叮叮小文库附录附录 1 英文原文Basic Machining Operations and Cutting TechnologyBasic Machining OperationsMachine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinsons boring mill. They are designed to provide rigid support for both the work piece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the work piece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface of a ductile work piece in the form of a severely deformed chip. The chip is a waste product that is considerably shorter than the work piece from which it came but with a corresponding increase in thickness of the uncut chip. The geometrical shape of work piece depends on the shape of the tool and its path during the machining operation.Most machining operations produce parts of differing geometry. If a rough cylindrical work piece revolves about a central axis and the tool penetrates beneath its surface and travels parallel to the center of rotation, a surface of revolution is produced, and the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface uniformly varying diameter is called taper turning, if the tool point travels in a path of varying radius, a contoured surface like that of a bowling pin can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be contour formed.Flat or plane surfaces are frequently required. They can be generated by radial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the work piece steady and reciprocate the tool across it in a series of straight-line cuts with a crosswise feed increment before each cutting stroke. This operation is called planning and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the work piece under it as in planning. The tool is fed at each reciprocation. Contoured surfaces can be produced by using shaped tools.Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10 times the drill diameter. Whether thedrill turns or the work piece rotates, relative motion between the cutting edge and the work piece is the important factor. In milling operations a rotary cutter with a number of cutting edges en gagesthe work piece. Which moves slowly with respect to the cutter. Pla ne or con toured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horiz on tal or vertical axes of rotati on may be used, and the feed of the work piece may be in any of the three coordi nate directi ons.Basic Machi ne ToolsMachi ne tools are used to produce a part of a specified geometrical shape and precise I size by removing metal from a ductile material in the form of chips. The latter are a waste product and vary from long con ti nu ous ribb ons of a ductile material such as steel, which are un desirable from a disposal point of view, to easily handled well-broken chips resulting from cast iron. Machine tools perform five basic metal-removal processes: I turning, planning, drilling, milling, and grinding. All other metal-removal processes are modificati ons of these five basic processes. For example, boring is internal turning; reaming, tapping, and counter boring modify drilled holes and are related to drilli ng; bobb ing and gear cutt ing are fun dame ntally milli ng operati ons; hack sawing and broaching are a form of planning and honing; lapping, super finishing. Polish ing and buffi ng are varia nts of grinding or abrasive removal operati ons. Therefore, there are only four types of basic mach ine tools, which use cutt ing tools of specific con trollable geometry: 1. lathes, 2. planers, 3. drilling machines, and 4. milling machines. The grinding process forms chips, but the geometry of the abrasive grain is uncon trollable.The amount and rate of material removed by the various mach ining processesmay be I large, as in heavy turning operations, or extremely small, as in lapping or super finishing operati ons where only the high spots of a surface are removed.A machi ne tool performs three major fun cti ons: 1. it rigidly supports the work piece or its holder and the cutt ing tool; 2. it provides relative moti on betwee n the work piece and the cutt ing tool; 3. it provides a range of feeds and speeds usually ranging from 4 to 32 choices in each case.Speed and Feeds in Machi ningSpeeds,feeds, and depth of cut are the three major variables for economical machining. Other variables are the work and tool materials, coolant and geometry of the cutti