Machinability is the process of removing metal
Cast iron, a versatile alloy, is one of the most free-machining ferrous materials accessible. In case of cast iron, consistent microstructure is the key to optimum machinability because cast iron can show a wide range of machining behavior depending upon its composition and microstructure.The microstructure features of cast iron - particle composition and dispersion, particle population density, and aspect ratios affect its machinability considerably. Cast iron's mechanical properties are enhanced by addition of nodulizing elements such as silicon, magnesium, chromium, molybdenum and copper.The important aspects of machinability include tool life, the surface finish of themachining material, the power or cutting force required and the form of chips produced during a machining operation. Tool requirements The perfect cutting tool material for machining cast iron should have high strength and hardness in addition to high fracture toughness. Although this combination of properties is practically impossible to achieve since high strength and low fracture toughness are synonymous, the selection of the proper cutting tool is important for machining various types of cast irons. Processes involved in machining At higher cutting speeds and feeds, the intense heat generated in the vicinity of the cutting edge of the tool elevates the metal's temperature in the affected zone up to 1112-1292F (600-700C), which plasticizes the iron. When deep hole is required as a part of the design of cast iron, lower manganese must be added. This must be specified for the cast component to reduce the amount of retained austenite. In such case, higher amounts of copper and nickelmust be added to obtain the required degree of hardenability. In case of roughing, the cast is run dry, without cutting fluid, to minimize problems with thermal cracks. It is prudent to use carbide inserts with thick coatings.To get the best results, the carbide inserts used to machine cast irons are coated with alumina, usually with one or more layers of titanium carbide and titanium nitride. The alumina provides the high hardness needed for abrasive resistance and outstanding chemical stability. If cutting fluid must be used to avoid dust, then choose the wet milling grades. Machining cost savings Casting iron offers many advantages and has wider practical applications in various industries. One of the main advantages provided by cast iron components is their ability to incorporate many design features that are not available in other manufacturing methods. Hence, it is possible to achieve cost savings in manufacturing processes such as machining. Opportunities for cost savings also exist in the subsequent processing of components themselves. In machining, however, the cost saving opportunities is available with an understanding of the casting iron's metallurgy and its place in the overall machining system.