中英文翻译(一)镗削加工和镗床

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英文翻译原文:

(一)BORING AND BORING MACHINES

As 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 length of the bore, tool deflection and, therefore, maintainance of

dimensional accuracy can be a significant problem.

The boring bar must be sufficiently stiff—that is, made of a material with high

elastic modulus, such as tungsten carbide –to minimize deflection and avoid vibration

and chatter. Boring 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 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

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 cutting 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 are 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 operaror

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 sizes 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 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 deflections of the boring bar due to

cutting forces.

c. Interrupted internal surfaces should be avoided.

（2）Fundamentals of Machine Tools

In 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 precise 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 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 material

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. 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 the constraint of accurate guiding

surfaces (the slideway).

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 transmissions

are reduced to a minimum.

(e) Transmission Linkage. Linkage is the general term used to denote the

mechanical, hydraulic, pneumatic or electric mechanisms which connect angular and

linear displacements in defined relationship.

There are two broad divisions of machining operations:

(a) Roughing, for which the metal removal rate, and consequently the cutting

force, is high ,but the required dimensional accuracy relatively low .

(b) Finishing, for which the metal removal rate, and consequently the cutting

force, is low, but the required dimensional accuracy and surface finish relatively high .

It follows that static loads and dynamic loads, such as result form an unbalanced

grindingwheel, are more significant in finishing operations than in roughing

operations, The degree of precision achieved in any machining process will usually be

influenced by the magnitude of the deflections, which occur as a result of the force

acting.

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摘要：

英文翻译原文:(一)BORINGANDBORINGMACHINESAscarriedoutonalathe,boringproducescircularinternalprofilesinhollowwork-piecesoronaholemadebydrillingoranotherprocess,Boringisdonewithcuttingtoolsthataresimilartothoseusedinturning.Becausetheboringbarhastoreachthefulllengthofthebore,tooldeflectionand,therefore,mainta...

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