Part 1 Unit 07 Metal Cutting.ppt

Unit 7 Metal Cutting Introduction Chip Formation Shear Zone Cutting Tool Materials Surface Finish Cutting Fluids 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. 机加工过程的重要性可通过日常生活使用的每件产品都直接或间接经历这一过程的事实来强调。 (1)在美国，每年花在机加工及其相关作业上的费用都多于千亿美元。 (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. (2) 用于制造业的全部机床中的大多数(多于80%)都经历过金属切削。 (3) 有估计显示美国生产的所有金属中约10到15%转变成了切屑。 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. 这些事实说明了金属切削在常规制造中的重要性。因此了解金属切削过程以充分利用它是重要的。 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. 在了解金属切削过程并运用这些知识帮助改善与金属切削有关的制造作业方面已经做了许多努力。 A typical cutting tool in simplified form is shown in Fig.7.1. The important features to be observed are follows. 典型切削刀具的简化形式如图7.1所示。要注意的重要特征如下。 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. 1.前角：它是被称为前倾面的刀具面与垂直机加工方向的夹角。前角越大，则切削越好且切削力越小，增加前角可以减少刀具前倾面上产生的金属阻塞。 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.