Cold heading, cold extrusion introduction to the basics
Cold extrusion is a precision plastic volumetric forming technology is an important component. Refers to cold extrusion in the cold state of the metal blank into a mold cavity, under strong pressure and constant speed effect, force the metal extruded from the die cavity, so that the desired shape, size, and has a mechanical performance of extrusion. Obviously, cold extrusion process is controlled by the metal mold flow, by a large number of transfer volume to shape metal parts.
Cold extrusion technology is a high-precision, high efficiency, high quality and low consumption of advanced production technology, more applied to small and medium-scale production of forgings. Compared with forging, warm forging process, and materials can be 30% to 50%, saving 40% to 80% and to improve the quality of forgings, improve the working environment.
Currently, cold extrusion technology has been more widely used in fasteners, machinery, instruments, electrical appliances, light industry, aerospace, shipbuilding, military and other industrial sectors, the metal has become an important means of processing plastic bulk forming technique indispensable one. After World War II, cold extrusion technology in the automotive, motorcycle, household appliances and other industries to foreign industrial countries has been widely applied in the development, while the new extrusion materials, mold new steel grades and large tonnage presses will expand its emergence development space. Japan 1980s claimed that its car production to the forging process for the production of parts, 30% to 40% is produced by cold extrusion process. With the advancement of technology and automobile, motorcycle, household appliances and other industries for product technical requirements continue to increase, cold extrusion technology has become the development direction of the production of small precision forgings. Compared with other cold extrusion process has the following advantages:
1) conservation of raw materials. Cold extrusion is the use of the plastic deformation of the metal to the desired shape of the formed parts, which can significantly reduce machining, improve material utilization. Cold extrusion material utilization in general can reach more than 80%.
2) improve labor productivity. Cold extrusion manufacturing process instead of machining parts, enabling productivity increases several times, several times, or even a hundred times.
3) parts to obtain the desired surface roughness can and dimensional accuracy. Precision parts up to IT7 ~ IT8 level, the surface roughness of up to R0.2 ~ R0.6. Thus, cold extrusion parts rarely re-machining, grinding simply conduct in place particularly high demands.
4) to improve the mechanical properties of the parts. Cold extruded metal work hardening, as well as streamline the parts inside the fiber to form a reasonable distribution of the strength of the parts is much higher than the strength of materials. In addition, reasonable cold extrusion process allows parts of the surface to form a compressive stress and improve fatigue strength. So, after some of the original parts need to be heat strengthened by cold extrusion process heat treatment process can be omitted, and some original parts requiring high strength steel manufacturing, cold extrusion process after the lower strength steels are available for use.
5) complex shape can be processed, it is difficult machining parts. As profiled, complex cavity, the inner tooth surfaces and invisible within ducts.
6) reduce component costs. Because of the cold extrusion process has to save raw materials, increase productivity, reduce the amount of machining parts advantages available material substitution poor quality materials, so as to greatly reduce the cost of the parts.
Difficulties in cold extrusion technology in application are:
1) high requirements on the mold. Cold extrusion rough by a significant increase in the mold leaving three deformation resistance to stress, which makes die than the general stress suffered large stamping dies, cold extrusion steel, mold suffered stress often up to 2000MPa ~ 2500MPa. Such as the manufacture of a diameter 38mm, thickness of 5.6mm, 100mm high, low carbon steel cup, for example, the use of the processing method of drawing the maximum deformation force only 17t, while the use of cold extrusion process, the deforming force is required 132t, then punch in the cold extrusion pressure of 2300MPa or more units. In addition to having a high strength die-givers need, the need to have enough toughness and wear resistance. Furthermore, the metal blank intense plastic deformation in the mold, the mold temperature will rise to about 250 ℃ ~ 300 ℃, therefore, mold material requires a certain temper resistance. Due to the above, the life of cold extrusion die stamping die far below.
2) require large-tonnage presses. Because of the rough when cold extrusion deformation resistance, required hundreds or even thousands of tons of tons of press.
3) Due to the high cost of cold extrusion die, generally only suitable for mass production of parts. It is desirable that the minimum quantities of 5 to 100 000.
4) the need for prior to extrusion rough surface treatment. This not only increases the process, the need to occupy a larger production area, but also difficult to achieve production automation.
5) should not be used for high-strength materials processing.
6) the cold extrusion of plastic parts, impact toughness is deteriorated, and the residual stress of parts is large, which causes deformation of parts and reduce corrosion resistance (stress corrosion)
Cold extrusion technology development at home and abroad
Modern cold extrusion technology is from the beginning of the 18th century, the French Revolution, France in the lead from the bullet hole in the extrusion is made to start a cold extrusion. 1830 has already been started in France, the use of mechanical presses, using anti-extrusion method of manufacturing a lead pipe and a tin tube. In 1906 the United States in order to suit the manufacturing brass buttons, it has been made a positive extrusion of hollow cup-shaped blank franchise. 1909 Americans patented Hooker Law – rushed forward extrusion method, the metal flow direction and the direction of the same punch squeeze is developed in 1906 bought the patent after the patent in the cup-shaped blank, is the use of pull deep manufacturing method. World War I, had been created by Hooker method brass shell casings, and in 1934, before World War II, German trial on the use of this method of steel casings, but seizing serious, without success. Until World War II, due to the introduction of a new mid-lubricating surface treatment – phosphate film formed on the surface of the workpiece, extrusion method for manufacturing steel casings to be successful. Since then, the cold extrusion technology to practical, cold forging technology has become the most widely used method.
The 1960s, the growth of the Japanese auto industry, for the development of cold extrusion technology has created favorable conditions. Judging from the cold extrusion equipment, since 1933, Japan’s production of Aida Co., Japan’s first 2000kN PK type fine press (toggle presses) since, so far, has produced more than 2,000 units PK Series Pressure machine. With the development of the automobile industry, the requirement for high-precision presses even more urgent, Aida Corporation has successfully developed a variety of forging presses. Meanwhile, Japan’s Komatsu developed with precision and ease of operation for the target LIC, LZC series of cold forging presses.
Cold extrusion products from the point of view, the success of Japan 70s Cold start squeezing the clutch gear, drive shaft spline, alternator pole core. 1980s, and the success of large-scale high-precision cold extrusion constant ball outer race, inner race, cross-axis, auto parts such as fine bevel gear differential. Japanese automotive performance and reduce production costs and make a great contribution.
Our cold extrusion technology with Japan starting time considerably. 70 years, China has been in the bike, automotive electronics and other mass-produced products, the promotion too cold extrusion production technology, but also the successful development of start-gear extrusion molding, and put into mass production. However, due to a series of technical problems unresolved processes, equipment, materials, molds, lubrication, automation devices and rough material of the original size, the original state, post-processing and other fundamental, and thus has not been greatly developed. 1980s, with the rapid development of home appliance and car and motorcycle industry, the introduction of cold extrusion process equipment and production technology, digestion, absorption, researchers tackled through the production of cold extrusion technology practice many problems at the same time cold forging equipment also has made great progress. At present, China has cold extrusion process can produce Case, bicycle flywheel, the central axis, forging gear, automotive constant velocity joints, internal combustion engine with spark plug and piston pins, car lifters, camera parts, auto starter orientation sleeve, start gear, etc., and has reached the same level abroad.
Cold extrusion technology trends
1) With the growing energy crisis, people will pay more attention to the quality of the environment, coupled with an increasingly competitive market, prompting forging production to efficient, high quality, refinement, energy and materials direction. So by means of extrusion processes such as the production of refined forging production, market competition will get a larger development.
2) Car of the light, high-speed, smooth direction, the dimensional accuracy of forgings, precision and mechanical properties of weight and so put forward higher requirements. Car engines such as forging links between the size of the head in addition to the errors have requirements, the weight of each error also requires no more than eight grams. High demand of new products, will promote the development of the production process refinement.
3) specialization, scale of production is still cold extrusion direction and trends. In France, in the extrusion process to produce a professional manufacturer of forgings 1991-1994 labor productivity, production output and value that each person extrusion, and were higher than the general production of die forgings or forgings manufacturers. In 1994, for example, per capita production of professional manufacturers extrusions for 51024KG, a value of 775,688 francs. The general production of forging parts manufacturers over the same period, per capita output was only 39344KG, the output value of 592,384 francs, the equivalent of only a professional manufacturer of extrusion of 77.1% and 76.37%. Free forging plant contrast is lower.
4) extrusion plane will become a trend. With the refinement of production development of small and medium forgings and cold extrusion, warm extrusion application process, multi-cold extrusion press, press and post fine opportunity for the design and manufacture of a forging the strong development.
Cold temperature extrusion of the definition and classification
Extrusion is force gold dust agglomerates plastic flow, through the clearance between the punch and the die or the die outlet, the manufacture of hollow or blank section smaller than the cross-section of a process for the part. If blank without heating it squeezed, they called cold extrusion. Cold extrusion is no chip, one of the few parts of the chip processing technology, so is the gold dust of plastic processing technology, an advanced method. If the blank is heated to a temperature below the recrystallization temperature of extrusion, it is called warm extrusion. Has the advantage of low temperature extrusion still no chips. According to the extrusion direction and the direction of the relationship between the metal flow between the punch movement,
Common extrusion methods can be divided into the following categories.
(A) positive pressure from the pressing, the flow direction of the metal convex transverse direction of movement coincide. They are squeezed into a solid piece extruded hollow pieces are being squeezed two kinds. Forward extrusion method can produce various shapes of solid and hollow parts, such as screws, spindles, tubes and shells and so on.
(B) anti-extrusion extrusion, the flow direction of gold dust and punch the opposite direction of movement, the anti-extrusion method can produce a variety of cup-shaped cross-section, such as instrument cover, gimbal bearing sets.
(C) extruding the composite extrusion, the blank portion of the metal flow direction and the direction of movement of the same punch, while the other part is gold dust flow direction and movement in the opposite direction of the punch, the composite extrusion is possible to manufacture dual cup-type parts, You can also manufacture glass rods and levers parts parts.
(D) reducing squeeze a lesser degree of deformation being perverted extrusion, rough section is only for mild reduction. The main difference for the manufacture of small diameter shaft parts as well as a deep stepped cup finishing processes.
Several more squeezed common features are: gold dust flow direction is parallel to the axis of the punch, it can be referred to as the axial compression method. Another radial compression and upsetting extrusion method.
The main contradiction of cold extrusion
Cold extrusion is in the cold state of metal, and is in a strong three-state deformation under compressive stress, and therefore large deformation resistance, such as to produce a diameter 38mm, thickness 5.6mm, 100mm high carbon steel parts of the cup-shaped lower for example, the use of deep drawing processing methods. Only the last stretch deformation processes and the use of force 170KN need cold extrusion deformation force 1320KN. Then acting on the punch unit pressure reaches 2300MP above atmospheric pressure equivalent to 23,000 times.
Due to the high deformation resistance, so it causes the following disadvantages:
(1) mold is easy to wear, easy to damage, thus requiring good mold material. The general mold steel, the maximum allowable stress can reach 2500MPa, the best tool steel is not more than 3000MPa. In order to solve the main contradiction of cold extrusion, you have to take a variety of technical measures to try to reduce the cold extrusion material deformation resistance at the same time, trying to improve the capacity of the mold. Facilitate smooth production of cold extrusion.
2) to squeeze higher equipment requirements, larger tonnage. In addition to requiring proper extrusion apparatus greater strength, it also requires a good stiffness. In addition. Also requires equipment with good precision and reliable safety device.
Cold extrusion and relatively warm extrusion of:
Notwithstanding the many advantages of cold extrusion, but large deformation resistance, limiting the size of the parts, but also limits the deformation resistance of materials using cold extrusion process.
Hot extrusion method, although the material deformation resistance becomes smaller, but due to the heating, oxidation, decarbonization and thermal expansion and other issues, reducing the dimensional accuracy and surface quality of the products, which generally have to go through a lot of cutting, in order to as a final product.
Warm extrusion is heated to a metal blank a temperature below the recrystallization temperature of a suitable extrusion. Since the metal is heated, rough deformation resistance decreases. Easy to mold, press tonnage can be reduced, and extend the life of the mold. But with different hot extrusion, since the heating in the low temperature range, the oxidation, the possibility of decarburization is small, the mechanical properties of the product with cold extrusion products are not very different. Materials particularly difficult to machine at room temperature, such as precipitation stainless steel, high carbon steel hardening phase, the high chromium content – more steel, superalloy, etc., when the temperature of the extrusion may become easy to be processed or processed.
Warm extrusion applies not only to the high deformation resistance difficult materials, is suitable for cold extrusion of low-carbon steel, but also for objects as warm extrusion, because there are easy to warm extrusion advantages organize continuous production. When cold extrusion, including low-carbon steel, including cold extrusion, generally prior to processing to be pre-softening annealing between cold extrusion process must be annealed. Before the cold extrusion to be passivated. This makes it difficult to produce a continuous production organization. When the extrusion temperature can not be pre-annealing and softening annealing between the various processes may not be subjected to surface treatment, which makes possible the continuous production of tissue. At least you can reduce the number of secondary processes *
Warm Extrusion large deformation can be used, so that you can reduce the number of processes. Tooling costs can be greatly reduced, and does not require expensive high rigidity forging equipment, you can use the generic forging equipment, so although warm extrusion requires heating the metal, but the total cost of processing is still relatively cheap, do not be in the manufacturing process when the complex non-axisymmetric shaped parts, especially warm extrusion can play its role.
Currently, the use of warm extrusion lubricant can not be completely satisfactory. At the same time, it also lacks some of the practical aspects of data processing, there are many technical issues to be resolved.
