文献翻译-冲压成形的特点与板材冲压成形性能

附录：Characteristics of stamping and properties of sheet metal formingStamping is a kind of plastic forming process in which a part is produced by means of the plastic forming of the material under the action of a die. Stamping is usually carried out under cold state, so it is also called cold stamping. Heat stamping is used only when the blank thickness is greater than 8100mm. the blank material for stamping is usually in the form of sheet or strip, and therefore it is also called sheet metal forming. Some non-metal sheets (such as plywood, mica sheet, asbestos, leather) can also be formed by stamping.Stamping is widely used in various fields of the metalworking industry, and is plays a crucial role in the industries for manufacturing automobiles, instruments, military parts and household electrical appliances, etc.The process, equipment and die are the three foundational problems that needed to be studied in stamping.The characteristics of the sheet metal forming are as follows:(1) high material utilization.(2) Capacity to produce thin-walled parts of complex shape.(3) Good interchangeability between stamping parts due to precision in shape and dimension.(4) Parts with lightweight, high-strength and fine rigidity can e obtained.(5) High productivity, easy to operate and to realize mechanization and automatization.The manufacture of the stamping die is costly, and therefore it only fits to mass production. For the manufacture of products in small batch and rich variety, the simple stamping die and the new equipment such as a stamping machining center, are usually adopted to meet the market demands.The materials for sheet metal stamping include mile steel, copper, aluminum, magnesium alloy and high-plasticity alloy-steel, etc.Stamping equipment includes plate shear and punching press. The former shears plate into strips with a definite width, which would be pressed later. The late can be used both in shearing and forming.Characteristics of stamping formingThere are various processes of stamping forming with different working patterns and names. But these processes are similar to each other in plastic deformation. There are following conspicuous characteristics in stamping:The force per unit area perpendicular to the blank surface is not large but is enough to cause the material plastic deformation. It is much less than the inner stresses on the plate plane directions. In most cases stamping forming can be treated approximately as that of the plane stress state to simplify vastly the theoretical analysis and the calculation of the process parameters.Due to the small relative thickness, the anti-instability capability of the blank is weak under compressive stress. As a result, the stamping process is difficult to proceed successfully without using the anti-instability device (such as blank holder). Therefore the varieties of the stamping processes dominated by tensile stress are more than those dominated by compressive stress.During stamping forming, the inner stress of the blank is equal to or sometimes less than the yield stress of the material. In this point, the stamping is different from the bulk forming. During stamping forming, the influence of the hydrostatic pressure of the stress state in the deformation zone to the forming limit and the deformation resistance is not so important as to the bulk forming. In some circumstances, such influence may bi neglected. Even in the case when this influence should be considered, the treating method is also different from that of bulk forming.In stamping forming, the restrain action of the die to the blank is not severe as in the case of the bulk forming (such as die forging). In bulk forming, the constraint forming is proceeded by the die with exactly the same shape of the part. Whereas in stamping, in most cases, the blank has a certain degree of freedom, only one surface of the blank contacts with the die. In some extra cases, such as the forming of the suspended region of sphere or cone, and curling at the end of tube, neither sides of the blank on the deforming zone contact with the die. The deformation in these regions are caused and controlled by the die applying an external force to its adjacent area.Due to the characteristics of stamping deformation and mechanics mentioned above, the stamping technique is different from the bulk metal forming:The importance of the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure per unit area on its surface. Instead, the techniques of the simple die and the pneumatic and hydraulic forming are developed.Due to the plane stress or simple strain state in comparison with bulk forming, more research on deformation or force and power parameters has been done. Stamping forming can be performed by more reasonable scientific methods. Based on the real time measurement and analysis on the sheet metal properties and stamping parameters, by means of stamping process is also in proceeding.It is shown that there is a close relationship between stamping forming and raw material. The research on the properties of the stamping forming, that is, forming ability and shape stability, has become a key point in stamping technology. The research on the properties of the sheet metal stamping not only meets the need of the stamping technology development, but also enhances the manufacturing technique of iron and steel industry, and provides a reliable foundation for increasing sheet metal quality.A stamping die is a special, one-of-a-kind precision tool that cuts and forms sheet metal into a desired shape or profile. Most dies are constructed of several basic components, including die plates, shoes, die sets, guide pins, bushings, heel blocks, heel plates, screws, dowels, and keys. Dies also need stripper, pressure, and drawing pads, as well as the devices used to secure themspools, shoulder bolts, keepers, and retainers; and gas, coil, or urethane springs.Stamping forming property of sheet metal and its assessing methodThe stamping forming property of the sheet metal is the adaptation capability of the sheet metal to stamping forming. It has crucial meaning to the investigation of the stamping forming property of the sheet metal. In order to produce stamping forming paramerters, it is necessary to understand clearly the properties of the sheet metal, so as to utilize the potential of the sheet metal fully in the prodection. On the other hand, to select plate material accurately and rationally in accordance with the characteristics of the shape and dimension of the stamping forming part and its forming technique is also necessary so that a scientific understanding and accurate judgment to the stamping forming properties of the sheet metal may be achieved.There are direct and indirect testing methods to assess the stamping property of the sheet metal. practicality stamping test is the most direct method to assess stamping forming property of the sheet metal. The simulation test is a kind of assessing method that after simplifying and summing up actual stamping forming methods, as well as eliminating many trivial factors, the stamping properties of the sheet metal are assessed, based on simplified axial-symmetric forming method under the same deformation and stress states between the testing plate and the actual forming states.A stamping die is a special, one-of-a-kind precision tool that cuts and forms sheet metal into a desired shape or profile. The dies cutting and forming sections typically are made from special types of hardenable steel called tool steel. Dies also can contain cutting and forming sections made from carbide or various other hard, wear-resistant materials.Most stamping dies are constructed of several basic components, including die plates, shoes, die sets, guide pins, bushings, heel blocks, heel plates, screws, dowels, and keys. Dies also need stripper, pressure, and drawing pads, as well as the devices used to secure them: spools, shoulder bolts, keepers, and retainers, as well as gas, coil, or urethane springs.1. Die Plates, Shoes, and Die SetsDie plates, shoes, and die sets are steel or aluminum plates that correspond to the size of the die. They serve as the foundation for mounting the working die components. These parts must be machinedmilled or groundso that they are parallel and flat within a critical tolerance. Although grinding is the most popular, a milled surface now can be obtained that is as accurate as a ground surface.Most die shoes are made from steel. Aluminum also is a popular die shoe material. Aluminum is one-third the weight of steel, it can be machined very quickly, and special alloys can be added to it to give it greater compressive strength than low-carbon steel. Aluminum also is a great metal for shock adsorption, which makes it a good choice for blanking dies.The upper and lower die shoes assembled together with guide pins create the die set. The lower die shoe often has machined or flame-cut holes that allow slugs and scrap created in the die to fall freely through the die shoe onto the press bed. The holes also may serve as clearances for gas springs and other die components.The die shoe thickness is based on how much force can be expected during cutting and forming. For example, a coining die, one that compresses metal by squeezing it between an upper and lower die section, requires a much thicker die shoe than a simple bending die.2. Guide Pins and BushingsGuide pins, sometimes referred to as guide posts or pillars, function together with guide bushings to align both the upper and lower die shoes precisely . They are precision-ground components, often manufactured within 0.0001 in. Although numerous specialty mounting methods can be used to install these components, there are only two basic types of guide pins and bushingsfriction pins and ball bearing-style pins.Friction pins are precision-ground pins that are slightly smaller than the guide bushings inside diameter. Pins are made from hardened tool steel, while bushings often are made from or lined with a special wear-resistant material called aluminum-bronze. The aluminum-bronze may contain graphite plugs that help to reduce friction and wear that occur to the pins and bushings.Friction pins also help to heel the die shoes and prevent them from moving from side to side.Precision or ball bearing-style guide pins comprise precision-hardened pins, ball cages, ball bearings, and bushings. Unlike friction pins, these pins ride on a series of ball bearings contained in a special aluminum ball cage that permits the bearings to rotate without falling out. These pins have several advantages. First, friction is reduced so the die can run at faster speeds without generating excessive friction and heat. Second, they allow the diemaker to separate the upper and lower die shoes easily. Third, because they use ball bearings, they can be manufactured with greater accuracy than friction pins.Remember, guide pins are meant to align the upper and lower die shoes, not to align a poorly maintained or sloppy ram in a press! Some companies try to compensate for a poorly maintained press by adding oversized guide pins or grinding the guide pin ends to a cone shape. Care must be taken when flipping die shoes over so that the guide pins are not bent. 3. Heel Blocks and Heel PlatesHeel blocks are special steel blocks that are precision-machined, screwed, doweled, and often welded to both the upper and lower die shoes. They contain components called wear plates and function to adsorb any side thrust that may be generated during the cutting and forming processes. They are especially important if the generated force is one-directional. Too much force generated from one direction only can cause the guide pins to deflect, which results in misalignment of critical cutting and forming components.Most heel blocks have steel heel plates, and the heel block on the opposite shoe has a wear plate made from aluminum-bronze or some other dissimilar metal. The plate selection process is critical. Using two opposing plates made of the same metal type can result in high friction, heat, and eventually galling or cold welding of the wear plates. Heel blocks can be used to heel the die in any or all directions. Box heels often are used to heel the die in all directions.4. Screws, Dowels, and KeysScrews fasten and secure the working components to both the upper and lower die shoes. The socket head cap screw is the most popular fastener used in stamping dies. This hardened tool steel screw, often referred to as an Allen head screw, offers superior holding power and strength.Dowels are hardened, precision-ground pins that precisely locate the die section or component in its proper location on the die shoe. Although dowels have much heeling ability, their main function is to locate the die section properly.Keys are small, rectangular blocks of precision-ground steel that are inserted into milled pockets in the die shoes and sections called keyways. Keys locate and heel die sections and components.5. PadsA pad is simply a pressure-loaded plate, either flat or contoured, that holds, controls, or strips the metal during the cutting and forming processes. Several types of pads are used in stamping dies. Depending on their function, pads can be made from soft low-carbon steel or hardened tool steel. Contoured pads must fit very closely to the mating die section. Precision requirements determine whether the pads are positioned with guide pins and bushings or left unguided.Stripper Pads/Plates. Stripper pads are flat or contoured spring-loaded plates that pull, or strip, the metal off the cutting punches. When it is cut, metal naturally tends to collapse around the body or shank of the cutting punches; this is especially true during piercing. The stripper pad surrounds the cutting punches and mounts to the upper die shoe. As the punch exits the lower die, the spring-loaded pad holds the metal down flush with the lower die section, which allows the cutting punches to withdraw from the sheet metal or piece part.Often stripper pads are inserted with a small block of steel called a pad window. This pad window usually is small and lightweight and can be removed easily to allow the die maintenance technician to remove the ball lock-style pierce punch from the retainer without removing the entire stripper pad. Stripper pads also function to hold the metal flat or to the desired shape during the cutting process.Pressure Pads/Plates. During the wipe bending process, the metal must be held down tightly to the lower die section before the forming punch contacts the metal. Pressure pads must apply a force that is at least equivalent to the bending force. Most pressure pads use high-pressure coil or gas springs. When loaded with very high-pressure springs, contoured or flat pads also can form sheet metal. These pad types often are referred to as power punches.Draw Pads. Draw pads control metal flow during the drawing process. In drawing, the amount of pressure, or downward force, exerted on the sheet metal determines how much metal is allowed to flow and enter the draw die cavity. Too much pressure may stop the metal from flowing and cause splitting; too little downward force may allow excess metal to flow inward and cause loose metal or wrinkling.Draw pads, often referred to as binders or blank holders, usually are made from hardened tool steel. They can be flat or contoured, depending on the piece part shape. Most drawing dies use a single draw pad; however, in special cases, some use two.6. Spools, Shoulder Bolts, and KeepersSpools, shoulder bolts, and keepers are used to fasten pads to the die shoes while allowing them to move up and down. They are secured to either the top or bottom die shoe with screws and often dowels for precision location. Of all of the components used for securing pads, spools are the most common, especially in larger dies.7. RetainersRetainers hold or secure cutting or forming die components to both the upper and lower die shoes. One of the most popular retainers is a ball-lock retainer, a high-precision, accurately manufactured die component that secures and aligns both cutting and forming punches. It uses a spring-loaded ball bearing to locate and secure the punches, which feature a precisely machined teardrop or ball seat. The spring-loaded ball bearing locks into the teardrop shape and prevents the punches from coming out of the retainer.The advantage of ball-lock retainers is that they allow the die maintenance technician to remove and reinstall punches quickly. The punch is removed by depressing the spring-loaded ball bearing and pulling up on the punch. Specialty retainers also can be made to hold and align irregular punch shapes, as well as headed-style punches and pilot pins.8. SpringsSprings supply the force needed to hold, strip, or form metal. Many different springs are used in stamping dies. Spring selection is based on many factors, including the required force and travel, the springs life expectancy, and, of course, cost. Among the most popular are gas springs, which, when filled with nitrogen, can supply a great deal of force. They also have an excellent life expectancy.Other types are coil and urethane springs, often called marshmallow springs. Coil springs are very popular when a reasonable amount of force is needed and budget constraints are present. Urethane springs work well in short-run or prototype stamping operations. They also are inexpensive. 冲压成形的特点与板材冲压成形性能冲压是通过模具使板材产生塑性变形而获得成品零件的一种成形方法。由于冲压通常在冷态下进行，因此也称冷冲压。只有当板材厚度超过 8100mm 时，才采用热冲压。冲压加工的原材料一般为板材或带材，故也称板材冲压。某些非金属板材（如木板、云母片、石棉、皮革等）亦可采用冲压成形工艺进行加工。冲压广泛应用于金属制品各行业中，尤其在汽车、仪表、军工、家用电器等工业中占有极其重要的地位。冲压成形需研究工艺、设备和模具三类基本问题。板材冲压具有下列特点：（1） 材料利用率高。（2） 可加工薄壁、形状复杂的零件。（3） 冲压件在形状和尺寸精度方面的互换性好。（4） 能获得质量轻而强度高、刚性好的零件。（5）