Die Casting: An Overview

What Is Die Casting?

Die casting is a process in which molten material is poured or forced into a mold cavity. This negative shape approach is identical in principle to all molding and casting processes, but it differs in almost every essential detail. The hardened tool-steel parts that form the cavity are pressed together by a hydraulic press, ensuring the closure faces meet precisely as a seal. Some parts require that the tool be heated at this point, while others form better with the cavity cold. 

It is called die casting because a "die" is a variably defined word for "tool". Most other casting processes such as sand casting and investment casting destroy the cavity in making a single part. Die casting is unique in leaving the cavity undamaged by casting a part. The earliest use of "die" as a term likely relates to the stamping tools for coins, which forge the metal in a cavity to form a precise shape.

Die casting originated with the casting of printer parts such as gears and bell cranks in the early/mid-19th century. The parts were simple: the tools were iron and coarsely made and the fill was hand poured from a ladle. The process developed over the 20th century to become a mainstay of high-volume metal component manufacture. Fully automated and complex production lines are now commonplace, although many of the more primitive origins of the process are still in meaningful commercial use—right through to hand ladle filling simple cavity tools.

Die casting is performed to produce low-cost, high-volume light metal components of high precision, repeatability, and strength. All alternative processes result in much higher cost parts, often of poorer quality and always much slower to manufacture.

It's an important process here at Xometry - we offer a leading die casting service.

How Die Casting Works

Die casting is performed by pressing the cavity together using a hydraulic press to ensure that the closure faces are sealed. Some tools are heated while others are left cold to create the part. Filling of the cavity with molten metal can be low pressure (gravity feed or gravity die-cast) or high pressure (pressure die-cast) using a hydraulic ram. Higher pressure allows finer features and thinner sections to fill effectively. Lower pressure requires lower-cost equipment and lighter tooling, but it is only suited to simpler profiles and thicker sections.

Fast processing tools for volume production are generally water-cooled, to speed solidification and reduce cycle times. However, cycle times are considerably longer than for the related plastic injection molding. The thermal capacity of metals is considerably higher, requiring bigger temperature reductions to reach an ejectable solid. 

Types of Die Casting

The different types of die-casting processes are listed below:

1. Cold-Chamber Die Casting

Cold chamber die casting is used for higher melt-point metals like aluminum and lower-volume production. The injection chamber is charged and injected with molten metal. The chamber relies on the heat of the charge to make a stable processing temperature. This is a lower cost to set up and requires less maintenance but can produce more variability as the production rate stabilizes, leading to a good injection temperature in time.

2. Hot-Chamber Die Casting

A hot chamber or goose-neck casting is the more widely used process. It is better suited to higher volume but requires more system costs and more maintenance to preserve good production quality. The injection chamber is immersed in the molten bath it is fed from, maintaining charge temperature levels at the optimum for chamber fill.

Different Types of Die Casting Processes

• Gravity or Low-Pressure Die Casting: Lower complexity parts with thicker sections can be low-pressure cast by gravity-fed (even hand-ladled) fill, reducing equipment complexity and tooling cost. This is best suited to aluminum parts that are circular and symmetric.

• Vacuum Die Casting: The tool is placed above the molten reservoir and draws up the charge by a vacuum applied to the cavity. This process leads to lower porosity and lower turbulence. Parts made in this way are well suited to heat treatment processes, after casting.

• Squeeze Die Casting: Typical for higher-viscosity melts, this process fills the tool and then squeezes it closed, forcing the fill into the smaller cavity areas that otherwise would not typically fill easily.

• Semisolid Die Casting: This process, also called thixoforming, heats the shot (made of small pieces) to the liquid-solid phase transition temperature (thixotropic state) and this is then pressure fed into the cavity. The lower operating temperature reduces processing times and allows higher accuracy, as the bulk of the melt expansion occurs at or soon after phase change, so shrinkage is reduced.
• Pressure Die Casting: Finer and more complex parts generally require the charge to be pushed in at high pressure, to fully fill/form all features.

Materials Suitable for Die Casting

The materials used in die casting include a wide range of alloys. Some examples include:

1. Magnesium

Magnesium alloys are widely used for lightweight and high-strength parts. There are limitations in the processing, but magnesium alloys can achieve among the thinnest sections in die casting, because of very low viscosity in the melt.

2. Zinc

Zinc is very widely die-cast for many lower-strength applications. Zinc and commercial alloys it is a major constituent of are low-cost, easily cast, and sufficiently strong for many components such as enclosures, toys, etc.

3. Copper

Copper is not widely used in die casting, as it has a tendency towards cracking. It requires a high melt temperature, creating increased thermal shock in the tooling. When it is die-cast, it requires careful handling and a high-pressure process. For more information, see our guide on Copper.

4. Pewter

Pewter is a soft alloy, mainly tin, with antimony and traces of copper and bismuth. It is used purely for decorative objects and die casts easily in low-pressure equipment.

5. Aluminum

Aluminum alloys are by far the most important materials in volume die-cast production. They respond best to a hot chamber and high pressure—or more recently vacuum die casting—and provide moderate to high strength and high precision parts. Aluminum alloys are still critically useful in lower-tech processes, too.

6. Lead

ROHS has resulted in a significant reduction in the use of lead parts. They, however, remain critically important in the manufacture of (ICE) automotive battery parts, particularly terminals. Much development in lead die casting has improved overall automation and process speeds—developments that have fed through to other materials processing.

7. Tin-Based Alloys

Tin-based alloys impose very low wear and stress on tools due to low viscosity and melting point. While high-tin alloys (other than pewter) are rarely used now, the need does arise and specialists exist to serve in this.

Advantages and Disadvantages of Die Casting

Key advantages include:

1. It can repeatably reproduce designs for extremely complex and intricate components, with thin-walled features.
2. The use of salt cores allows complex internal galleries to be formed without tooling complexity or design compromise.
3. Some disadvantages include:
4. Parts are susceptible to shock loading and sensitive to high loads. Parts must be carefully designed with these limits (and a factor of safety, FOS) in mind, to ensure good part service life.
5. Typical tool costs start at $10,000 for a small part and rise rapidly with component size. Typical tool life between major services (resurfacing, new bearings, etc.) is around 100 to 150k shots.
6. Non-ferrous metals can only be die cast at lower melting temperatures.
7. Die casting can easily generate porosity in parts when the casting pressure is low (gravity die casting).
8. Only limited undercuts are possible, and these increase tooling costs and reduce service life. Most die-cast tools aim for open and shut—all features being in the line of draw/ejection. Where draws are required, the part design must flex to accommodate tool robustness and simplicity.

Common Applications of Die Casting in Key Industries

Some examples of die-casting applications are listed below:

1. Aerospace: A wide range of engines, seating, interior fitting, cockpit control, and other parts are die-cast in aluminum.
2. Toys: Many toys were formerly manufactured from die-cast zinc alloys such as ZAMAK (formerly MAZAK). This process is still widely used despite plastics taking over much of the sector.
3. Automotive: Many ICE and EV car parts are made by automotive die casting: major engine/motor components, gearbox/differential housings, vehicle wheels, thermostat housings, suspension parts, interior strength members, and more.
4. Electronics: Enclosures, heat sinks, hardware.
5. Military: Vehicle, weapon, and system components.
6. Furniture: Chair legs, decorative parts, joiners.
7. Consumer: Product heat-distribution chassis, enclosures, decorative and structural parts.

The Costs of Die Casting

The establishment costs for die casting are high. Tooling is complex and expensive and is built to be super robust. Because of this, die casting is not an appropriate method for low-volume manufacturing. However, the “sweet spot” for volume, when the higher cost of CNC-machined (from solid metal, or sand cast and post-machined) parts begin to match the tool amortization can be as low as hundreds of parts.

Xometry provides a wide range of manufacturing capabilities including die casting services as well as CNC machining, 3D printing, injection molding, laser cutting, and sheet metal fabrication. Get your instant quote today.

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