Die-casting and Precision Machining

Each of the metal alloys available for die casting offer particular advantages for the completed part .al die casting.

Zinc - The easiest alloy to cast, it offers high ductility,zinc die casting high impact strength and is easily plated. Zinc is economical for small parts, has a low melting point and promotes long die life.

Aluminum - This alloy is lightweight, while possessing high dimensional stability for complex shapes and thin walls. Aluminum has good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures.Aluminum die casting

Magnesium - The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast.

Copper - This alloy possesses high hardness, high corrosion resistance and the highest mechanical properties of alloys cast. It offers excellent wear resistance and dimensional stability, with strength approaching that of steel parts.die casting

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.al die casting.

Die casting vs. plastic molding - Die casting  produces stronger parts with closer tolerances that have greater stability and durability. Die cast parts have greater resistance to temperature extremes and superior electrical properties.

Die casting  vs. sand casting - Die casting produces parts with thinner walls, closer dimensional limits and smoother surfaces.al die casting Production is faster and labor costs per casting are lower. Finishing costs are also less.

Die casting  vs. permanent mold - Die casting  offers the same advantages versus permanent molding as it does compared with sand casting.

Die casting  vs. forging -Die casting produces more complex shapes with closer tolerances, al die casting thinner walls and lower finishing costs. Cast coring holes are not available with forging.

Die casting vs. stamping - Die casting produces complex shapes with variations possible in section thickness. al die casting One casting may replace several stampings, resulting in reduced assembly time. zinc die casting

Die casting vs. screw machine products -Die casting produces shapes that are difficult or impossible from bar or tubular stock, while maintaining tolerances without tooling adjustments.Die casting requires fewer operations and reduces waste and scrap.

The basic die casting process consists of injecting molten metal under high pressure into a steel mold called a die. Al die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 400 tons to 4000 tons. Al die casting Regardless of their size, the only fundamental difference in die casting  machines is the method used to inject molten metal into a die. zinc die casting The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.Al die casting.

Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.

High-speed production - Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical al die castings can be produced before additional tooling is required.

Dimensional accuracy and stability - Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.

Strength and weight - Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process al die casting.

Multiple finishing techniques - Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.

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.

Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.

High-speed production - Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical al die castings can be produced before additional tooling is required.

Dimensional accuracy and stability - Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.

Strength and weight - Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process al die casting.

Multiple finishing techniques - Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.

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.

1.4 STRATEGIES TO IMPROVE DIE CASTING
CAPABILITIES
Several efforts have proven successful in stretching the capabilities
of conventional die casting while preserving short cycle times and
providing dimensional stability and other beneficial characteristics.
In these efforts, three strategies have extended the capabilities
of the al die casting process:
1. eliminating or reducing the amount of entrapped gases,
2. eliminating or reducing the amount of solidification shrinkage,
and zinc die casting
3. altering the microstructure of the metal.
The first two strategies noted affect each of the major quantities
that contribute to porosity as defined in Equation 1.1. The third
strategy addresses the mechanical properties by modifying the
fundamental structure of the die cast machining components
1.5 HIGH INTEGRITY DIE CASTING PROCESSES
Three high integrity die casting  processes have been successfully
developed and deployed for commercial use in high volume production.
These processes are vacuum die casting , squeeze casting,
and semi-solid metalworking (SSM). al die casting

Vacuum die casting utilizes a controlled vacuum to extract
gases from the die cavities and runner system during metal injection.
This process works to minimize the quantities of Entrained and
Lube as defined in Equation 1.3. Porosity due to entrapped gases
is virtually eliminated.al die casting
Squeeze casting is characterized by the use of a large gate area
and planar filling of the metal front within the die cavity. As with
vacuum die casting, this process works to minimize the quantities
of Entrained and Lube as noted in Equation 1.3. The mechanism,
however, is much different. Planar filling allows gases to escape
from the die, as vents remain open throughout metal injection.
Furthermore, the large gate area allows metal intensification pressure
to be maintained throughout solidification, reducing the magnitude
of V* as defined in Equation 1.2. Both porosity from
entrapped gas and solidification shrinkage are reduced by using
squeeze casting.
Semi-solid metalworking is the most complex of the high integrity
die casting processes. During semi-solid metalworking a
partially liquid–partially solid metal mixture is injected into the
die cavity. The fill front is planar, minimizing gas entrapment, as
in squeeze casting. Moreover, solidification shrinkage is greatly
reduced, as a significant portion of the metal injected into the die
cavity is already solid. Semi-solid metalworking addresses both
sides of the porosity relationship defined in Equation 1.1.
In addition to reducing porosity, a unique microstructure is generated
during semi-solid metalworking. The mechanical properties
inherent to this microstructure are superior to those created in
conventionally die cast components.al die casting
Products produced using high integrity die casting processes
have little or no porosity. Moreover, the mechanical properties are
much improved in comparison to conventional die cast components.
This is due to reduced levels of porosity, the viability of
subsequent heat treating, and formation of microstructures not
possible with the conventional zinc die casting process.

al die casting ,zinc die casting ,die casting ,machining components , ikd

1.3 PROBLEMS WITH CONVENTIONAL DIE CASTING
Conventional die casting is utilized to produce many products in
the current global market. Unfortunately, conventional die casting
has a major limitation that is preventing its use on a broader scale.
A potential defect, commonly found in conventionally die cast
components, is porosity.zinc die casting
Porosity often limits the use of the conventional die casting
process in favor of products fabricated by other means. Pressure
vessels must be leak tight. Conventional die casting often are
unable to meet this requirement. Moreover, the detection of porosity
is difficult. In some cases, an ‘‘as-produced’’ component is
acceptable. al die casting, Subsequent machining, however, cuts into porosity
hidden within the component, compromising the integrity of the
product.
Porosity is attributed to two main sources: solidification shrinkage
and gas entrapment. al die casting Most alloys have a higher density in their
solid state as compared to their density in the liquid state. As a
result, shrinkage porosity forms during solidification. Due to the
turbulent manner in which metal enters and fills the die cavity,zinc die casting
gas often becomes entrapped in the metal, resulting in porosity.
Porosity also affects the mechanical properties of conventionally
die cast components. In structural applications, porosity can
act as a stress concentrator creating an initiation site for cracks.
Numerous studies have documented how porosity in die castings
varies with several operating conditions.3–8 A method has
been developed for quantifying the porosity in die cast components.
9 The total porosity contained in a component is defined
using the equation al die casting
%P
(solidification shrinkage)  (gas contribution) (1.1)
which can be further defined as where
%P
percent porosity,


solidification shrinkage factor in percent,
V*
volume of liquid in casting cavity that is not supplied
liquid during solidification in cubic centimeters,
Vc
volume of the al die casting cavity in cubic centimeters,
T
temperature of the gas in the casting cavity in degrees
Kelvin,
P
pressure applied to the gas during solidification in atmospheres,

fraction of the gas that does not report to the solidification
shrinkage pores,

liquid alloy density at the melting temperature in grams
per cubic centimeter,zinc die casting

quantity of the gas contained in the casting at standard
temperature and pressure conditions (273 K at 1 atm)
in cubic centimeters per 100 g of alloy, and
*
solubility limit of gas in the solid at the solidus temperature
at standard temperature and pressure conditions
in cubic centimeters per 100 g of alloy.zinc die casting
The first portion of Equation 1.2 is a relationship for porosity due
to solidification shrinkage. The second portion of Equation 1.2
describes the porosity due to gas entrapment. The total gas contained
in the die casting includes gas from physical entrapment, gas
from lubricant decomposition, and gas dissolved in the alloy. This
relationship can also be described mathematically,

     (1.3) Entrained Lube Soluble gas
Each of the gas contributions in Equation 1.3 is expressed in cubic
centimeters at standard temperature and pressure conditions per
100 g of alloy.
In addition to porosity, the microstructures inherent with the
conventional al die casting cannot meet the mechanical requirements
needed for many applications. Subsequent heat treating, which can
alter the microstructure, is rarely possible due to defects that
emerge during thermal processing, such as blistering.
Regardless of the limitations found in conventional zinc die casting
components, demands exist for high integrity products. In many
cases, product engineers and designers turn to investment casting,
forging, injection molding, and assembled fabrications to meet
necessary requirements. Typically, these processes are more costly
than conventional die casting in both processing time and raw
material costs.

Conventional die casting (CDC) is a net-shape manufacturing process
using a permanent metal al die casting  that produces components ranging
in weight from a few ounces to nearly 25 kg quickly and
economically. Traditionally, die casting is not used to produce
large products; past studies, however, have shown that very large
products, such as a car door frame or transmission housing, can
be produced using die casting  technologies.2 Conventional die cast
components can be produced in a wide range of alloy systems,
including aluminum, zinc, magnesium, lead, and brass.
Two basic conventional die casting processes exist: the hotchamber
process and the cold-chamber process. These descriptions
stem from the design of the metal injection systems utilized.
A schematic of a hot-chamber zinc die casting machine is shown in
Figure 1.2. A significant portion of the metal injection system is
immersed in the molten metal at all times. This helps keep cycle
times to a minimum, as molten metal needs to travel only a very
short distance for each cycle. Hot-chamber machining Components are rapid in
operation with cycle times varying from less than 1 sec for small
components weighing less than a few grams to 30 sec for castings
of several kilograms. Dies are normally filled between 5 and 40
msec. Hot-chamber die casting  is traditionally used for low melting
point metals, such as lead or zinc alloys. Higher melting point
metals, including al die casting alloys, cause rapid degradation of the
metal injection system.
Cold-chamber al die casting machines are typically used to conventionally
die cast components using brass and aluminum alloys.machining Components
An illustration of a cold-chamber die casting machine is presented
in Figure 1.3. Unlike the hot-chamber machine, the metal injection
system is only in contact with the molten metal for a short period

1.1 ORIGINS OF HIGH PRESSURE DIE CASTING
Casting processes are among the oldest methods for manufacturing
metal goods. In most early casting processes (many of which
are still used today), the mold or form used must be destroyed in
order to remove the product after solidification. The need for a
permanent mold, which could be used to produce components in
endless quantities, was the obvious alternative.al die casting
In the Middle Ages, craftsmen perfected the use of iron molds
in the machining Components of pewterware. Moreover, the first information
revolution occurred when Johannes Gutenberg developed a
method to manufacture movable type in mass quantities using a
permanent metal mold. Over the centuries, the permanent metal
mold processes continued to evolve. In the late 19th century processes
were developed in which metal was injected into metal dies
under pressure to manufacture print type. These developments culminated
in the creation of the linotype machine by Ottmar Mergenthaler.
However, the use of these casting methods could be
applied to manufacture more than type for the printing press.
H. H. Doehler is credited with developing die casting for the
production of metal components in high volumes. Shown in Figure
1.1 are diagrams filed with patent 973,483 for his first production
die casting machine.1 Initially, only zinc die casting alloys were used
in die casting . Demands for other metals drove the developmentof new die materials and process variants. By 1915, aluminum die casting
alloys were being die cast in large quantities.2 zinc die casting
Much progress has been made in the development of die casting
technologies over the last century. Developments continue to be
made driving the capabilities of the process to new levels and
increasing the integrity of die cast components.

Figures 1 and 2 show a gear used in the lead screw drive train of a screw cutting lathe that was
made in about 10 minutes with an abrasive waterjet. This custom gear was needed to achieve a
1/2-in. pitch for a spring winding application. It ran as smoothly and quietly as the other gears in the

train. machining Components,Note in Figure 2 that the keyway and close-fitting bore also were made with the abrasive
waterjet.
Figure 3 is a planetary gear system in which the round holes
in the planets are used to carry workpieces in a lapping
machine. The total time to make the entire system in 1/8-in.
steel was less than 40 minutes.machining Components
Figure 4 is an internal gear driven by a spur gear for an
application in a winch. In this case, the key is built into the
spur gear rather than using a keyway. Note that the ratchet
and pawl also are abrasive waterjet machine-made parts.
Even odd-shaped gears can be made by an abrasive
waterjet, which also can form racks and mating gear sectors
in a manner that easily facilitates a linear motion by pulling a
lever.
Sprockets and Chains
Ordinarily you would not make your own chain, but what if
you wanted to lift 300 tons? You then would be forced to make your own. Links in the chain in
shown in Figure 5 were made with an abrasive waterjet and assembled into a chain that can lift a
300-ton object.machining Components
It would be more common to make a sprocket and
buy the chain. Sprocket geometry can be found in
Machinery's Handbook, and it is quite easy to
follow the specifications, machining Components,draw the desired sprocket,
and produce it with an abrasive waterjet.
Cams
With the advent of low-cost servo drives and
control systems, cams are used less than they
were in earlier times, but they still provide a lowcost
means of making particular motion profiles.
Cams also can be used as wedging mechanisms
for locking movable elements in place.
Cams can be made very quickly on an abrasive
waterjet. The major portion of the work is
determining the desired cam shape. Once the
shape is known, making the cam is as simple as
loading the CAD file into the machine and pressing
go[START?].machining Components
Figure 6 shows a cam ready to be cut according to the function:
R = 2 + Sin(Theta)
machining Components,A hole with a keyway has been added so the cam can provide a reciprocating motion.
Springs and Flexures
Two types of springs can be made on an abrasive waterjet. One type flexes normal to the plane of
the X-Y table, and the other flexes parallel to it. Figure 7 shows a spiral spring typically made from
a thin sheet of heat-treated spring stock. The spring is held on its outer diameter, and the moving
member is attached to the central hole. machining Components,The spring is very rigid in the radial direction, but quite
flexible in the axial direction. If two such springs are placed a short distance apart, one above the
other, they provide a quite good flexural bearing for limited motion.

Many machine components formerly made with conventional machining techniques
now can be made easily and cost-effectively with abrasive waterjet cutting. This
article discusses some of these components. machining Components,It also gives examples of abrasive
waterjet-produced signs and labels that can be used to enhance your products.

An article published previously on
thefabricator.com, How one shop benefited from
abrasive waterjet technology, presented novel
construction techniques that can be implemented
effectively with an abrasive waterjet machining Components to
lower the costs of building fabricated structures.
But abrasive waterjet machines can be used to
make machining Components, too, such as gears and parts
with gear segments; sprockets and chains; cams;
ratchets; springs and flexures; keys and keyways;
wrenches; hand wheels; clamps; brake disks; and
even signs and labels that might be added to a
structure to form a completed machine. These
machining Components, which formerly may have been made
using conventional machining techniques, now can
be made cost-effectively in a fabrication shop with
an abrasive waterjet.
The key to producing many of these machine elements successfully is using precision waterjet
equipment. Many components also require the taper-free cutting discussed in the article Improving
waterjet cutting precision by eliminating taper.
Since most modern abrasive waterjet machining Components make parts directly from a CAD file (usually a 2-D
dxf file), the ease of making the part depends on how easy it is to make the CAD file. Many good
CAD programs are available. This article presents design ideas only and is not intended to promote
a particular CAD program.
Gearing
An abrasive waterjet usually is not thought of as a gear-making machining Components, but a gear tooth is just
one particular shape that can be made easily with an abrasive waterjet. A precision abrasive
waterjet often can stay within 0.001 in. of the desired contour, and an ordinary machine can stay
within 0.005 in. For many applications this tolerance is sufficient.