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1、<p><b>  畢業(yè)設計譯文</b></p><p>  題 目: 礦井提升及總體設計 </p><p>  學(xué)生姓名: 杜雨航 準考證號: 080112200473 </p><p>  指導老師: 張冬梅 </p><p><b>  2012年<

2、;/b></p><p><b>  LATHES</b></p><p>  The basic machines that are designed primarily to do turning, facing and boring are called lathes. Very little turning is done on other types

3、of machine tools, and nine can do it with equal facility. Because lathe can do boring, facing, drilling, and reaming in addition to turning, their versatility permits several operations to be performed with a single setu

4、p of the workpiece. This accounts for the fact that lathes of various types are more widely used in manufacturing than any other machine t</p><p>  Lathes in various forms have existed for more than two thou

5、sand years. Modem lathes date from about 1797, when Henry Maudsley developed one with a leadscrew. It provided controlled, mechanical feed of the tool. This ingenious Englishman also developed a change-gear system that c

6、ould connect the motions of the spindle and leadscrew and thus enable threads to be cut.</p><p>  Lathe Construction. The essential components of a lathe are depicted in the block diagram of Fig.15-1.These a

7、re the bed, headstock assembly, tailstock assembly, carriage assembly, quick-change gear box, and the leadscrew and feed rod.</p><p>  The bed is the backbone of a lathe. It is usually made of well-normalize

8、d or aged gray or nodular cast iron and provides a heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on th

9、e upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets. Because several other components are mounted and/or move on the</p>

10、<p>  The headstock is mounted in a fixed position on the inner ways at one end of the lathe bed. It provides a powered means of rotating the work at various speeds. It consists, essentially, of a hollow spindle, mo

11、unted in accurate bearings, and a set of transmission gears---similar to a truck transmission---through which the spindle can be rotated at a number of speeds. Most lathes provide from eight to eighteen speeds, usually i

12、n a geometric ratio, and on modern lathes all the speeds can be obtaine</p><p>  Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings

13、, usually preloaded tapered roller or ball types. A longitudinal hole extends through the spindle so that long bar stock can be fed through it. The size of this hole is an important size dimension of a lathe because it d

14、etermines the maximum size of bar stock that can be machined when the material must be fed through the spindle.</p><p>  The inner end of the spindle protrudes from the gear box and contains a means for moun

15、ting various types of chucks, face plates, and dog plates on it. Whereas small lathes often employ a threaded section to which the chucks are screwed, most large lathes utilize either cam-lock or key-drive taper noses. T

16、hese provide a large-diameter taper that assures the accurate alignment of the chuck, and a mechanism that permits the chuck or face plate to be locked or unlocked in position without the necess</p><p>  Pow

17、er is supplied to the spindle by means of an electric motor through a V-belt or silent-chain drive. Most modern lathes have motors of from 5 to 15 horsepower to provide adequate power for carbide and ceramic tools at the

18、ir high cutting speeds.</p><p>  The tailstock assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clampin

19、g the entire assembly in any desired location. An upper casting fits on the lower one and can be moved transversely upon it on some type of keyed ways. This transverse motion permits aligning the tailstock and headstock

20、spindles and provides a method of turning tapers. The third major component of the assembly is the tailsto</p><p>  The carriage assembly provides the means for mounting and moving cutting tools. The carriag

21、e is a relatively flat H-shaped casting that rests and moves on the outer set of ways on the bed. The transverse bar of the carriage contains ways on which the cross slide is mounted and can be moved by means of a feed s

22、crew that is controlled by a small handwheel and a graduated dial. Through the cross slide a means is provided for moving the lathe tool in the direction normal to the axis of rotation of t</p><p>  On most

23、lathes the tool post actually is mounted on a compound rest. This consists of a base, which is mounted on the cross slide so that it can be pivoted about a vertical axis, and an upper casting. The upper casting is mounte

24、d on ways on this base so that it can be moved back and forth and controlled by means of a short lead screw operated by a handwheel and a calibrated dial.</p><p>  Manual and powered motion for the carriage,

25、 and powered motion for the cross slide, is provided by mechanisms within the apron, attached to the front of the carriage. Manual movement of the carriage along the bed is effected by turning a handwheel on the front of

26、 the apron, which is geared to a pinion on the back side. This pinion engages a rack that is attached beneath the upper front edge of the bed in an inverted position.</p><p>  To impart powered movement to t

27、he carriage and cross slide, a rotating feed rod is provided. The feed rod, which contains a keyway throughout most of its length, passes through the two reversing bevel pinions and is keyed to them. Either pinion can be

28、 brought into mesh with a mating bevel gear by means of the reversing lever on the front of the apron and thus provide “forward” or “reverse” power to the carriage. Suitable clutches connect either the rack pinion or the

29、 cross-slide screw to provide</p><p>  For cutting threads, a second means of longitudinal drive is provided by a lead screw. Whereas motion of the carriage when driven by the feed-rod mechanism takes place

30、through a friction clutch in which slippage is possible, motion through the lead screw is by a direct, mechanical connection between the apron and the lead screw. This is achieved by a split nut. By means of a clamping l

31、ever on the front of the apron, the split nut can be closed around the lead screw. With the split nut closed, th</p><p>  Modern lathes have a quick-change gear box. The input end of this gear box is driven

32、from the lathe spindle by means of suitable gearing. The output end of the gear box is connected to the feed rod and lead screw. Thus, through this gear train, leading from the spindle to the quick-change gear box, thenc

33、e to the lead screw and feed rod, and then to the carriage, the cutting tool can be made to move a specific distance, either longitudinally or transversely, for each revolution of the spindle. A </p><p>  CU

34、TTING TOOL</p><p>  Shape of cutting tools, particularly the angles, and tool material are very important factors. The purpose of this unit is to introduce the cutting tool geometry and tool materials.</p

35、><p>  Cutting Tool Geometry</p><p>  Angles determine greatly not only tool life but finish quality as well. General principles upon which cutting tool angles are based do not depend on the partic

36、ular tool. Basically, grinding wheel are being designed. Since, however, the lathe (turning) tool, depicted in Fig.14-1, might be easiest to visualize, its geometry is discussed.</p><p>  Tool features have

37、been identified by many names. The technical literature is full of confusing terminology. Thus in the attempt to clear up existing disorganized conceptions and nomenclature, the American Society of Mechanical Engineers p

38、ublished ASA Standard B5-22-1950. what follows is based on it.</p><p>  A single-point tool is a cutting tool having one face and one continuous cutting edge. Tool angles identified in Fig. 14-2 are as follo

39、ws: (1) Back-rake angle, (2) Side-rake angle, (3) End-relief angle (4) End-relief angle (5) Side-relief angle (6) End-cutting-edge angle, (7) Side-cutting-edge angle, (8) Nose angle, (9) Nose radius.</p><p>

40、  Tool angle 1, on front view, is the back-rake angle. It is the angle between the tool face and a line parallel to the base of the shank in a longitudinal plane perpendicular to the tool base. Then this angle is downwar

41、d from front to rear of the cutting edge, the rake id positive; when upward from front to back, the rake is negative. This angle is most significant in the machining process, because it directly affects the cutting force

42、, finish, and tool life. </p><p>  The side-rake angle, numbered 2, measures the slope of the face in a cross plane perpendicular to the tool base. It, also, is an important angle, because it directs chip fl

43、ow to the side of the tool post and permits the tool to feed more easily into the work.</p><p>  The end-relief angle is measured between a line perpendicular to the base and the end flank immediately below

44、the end cutting edge; it is numbered 3 in the figure. It provides clearance between work and tool so that its cut surface can flow by with minimum rubbing against the tool. To save time, a portion of the end flank of the

45、 tool may sometimes be left unground, having been previously forged to size. In such case, this end-clearance angle, numbered 4, measured to the end flank surface below t</p><p>  Often the end cutting edge

46、is oblique to the flank. The relief angle is then best measured in a plane normal to the end cutting edge perpendicular to the base of the tool. This clearance permits the tool to advance more smoothly into the work.<

47、/p><p>  The side-relief angle, indicated as 5, is measured between the side flank, just below the cutting edge, and a line through the cutting edge perpendicular to the base of the tool. This clearance permits

48、 the tool to advance more smoothly into the work.</p><p>  Angle 6 is the end-cutting-edge angle measured between the end cutting edge and a line perpendicular to the side of the tool shank. This angle preve

49、nts rubbing of the cut surface and permits longer tool life.</p><p>  The side-cutting-edge angle, numbered 7, is the angle between the side cutting edge and the side of the tool shank. The true length of cu

50、t is along this edge. Thus the angle determines the distribution of the cutting force. The greater the angle, the longer the tool life; but the possibility of chatter increases. A compromise must, as usual, be reached.&l

51、t;/p><p>  The nose angle, number 8, is the angle between the two component cutting edges. If the corner is rounded off, the arc size is defined by the nose radius 9. the radius size influences finish and chatt

52、er.</p><p>  Cutting Tool Materials</p><p>  A large number of cutting tool materials have been developed to meet the demands of high metal-removal rates. The most important of these materials a

53、nd their influence on cutter design, are described below.</p><p>  High Carbon Steel. Historically, high carbon steel was the earliest cutting material used industrially, but it has now been almost entirely

54、superseded since it starts to temper at about 220℃ and this irreversible softening process continues as temperature increases. Cutting speeds with carbon steel tools are therefore limited to about 0.15m/s (30ft/min) when

55、 cutting mild steel, and even at these speeds a copious supply of coolant is required.</p><p>  High-speed Steel. To overcome the low cutting speed restriction imposed by plain carbon steels, a range of allo

56、y steels, known as high-speed steels, began to be introduced during the early years of this century. The chemical composition of these steels varies greatly, but they basically contain about 0.7% carbon and 4% chromium,

57、with addition of tungsten, vanadium, molybdenum and cobalt in varying percentages. They maintain their hardness at temperatures up to about 600℃, but soften rapidly at c</p><p>  Sintered Carbides. Carbide c

58、utting tools, which were developed in Germany in the late 1920s, usually consist of tungsten carbide or mixtures of tungsten carbide and titanium or tantalum carbide in powder form, sintered in a matrix of cobalt or nick

59、el. Because of the comparatively high cost of this tool material and its low rupture strength, it is normally produced in the form of tips which are either brazed to a steel shank or mechanically clamped in a specially d

60、esigned holder. Mechanically cla</p><p>  The high hardness of carbide tools at elevated temperatures enables them to be used at much faster cutting speeds than high-speed steel (of 3-4m/s(600-800ft/min)when

61、 cutting mild steel). They are manufactured in several grades, enabling them to be used for most machining applications. Their earlier brittleness has been largely overcome by the introduction of tougher grades, which ar

62、e frequently used for interrupted cuts including many arduous face-milling operations.</p><p>  Recently, improvements have been claimed by using tungsten carbide tools coated with titanium carbide or titani

63、um nitride (about 0.0005mm coating thickness). These tools are more resistant to wear than conventional tungsten carbide tools, and the reduction in interface friction using titanium nitride results in a reduction in cut

64、ting forces and in tool temperatures. Hence, higher metal removal rates are possible without detriment to tool life or alternatively longer tool lives could be achieved </p><p>  The uses of other forms of c

65、oating with aluminum oxide and polycrystalline cubic boron nitride are still in an experimental stage, but it is likely that they will have important applications when machining cast iron, hardened steels and high meltin

66、g point alloys.</p><p>  Ceramics. The so-called ceramic group of cutting tools represents the most recent development in cutting tool materials. They consist mainly of sintered oxides, usually aluminum oxid

67、e, and are almost invariably in the form of clamped tips. Because of the comparative cheapness of ceramic tips and the difficulty of grinding them without causing thermal cracking, they are made as throw-away inserts.<

68、;/p><p>  Ceramic tools are a post-war introduction and are mot yet in general factory use. Their most likely application is in cutting metal at very high speeds, beyond the limits possible with carbide tools.

69、Cramics resist the formation of a built-up edge and in consequence produce good surface finishes. Since the present generation of machine tools is designed with only sufficient power to exploit carbide tooling, it is lik

70、ely that, for the time being, ceramics will be restricted to high-speed finish m</p><p>  As they are poorer conductors of heat than carbides, temperatures at the rake face are higher than in carbide tools,

71、although the friction force is usually lower. To strengthen the cutting edge, and consequently improve the life of the ceramic tool, a small chamfer or radius is often stoned on the cutting edge, although this increases

72、the power consumption.</p><p>  Diamonds. For producing very fine finishes of 0.05-0.08um(2-3um) on non-ferrous metals such as copper and aluminum, diamond tools are often used. The diamond is brazed to a st

73、eel shank. Diamond turning and boring are essentially finishing operations, as the forces imposed by any but the smallest cuts cause the diamond to fracture or be torn from its mounting. Under suitable conditions diamond

74、s have exceptionally long cutting lives. </p><p>  Synthetic polycrystalline diamonds are now available as mechanically clamped cutting tips. Due to their high cost they have very limited applications, but a

75、re sometimes used for machining abrasive aluminum-silicon alloys, fused silica and reinforced plastics. The random orientation of their crystals gives them improved impact resistance, making them suitable for interrupted

76、 cutting.</p><p><b>  車(chē)床</b></p><p>  用于車(chē)外圓、端面和鏜孔等加工的機床稱(chēng)作車(chē)床。車(chē)削很少在其他種類(lèi)的機床上進(jìn)行,因為其他機床都不能像車(chē)床那樣方便地進(jìn)行車(chē)削加工。由于車(chē)床除了用于車(chē)外圓還能用于鏜孔、車(chē)端面、鉆孔和鉸孔,車(chē)床的多功能性可以是共建在一次定位安裝中完成多種加工。這種是在生產(chǎn)中普遍使用的各種車(chē)床比其他種類(lèi)的機床都要多

77、的原因。</p><p>  兩千多年前就已經(jīng)有了車(chē)床?,F代車(chē)床可以追溯到大約1797年,那時(shí)亨利·莫德斯利發(fā)明了一種具有絲杠的車(chē)床。這種車(chē)床可以控制工具的機械進(jìn)給。這位聰明的英國人還發(fā)明了一種把主軸和絲杠相連的變速裝置,這樣就可以切削螺紋。</p><p>  圖15-1中標出了車(chē)床的主要部件:床身、主軸箱組件、尾架組件、拖板組件、變速齒輪箱、絲杠和光杠。</p>

78、<p>  床身是車(chē)床的基礎件。它通常是由經(jīng)過(guò)充分正火或時(shí)效處理的灰鑄鐵或者球墨鑄鐵制成,它是一個(gè)堅固的剛性框架,所有其他主要部件都安裝在床身上。通常在床身上那個(gè)面有內外另組平行的導軌。一些制造廠(chǎng)生產(chǎn)的四個(gè)條導軌都采用倒“V”形,而另一些制造廠(chǎng)則將倒“V”形導軌和平面導軌相結合。由于其他的部件要安置在導軌上并(或)在導軌上移動(dòng),導軌要經(jīng)過(guò)精密加工,以保證其裝配精度。同樣地,在操作中應該小心,以避免損傷導軌。導軌上的任何誤差,

79、常常會(huì )使整個(gè)機床的精度遭到破壞。大多數現代車(chē)床的導軌要進(jìn)行變面淬火處理,以減少磨損和擦傷,具有更大的耐磨性。</p><p>  主軸箱安裝在車(chē)身一端內導軌的固定位置上。它提供動(dòng)力,使工件在各種速度下旋轉。它基本上有一個(gè)安裝在精密軸承中的空心主軸和一系列變速齒輪——類(lèi)似于卡車(chē)變速箱所組成,通過(guò)變速齒輪,主軸可以在許多種轉速下旋轉。大多數車(chē)床有8~18種轉速,一般按等比級數排列。在現代車(chē)床上只需扳動(dòng)2~4個(gè)手柄,就

80、能得到全部檔位的轉速。目前發(fā)展的趨勢是通過(guò)電氣的或機械的裝置進(jìn)行無(wú)極變速。</p><p>  由于車(chē)床的精度在很大程度上取決于主軸,因此主軸的結構尺寸較大,通常安裝在緊密配合的重型圓錐滾子軸承或球軸承中。主軸中有一個(gè)貫穿全長(cháng)的通孔,長(cháng)棒料可以通過(guò)該孔送料。主軸孔的大小是車(chē)床的一個(gè)重要尺寸,因為當工件必須通過(guò)主軸孔供料時(shí),它確定了能夠加工棒料毛坯的最大外徑尺寸。</p><p>  主軸的

81、內端從主軸箱中凸出,其上可以安裝多種卡盤(pán)、花盤(pán)和擋塊。而小型的車(chē)床常有螺紋截面供安裝卡盤(pán)之用。很多大車(chē)床使用偏心夾或鍵動(dòng)圓錐軸頭。這些附件組成了一個(gè)大直徑的圓錐體,以保證對卡盤(pán)進(jìn)行精確地裝配,并且不用旋轉這些笨重的附件就可以鎖定或松開(kāi)卡盤(pán)或花盤(pán)。</p><p>  主軸由電動(dòng)機經(jīng)V帶或無(wú)聲鏈裝置提供動(dòng)力。大多數現代車(chē)床都裝置有5~15馬力的電動(dòng)機,為硬質(zhì)合金和金屬陶瓷合金刀具提供足夠的動(dòng)力,進(jìn)行高速切削。<

82、;/p><p>  尾座組件主要由三部分組成。底座與床身的內側導軌配合,并可以子導軌上做縱向移動(dòng),底座上有一個(gè)可以使整個(gè)尾座組件加緊在任意位置上的裝置。尾座安裝在底座上,可以沿鍵槽在底座上橫向移動(dòng),使尾座與主軸箱中的主軸對中并為切削圓錐體提供方便。尾座組件的第三部分是尾座套筒,它是一個(gè)直徑通常在2~3英寸之間的鋼制空心圓柱軸。通過(guò)手輪和螺桿,尾座套筒可以在尾座體中縱向移入和移出幾英寸?;顒?dòng)套筒的開(kāi)口一端具有莫氏錐度,

83、可以用于安裝頂尖或諸如鉆頭之類(lèi)的各種刀具。通常在活動(dòng)套筒的外表面刻有幾英寸長(cháng)的刻度,以控制尾座的前后移動(dòng)。鎖定裝置可以使套筒在所需的位置上夾緊。</p><p>  拖板組件用于安裝和移動(dòng)切削工具。拖板是一個(gè)相對平滑的H形鑄件,安裝在床身外側導軌上,并可以在上面移動(dòng)。大拖板上有橫向導軌,使橫向拖板可以安裝在上面,并通過(guò)絲杠使其運動(dòng),絲杠由一個(gè)小手柄和刻度盤(pán)控制。橫拖板可以帶動(dòng)刀具垂直于工件的旋轉軸線(xiàn)切削。<

84、/p><p>  大多數車(chē)床的刀架安裝在復式刀座上,刀座上有底座,底座安裝在橫拖板上,可繞垂直軸和上刀架轉動(dòng)。上刀架安裝在底座上,可用手輪和刻度盤(pán)控制一個(gè)短絲杠使其前后移動(dòng)。</p><p>  溜板箱裝在大拖板前面,通過(guò)溜板箱內的機械裝置可以手動(dòng)和動(dòng)力驅動(dòng)大拖板以及動(dòng)力驅動(dòng)橫拖板。通過(guò)轉動(dòng)溜板箱前的手輪,可以手動(dòng)操作拖板沿床身移動(dòng)。手輪的另一端與溜板箱背面的小齒輪連接,小齒輪與齒條嚙合,齒條

85、倒裝在床身前上邊緣的下面。</p><p>  利用光桿可以將動(dòng)力傳遞給大拖板和橫拖板。光桿上有一個(gè)幾乎貫穿于整個(gè)光杠的鍵槽,光杠通過(guò)兩個(gè)轉向相反并用鍵連接的錐齒輪傳遞動(dòng)力。通過(guò)溜板箱前的換向手柄可使嚙合齒輪與其中的一個(gè)錐齒輪嚙合,為大拖板提供“向前”或“向后”的動(dòng)力。適當的離合器或者齒條小齒輪連接或者與橫拖板的螺桿連接,是拖板縱向移動(dòng)或使橫拖板橫向移動(dòng)。</p><p>  對于螺紋加工

86、,絲杠提供了第二種縱向移動(dòng)的方法。光杠通過(guò)摩擦離合器驅動(dòng)拖板移動(dòng),離合器可能會(huì )產(chǎn)生打滑現象。而絲杠產(chǎn)生的運動(dòng)是通過(guò)滑板箱與絲杠之間的直接機械連接來(lái)實(shí)現的,對于螺母可以實(shí)現這種連接。通過(guò)溜板箱前面的夾緊手柄可以使對開(kāi)螺母緊緊包合絲杠。當對開(kāi)螺母閉合時(shí),可以沿絲杠直接驅動(dòng)拖板,而不會(huì )出現打滑的可能性。</p><p>  現代車(chē)床有一個(gè)變速齒輪箱,齒輪箱的輸入端有車(chē)床主軸通過(guò)合適的齒輪傳動(dòng)來(lái)驅動(dòng)。齒輪箱的輸出端與光杠

87、和絲杠連接。主軸就是這樣通過(guò)齒輪傳動(dòng)鏈驅動(dòng)變速齒輪箱,在帶動(dòng)絲杠和光杠,然后帶動(dòng)拖板,刀具就可以按主軸的轉數縱向地或橫向地精確移動(dòng)。一臺典型的車(chē)床的主軸每旋轉一圈,通過(guò)光杠可以獲得從0.002到0.118英寸尺寸范圍內的48種進(jìn)給量;而使用絲杠可以車(chē)削從1.5到92牙/英寸范圍內的48種不同螺紋。一些老式的或價(jià)廉的車(chē)床為了能夠得到所有的進(jìn)給量和加工出多有螺紋,必須更換主軸和變速箱之間的齒輪系中的一個(gè)或兩個(gè)齒輪。</p>&

88、lt;p><b>  金屬切削刀具</b></p><p>  刀具的形狀(特別是其角度)和材料是刀具的兩個(gè)非常重要的因素。本文向大家介紹刀具的幾何參數和刀具材料。</p><p><b>  刀具幾何參數</b></p><p>  刀具的角度不僅在很大程度決定了刀具的壽命,而且也決定加工的表面質(zhì)量。刀具角度設計的

89、一般性原則不因某種特殊刀具而變。車(chē)刀、銑刀、鉆頭甚至是砂輪的設計,所要考慮的因素基本相同。圖14.1所示的車(chē)刀外形易于觀(guān)察,我們即以此為例來(lái)討論刀具的幾何參數。</p><p>  刀具特征參數名目繁多,技術(shù)文獻中術(shù)語(yǔ)使用也很混亂。為了澄清已有的混亂的概念和術(shù)語(yǔ),美國機械工程師協(xié)會(huì )頒布了ASA標準B5-22—1950,本文的術(shù)語(yǔ)即以此為依據。</p><p>  單尖刀具是指只有一個(gè)前刀面

90、和一條連續切削刃的刀具。圖14-2所示各個(gè)角度定義如下:</p><p>  主視圖中的角度1為背前角,它是在垂直于刀具基面的縱向剖面內的平行于刀柄的一條直線(xiàn)與刀面之間的夾角。如該角后傾,則為正角,否則為負角。背前角對加工過(guò)程影響很大,它直接影響刀具的切削力、表面光潔度以及刀具耐用度。</p><p>  角度2為側前角,它是刀具前刀面在垂直于刀具基面的橫向剖面內的傾斜角。側前角也是一個(gè)重

91、要的幾何角度,它能把切屑引向刀架的一側,并能使進(jìn)給更加容易。</p><p>  端后角是刀具基面的垂線(xiàn)與緊靠端切削刃下的斷后刀面之間的夾角,即圖中角度3。它確保工件和刀具之間有間隙使得切屑經(jīng)過(guò)刀具時(shí)摩擦最小。為了節省磨刀時(shí)間,刀具段后刀面的一部分有時(shí)可以直接鍛造成形,而不需要進(jìn)行磨削。在這種強況下,從斷后刀面刃磨部位下量出的角度(角度4)比端后角大。</p><p>  通常端切削刃與端

92、后刀面是斜交的,因此,端后角最好是在于端切削刃相垂直的平面內進(jìn)行測量。后角也可用刀具的側面和端面的視圖來(lái)表示。</p><p>  角度5表示側后角,它是端切削刃下面的側后刀面與通過(guò)切削刃并垂直于刀具基面的直線(xiàn)之間的夾角。側后角能使刀具更平穩的切入工件。</p><p>  角度6為端切削刃角,它是端切削刃和垂直于刀具柄側面的直線(xiàn)之間的夾角。該角可減少刀具和已加工表面之間的摩擦,延長(cháng)刀具的

93、使用壽命。</p><p>  角度7為側切削刃角,它是測切削刃和刀柄側面之間的夾角。由于刀具切削長(cháng)度是沿著(zhù)此切削刃的,因此,側切削刃角決定了切削力的分布。該角度越大,刀具壽命越長(cháng),但顫振的可能性也隨之增加。設計時(shí),這兩方面的因素都要兼顧。</p><p>  角度8為刀尖角,它是兩條切削刃之間的夾角。刀尖采用圓弧過(guò)渡時(shí),圓弧的尺寸可用弧半徑9來(lái)表示。刀尖圓弧半徑的尺寸對表面光潔度及顫振有

94、影響。</p><p><b>  刀具材料</b></p><p>  已有許多刀具材料能滿(mǎn)足高金屬切削率的要求。下面討論最重要的幾種材料和它們對刀具設計的影響。</p><p>  1.高碳鋼:才刀具歷史上,高碳鋼是最早用于工業(yè)上的刀具材料,但目前已幾乎全部被廢棄不用了,因為它在220°C左右開(kāi)始回火,而且這種軟化過(guò)程隨著(zhù)溫度的升

95、高而繼續。因此,在切削低碳鋼時(shí),高碳鋼刀具的切削速度限于大約0.15mm/s(30ft/min),即使在這種速度時(shí)也要連續供應切削液。</p><p>  2.高速鋼:為克服普通碳素鋼切削速度較低的特點(diǎn),本世紀初,幾種稱(chēng)為高速鋼的合金鋼開(kāi)始用于金屬切削。這些鋼的化學(xué)成分差別很大,但基本上都含有大約0.7%碳和4%鉻,另外還有比例不一樣的鎢、釩、鉬和鈷。它們在高達600°C時(shí)仍能保持硬度,但在更高溫度下會(huì )

96、迅速軟化。實(shí)驗表明:高速鋼切削低碳鋼時(shí),如速度超過(guò)1.8m/s(350ft/min),就會(huì )很快失效,而且許多高速鋼材料在速度超過(guò)0.75m/s(150ft/min)時(shí),就不能成功切削低碳鋼。</p><p>  3.硬質(zhì)合金:這是20世紀20年代晚期德國出現的硬質(zhì)合金刀具,通常是將碳化鎢或碳化鎢和碳化鈦或碳化鉭的混合物以粉末形式沉積在鈷或鎳的基體上。因為較高成本和較低的斷裂強度,它們通常以刀片形式銅焊在鋼質(zhì)刀柄上

97、或機械夾持在特質(zhì)夾具撒上。機夾形式刀頭經(jīng)常做成不重磨形式,當所有刀刃都用廢時(shí),就將刀片丟棄,因為重磨成本比新刀片的成本高得多。</p><p>  硬質(zhì)合金刀具在高溫時(shí)具有高硬度,故它們的切削速度比高速鋼高得多,切削低碳鋼時(shí)為3~4m/s(600-800ft/min),它們有幾種牌號專(zhuān)用于大多數加工場(chǎng)合。韌性更高的硬質(zhì)合金大大克服了早期產(chǎn)品的脆性,故也能用于斷續切削,包括許多費力的面銑加工。</p>

98、<p>  最近,已經(jīng)出現碳化鈦或氮化鈦涂層碳化鎢刀具(涂層大約厚0.0005mm)。這些刀具比普通碳化鎢硬質(zhì)合金刀具更耐磨,使用氮化鈦涂層界面摩擦力減小,導致切削力和刀具溫度降低。因此,不降低刀具壽命就可得到較高的金屬切削率,或不改變金屬切削率而延長(cháng)刀具壽命。</p><p>  使用氧化鋁涂層和多晶氮化硼的其他涂層尚處于實(shí)驗階段,但它們很可能在加工鑄鐵、淬硬鋼和高熔點(diǎn)合金時(shí)有重要應用。</p

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