A forging method for pressing a blank placed in a female die with a punch or punch to make it flow plastically, so as to obtain a part corresponding to the shape of a die hole or a concave-convex die. During extrusion, the blank produces three-dimensional compressive stress, and even the blank with low plasticity can be extruded. Extrusion, especially cold extrusion, has the advantages of high material utilization rate, improved material structure and mechanical properties, simple operation and high productivity, and can be used to make long rod, deep hole, thin wall and special-shaped cross-section parts, which is an important machining process with little cutting. Extrusion is mainly used for the forming of metals, and can also be used for the forming of nonmetals such as plastics, rubber, graphite and clay blanks. In the 17th century, the French used a manual screw press to extrude lead pipes for water pipes, which was the beginning of cold extrusion. The cold extrusion of zinc, copper and copper alloys was realized at the end of 19th century, and expanded to the extrusion of aluminum and aluminum alloys at the beginning of 2th century. In 193s, Germans invented phosphating and saponifying surface antifriction and lubrication treatment technology, which made the cold extrusion of steel successful, and was originally used to extrude steel casings. After World War II, cold extrusion of steel was extended to other countries and its application scope was expanded. The molten glass lubrication method was adopted in 195s, and the hot extrusion of steel was applied and developed in metallurgy and machinery industry. Classified extrusion can be divided into three types according to blank temperature: hot extrusion, cold extrusion and warm extrusion. The extrusion of metal blank above recrystallization temperature (see plastic deformation) is hot extrusion; The extrusion at room temperature is cold extrusion; Extrusion above normal temperature but not above recrystallization temperature is warm extrusion. According to the plastic flow direction of the blank, extrusion can be divided into: forward extrusion with the same flow direction and pressure direction, backward extrusion with the opposite flow direction and composite extrusion with the blank flowing in both directions. Hot extrusion is widely used to produce pipes and profiles of non-ferrous metals such as aluminum and copper, which belongs to metallurgical industry. Hot extrusion of steel is not only used to produce special pipes and profiles, but also used to produce solid carbon steel and alloy steel parts with holes (through holes or not) that are difficult to be formed by cold extrusion or warm extrusion, such as bars, barrels and containers with thick heads. The dimensional accuracy and surface smoothness of hot extrusion parts are better than those of hot die forgings, but the mating parts still need finishing or cutting. Cold extrusion was originally only used to produce pipes and profiles of lead, zinc, tin, aluminum and copper, as well as toothpaste hoses (lead coated with tin), dry battery shells (zinc), shell casings (copper) and other products. In the mid-2th century, cold extrusion technology began to be used for carbon structural steel and alloy structural steel parts, such as bars and rod-shaped parts with various cross sections, piston pins, wrench sleeves, spur gears, etc., and later it was used to extrude some high carbon steel, rolling bearing steel and stainless steel parts. Cold extruded parts have high precision and smooth surface, and can be directly used as parts without cutting or other finishing. Cold extrusion operation is simple, and it is suitable for mass production of smaller parts (the diameter of steel extruded parts is generally not more than 1 mm). Warm extrusion is an intermediate process between cold extrusion and hot extrusion. Under suitable conditions, warm extrusion can have both advantages. However, warm extrusion needs to heat the blank and preheat the die, and high-temperature lubrication is not ideal, and the die life is short, so it is not widely used. Technological characteristics Extrusion processing has some technological characteristics in terms of blank treatment, extrusion pass, extrusion force, die life and extrusion equipment, depending on the requirements of blank and extrusion parts. In order to reduce the hardness, deformation resistance and improve plasticity of hard aluminum, copper and steel, it is necessary to soften and anneal the blank first. Hot extrusion does not need annealing treatment. Lubrication and surface treatment In order to reduce the extrusion force and the wear rate of the die, and prevent the thermal bonding between the metal blank and the die surface, good lubrication is necessary during extrusion. In order to prevent lubricating grease from being extruded under high pressure, it is necessary to reduce friction and lubricate the surface of the blank. The most common method is phosphating to form a rough and porous phosphate surface layer, and then coating the surface layer with soap materials (such as zinc stearate and sodium stearate) to fill the pores. During extrusion, the phosphating layer constantly releases soap to play an effective lubrication role. Warm extrusion and hot extrusion are not suitable for phosphating-saponification lubrication because of their high temperature. Generally, glass powder (melted at high temperature), molybdenum disulfide, graphite and other oils are used for lubrication. The deformation degree and the extrusion deformation degree of extrusion pass are expressed by the reduction rate of cross-sectional area of blank before and after deformation. The ultimate deformation degree of blank without cracks during primary deformation is called allowable deformation degree. When the billet is extruded under triaxial compressive stress, the allowable deformation degree is high. The allowable deformation degree of low carbon steel is more than 75% in cold forward extrusion, but it can reach more than 9% in hard aluminum, copper and brass, and it is slightly lower in reverse extrusion. In the hot state, the allowable deformation degree can be greatly improved, and the increase range increases with the increase of temperature. The deformation degree is large, the extrusion force required is also large, the wear of the die is accelerated, and it is easy to be damaged, so the limit value of allowable deformation degree is generally not adopted, for example, 6% of the deformation limit value is used as the allowable degree of primary deformation when cold extruding carbon steel. If the total deformation degree from blank to finished product is great, it is divided into several extrusion passes and gradually formed. During cold extrusion, it is necessary to carry out softening annealing between processes. The allowable deformation degree of hot extrusion and warm extrusion is larger, which is beneficial to reduce extrusion force and extrusion passes. Extrusion force extrusion force is the main factor to determine the strength of die and select the nominal pressure of extruder. The extrusion force is related to the pressing area of the punch, the mechanical properties of the blank at the extrusion temperature, the deformation degree, the shape of the die, the lubrication effect and other factors. In cold extrusion of hard aluminum, copper and other materials, the extrusion force per unit area is generally below 1 N/cm2; Cold extrusion of carbon steel and alloy steel is generally above 1 N/cm2, and the height can reach 25 ~ 3 N/cm2. Because of the large extrusion force per unit area, most female dies subjected to expansion stress adopt 2 or 3 layers of prestressed structure to improve their strength and rigidity, and make the wear only appear in the innermost layer, which is beneficial to the repair of the die (only replacing the inner layer of the female die). Prolonging die life is an important factor to reduce extrusion processing cost. The size and shape errors of the extrusion parts may exceed the allowable values due to the longitudinal crack of the die or the wear of the forming cavity and hole. The former can be avoided by correct design and manufacture; The latter can be slowed down by correctly selecting the die material and its heat treatment and surface treatment process, correctly determining the extrusion process and lubrication, so as to prolong its service life. The small extrusion parts of extrusion equipment are generally extruded by general mechanical presses, hydraulic presses and screw presses. Large extrusion parts and long extrusion parts are often extruded by special extrusion machines. Since the development of the second half of the 2th century, hydrostatic extrusion technology has appeared. Static pressure extrusion adopts normal temperature extrusion. The blank is extruded from the die hole under the longitudinal and peripheral static pressure of the injected high-pressure liquid in the die. The friction coefficient of hydrostatic friction between the periphery of the blank and the extrusion cylinder wall is extremely low, and the transverse compressive stress ratio of the deformation zone of the blank increases under general extrusion conditions, which reduces the resistance to extrusion deformation and further improves the plasticity of the blank. High strength and low plasticity metal materials such as high speed steel, titanium alloy, zirconium alloy and nickel-based alloy can be formed by static extrusion without cracks. However, the problem of high-pressure sealing needs to be improved, and hydrostatic extrusion is still in the further research stage. Loss caused by slight bending of optical fiber when it is squeezed. Stamping processing is a production technology that makes the sheet metal directly subjected to deformation force in the mold with the help of the power of conventional or special stamping equipment, so as to obtain a certain shape, size and performance of product parts. Sheet metal, die and equipment are the three elements of stamping. Stamping is a cold deformation processing method of metal. Therefore, it is called cold stamping or sheet metal stamping for short. It is one of the main methods of metal plastic working (or pressure working) and also belongs to material forming engineering technology. The die used in stamping is called stamping die, or die for short. Stamping die is a special tool for batch processing materials (metal or nonmetal) into required stamping parts. Stamping die is very important in stamping. Without the required stamping die, it is difficult to carry out mass stamping production. Without advanced stamping die, advanced stamping technology cannot be realized. Stamping process, die, stamping equipment and stamping materials constitute three elements of stamping processing, and only when they are combined with each other can stamping parts be obtained. Compared with other methods of mechanical processing and plastic processing, stamping has many unique advantages both in technology and economy. The main performance is as follows. (1) The stamping process has high production efficiency, convenient operation and easy mechanization and automation. This is because stamping depends on the stamping die 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, and it is possible to get a punch for each stamping stroke. (2) During stamping, because the die ensures the accuracy of the size and shape of the stamping parts, and generally does not damage the surface quality of the stamping parts, and the life of the die is generally long, the stamping quality is stable, interchangeability is good, and it has the characteristics of "identical". (3) Parts with large size range and complex shapes can be processed by stamping, such as stopwatches as small as clocks and watches, as large as automobile longitudinal beams and panels, etc. In addition, the cold deformation hardening effect of materials during stamping makes the stamping strength and rigidity higher. (4) Stamping generally does not generate chips and scraps, consumes less materials, 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 lower. Because stamping has such advantages, stamping processing is widely used in various fields of national economy. For example, there are stamping processes in aerospace, aviation, military industry, machinery, agricultural machinery, electronics, information, railways, posts and telecommunications, transportation, chemical industry, medical appliances, household appliances and light industry. Not only does the whole industry use it, but everyone is directly related to stamping products. There are many large, medium and small stamping parts on airplanes, trains, cars and tractors. The car body, frame and rim are all stamped and processed. According to relevant investigation and statistics, 8% of bicycles, sewing machines and watches are stamped parts; 9% of TV sets, tape recorders and cameras are stamped parts; There are also food metal cans, steel boilers, porcelain bowls and stainless steel tableware, all of which are stamping products using molds; Even the hardware of the computer is indispensable for stamping parts. However, the dies used in stamping processing are generally special, and sometimes a complex part needs several sets of dies to be processed and formed, and the precision of die manufacturing is high, and the technical requirements are high, so it is a technology-intensive product. Therefore, only when the stamping parts are produced in a large batch can the advantages of stamping be fully reflected, so as to obtain better economic benefits. Of course, there are also some problems and shortcomings in stamping. It is mainly manifested in the noise and vibration caused by stamping, and the safety accidents of operators occur from time to time. However, these problems are not entirely due to the stamping process and the die itself, but mainly due to the traditional stamping equipment and backward manual operation. With the progress of science and technology, especially the development of computer technology, and the progress of electromechanical integration technology, these problems will be solved as soon as possible.
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