First, common types of blanks Common types of blanks are the following: (I) Castings For the more complex shape of the blank, generally available casting method. At present, most castings use sand casting. For small castings with higher dimensional accuracy, special castings such as permanent casting, precision casting, pressure casting, investment casting, and centrifugal casting can be used. Various casting methods and process features are shown in Table 3-9. (B) Forgings Forging blanks can obtain continuous and uniform metal fiber structure after forging. Therefore, the mechanical properties of the forgings are better, and they are often used for important steel parts with complex forces. Among them, free forgings have low precision and productivity, and are mainly used for the manufacture of small batches and large forgings. The dimensional accuracy and productivity of the forged parts of the model are higher, and they are mainly used for small and medium-sized forgings with large output. Forging method and process characteristics are shown in Table 3-9. (c) Profiles Profiles are mainly plate, bar, wire and so on. Common cross-sectional shapes are round, square, hexagonal, and special cross-sectional shapes. Its manufacturing methods can be divided into hot-rolling and cold-drawing two major categories. Hot rolled sections are larger in size and less accurate and are used for general mechanical parts. The cold-drawn profiles are small in size and high in precision, and are mainly used for small and medium-sized parts with high requirements for blank accuracy. (four) welding parts Welded parts are mainly used for single-piece small batch production and large parts and prototypes. Its advantages are simple manufacturing, short production cycle, material saving and weight reduction. However, its anti-vibration performance is poor and its deformation is large. It is necessary to perform mechanical processing after aging treatment. (e) Other blanks Other blanks include stampings, powder metallurgy, cold extrusions, plastic extrusions, etc. Second, the principle of rough selection When choosing a blank, consider the following factors: (I) Production Plan of Parts Mass-produced parts should be chosen for precision and high-manufactured billet manufacturing methods, and the expensive costs for billet manufacturing can be compensated by the reduction in material consumption and the reduction in machining costs. Such as castings using metal mold machine modeling or precision casting; forgings using forging, precision forging; selection of cold-drawn and cold-rolled profiles. Smaller batches should be selected for single-piece production methods with less precision and lower productivity. (b) Processability of part materials For example, cast iron or bronze parts should be selected for casting blanks; when steel parts are not complex in shape and the mechanical properties are not too high, profiles can be selected; important steel parts should be selected for forging to ensure their mechanical properties. Blanks. (3) Structure, shape and size of parts Shaped blanks are generally manufactured by casting methods. Thin-walled parts are not suitable for sand casting. For general-purpose stepped shafts, if the diameters of the segments are not much different, round bars may be used. If the diameters of the segments are relatively large, in order to reduce the material consumption and the amount of labor required for machining, forging blanks should be used, and large-size parts are generally used. Choose free forging, small and medium-sized parts can consider the choice of die forgings. (D) Existing production conditions When selecting blanks, we must also consider the factory's rough manufacturing level, equipment conditions, and the possibility of external associations and economical. Third, the shape and size of the blank The shape and size of the blank are mainly determined by factors such as the shape, structure, size, and machining allowance of the component composition surface, and are as close as possible to the component so as to reduce the amount of labor for machining and strive to achieve little or no cutting. However, due to the limitations of the existing billet manufacturing technology and cost, as well as the increasing processing precision and surface quality requirements of the product parts, some surfaces of the billet still need to have a certain allowance for machining. Meet the technical requirements of the parts. The difference between the blank size and the part drawing size is called the blank allowance. The difference between the maximum size and the minimum size allowed for the casting nominal size is called the casting size tolerance. The blank allowance is related to the size, location, and shape of the blank. Such as the casting blank machining allowance, is the casting by the largest size, nominal size (the maximum distance between the two relative processing surface or the reference surface to the processing surface distance), the blank casting position (top, bottom, side), casting hole The dimensions are determined by other factors. For a single batch of small batch production, holes with a diameter of 30 mm on the casting and a diameter of less than 60 mm on the steel casting may not be cast. For the forgings, if free forging is used, the holes with an opening diameter of less than 30 mm or an aspect ratio of more than 3 may not be forged. Forgings should consider forged fillets and swaged slopes. Forgings with holes can not be directly forged through holes, punching holes should be left with the skin. The determination of the shape and size of the blanks, in addition to attaching the blanks to the corresponding machined surfaces of the parts, sometimes also takes into account the influence of process factors such as the manufacture of the blanks, the machining and the heat treatment. In this case, the shape of the blank may differ from the shape of the workpiece. For example, for easy installation during processing, some casting blanks need to be cast with the necessary process bosses, as shown in Figure 3-17. The process bosses should generally be cut after the parts are machined. Another example is the opening and closing of the nut shell lathe, which consists of two parts of a composite casting, to be processed after a certain period and then cut to ensure the processing quality and processing convenience. As shown in Figure 3-18. In order to increase the productivity and to facilitate the installation during machining, some small parts can be combined into one blank, as shown in Fig. 3-19. The sliding keys are forgings. Several parts can be combined to form a blank firstly, on both sides and After the plane is processed, it is cut into individual parts. As shown in Fig. 3-20, washer parts should also be combined into several blanks. The blank can take a long tube and its inner hole diameter should be smaller than the inner diameter of the washer. When turning, clamp one end of the outer circle with a chuck, and the other end with the top, then you can use the outer circle and the groove, then use the chuck to clamp the longer part of the outer circle to drill with a φ 16mm bit. It can be divided into several washer parts. 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The choice of blank types not only affects the manufacturing process and cost of the blank, but also is closely related to the machining process and the quality of the parts. For this purpose, it is necessary to closely cooperate with the craftsmen of both blank manufacturing and mechanical processing, reasonably determine the type, structure and shape of the blank, and draw a rough drawing.