中英文对照外文翻译文献
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原文：
Drilling and Milling Machines
Upright drilling machines or drill presses are available in a variety of sizes and types, and are equipped with a sufficient range of apindle speeds and automatic feeds to fit the neds of most industries. Speed ranges on a typical machine are from 76 to 2025 rpm., with drill feed from 0.002 to 0.020 in.per revolution of the spindle.
Radial drilling machines are used to drill workpieces that are too large
or cumbersome to conveniently move. The spindle with the speed and feed changing mechanism is mounted on the radial arm; by combining the movement of the radial arm around column and the movement of the spindle assembly along the arm, it is possible to align the spindle and the drill to any position within reach of the machine. For work that is too large to conveniently support on the base, the spindle assembly can be swung out over the floor and the workpiece set on the beside the machine. Plain radial drilling machines provide only for vertical movement of the spindle; universal machines allow the spindle to swivel about an axis normal to the radial arm and the radial arm to rotate about a horizontal axis, thus permitting drilling at any angle.
A multispindle drilling machine has one or more heads that drive the spindles through universal joints and telescoping splined shafts. All spindles are usually driven by the same motor and fed simultaneously to drill the desired number of holes. In most machines each spindle is held in an adjustable plate so that it can be moved relative to the others. The area covered by adjacent spindles overlap so that the machine can be set to drill holes at any location within its range.
The milling operation involves metal removal with a rotating cutter. It includes removal of metal from the surface of a workspiece, enlarging holes, and form cutting, such as threads and gear teeth.
Within an knee and column type of milling machine the column is the
main supporting member for the other components, and includes the base containing the drive motor, the spindle, and the cutters. The cutter is mounted on an arbor held in the spindle, and supported on its outer extremity by a bearing in the overarm. The knee is held on the column in dovetail slots, the saddle is fastened to the knee in dovetail slots, and the table is attached to the saddle. Thus, the build-up the knee and column machine provides three motions relative to the cutter. A four motion may be provided by swiveling the table around a vertical axis provided on the saddle.
Fixed-bed milling machines are designed to provide more rigidity than the knee and column type. The table is mounted directly on the machine base, which provides the rigidity necessary for absorbing heavy cutting load, and allows only longitudinal motion to the table. Vertical motion is obtained by moving the entire cutting head.
Tracer milling is characterized by coordinated or synchronized movements of either the paths of the cutter and tracing elements, or the paths of the workpiece and model. In a typical tracer mill the tracing finger follow the shape of the master pattern, and the cutter heads duplicate the tracer motion.
The following are general design considerations for milling:
1. Wherever possible, the part should be designed so that a maximum number of surfaces can be milled from one setting.
2. Design for the use of multiple cutters to mill several surfaces simultaneously.
3. The largest flat surface will be milled first, so that all dimensions are best referred to such surface.
4. Square inside corners are not possible, since the cutter rotates.
Grinding Machines and Special Metal-removal Process
Random point-cutting tools include abrasives in the shape of a wheel, bonded to a belt, a stick, or simply suspended in liquid. The grinding process is of extreme importance in production work for several reasons.
1.It is most common method for cutting hardened tool steel or other heat-treated steel. Parts are first machined in the un-heat-treated condition, and then ground to the desired dimensions and surface finish.
2.It can provide surface finish to 0.5μm without extreme cost. 3.The grinding operation can assure accurate dimensions in a relatively short time, since machines are built to provide motions in increments of ten-thousandths of an inch, instead of thousandths as is common in other machines.
4.Extremely small and thin parts can be finished by this method, since light pressure is used and the tendency for the part to deflect away from the cutter is minimized.
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