
Vacuum and high Vacuum Die casting
High vacuum lower
than 50 mbar
Dosing
Start
Evacuation
Turbulence-free filling
Additional measures
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Die concept (sealing)
Die spraying
Melt treatment
Metal dosing
Valve closing
Intensification
Vacuum and high Vacuum Die casting
Requirements to structural parts
Rp0,2
120-150 Mpa
Rm
>180 Mpa
A5
>15%
Vacuum and high Vacuum Die casting
Additional advantages
 Cast parts are easily heat treatable and weld able
 High mechanical properties are reachable
 High consistency of this properties
 Expensive but high quality alloys can be cast economically
Vacuum and high Vacuum Die casting
An entire new part
spectrum for the
die caster
Typical vacuum
die cast parts
Space frame node
Climate control
Advantages of Die Casting
• Mass Production Process
• Consistent quality over mass production
• Least dependence on human skill Higher
engineering strength of materials
BUT
It is an energy intensive process
Continuous energy
input is a
PREREQUISITE!
And Energy is
going to be ever
COSTLIER!
Aluminum
is the most widely used metal
for die casting!
This is because:
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It responds well to mold filling
It is light in weight
Its thermal properties are excellent
Its engineering strength is comparable with
steel.
• It is non-corrosive hence longer functional life.
BUT
At higher temperature it has:
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Affinity for oxygen (oxide formation)
Affinity for hydrogen (causing gas porosity)
Oxidation causes metal loss
Porosity causes rejection
Facility to control melting, holding of metal
and casting parameters is essential!
Other Metals Used In Die Casting
1. Magnesium
2. Brass
3. Zinc
Initial cost of equipment to
melt and hold liquid metal is
high!
Investment is called for in
Quality Assurance and
Energy Saving Activities!
High Pressure Die Casting!
Casting parameters are best
controlled by this process!
It is also the most productive
process of casting with least
energy consumption
Because
• Casting process is carried out on machine.
• Modern machines are equipped with strict casting
parameter controls.
• Strength of castings, thus produced, is high.
• Rejection is least.
• Any deviation from set parameters is reported by
audio signal and further production is halted.
• Deviation report is available on microprocessor hence
quick rectification.
BUT
• It does not accept any collapsible mold (e.g. Sand
Cores)
• Each machine is designed for a specific range of casting
size!
• Larger castings cannot be made on a smaller machine
size.
• Smaller castings can be manufactured on larger
machine size using multi-cavity mold scheme.
• Multi-cavity mold scheme is justified for large and
constant quantum off-take.
• Such machines are costly!
• Levels required of plant cleanliness and tool & machine
maintenance are high.
Some facts
• Modern Casting Purchasers
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Envisage excellent capability of vendor to produce large
series.
Expect in-time casting delivery of goods.
Presume High and Consistent Quality & Productivity
Standards.
Encourage only those vendors with ISO Quality
Certification.
ISO Quality Certification necessitates
strict parameter control and
Documentation thereof.
Market Prospects
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HPDC Castings are mainly consumed all
over the world by:
1. Automobile Industry
2. Electrical & Electronic Industry
3. Communication Industry (Mobile Phones,
Laptop Bodies, etc.)
Export Market for the die cast
products is not exploited at all
by Indian Die Casting
Industry!
All this for the fear
and magnitude of
Initial Investment!!!
Installing HPDC Capability requires
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Excellent marketing strategy
Strong financial capability
Alert Purchase Policy
Accurate choice of machines
Selective customer base
Customers requiring large
series quantities
• Customers with good credit
rating
• Uninterrupted energy supply
• High tool design capability
• Equipment to closely control
production parameters
• High maintenance standard
• Limited, yet skilled, manpower
• Strong and alert marketing
personnel
• Efficient accounting system
Conclusion
Advantages
High productivity
High dimensional accuracy
Good surface; polishable
Near net shape
High strength of the surface layer
Inserts, composites casting well
realizable
Very economical with large quantities
Disadvantages
Pore-free structure difficult to produce
High investment costs
Limited freedom in design
Low elongation
Castings only limited heat
treatable and weldable
Decorative coatings
almost impossible
Pressure Die Casting Process is
Economical
When
1. Large Quantum Production is envisaged
2. High Quality of produce over large quantum is the
requirement
3. Machine ‘down time’ due to lack of contracts is
least
4. Machine ‘down time’ due to breakdowns is least
5. Material purchase cost is well controlled
6. Technical parameters are strictly adhered to.
Good luck!
Conventional
diedie
casting
The conventional
casting is one
of the most economical casting
process
Venting slots
Dosing of metal
from the top
Die filling
real-time controlled
Die opening
ejection of die casting