1、 Metal-cutting process Metal-cutting processes are extensively used in the manufacturing industry. They are characterized by the fact that the size of the original workpiece is sufficiently large that the final geometry can be circumscribed by it ,and that the unwanted meterial is removed as chips,p
2、articles ,and so on. The chips are a necessary means to obtain the desired tolerances, and surfaces. The amount of scrap may vary from a few percent to 70%80% of the volume of the original work material. Owing to the rather poor material utilization of the metal-cutting processes, the anticipated sc
3、arcity of materials and energy, and increasing costs,the development in the last decade has been directed toward an increasing application of metal-forming processes. However, die costs and the capital cost of machines remain rather high； consequently, metal-cutting processes are, in many cases, the
4、 most economical, in spite of the high material waste,which only has value as scrap. Therefore, it must be expected that the material removal processes will for the next few years maintain their important position in manufacturing. Furthermore, the development of automated production systems has pro
5、gressed more rapidly for metal-cutting processes than for metal-forming processes. In metal-cutting processes, the imprinting of imformation is carried out by a rigid medium of transfer, which is moved relative to the workpiece, and the mechanical energy is supplied through the tool. The final geome
6、try of the tool and the pattern of motions of the tool and the workpiece. The basic process is mechanical: actually, a shearing action combined with fracture. As mentioned previously, the unwanted material in metal-cutting processes is removed by a rigid cutting tool ,so that the desired geometry, t
7、olerances, and surface roughness are obtained. Examples of processes in this group are turning, drilling, reaming, milling, shaping, planing, broaching, grinding, honing, and lapping. Most of the cutting or machining processes are bases on a two-dimensional surface creation,which means that two rela
8、tive motions are necessary between the cutting tool and the work material. These motions are defined as the primary motion, which mainly determines the cutting speed, and the feed motion, which provides the cutting zone with new material. In turning the primary motion is provided by the rotation of
9、the workpiece,and in planing it is provided by the translation of the table； in turning the feed motion is a continuous translation of the tool, and in planing it is an intermittent translation of the tool. Cutting Speed The cutting speed v is the instantaneous velocity of the primary motion of the
10、tool relative to the workpiece(at a selected point on the cutting edge). The cutting speed for turning,drilling, and milling processes can be expressed as V=dn m/min Where v is cutting speed in m/min,d the diameter of the workpiece to be cut in meters, and n the workpiece or spindle rotation in rev/
11、min. thus v, d, and n may relate to the work material or the tool, depending on the specific kinematic pattern. In grinding the cutting speed is normally measured in m/s. Feed The feed motion f is provided to the tool or the workpiece and, when added to the primary motion, leads to a repeated or con
12、tinuous chip removal and the creation of the desired machined surface. The motion may proceed by steps or continuously. The feed speed vf is defined as the instantaneous velocity of the feed motion relative to the workpiece(at a selected point on the cutting edge) For turning and drilling, the feed
13、f is measured per revolution (mm/rev) of the workpiece or the tool； for planing and shaping f is measured per storke (mm/stroke) of the tool or the workpiece. In milling the feed is measured per tooth of the cutte fz (mm/touth)； that is,fz is the displacement of the workpiece between the cutting act
14、ion of two successive teeth。 The feed speed vf（ mm/min） of the table is therefore the product of the number of the teeth z of the cutter ,the revolutions per minute of the cutter n,and the feed per tooth (vf=nzfz) . A plane containing the directions of the primary motion and the feed motion is defin
15、e as the working plane, since it contains the motions responsible for the cutting action. Depth of Cut (Engagement) In turning the depth of cut a (sometimes also called back engagement) is the distance that the cutting edge engages or projects below the original surface of the workpiece. The depth o
16、f cut determines the final dimensions of the workpiece. In turning, with an axial feed, the depth of cut is a direct measure of the decrease in radius of the workpiece and with radial feed the depth of cut is equal to the decrease in the length of workpiece. In drilling, the depth of cut is equal to
17、 the diameter of the drill. For milling, the depth of cut is defined as the working engagement ae and is the radial engagement of the cutter. The axial engagement (back engagement) of the cutter is called ap. Chip Thickness h1 in the undeformed state is the thickness of the chip measured perpendicul
18、ar to the cutting edge and in a plane perpendicular to the direction of cutting. The chip thickness after cutting (i.e., the actual chip thickness h2) is larger than the undeformed chip thickness, which means that the cutting ratio or chip thickness ratio r=h1/h2 is always less than unity. Chip Widt
19、h The chip width b in the undeformed state is the width of the chip measured along the cutting edge in a plane perpendicular to the direction of cutting. Area f Cut For single-point tool operations, the area of cut A is the product of the undeformed chip thickness h1 and the chip width b (i.e., A=h1b).The area of cut can also be expressed by the feed f and the depth of cut a as follows: h1=f sink and b=a/sink (27.2) where k is the major cutting edge angle (i.e.,the angle that the cutting edge forms with the working place). Consequently, the area of cut is given by A=fa
