Answering the 25 most asked questions about aluminum casting

22 May 2023

We answered the top 25 most frequently asked questions about the permanent mold aluminum casting process.

The Basics

1. What’s a casting?

While the word casting (noun) can be used to describe the finished product, casting (verb) can also be used to the describe the manufacturing method.

Metal casting is the process of pouring molten metal into a custom mold and shaping the metal as it solidifies.

2. Are there different casting processes?

There are three common casting methods: sand casting, die casting, and permanent mold casting. Other, less common, casting methods include lost foam casting and investment casting.

3. What metals are used for casting?

Iron, aluminum, bronze, zinc, steel, and copper are common metals used in casting. At Batesville Products, we cast aluminum (A356) and zinc (ZA5 and ZA12).

4. What aluminum alloys can be cast?

There are a variety of aluminum casting alloys, but we prefer A356. This alloy is preferred because of its castability, strength, weight, and corrosion resistance. A356 is also medical-grade and food-safe.

aluminum metal

Properties of Aluminum

5. Is cast aluminum heavy?

Compared to other metals, cast aluminum is very lightweight. The weight of the casting depends on the size, hollows, and density of the part.

For example, this large casting used on building corners is about twenty pounds.

6. Is cast aluminum strong?

Cast aluminum is very strong. Since it can withstand weight and stress, it’s often used in construction and industrial machinery.

To further increase strength and remove flexibility properties, aluminum castings can be heat treated. T5 and T6 are common heat treatments.

7. Where does aluminum come from?

Rio Tinto, a North American based aluminum producer, uses an advanced hydropower damming system to produce aluminum. Did you know that 40% of the cost of making aluminum is electricity? This hydropower system gives a competitive edge in comparison to coal burning smelters.

However, lots of aluminum in use today is recycled, or secondary. Aluminum is fully recyclable and can be recycled indefinitely without losing quality. Did you know 75% of all aluminum ever produced is still in use today?

8. Can cast aluminum be painted?

There are special air-dry or bake-on primers and paints for aluminum castings.

9. Can cast aluminum be powder coated?

Powder coating is one of the most common cast aluminum finishes. Know that castings must be prepped, cleaned, and degassed before powder coating for the best results.

10. Can cast aluminum be anodized?

Aluminum castings can be anodized or chromated to provide corrosion resistance, oxidation protection, wear resistance, strong insulation, heat transfer properties, and an aesthetic appearance.

11. What can you cast with aluminum?

You can cast almost anything with aluminum! From frying pans to dental chairs, fan blades to electrical housings. Here are some examples.

Where’s aluminum used? Aluminum is used to make products in hundreds of industries, including…

  • Electrical and Telecommunications
  • Medical Equipment
  • Food and Beverage Equipment
  • Industrial Machinery
  • Agriculture and Tools
  • Water Distribution
  • Mining
  • Décor, Architecture, Landscaping
  • Automotive, Transportation, Motorized Vehicles
  • Aerospace and Defense

12. Will cast aluminum rust?

Unlike iron, aluminum will not rust. To protect against other forms of corrosion, aluminum can be anodized or coated.

13. Will cast aluminum bend?

Aluminum is known for its high ductility. Unlike other metals, aluminum will bend before it breaks.

14. Can aluminum be welded?

Cast aluminum can be welded. It’s possible to cast different aluminum parts and welded them together to assemble your final product.

However, casting your product into 1 piece rather than machining and welding many pieces together saves a lot of time and money. We recommend working with one of our expert engineers to see how you can turn your project into 1 piece.

permanent mold casting

Permanent Mold Casting

15. What’s permanent mold casting?

Permanent mold casting is the gravity-fed process of pouring molten metal into a reusable steel mold.

16. How’s permanent mold casting different from die casting?

Both processes use a reusable steel mold to form metal castings. And both processes have a great as-cast surface finishes.

The main difference between die casting and permanent mold casting is the way the metal is fed into the mold. Die castings are quickly pressure injected, while permanent mold castings are gravity-fed by a slow tilt. This slow tilt means less internal porosity that could become an issue during machining.

Die casting tooling is more complex, meaning it can be up to five times more expensive than permanent mold tooling. Therefore, die casting process is ideal for high volume production runs (example: 50,000 pieces per year). It’s commonly used in the automotive industry. Permanent mold is ideal for moderate volume production runs (example: 5,000 pieces per year).

17. Why permanent mold?

Permanent mold is known for high-quality surface finish, low-porosity, high precision, repeatability, and easy secondary machining.

Permanent mold castings are denser than die or sand castings. Permanent mold is ideal for moderate volume production (500-20,000 pieces per year).

18. How much does permanent mold cost?

9 factors impact the cost of a casting.

The primary cost driver is mold tooling. Permanent mold casting is less expensive than die casting, but more expensive than sand casting.

Sand molds are one-time use, while permanent molds are reusable steel tools. Sand casting’s low-cost tooling and high piece price makes it ideal for low-volume production. However, you will often see a return on investment on permanent mold tooling if you are producing over 1,000 parts per year.

Die casting molds are complex steel molds that take longer to produce and can be up to five times more expensive than permanent mold. Therefore, you see best ROI on high volume production in die casting, and moderate volume production in permanent mold.

Keep in mind, all parts are custom. For a better cost estimate, please request a quote.

19. What’s the permanent mold as-cast surface finish?

Permanent mold castings generally have a surface finish of RMS 200-420.

coated and uncoated parts

Designing for Permanent Mold

20. What’s draft? Why do I need draft?

Draft is also known as taper. It is necessary in casting because it helps parts easily eject from the mold.

21. What’s the minimum wall thickness for permanent mold casting?

For permanent mold casting, we recommend a minimum wall thickness of 0.180 inches.

Avoid isolated thin or thick sections. These can negatively impact flow and solidification, and cause shrinkage.

22. What are as-cast tolerances for permanent mold casting?

Permanent mold holds tight as-cast tolerances. For even tighter tolerances, consider adding a quick secondary machining operation.

linear tolerance permanent mold casting


23. Why CNC machine a casting?

Castings are near-net shape of the final product. Sometimes, a secondary CNC machining operation is required to achieve tighter tolerances than permanent mold is capable of.

CNC machining also completes drilling, tapping, threading, or milling.

Casting then secondary machining is a great way to create a complex part. By first casting your project, you have a great starting point. Machining a near-net shape instead of a block of billet speeds up the CNC machining process. You can produce a complex part more efficiently.

Not sure if your casting needs CNC machining? Take this quiz.

24. What types of finishing options are available?

Permanent mold has a great as-cast surface finish. Aluminum casting finishing options are:

Zinc castings are preferred for mirror buffing or plating.

Not sure which finish to use? Use this flowchart to find your ideal finish.

25. How much extra material should be added for machining?

If you do not include a machine stock allowance in your design, the final part may be out of spec. Account for extra material if CNC machining your casting.

machine stock allowance casting

More Questions?

We’re ready to answer them. Contact our team today.

It never hurts to check

Request a quote and a Batesville team member will be in touch to discuss your metalcasting goals and how our metalcasting experts can help make your next project a success.