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Note for Basics of Mechanical Engineering - BME By Suman Kumar Acharya

  • Basics of Mechanical Engineering - BME
  • Note
  • Biju Patnaik University of Technology Rourkela Odisha - BPUT
  • 9 Topics
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• Cut-off • Drilling • Boring • Tapping • Reaming Face turning or facing Face turning is also known as facing operation. The work piece material is fixed in between the chucks that are mounted on the lathe machine. The chucks rotate in the shaft direction. The tool is rotated along the perpendicular direction to the axis of the work piece material. This process is used to produce a square surface at the end of the work piece material or to get a chosen length. Straight turning In this process of straight tuning the work piece is fixed in between the chucks, with the help of tool feed that is provided along the longitudinal direction with required depth of cut. Straight turning operation is used to produce a cylindrical surface by removing the excess materials by providing the required depth. Eccentric turning If the work piece material has more than one axis of rotation at that case the axis is parallel to one another but never coincides. Cylindrical operation is performed on the different surfaces which is called eccentric turning. Shoulder turning Shoulder turning is also known as step turning operation. On the work piece material with different diameters are used for the performance, at that instance shoulder turning operation is used. There are different types of the shoulder turning they are beveled shoulder, radius shoulder and squared shoulder. Tapper turning Tapper turning is used to produce tapper surface on the cylinder. With the help of the tapper turning conical shapes are produced. Grooving With the help of the single point cutting tool, to the sides of the material tool moves radially. To make the groove, large multiple cuts are made on the work piece material. To do the same special tools and tool width are used with different geometries. Thread cutting The thread cutting tool moves along the axial direction and they are with an angle of 60 degrees. With the multiple pass of the tool toward the work piece we get the threads. The threads are arranged on the work piece material with specific pitch and specific length. Cut-off It is also similar to the grooving. In this process single point cutting tool moves along the side of the work piece. The cut off process is performed until it reaches the center of the work piece. Drilling The drill bit enters into work piece axially and makes a hole which is equal to the diameter of the drill bit. Boring A single point cutting tool is entered into the material axially to perform the operations like chamfers, tapers, step turning etc. Boring operation is performed after the drilling. To enlarge the diameter of the hole boring is required. Tapping In the existing holes, to perform the internal threads, tapping process is used. After the completion of the drilling process tapping is operated. Reaming

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The tool should be placed into the work piece axially to expand the holes. In the reaming process we can see the minimum amount of the metal removal rate. Mainly the process is used to enlarge the existing holes, by using this process we find a good internal finish with accurate diameters. Advantages: • In turning operation all types of materials are used for the process. • Short lead times • Very good tolerance Disadvantages: • Several operations are performed • Equipment cost is high • Scrap content is large • Significant tool rate • Limited to rotational parts Factors Affecting the turning Process Surface Roughness: The most significant factor is feed and depth of cut followed by speed. Also lubricant and nose radius has significant effect in obtaining better finish. Material Removal Rate:Depth of cut and feed is the significant factor followed by speed. Tool wear: Feed and depth of cut is the dominant factor followed by speed. Feed Force: Feed and depth of cut is the significant factor followed by speed and tool material. Thrust Force: Feed and depth of cut is the dominant factor followed by speed and tool material. Tangential Force: Depth of cut and feed is the significant factor followed by speed. Tool Life: Speed and feed is the significant factor followed by depth of cut. Surface Temperature: Depth of cut and feed is the significant factor followed by speed. Machining Machining is the manufacturing process by which parts can be produced to the desired dimensions and surface finish from a blank/workpiece by gradual removal of the excess material in the form of chips with the help of a sharp cutting tool. Almost 90% of the all engineering components are subjected to some kind of machining during manufacture. It is very important to design those parts in such a way that would lead to the increase in efficiency of the machining process, enhancement of the tool life and reduction of the overall cost of machining. To achieve these targets, a brief knowledge of various machining processes is required. Figure 1 depicts a brief classification of various machining processes that are widely used in the manufacturing and fabrication industries of all

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Figure 1: classification of machining process 1. Turning Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, bit describes a helix tool path by moving more or less linearly while the workpiece rotates. This operation is one of the most basic machining processes. That is, the part is rotated while a single point cutting tool is moved parallel to the axis of rotatio rotation. n. Turning can be done on the external surface of the part as well as internally (boring). The starting material is generally a workpiece generated by other processes such as casting, forging, extrusion,, or drawing. The cutting tool is fed either linearly in the direction parallel or perpendicular to the axis of rotation of the workpiece, or along a specified path to produce complex rotational shapes. The primary motion of cutting in turning is the rotation of the workpiece, and the secondary motion of cutting is the feed motion. Figure 2: Schematic description of turning

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Figure 2, depicts a typical turning operation in lathes. Different types of lathes are available today from general purpose to specific job oriented special purpose machines. In general, turning refers to a class of processes carried out on a lathe. 1. 1. Different variable machining parameters in turning Cutting speed is defined as the speed at which the work moves with respect to the tool (usually measured in meters per minute). Feed rate is defined as the distance the tool travels during one revolution of the part/workpeice (usually measured in mm per RPM). Depth of cut is the measurement (normally in inches or millimeters) of how deep the tool cuts into the workpiece (usually measured in mm). 1. 2. A brief outline of some the sub-class of turning processes (different types of turning) are presented below. Straight turning is used to reduce the diameter of a part to a desired dimension (Figure 3, a). The resulting machined surface is cylindrical. Contour turning and Taper turning (Figure 3, b) are performed by employing a complex feed motion using special attachments to a single point turning tool thus creating a contoured shape on the workpiece. Taper turning can also be performed by swiveling the compound rest and shifting the tailstock of the lathe. Facing (Figure 3, c) is done to create a smooth, flat face perpendicular to the axis of a cylindrical part. The tool is fed radially or axially to create a flat machined surface. Thread cutting (Figure 3, d) is possible in lathe by advancing the cutting tool at a feed exactly equal to the thread pitch. The single-point cutting tool cuts in a helical band, which is actually a thread. The tool point must be ground so that it has the same profile as the thread to be cut. Thread can be both external and internal types. In form turning (Figure 3, e), the shape of the cutting tool is imparted to the workpiece by plunging the tool into the workpiece. In form turning, the cutting tool can be very complex and expensive but the feed will remain linear and will not require special machine tools or devices. Boring (Figure 3, f) is similar to straight turning operation but differs in the fact that it can produce internal surface of revolution, which is often considered to be difficult due to overhanging condition of the tool.

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