Manufacturing Technology 1 (MEC 112) Basic Concepts PDF

08/10/2024 Benha University Faculty of Engineering (Shoubra) Mechanical Engineering Department (1st year) Manufacturing Technology 1 (MEC 112) Basic Concepts 1 INTRODUCTION Manufacturing is the industrial activity th...

08/10/2024 Benha University Faculty of Engineering (Shoubra) Mechanical Engineering Department (1st year) Manufacturing Technology 1 (MEC 112) Basic Concepts 1 INTRODUCTION Manufacturing is the industrial activity that changes the form of raw materials to create products. Manufacturing technology constitutes all methods used for shaping the raw metal materials into a final product. Manufacturing technology includes forming, casting, welding, and machining technologies. Machining is the removal of the unwanted material (machining allowance) from the workpiece (WP), to obtain a finished product of the desired size, shape, and surface quality. Nontraditional machining techniques offered alternative methods for machining parts of complex shapes in hard, stronger, and tougher materials that are difficult to cut by traditional methods. 2 2  08/10/2024 3 3 MACHINING In machining a cutting tool is used to remove metal. If the tool is held by hand, it is called a hand tool; examples of hand cutting tools are:  chisels,  files,  hacksaw blades. For each of the above tools the energy required to remove the metal is provided by muscular effort, and this means that the use of hand cutting tools is usually a slow and expensive method of removing metal. This fact has led to the introduction of machine tools. A machine tool may be defined as a power- operated device designed to produce a given surface, metal 4 being removed in this process. 4  08/10/2024 5 5 Generating motions of machine tools  The principle used in all machine tools is generating the surface required by providing suitable relative motions between the cutting tool and the workpiece.  The cutting edge or edges on the cutting tool remove a layer of work material; the removed material is called chip.  The simplest surfaces to generate are flat surfaces and internal or external cylindrical surfaces. Such surfaces can be generated by providing two kinds of relative motions (primary and secondary motions) by a metal cutting machine tool. 6 6  08/10/2024 7 7 8 8  08/10/2024  The primary motion is the main motion provided by a machine tool or manually to cause relative motion between the tool and workpiece so that the face of the tool approaches the workpiece material.  The secondary or feed motion is a motion that may be provided to the tool or workpiece by a machine tool which, when added to the primary motion, leads to a repeated or continuous chip removal and the creation of a machined surface with the desired geometric characteristics. Usually, the primary motion absorbs most of the total power required to perform a machining operation, while the feed motion absorbs only a small proportion of that power. 9 9 10 10  08/10/2024 11 11 Values of cut (machining variables)  Cutting speed (v) : It is the relative surface speed between the tool and the workpiece in the direction of cut.  For turning , drilling and milling the cutting speed is given by: π𝑫𝑵 𝒗= (m/min) 𝟏𝟎𝟎𝟎 𝑫 = Workpiece dia. in turning ( mm ) = Cutting tool dia. in drilling and milling (mm) 𝑵 = spindle rotational speed ( rpm ) 12 12  08/10/2024  For shaping the cutting speed is given by: 𝒗 𝑳𝑵(𝟏 𝒗 ) 𝟏𝟎𝟎𝟎 𝒓 (m/min) = stroke length (mm) = reciprocation speed (stroke/min) 𝒓 = rapid return speed (m/min) 13 13  Such formula can be deduced as follows; 𝑳  The time consumed by cutting stroke = (𝒎𝒊𝒏) 𝟏𝟎𝟎𝟎 𝒗 Where; 𝑳 = Stroke length (mm) 𝒗 = Cutting speed (m/min) 𝒌𝑳  The time consumed by return stroke = (𝒎𝒊𝒏) 𝟏𝟎𝟎𝟎 𝒗 Where; 𝑻𝒉𝒆 𝒕𝒊𝒎𝒆 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒃𝒚 𝒓𝒆𝒕𝒖𝒓𝒏 𝒔𝒕𝒓𝒐𝒌𝒆 𝒕𝒓 𝑳⁄𝒗𝒓 𝒗 𝒌= = = = 𝑻𝒉𝒆 𝒕𝒊𝒎𝒆 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒃𝒚 𝒄𝒖𝒕𝒕𝒊𝒏𝒈 𝒔𝒕𝒓𝒐𝒌𝒆 𝒕𝒄 𝑳⁄ 𝒗 𝒗𝒓 (𝒌 𝒊𝒔 𝒂𝒍𝒘𝒂𝒚𝒔 < 𝟏) 𝒗𝒓 = Rapid return speed (m/min) > 𝒗 to reduce the idle return time. 14 14  08/10/2024  Total time consumed for one full (double) stroke 𝑳 𝒌𝑳 = + 𝟏𝟎𝟎𝟎 𝒗 𝟏𝟎𝟎𝟎 𝒗 𝑳(𝟏 𝒌) = (𝒎𝒊𝒏) 𝟏𝟎𝟎𝟎 𝒗  Number of full (double) strokes per minute 𝟏 𝑵 = 𝑻𝒐𝒕𝒂𝒍 𝒕𝒊𝒎𝒆 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒇𝒐𝒓 𝒐𝒏𝒆 𝒇𝒖𝒍𝒍 (𝒅𝒐𝒖𝒃𝒍𝒆) 𝒔𝒕𝒓𝒐𝒌𝒆 𝟏 = 𝑳(𝟏 𝒌)⁄𝟏𝟎𝟎𝟎 𝒗 𝒗 𝟏𝟎𝟎𝟎 𝒗 𝑳𝑵(𝟏 𝒌) 𝑳𝑵(𝟏 ) = 𝑳(𝟏 𝒌) 𝑺𝒕/𝒎𝒊𝒏 𝒗= 𝟏𝟎𝟎𝟎 = 𝟏𝟎𝟎𝟎 𝒗𝒓 (𝒎⁄𝒎𝒊𝒏) Where; 𝑵 = 𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒇𝒖𝒍𝒍 (𝒅𝒐𝒖𝒃𝒍𝒆) 𝒔𝒕𝒓𝒐𝒌𝒆𝒔 𝒑𝒆𝒓 𝒎𝒊𝒏𝒖𝒕𝒆 = 𝑹𝒆𝒄𝒊𝒑𝒓𝒐𝒄𝒂𝒕𝒊𝒐𝒏 𝒔𝒑𝒆𝒆𝒅 (𝑺𝒕𝒓𝒐𝒌𝒆/𝒎𝒊𝒏) 15 15  Feed (s) : is the feed travel per revolution of workpiece for turning and drilling (mm/rev) or for shaping (mm/stroke). In case of milling the feed per tooth (sz) is used.  The feed rate (U) is given by: 𝑼 = 𝒔 𝑵 (𝒎𝒎⁄𝒎𝒊𝒏) for turning and drilling 𝑼 = 𝒔𝒛 𝒛 𝑵 (𝒎𝒎⁄𝒎𝒊𝒏) for milling 𝒔 = 𝒔𝒛 𝐳 𝒎𝒎⁄𝒓𝒆𝒗 𝒔𝒛 = 𝒇𝒆𝒆𝒅 𝒑𝒆𝒓 𝒕𝒐𝒐𝒕𝒉 (𝒎𝒎⁄𝒕𝒐𝒐𝒕𝒉) 𝒛 = 𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒖𝒕𝒕𝒆𝒓 𝒕𝒆𝒆𝒕𝒉  Depth of cut (a) : is the distance moved by the tool nose relative to the workpiece normal to the working plane. 16 16  08/10/2024 Cutting Tools  If a cutting tool is to shear or cut metal efficiently it is important that the angles that make up the wedge shape of the tool be of the correct value according to the nature of the machining operation and the metal being machined. Rake Angle The rake angle of a cutting tool is the angle which facilitate the chip formation. Clearance Angle The purpose of the clearance angle is to reduce the energy required to shear the metal, by removal or reduction of the friction arising from the rubbing action between the tool and the workpiece. 17 17 Tool Geometry 18 18  08/10/2024 19 Left and right cut tools 19 CUTTING TOOL MATERIALS In order to penetrate the workpiece, the cutting tool material should be sufficiently harder than the workpiece material (especially harder than the deformed chip). The tool must be strong enough to withstand the cutting forces exerted on it. Due to the relative motion and the friction between the workpiece and the tool flank as well as between the chip and the tool face, it is subjected to wear on both flank and rake faces. 20 20  08/10/2024  Plain carbon tool steels  Alloy tool Steels  High speed steels  Cemented Carbides  Ceramics ( Cemented oxides)  Diamonds 21 21 End of Lecture 22 22