Frequently Asked Questions (FAQ)

Table of Contents

  1. What is die casting?
  2. What is the process typically capable of?
  3. What are some of the alloys used at Empire Die Casting Company?
  4. Is there a cross reference table between die cast alloys?
  5. What are some of the mechanical & physical properties of die cast alloys?
  6. What are some of the characteristics of these alloys?
  7. What are some common die casting defects?
  8. What is a die cast machine?
  9. How is required machine tonnage calculated?
  10. What is a die cast die?
  11. What is a trim die?
  12. What are some of the secondary operations performed on die castings?
  13. Resources ...

1. What is die casting?

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.

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2. What is the process typically capable of?

The table below summarizes the capability of the metals used at Empire Die Casting Company.

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3. What are some of the alloys used at Empire Die Casting Company?

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.

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4. Is there a cross reference table between die cast alloys?

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.

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5. What are some of the mechanical & physical properties of the alloys?

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.

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6. What are some of the characteristics of these alloys?

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7. What are some common die casting defects?

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8. What is a die casting machine?

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.

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9. How is required machine tonnage calculated?

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.)

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10. What is a die cast die?

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:

  1. A tool must be manufactured such that the geometry to make the part needed is cut directly into the die steel.
  2. A tool must provide for a delivery system to transport the metal from the shot sleeve into the cavity (a runner system).
  3. It must provide for a method to cool the molten metal quickly so the solidified part can be extracted.
  4. 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.

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11. What is a trim die?

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.

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12. What are some of the secondary operations commonly performed on die castings?

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.

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13. Resources ...

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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