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Brass and Aluminum Die Casting - An Overview

Die casting is a manufacturing process that can produce precisely dimensioned, sharply defined metal parts through the use of reusable molds, called dies. Molten metal is forced into the dies under high pressure and held under pressure until it solidifies. The process is known for its ability to produce complex geometries with good dimensional accuracy and repeatability at a relatively low cost. Die casting is widely used across many industries to create metal components for applications ranging from automotive parts to consumer products. Two of the most commonly die cast metals are brass and aluminum.

Brass Die Casting

Brass is a copper-zinc alloy with good strength and ductility along with excellent machinability, wear resistance and corrosion resistance. The brass used for die casting typically contains 60-65% copper with the balance being zinc. Brass die castings can be produced with excellent dimensional tolerance and smooth, defect-free surfaces at a relatively low cost.

Some key advantages of brass die casting include:

- Excellent dimensional accuracy and tolerances compared to other casting processes due to the high pressures involved. Complex shapes can be cast with very tight tolerances.

- Good surface finish quality that minimizes or eliminates secondary machining. The die cavity surfaces can be polished to produce castings that do not require surface finishing.

- Faster production rates and lower labor costs compared to sand casting or investment casting. High production rates are possible.

- Wide range of available alloy compositions to suit different property requirements. Leaded brass alloys provide excellent machinability.

- Excellent mechanical properties. Brass castings can be age hardened to high strengths.

- Very good corrosion resistance and wear properties in many environments.

Brass die castings are commonly used for:

- Plumbing fixtures, valves, and pipe fittings
- Electrical components, terminals, connectors and switchgear
- Automotive parts like locks, knobs, and hinges
- Musical instruments
- Costume jewelry
- Zippers, buckles, and other garment hardware

Aluminum Die Casting

Aluminum is a lightweight, corrosion resistant metal with excellent castability. Aluminum die castings offer a good strength-to-weight ratio along with high dimensional accuracy. The aluminum alloys used for die casting contain over 90% aluminum and are available in different alloy compositions with silicon and/or magnesium as the main alloying elements.

Some key benefits of aluminum die casting:

- Light weight compared to zinc or brass die castings. Density is around one third that of brass.

- Excellent castability for complex, thin-walled castings. Casting thin walls down to 1 mm thickness is possible.

- Fast production rates and lower costs versus other processes like sand casting.

- Very good dimensional consistency for tight tolerance requirements.

- Wide range of mechanical properties depending on alloy. Heat treatable alloys can achieve high strengths.

- Good corrosion resistance in many environments. Protective anodizing coatings can further improve corrosion protection.

- Excellent thermal and electrical conductivity.

- Can be cast into permanent molds for lower cost, higher volume production.

Common applications of aluminum die castings:

- Automotive parts like housings, pistons, and valve bodies
- Consumer appliances and electronics
- Furniture hardware
- Computer and business equipment housings
- Lighting components
- Medical equipment parts

The aluminum die casting process is suitable for producing high volumes of net-shape components at low cost. Aluminum is the most widely die cast metal today due to its many benefits.

The Die Casting Process

While brass and aluminum are the two most commonly die cast metals, others like zinc and magnesium can also be die cast. The basic die casting process steps are similar regardless of the alloy:

1. Molten metal is poured from a furnace into a shot sleeve. The metal needs to be maintained within a certain temperature range specific to the alloy, usually 700-1500°F depending on the metal.

2. A hydraulic or mechanical piston then forces the metal from the shot sleeve into the die cavity at high speeds and under high pressure. Typical pressures range from 5000 - 20,000 psi depending on the metal and application.

3. The metal rapidly fills the die cavity, taking on the shape of the part. It is held under pressure until fully solidified.

4. After solidification, the die opens and the casting is ejected. The casting will be close to the final shape, with fine details faithfully reproduced from the precision machined die.

5. Secondary operations like trimming, grinding or machining may be required to bring the casting to the final dimensions. Surface treatments like polishing or plating can also be done.

6. The dies are sprayed and lubricated then closed again to repeat the high speed cycle. With multiple cavities in a die, production rates can be quite high.

Die casting owes its name to the hardened tool steel dies which shape each casting. These dies come in two halves - a fixed half and a moveable half. They must withstand tremendous temperature and pressure cycles throughout production. Precision CNC machining is used to create the die cavity surfaces as well as internal water cooling channels in the dies. Dies require ongoing maintenance and repair as they wear over time. New dies are manufactured when design changes are needed.

Quality Considerations

Like any manufacturing process, die casting has certain limitations in terms of tolerances, surface finishes and properties. Engineers and designers need to account for these factors when designing parts for die casting production.

Some key design considerations for die casting include:

- Minimum wall thickness requirements based on the alloy - typically 0.5 mm for aluminum and 0.8 mm for brass

- Generous internal radii needed to avoid thin sections

- Draft angles on surfaces to allow for die ejection

- Positioning holes and bosses away from parting lines

- Accounting for typical dimensional tolerance capabilities

- Avoiding overly complex geometries or small deep pockets

- Designing uniform wall sections to prevent sink marks or voids

- Accounting for post-cast machining requirements

Working closely with an experienced die caster in the design phase helps ensure that parts are designed for optimal manufacturability and quality via the die casting process. Computer modeling and structural analysis are also used to simulate and optimize the fill dynamics of a proposed die casting design today.

Die casters employ numerous quality control checks during and after production. Dimensions, wall thickness, surface finish, mechanical properties, leak testing and performance testing may all be conducted per internal specifications or customer requirements to ensure each production run meets quality standards. With its ability to produce quality, precision cast metal components at high production rates, die casting will continue to be a valued manufacturing process across many essential industries. Both brass and aluminum die casting offer unique performance benefits suitable for a wide range of demanding applications. CNC Milling