金属切削外文翻译.docVIP

METAL CUTTING The importance of machining processes can be emphasised by the fact that every product we use in our daily life has undergone this process either directly or indirectly. (1) In USA, more than $100 billions are spent annually on machining and related operations. (2) A large majority (above 80%) of all the machine tools used in the manufacturing industry have undergone metal cutting. (3) An estimate showed that about 10 to 15% of all the metal produced in USA was converted into chips. These facts show the importance of metal cutting in general manufacturing. It is therefore important to understand the metal cutting process in order to make the best use of it. A number of attempts have been made in understanding the metal cutting process and using this knowledge to help improve manufacturing operations which involved metal cutting. A typical cutting tool in simplified form is shown in Fig.7.1. The important features to be observed are follows. 1. Rake angle. It is the angle between the face of the tool called the rake face and the normal to the machining direction. Higher the rake angle, better is the cutting and less are the cutting forces, increasing the rake angle reduces the metal backup available at the tool rake face.This reduces the strength of the tool tip as well as the heat dissipation through the tool. Thus, there is a maximum limit to the rake angle and this is generally of the order of 15°for high speed steel tools cutting mild steel. It is possible to have rake angles at zero or negative. 2. Clearance angle. This is the angle between the machined surface and the underside of the tool called the flank face. The clearance angle is provided such that the tool will not rub the machined surface thus spoiling the surface and increasing the cutting forces. A very large clearance angle reduces the strength of the tool tip, and hence normally an angle of the order of 5~6°is used. The conditions which have an