Air & Vacuum Melting Investment Casting
Air and vacuum melting are two different methods for heating metals for the investment casting process. What differentiates the methods, and when should you use one method vs another? Read on in today's blog to learn more!
Alloys used in extreme, failure-critical environments (such as jet engine components) often use vacuum melting.
What is Air Melting?
As its name suggests, air melting is an alloy melting method conducted in an open-air environment. Many alloys can be poured via air melt, including low and medium-carbon steels ( such as 1020 or 4140 steel), stainless steels, copper alloys, tool steels, and even super alloys like inconel.
Compared to vacuum melting, air melting is more straightforward and requires less sophisticated equipment, often making it a cheaper method for precision cast parts.
Why Not Always Use Air Melt?
Pouring in an open-air environment can introduce impurities and inclusions into the melted metal. Ambient air inside a foundry contains oxygen, nitrogen, hydrogen, other trace elements, and dust/other impurities, which can find their way into your components (creating oxides and other negative inclusions).
For many applications, these inclusions will have little to no impact on performance, especially when poured by a reputable foundry that pours metals to specifications and has a robust QC process. However, vacuum melting may be essential for more exotic materials with reactive components or failure-critical applications (like jet turbines).
What is Vacuum Melting?
Vacuum melting is when the casting process is conducted in a vacuum or low-pressure environment. This prevents impurities found in ambient air from being introduced into the metal(s). Vacuum melting requires more specialized equipment and is typically more expensive than air melt casting. While essentially any alloy can be vacuum-melted, it is normally used for metals with very high melting points, for very reactive materials, or alloys used in the harshest environments where purity and performance are essential (jet turbines, nuclear facility pressure valves, etc.)
What Alloys are Typically Vacuum-Melted?
Titanium alloys, aluminum alloys, many cobalt and nickel base super alloys, and many high-strength steels.
In short, materials with very high melting points or alloys deployed in failure-critical environments (aerospace, military, nuclear power generation, etc.) will often require vacuum melting.
Should I use Air Melt or Vacuum Melt?
Opting for vacuum melt can come with a premium cost, but if you are using a high-performance material that will be pushed to extremes, the premium cost is well worth the premium performance. Some materials, like aluminum, outright require the vacuum melt process, and air melt simply isn't an option.
This being said air-melt alloys will perform admirably in most applications as long as chemistry specs are met! When shopping for foundries, find a partner with a solid production track record with a robust QC process. An experienced metalworker utilizing air melt methods can create exceptionally strong components with beautiful surface finishes and high-quality chemical composition. If you have questions about materials for your specific project, contact us today! Our engineering department is always happy to help.
To sum up, both air melt and vacuum melt methodologies have their uses. Air melt is a perfect choice for a wide variety of alloys and is often more cost-friendly. In contrast, vacuum melt provides next-level purity and the ability to use exotic, high-performance materials. Opting for one or the other typically comes down to the usage scenario for your component and its margin for error.
Disclaimer:
This blog is designed to provide a quick look at air and vacuum melting in the investment casting process. We make no claims to the completeness of the information herein and encourage you to do robust research and/or contact experts for advice suited to your project's nuances.