Why would a product designer choose a die casting over a component manufactured by another competing process?

What are the capabilities of a product made with the die casting?

During this session, we will answer those questions. We will also explore the length and breadth of die casting applications, and explain the unique characteristics and optimum die casting configuration.

After completing this chapter, you will be able to:

  • List the advantages of using die casting process
  • Identify die casting

    die casting parts

    The large aluminum automotive transmission housing shown on the above is produced on a 3500 ton cold chamber die casting machine. The aluminum fills the complex die cavity in less than ½ second and a completely formed solidified casting is ejected from the die every two minutes. Transmission housings weigh up to 35 lb. In contrast, the small zinc line connector for a cook stove is produced on a much smaller machine. The zinc fills the cavity on the order of a few hundredths of a second and several castings are ejected every minute. The weight of each of these castings is 0.5 ounces.

  • List the characteristics of the optimum die casting configure
  • Identify the components of the die casting shot

The information presented in this chapter is of general interest and is background information for material presented in following chapters.

In the previous information you learned general information about the die casting industry in China.  In this chapter you will learn specific information about the die casting.

The following new terms are used in this chapter.

  • Die casting “shot”      Defined as a noun in this chapter, not a verb.
  • Sprue                       Cone-shaped metal part of the shot that connects the nozzle and runner.
  • Overflows    Small pockets of metal around the perimeter of the part and also in openings.
  • Runner  The path the metal must flow through to get from the sprue or biscuit to the casting.

The Die Casting Advantage

Die casting produces components at high speed from a range of durable zinc, magnesium , and aluminum alloys while faithfully capturing the most intricate design details.

This capability makes it a prime production option for high volume production components. The ability to maintain close tolerances, often eliminating all machining, can make the process the optimum choice for lower-volume production as well.

Modern process technology that insures consistent qualityComputer control of the significant process variables has led to consistent dimensional control and internal integrity.  The process responds to statistical control and statistical problem solving techniques.
Freedom to design intricate configurationsDesign configuration is only limited to the designer’s imagination and the mold maker’s ingenuity to build the casting die.  A typical example of an intricate configuration is the automotive transmission valve body.
Net-shape casting economies, even at lower volumesElimination of machining and secondary operations can make die casting competitive at low production volumes.
Wide variety of available alloys and alloy propertiesRecall that the typical metals are alloys of aluminum, magnesium and zinc.  Small volumes of alloys made from copper and lead are also routinely die cast.  Iron and titanium materials have also been die cast.  Current alloy development includes the use of composite materials, aluminum and silicon carbide for example.
The rigidity, look and feel of metalThe perceived quality of a metal component is higher than that made from a non-metallic material. Rigidity is analogous to strength, and is based on the modulus of elasticity, and configuration.  Good rigidity also reduces vibration.
Meets moderate to high strength performanceDie cast alloy strengths are above plastics and slightly below those of sheet steels.
Moderate to high impact and dent resistanceSelected alloys have very high-energy absorption capability.
Documented fatigue strength characteristicsPublished values of fatigue strength are conservative.  High density casting processes minimize defects, such as porosity, that initiate fatigue.
Excellent sound damping propertiesStudies indicate zinc and ZA alloys are good at sound damping. Magnesium has demonstrated sound damping in drive train components.
Bearing properties that often eliminate separate bearingsZA alloys have good bearing properties.  Aluminum 390 alloy shows good wear resistance.
Inherent EMI shielding for electronic applicationsHigh conductivity provides inherent shielding
Pressure tightness for hydraulic and pneumatic componentsAlloy selection, gating technology and vacuum systems greatly reduce trapped gases and shrinkage porosity.
High quality surface finishes for decorative applicationsGood surface finish is relatively easy to achieve.  A variety of surface treatments are easy to apply.
Meets criteria for serviceability and recyclabilityAlloys are “green”, easily recycled.  The aluminum alloys are usually produced from recycled materials. The die casting alloy recycling stream is based on a worldwide metal reclamation infrastructure that has been operative for more than 50 years.

Today, with the introduction of new, higher performing die casting alloys and new process technologies, many of the old design assumptions about process limitations have become obsolete.

  • New specifications for dimensional control, draft and flatness have been issued. These specifications are reviewed and updated on a periodic basis.
  • New process enhancements including vacuum technology, squeeze casting, semi-solid casting and thixotropic molding have been developed and have led to significantly reduced levels of porosity.

The Optimum Die Casting Configuration

Before a die casting project is undertaken, the casting design should be evaluated in terms of manufacturability.  In other words, can the casting be manufactured?  Is the casting design optimum?

The optimum die casting configuration will:

  • Fill completely with metal.
  • Solidify quickly without defects.
  • Eject readily from the die.

The optimum casting configuration does not just happen.

Engineers and designers must work together to make sure the casting design fulfills the product requirements and can be manufactured.  To achieve both of these goals, the die casting must be designed with features that capitalize on the characteristics of the die casting process.  The following six principles should be used in working toward and developing the optimum die casting configuration.