机械制造技术基础课件-CHAPTER1-eng-10

1、Chapter 1 Fundamentals of CuttingChapter 1 Fundamentals of CuttingAbstract 1.1 Basic definition1.2 Material of the cutting toolProfessional words in this chapterCutting tool 刀具Velocity 速度Main motion 主运动 Feed motion 进给运动Resultant motion 合成运动Reference system (frame) 参考系 （坐标）Reference plane 基面Cutting e

2、dge plane 切削平面Main section plane 主剖面Normal section plane 法剖面Rake angle (surface) 前角（前刀面）Relief angle (surface，flank) 后角 （后刀面）Cutting edge angle 偏角 Inclined angle 刃倾角Cutting nose 刀尖Teaching time 5 hours (2 hours experiment) Basic requirement: Concepts and definition of cutting tool geometry (刀具几何角度定义

3、） and reference system（参考系）, usually used cutting tool material（常用刀具材料） Teaching method: 2-D and 3-D figure to show the definition using lathe cutting tool. Main Clues of the development of cutting tool material.Difficulty of the chapter Explain the change of tool working angles Understand the chang

4、e of tool geometry from one system to another system （刀具角度在不同坐标系之间的变换) Solution: Draw the 3-D figure of a cutting tool and mark the different surfaces, angles. Two parts concerning the fundamental of metal cutting process are involved in this chapter 1 Basic definitionincluding basic concepts in cut

5、ting process,such as cutting motions (切削运动）,parameters(切削参数）, reference frame （参考坐标系）,marked angles（标注角度）, cutting layer parameters 2 cutting tool materialincluding the necessary performance of cutting tool material(hardness, wear resistance,strength,toughness, hot hardness ), two kinds of normal ma

6、terial for cutting tool(HSS and carbide alloy) and the other material(coating,ceramics diamond and cubic boron Nitride )1.1 Basic definition1.1.2 basic definition of the cutting region1.1.3 exchange of the cutting angles1.1.5 cutting layer parameters and mode 1.1.4 work angles of the cutting tool1.1

7、.1 cutting motion and parameters For example,in turning,the workpiece rotates,the cutting tool moves longitudinally, the mixture of the two motions forms the external cylindrical surface.There are three surfaces created in turn during the new surface is forming（Figure1.1）：Fig 1.1cutting motions in t

8、urningSurface to be machined：means the surface in which the material is to be removedMachining surface：means the surface is being machined by the cutting edgeMachined surface：means the surface in which the material has been removed1.1.1 cutting motions and parameters1.1.1.1 Cutting motion The basic

9、motion for a machine tool includes linear motion and rotational motion. If classified according to the functions of the cutting tool in relation with the workpiece, they are called the main motion and the feed motion,shown as Fig.1.1（1）the main motion the main motion required to remove the metal. Us

10、ually it has the biggest velocity, and consumes most of the power（2） the feed motion It brings the new metal into cutting constantly. It can be continuous or interrupted. When the main motion and the feed motion take part in cutting simultaneously, the velocity in one point of the cutting edge relat

11、ive to the workpiece is called resultant cutting motion, its size and direction can be represented with a vector ve, shown as Fig.1.3, and it equals the vector sum of the two motions ve=vc+vf (1.1)（3）resultant motion and velocityFig.1.2 The resultant velocity in cutting1.1.1.2 Three elements in cutt

12、ing ve、f 、 ap are called the three elements in cutting1000dn（1）Cutting speed Most of the main cutting motions are rotational motion.The velocity in one point of the rotating body(cutting tool or workpiece) can be calculated using the following formula vc= m/s or m/min (1.2) where dthe rotational dia

13、meter of one point in the workpiece or the cutting tool（mm) nnumber of revolution per second or per minute (r/s or r/min). （r/s or r/min) Feeding speed vf is the feed in a unit time (m/s or m/min) Feed is the relative displacement between the workpiece and the cutter along the direction of feeding m

14、otion per revolution or per stock (mm/r)。 For multiple teeth cutting tools, such as milling cutter, reamer, broach, gear hob etc. feed fz may be measured in millimeters per tool tooth (mm/z). Obviously，vf=fn=fzzn mm/s or mm/min （1.3） （2） Feeding speed, feed and feed per tooth（3）Back engagement of th

15、e cutting edge For turning and planing, the back engagement of the cutting edge ap is equal to the normal distance between the machined surface and the workpiece surface to be cut(mm). For cylindrical turning, ap=（dw-dm）/2 mm (1.4) For drilling ap=dm/2 mm (1.5) where dmdiameter of machined surface（m

16、m） dwdiameter of workpiece surface to be cut （mm）1.1.2 Essential definitions for the working Essential definitions for the working parts of cutting toolsparts of cutting tools1.1.2.1 The basicThe basic elements for the elements for the working part of cutting toolworking part of cutting toolFig.1.3

17、components of typical turning tool(1) Rake surface(3) Cutting edge(2) Flank(4) Tool nose(1) Rake face Rake face Ar is the surface on which the chip acts directly and which can tools the direction of the chip flowing out . The part adjoining the major cutting edge is referred to as the major rake fac

18、e; the part adjoining the minor cutting edge is referred to as the minor rake face.（2）Flank There are a major flank and a minor flank. The major flank A is the surface which is opposite to the surface on the workpiece; the minor flank Ais the surface which is opposite to the machined surface on the

19、workpiece（3）Cutting edge Cutting edges are the edges engaged in cutting on rake face. There are major cutting edge and the minor cutting edge. The major cutting edge is an intersecting line between the rake face and major flank, it performs the principal work of metal removal. The minor cutting edge

20、 is an intersecting line between the rake face and the minor flank, it plays a subsidiary role in cutting.（4）Tool nose The tool nose may be an intersecting point of major and minor cutting edges, or an intermediate straight line or a circular arc.1.1.2.2 Reference system（参考系）（参考系） for the marked ang

21、les of cutting tools Predetermined (假想） motion condition：first, predetermine the direction of main motion and the direction of feeding motion of the tool, then, assume that the feeding speed is very low so that the main motion vector vc can substitute for the combined speed vector ve approximately,

22、then the reference system can be composed of coordinate planes that are parallel or perpendicular to the direction of the main motion. Predetermined condition for setup: assume the planes in reference system are parallel or perpendicular to the base plane of the tool which is easy for grinding and s

23、etupThe reference system consists of the following planes： （1）Tool reference plane Pr （基面） Pass through a designated point on the cutting edge and is perpendicular to the vector ve of combined speed. Usually it is parallel or normal to the setup plane or axis of the tool arbor. For instance, in Fig.

24、1.6, Fig.1.6 The reference plane Pr of an ordinary turning tool(2) Tool cutting edge plane Ps（切削平面）Pass through a designated point on the cutting edge and is tangential to the cutting （3） Main section P0 and main section reference system（4）Normal section Pn and normal section reference system Main s

25、ection plane Po Pass through a designated point on the cutting edge and is perpendicular to the tool reference plane Pr and the tool cutting edge plane Ps simultaneously. Fig.1.8 shows a main section reference system composed of Pr Ps P0 Normal section Pn , pass through a designated point on the cut

26、ting edge and is perpendicular to the cutting edge. The normal section reference system is composed of PrPsPn ,shown as Fig 1.8Fig.1.8 main section and normal section reference systemVideo(5) Transverse section Pf, longitudinal section Pp, Transverse section or longitudinal section system Transverse

27、 section Pf p a s s i n g t h r o u g h a designated point on cutting edge and parallel to the direction of f e e d i n g m o t i o n a n d perpendicular to the tool r e f e r e n c e p l a n e P rFig.1.9 Transverse section Pf, longitudinal section PpPr PfPp Longitudinal section Pp passing through a

28、 designated point on the cutting edge and perpendicular to the tool reference plane Pr and the transverse section Pf1.1.2.3 Reference system for the working angles of cutting tools In the definition of tool reference plane Pr the feeding motion is not considered, i.e. the marked angles of the cuttin

29、g tool is determined under the predetermined conditions . It is no true in practice,where only the resultant ve reflects the situation. For example，Fig.1.10 shows three tools having the same marked angles,but the practical conditions,like the contact and friction,are very different It is same consid

30、ering the affection of the tool setup position, except that ve is replaced by vc，where vc is the practical feeding direction instead of the predetermined direction.Fig.（a）it is normal, where there is clearance between the flank and the workpiece.(a)Fig.1.10 the working angle of the toolFig.（b）, two

31、surfaces are completely contacted, causing serious friction；(b)Fig.1.10 Working angles of the tool in Fig.（c）,the cutting edge can not enter into the metal.Therefore, only consider the main motion is not proper. The working angles of the tool must be decided by the working reference system, i.e.,con

32、sider the direction of the resultant motion Fig.1.10 the working angles of the tool1.1.2.4 How to mark the tool angle The angles between the cutting edge and the tool surface determined in the reference system for the marked angles are called “marked angles of cutting tool” .If the cutting edge is c

33、urved, or the rake surface or flank surface is curved, a tangential line or surface passing through a point in the edge is used to define the angles.Fig.1.11 shows the name, symbol and definition of the marked angles in the main section reference system Likewise, there are four angles related with t

34、he minor cutting edge, which are, minor cutting edge angler ，minor inclination angle s，minor rake 0，minor clearance angle 0. The definition is similar to that of the main cutting edgeRake0clearance angle0Cutting edge angle rrinclination angless rake0：the angle between the rake surface and the refere

35、nce plane（measured in main section ）。Fig.1.11(a) the tool angle marked in the main section systemClearance angle0：angle between flank and cutting edge plane（measured in main section)Fig.1.11(b) the tool angle marked in the main section systemFig.(c) the tool angle marked in the main section systemkr

36、Cutting edge angle r, measured in the reference plane,formed by the cutting edge and feed directionInclination angle s：measured in the cutting edge plane, formed by cutting edge and reference planeFig.1.11(d) the tool angle marked in the main section system When the cutting edge and minor cutting ed

37、ge are all on the rake face, like Fig.1.11, 0、 s can be educed from 0、 s、 r、 r ，and it is called derived angles. There are 6 independent marked angles for lathe cutting tool. In addition，as required in analysis, there are some other derived angles, which are： wedge angle0 ：measured in main section,f

38、ormed by rake face and flank. 090 （0 0） （1.6） tool tip(nose) angler ：the angle formed by cutting edge and minor cutting edge in the reference plane. r180 （ r r ） （1.7） The sign of 0、 0 、 s、 r、 r is specified as in Fig.1.12：in the main section, if rake face is parallel to the reference plane, 0=0, ，i

39、f the angle is less than 90 , it is positive, otherwise, it is negative. The sign of the inclination angle is shown in Fig.1.12 .(a)s0(b)s(c)+ sFig.1.12 the sign of inclination angle1.1.3 Tool angle conversion in different system1.1.3.1 tool angle conversion from main section to normal section This

40、conversion is used in tool design, manufacturing,tool grinding and inspection,especially for large inclination tool, the angles must be marked in normal section system. It is necessary to convert the marked angle from one system to another system in tool design and manufacturing. i.e, among main sec

41、tion system,normal section system, transverse system and longitudinal system1.1.3.1 conversion from main section to normal sectionMaacntanMaabotansonabacabMaMaaccostantansoncostantantann =tan0.cosscotn =cot0.coss 1.1.3.2 angle conversion from main section to any section rake angle in any section P：

42、tan then tantan0.sin+tans.cos （1.10）ABBCABDCBDABDCEF ABsDFAEtantan0sABDFABAEtan.tan.0When 0: tan=tans ，swhen90kr，the longitudinal rake anglep: tanp=tan 0.cos krtan s .sin kr （1.11）when180kr，the transverse rake anglef: tanf=tan 0.sin krtan s .coskr （1.12） the maximum rake angleg obtained by different

43、ial quotient of formula 1.10 tan g （1.13）or tan g （1.14）s202tantanpf22tantan1.1.3.2 angle conversion from main section to any section The angle formed by the plane where the maximum angle is and the cutting edge projected on the reference plane max： tan max （1.15）similarly，the clearance angle of any

44、 given section： when90kr： when180kr:stantan0rsrpkksin.tancos.cotcot0(1.17)rsrfkkcos.tansin.cotcot0(1.18)1.1.3.2 angle conversion from main section to any section1.1.4 working angles(1) Transverse turning shown as Fig.5.15: In cut-off turning, without considering feed motion，the cutting path is circu

45、lar,while considering the feed motion, it becomes helical, and cutting edge plane changes from Ps to Pse，the angle variation is 。The working angles in the reference system（ Pre、 Pse、 P0e）are： 0e 0 +; 0e=0。1.1.1.4 working angles influenced by feed motion is the resultant cutting speed angle，formed by

46、 the main cutting speed and resultant speed. From the definition： tan = (1.19) cfvvdf(1) Transverse turningWhere d is the workpiece diameter changed with the tool feeding. becomes bigger when the cutting tool approaches the center of the work；when the cutting tool is 1mm far away from the work cente

47、r under normal feed rate, 140；going further, increases suddenly, and clearance angle becomes negative.（2）Longitudinal turning Similarly, the working angles will change because of the resultant speed in longitudinal turning ，shown as 1.16，supposing s0，without considering feed motion, the marked angle

48、s are 0、0；otherwise the working cutting edge plane P Pse is tangent to the helical surface and the tool working system （ Pse、 Pre ）has an inclination angle，the working angles in working feed section are：fef +；fef According to the definition of the resultant speed： tan= where ffeed rate dwthe diamete

49、r of the surface to be machined on the designated point A of the cutting toolConverse it to the main section： tan0tan.sinkr； 0e00 （1.20） We know from formula 1.20： is not only related with feed rate f, but also related with the work diameter dw；the smaller dw，the bigger of the angle variation.wdf（2）

50、 Longitudinal turning1.1.4.2 Working angles influenced by tool setup（1）Influenced by tool tip setup When the tool tip is higher than the center of the work, the working cutting edge plane will be turned into Pse，working reference plane into Pre，working anglepe becomes increases，pe decreases。In the l

51、ongitudinal plane PP, the variation of p is ： tanp （1.21） Where hthe deviation from the tool tip to the work center line（mm）； dwdiameter of the work222hdhwThe working angles ： pepp or pepp （1.22）The above angles are marked in the system（PpPp），they should be converted into the working main section pl

52、ane： tan0 （1.23）or ； （1.24）rwkhdhcos222000e000 aae（1） Influenced by tool tip setup（2）Influenced by the tool bar setup If the tool bar is not perpendicular to the feed direction,the working cutting edge angle kre and minor cutting edge angle kre will change： ； （1.25） Where Gangle formed by predetermi

53、ned feed section and working feed section，measured on the reference plane。It is also the angle formed by the normal line of feed direction and the center line of the tool barGkkre0Gkkrre 1.1.5 parameters of the cutting layer and cutting mode1.1.5.1 cutting layer All the cutting parameters can be exp

54、lained by the typical cylindrical turning,shown as Fig.1.19. The motional path of any designated point on the cutting edge relative to the workpiece is a spatial helix .The definition and explanation are as follows： Feed, the move distance of the cutting tool per workpiece revolution（f，mm/r）.Cutting

55、 layer,the layer where the metal is being cuttedUnder special situation（kr90）it is rectangle.In longitudinal turning, and when kr0、s0，the the cutting layer geometry is parallelogram(1) Cutting thickness In order to make the calculation simple, the layer geometry and dimension are usually observed an

56、d measured in plane Pr. The parameters are：Measured in the normal direction of the cutting surface(Fig.1.19),represented with hD. In longitudinal turning（s0）： hDf.sinkr （1.26）（2）Cutting width Measured along the cutting surface， represented with bD. In longitudinal turning（s0 ） bD=ap/sinkr （1.27）Conc

57、lusion: when f and ap are definite, the bigger the kr，the bigger the hD，and the smaller the bD；Vice versa. When kr90，hDf。 For circular cutting edge, the thickness in different position of the cutting edge and cutting layer is different.（3）Cutting areaThe area of the cutting layer projected on Pr is

58、called the cutting area，represented with AD. It can be calculated with the following formula: AD=hD.bD （1.28） For turning,no matter what the geometry of the cutting tool is,the cutting area is： ADhD.bD=f.ap （1.29） Actually,the area calculated is the nominal cutting area. The actual cutting area equa

59、ls the nominal area minus the residual area , Residual area is the section area of the uneven part residue on the finished surface when kr0, shown as ABE.1.1.5.2 Cutting mode（1）Orthogonal cutting and oblique cutting The cutting edge is perpendicular to the resultant cutting direction is called ortho

60、gonal cutting or right-angle cutting, otherwise it is called oblique cutting. Fig.1.23 shows the two modes of cuttingFig.1.23 Orthogonal cutting and oblique cutting（a）（b）（2）free cutting and constrained cutting Free cuttingthe major cutting edge is straight and only the major cutting edge takes part