Die-casting and Precision Machining

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.

Part Cooling Requirements
Once the part is extracted from the die casting, it may need to be cooled prior to further processing or transfer to other
equipment. This can be a liquid quenching or air cooled process based on the product and the desired material
characteristics. For liquid cooled operations, the equipment could be as simple as a quench tank into which the
robot dips the hot part once it is extracted from the al die casting. For air cooled operations, a small fixture or buffer stand
may need to be designed so that the robot can unload the parts. Robotic simulation is a great tool to validate
buffer stand reach and location.
Degating/ Flash Trimming
In some manufacturing operations like engine parts, thedie casting may have metal extensions known as gates or
runners that are deliberately created in the al die casting  process to eliminate air and porosity in the main casting part.
These gates can be removed by several different methods based on the quality and finish requirements of the end
product. In most cases, the gates are removed by using a “knock-off” stand. The degating process generally has
specific orientation and direction requirements to remove the excess material. Robotic simulation must be used to
ensure that the robot can access the desired knock-off position without any reach issues.zinc die casting
An extension of metal is formed on die castings at the parting line of the two die plates and where moving die
components operate. This is known as “flash” and is an unwanted by-product of the manufacturing process. This
flash is generally removed using a trim press or in some cases a CNC machine. The robot loads the casting into
the press or CNC machine, waits for the equipment to cycle before unloading the finished part. Using robotic
simulation to validate this load/ unload sequence is important to ensure that there is sufficient opening and clearance
to enter the machine.
Part Transfer/ Exit
die casting parts may be transferred out of the system in several different ways based on customer requirements.
Some parts may be transferred out onto conveyors for further processing while others may require robotic palletizing
into racks. Robotic simulation is again a
valuable tool to ensure that the robot can reach all
extremes of all pallets at all heights. al die casting,The simulation
can also be used to analyze cycle time based
on stack pattern requirements.zinc die casting
 

Floor Space
The amount of floor space required to automate a die casting operation depends largely on part processing
requirements as well as peripheral equipment design and sizes. The most effective way to ensure that appropriate
space is earmarked for the robotic automation
process is by performing a simulation of all the robotic
operations. Al die casting,This will ensure that equipment is placed
in locations that will suit all process requirements and
sequence of operations. A significant benefit of using
robotic simulation is the ability to test multiple product
styles and dies to arrive at a common layout configuration
which reduces changeover time and associated
costs. The simulation done in conjunction with
mechanical design and layout development will act as
a virtual three dimensional integrated cell.
Payload and Robot Selection
Robot selection is driven not only by environmental conditions but also based on payload, reach and part access
within the die. Al die casting,The mass, center of gravity and moments of inertia about the mounting face of the robot determines
the robot model based on payload capacity. The mass data for the payload analysis can be generated from
the mechanical design CAD package as long as the data entered into the system for material properties is accurate.
The mass data that is generated can then be entered into a payload calculation program to determine the
robot model that can withstand the payload requirements. die casting ,Apart from payload, other factors that help drive robot
selection are – die travel (horizontal vs. vertical), gantry vs. floor mounted robots based on equipment size and
access and cycle time requirements.
Cycle Time Validation
The main driver for production rate on a die casting system is the time it takes for one cycle of the press and the
unload time. Once this data is known, process design must focus on ensuring that the press spends a minimum
wait time on other pieces of automation. The time
spent by the robot after unloading the part from the
dies should not exceed the time required by the
press to cycle and generate a new zinc die casting.
Robotic simulation in conjunction with external robot
controller software (RCS) can be used to generate
accurate robot motion cycle time. The use of virtual
controls replicates real-world conditions and allows
for evaluation of both individual processes and
coordinated activities of robots within a system.

Designing a Robotic Cell for Die Casting
If business requirements drive the die casting cell to be automated, there are many factors that need to be considered
during the design of the cell.
Product and Die Design
The size and shape of the cast product essentially drives the design of the dies used for casting the product.
Shape, size and stroke of the die have a strong impact on the automation in terms of robot reach and accessibility.
In today’s technologically advanced climate, almost all manufacturers have their product and dies designed in 3D
CAD packages.al die casting ,This 3D data is critical for accurate end-effector design as well as design of storage racks or
conveyor pallets. Ensure that this data is at the latest revision and the product used for equipment design is
displayed in the form and shape that it is expected to be in after exiting the die cast machine.
Environmental Factors al die casting
Safety is a major issue in die casting operations due to the extreme heat and emissions that are generated during
the die casting process. Robots are used primarily to avoid humans from being exposed to this dangerous environment.
Most robot OEM’s have a “foundry” series of robots that are designed and manufactured using strong heat
resistant materials which could be used if applicable. End-effector component materials should be selected based
on heat resistance since these parts interact with the high temperature product as it exits the die.zinc die casting
End-effector Design
While the size and shape of the die casting
product is the major factor in the design of the
robotic end-effector, other factors like
temperature, payload, and force requirements
should be taken into account. al die casting
 3D product,fixtures and die models should be used to
design the end-effector to ensure that the
design has appropriate clearances to
surrounding parts within the die. Clamping
surfaces are generally based on quality and
finish requirements and should be carefully
chosen with the customer. End-effector design
should be developed in conjunction with
robotic simulation to ensure that the design is
suitable for all robot tasks and associated
equipment. In cases where removal of gates,
risers and “biscuits” on the product is required,
the end-effector may need to be designed with
the appropriate force compensation or compliance
devices.al die casting

Abstract
This paper identifies key reasons for automating die casting operations, the impact of robots on the automation,
and the advantages of using Product Life Cycle Management (PLM) tools to generate and validate the automation
process.
Introduction
Die casting is a process that has been around for several decades. It is a flexible process for producing metal
parts by forcing molten metal under pressure into reusable steel molds or dies. The dies can be designed to
produce highly accurate and repeatable complex shaped parts.
Die cast products are the bulk of mass-produced items manufactured by the metalworking industry, with applications
in a variety of consumer, commercial and industrial products. Various products ranging from alloy based toys
to automotive engine parts are manufactured using this process. Based on the size of the end product and the
volume requirements, automation of die casting operations can be critical for a successful manufacturing process.
Business Drivers for Die casting Automation
In the last 25 years, there has been a steady increase in the role of industrial robots in manufacturing. With over
15,000 industrial robots sold every year, robots have become a mainstay in the manufacturing industry. Their
flexibility, reliability and repeatability, to name a few advantages, have made them a vital component in the automation
process for die casting applications.
Some of the business drivers for automation of al die casting and zinc die casting operations are:
• Low cost of robots leading to cost effective automation with quick return on investment (ROI).
• Increased requirements for system flexibility to produce multiple parts.
• Ever increasing focus on the human factor/ workcell safety.
• Variety of production rate requirements based on market for cast products.
• Cycle time requirements by station or operation.
• Life cycle of manufactured product to ensure acceptable ROI.
• Product handling requirements.
• Maintenance requirements.
• Safety standards related to heat and gas exposure in casting operations.