A high strength-to-weight ratio, excellent thermal conductivity and good corrosion-resistance are just some of the reasons for using aluminum. If you’re looking for low mass, good heat transfer, or the opportunity to avoid coating processes, precision aluminum investment casting is probably the process to use. Here’s an explanation of why that is.

Applications for Aluminum Alloys

Aluminum is a good choice for weight-sensitive applications like those found in automotive and especially aerospace. A strong affinity for oxygen means it quickly develops an oxide layer that resists corrosion, and this can also remove the need for coating. This makes it popular in architectural and marine applications. In addition, it’s widely used as a material for heat-exchangers, often in the form of fins cast onto a surface.

Investment Casting Facilitates Near Net Shape Manufacturing

Investment casting is ideal for producing metal shapes that need little to no secondary machining. This stems from the manner by which the casting mold is produced.

This mold is made by coating a wax pattern with a ceramic slurry. After applying multiple layers and allowing this “shell” to dry, the wax is melted out, leaving a cavity for the metal to fill. The wax pattern needs no draft angles as it shrinks enough to release easily from the mold it’s formed in, and the surface finish is determined by the size of particles in the first ceramic layer.

These characteristics mean investment casting can reproduce fine detail and create surfaces that don’t need machining. Walls can be as thin as 0.070” and surface finishes of 125 (Cast microfinish comparator) RMS or better are achievable. Linear accuracy is usually quoted as +/-0.010” per inch although +/-0.020” is possible over a length of 3”.

Investment Casting Aluminum

Aluminum melts at a relatively low 1,250 – 1,350 °F and exhibits more fluid behavior than many other alloys. This lets it flow easily into thin sections like those required for heat-exchanger fins.

Many aluminum alloys are suitable for investment casting. Those most commonly used are A356 and C355. These are typically heat treated after casting to increase toughness.

Where a cast part requires internal features or cavities these are produced by using cores in the wax pattern. If these are to be removed before shell coating they are made from a soluble form of wax that washes out with soft Citric acid solution. Alternatively, if they will be incorporated into the ceramic mold they are made from a ceramic and broken out after the metal has solidified.

Benefits of Producing Aluminum Parts by Investment Casting

Investment casting parts in aluminum supports mass reduction goals by minimizing the amount of metal needed. The ability to get very close to final geometry also reduces machining, which can lead to significant cost savings and reduce manufacturing lead time. It can also improve part functionality, as when cooling fins are incorporated into a design.

Another benefit is that, using investment casting, otherwise separate parts can be consolidated into a single larger part. This avoids the need for welding, which can be challenging with aluminum, and the alternative of using fasteners, and usually simplifies assembly.

Impro Can Help You Explore Investment Casting Feasibility

By investment casting parts designed to be made in aluminum it’s possible to reduce mass, improve functionality, and save money. This results from the near net shape nature of investment casting, combined with the excellent castability of most aluminum alloys.

Our foundry specialists can help determine the potential for investment casting a particular design in aluminum. Contact us to schedule that discussion.