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36 ISCAR ENGINEERING MATERIALSEngineering Materials Machinability, Cutting Tool Material ApplicabilityCutting tools are intended for machining engineering materials %u2013 the materials which are used for producing numerous structures and their elements, machine parts and other components. Engineering materials include ferrous and non-ferrous metals, composites and plastics, ceramics etc. The materials vary in their physical and mechanical properties . Some materials are easier to cut, others are more difficult. Machinability of a material is the material property that reflects how easily this material can be machined, the ability of the material to be cut under set machining data. There are various factors that impact material machinability, such as the material chemistry, hardness, fabrication methods etc. Machinability can be represented through the machinability index (factor, rating, ratio). This parameter shows how easy (or hard) a material is cut when compared to a basic material. Today, the machinability index is determined for most engineering materials. Finding the index relates to a myriad of test data and its analysis.Assume that we chose a material and will machine it by a tool of suitable cutting geometry to define the cutting speed, which provides predetermined tool life and ensures acceptable surface finish. Let%u2019s agree to consider this material as a reference, and the machinability index of the reference material as 100% (or 1). Then, we will repeat the same test for another material, and will find the appropriate cutting speed that facilitates the same tool life. The machinability index for the tested material will be the ratio of the found cutting speed to the cutting speed of the reference material:Km= vcm/vcrin terms of numbers, (5.1a)orKm%= vcm/vcr%u00d7100% in percentage terms (5.1b)whereKm and Km% %u2013 a material machinability index (factor, rating, ratio) in terms of numbers or percentagevcr %u2013 the cutting speed for machining a material, chosen as a reference, for the tool life Tvcm %u2013 the cutting speed, at which the same tool life T is observed.