An Introduction to Die Casting | CMP Group Ltd.

An Introduction to Die Casting

Pictured above is a die casting machine manufactured by Zitai Precision Machinery1

If you’re in charge of manufacturing a product, chances are you have faced the following question: How do you obtain a large volume of parts with complex net shapes and internal features that minimize secondary operations? The answer is die casting.

Die casting is a quick, reliable and cost-effective manufacturing process characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is made of steel and is uniquely designed for each project. Also known as tools or dies, mold cavities have a high degree of accuracy and are able to produce parts with tight tolerances. The pressure is maintained in the ‘die’ long enough to allow the metal to solidify, after which the die opens to permit the casting to be ejected. The die is then closed and prepared for the next shot as it is capable of being reused immediately. In this way, the die is able to produce thousands of castings in rapid succession.

The die casting machine consists mainly of two heavy platens, one fixed and one moving, which accommodate the dies, these normally being fabricated in two halves. The whole design is massive enough to withstand the very high pressures used, typically thousands of pounds per square inch. It is essential to keep the dies well-lubricated to prevent the casting from adhering to them as well as to provide a better finish. Cleaning of the dies is also a necessary routine, especially to remove unwanted scraps of metal which might prevent the dies from closing on the next shot with resulting  damage2.

The benefits of die casting3  as a manufacturing process are:

·         High-speed production

·         Dimensional accuracy and stability

·         Good strength to weight ratio

·         Corrosion resistant

·         Multiple finishing techniques (i.e. smooth or textured)

·         Simplified Assembly

 

A Brief History

The art of casting metal in permanent molds can be traced back millennia. Archeologists have uncovered evidence which indicates that ancient human beings had learned to fashion and bake clay into useful objects. In the Bronze Age, the molds were one piece and open-topped; the castings produced were flat on one side and required to be hammered to make the final shapes. By 3000 B.C., copper and bronze were fabricated and cast into weapons, tools as well as vessels designated for ritual practices4.

The advent of the die casting as a manufacturing process in modern times can be attributed to the need to improve printing methods. In 1439, Johann Gutenberg invented a process for making printers’ type-letters or a continuous text—from a lead alloy cast into a permanent mold. Hence, each letter was identical to every other casting of the same letter. This greatly expanded the capabilities of the printing industry. The first patent was awarded in 1849 for a small, hand-operated machine that helped to mechanize print production. 

Application of Die Casting

  • Automotive parts
  • Engine components
  • Plumbing parts
  • Aerospace castings
  • Appliance housing parts
  • Electric motor housings
  • Hand and power tool components

 

Example of a part produced through die casting

 

Die casting is apt for producing small- to medium-sized parts with intricate details. Most die castings are created from non-ferrous metals such as zinc, aluminum, lead and magnesium due to their excellent properties. Here is what each alloy is good for:

Zinc:

Zinc base alloys are the easiest to die cast. Ductility is high and impact strength is excellent, making these alloys suitable for a wide range of products.

The flow properties of zinc alloys allow for thinner walls and longer tool life. Zinc castings are ideal for metal plating or polishing. The potential drawback to zinc alloys is the weight (approx. 2.5 times the weight of aluminum).

Aluminum:

Aluminum die casting alloys are lightweight, offer good corrosion resistance, ease of casting, good mechanical properties and dimensional stability.

The lightweight of aluminum is ideal for keeping manufacturing costs down. Aluminum castings are best used as-cast or with an anodized coating and/or powder-coating. For nickel, chrome and gold plating, zinc castings are suggested.

 

Visit http://cmpdiecasting.com/casting-terminology to access a glossary of die casting terms.

 

Sources:

1. Picture source: Zitai Precision Machinery website

2.  NADCA (North American Die Cast Association)

 Robotics in Practice by Joseph F. Engelberger

4. Die Casting Metallurgy by Alan Kaye & Arthur Street