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The term machinability refers to the ease with which a metal can be cut permitting the removal of the material with a satisfactory finish at low cost.〔Degarmo, p. 542.〕 Materials with good machinability require little power to cut, can be cut quickly, easily obtain a good finish, and do not wear the tooling much; such materials are said to be free machining. The factors that typically improve a material's performance often degrade its machinability. Therefore, to manufacture components economically, engineers are challenged to find ways to improve machinability without harming performance. Machineability index (%) = (cutting speed of material for 20 min tool life) / (cutting speed of free cutting steel for 20 min tool life) * 100% Machinability can be difficult to predict because machining has so many variables. Two sets of factors are the condition of work materials and the physical properties of work materials.〔Schneider, George, "Machinability of Metals," ''American Machinist'', December, 2009.〕 The condition of the work material includes eight factors: microstructure, grain size, heat treatment, chemical composition, fabrication, hardness, yield strength, and tensile strength.〔Schneider, "Machinability."〕 Physical properties are those of the individual material groups, such as the modulus of elasticity, thermal conductivity, thermal expansion, and work hardening.〔 Other important factors are operating conditions, cutting tool material and geometry, and the machining process parameters.〔 ==Quantifying machinability== There are many factors affecting machinability, but no widely accepted way to quantify it. Instead, machinability is often assessed on a case-by-case basis, and tests are tailored to the needs of a specific manufacturing process. Common metrics for comparison include tool life, surface finish, cutting temperature, and tool forces and power consumption.〔〔Schneider, p. 8.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「machinability」の詳細全文を読む スポンサード リンク
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