机械加工及其加工工具

1、剑五汽蹿辽漫晦墅蘼莼Machining Techniques And Tool永滞津翠暑舜懑碱弟沭Drilling and Drills瓿倒苎畈邈砖翠敖狁辨Drilling involves producing through or blind holes in a workpiece by forcing a tool, which rotates around its axis, against the workpiece.日辏烬嫂殆猢鸠废舨骏Consequently, the range of cutting from that axis of rotation is equal to

2、the radius of the required hole. In practice, two symmetrical cutting edges that rotate about the same axis are employed.糈黠捍咔旃卉轷瞳缔瀑Drilling operations can be carried out by using either hand drills or drilling machines. The latter differ in size and construction. Nevertheless, the tool always rotate

3、s around its axis while the workpiece is kept firmly fixed. This is contrary to drilling on a lathe.抗挑险解绺投假化慷辍Cutting Tool for Drilling Operation描井瓷厅纣指冒铒营么In drilling operations, a cylindrical rotary-end cutting tool, called a drill, is employed. The drill can have either one or more cutting edges a

4、nd corresponding flutes, which can be straight or helical.淮潮金戽馇疡岈纫绷蝣The function of the flutes is to provide outlet passages for the chips generated during the drilling operation and also to allow lubricants and coolants to reach the cutting edges and the surface being machined. Following is a surve

5、y of the commonly used drills.奶瞽脆脉黉熠稃脞炅噎Twist drill. The twist drill is the most common type of drill. It has two cutting edges and two helical flutes that continue over the length of the drill body,. The drill also consists of a neck and a shank that can be either straight or tapered.舵菩无螭字品蚓枵胚击In t

6、he latter case, the shank is fitted by the wedge action into the tapered socket of the spindle and has a tang, which goes into a slot in the spindle socket, thus acting as a solid means for transmitting rotation.迤钙帽陌兀瞥噬蠢蚋彩On the other hand, straight-shank drills are held in a drill chuck that is, in

7、 turn, fitted into the spindle socket in the same way as tapered shank drills.穰省捱钯畅肯挚判慧绀The two cutting edges are referred to as the lips, and are connected together by a wedge, which is a chisel-like edge. The twist drill also has two margins, which enable proper guidance and locating of the drill

8、while it is in operation.亡本吖狰肉桥酩俳锓茎The tool point angle (TPA) is formed by the two lips and is chosen based on the properties of the material to be cut. The usual TPA for commercial drills is 118, which is appropriate for drilling low-carbon steels and cast irons.襁糟忿挥里距坷扶坠褴For harder and tougher met

9、als, such as hardened steel, brass and bronze, larger TPAs (130or 140) give better performance. The helix angle of the flutes of the commonly used twist drills ranges between 24and 30. When drilling copper or soft plastics, higher values for the helix angle are recommended (between 35and 45).蹦咛敕镤瓢曙妣

10、柁褥肢Twist drills are usually made of high-speed steel, although carbide-tipped drills are also available. The sizes of twist drills used in industrial practice range from 0.01 up to 3.25 in. (i. e., 0.25 up to 80 mm).是括肌救隰忻鳔矛铞吻Core drills. A core drill consists of the chamfer, body, neck, and shank.

11、This type of drill may have either three or four flutes and equal number of margins, which ensure superior guidance, thus resulting in high machining accuracy.遒妒羔朕僚夺浈寤边菪that a core drill has flat end. The chamfer can have three or four cutting edges or lips, and the lip angle may vary between 90and

12、120.惑儡俩眵镊纫始腭哟轧Core drills are employed for enlarging previously made holes and not for originating holes. This type of drill is characterized by greater productivity, high machining accuracy, and superior quality of the drilled surfaces.炜怙褫兰嘻参藕惹檬蔫Gun drills. Gun drills are used for drilling deep hol

13、es. All gun drills are straight-fluted, and each has a single cutting edge. A hole in the body acts as a conduit to transmit coolant under considerable pressure to the tip of the drill.鐾寤龠保泐辛应聪允童There are two kinds of gun drills, namely, the center-cut gun drill used for drilling blind holes and the

14、 trepanning drill. The latter has a cylindrical groove at its center, thus generating a solid core, which guides the tool as it proceeds during the drilling operation.祜圩身铬斐涎艾宦埂丿Spade drills. Spade drills are used for drilling large holes of 3.5 in.(90mm) or more. Their design results in a marked sav

15、ing in cost of the tool as well as a tangible reduction in its weight, which facilitates its handling. Moreover, this type of drill is easy to grind.片蛎兵疬粤匦篇蜗掮莲Milling and Milling Cutter瓤裤描宛籽贸觯铮肚Milling is a machining process that is carried out by means of a multiedge rotating tool known as a millin

16、g cutter.渺篱罪囟郾爱九咛尖希In this process, metal removal is achieved through combining the rotary motion of the milling cutter and linear motions of the workpiece simultaneously. Milling operations are employed in producing flat, contoured and helical surfaces as well as for thread- and gear-cutting operat

17、ion.菊祈党鲦蛊霈顷鼎骥齿Each of the cutting edges of a milling cutter acts as an individual single-point cutter when it engages with the workpiece metal. Therefore, each of those cutting edges has appropriate rake and relief angles.笏鲦钱璐班堋颛睡後踪Since only a few of the cutting edges are engaged with the workpiece

18、 at a time, heavy cuts can be taken without adversely affecting the tool life. In fact, the permissible cutting speeds and feeds for milling are three to four times higher than those for turning or drilling.吹录卸枭扇醺聆蕲虑叛Moreover, the quality of the surfaces machined by milling is generally superior to

19、the quality of surfaces machined by trning, shaping, or drilling.殛焖吻悚卿拎胶拘垭刻A wide variety of milling cutters is available in industry. This, together with the fact that a milling machine is a very versatile machine tool, makes the milling machine the backbone of a machining workshop.岗扮你劭癍枕诒屏焕法As far

20、 as the direction of cutter rotation and workpiece feed are concerned, milling is performed by either of the following two methods.貉累独倍槽谍综锺缰胝Up milling (conventional milling). In up milling the workpiece is fed against the direction of cutter rotation. As we can see in that figure, the depth of cut

21、(and consequently the load) gradually increases on the successively engaged cutting edges.播邻乘墩铡何疗瞠扳拳Therefore, the machining process involves no impact loading, thus ensuring smoother operation of the machine tool and longer tool life. The quality of the machined surface obtained by up milling is no

22、t very high. Nevertheless, up milling is commonly used in industry, especially for rough cuts.航榷裱梨愿鹱墀矾壮狷Down milling (climb milling).In down milling the cutter rotation coincides with the direction of feed at the contact point between the tool and the workpiece. It can also be seen that the maximum

23、depth of cut is achieved directly as the cutter engages with the workpiece.倨俏楫登托檬忧咻怫捕This results in a kind of impact, or sudden loading. Therefore, this method cannot be used unless the milling machine is equipped with a backlash eliminator on the feed screw. The advantages of this method include h

24、igher quality of the machined surface and easier clamping of workpieces, since the cutting forces act downward.汝访斑侥岣秭霁艰瑁鳟Types of Milling Cutters账旅腐信霜够銮挪饪蚌There is a wide variety of milling cutter shapes. Each of them is designed to perform effectively a specific milling operation.赣夯涠邕菸豕围蝉轵料Generall

25、y, a milling cutter can be described as a multiedge cutting tool having the shape of a solid of revolution, with the cutting teeth arranged either on the periphery or on an end face or on both. Following is a quick survey of the commonly used types of milling cutters.锲蛱借毋湍埠扛钷莜羞Plain milling cutter.

26、A plain milling cutter is a disk-shaped cutting tool that may have either straight or helical teeth. This type is always mounted on horizontal milling machines and is used for machining flat surfaces.岚若腆悖跑阶舾搜鼋蹦Face milling cutter. A face milling cutter is also used for machining flat surfaces. It is

27、 bolted at the end of a short arbor, which is in turn mounted on a vertical milling machine.捉旺佰埠粲樊福嗝父移Plain metal slitting saw cutter.Indicates a plain metal slitting saw cutter. we can see that it actually involves a very thin plain milling cutter.琏绮缃附萎蓝椟划拣Side milling cutter. A side milling cutter

28、 is used for cutting slots, grooves, and splines.It is quite similar to the plain milling cutter, the difference being that this type has teeth on the sides. As is the case with the plain cutter, the cutting teeth can be straight or helical.狗瑚常唛貌俑骄裙淄冀Angle milling cutter. An angle milling cutter is

29、employed in cutting dovetail grooves, ratchet wheels.濉鬏孬傥迳轫籁蓄辐偎T-slot cutter. A T-slot cutter involves a plain milling cutter with an integral shaft normal to it. As the name suggests, this type is used for milling T-slots.恿泄筮迈谎矢杩锊抉不End mill cutter. End mill cutters find common applications in cutti

30、ng slots, grooves, flutes, splines, pocketing work, and the like.Indicates an end mill cutter. The latter is always mounted on a vertical milling machine and can have two or four flutes, which may be either straight or helical.钝碰侍酒毽际柔攴铈盎Form milling cutter. The teeth of a form milling cutter have a

31、certain shape, which is identical to the section of the metal to be removed during the milling operation. Examples of this type include gear cutters, gear hobs, convex and concave cutters, and the like. From milling cutters are mounted on horizontal milling machines.骼汔腚困霰匍绶蕾驻偏Materials of Milling Cu

32、tters肃幂蚀训耻淆牛凡狁痔The commonly used milling cutters are made of high-speed steel, which is generally adequate for most jobs.裟傲坚暗料素昙栖蚴岜Milling cutters tipped with sintered carbides or cast nonferrous alloys as cutting teeth are usually employed for mass production, where heavier cuts and/or high cutting

33、 speeds are required.靛示斡贱沧罗澌却肺雕It has already been stated that the workpiece must be located relative to the cutting tool, and be secured in that position. After the workpiece has been marked out, it is still necessary to position it with respect to the machine movements, and to clamp it in that pos

34、ition before machining is started.膺们媲驸馆蔸篮涣倩蒇When several identical workpieces are to be produced the need to mark out each part is eliminated by the use of jigs and fixtures, but if a casting or forging is involved, a trial workpiece is marked out, to ensure that the workpiece can be produced from i

35、t, and to ensure that ribs, cores, etc. have not become misplaced.掠溅姐伏庠卵僳後驱荃Jigs and fixtures are alike in that they both incorporate devices to ensure that the workpiece is correctly located and clamped, but they differ in that jigs incorporate means of tool guiding during the actual cutting operat

36、ion, and fixtures do not.阊掺郛蛙筇舾疡谦珀黍In practice, the only cutting tools that can be guided while actually cutting are drills, reamers, and similar cutters; and so jigs are associated with drilling operations, and fixtures with all other operations. Fixtures may incorporate means of setting the cuttin

37、g tools relative to the location system.串倥蔷绕于捶叶袷觏昆The advantages of jigs and fixtures can be summarised as follows:诣芩烊骞镑截画莆璜灯1)Marking out and other measuring and setting out methods are eliminated;龆樗龊鑫胁秋蹑仲缱揭2)Unskilled workers may proceed confidently and quickly in knowledge that the workpiece can

38、be positioned correctly, and the tools guided or set;骑诳喙恨疾就蠢吗糕金3)the assembly of parts is facilitated, since all components will be identical within small limits, and “trying” and filing of work is eliminated;髑痃莲段价潆抵涵髀苁4)The parts will be interchangeable, and if the product sold over a wide area, th

39、e problem of spare parts will be simplified.廉俾柱檀酌琦犊幔烫窘Bolt holes often have 1.5mm or even 3.0mm clearance for the bolt, and the reader may doubt the necessity of making precision jigs for such work. It must be remembered that the jigs, once made, will be used on many components, and the extra cost o

40、f an accurately made jig is spread over a large output.拖报彭仍缪捺鹣斡丿窄Furthermore, it is surprising how small errors accumulate in a mechanism during its assembly. When a clearance is specified, it is better to ensure its observance, rather than to allow careless marking out and machining to encroach upo

41、n it讹胎肮蔹洞旨拆取踝怩1) The location of workpiece. Represents a body that is completely free in space. In this condition it has six degrees of freedom. Consider these freedoms with respect to the three mutually perpendicular axes XX, YY, and ZZ.渣郑娇唿呶矮雀驰奁蚂The body can move along any of these axes; it theref

42、ore has three freedoms of translation. It can also rotate about any of the three axes; it therefore has three freedoms of rotation. The total number of freedoms is six. When work is located, as many of these freedoms as possible must be eliminated, to ensure that the operation is performed with the

43、required accuracy.昃嗔秀蓼糁越篙辖澳蛄Accuracy is ensured by machining suitable location features as early as possible, and using them for all location, unless other considerations mean that other location features must be used. If it is necessary, the new location features must be machined as a result of loc

44、ation from the former location features.壅圹刎禧猊控迭律霹迥2) The clamping of the workpiece. The clamping system must be such that the workpiece is held against the cutting forces, and the clamping forces must not be so great as to cause the workpiece to become distorted or damaged.曾赣巯卞颅桐锸吝堕饽The workpiece mu

45、st be supported beneath the point of clamping, to ensure that the forces are taken by the main frame of the jig or fixture, and on to the machine table and bed. When jigs and fixtures are designed, the clamping system is designed to ensure that the correct clamping force is applied, and that the cla

46、mps can be operated quickly but with safety.戛遂龋蛑裙貂怒谂罚旮Definition of a Drill Jig抒蹴韦杳财枚蛙稆壤痹A drill jig is a device for ensuring that a hole to be drilled, tapped, or reamed in a workpiece will be machined in the proper place.冷疵猡彦丙冤桄畎诰伺Basically it consists of a clamping device to hold the part in posi

47、tion under hardened-steel bushings through which the drill passes during the drilling operation. The drill is guided by the bushings.徙炯羿昀啡嘉柚寡阄隘If the workpiece is of simple construction, the jig may be clamped on the workpiece. In most cases, however, the workpiece is held by the jig, and the jig is

48、 arranged so that the workpiece can be quickly inserted and as quickly removed after the machining operation is performed.赉伛愤墙润掣寝漱嚎醇Jigs make it possible to drill, ream, and tap holes at much greater speeds and with greater accuracy than when the holes are produced by conventional hand methods. Anot

49、her advantage is that skilled workers are not required when jigs are used. Responsibility for the accuracy of hole location is taken from the operator and given to the jig.斧律影公驳尚讫滴咎砼The term jig should be used only for devices employed while drilling, reaming, or tapping holes. It is not fastened to

50、 the machine on which it is used and may be moved around on the table of the drilling machine to bring each bushing directly under the drill. Jigs physically limit and control the path of the cutting tool.酡烦谫塬叩後佰晚烧气If the operation includes machining operations like milling, planing, shaping, turnin

51、g, etc., the term fixture should be used. A fixture holds the work during machining operations but does not contain special arrangements for guiding the cutting tool ,as drill jigs do.抡亩懦慨拖岷门待橛懂Typical Jigs and Fixtures矾沔默携喀塘唤绾葺鸽Typical drill jig. Illustrates a drilling jig for drilling four holes i

52、n the flange of a workpiece that has been completed except for the four holes. 半聒烂猱儒腆溷鹎喔巴The workpiece has an accurately machined bore, and is located from the bore and the end face, from a cylindrical post. There is no need to control the rotational position about the axis of the bore, because up t

53、o the time when the holes are drilled, it is symmetrical about that axis钵拦荟丌鸷谰藤崭采颈The four bushes used to control the drill are held in the drill plate, which, with the hand nut, is used to clamp the workpiece against the base of the fixture.裣卖陶壶毁淹醐笛斐保Typical milling fixture. Figure 13.3 illustrates

54、 a simple milling fixture for milling the slot in the otherwise completed workpiece shown. The workpiece is located from two of the four holes in its base, and from the underside of the base.卩町吏扎赫庞醣飘祀寮The workpiece is clamped in position, and cutter is located against the setting block, which provid

55、es setting or cutter position and depth of cut.泳孀陧鲺德炖绷榘苔欧The fixture must be positioned relative to the machine table, The fixture is secured to the machine table with T-bolts, also engaging in the slots in the table.缅汆乡觏臾堰澎飨鹂俅绘钞抖舂寞骐食税擤寞读悛等菥鲮矫肠窄髀旁焓哺掴剖霉墓竭鸥刖闾妞崆洌涫摞之瓜葵露科馍耗魈舡佬甙糜睑蚰惨潜既令丽粢柑阋岱母徨醵诤蛇醇彳炮贿菸莱咨臼醍瞧

56、培骂辛宪艚当骡钫诫榴喱麟瑜獒阙死绦膜焕玄繇跞鲣窀鲛瓞恿俎炎恕繁饣惮瓮钞翌跸踺镤祭霄盎噔代甫酱蛄泞苊争速鲟兴知萌呸添羔蜷杀娴窬嗓虏先炫锫朱析扁程翰今术攻癔胬绽槽珊豉碲谐沉禄镁鸬屉辜鲣柬巩蝴骱铁掳罡机械加工及其加工工具鹬弹脊邙榧朱阿所醪憾钻削和钻头镰泰睬款汆厂逮釜豪颓钻削就是通过迫使绕自身轴线旋转的切削刀具进入工件而在其上生成通孔或盲孔。娠肯浦洫逍馏岫个皮猊因此，从旋转轴线开始的切削范围等于所需孔的半径。实际上，使用的是两条围绕相同轴线旋转的对称切削刃。阮簸璀太心翅囝撵吡斗钻削作业既能采用手钻也能采用钻床来实现。钻床在尺寸和结构上虽有差别，然而始终都是切削刀具围绕自身轴线旋转、工件稳固定位的形式。

57、这正好与在车床上钻孔相反。菔滴歃跫劢诱狸霓甭酥用于钻削作业的切削刀具舞寰粹络鲒椿铝髫驰绉在钻削作业中，要用到被称为钻头的圆柱形回转端切削刀具。钻头可以有一条或多条直的或是螺旋状的切削刃以及相应的出屑槽。魈危糕困芒簖忘劝魃疾出屑槽的功能是给钻削作业中产生的切屑提供排出通道，并允许润滑剂和冷却液到达切削刃和正在被加工的表面。下面是常用钻头的概述。嗤萎蒯北蚴慌隰右呻坑麻花钻：麻花 纶柜煲融懑淠娌凉飨霾钻是最常用的钻头类型。它有两条切削刃和两条沿钻头体全长连续的螺旋状出屑槽。麻花钻还包括钻颈和钻柄，钻柄可以是直的也可以是锥形的。晒倩江痰托橱危藏鸹懒锥形钻柄通过楔入动作安装在主轴的锥形轴孔中，钻柄上还有

58、柄舌插入主轴轴孔中的插槽，从而作为传递转动的可靠方法。谖偬攫川冒挠锻芒锵鞍另一方面，直柄钻头用钻头卡盘夹住，接下来钻头卡盘则象锥形钻柄钻头一样安装在主轴轴孔内。壕劲莛坷忑柄舻佤邡肆两条切削刃就是钻唇，通过凿子状边缘的楔形体连在一起。麻花钻还有两条导向边，用于作业中钻头的正确导向和定位。柜渍霈入威後韶瘢搜敛两条钻唇形成钻顶角，并根据被钻削材料的性能来选取其大小。商品化钻头的钻顶角一般为118，这适用于钻削低碳钢和铸铁。强特凸嗽炕陀瘳蟛革攀对于更硬更韧的金属，诸如淬火钢、黄铜和青铜，更大的钻顶角(130或140)才能有更好的效果。麻花钻常用的出屑槽螺旋角范围为24到 30。钻削紫铜或软塑料时，推荐

59、采用更大的螺旋角(35到45)。糨亍押敖缃爽测京炅阗虽然也有硬质合金刀尖的钻头，麻花钻一般用高速钢制成。工业实际中使用的麻花钻尺寸范围为0.01到3.25英寸(即0.25到80毫米)。咛弓歌鸨矫虿徽念用烂空心钻：空心钻包括斜面、钻头体、钻颈和钻柄。这类钻头可以有三条或四条出屑槽及相同数量的保证良好导向的导向边，这样使得加工有高精度。缤纱按倚塾抓罢蒋抗篓在中同样能看到，空心钻具有平坦的端部。斜面可以有三或四条切削刃或钻唇，并且钻唇角可以在90到120之间变化。祈括炙菊辈乎计打慌嗦空心钻用于扩大已有的孔而不是打孔。这类钻头具有较大生产率、高加工精度和优良钻削表面质量的特性。窃竦艘椎寞牛辫贵杂悯深孔钻：深孔钻用于钻深孔。所有深孔