Die casting uses a two-part, tool-steel cavity to create a negative shape of the required component. This “hole” is then filled with molten metal which is chilled back to solid before the cavity is opened and the cast metal part removed. Die casting is often used in the production of low-cost light metal components with high precision and strength. This article will define die casting, the types, materials, where it is used, and its benefits.
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 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.
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.
3D printing helps die casting in terms of costs. The investment costs in preparation for die casting are significant. Tooling is generally made from pre-hardened steel, with cavities and tool features that must be spark eroded. Errors in the construction of such dies are very expensive. It is normal to make three or more generations of 3D-printed plastic prototypes for design validation. This will allow the designer to develop confidence in the limits, fits, force distribution, stress concentrations, and obvious failure modes. With the design evaluated in plastic 3D prints, it is always recommended to make a CNC machined or high-quality metal 3D printed prototype. This final generation is a performance and stress testing tool that allows complete design confidence before tool steel is cut. This way, ~$2,000 worth of prototypes will avert ~$10,000–$30,000 of errors, and weeks of potential delay. For more information, see our guide on 3D Printing.
The different types of die-casting processes are listed below:
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.
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.
The various types of die casting processes are:
The materials used in die casting include a wide range of alloys. Some examples include:
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.
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.
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.
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.
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.
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.
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.
Some benefits of die casting are:
Some limitations of die casting are listed below:
Some examples of die-casting applications are listed below:
It depends. Durability in die-cast parts is often a design issue—a matter of ensuring that the properties (strengths and weaknesses) of die-casting are properly considered. It is common for die-cast parts to give decades of service when the design of the part is correctly proportioned and allows for the loads and working conditions the part experiences.
Die-cast parts can be susceptible to corrosion, poor at abrasion resistance, lacking in ultimate tensile strength, ductile under shock loads and overloads, susceptible to creep, and susceptible to fracture. However, with good consideration of the weaknesses and good use of the great strengths of the process, die-cast parts can offer long service in high-demand applications and essentially unlimited service in lower-stress applications.
It depends. Expensive is a relative term, and the following considerations must be taken into account:
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 manufacture. 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.
This article presented die casting, explained what it is, and discussed the manufacturing process and its various applications. To learn more about die casting, contact a Xometry representative.
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