Tackling cast iron machining complexities

It wasn’t that long ago when manufacturers viewed cast iron as cheap, brittle and dirty metal. Today, however, through production advancements, cast iron comes in a wide variety of types that are stronger and provide better machinability than ever before. Keep in mind though the level of strength and machinability varies between and within each type.

Grey cast iron (GJL), among the most common and least expensive of all the types, contains carbides in the form of lamellar graphite particles, which gives it excellent vibration damping properties and makes it ideal choice for engine components. It also has the highest level of machinability when compared to the other types.

Vermicular graphite cast iron (GJV), also known as compacted graphite iron, gets its name from the worm-like appearance of its graphite particles. It offers greater strength and lower weight when compared to grey cast iron. Because vermicular cast iron is suitable for components subjected to both mechanical and thermal stress, automotive manufacturers are using it for the production of certain components e.g. diesel engine parts.

Silicon alloyed ferritic ductile cast iron is ideal for the production of wheel hubs and axles. Given its high degree of machinability and excellent mechanical properties, the material is becoming increasingly popular within the automotive industry.

Nodular ductile cast iron (GJS), which consists of spheroid nodular graphite particles in ferrite and/or pearlite matrix, possesses high ductility, good fatigue strength, superior wear resistance and a high modulus of elasticity, and hence have been the choice of material for transmission housings and wheel suspension parts within the automotive and heavy equipment industry. Besides, special alloys of ductile iron are used in the production of high-temperature components such as exhaust pipes and turbocharger housings.

Austempered ductile iron, which is manipulated through a sophisticated heat treating process, offers high strength, high fatigue strength, good wear resistance and high values of elongation to fracture, making it a very competitive material in relation to many cast and forged steels. Because of great strength and elastic properties, austempered ductile iron has the lowest level of machinability when compared to the other types of cast iron mentioned here.

Advanced coating processes
Some cutting tool companies are using advanced coating processes to create two- and three-grade strategies for their customers. Seco Tools, for example, has a two-grade turning strategy made possible via its exclusive Duratomic? coating technology grades where aluminium and oxygen are manipulated at the atomic level to create inserts with a combination of exceptional toughness and abrasion resistance for cast irons.

In terms of actual cast iron turning operations, everything is dependent upon a manufacturer’s specific application. Manufacturers must determine the number of operations necessary to accomplish their goals, no more and no less. If the workpiece properties are unknown, a manufacturer may opt to include an extra finishing cut, which impacts product lead times. However, by applying the right tooling for the conditions and requirements of the component, a manufacturer can reduce the number of operations.

A more specific turning operation scenario might involve a manufacturer machining components within a just-in-time supply chain as indicated earlier. In such a situation, batches of as-cast workpieces are sometimes out of specification in terms oAir Jordan XIV High