Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high-volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small- to medium-sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.
ALUMINUM CASTING METALS
Aluminum castings are lightweight and able to withstand the highest operating temperatures of all die cast alloys. As a fabrication process, die casting is notable for its capacity to manufacture parts with a high degree of uniformity, close design accuracy, and quality surface finishes. In many cases, die casting can reduce or eliminate the need for post-production machining, raising the cost-efficiency of the process and shortening fabrication time. While it may be difficult to die cast sturdier metals, such as certain grades of steel, there are many other types of well-suited for die casting methods.
Die casting molds are usually constructed from hardened steel and they are often the most expensive component in a die casting machine. These molds can handle a range of different alloy families with varying results, but die casting is generally most effective on metals with low fusing temperatures. For this reason, the common die casting alloys fall into a handful of categories based on their composition and material properties.
Aluminum Alloy Characteristics:
High operating temperatures
Outstanding corrosion resistance
Very good strength and hardness
Good stiffness and strength-to-weight ratio
Excellent EMI and RFI shielding properties
Excellent thermal conductivity
High electrical conductivity
Good finishing characteristics
Aluminum’s strength, corrosion resistance, and heat dissipating properties offer mechanical designers significant advantages. And our proprietary Thin Wall Aluminum Technology has made aluminum die casting an option for even more applications. Die cast aluminum alloys are often found in automobile parts and gears, and have been used to create surgical instruments in the past. They are generally stronger and lighter than most zinc-based materials, but tend to be more expensive to create. Using aluminum alloys can reduce the need for finishing treatments, such as plating, and a common grade is composed of 92 percent aluminum mixed with 8 percent copper. Magnesium may be added to this alloy to improve its tensile strength from around 21,000 pounds per square inch to approximately 32,000 per square inch, while nickel can be included to increase rigidity and provide a higher surface finish. The melting point for an aluminum alloy is around 1150 degrees Fahrenheit.
Advantages of Aluminum Die Casting
One of the most significant benefits of aluminum die casting is that it creates lighter parts—with more surface finishing options than other die cast alloys. Aluminum can also withstand the highest operating temperatures of all the die cast alloys. Moreover, cast aluminum is versatile, corrosion resistant; it retains high dimensional stability with thin walls and can be used in almost any industry.
Read more about thin-wall aluminum die casting.
Aluminum Die Casting Applications:
Aluminum castings improve automotive fuel efficiency by contributing to weight saving requirements
Aluminum is used in a broad range of networking and infrastructure equipment in the telecom and computing industries because RF filter boxes and housings require heat dissipation
In handheld devices, aluminum castings provide EMI/RFI shielding, rigidity, and durability with minimal weight
Because of aluminum’s excellent electrical performance and shielding properties, even in high-temperature environments, die cast aluminum is ideal for electronic connectors and housings
Recycling Aluminum Die Castings
Did you know that over 95 percent of aluminum castings made in North America are made of post- consumer recycled aluminum?
There is very little functional difference between primary (extracted or pure) and secondary (recycled) aluminum when it refers to die casting. Secondary aluminum alloys are derived from mixing and melting pure aluminum with other materials such as magnesium, iron, and copper. The use of pure aluminum in casting is quite rare due to the cost of extraction. The ease of use in die casting combined with lighter weight and durability make aluminum alloys a top choice for designers from nearly any industry.
Secondary aluminum is more economical to produce than primary aluminum because it only requires 5 percent as much energy to produce. Most of the energy consumption in aluminum die casting is used to heat and re-melt the metal during fabrication.
Pure aluminum is not suitable for most die castings. Aluminum is alloyed with a number of other metals to form a material that is very fluid at casting temperatures to promote proper die filling. Alloys are more resistant to soldering which prevents unnecessary wear on the part or die.
Aluminum Alloy A380
A380 is one of the most commonly specified aluminum alloys with a number of significant benefits and it offers a good balance of material properties along with ease of casting. The high usage of this also typically makes it the least expensive in terms of cost per pound. Typical applications include everything ranging from engine components and electronic devices to simple brackets and hardware.
Aluminum Alloy 383
If your component is highly intricate, 383 is often used as an alternative to A380.
B390 is an aluminum alloy with high hardness and good wear resistance.
A413 is an aluminum alloy with excellent pressure tightness, corrosion resistance, and resistance to hot cracking. It is among the easiest of the die cast alloys to cast and can be useful for making intricate components as well as pressure tight vessels such as pneumatic or hydraulic cylinders.
413 is an aluminum based alloy that is used for die casting parts.
K-Alloy is an aluminum, cold-chamber die cast alloy that was engineered to protect components against harsh operating environments.
A360 is an aluminum alloy with excellent pressure tightness and fluidity. It alloy has increased corrosion resistance and thus offers better protection for unpainted or scratched surfaces when exposed to corrosive environments. It also offers better strength properties at elevated temperatures and slightly improved ductility. These characteristics are offset by an increased difficulty to cast which results in higher cost to manufacture parts.
DCA1 is ideal for components such as cases or heatsinks that require high thermal and electrical conductivity, as well as corrosion resistance.
518 alloy offers the best combination of corrosion resistance, strength, and ductility but is one of the most difficult to cast. The low amount of Silicon in its composition contributes to this difficulty to cast but also gives it high machinability and the best finishing characteristics when it comes to polishing and anodizing. This alloy is also typically more harsh on tooling, resulting in a lower tooling life.
Zinc-based materials are relatively easy to die cast, and respond well to the die molding process. These materials are comprised of multiple metals in specific ratios. For example, a typical zinc-based die casting work piece consists of 86 percent zinc, 4 to 7 percent copper, and 7 to 10 percent tin. Slightly higher proportions of tin make the work piece more flexible, while increased copper levels improve rigidity. Zinc alloys have a melting point in the range of 700 to 800 degrees Fahrenheit.
Zinc Die Castings
Zinc die castings are often used in place of cast iron or brass, but tend to have lower tensile strength than their sturdier counterparts. Unless it is specially reinforced during the alloying process, zinc-based material cannot exceed approximately 17,000 pounds per square inch of force. As a result, die cast zinc products are generally not used in applications involving high mechanical loads. Zinc castings can also be corroded by alkaline substances or salt-water, and are often plated to preserve their luster despite atmospheric conditions.
Tin, Bronze / Brass, & Lead Alloys
Alloys composed with a significant amount of tin as a base metal are most often used in applications requiring corrosion resistance, such as those involving the food industry or internal and external bearings. While the proportion of metals in these alloys can vary widely, a typical tin alloy consists of 90 percent tin, 6 percent antimony, and 4 percent copper, which is added to strengthen the material’s durability. Tin alloy die castings generally weigh under ten pounds and rarely exceed 1/32 of an inch in thickness. They are valued for their resistance to alkaline, acids, and water, but feature a comparatively low tensile strength rating of below 8,000 pounds per square inch.
Bronze / Brass Alloys
Most bronze and brass materials can be die cast as effectively as zinc-based alloys, although small holes can only be drilled into the work piece after casting, rather than during the casting process. Bronze and brass are commonly used to create washers, camshaft components, and decorative products (due to their distinctive coloring and potential for surface finishes). A typical brass alloy consists of 60 percent copper, 40 percent zinc, and 2 percent aluminum, but there are many variations on this mixture. Die casting bronze and brass is capable of yielding products with a durable surface and highly accurate interior specifications.
Like tin alloys, lead-based materials tend to be used for their corrosion resistance and in applications requiring no more than 8000 pounds of tensile strength per square inch. Common applications include fire-safety equipment, bearings, and various decorative metal goods. They are relatively inexpensive for producing castings under 15 pounds, but lead alloys cannot be used for products that will be in contact with food. A typical lead alloy might be 90 percent lead and 10 percent antimony, with tin being a common addition as well. The melting point is usually around 600 degrees Fahrenheit, and product thickness rarely exceeds 1/32 of an inch.