Extrusion with a punch or a convex die placed in the concave die billet pressure, so that it produces plastic flow, so as to obtain the corresponding mold hole or concave-convex mold shape of the forgery method. When extruding, the billet produces three-way compressive stresses, and even billets with low plasticity can be extruded. Extrusion, especially cold extrusion, high material utilization, material organization and mechanical properties have been improved, simple operation, high productivity, can make long rod, deep hole, thin-walled, shaped section parts, is an important less cutting-free machining process. Extrusion is mainly used for metal forming, can also be used for plastics, rubber, graphite and clay billets and other non-metallic forming. In the 17th century, the French used manual screw presses to extrude lead pipes, used as water pipes, is the beginning of the cold extrusion. the late 19th century to achieve the cold extrusion of zinc, copper and copper alloys, the early 20th century to expand to the extrusion of aluminum and aluminum alloys. the 30's German invention of phosphate, saponification of the surface of friction lubrication treatment technology to make the steel of the cold extrusion has been a success, initially used for extrusion of steel cartridge cases. After the second world war, the cold extrusion of steel to other countries, and expand the scope of application. 50's began to use molten glass lubrication method, the hot extrusion of steel so in the metallurgical and mechanical industries have been applied and developed. Classification Extrusion according to the billet temperature distinction between hot extrusion, cold extrusion and warm extrusion 3 kinds. Metal billet in the recrystallization temperature (see plastic deformation) above the extrusion for the hot extrusion; at room temperature extrusion for the cold extrusion; higher than room temperature but not more than the recrystallization temperature under the extrusion for the temperature extrusion. According to the plastic flow direction of the billet, extrusion can be divided into: the flow direction and the same direction of the pressurized positive extrusion, the flow direction and the opposite direction of the pressurized counter-extrusion, the billet to the positive and negative direction of the flow of the composite extrusion. Application Hot extrusion is widely used in the production of aluminum, copper and other non-ferrous metals such as tubes and profiles, belonging to the scope of the metallurgical industry. Hot extrusion of steel is used to produce special tubes and profiles, but also for the production of carbon and alloy steel parts that are difficult to form with cold or warm extrusion of solid and porous (through-hole or not through-hole), such as rods with large heads, barrels, containers and so on. Hot extrusion parts of the dimensional accuracy and surface finish is better than hot die forging parts, but with parts generally still need to go through the finishing or cutting process. Cold extrusion was originally used only for the production of lead, zinc, tin, aluminum, copper and other tubes, profiles, as well as toothpaste hose (lead outside the bread tin), dry battery shells (zinc), shells (copper) and other parts. the mid-20th century cold extrusion technology began to be used for carbon structural steel and alloy structural steel parts, such as a variety of cross-sectional shapes of rods and rods, piston pins, wrench sockets, straight toothed cylindrical gears, etc., and then used to extrude some of the Later, it is used to extrude certain high carbon steel, rolling bearing steel and stainless steel parts. Cold extruded parts with high precision and clean surface can be directly used as parts without cutting or other finishing. Cold extrusion is simple to operate and is suitable for the mass production of smaller parts (steel extrusions are generally no larger than 100 mm in diameter). Warm extrusion is between cold extrusion and hot extrusion intermediate process, in the appropriate circumstances using warm extrusion can have the advantages of both. But warm extrusion needs to heat the billet and preheat the die, high temperature lubrication is not ideal, die life is shorter, so it is not widely used. Process characteristics Extrusion processing in the billet processing, extrusion channel, extrusion pressure, die life and extrusion equipment according to the billet and extrusion requirements of different parts have some process characteristics. Soft annealing Cold extrusion of hard aluminum, copper and steel, etc., in order to reduce the hardness of the material, deformation resistance and improve the plasticity, you need to soften the billet annealing treatment. Hot extrusion does not require an annealing process. Lubrication and surface treatment In order to reduce the extrusion pressure and die wear rate, and to prevent the metal billet and die surface of the thermal adhesion, extrusion must be well lubricated. In order to keep the lubricating grease from being extruded at high pressures, the surface of the billet must be treated for friction reduction and lubrication. The most commonly used method is: first phosphate, in order to form a rough and porous phosphate surface layer, and then to the soap material (such as zinc stearate, sodium stearate) coating the surface layer and make it full of pores. When extruded, the phosphate layer continuously releases soap material and plays an effective lubricating role. Warm extrusion and hot extrusion due to high temperature, not suitable for phosphating - soaping lubrication, generally used glass powder (molten at high temperatures), molybdenum disulfide, graphite and other formulated oil lubricant. Deformation degree and extrusion channel Extrusion deformation degree to the billet before and after the deformation of the sectional area before and after the rate of reduction to indicate. Billet in a deformation process without cracking the limit of deformation degree is called the allowable degree of deformation. When the billet is extruded under three-way compressive stress, the permissible degree of deformation is higher. In the cold state of positive extrusion, mild steel allowable degree of deformation in more than 75%, and duralumin, copper, brass, etc. can reach more than 90%, counter-extrusion are slightly lower. In the hot state, the allowable degree of deformation can be greatly increased, the magnitude of the increase with the increase in temperature. Deformation degree is large, the required extrusion pressure is also large, mold wear and tear accelerated, and easy to damage, so generally do not use the limit value of the degree of deformation allowed, for example, in the cold extrusion of carbon steel using the limit value of 60% of the deformation as a deformation of the permissible degree of deformation. If the total degree of deformation from the billet to the finished product is very large, it is divided into several extrusion channel gradually forming. In cold extrusion, an inter-process soft anneal is required between passes. Hot and warm extrusion have a larger permissible degree of deformation, which is conducive to lowering the squeezing force and reducing the number of extrusion passes. Extrusion Pressure Extrusion pressure is the main factor in determining the strength of the die and in selecting the nominal pressure of the extruder. The size of the extrusion pressure and the convex die pressurized area, the mechanical properties of the blank at the extrusion temperature, the degree of deformation, die shape, lubrication effect and other factors. In the cold extrusion of hard aluminum, copper and other materials, extrusion pressure per unit area is generally in the 1000 N / cm 2 or less; cold extrusion of carbon steel and alloy steel are generally in the 1000 N / cm 2 or more, high up to 2500 ~ 3000 N / cm 2. Because the unit area of extrusion pressure is very large, bear the expansion stress of the concave die mostly 2, 3 layers of pre-stressed structure, in order to improve its strength and stiffness, and so that the wear and tear only in the innermost layer, is conducive to the repair of the mold (only the replacement of concave die of the inner layer). Die life Extending die life is an important factor in reducing extrusion processing costs. Dies can exceed the permissible size and shape errors of extruded parts due to longitudinal cracking of the die or wear of the formed cavities and holes. The former can be avoided through the correct design and manufacture; the latter rely on the correct choice of die material and its heat treatment and surface treatment process, the correct decision extrusion process and lubrication and other measures to slow down in order to extend its service life. Extrusion equipment Small extrusions are generally extruded by general-purpose mechanical presses, hydraulic presses, screw presses. Large extruded parts and long extruded parts are more often used in special extrusion presses. Development Since the second half of the 20th century, the emergence of hydrostatic extrusion process. Hydrostatic extrusion uses positive extrusion at room temperature. Billet in the concave die by the injection of high-pressure liquid longitudinal and around the hydrostatic pressure, from the hole extrusion. The friction coefficient of the hydrostatic liquid friction generated between the billet periphery and the wall of the extrusion cylinder is extremely low, and the transverse compressive stress in the deformation zone of the billet increases compared with that under general extrusion conditions, and the resistance to extrusion deformation decreases, which further improves the plasticity of the billet. High-speed steel, titanium alloy, zirconium alloy, nickel-based alloys and other high-strength low-plasticity metal materials can be static extrusion molding without cracks. However, the high-pressure sealing problem needs to be perfected, and hydrostatic extrusion is still in the stage of further research. Optical fiber is extruded by the loss caused by a small bending. Stamping
Stamping is the power of conventional or special stamping equipment, so that the sheet in the mold is directly subject to deformation force and deformation, so as to obtain a certain shape, size and performance of the product parts of the production technology. Sheet, mold and equipment is the three elements of stamping. Stamping is a kind of metal cold deformation processing method. Therefore, it is called cold stamping or sheet metal stamping, or stamping for short. It is one of the main methods of metal plasticity processing (or pressure processing) and is also affiliated with material forming engineering technology. The mold used for stamping is called a stamping die, or stamping die for short. The die is a special tool for batch processing of materials (metallic or non-metallic) into the required punched parts. Stamping die in stamping is crucial, no meet the requirements of the stamping die, batch stamping production is difficult to carry out; no advanced stamping die, advanced stamping process can not be realized. Stamping process and molds, stamping equipment and stamping materials constitute the three elements of stamping processing, only they are combined with each other in order to come up with stamped parts. Compared with other methods of machining and plasticity processing, stamping process has many unique advantages in terms of technology and economy. The main performance is as follows. (1) the high productivity of stamping, and easy to operate, easy to realize mechanization and automation. This is because the stamping is relying on the stamping die and stamping equipment to complete the process, the number of ordinary press strokes per minute up to dozens of times, high-speed pressure per minute up to hundreds or even thousands of times above, and each stamping stroke may be a punch. (2) Stamping due to the mold to ensure the size and shape of the stamped parts of the precision, and generally do not damage the surface quality of the stamped parts, and the mold life is generally longer, so the quality of stamping is stable, interchangeable, and has the characteristics of the "one and the same". (3) Stamping can be processed to produce parts with larger size range and more complicated shapes, such as small stopwatches for clocks and watches, large longitudinal beams for automobiles, coverings and so on, coupled with the cold deformation and hardening effect of the material during stamping, the strength and stiffness of stamping are higher. (4) Stamping generally does not generate chips and debris, less material consumption, and does not require other heating equipment, so it is a kind of material-saving, energy-saving processing methods, the cost of stamped parts is lower. Due to the superiority of stamping, stamping is widely used in various fields of national economy. For example, stamping is used in aerospace, aviation, military, machinery, agricultural machinery, electronics, information, railway, post and telecommunications, transportation, chemical industry, medical equipment, daily appliances and light industry. Not only does the whole industry use it, but everyone is directly related to stamping products. Like airplanes, trains, automobiles, tractors, there are many large, medium and small stamping parts. Small car body, frame and rim and other parts are stamping processed out. According to relevant survey statistics, bicycles, sewing machines, watches, 80% of the stamping parts; TV, recorders, video cameras, 90% of the stamping parts; and food metal cans and shells, steel pots and pans stove, enamel pots and bowls and stainless steel cutlery, all of which is the use of molds of the stamping process products; even the computer hardware is also missing in the stamping parts. However, the mold used in the stamping process generally has a speciality, sometimes a complex part requires several sets of molds in order to be processed and shaped, and high precision mold manufacturing, high technical requirements, is a technology-intensive products. Therefore, only in the case of larger production batch of stamping parts, the advantages of stamping processing can be fully realized, so as to obtain better economic benefits. Of course, stamping processing also has some problems and shortcomings. Mainly in the stamping processing of noise and vibration generated by the two public nuisances, and the operator's safety accidents occur from time to time. However, these problems are not entirely due to the stamping process and mold 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, with the progress of mechatronics technology, these problems will be solved as soon as possible.
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