Considerations of Exotic Metal Fabrication
While raw materials such as iron and steel are usually subject to fabrication processes, exotic metals can also be fabricated depending on the product. Some of the commonly used exotic metals in fabrication are Titanium, Waspaloy and Inconel which have varied applications in industry. These materials can be challenging from a fabrication standpoint because they require different considerations around their intrinsic properties, features and applicable processes during the design phase. Thus, it is important to learn about the availability of raw materials and finished components made from these materials. This blog will look to highlight some primary considerations when using exotic metals in manufacturing.
Features of Exotic Metals
- Non-Standard Tooling: Exotic metals such as steels, titanium, or Inconel have different features which impacts the type of tooling needed to machine these materials. For example, tools may need to be larger than standard materials. They also generally need a higher spindle speed, higher horsepower, and more horsepower per tooth than steel, which is particularly true when machining hard materials.
- Different Thermal Properties: Most exotic metals have very different thermal properties compared to common steels impacting the type of equipment used to machine, grind or form these materials. Exotic metals also have different thermal expansion properties than common steels; therefore, a standard machine tool may not work well for these. Some materials can have thermal gradients 50-100 times greater than steel.
- Brittleness of Materials: Most exotic metals are very brittle and fracture easily. Exotic metals also chip and shatter, making it difficult to machine intricate shapes using hand tools, which is challenging when forming these materials by pressing. They may also experience thermal cracking, particularly in thin sections, where it is more prevalent when the material is in its hardened condition.
Distinct Features of Inconel and Waspaloy
- Inconel: Inconel is very difficult to fabricate because of the tendency to “critical” or crack during fabrication, meaning it develops a crack without a specific load being applied. It is important to follow recommended fabrication practices, such as using shear-to-break-off fixtures, tool temperature limits, and slow speeds. Inconel also tends to work-harden, meaning the hardness increases as the material deforms, causing the part to fracture if formed too thin or if they leave the edges too sharp.
- Waspaloy: Waspaloy is an age-hardening austenitic nickel-based superalloy typically used in higher temperature applications, such as gas turbines. The alloy is much harder to weld than common steel, such as carbon steel, Inconel, or stainless steel, because it has a very low carbon content, making it more difficult to achieve sufficient penetration. Waspaloy also has a very low thermal conductivity, making the heat-affected zone more severe. When welding Waspaloy, it is important to use a low-hydrogen-content filler metal, such as ER70S-6.
Since exotic metals are usually very brittle, tools must be extremely sharp to prevent deflection and breakage. It may also be necessary to employ ultra-high-speed spindle speeds to avoid material sticking and excessive tool wear. Exotic metals are often difficult to chip, so it may be necessary to use a break-off or shut-off technique, particularly when using mining plant and equipment.
While exotic metals have individual characteristics which make it suitable for certain types of steel fabrication jobs, they are less versatile than commonly used fabrication raw materials. Thus, there are a limited number of suppliers of these exotic materials and the demand is correspondingly less as well. Thus, while the “exotic” nature of these metals provides a new perspective to metal fabrication, the bread and butter of fabrication jobs is still the reliable iron and steel!