Coining and gear forging are examples of closed die forging Figs. Examples are wire drawing, tube drawing, deep drawing etc. 2.8(c). In the direct extrusion a considerable part of press capacity is used against the frictional forces on the cylinder wall. Figures 2.13(a) and (b) show redrawing with the help of retaining rings. 2.4(b). Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. A fixed tool of the shape of a bar is fixed at the center. To cover the entire circumference either the fixture carrying the die sets is rotated or the rotating tool axis is oscillated around the work piece axis. Strip is continuously bent by roller dies to make the tubular form which is then seam welded with the help of rotating circular electrodes (Fig. The different extrusion processes are listed (Fig. To understand the forming (by deformation process) of metal, it is important to know the structure of metals. It requires less force compare to cold working. Account Disable 12. Thus, there are compressive forces all around though of different magnitudes at different locations and in different directions. A number of components like antenna dishes, nose-cones of rockets and missiles, tumblers and other similar components are manufactured by spinning. Figure 2.13(c) illustrates reverse redrawing in which case the cup is place upside down with bottom at the top and diameter is reduced by drawing into a die with help of a smaller diameter punch. In hot working process, the temperature at which deformation takes place is important because further increase in temperature increase grain growth thus decrease mechanical properties. 2.19 a), embossing (Fig. 2.6(d). The main benefit of this process is that a large reduction up to 95% may be achieved in single pass while in a conventional rolling pass it is nearly 30% only. (iii) Extrusion ratio as high as 1600 could be achieved. In the rolling process in Fig. The surface produced by curved tools is not flat. Stresses, strains, and metal flow in the plastic zone, occurring in metal forming processes, are shown to be strongly influenced by the work material used. However, there is net forward force which extrudes the metal through the die hole. 2.17). If the temperature of the metal exceeds its recrystallization temperature, the process is called hot rolling, otherwise is called cold rolling. Examples are forging, extrusion, rolling, indenting, coining, etc. A major advantage of the process is that it is noiseless. If you have any query regarding this article, ask by commenting. Forming by laser is an important process because it can be used for fabrication in outer space. During unaided bending of pipes and tubes the circular shape is flattened out. The amount of deformation is limited according to the press size. This is done with or without actual heating but the achieved temperature should below its recrystallization temperature. 2.4(d). 2.8. The structure at that temperature mainly consists of grains floating in liquid matrix. Rolling, forging and extrusion are in fact groups of processes. Pieces of sheet or strips are bent in V-shaped or U-shaped tools (Fig. It increase strength and hardness of the material due to strain hardening. These two processes involve both shear forming and bending, Spinning, illustrated in Fig. On NC/CNC spinning machines, however, identical components with close dimensional tolerances may be obtained. Figure 2.8(b) illustrates flattening as well as elongating with the help of flat tools. Self reading for your interestSelf reading for your interest Defects in metal forming processesDefects in metal forming processes and their remedies. As the wheel rotates, the frictional force on the three sides of the groove pushes the billet against the die. 2.14). 2.12c), the flange is kept pressed between the blank holding plate and the die surface while the press ram pushes the sheet into the die. Drawing out and fullering processes are used for elongating a bar with the help of flat or curved dies in Figs. Rotary forging in Fig. Copyright 10. In such an arrangement blank is rolled between two master gears. The work piece material is compressed by die and mandrel, while it is pulled through the die. Figure 2.18 shows the types of stresses developed during bending of a strip or bar. The main advantages of extrusion in mashy state are as below: (i) The extrusion force decreases with decrease in the solid fraction but the decrease is less than the decrease in yield strength. The machine consists of a small diameter inner roll and a big diameter outer roll. These metal forming processes require higher force to deform the work piece. 2.16(a, b)). In these processes shapes are rolled on the periphery of cylindrical work pieces. When the metal forming process done above the recrystallization temperature of material, it is known as hot working process. This method has the advantage that no blank holder plate is used, however, it can only be used for drawing relatively thicker sheets. Plagiarism Prevention 5. 2.12, are also used for the purpose. It may also be used for rolling of shaped small shafts of different cross-sections. Hydrostatic extrusion process is illustrated in Fig. Since bottom layer is still at a low temperature, the material in the heated band expands and suffers plastic deformation. These mills are called by the name of product they produce. In these processes the plastic state is reached by application of uni-axial or multi-axial compressive forces. Forming of metals at temperatures just above the solidus line but below liquid us is being developed and is called forming in mashy state. Figure 2.4 illustrates four types of longitudinal rolling processes. The examples are stretch forming, expanding (bulging) with the help of hydraulic pressure or rubber pad (Fig. Compressive Forming Processes: In these processes the plastic state is reached by application of uni-axial or multi-axial compressive forces. to deformed the raw material. In drawing cups of square or rectangular shapes additional radial stresses may have to be induced in the sheet which forms the flat portion of cup. Examples are forging, extrusion, rolling, indenting, coining, etc. Metal forming processes involve the application of tensile, The plastic deformation takes place under the die pressure and the tension due to pull. Metal forming processes can be carried out in Hot or Cold conditions. Cold worked work piece can be handle easily. (Fig. 1. 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