a篇外文翻译：
寻找我的钱包Fundamentals Of Machine Tools
telephonenumberIn many cas products from the primary forming process must undergo further refinements in size and surface finish to meet their design specification. To meet such preci tolerances the removal of small amounts of material is needs. Usually machine tools are ud for such operation.rious是什么意思
In the United States material removal is a big business--in excess of $9
3610 per year, including material, labor, overhead, and machine-tool shipments. Since 60 percent of the mechanical and industry engineering and technology graduates have something connected with the machining industry either through sale, design, or operation of machine shops, or working in related industry, it is wi 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 a required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic member, which are as follows:convinces
(1) 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.
(2) Slides and Slideways. 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 sildeway).moves like jagger什么意思>windmills
(3) 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.
(4) 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.
(5) Transmission Linkage. Linkage is the general term ud to denote the mechanical, hydraulic, pneumatic mechanisms which connect angular and linear displacements in defined relationship.
There are two broad divisions of machining operations:
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(1) Roughing, for which the mental removal rate, and conquently the cutting force, is high, but the required dimensional accuracy relatively low.
(2) Finishing, for which the metal removel rate, and conquently 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.
Machine tool frames are generally made in cast iron, although some may be
steel casting or mild-steel fabrications. Cast iron is chon becau of its cheapness, rigidity, compressive strength and capacity for damping the vibration t-up in machine operations. To avoid massive ctions in castings, carefully designed systems of ribbing are box and diagonal. The box formation is convenient to produce, apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing provides greater torsional stiffness and yet permits swarf to fall between the ctions; it is frequently ud for lathe beds.
The slides and slideways of a machine tool lacate and guide members which move relative to each other, usually changing the position of the tool relative to the workpiece. The movement generally takes the form of translation in a straight line, but is sometimes angular rotation, e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding with the helix angle of the workpiece threads. The basic geometric elements of slides are flat, vee, dovetail and cylinder. The elements may ud parately or combined in various ways according to the applications. Features of slideways are as follows:
(1) Accuracy of Movement. Where a slide is to be displaced in a straight line, this line must lie in two mutually perpendicular planes and there must be no slide rotation. The general tolerance for straightness of machine tool slideways is 0~0.02 mm per 1000 mm; on horizontal surfaces this tolerance may be dispod so that a convex surface results, thus countering the effect of “sag” of the slideway.
holister(2) Means of Adjustment. To facilitate asmbly, maintain accuracy and eliminate “play” between sliding members afte r wear has taken place, a strip is
sometimes inrted in the slides. This is called a gib-strip. Usually, the gib is retained by socket-head screws passing through elongated slots; and is adjusted by grub-screws cured by lock nuts.
(3) Lubrication. Slideways may be lubricated by either of the following systems:
(i) Intermittently, through grea or oil nipples, a method suitable where movements are infrequent and speed low.
(ii) Continuously, e.g. by pumping through a metering valve and pipe-work to the point of application; the film of oil introduced between surfaces by the means must be extremely thin to avoid the slide “floating”. If sliding surfaces were optically flat oil would be squeezed out, resulting in the surfaces sticking. Hence in practice slide surfaces are either ground using the edge of a cup wheel, or scraped. Both process produce minute surface depressions which retain “pocket” of oil, and complete paration of the parts may not occur at all points ; positive location of the slides is thus retained.
(4).Protection. To maintain slideways in good order, the following conditions must be met:
(i) Ingress of foreign matter, e.g. swarf, must be prevented. Where this is no possible, it is desirable to have a form of slideway, which does not retain swarf, e.g. the inverted vee.
(ii) Lubricating oil must be retained. The adhesive property of oil for u on vertical or inclined slide surface is important; oils are available which have been
attendance
specially developed for this purpo. The adhesiveness of oil also prevents it being washed away by cutting fluids.
(iii) Accidental damage must be prevented by protective guards.
Lathes
A machine tool performs three major functions: (i) it rigidly supports the workpiece or its holder and the cutting tool; (ii) it provides relative motion between the workpiece and the cutting tool; (iii) it provides a range of feeds and speeds.
Machines ud to remove metal in the form of chips are classified as follows: Machines using basically the single-point cutting tools include: engine lathes, turret lathes tracing and duplicating lathes, single-spindle automatic lathes, multi-spindle automatic lathes, shapers and planers, boring machines.
Machines using multipoint cutting tools include: drilling machines, milling machines, broaching machines, sawing machines, gear-cutting machines.
Machines using random-point cutting tools (abrasive) include: cylindrical grinder, centreless grinders,
surface grinders.
Special metal removal methods include: chemical milling, electrical discharge machining, ultrasonic machining.
The lathe removes material by rotating the workpiece against a cutter to produce external or internal cylindrical or conical surfaces. It is commonly ud for the production of surfaces by facing, in which the work piece is rotated while the cutting tool is moved perpendicularly to the axis of rotation.
