機(jī)械外文翻譯--基本加工工序和切削技術(shù)

1、<p><b>　　附錄</b></p><p><b>　　附錄1</b></p><p><b>　　英文原文</b></p><p>　　Basic Machining Operations and Cutting Technology</p><p>　　Ba

2、sic Machining Operations </p><p>　　Machine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinson's boring mill. They are designed to provide rigid support for both the

3、 workpiece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather n

4、arrow strip of metal from the surface of a ductile workpiece in the form of a severely deformed chip. The chip i</p><p>　　Most machining operations produce parts of differing geometry. If a rough cylindrical

5、 workpiece 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 t

6、ube 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 trav</p><p>　　Fl

7、at 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 workpiece s

8、teady 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 i

9、t is easier to keep the tool stationary and draw the workp</p><p>　　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.

10、 Whether the </p><p>　　drill turns or the workpiece rotates, relative motion between the cutting edge and the workpiece is the important factor. In milling operations a rotary cutter with a number of cutting

11、 edges engages the workpiece. Which moves slowly with respect to the cutter. Plane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of rotat

12、ion may be used, and the feed of the workpiece may be in any of the three coordinate directions.</p><p>　　Basic Machine Tools </p><p>　　Machine tools are used to produce a part of a specified ge

13、ometrical 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 continuous ribbons of a ductile material such as steel, which are undes

14、irable 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 othe

15、r </p><p>　　The amount and rate of material removed by the various machining processes may be I large, as in heavy turning operations, or extremely small, as in lapping or super finishing operations where on

16、ly the high spots of a surface are removed. </p><p>　　A machine tool performs three major functions: 1. it rigidly supports the workpiece or its holder and the cutting tool; 2. it provides relative motion be

17、tween the workpiece and the cutting tool; 3. it provides a range of feeds and speeds usually ranging from 4 to 32 choices in each case. </p><p>　　Speed and Feeds in Machining </p><p>　　Speeds, f

18、eeds, 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 cutting tool. The rate of metal removal and power required for m

19、achining depend upon these variables. </p><p>　　The depth of cut, feed, and cutting speed are machine settings that must be established in any metal-cutting operation. They all affect the forces, the power,

20、and the rate of metal removal. They can be defined by comparing them to the needle and record of a phonograph. The cutting speed (V) is represented by the velocity of- the record surface relative to the needle in the ton

21、e arm at any instant. Feed is represented by the advance of the needle radially inward per revolution, or is the differen</p><p>　　Turning on Lathe Centers </p><p>　　The basic operations perform

22、ed on an engine lathe are illustrated. Those operations performed on external surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and lapping, the operations on internal surfaces a

23、re also performed by a single point cutting tool. </p><p>　　All machining operations, including turning and boring, can be classified as roughing, finishing, or semi-finishing. The objective of a roughing op

24、eration is to remove the bulk of the material as rapidly and as efficiently as possible, while leaving a small amount of material on the work-piece for the finishing operation. Finishing operations are performed to obtai

25、n the final size, shape, and surface finish on the workpiece. Sometimes a semi-finishing operation will precede the finishing operati</p><p>　　Generally, longer workpieces are turned while supported on one o

26、r two lathe centers. Cone shaped holes, called center holes, which fit the lathe centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the t

27、ailstock is always supported by a tailstock center, while the end near the headstock may be supported by a headstock center or held in a chuck. The headstock end of the workpiece may be held in a four-jaw chuck, or i<

28、/p><p>　　Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver plate mounted on the spindle nose. On

29、e end of the Workpiece is mecained;then the workpiece can be turned around in the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry

30、the weight of the workpiece  and to resist the cutting forces. After the workpi</p><p>　　While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headst

31、ock end by faceplate jaws to obtain the smooth power transmission; moreover, large lathe dogs that are adequate to transmit the power not generally available, although they can be made as a special. Faceplate jaws are li

32、ke chuck jaws except that they are mounted on a faceplate, which has less overhang from the spindle bearings than a large chuck would have. </p><p>　　Introduction of Machining </p><p>　　Machinin

33、g as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chi

34、p form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported workpiece. </p><p>　　Low setup cost for sma

35、ll Quantities. Machining has two applications in manufacturing. For casting, forging, and press working, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may he pr

36、oduced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining; to start with nearly

37、any form of raw material, so tong as t</p><p>　　Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined

38、 in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process. On the other hand, many parts are given their general shapes by some high quantity deformati

39、on process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are se</p><p>　　Primary Cutting Parameters </p><p>　　The basic tool-work relati

40、onship in cutting is adequately described by means of four factors: tool geometry, cutting speed, feed, and depth of cut. </p><p>　　The cutting tool must be made of an appropriate material; it must be strong

41、, tough, hard, and wear resistant. The tool s geometry characterized by planes and angles, must be correct for each cutting operation. Cutting speed is the rate at which the work surface passes by the cutting edge. It ma

42、y be expressed in feet per minute. </p><p>　　For efficient machining the cutting speed must be of a magnitude appropriate to the particular work-tool combination. In general, the harder the work material, th

43、e slower the speed. </p><p>　　Feed is the rate at which the cutting tool advances into the workpiece. "Where the workpiece or the tool rotates, feed is measured in inches per revolution. When the tool o

44、r the work reciprocates, feed is measured in inches per stroke, Generally, feed varies inversely with cutting speed for otherwise similar conditions. </p><p>　　The depth of cut, measured inches is the distan

45、ce the tool is set into the work. It is the width of the chip in turning or the thickness of the chip in a rectilinear cut. In roughing operations, the depth of cut can be larger than for finishing operations. </p>

46、<p>　　The Effect of Changes in Cutting Parameters on Cutting Temperatures </p><p>　　In metal cutting operations heat is generated in the primary and secondary deformation zones and these results in a

47、complex temperature distribution throughout the tool, workpiece and chip. A typical set of isotherms is shown in figure where it can be seen that, as could be expected, there is a very large temperature gradient througho

48、ut the width of the chip as the workpiece material is sheared in primary deformation and there is a further large temperature in the chip adjacent to the face as th</p><p>　　Since virtually all the work done

49、 in metal cutting is converted into heat, it could be expected that factors which increase the power consumed per unit volume of metal removed will increase the cutting temperature. Thus an increase in the rake angle, al

50、l other parameters remaining constant, will reduce the power per unit volume of metal removed and the cutting temperatures will reduce. When considering increase in unreformed chip thickness and cutting speed the situati

51、on is more complex. An incr</p><p>　　The most direct and accurate method for measuring temperatures in high -speed-steel cutting tools is that of Wright &. Trent which also yields detailed information on

52、 temperature distributions in high-speed-steel cutting tools. The technique is based on the metallographic examination of sectioned high-speed-steel tools which relates microstructure changes to thermal history. </p&g

53、t;<p>　　Trent has described measurements of cutting temperatures and temperature  distributions for high-speed-steel tools when machining a wide range of workpiece materials. This technique has been further d

54、eveloped by using scanning electron  microscopy to study fine-scale microstructure changes arising from over tempering of the tempered martens tic matrix of various high-speed-steels. This technique has also been us

55、ed to study temperature distributions in both high-speed -steel single point turning </p><p>　　Wears of Cutting Tool </p><p>　　Discounting brittle fracture and edge chipping, which have already

56、been dealt with, tool wear is basically of three types. Flank wear, crater wear, and notch wear. Flank wear occurs on both the major and the minor cutting edges. On the major cutting edge, which is responsible for bulk m

57、etal removal, these results in increased cutting forces and higher temperatures which if left unchecked can lead to vibration of the tool and workpiece and a condition where efficient cutting can no longer take pl</p&

58、gt;<p>　　Because of the stress distribution on the tool face, the frictional stress in the region of sliding contact between the chip and the face is at a maximum at the start of the sliding contact region and is

59、zero at the end. Thus abrasive wear takes place in this region with more wear taking place adjacent to the seizure region than adjacent to the point at which the chip loses contact with the face. This result in localized

60、 pitting of the tool face some distance up the face which is usually referre</p><p>　　At the end of the major flank wear land where the tool is in contact with the uncut workpiece surface it is common for th

61、e flank wear to be more pronounced than along the rest of the wear land. This is because of localised effects such as a hardened layer on the uncut surface caused by work hardening introduced by a previous cut, an oxide

62、scale, and localised high temperatures resulting from the edge effect. This localised wear is usually referred to as notch wear and occasionally is very severe</p><p>　　If any form of progressive wear allowe

63、d to continue, dramatically and the tool would fail catastrophically, i. e. the tool would be no longer capable of cutting and, at best, the workpiece would be scrapped whilst, at worst, damage could be caused to the mac

64、hine tool. For carbide cutting tools and for all types of wear, the tool is said to have reached the end of its useful life long before the onset of catastrophic failure. For high-speed-steel cutting tools, however, wher

65、e the wear tends to be</p><p>　　Mechanism of Surface Finish Production </p><p>　　There are basically five mechanisms which contribute to the production of a surface which have been machined. The

66、se are:</p><p>　　(l) The basic geometry of the cutting process. In, for example, single point turning the tool will advance a constant distance axially per revolution of the workpiecc and the resultant surfa

67、ce will have on it, when viewed perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut. </p><p>　　(2) The efficienc

68、y of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a surface which contains hard built-up-edge fragments which will result in a degradation of the surface fin

69、ish. It can also be demonstrated that cutting under adverse conditions such as apply when using large feeds small rake angles and low cutting speeds, besides producing conditions which lead to unstable built-up-edge prod

70、uction, the cutting process itself can beco</p><p>　　(3) The stability of the machine tool. Under some combinations of cutting conditions; workpiece size, method of clamping ,and cutting tool rigidity relati

71、ve to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions this vibration will reach and maintain steady amplitude whilst under other conditions the vibratio

72、n will built up and unless cutting is stopped considerable damage to both the cutting tool and workpiece may occur. This pheno</p><p>　　(4)The effectiveness of removing swarf. In discontinuous chip productio

73、n machining, such as milling or turning of brittle materials, it is expected that the chip (swarf) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not

74、influence the cut surface in any way. However, when continuous chip production is evident, unless steps are taken to control the swarf it is likely that it will impinge on the cut surface and mark it. Inevitab</p>

75、<p>　　(5)The effective clearance angle on the cutting tool. For certain geometries of minor cutting edge relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting

76、edge. This can produce a good surface finish but, of course, it is strictly a combination of metal cutting and metal forming and is not to be recommended as a practical cutting method. However, due to cutting tool wear,

77、these conditions occasionally arise and lead to a marked change in the s</p><p>　　Limits and Tolerances </p><p>　　Machine parts are manufactured so they are interchangeable. In other words, each

78、 part of a machine or mechanism is made to a certain size and shape so will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that wil

79、l fit the mating part in the correct way. It is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools become worn. A sl</p><p>

80、;　　A tolerance is the total permissible variation in the size of a part. </p><p>　　The basic size is that size from which limits of size arc derived by the application of allowances and tolerances. </p>

81、;<p>　　Sometimes the limit is allowed in only one direction. This is known as unilateral tolerance.</p><p>　　Unilateral tolerancing is a system of dimensioning where the tolerance (that is variation)

82、is shown in only one direction from the nominal size. Unilateral tolerancing allow the changing of tolerance on a hole or shaft without seriously affecting the fit.</p><p>　　When the tolerance is in both dir

83、ections from the basic size it is known as a bilateral tolerance (plus and minus). </p><p>　　Bilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is split and is shown on

84、 either side of the nominal size. Limit dimensioning is a system of dimensioning where only the maximum and minimum dimensions arc shown. Thus, the tolerance is the difference between these two dimensions. </p>&l

85、t;p>　　Surface Finishing and Dimensional Control </p><p>　　Products that have been completed to their proper shape and size frequently require some type of surface finishing to enable them to satisfactoril

86、y fulfill their function. In some cases, it is necessary to improve the physical properties of the surface material for resistance to penetration or abrasion. In many manufacturing processes, the product surface is left

87、with dirt .chips, grease, or other harmful material upon it. Assemblies that are made of different materials, or from the same materia</p><p>　　Surface finishing may sometimes become an intermediate step pro

88、cessing. For instance, cleaning and polishing are usually essential before any kind of plating process. Some of the cleaning procedures are also used for improving surface smoothness on mating parts and for removing burr

89、s and sharp corners, which might be harmful in later use. Another important need for surface finishing is for corrosion protection in a variety of: environments. The type of protection procedure will depend largely up<

90、;/p><p>　　Satisfying the above objectives necessitates the use of main surface-finishing methods that involve chemical change of the surface mechanical work affecting surface properties, cleaning by a variety o

91、f methods, and the application of protective coatings, organic and metallic. </p><p>　　In the early days of engineering, the mating of parts was achieved by machining one part as nearly as possible to the re

92、quired size, machining the mating part nearly to size, and then completing its machining, continually offering the other part to it, until the desired relationship was obtained. If it was inconvenient to offer one part t

93、o the other part during machining, the final work was done at the bench by a fitter, who scraped the mating parts until the desired fit was obtained, the fitter</p><p>　　When one part can be used 'off th

94、e shelf' to replace another of the same dimension and material specification, the parts are said to be interchangeable. A system of interchangeability usually lowers the production costs as there is no need for an ex

95、pensive, 'fiddling' operation, and it benefits the customer in the event of the need to replace worn parts. </p><p>　　Automatic Fixture Design </p><p>　　Traditional synchronous grippers

96、for assembly equipment move parts to the gripper centre-line, assuring that the parts will be in a known position after they arc picked from a conveyor or nest. However, in some applications, forcing the part to the cent

97、re-line may damage cither the part or equipment. When the part is delicate and a small collision can result in scrap, when its location is fixed by a machine spindle or mould, or when tolerances are tight, it is preferab