Die casting is a manufacturing process that injects molten metal between two mold castings under high pressure. It’s ideal for companies that need a dependable, quality source of high-volume, complex metal parts. The die-casting process is most commonly used to produce light metal original equipment manufacturer (OEM) parts for automotive, power vehicles, appliances, motorcycles, plumbing fixtures and other applications.
Die Casting Techniques
There are two different die-casting techniques: cold-chamber die casting and hot-chamber die casting. These approaches each offer different production advantages.
Hot-Chamber Casting
- This method is primarily used for casting low melting-point metals such as zinc, lead and tin.
- The metal is heated, melted and transferred to an injector inside the equipment.
- The melting furnace and molten metal holding cauldron are built within the casting equipment.
- The casting equipment is sometimes referred to as gooseneck equipment due to the shape of the injection conduit.
Cold-Chamber Casting
- This is the casting method of choice for high melting-point metals such as aluminum, magnesium, copper and high-aluminum zinc alloys
- The raw material metal is melted with a furnace that is external to the casting equipment.
- Molten metal is moved from the melting cauldron to the injection chamber using a ladle or other transfer device.
- This approach uses higher temperatures and pressures than the hot-chamber casting method.
The Die-Casting Process
The die-casting process involves the following four steps:
Step One: Melting the Metal
First, the metal to be used is melted in a heated cauldron. This may be internal to the equipment in the case of a hot-chamber casting process, or it may be external to the equipment in the case of a cold-chamber casting process. Because the process is continuous, a constant supply of molten metal is needed, so metal must be added to the melt as production proceeds.
Step Two: Measuring the Shot and Preparing the Mold
Next, a precise and predetermined quantity of molten metal is drawn into a “shot,” or pressure chamber. This shot or quantity of metal will be injected into the mold.
The mold itself (or die) is made of two halves: the cover die and the ejector die. The cover die (half of the mold) is held in place by a stationary platen, a heavy, unmovable steel block that holds the cover die in place during the casting process. The ejector die (the other half of the mold) is mounted on a movable platen that slides back and forth. This half of the die contains a hole through which the molten metal is injected.
Step Three: Closing the Die and Injecting the Metal
To begin the molding cycle, the movable platen holding the ejector die slides forward and presses against the cover die. The two die halves are then held together under high pressure — up to 1900 tons of force.
While the two halves of the die are squeezed together, the molten metal in the shot chamber is injected into the die using tremendous force. This step must be completed rapidly to prevent any solidification of the casting metal before the die is filled.
Step Four: Opening the Die and Removing the Cast Part(s)
The platens hold the die halves together until the metal freezes. Once the casted part is in a solid state, the movable platen retracts, carrying the ejector half of the die along with the completed piece.
Tongs (often robotic) grasp the completed part, while ejector pins in the ejector half of the die push the completed part out of the die. The part is then held while excess material, known as flashing and sprue, is removed. In many cases, this excess material can be re-melted and reused. The piece then moves to finishing.
What Are the Advantages of Die Casting?
In addition to the economical production of high volumes of quality parts, die casting offers the following advantages to manufacturers:
- Excellent part dimensional accuracy
- Inserts can be cast-in
- Thinner walls, compared to other casting methods
- Quick delivery of high production volumes
- Smooth surface finishes and reduced secondary machining requirements
- Long mold life — 100,000 shots or more
Die-cast parts also offer excellent dimensional accuracy, as well as outstanding structural and mechanical properties such as dense, fine-grained surface textures and high fatigue strength. Depending on metals used and parts design, metal densities and porosities can be controlled. Parts made from many non-ferrous metals are excellent candidates for the die cast process. Many of these include:
- Aluminum
- Zinc
- Copper
- Magnesium
- Lead and pewter
Final part characteristics vary depending on part geometry, metals used, end-use requirements and size. Following casting, parts are deburred and can be machined, assembled to other parts or polished. Also, final processing can apply surface coatings such as painting, plating, powder coating or printing.
Connect With VPIC To Discover Our Aluminum Die-Casting Capabilities
Outstanding aluminum die-casting capabilities are only one of many OEM parts manufacturing processes VPIC offers our customers. To see our full range of services, visit our website or connect with us via our web-based contact form to discuss your next project and receive a quote.
