Impro Expanded Process Capabilities for Superalloy Investment Casting
High-temperature strength and corrosion resistance make superalloys invaluable in a range of challenging applications. The problem is, they’re not easy to cast or machine, and that’s why vacuum investment casting is often preferred. To expand our superalloy investment casting capabilities we recently commissioned state-of-the-art casting equipment at our plant in Wuxi, China. Here are the details.
Reasons Why Superalloys Are Investment Cast
Superalloys are high-toughness metals with excellent strength at high temperatures and good corrosion resistance. This makes them ideal for applications in aerospace, chemical processing, power generation and the oil and gas industry. However, producing parts in superalloys is difficult because of the properties of these materials.
Toughness makes superalloys difficult to machine. It takes rigid CNC machine tools, careful choice of cutting inserts, and appropriate feeds and speeds. Tool wear is often high as chips tend to stick to the inserts, and this increases downtime.
To minimize machining, complex part designs calling for superalloys are typically investment cast. The high precision and repeatability of this process minimizes the amount of metal to remove and the machining allowances placed on specific dimensions.
While technically possible under very specific conditions, superalloys are generally considered not weldable. The problem is that melting and cooling leads to separation of elements that solidify at different temperatures. To get around this, large parts designed in superalloy materials must be joined mechanically.
A third issue is that nickel and cobalt superalloys have a very strong affinity for oxygen, as does the titanium often used in superalloys. This results in oxide formation, which in turn leads to defects within the metallic structure.
These defects reduce strength by providing crack initiation points. Since many superalloy applications involve high stresses, it’s important to minimize oxide formation. The way to do this is by casting either under vacuum or in an inert atmosphere.
Vacuum Investment Casting
Two things are necessary to investment cast superalloys under vacuum: the metal must be melted under vacuum, and then, while still under vacuum, poured into a ceramic shell mold from which all the air has been evacuated.
Melting and pouring is performed in a vacuum induction melting machine (VIM). VIMs are produced in two principal configurations: two chamber and three chamber.
In a two-chamber VIM the ceramic shell is placed in a chamber from which all the air is pumped out. It’s raised into position close to the melt crucible and filled, before being removed from the vacuum chamber to solidify.
A three-chamber VIM has isolation valves between chambers that increase vacuum level consistency. Efficiency is higher because the crucible can be filled and metal melted during the casting cycle, which provides for more melts and more pounds poured per hour. At the same time, maintaining high vacuum levels results in better casting quality.
New Superalloy Processing Capabilities in Wuxi
Recognizing a need for more superalloy investment casting capacity, and seeing that customers want to produce larger parts in superalloys, Impro took the decision to expand the capabilities available at the Impro Aerotek factory in Wuxi, China, just outside of Shanghai.
The new equipment is a three chamber vacuum melt and pour furnace, (or VIM,) manufactured by the German company, ALD. With roots in the well-known companies of Leybold, Heraeus and Degussa, ALD is a global leader in vacuum metallurgy. Their machines are engineered and constructed to the highest standards and incorporate both decades of experience and the latest casting, vacuum and control technologies. Commissioning was completed in June 2022 with the successful investment casting of a part weighing 85Kg (187lbs).
While this is a large investment casting, it’s not the biggest the new equipment is capable of. Maximum part weight and dimensions are 115Kg (254lbs) and Ø1,100×1,200mm (Ø43.3×47.2”). Although capable of melting and pouring a wide range of metals, high and consistent vacuum capabilities make it ideal for those with a strong affinity for oxygen, such as the nickel and cobalt superalloys.
Meeting Customer Needs for Larger Superalloy Parts
The new equipment in Wuxi lets Impro investment cast larger parts in superalloys. This gives customers the opportunity to consolidate smaller parts that require assembly into a single casting. Assembly work is avoided, as is mechanical joining, and product strength and integrity are higher.
If you’re interested in having larger parts investment cast in a superalloy, contact us today.