Five technical requirements in flange forging process (part one)
The use conditions of flanges refer to the importance, working conditions, assembly and disassembly difficulty, complexity of them, as well as force, working temperature, corrosion degree, and other factors.
From the basic principle that the forging is to serve and meet the use conditions of the parts, the technical requirements of the forging should include two aspects, one is the requirements of the shape, size and surface of the forgings, and the other is the requirements of structure and mechanical performance.
The key to meeting the requirements of forgings is correctly selecting the raw materials, and strictly controlling the production process as well as the quality of the raw materials. Furthermore, through reasonable development of the production process of forgings, effective quality control is implemented.
The selection of forgings is usually determined by the product design, and it is stipulated that in addition to the basic properties of the material, namely the yield strength, tensile strength, plasticity and fracture toughness, in order to reduce the structure weight, besides two important parameters, strength-to-weight ratio and stiffness-weight ratio, the physical properties, process properties (malleability, hardenability, machinability, weldability, etc.) and economic efficiency must also be taken into account.
1. Requirements for choosing raw materials
Choosing the most reliable raw materials is a prerequisite for the quality of the forgings. The main processes of determining the quality of raw materials are smelting, ingot casting, and semi-product processing. The technical requirements for selecting raw materials can be summarized as follows.
Chemical composition - The content of alloying elements, harmful impurities, gases and residual elements in the materials should comply with the technical standards and relevant technical conditions or agreements, and be controlled as strictly as possible based on the production conditions. There must be certain requirements for the distribution uniformity of alloying elements.
Smelting technique - Ultra-high-strength steel, titanium alloy and high-temperature alloy are produced by vacuum arc remelting method, among which, titanium alloy and high-temperature alloy require no less than two times; Alloy structural steel, stainless steel and heat-resistant steel are produced by electric arc furnace, or dual process with electric arc furnace and electroslag remelting, or other better smelting methods; Aluminum alloys are usually smelted by flame furnace, electric resistance furnace and induction furnace, and high-quality aluminum alloys require a series of technological measures to strictly control the impurity content and diversify the heat treatment conditions of the materials.
Material specifications, surface quality and dimensional tolerances are based on the production process and quality requirements of forgings. The specifications of the materials include ingots, bars (rolled, forged, extruded), billets, flats, etc. When forgings have strict streamline distribution requirements, care should be taken to select the flow direction of the raw material to coordinate with the streamline distribution specified by the forging. Surface defects of raw materials, such as cracks, folds, crusting, double skin, etc., may cause problems on the surface of the forging, and therefore should be avoided. The dimensional tolerance of raw materials has an important influence on the precise forming of forgings, so the requirements of this should be clearly defined.
Material forging ratio - Materials should be guaranteed to have a sufficiently large degree of deformation, that is, the forging ratio should be specified within a suitable range to ensure sufficient deformation of the material and to reduce or eliminate the cast structure in the material. For large forgings, the forging ratio of raw materials is generally required to be greater than 6-8.
From the basic principle that the forging is to serve and meet the use conditions of the parts, the technical requirements of the forging should include two aspects, one is the requirements of the shape, size and surface of the forgings, and the other is the requirements of structure and mechanical performance.
The key to meeting the requirements of forgings is correctly selecting the raw materials, and strictly controlling the production process as well as the quality of the raw materials. Furthermore, through reasonable development of the production process of forgings, effective quality control is implemented.
The selection of forgings is usually determined by the product design, and it is stipulated that in addition to the basic properties of the material, namely the yield strength, tensile strength, plasticity and fracture toughness, in order to reduce the structure weight, besides two important parameters, strength-to-weight ratio and stiffness-weight ratio, the physical properties, process properties (malleability, hardenability, machinability, weldability, etc.) and economic efficiency must also be taken into account.
1. Requirements for choosing raw materials
Choosing the most reliable raw materials is a prerequisite for the quality of the forgings. The main processes of determining the quality of raw materials are smelting, ingot casting, and semi-product processing. The technical requirements for selecting raw materials can be summarized as follows.
Chemical composition - The content of alloying elements, harmful impurities, gases and residual elements in the materials should comply with the technical standards and relevant technical conditions or agreements, and be controlled as strictly as possible based on the production conditions. There must be certain requirements for the distribution uniformity of alloying elements.
Smelting technique - Ultra-high-strength steel, titanium alloy and high-temperature alloy are produced by vacuum arc remelting method, among which, titanium alloy and high-temperature alloy require no less than two times; Alloy structural steel, stainless steel and heat-resistant steel are produced by electric arc furnace, or dual process with electric arc furnace and electroslag remelting, or other better smelting methods; Aluminum alloys are usually smelted by flame furnace, electric resistance furnace and induction furnace, and high-quality aluminum alloys require a series of technological measures to strictly control the impurity content and diversify the heat treatment conditions of the materials.
Material specifications, surface quality and dimensional tolerances are based on the production process and quality requirements of forgings. The specifications of the materials include ingots, bars (rolled, forged, extruded), billets, flats, etc. When forgings have strict streamline distribution requirements, care should be taken to select the flow direction of the raw material to coordinate with the streamline distribution specified by the forging. Surface defects of raw materials, such as cracks, folds, crusting, double skin, etc., may cause problems on the surface of the forging, and therefore should be avoided. The dimensional tolerance of raw materials has an important influence on the precise forming of forgings, so the requirements of this should be clearly defined.
Material forging ratio - Materials should be guaranteed to have a sufficiently large degree of deformation, that is, the forging ratio should be specified within a suitable range to ensure sufficient deformation of the material and to reduce or eliminate the cast structure in the material. For large forgings, the forging ratio of raw materials is generally required to be greater than 6-8.
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