Gravity Die Casting
Gravity Die Casting employs cast iron moulds which allow aluminium &
zinc castings to be produced more accurately and cheaply than with
sand castings. Tooling costs of gravity die casting are a fraction
of those needed for high pressure die castings. The rapid chilling
gives excellent mechanical properties whilst non-turbulent filling
ensures production of heat treatable gravity castings with minimal
Gravity Die Casting Application
Motorcycle engine, cylinder head, intake manifold.
Water pump, air pump, electric, steeling components.
Hydraulic, marine, medical, sports equip, parts.
Pressure Die Casting
The molten metal is injected into the mould under pressure. This results in a
more homogeneous part, generally good surface finish and good dimensional
accuracy, compared to that achieved using conventional casting methods. A
result of this is the significant reduction in the requirement for post casting
processing to achieve the required final configuration.
The process cycle has 5 main steps.
The cleaned and lubricated 2 halves of the die are clamped together inside the
Injection:- Of the shot (a predetermined volume) of molten metal at
high pressure into the die.
Cooling:- The solidification of the shot in the die cavity adopting
the desired final shape.
Ejection:- Of the casting from the die cavity.
Trimming:- The excess material from casting
Hot vs Cold
Hot chamber machines are used primarily for alloys with low melting points in
particular zinc, tin, lead and other low melting point alloys that do not readily
attack and erode metal pots, cylinders and plungers.
Cold chamber machines are used for alloys such as aluminum brass and magnesium
and any other alloys with high melting points
Pressure Die Casting Application
Pressure Die Casting Applications
Automotive parts., wheels, blocks, cylinder heads, manifolds etc.
Electric motor housings.
Cabinets for the electronics industry.
General hardware appliances, pump parts, plumbing parts
Kitchen ware such as pressure cooker.
The Benefits of Die Casting
Cost effective:- An efficient, economical process offering a broad
range of component shapes.
Precision:- High-speed production of complex shapes within
Dimensional accuracy and stability:- Components that are durable and
dimensionally stable, while maintaining close tolerances. They are also heat
Strength and weight:- Die cast parts are stronger than plastic
injection mouldings that have similar dimensions. Thin wall castings can be
stronger and lighter compared to components from other casting methods.
Simplified Assembly:- Die castings provide integral fastening
elements, such as bosses and studs. Holes can be cored and made to tap drill sizes,
or external threads can be cast.
Common Alloys Used in Die Casting
Alloys of Aluminum, Magnesium, Zinc, Copper, Lead & Tin are the materials widely used in die-casting.
Aluminum:- Is cast at a temperature of 650 ºC. It is often
alloyed with Silicon and Copper. Silicon increases the melt fluidity whilst
it reduces machinability, Copper increases hardness and reduces the ductility.
A low amount of Copper (less than 0.6%) gives improved chemical resistance, and
is often used in marine applications. A high silicon content (improved wear
resistance), is often used in automotive applications where wear resistance
Zinc:- Alloys used for closer tolerances and thinner walls than
is possible with Aluminum, due to its high melt fluidity. Zinc is usually alloyed with
Aluminum to give improved strength and hardness. The casting is done at a fairly
low temperature of 425 ºC allowing the parts to be ejected from the dies earlier
resulting in shorter cycle times. Zinc alloys are typically used to produce precision
parts such as sprockets, gears, and connector housings.
Copper:- This alloy possess high hardness and high corrosion
resistance. It offers excellent wear resistance and dimensional stability,
with strength approaching that of steel parts. Typically used in plumbing,
electrical and marine applications where corrosion and wear resistance is
Magnesium:- The easiest alloy to machine, magnesium has an excellent
strength-to-weight ratio and is the lightest alloy commonly die cast
Lead and Tin:- These alloys offer high density and are capable
of producing parts with extremely close dimensions. They are also used for
special forms of corrosion resistance.
Die-castings are typically limited to 5 kg max for copper alloys, up to 35 kg max for
Zinc. Large castings tend to have greater porosity problems, due to entrapped air,
caused by the melt solidifying before it gets to the furthest extremities of the
die-cast cavity. The porosity problem can be somewhat overcome by vacuum die
From a design point of view, it is best to engineer parts with uniform wall
thicknesses to ensure uniform cooling, and to have cores of simple shapes.
It is preferable to have thin sections, as heavy sections can result in cooling
problems, trapping gases causing porosity. All corners should be radiused with
internal radii at least equal to the wall thickness to avoid stress concentration.
Draft allowance should be provided to all sides to ease the releasing the parts
from the tool, these are typically from 0.25º to 0.75º per side depending on the
material. Undercuts are undesirable as they generally result in more
|Min Draft Angle
|Max wt Kg
Tooling Cost:- The primary influence is the complexity of the
machining required to produce the die set. There are two main drivers, the size
of the components to be cast, (large parts require large tooling), plus the number
Production Cost:- The two main drivers are hourly rate & cycle
time. The hourly rate is dependent on the cost and utilisation of the machine.
The cycle time is broken down into three components, setting, injection and
cooling. Wall thickness has a significant impact on both the injection time
and the cooling time. Setting time, the time between shots, is dependent on the
ergonomics and transit time of the machine.
Material Cost:- Determined by the shot weight of the component
and the prevailing market costs for the material constituents. The shot weight of
the component is the finished weight plus the material used in the filling channels.