Forging is a combination of forging and stamping. It is a forming processing method that uses hammers, anvils, punches or dies of forging machinery to exert pressure on the blank to produce plastic deformation, so as to obtain the required shape and size. Forging is mainly classified according to forming mode and deformation temperature. Forging can be divided into forging and stamping according to the forming method; According to deformation temperature, forging can be divided into hot forging, cold forging, warm forging and isothermal forging.
In the forging process, the billet has obvious plastic deformation and a large amount of plastic flow; In the stamping process, the blank is formed mainly by changing the spatial position of the area of each part, and there is no plastic flow within the blank with a large distance. Forging is mainly used to process metal parts, but also can be used to process some nonmetals, such as engineering plastics, rubber, ceramic blanks, brick blanks and the forming of composite materials.
stamping
The forming and processing method of work-piece (stamping part) with required shape and size by applying external force on sheet, strip, pipe and profile by press and die to cause plastic deformation or separation. Stamping and forging belong to plastic processing (or pressure processing), which is called forging. Stamped blanks are mainly hot-rolled and cold-rolled steel plates and strips. In the world, 60~70% of steel products are plates, most of which are made into finished products by stamping.
Compared with other methods of mechanical processing and plastic processing, stamping has many unique advantages both in technology and economy. The main performances are as follows.
(1) The stamping process has high production efficiency, convenient operation, and is easy to realize mechanization and automation. This is because stamping depends on stamping dies and stamping equipment to complete the processing. The number of strokes of ordinary presses can reach dozens of times per minute, and the high-speed pressure can reach hundreds or even thousands of times per minute. In addition, each stamping stroke may result in a stamping part.
(2) During stamping, because the die ensures the size and shape accuracy of the stamping part, and generally does not damage the surface quality of the stamping part, and the life of the die is generally long, the stamping quality is stable, the interchangeability is good, and the stamping is "exactly the same".
(3) Stamping can process parts with large size range and complex shape, such as stopwatches of clocks and watches, automobile longitudinal beams, covering parts, etc. In addition to the cold deformation hardening effect of materials during stamping, the strength and stiffness of stamping are high.
(4) Stamping generally has no generation of chips, less material consumption, and does not need other heating equipment, so it is a material saving and energy-saving processing method, and the cost of stamping parts is low.
Because stamping has such advantages, stamping processing is widely used in various fields of the national economy. For example, stamping is carried out in aerospace, aviation, military, machinery, agricultural machinery, electronics, information, railway, post and telecommunications, transportation, chemical industry, medical appliances, household appliances and light industry. Not only does the whole industry use it, but everyone is directly connected with stamping products. There are many large, medium and small stamping parts on airplanes, trains, cars and tractors. The car body, frame, rim and other parts are all stamped. According to relevant statistics, 80% of bicycles, sewing machines and watches are stamped parts; 90% of TV sets, radio recorders and video cameras are stamping parts; There are also metal cans and shells for food, refined steel boilers, enamel basins and bowls, and stainless steel tableware, all of which are stamping products using molds; Even the hardware of the computer is not lack of stamping parts.
However, the dies used for stamping processing are generally special. Sometimes a complex part needs several sets of dies to be processed and formed, and the die manufacturing has high precision and technical requirements, which is a technology intensive product. Therefore, the advantages of stamping can be fully reflected only when the production batch of stamping parts is large, so as to obtain better economic benefits.
Compared with castings and forgings, stamping parts are thin, uniform, light and strong. Stamping can produce workpieces with stiffeners, ribs, undulations or flanging that are difficult to manufacture by other methods to improve their rigidity. Due to the use of precision die, the precision of the workpiece can reach the micron level, and the repetition precision is high, the specification is consistent, and the holes and sockets, bosses, etc. can be punched. Cold stamping parts are generally no longer subject to machining, or only require a small amount of machining. The precision and surface condition of hot stamping parts are lower than those of cold stamping parts, but they are still better than castings and forgings, with less machining.
The precision and structure of die directly affect the forming and precision of stamping parts. Die manufacturing cost and life are important factors that affect the cost and quality of stamping parts.
The surface and internal properties of sheet metal for stamping have a great impact on the quality of the finished stamping products. Requirements for stamping materials are:
① The thickness is accurate and uniform. The stamping die is precise, with small clearance. Excessive thickness of sheet metal will increase the deformation force, cause material jamming, and even crack the female die; If the sheet metal is too thin, the quality of the finished product will be affected, and even cracks will occur during drawing.
② The surface shall be smooth and clean without spot, scar, scratch, surface crack, etc. All surface defects will remain on the surface of the finished workpiece, and the crack defects may expand in the bending, drawing, forming and other processes, resulting in waste products.
③ The yield strength is uniform without obvious directivity. Anisotropy (see the plastic deformed sheet metal in the stamping process of deep drawing, flanging, bulging, etc., due to the occurrence of anisotropic yielding in sequence, the plastic deformation amount is inconsistent, which will cause uneven deformation, resulting in inaccurate forming and defective products or waste products.
④ High uniform elongation. In the tensile test, the elongation before the thin necking of the specimen occurs is called the uniform elongation. During drawing, the deformation of any area of the sheet metal shall not exceed the uniform extension range of the material, otherwise uneven deformation will occur.
⑤ Low yield ratio. The ratio of yield limit to strength limit of materials is called yield strength ratio. Low yield ratio can not only reduce the deformation resistance, but also reduce the tendency of wrinkling during drawing, reduce the springback after bending, and improve the accuracy of bending parts.
⑥ Low work hardening. The work hardening after cold deformation will increase the deformation resistance of the material, making it difficult to continue deformation, so the plate with low hardening index is generally used. However, the materials with high hardening index have good plastic deformation stability (that is, the plastic deformation is more uniform), and are not prone to local tension cracking.
Forging is a processing method that uses forging machinery to exert pressure on metal blank to make it produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes. Forging (forging and stamping) is one of the two major components. Forging can eliminate as cast porosity and other defects produced in the smelting process of metal, optimize the microstructure. At the same time, due to the preservation of complete metal streamline, the mechanical properties of forgings are generally superior to castings of the same material. For important parts with high load and severe working conditions in related machinery, forgings are mostly used, except for simple rolled plates, profiles or weldments.
According to the deformation temperature, forging can be divided into hot forging (forging temperature is higher than the recrystallization temperature of billet metal), warm forging (forging temperature is lower than the recrystallization temperature of metal) and cold forging (normal temperature). The initial recrystallization temperature of steel is about 727 ℃, but 800 ℃ is generally used as the dividing line, and hot forging is used above 800 ℃; It is called warm forging or semi hot forging when the temperature is between 300 ℃ and 800 ℃
The microstructure and mechanical properties of metal can be improved after forging. Due to the deformation and recrystallization of the metal, the original coarse dendrites and columnar grains are transformed into equiaxed recrystallized structures with finer grains and uniform size after the casting structure is deformed by hot working by forging method. The original segregation, looseness, porosity, slag inclusion, etc. in the ingot are compacted and welded, and the structure becomes more compact, which improves the plasticity and mechanical properties of the metal.
The mechanical properties of castings are lower than those of forgings of the same material. In addition, the forging process can ensure the continuity of the metal fiber structure, keep the fiber structure of the forging consistent with the shape of the forging, and ensure that the metal streamline is complete. It can ensure that the parts have good mechanical properties and long service life. Forgings produced by precision die forging, cold extrusion, warm extrusion and other processes are incomparable to castings
Forging is an article in which metal is pressed to shape the required shape or suitable compression force through plastic deformation. This force is typically achieved by using a hammer or pressure. The casting process creates a refined granular structure and improves the physical properties of the metal. In the practical use of components, a correct design can make the particle flow in the direction of the main pressure. Castings are metal shaped objects obtained by various casting methods, that is, the molten liquid metal is poured into the prepared mold by pouring, injection, suction or other casting methods, and the objects with certain shape, size and performance are obtained after cooling, sand falling, cleaning and post-treatment.
