What Is Die Casting?

by Sarah Maher, October 2, 2017

What is Die Casting?

Die casting is a type of metal casting that uses the process of forcing molten metal into two steel dies that make up a cast. Die casting is typically used in a high-volume production setting and is known for producing a high-quality, consistent product. The foundry equipment used for the die casting process typically has a higher initial cost compared to processes that use sand molds. However, the day-to-day cost of manufacturing using die casting tends to be on the lower end, producing a lower cost per item.

History of Die Casting

The die casting process was originally devised in 1838 to create “movable type” machines (think of a giant stamp with movable letters). The first patent related to the die casting process was eventually received in 1849 about 20 years later. When die casting equipment became available to the North American market the applicable uses spread as well. In the 1900s, a mixture of tin and lead were used for die casting and would go through several different trends before the use of aluminum became the best option.

Why is it Called Die Casting?

Die casting gets its name from the dies used in the molding process. The molds in which the molten metals are injected are referred to as ‘dies’, creating the name for the technique, die casting.

Metals Used in Die Casting

The metal used in die casting is determined by the purpose of the product being made. For example, automobiles and similar projects typically use aluminum because it is lightweight while medical supplies commonly use stainless steel for its corrosion resistance, manufacturing precision, and hygienic qualities. While various metals can be used in die casting, the metal being used must be able to maintain its properties during the melting process.

The most commonly used metals used in die casting are:

Aluminum
Zinc
Tin
Magnesium
Lead
Copper alloys
Stainless steel

Modern Methods

Low-pressure die casting is performed using a vertical process that shoots the molten metal upward against gravity. The metal travels from the furnace below by a piston using low pressure through a shot chamber into the two molds. The two molds are made of aluminum alloys; one is fixed while the other is able to be pulled away to let the casting free itself from the mold once cooled. The pressure is maintained in the mold while the metal cools to ensure an even and accurate fill. As the metal cools, further molten metal can be added to fill any missed or shrinking cavities. The only downside to low-pressure is the slower casting cycle, however, this die casting process is a cheaper, less-complicated technology as compared to high-pressure die casting, and lends itself to automation.

Pros:

Good strength values
No complicated machinery and die technology
High material utilization, No feeders needed
Well-suited for automation
High dimensional accuracy

Cons:

Slow casting cycles
Has a minimum wall thickness of 3mm (in die)

High-pressure die casting is the new craze when it comes to this method of metal casting. As opposed to low-pressure die casting, high-pressure die casting has a shorter casting cycle and utilizes a horizontal casting process instead of vertical. High-pressure die casting is created by two machine plates on either side that lock together to create a mold in the middle, like a die casting sandwich. The molten metal is pushed through the chamber with a piston at high speed and high pressure to fill the mold. Once the metal has solidified, the die is opened and the casting removed. Because of the expensive nature of the machine and its dies, high-pressure die casting should be reserved for high-volume production runs.

Pros:

Short casting cycles
Good for thin-walled components
Smooth surfaces
Good for automation

Cons:

Complicated and expensive dies
Lower strength values
Die-cast weight limited by the locking force of the machine

While this new trend speeds up the process, there are a few drawbacks to using high-pressure die casting. High-pressure die casting is a big investment while low-pressure die casting is a cheaper option. The process is also limited to smaller parts as the locking mechanism can only handle up to a certain weight. However, this has prompted the ability to make stronger castings of lesser weight using aluminum alloy, a change that has brought great benefits to other industries looking to minimize the weight of their cast parts and components, including automotive, aviation, electronics, and general hardware.

Hot Chamber Die Casting

The hot chamber die casting process, sometimes referred to as gooseneck casting, is an efficient die casting process when working with metals that have lower melting points such as magnesium, zinc, and lead. The holding pot is filled with metal and is melted by a built-in furnace. The piston then quickly pushes the metal into the die. The average hot chamber die casting cycle takes approximately 15 seconds.

Pros:

Short casting cycles
Fewer steps in die casting process
Metal melted within machine

Cons:

High melting point metals cannot be used
Limited product complexity

Cold Chamber Die Casting

This form of die casting uses a separate furnace to melt the metal. Once the metal is molten, it is transferred to the machine via an injection cylinder. The injection cylinder forces the metal into the die with a piston.

This process takes longer than hot chamber die casting because it requires a separate furnace and transferring the molten metal into the machine adds time to the production cycle. While cold chamber die casting takes longer, it allows its user more variability in the metals being used as the separate furnace can reach higher temperatures, allowing for metals with a greater melting point to be injected into the die.

Pros:

Compatible with high melting point metals
Allows for greater product complexity

Cons:

Longer cycle time compared to hot chamber die casting
More machinery required

Why Choose Vibratory For Die Casting?

After the die casting process, castings are moved for further processing or checked for quality. In some cases, if the standards are not met the casting will be sent back to the furnace to be melted and recreated. This process requires a system of vibratory conveyors and feeders to move the castings where they need to go.

Why is vibratory better? Belt conveyors simply cannot handle as much volume and wear quickly, while vibratory conveyors and feeders can handle larger castings and scrap without being damaged or melting from the heat. General Kinematics offers a wide range of die casting equipment, including the V-TROUGH® Vibratory Inclined Conveyor, TRENCHVEYOR™, and TWO-WAY™ Vibratory Feeders. Each of our pieces of equipment is customizable to fit your needs.