tailieunhanh - Manufacturing Processes phần 6

loại chip được sản xuất trong việc cắt giảm kim loại cơ bản: (a) liên tục chip với hẹp, khu vực cắt thẳng chính, (b) vùng trung cắt tại giao diện công cụ-chip, (c) liên tục chip với vùng cắt chính lớn; (d) liên tục chip với cạnh xây dựng, (e) phân đoạn hoặc nonhomogeneous con chip, (f) không liên tục con chip. | BASIC MECHANICS OF METAL CUTTING 13-51 Fig. Basic types of chips produced in metal cutting a continuous chip with narrow straight primary shear zone b secondary shear zone at the tool-chip interface c continuous chip with large primary shear zone d continuous chip with built-up edge e segmented or nonhomogeneous chip f discontinuous chip. Source After M. C. Shaw. Discontinuous chips consist of segments which are produced by fracture of the metal ahead of the tool. The segments may be either loosely connected to each other or unconnected. Such chips are most often found in the machining of brittle materials or in cutting ductile materials at very low speeds or low or negative rake angles. Inhomogeneous serrated chips consist of regions of large and small strain. Such chips are characteristic of metals with low thermal conductivity or metals whose yield strength decreases sharply with temperature. Chips from titanium alloys frequently are of this type. Built-up edge chips consist of a mass of metal which adheres to the tool tip while the chip itself flows continuously along the rake face. This type of chip is often encountered in machining operations at low speeds and is associated with high adhesion between chip and tool and causes poor surface finish. The forces acting on the cutting tool are shown in Fig. . The resultant force R has two components Fc and Ft. The cutting force Fc in the direction of tool travel determines the amount of work done in cutting. The thrust force Ft does no work but together with Fc produces deflections of the tool. The resultant force also has two components on the shear plane Fs is the force required to shear the metal along the shear plane and Fn is the normal force on this plane. Two other force components also exist on the face of the tool the friction force F and the normal force N. Whereas the cutting force Fc is always in the direction shown in Fig. the thrust force Ft may be in the opposite direction to that