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1、英文翻译原文:(一)BORING AND BORING MACHINESAs carried out on a lathe, boring produces circular internal profiles in hollow work-pieces or on a hole made by drilling or another process, Boring is done with cutting tools that are similar to those used in turning. Because the boring bar has to reach the full
2、length of the bore, tool deflection and, therefore, maintainance of dimensional accuracy can be a significant problem.The boring bar must be sufficiently stiffthat is, made of a material with high elastic modulus, such as tungsten carbide to minimize deflection and avoid vibration and chatter. Borin
3、g bars have been designed with capabilities for damping vibration.Although boring operations on relatively small work-pieces. Can be carried out on a lathe, boring mills are used for large work-pieces. These machines are either vertical or horizontal, and are capable of performing operations such as
4、 turning, facing, grooving, and chamfering. A vertical boring machine is similar to a lathe but has a vertical axis of work-piece rotation.The cutting tool (usually a single point made of M-2 and M-3 high-speed steel and C-7 and C-8 carbide) is mounted on the tool head, which is capable of vertical
5、movement (for boring and turning) and radial movement (for facing), guided by the cross-rail. The head can be swiveled to produce conical (tapered) surfaces.In horizontal boring machine, the work-piece is mounted on a table that can move horizontally in both the axial and radial directions. The cutt
6、ing tool is mounted on a spindle that rotates in the headstock, which is capable of both vertical and longitudinal movements. Drills, reamer, taps, and milling cutters can also be mounted on the machine spindle.Boring machine are available with a variety of features. Although work-piece diameters ar
7、e generally 1 m-4 m(3ft-12ft),work-piece as large as 20 m(60ft) can be machined in some vertical boring machines. Machine capacities range up to 150 kw (200hp).these machines are also available with computer numerical controls, which allow all movements to be programmed. With such controls, little o
8、peraror involvement is required and consistency and productivity are improved. Cutting speeds and feeds for boring are similar to those for turning.(For capabilities of boring operations)Jig borers are vertical boring machines with high precision bearings. Although they are available in various size
9、s and used in tool rooms for making jigs and fixtures, they are now being replaced by more versatile numerical control machines.Design considerations for boring. Guidelines for efficient and economical boring operations are similar to those for turning. Additionally, the following factors should be
10、considered：a. Whenever possible, through holes rather than blind holes should be specified.(The term blind hole refers to a hole that does not go though the thickness of the work-piece )b. The greater the length to bore-diameter ratio, the more difficult it is to hold dimensions because of the defle
11、ctions of the boring bar due to cutting forces.c. Interrupted internal surfaces should be avoided. （2）Fundamentals of Machine ToolsIn many cases products form the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications. To meet such p
12、recise tolerances the removal of small amounts of material is needed. Usually machine tools are used for such operation.In the United States material removal is a big business-in excess of $ per year, including material, labor, overhead, and machine-tool shipments, is spent. Since 60 percent of the
13、mechanical and industrial engineering and technology graduates have something connection with the machining industry either through sale, design, or operation of machine shops, or working in related industry, it is wise for an engineering student to devote some time in his curriculum to studying mat
14、erial removal and machine tools.A machine tool provides the means for cutting tools to shape a workpiece to required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members, which are as follow:(a) Bed, Structure or Frame.
15、 This is the main member which provides a basis for, and a connection between, the spindles and slides; the distortion and vibration under load must be kept to a minimum. (b) Slides and Sideways. The translation of a machine element (e.g. the slide) is normally achieved by straight-line motion under
16、 the constraint of accurate guiding surfaces (the slideway).(c) Spindles and Bearings. Angular displacements take place about an axis of rotation; the position of this axis must be constant within extremely fine limits in machine tools, and is ensured by the provision of precision spindles and bearings.(d) Power Unit. The electric motor is the universally adopted power unit for machine tools. By suitably positioning individual motors, belt and gear
