Free Cutting Steels

Free Cutting Steels Free cutting steels also known as free machining steels are those steels which form small chips when machined. This increases the machinability¬†of the material by breaking the chips into small pieces, thus avoiding their entanglement in the machinery. This enables automatic run of the equipment without human interaction. Free cutting steels with lead also allow for higher machining rates. As a thumb rule, free cutting steel normally costs 15 % to 20 % more than the standard steel. However this is made up by increased machining speeds, larger cuts, and longer tool life. The cutting (machining) operation is shown in Fig 1. Fig 1 Cutting operation In turning, milling and drilling operations commonly known as machining operations, deformation/welding of the tool/work piece interface occurs rather than chip formation. During the machining operations surface finish is impaired, cutting temperature increased and tool life reduced significantly. A large ‘built-up edge’ is formed on the tool tip at very low sulfur contents. This requires frequent dressing or changing of tools, reduced productivity and higher costs. The term machinability is characterized by the following three parameters. Speed of machining Surface finish of the machined components Tool life of the cutting tools employed for machining operation. The term machinability relates to the ease and cost of achieving a production schedule for machined parts. It deals with consistent production of machined components which are able to satisfy product property specifications and in service performance requirements, at minimum through cost. Machinability can be measured in terms of surface finish, chip form, tool life, power consumption, and production rate. Machinability is not a unique material property like tensile strength, since it depends on the criterion selected, the type of cutting tool, cutting operation, cutting conditions and the machine tool...