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Aluminum and Brass Die Casting - An Overview of Two Popular Metal Casting Processes

Die casting is a metal casting process that involves forcing molten metal under high pressure into a mold cavity to form parts and products. Two of the most commonly die cast metals are aluminum and brass. Aluminum and brass die casting offer several benefits over other manufacturing techniques and both have their specific advantages and applications. In this article, we’ll provide an overview of aluminum and brass die casting, their differences, benefits, and uses.

What is Die Casting?

Die casting is a manufacturing process in which molten metal is injected with force, using a die casting machine, into a mold cavity or die to form products and parts. The mold cavity is created using two hardened steel dies which have been machined into the desired shapes. The molten metal, usually non-ferrous metals such as aluminum, zinc, or copper alloys, solidifies within the die cavity and the part is then ejected once fully solidified and cooled.

Die casting is characterized by its high production rates, ability to produce complex shapes with tight tolerances, and smooth cast surfaces which often don’t require additional finishing work. It’s an efficient process suitable for high volume production of small to medium sized metal parts and products. The most common metals used in die casting are aluminum, zinc, magnesium, copper, and alloys of these.

Aluminum Die Casting

Aluminum is one of the most popular metals used in die casting. Aluminum parts can be produced quickly and precisely through die casting. Some major benefits of aluminum die casting include:

- High dimensional accuracy and repeatability - aluminum castings can hold tight tolerances down to +/- 0.005 inches.

- Smooth cast surfaces with good finishing - minimizes the need for secondary machining or finishing.

- Fast production rates - aluminum has a short solidification time which allows for faster cycling of the process.

- Excellent corrosion resistance and weatherability - suitable for outdoor applications and exposure to weather.

- Lightweight - aluminum is a lightweight metal which can produce lightweight, strong castings.

- Highly durable and wear resistant.

- Ability to produce complex shapes, internal cavities, and thin walls in castings.

- Lower melting point than steel and iron allows easier casting and flow into the mold.

Aluminum die castings are popular across many industries including automotive, aerospace, electronics, industrial machinery, and consumer products. Major automotive parts produced via aluminum die casting include engine blocks, cylinder heads, transmission housings, and wheels. Other common aluminum die cast products include electronic housings, power tools, appliances, furniture, and medical equipment components.

The most commonly used aluminum alloys for die casting include 380, 383, and 413. Alloy 380 offers excellent corrosion resistance, 410 has high strength, and 413 provides optimal castability.

Brass Die Casting

Brass is an alloy composed mainly of copper and zinc. Like aluminum, brass is commonly die cast into a variety of products and parts taking advantage of its beneficial properties. Some major advantages of brass die casting include:

- Excellent machinability - brass is easy to drill, saw, and machine.

- High corrosion resistance - brass has good corrosion resistance especially in non-saltwater environments.

- High dimensional accuracy - can achieve precise tolerances in brass castings.

- Good impact and wear resistance - durable for parts subject to friction and movement.

- Attractive appearance - provides bright, golden color and luster.

Brass die castings are used for indoor applications that need to resist corrosion such as plumbing fittings and valves, gears, musical instruments, door hardware, and marine components. Brass alloys used for die casting include yellow brass (copper-zinc), naval brass (copper-tin-zinc), and others. Two popular specific brass alloys used in die casting are alloy 360 which has excellent corrosion resistance and alloy 377 which has high strength.

Aluminum vs. Brass Die Casting

When deciding between aluminum and brass die casting, there are some key differences that help determine the best material choice:

- Aluminum is lighter in weight than brass. Aluminum has a density about one third that of brass.

- Brass has higher hardness and is stronger than most cast aluminum alloys.

- Brass has superior machinability compared to aluminum.

- Aluminum has better corrosion resistance than brass, especially in marine environments.

- Brass maintains its strength and hardness at higher temperatures compared to aluminum.

- Die cast aluminum parts can be produced faster than brass, due to faster solidification time.

- Brass provides an attractive golden color while aluminum has a greyish appearance.

- Aluminum die casting is overall a cheaper process than brass die casting.

- Brass produces less flash during the casting process resulting in lower finishing costs.

In general, aluminum die casting is preferred for applications requiring lightweight parts with good corrosion resistance such as automotive components, outdoor products, and consumer appliances. Brass die casting is ideal for indoor corrosion-resistant parts, products needing good machinability and wear resistance, and attractive decorative components.

The Die Casting Process

The die casting process consists of three main steps - filling the die, solidification, and part ejection:

1. The mold halves (dies) are sprayed with lubricant and closed together to form the mold cavity. Molten metal, heated to between 900-1650°F is shot into the die under high pressures of 10,000-45,000 psi.

2. Once the mold cavity is filled, the metal rapidly cools and solidifies into the final part shape, aided by water cooling channels in the dies. This solidification happens quickly, often in 15-90 seconds.

3. After full solidification, the mold halves open and the cast part is ejected using ejector pins. The part may then undergo secondary finishing operations if required, such as surface treatments, drilling, or polishing.

Die casting produces 1-4 parts per cycle and several thousand parts per hour. It is ideal for complex, high volume production. The most commonly used die casting machines are cold chamber and hot chamber. Cold chamber machines are used for metals with higher melting temperatures like aluminum and brass.

Benefits of Die Casting

Some of the many benefits and advantages of the aluminum and brass die casting process include:

- Ability to produce intricate, complex shapes and geometries within tight tolerances.

- Smooth cast surfaces and accurate details from the hardened steel dies.

- Rapid production rates make die casting ideal for high volume production.

- A wide selection of alloy compositions available for die casting.

- Parts have excellent uniformity and consistency.

- Low labor requirements after initial die fabrication. Highly automated process.

- Minimal scrap losses due to reusable sprues and runners.

- Applicable to small parts weighing just ounces up to much larger components.

- Allows consolidation of parts into one component.

Aluminum and brass die casting is an efficient, precise manufacturing process capable of producing millions of consistent, complex metal parts. Both aluminum and brass offer their own advantages and are used widely across many industries. With its rapid production rates, high accuracy, and flexibility, die casting using these two versatile metals will continue seeing significant use for years to come. CNC Milling