FAQ


Die Casting primarily refers to processes in which molten metal is injected into a mold, allowed to solidify, then removed to allow for the casting of another part, using the same mold. In general, Die Casting can be subdivided into two general processes, Low Pressure Die Casting (such as gravity casting, perm-molding, etc), and High Pressure Die Casting. Empire Die Casting Company specializes in the High Pressure Die Casting process using Aluminum or Zinc alloys.
The table below summarizes the capability of the metals used at Empire Die Casting Company.

Aluminum Alloys Zinc Alloys
Die Life 100,000 Shots 1,000,000 Shots
Wall Stock 0.08 in. min. 0.03 in. min.
Radii 0.09 min. 0.04 min.
Draft 1º min. (per side) 1/2º min. (per side)
Core Diameters 0.09 min. 0.04 min.
Tolerance +/- 0.003 in. / in. +/- 0.001 in. / in.
Shrink 0.006 in. / in. 0.006 in. / in.
Plating Cost in Dollars Cost in Cents
Weight / Density 0.097 lb / in3 0.240 lb / in3
Each metal is alloyed with other elements such as silicon, copper, magnesium, and iron and other elements in trace quantities. These alloying elements change the physical properties of the metals. The table below lists the constituents of each alloy for both Aluminum & Zinc alloys.

Aluminum Alloys (Ingot)

Alloy Silicon Iron Copper Manganese Magnesium Chromium Nickel Zinc Tin Titanium Other Elements Aluminum
360.1 9.0-10.0 1.0 0.6 0.35 0.45-0.6 0.1 0.1 0.1 0.1 Remainder
380.1 7.5-9.5 1.0 3.0-4.5 0.50 0.10 0.50 2.9 0.35 0.5 Remainder
383.1 9.5-11.5 0.6-1.0 2.0-3.0 0.5 0.1 0.3 2.9 0.15 0.5 Remainder
384.1 10.5-12.0 1.0 3.0-4.5 0.5 0.1 0.5 2.9 0.35 0.5 Remainder
B390.1 16.0-18.0 1.0 4.0-5.0 0.5 0.5-0.65 0.1 1.4 0.2 0.2 Remainder
A413.1 11.0-13.0 1.0 1.0 0.35 0.1 0.5 0.4 0.15 0.25 Remainder

Table Derived from ASTM B179-03 Standard (2006). All Figures in Percent (%)

Zinc Alloys (Ingot)

Alloy Aluminum Magnesium Copper Iron (Max) Lead (Max) Cadmium (Max) Tin (Max) Nickel Zinc
Zamak 3 3.9-4.3 0.025-0.05 0.1 max 0.075 0.004 0.003 0.002 Remainder
Zamak 7 3.9-4.3 0.01-0.02 0.1 max 0.075 0.0020 0.002 0.001 0.005-0.002 Remainder
Zamak 5 3.9-4.3 0.03-0.06 0.75-1.25 0.075 0.004 0.003 0.002 Remainder
Zamak 2 3.9-4.3 0.025-0.05 2.6-2.9 0.075 0.004 0.003 0.002 Remainder
ZA-8 8.2-8.8 0.02-0.03 0.8-1.3 0.065 0.005 0.005 0.002 Remainder
ZA-12 10.8-11.5 0.02-0.03 0.5-1.2 0.065 0.005 0.005 0.002 Remainder
ZA27 25.5-28.0 0.12-0.02 2.0-2.5 0.072 0.005 0.005 0.002 Remainder

Table Derived from ASTM B240-05 Standard (2006). All Figures in Percent (%)

Die cast alloys have an equivalent alloy across the international standards. Although the alloying elements are not exactly the same, the physical properties of each alloy is very similar, and therefore can sometimes be used interchangeably. An equivalency cross reference table is shown below.

Commercial UNS ANSI AA ASTM B85 SAE J452 Federal QQ-A-591 DIN 1725 JIS H5302
A360 A13600 A360.1 SG100A 309 Note 1 233 ADC3
A380 A13800 A380.0 SC84A 306 Note 1 226A ADC10
383 A03830 383.0 SC102 383 Note 1 226A ADC12
384 A03840 384.0 SC114A 303 Note 1 ADC12
390 A23900 B390.0 SC174B Note 1
A13 A14130 A413.0 S12A Note 1 231D ADC1

Note 1: Federal QQ-A-591 designations use the ANSI AA designations.

Table Derived from the NADCA Product Design for Die Casting.

This table cross references the material and physical properties of several zinc and aluminum alloys when die cast, perm. molded, or sand cast, along with typical iron and plastic materials as a reference point. Empire Die Casting Company is providing this information as a courtesy, and cannot guarantee or warrant the accuracy or applicability of this information. (NA = Data Not Available)

This table is a compilation of information taken from four tables in the NADCA Product Specification Standards for Die Castings. The information is provided without any guarantees.

Zinc / Zamak Alloys. 1 = Most desirable, 5 = Least desirable.

Zinc ZAMAK
No. 2 No. 3 No. 5 No 7 ZA-8 ZA-12 ZA-27
Resistance to Hot Cracking 1 1 2 1 2 3 4
Pressure Tightness 3 1 2 1 3 3 4
Casting Ease 1 1 1 1 2 3 3
Part Complexity 1 1 1 1 2 3 3
Dimensional Accuracy 4 2 2 1 2 3 4
Dimensional Stability 2 3 3 2 2 2 1
Corrosion Resistance 2 3 3 2 2 2 1
Resistance to Cold Defects 2 2 2 1 2 3 4
Machining ease and Quality 1 1 1 1 2 3 4
Polishing Ease and Quality 2 1 1 1 2 3 4
Electroplating Ease and Quality 1 1 1 1 1 2 3
Anodizing 1 1 1 1 1 2 2
Chemical Coat 1 1 1 1 2 3 3

Aluminum Alloys. 1 = Most desirable, 5 = Least desirable.

360 380 383 384 390 413
Resistance to Hot Cracking 1 2 1 2 4 1
Pressure Tightness 2 2 2 2 4 1
Die filling capacity 3 2 1 1 1 1
Anti-Soldering to the die 2 1 2 2 2 1
Corrosion Resistance 2 4 3 5 3 2
Machining ease and Quality 3 3 2 3 5 4
Polishing Ease and Quality 3 3 3 3 5 5
Electroplating Ease and Quality 2 1 1 2 3 3
Anodizing 3 3 3 4 5 5
Chemical Coat 3 4 4 5 5 3
Strength at elevated temp 1 3 2 2 3 3
A die casting machine is the equipment used into which a die casting tool is mounted to make cast parts. The primary purpose of a die casting machine is to inject metal into the die, and to keep the die shut during injection and intensification and solidification of the metal. Finally, the die cast machine is used to push plates in the die cast die to eject the part. It is composed of two major systems – the clamp end, and the shot end. The shot end is where the metal is poured and accelerated into the die, while the clamp end (platens) is where the die is mounted and kept shut during the injection and intensification process, and from where the part is ejected and extracted from the die.

Although there are several types of die casting machines, the majority of the machines used in the die cast industry have vertical platens that open and close horizontally. These machines can be subdivided into two main categories: cold and hot chamber machines. Most modern equipment uses a hydraulic clamp end, and a pneumatic shot end, although many variations on these types of machines exist.

Force needed to keep the die shut = Cavity Pressure x Projected Area of the casting.

F = Force (clamping)

P = Intensification Pressure.

A = Projected Area of all of the surfaces that see aluminum.

The more intensification that is applied, the more clamping force is needed to keep the machine shut.

In other words:

Approximate machine tonnage needed to keep the die shut = (Force needed to keep the die shut, plus an additional 60% for the runner and an additional 20% for the safety factor.)

View Details

A die casting die is the piece of equipment that is used to make the part. A die casting die, also commonly referred to as a tool, has the following primary functions:

A tool must be manufactured such that the geometry to make the part needed is cut directly into the die steel.
A tool must provide for a delivery system to transport the metal from the shot sleeve into the cavity (a runner system).
It must provide for a method to cool the molten metal quickly so the solidified part can be extracted.
It must provide for a method with which to extract or eject the part.

Die casting dies are usually manufactured using different grades of steel. The cavity portion or the die components that see aluminum are usually made from high grade H-13 steel. The steel is heat treated, typically in a vacuum furnace to a hardness of anywhere between 42 to 48 Rockwell depending on the application and size of the cavity. The shoe or holders and ancillary components are usually made from different grades of steel such as 4140, hot roll or even cold roll steels depending on their application. Tools typically last for 100,000 shots in aluminum, and 1,000,000 shots in zinc. Prior to 100,000 shots, it is highly recommended that the cavity portion of the tool be replaced so that a catastrophic failure is avoided before reaching the 100,000 shots mark.

The reason that tooling needs to be replaced is due to the extreme temperature fluctuations a die cast die is typically exposed to.

During the injection cycle in aluminum for example, the die surfaces are exposed to 1250°F instantly. Once the part is ejected, the die surfaces are quenched with 90-95% water and a die lube (remainder) mixture at room temperature. The constant fluctuation in surface temperature induces tensile stresses in the die surface. These stresses result in cracks which are commonly referred to as heat checking. In some severe situations, a stress riser, such as a sharp corner in the die steel, can cause gross cracking, after which the tooling becomes unusable due to these temperature fluctuations. It is therefore highly recommended that tooling be replaced every 100,000 shots to avoid unforeseen catastrophic failure.

An Isometric view of a section through a typical die cast die is shown below.

A trim is a tool that is used to remove the gate and flash from the part after the casting operation. A trim tool is used in a trim press. It is composed of a lower and an upper half. The entire shot is placed into the lower half of the tool, on the fixed half of the trim press, and the upper moving half either blanks or shears off any gates, overflows, and flash. A trim tool also punches any flash in holes and cleans up the part.
Once the part is cast trimmed, it is typically exposed to secondary operations such as machining, anodizing, or powder coating, just to name a few. These processes typically add or change a characteristic that is usually not achievable in the as-cast state. For example, parts can be machined to attain a level of accuracy that is typically not achievable with a raw die casting, or holes can be threaded. Also, casting can be powder coated to add color, or anodized to enhance corrosion resistance.

Below is a table showing what secondary operation is needed to attain a certain characteristic.

Secondary Process Purpose
Vibe Deburr Parts are vibrated through a tub filled with
specially
polished stone. This removes flash and loose burrs from the casting,
and
smoothes any sharp edges. The surface of casting has a dull luster
to it
once done.
Thermal Deburr Same as above, but the process is done in an oven.
The
casting’s surface color and finish does not change significantly.
Shot Blast Shot Blasting is a process whereby the casting is blasted with steel media. This removes any surface discolorations, and
light
heat checking. The die cast surface ends up having an even, matt
finish. The
part will look cosmetically pleasing.
Machining Machining is probably the most common of all
secondary
operations. It is used to make a part usable in an assembly. For
example,
threads can be added, surfaces can be milled flat to within
thousands, or
large diameters can be bored to add seal rings or gears in them.
Machining
and casting are integral to the manufacture of aluminum components
in
practically any industry that uses cast aluminum parts.
Broaching A spline is a feature that gets commonly broached in
a die casting.
Powder Coating Adds color – practically any color is possible.
Anodize Adds corrosion resistance to a part so that it can
survive
salt or corrosive atmospheres. This process can also be used to
improve
surface hardness, allow dyeing, improve lubrication, or improve
adhesion.
Specifically, the process increases the thickness of the oxide layer
on the
surfaces of metals, including aluminum alloys. The particular
anodize
process and/or color to be used is typically specified on the print
as a MIL
specification.
Chemical Film / Yellow Chromate Chemical Film, or chromate conversion, produces very
similar
results to anodizing in an aluminum casting, however, whereas
anodizing
simply increases the thickness of the oxide layer on a metal,
chemical film
adds a chromate conversion film that minimizes surface oxidation,
corrosion,
and allows for improved adhesion and painting.
Plating Plating can be added to a part after it is polished.
Plating
tends to be much more economical in zinc than in aluminum. Plating
can add a
deep, lustrous mirror finish to a casting. For example die castings
are
commonly platted with a chrome, or nickel finish.
Impregnation Impregnation is a common process used to make die
castings
pressure tight. It is commonly performed in a vacuum. The process
impregnates the die casting with a polymer resin that seeps into any
micro
cracks or micro porosity present in the casting and seals them.
Depending on
the pressure requirements, multiple impregnations may be needed.
Heat Treatment Heat treating is usually done to increase the
hardness, and
therefore the UTS of a casting. Heat treatment is a tricky process
in die
casting since it may expose internal defects such as porosity, as
evidenced
by blistering. High pressure die castings can be treated up to a T5
with
little complications. High Pressure die castings are very difficult
to heat
treat to a T6.
The majority of this FAQ was generated using our experience and the following guides:

NADCA Product Specification Standards for Die Castings, 2009 7th Edition, NADCA Publication #402
NADCA Product Design for Die Casting, 2009 6th Edition, NADCA Publication #E-606
The ASTM 2006 Edition.
www.diecasting.org

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