机械制造技术基础课件-新第1章课件.ppt

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1、Chapter 1 Fundamentals of Machining,Abstract,1.1 Basic definitions,1.2 Materials of cutting tools,Most of metal parts are shaped by machining at present. Machining means that the excess metal on a blank is cut off by a cutting tool, thus forming it into a required part. In this chapter we will study

2、 the fundamental knowledge concerning metal machining process. There are two parts: 1. Basic definitions cutting motions and parameters, tool angles and reference frame, cutting layer parameters etc. 2. Cutting tool materials the necessary properties, some normal cutting tool materials.,Absract,1.1

3、Basic definition,1.1.2 Basic definitions of cutting toolworking region,1.1.3 Marked angles of cutting tool and their exchange,1.1.5 Cutting layer parameters and cutting mode,1.1.4 Working angles of cutting tool,1.1.1 Cutting motions and parameters,Machining includes some different processes such as

4、turning, drilling, milling, planing and broaching etc. But no matter what machining process, it is a interaction course between the cutting tool and the workpiece.,1.1.1 Cutting motions and parameters,Fig.1.1 turning and milling,There exist common rules and phenomenon: The workpiece is holden in mac

5、hine by a clamper, so is the cutting tool; In order carrying out machining, there must be a relative motion between the workpiece and cutting tool, that is, cutting motion, which is provided by the machine; The machine, clamper, workpiece and cutting tool constitute a machining processing system.,Co

6、mparing various cutting tools used in different processes, they are some parts similar to a simple turning cutter. Then, taking turning as an example to introduce the cutting motion. In external cylinder turning, the workpiece rotates and the cutting tool moves longitudinally. The two motions compos

7、e the external cylindrical surface.,There are three surfaces in the workpiece: Machined surface：means the surface in which the material has been removed.,Fig 1.2 Cutting motions in turning,1.1.1 Cutting motions and parameters,Surface to be mchined,workpiece rotates,Machined surface,Surface being mac

8、hined,cutter moves longitudinally,Machining surface：means the surface which is being machined by the cutting edge.,Surface to be machined：means the surface in which the material is to be removed.,There are similar three surfaces in other machining processes:,Fig 1.3 Cutting motions in planing, drill

9、ing and milling,1.1.1 Cutting motions and parameters,1. Cutting motion The basic motion for a machine includes linear motion and rotational motion. If classified according to their cutting functions, they may be divided into main motion and feeding motion.,（2）feed motion It is the rate at which the

10、cutting tool advances into the workpiece. It brings the new metal into cutting constantly so that the machined surface is produced. Feed motion may be continuous motion or intermittent motion, in general it utilizes less machine power. In a machining process there may be two or more feed motions.,1.

11、1.1 Cutting motions and parameters,（1）main motion It is the most necessary and important motion in the process of removing the excess metal from the workpiece. Most of the main cutting motions are rotational motion, usually it has the highest velocity and consumes most of the machine power. There is

12、 only one main motion in a machining process.,（3）resultant motion and velocity When the main motion and the feed motion take part in cutting simultaneously, the relative motion of a certain point on the cutting edge against the workpiece called resultant cutting motion. The resultant velocity of the

13、 cutting motion is represented by the vector ve , it is equal to the vector sum of the main motion plus the feeding speed.,1.1.1 Cutting motions and parameters,Fig.1.4 Resultant cutting motion in turning,1. Cutting motion,ve=vc+vf (1.1),2. Cutting parameter,The speed of the main motion is the cuttin

14、g speed vc. For a rotating main motion: m/s or m/min (1.2) where dthe rotational diameter of one point in the rotating workpiece or cutting tool（mm) nnumber of revolution per second or per minute (r/s or r/min),1.1.1 Cutting motions and parameters,In cutting process, there are three cutting paramete

15、rs: cutting speed vc, feed f or feeding speed vf, and back engagement of the cutting edge ap.,（1）cutting speed,Feed f is the relative displacement between the workpiece and the cutter along the direction of feeding motion per revolution or per stock (mm/r). Feeding speed vf is the feed in a unit tim

16、e (m/s or m/min). For multiple teeth cutting tools, such as milling cutter, reamer, broach, gear hob etc. feed per tool tooth fz may be measured (mm/z). mm/s or mm/min （1.3）,（2）feed, feeding speed and feed per tooth,1.1.1 Cutting motions and parameters,2. Cutting parameter,（3）back engagement of the

17、cutting edge,1.1.1 Cutting motions and parameters,For turning and planing, 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: mm (1.4),2. Cutting parameter,For drilling: mm (1.5) where

18、dmdiameter of machined surface（mm） dwdiameter of workpiece surface to be cut （mm）,1.1.2 Essential definitions for the working parts of cutting tools,1. The basic elements for the working part of cutting tool,rake surface,Fig.1.5 Components of typical turning tool,Tool bit(Working part),main flank,si

19、de flank,Main cutting edge,side cutting edge,tool nose,shank,(1) Rake face Rake face Ar is the surface on which the chip flowing out. The part adjoining the major cutting edge is called the major rake face; the part adjoining the minor cutting edge is called the minor rake face.(2) Flank There are a

20、 major flank and a minor flank. The major flank A is the surface which is opposite to the machining surface on the workpiece; the minor flank A is the surface which is opposite to the machined surface on the workpiece.,1.1.2 Essential definitions for the working parts of cutting tools,1. The basic e

21、lements for the working part of cutting tool,(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

22、metal removal. The minor cutting edge 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.,Fig.1.6 Tool n

23、ose shape,1.1.2 Essential definitions for the working parts of cutting tools,1. The basic elements for the working part of cutting tool,ISO builds up a reference system for marking tool angles. The marked angles are the angles taken for the tool drawing and tool grinding, i.e. the angles under a pre

24、determined condition. Some reasoned predetermined conditions must be provided in advance: Predetermined 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 v

25、c can substitute for the resultant speed vector ve approximately, then the reference system can be composed of coordinate planes that are parallel or perpendicular to the direction of the main motion. Namely, feeding motion is not taken into consideration for the marked angles. Predetermined setup c

26、ondition: assume the base plane of the tool for grinding and setup to be normal or parallel to the tool reference plane. For instance, the tool nose is at the same height as the center line of the workpiece and the center line of the tool bar is perpendicular to the direction of feeding.,2. Referenc

27、e system for the marked angles of cutting tools,1.1.2 Essential definitions for the working parts of cutting tools,The reference system consists of three planes：,（1）Tool reference plane Pr Pr is a plane which passes through a designated point on the cutting edge and is perpendicular to the vector re

28、sultant speed ve or normal to the setup plane or axis of the tool arbor.,Fig.1.7 The reference plane Pr of an ordinary turning tool,tool reference plane,point on the cutting edge,base plane of the cutting tool.,1.1.2 Essential definitions for the working parts of cutting tools,2. Reference system fo

29、r the marked angles of cutting tools,Fig.1.8 The reference plane Pr of an twist drill,(2) Tool cutting edge plane Ps Ps is a plane which passes through a designated point on the cutting edge and is tangential to the cutting surface, namely, the plane formed by vector ve of resultant speed and the ta

30、ngent line of a designated point on the cutting edge.,1.1.2 Essential definitions for the working parts of cutting tools,2. Reference system for the marked angles of cutting tools,.,(3) Main section Po and main section reference system Main section Po is a plane which passes through a designated poi

31、nt on the cutting edge and is perpendicular to the tool reference plane Pr and the tool cutting edge plane Ps simultaneously.,Add Fig. Main section and main section reference system,Pr -Ps -Po compose a main section reference system.,Main section Po,Main cutting edge,Main flank,Rake surface,Side cut

32、ting edge,Tool cutting edge plane Ps,Tool reference plane Pr,1.1.2 Essential definitions for the working parts of cutting tools,2. Reference system for the marked angles of cutting tools,Add Fig. Main section reference system Pr-Ps-Po,（4）Normal section Pn and normal section reference system,Pn is a

33、plane which passes through a designated point on the cutting edge and is perpendicular to the main cutting edge. The normal section reference system is composed of Pr-Ps-Pn .,Fig.1.9 main section and normal section reference system,1.1.2 Essential definitions for the working parts of cutting tools,2

34、. Reference system for the marked angles of cutting tools,Note: Pr -Ps -Po and Pr-Ps-Pn are the main reference systems for marking the cutting tool angles.The main section Po is not necessarily perpendicular to the main cutting edge.The normal section Pn is not necessarily perpendicular to the tool

35、reference plane.The two systems all have Pr and Ps, the difference is in Po and Pn.,Pf is a plane passing through a designated point on cutting edge and parallel to the direction of feeding motion and perpendicular to the tool reference plane Pr. Pp is a plane passing through a designated point on t

36、he cutting edge and perpendicular to Pr and Pf simultaneously.,1.1.2 Essential definitions for the working parts of cutting tools,2. Reference system for the marked angles of cutting tools,(5) Transverse section Pf , longitudinal section Pp , transverse section or longitudinal section system,Pr-Pf -

37、Pp compose a transverse - longitudinal section system. It is used in some situations for marking angles of complex cutting tools.,Fig.1.10 Transverse - longitudinal section reference system,The reference system for the marked angles of the cutting tool is determined under the predetermined condition

38、s for motion and setup. Because the feeding motion is not taken into consideration when defining the tool reference plane Pr, and the tool nose is not certainly at the same height as the center line of the workpiece, or the center line of the tool bar is not certainly perpendicular to the direction

39、of feeding, so the marked angles of cutting tool can not give the real cutting status sometimes. The angles determined according to the reference system in cutting are called the working angles, which can coincide with the real cutting status.,1.1.2 Essential definitions for the working parts of cut

40、ting tools,3. Reference system for the working angles of cutting tools,Fig.1.11 The influence of feed motion on the tools working angle The three tools have the same marked angle but their working angles 0 are different because their resultant speed vector ve are different.,The azimuth angles betwee

41、n the cutting edge and the tool surface determined in the reference system are called “marked angles of cutting tool” . Since the reference system may vary along the cutting edge length, the point on which the tool angles are defined should be indicated. If the cutting edge is curved, or the rake su

42、rface or flank surface is curved, a tangential line or surface passing through a point in the edge or surface is used to define the angles.,1.1.2 Essential definitions for the working parts of cutting tools,4. Marked angles of the cutting tool,1.1.2 Essential definitions for the working parts of cut

43、ting tools,4. Marked angles of the cutting tool,For a ordinary turning cutter, there are four independent angles concerned with its main cutting edge:,Cutting edge angle r the included angle between the projection of the major cutting edge on the tool reference plane and the direction of feeding.,Fi

44、g.1.12 A turning cutter angles in main section reference system,Pr,r,Rake angle o the included angle between the rake face and the tool reference plane.,Ps,Pr, o,Clearance angle o the included angle between the major flank and the tool cutting edge plane., o,Tool cutting edge inclination angle s the

45、 included angle between the major cutting edge and the tool reference plane.,A,s,Note: The angle subscript symbol r, s, o means the angle is measured in Pr, Ps, or Po respectively.,Po,Pr,1.1.2 Essential definitions for the working parts of cutting tools,4. Marked angles of the cutting tool,Likewise,

46、 there are four angles related with the minor cutting edge: minor cutting edge angle r, minor rake o, minor clearance angle 0 and minor inclination angle s. The definition is similar to that of the main cutting edge.,Fig.1.12 A turning cutter angles in main section reference system,1.1.2 Essential d

47、efinitions for the working parts of cutting tools,4. Marked angles of the cutting tool,There are some derivative angles: Wedge angle o the included angle between the rake face and the major flank.o +o +o =90 or o =90- (o +o) (1.6)Tool included angle r the included angle between the projection of the

48、 major and minor edges on the tool reference plane.r =180- (r +r) (1.7) o, o, s, r, r are essential angles, while 0, r can be gotten by educing. o and s determine the azimuth of rake face, o and r determine the azimuth of flank, r and s determine the azimuth of main cutting edge.,The sign of o is sp

49、ecified： if the main cutting edge is the lowest line on the rake face, o is negative; contrarily, it is positive. When the rake face has no any tilt, o =0.,4. Marked angles of the cutting tool,Note 1: the difference between the rake angle o and the inclination angle s.,Note 2: the clearance angle o

50、must be positive, that is, the flank must be invaginated.,1.1.2 Essential definitions for the working parts of cutting tools,The sign of s is specified：if the tool nose is the lowest point on the cutting edge, s is negative; if the tool nose is the highest point on the cutting edge, it is positive.