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    Module 1 Classification of Metal Removal Processes and Machine tools Version 2 ME IIT, Kharagpur    Lesson 2 Basic working principle, configuration, specification and classification of machine tools Version 2 ME IIT, Kharagpur    Instructional Objectives  At the end of this lesson, the students should be able to : (a) Describe the basic functional principles of machine tools (i) Illustrate the concept of Generatrix and Directrix (ii) Demonstrate Tool – work motions (iii) Give idea about machine tool drives (b) Show configuration of basic machine tools and state their uses (c) Give examples of machine tools - specification (d) Classify machine tools broadly. Basic functional principles of machine tool operations   Machine Tools produce desired geometrical surfaces on solid bodies (preformed blanks) and for that they are basically comprised of; ã  Devices for firmly holding the tool and work ã  Drives for providing power and motions to the tool and work ã  Kinematic system to transmit motion and power from the sources to the tool-work ã  Automation and control systems ã  Structural body to support and accommodate those systems with sufficient strength and rigidity. For material removal by machining, the work and the tool need relative movements and those motions and required power are derived from the power source(s) and transmitted through the kinematic system(s) comprised of a number and type of mechanisms. (i) Concept of Generatrix and Directrix ã  Generation of flat surface The principle is shown in Fig. 2.1 where on a flat plain a straight line called Generatrix (G) is traversed in a perpendicular direction called Directrix (D) resulting a flat surface. ã  Generation of cylindrical surfaces The principles of production of various cylindrical surfaces (of revolution) are shown in Fig. 2.2, where,  ⎯   A long straight cylindrical surface is obtained by a circle (G) being traversed in the direction (D) parallel to the axis as shown in Fig. 2.2(a)  ⎯   A cylindrical surface of short length is obtained by traversing a straight line (G) along a circular path (D) as indicated in Fig. 2.2(b)  ⎯   Form cylindrical surfaces by rotating a curved line (G) in a circular path (D) as indicated in Fig. 2.2 (c and d). Version 2 ME IIT, Kharagpur   G D D G (a) (b) Fig. 2.1  Generation of flat surfaces by Generatrix and Directrix. Fig. 2.2  Generation of cylindrical surfaces (of revolution) (ii) Tool – work motions The lines representing the Generatrix and Directrix are usually produced by the locus of a point moving in two different directions and are actually obtained by the motions of the tool-tip (point) relative to the work surface. Hence, for machining flat or curved surfaces the machine tools need relative tool work motions, which are categorized in following two groups: ã  Formative motions namely  ⎯   Cutting motion (CM)  ⎯   Feed motion (FM) ã  Auxiliary motions such as  ⎯   Indexing motion  ⎯   Additional feed motion  ⎯   Relieving motion The Generatrix and Directrix, tool and the work and their motions generally remain interconnected and in different way for different machining work. Such interconnections are typically shown in Fig. 2.3 for straight turning and in Fig. 2.4 for shaping. Version 2 ME IIT, Kharagpur
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