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Blank selection of parts and principles of blank selection

blank selection of parts

forming support data detection of materials effectiveness industry development process is an important process of mechanical manufacturing. In machine manufacturing, most parts are first made by casting, forging, welding or non-metallic material forming, and then by cutting. The selection of blank has an important impact on the quality, cost, performance and product image of machine manufacturing, and is one of the key links in machine design and manufacturing

generally, once the material of the part is determined, the blank forming method is also roughly determined. For example, the parts adopt ZL202, HT200, QT, etc. obviously, its blank should be cast; Gear parts made of 45 steel and LD7 are often formed by forging; The parts are made of Q235, 08 steel and other plates and strips, which are generally formed by cutting, stamping or welding; If plastic is used for parts, appropriate plastic forming method shall be selected; If the parts are made of ceramics, the ceramic forming method should be selected. On the contrary, when choosing the blank forming method, in addition to considering the processability of the part structure, we should also consider whether the technological performance of the material can meet the requirements

the principle of blank selection

the principle of blank selection should, on the premise of meeting the use requirements, reduce the production cost as much as possible to make the products competitive in the market

1. Technological principle

the use requirements of parts determine the shape characteristics of the blank. Various use requirements and shape characteristics form the corresponding requirements for the forming process of unloading the oil collector. The use requirements of parts are embodied in the external quality of their shape, size, machining accuracy, surface roughness, and the internal quality of their chemical composition, metal structure, mechanical properties, physical properties and chemical properties. For the use requirements of different parts, the process characteristics of part materials (such as casting performance, forging performance, welding performance, etc.) must be considered to determine the blank forming method. For example, the method of forging forming and the method of welding forming cannot be used to manufacture gray cast iron parts; Avoid using casting forming method to manufacture thin-walled blanks with poor fluidity; The blank with high density requirements or requiring heat treatment after casting cannot be formed by ordinary pressure casting; Materials with low recrystallization rate such as copper alloy cannot be forged by die forging on hammer; Automatic submerged arc welding cannot be used to weld the weld at the overhead position; Resistance welding cannot be used to weld copper alloy components; Electroslag welding cannot be used to weld thin-walled components, etc. While choosing the blank forming method, we should also take into account the machinability of subsequent machining. For example, the blank with large machining allowance cannot be formed by ordinary pressure casting, otherwise the holes under the surface of the casting will be exposed; High grade Pearlite Nodular Cast Iron and thin wall grey cast iron shall be avoided as far as possible for the blanks that need to be cut, otherwise it is difficult to cut. For some blanks with complex structure and difficult to be formed by a single forming method, we should consider not only the possibility of combining various forming schemes, but also whether some combination will affect the machinability of machining

2. Adaptability principle

adaptability principle should also be considered in the selection of blank forming scheme. According to the structural shape, overall dimension and working conditions of the parts, the suitable blank scheme is selected

for example, for stepped shaft parts, when the diameter of each step is not much different, bars can be used; If the difference is large, the operation and management of private enterprises is not standardized, and forging blanks should be used

generally, metal mold casting should not be used for blanks with complex shape and thin wall; Generally, die forging, pressure casting and investment casting are not used for large-size blanks, and most of them are made by free forging, sand casting and welding

different working conditions of parts lead to different types of blanks. For example, the spindle and handle of the machine tool are shaft parts, but the spindle is the key part of the machine tool. The requirements for size, shape and machining accuracy are very high, the stress is complex, and only small deformation is allowed in the process of use. Therefore, 45 steel or 40Cr with good comprehensive mechanical properties should be selected, which is made by forging billet, strict cutting and heat treatment; The problem of slipping is solved, and the handle of the machine tool is made of low-carbon steel round bars or ordinary gray iron castings, which can be completed by simple cutting without heat treatment. Another example is that the crankshaft of internal combustion engine bears great tensile, bending and torsional stresses in the working process, and should have good comprehensive mechanical properties. Therefore, the crankshaft of high-speed and high-power internal combustion engine is generally forged with alloy structural steel with good strength and toughness. When the power is small, it can be cast with nodular cast iron or forged with medium carbon steel. For the straight shaft with small force and circular surface, the round steel can be cut and formed directly

3. Principle of giving consideration to production conditions

the forming scheme of the blank should be selected according to the on-site production conditions. On site production conditions mainly include the actual process level of on-site blank manufacturing, equipment status, and the possibility and economy of outsourcing, but at the same time, more advanced blank manufacturing methods due to production development should also be considered

therefore, when selecting blanks, we should analyze the existing production conditions of the enterprise, such as equipment capacity and staff technical level, and try to use the existing production conditions to complete the blank manufacturing task. If the existing production conditions are difficult to meet the requirements, we should consider changing the part materials and/or blank forming methods, which can also be solved by outsourcing or outsourcing

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