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Brass and Aluminum 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 steel mold or die to produce parts with tight tolerances and smooth surfaces. Two of the most popular metals used in die casting are brass and aluminum due to their favorable physical properties and relatively low melting points. In this article, we’ll provide an overview of brass and aluminum die casting, their typical applications, benefits and limitations.

Brass Die Casting

Brass is an alloy composed primarily of copper and zinc. The proportions of copper and zinc can be varied to produce different types of brasses with differing properties per specifications. Brass is highly malleable and has a warm golden color which makes it popular for decorative hardware, musical instruments, valves and plumbing fittings.

Brass die casting utilizes specialized machines to force molten brass at high velocity into the die cavities under high pressure. Typical clamping forces range from 55 to 150 tons. The most common brass alloys used for die casting include yellow brasses (15-37% zinc) and high-strength red and semi-red brasses (37-45% zinc). Brass melts at around 900°C making it easy to achieve and maintain proper molten metal temperatures.

The excellent fluidity, high ductility and ability to capture fine details makes brass well-suited for complex die cast parts. Brass die castings can be produced with very thin walls, intricate shapes and precise dimensional accuracy. Parts can be die cast near net shape, minimizing the need for secondary machining. Common brass die cast parts include valves, pump components, connectors, electrical fittings, door hardware and automobile parts like locks, latches and carburetor components.

Key benefits of brass die casting:

- Excellent dimensional accuracy and repeatability. Parts can be produced to tolerances of ±0.005 inches.

- Smooth cast surfaces with fine details. Minimal draft angles are required.

- Cast walls can be made very thin, maximizing material utilization.

- High production rates possible for large volume runs.

- Variety of attractive finishes possible like chrome plating.

- Suitable for intricate components with complex geometries.

- Very high mechanical strength and hardness.

- Recyclability - surplus brass is reusable.

Limitations of brass die casting:

- Relatively high part cost for small batch production. Significant upfront costs for dies.

- Size limitations based on die casting machine capacity. Generally under 4 pounds.

- Not suitable for parts with cross-sections less than 0.060 inches.

- Requires expert control of production variables (temperature, timing, pressure etc.)

Aluminum Die Casting

Aluminum is a lightweight, corrosion resistant metal with high thermal and electrical conductivity. It has roughly 1/3 the density and weight of brass. The most common alloy used for aluminum die casting is ADC (Aluminum Die Casting) which contains >90% aluminum along with silicon, copper, magnesium and zinc.

The low melting point (660°C), excellent fluidity and resistance to hot cracking make aluminum well suited for the high pressure die casting process. Shot speeds up to 1200 inches/second can be achieved. Clamping forces typically range from 150 to over 1,000 tons depending on part size. High production rates are possible with fast cycle times.

Aluminum die cast parts have high dimensional stability and repeatability. Complex shapes and thin walls down to 0.060 inches are possible. The high quality surface finish, corrosion resistance, strength-to-weight ratio and ability to integrate fine details makes aluminum a preferred choice for housings, covers, automotive parts, consumer products and industrial components.

Key benefits of aluminum die casting:

- Light weight. Density is 1/3 that of brass.

- Excellent dimensional precision and stability.

- Thin walls are possible to minimize material usage.

- Corrosion resistant and durable finish.

- High production rates and low cost per part, ideal for high-volume runs.

- Handles complex geometries well.

- Heat and electricity conductive.

Limitations of aluminum die casting:

- Relatively low melting point can limit service temperatures.

- Not as strong or hard as steel or iron castings.

- Limited in size based on machine capacity, usually under 15 pounds.

- Not suitable for parts with thin cross-sections below 0.060 in.

- Significant tooling investment for dies. Economical for long production runs.

- Tight control of process parameters needed for best results.

Die Casting Process Overview

The production of a die cast part involves several steps:

1. Molten metal is prepared - Brass is melted to 900-920°C while aluminum melts at 660-680°C. Precise control of melt temperatures is critical.

2. Mold lubrication - The die surfaces are sprayed with lubricant to facilitate easy part ejection.

3. High pressure injection - The molten metal is forcefully injected into the die cavity at speeds up to 1200 inches/second.

4. Cooling and solidification - Cooling lines surrounding the die quickly dissipate heat allowing the metal to solidify into the desired shape.

5. Part ejection - After full solidification, the die halves separate and the part is ejected using ejector pins.

6. Finishing - Secondary operations like trimming, drilling or tapping may be required to produce the final part. Surface treatments can be applied.

The entire cycle is usually completed in less than 60 seconds and can produce components with excellent quality and precision at fast rates. Die cast parts can be produced to net shape or near-net shape, often eliminating costly secondary machining operations. However, the high cost of custom tooling and machines makes die casting most economical for large production volumes, typically over 10,000 parts. The detailed design process and production trials ensure optimal die and product design before large scale manufacturing.

Choosing the Right Process

Determining if aluminum or brass die casting is most suitable depends on factors like:

- Annual volume or production quantity needed

- Complexity of part geometry

- Size and weight limitations

- Strength and hardness requirements

- Desired finish characteristics

- Operating temperature range

- Corrosion resistance needs

- Cost targets

- Mechanical property needs

Brass and aluminum die casting are complementary processes with some overlap in applications. Aluminum is usually preferred for larger, lighter components and housings. Brass is ideal for smaller, high strength and more intricate components like fittings, valves and intricate components. For moderate run sizes under 5,000 units, aluminum and brass investment casting may offer lower costs. Both brass and aluminum die casting offer optimal quality and value for medium to high volume production for parts that demand precision, repeatability and high strength. CNC Milling