Which is NOT a type of furnace commonly used in metalworking?

The choice indicating "Heat treating furnace" as not being a common type of furnace used in metalworking is based on a distinction regarding furnace types and their designated primary functions in the metalworking industry.

A cupola furnace and a crucible furnace are both well-known types of melting furnaces, specifically designed for melting and casting metals. The cupola furnace is traditionally used for melting cast iron, characterized by its vertical cylindrical shape, while the crucible furnace is used for melting smaller quantities of metals or alloys in a crucible, allowing for better control over the melting process.

The term "normalized furnace" may be less familiar, yet it refers to a furnace used specifically for the normalizing heat treatment process. Heat treating furnaces are indeed common in metalworking, as they are essential for altering the physical and sometimes chemical properties of alloys, improving hardness, ductility, or stress relief.

In this context, the term "normalized furnace" can be seen as a subset of heat treating processes rather than a standalone furnace type. Thus, recognizing heat treating as a distinct functional category could lead to identifying it as less of a traditional furnace type compared to cupola or crucible furnaces, lending validity to its selection as the answer in this scenario.