金属切削外文翻译

金属切削外文翻译内容摘要：

it can be observed that a higher rake angles give rise to higher shear angles. Cutting Tool Materials Various cutting tool materials have been used in the industry for different applications. A number of developments have occurred in the current century. A large variety of cutting tool materials has been developed to cater to the variety of materials used in these programmes. Before we discuss the properties of these materials, let us look at the important characteristics expected of a cutting tool material. 1. Higher hardness than that of the workpiece material being machined, so that it can perate into the work material. 2. Hot hardness, which is the ability of the material to retain its hardness at elevated temperatures in view of the high temperatures existing in the cutting zone. 3. Wear resistance—The chiptool and chipwork interfaces are exposed to such severe conditions that adhesive and abrasion wear is very mon. The cutting tool material should therefore have high abrasion resistance to improve the effective life of the tool. 4. Toughness—Even though the tool is hard, it should have enough toughness to withstand the impact loads that e in the beginning of cut or force fluctuations due to imperfections in the work material. This requirement is going to be more useful for the interrupted cutting, . milling. 5. Low friction—The coefficient of friction between the chip and tool should be low. This would allow for lower wear rates and better chip flow. 6. Thermal characteristics—Since a lot of heat is generated at the cutting zone, the tool material should have higher thermal conductivity to dissipate this heat in the shortest time, otherwise the tool temperature would bee high, reducing its life. All these characteristics may not be found in a single tool material. Improved tool materials have been giving a better cutting performance. Surface Finish Machining operations are utilized in view of the better surface finish that could be achieved by it pared to other manufacturing it is important to know what would be the effective surface finish that can be achieved in a machining operation. The surface finish in a given machining operation is a result of two factors: (1) the ideal surface finish, which is a result of the geometry of the manufacturing process which can be determined by considering the geometry of the machining operation, and (2) the natural ponent, which is a result of a number of uncontrollable factors in machining, which is difficult to predict. Ideal Surface Finish in Turning The actual turning tool used would have a nose radius in place of the sharp tool point, which modifies the surface geometry as shown in . If the feed rate is very small, as is normal in finish turning, the surface is produced purely by the nose radius alone as shown in . For the case in , the surface roughness value is to be Ra=8f2/(18R√3) Where: Ra is the surface roughness value R is the nose radius f is the feed rate The above are essentially geometric factors and the values represent an ideal situation. The actual surface finish obtained depends to a great extent upon a number of factors such as: (1) the cutting process parameter, speed, f。