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1、Machining Operations and Turning Machines,Part I Technical and Practical Reading,Passage A Machining Operations,Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven machine tools, such as lathes, milling machi
2、nes, and drill presses are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the manufacture of almost all metal products. It is not uncommon for other materials to be machined. A person who specializes in machining is called a ma
3、chinist. Machining is also a hobby. A room, building, or company where machining is done is called a machine shop. Much of modern day machining is controlled by computers using Computer Numerical Controlled (CNC) machining.,Machining operations The three principal machining processes are classified
4、as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planning, boring, broaching and sawing.,Turning operations are operations that rotate the work-piece as the primary method of moving metal against the cutting tool. Lathes are the principal mach
5、ine tool used in turning. Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the work-piece. Milling machines are the principal machine tool used in milling. Drilling operations are operations in which holes are produced or refined by bringing
6、a rotating cutter with cutting edges at the lower extremity into contact with the work-piece. Drilling operations are done primarily in drill presses but not uncommonly on lathes or mills.,More recent, advanced machining techniques include electrical discharge machining (EDM), electro-chemical erosi
7、on, laser, or water jet cutting to shape metal work-pieces. Machining requires attention to many details for a work-piece to meet the specifications set out in the engineering drawings or blueprints.,Types of machining operation There are many kinds of machining operations, each of which is capable
8、of generating a certain part geometry and surface texture. In turning, a cutting tool with a single cutting edge is used to remove material from a rotating work-piece to generate a cylindrical shape. The speed motion in turning is provided by the rotating work-part, and the feed motion is achieved b
9、y the cutting tool moving slowly in a direction parallel to the axis of rotation of the work-piece.,Drilling is used to create a round hole. It is accomplished by a rotating tool that is typically has two cutting edges. The tool is fed in a direction parallel to its axis of rotation into the work-pa
10、rt to form the round hole.,In boring, the tool is used to enlarge an already available hole. It is a fine finishing operation used in the final stages of product manufacture. In milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or strai
11、ght surface. The direction of the feed motion is perpendicular to the tools axis of rotation. The speed motion is provided by the rotating milling cutter.,Overview of machining technology Machining is not just one process; it is a group of processes. The common feature is the use of a cutting tool t
12、o form a chip that is removed from the work-part, called swarf . To perform the operation, relative motion is required between the tool and work. This relative motion is achieved in most machining operation by means of a primary motion, called cutting speed and a secondary motion called feed. The sh
13、ape of the tool and its penetration into the work surface, combined with these motions, produce the desired shape of the resulting work surface.,Notes,1. Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven ma
14、chine tools, such as lathes, milling machines, and drill presses are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. 在这个长句中，主语是Conventional machining，谓语动词为is。one of the mostmethods是插入语。in which 引导定语从句，其先行词为processes。在定语从句中，are used是定语从句中的谓语动词。此句可译为：常规
15、加工是集材料加工过程于一体的最重要的切削材料方法之一，在此过程中电动机床，如车床、铣床和钻床通过锋利的刀具被用来进行机械加工以获得期望的几何形状。 2. Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the work-piece. 在此句中，in which 引导定语从句，修饰先行词operations。by表示方法
16、、方式。bring with 表示带有。into contact with 意为“与接触”。本句可译为：钻削操作是通过带有刀刃的旋转刀具对工件进行深加工孔或深精加工孔的操作。 3. The shape of the tool and its penetration into the work surface, combined with these motions, produce the desired shape of the resulting work surface. 在此句中，主语是由and连接的并列主语，谓语动词为produce。combined with是分词作状语。整句意思为：刀具的形状、刀具与工件面的划入接触加上它们之间的运动生成了最终的工件面。,1. The principal machining processes are generally regarded as three parts: turning, drilling and boring. 2. Milling machines are the principal machine tool
