Stamping parts
In the world, 60~70% of steel products are plates, most of which are finished products after stamping. The car body, chassis, fuel tank, radiator sheet, boiler drum, container shell, motor, electrical iron core silicon steel sheet, etc. are all processed by stamping. Instruments, household appliances, bicycles, office machinery, household utensils and other products also have a large number of stamping parts.
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.
Stamping machine
Stamping machine
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.
Stamping is an efficient production method. Using compound die, especially multi position progressive die, multiple stamping processes can be completed on one press to realize fully automatic production from strip uncoiling, leveling, blanking to forming and finishing. High production efficiency, good working conditions, low production cost, generally hundreds of pieces can be produced per minute.
Stamping is mainly classified by process, which can be divided into two categories: separation process and forming process. The separation process is also called blanking, which aims to separate the stamping parts from the sheet metal along a certain contour line and ensure the quality requirements of the separation section. The surface and internal properties of the sheet metal used for stamping have a great impact on the quality of the finished stamping products. It is required that the thickness of the stamping material be accurate and uniform; The surface shall be smooth and clean without spot, scar, scratch, surface crack, etc; The yield strength is uniform without obvious directivity; High uniform elongation; Low yield ratio; Low work hardening.
main features
Stamping parts are mainly formed by stamping metal or non-metallic sheets with the help of the pressure of the press and through the stamping die.
They mainly have the following characteristics:
⑴ Stamping parts are manufactured by stamping under the premise of small material consumption. The parts are light in weight and have good stiffness. After plastic deformation of the sheet metal, the internal structure of the metal is improved, so that the strength of the stamping parts is improved.
⑵ Stamping parts shall have high dimensional accuracy, uniform and consistent dimensions with the module, and have good interchangeability. General assembly and use requirements can be met without further machining.
(3) During the stamping process, the surface of the stamping parts will not be damaged, so they have good surface quality, smooth and beautiful appearance, which provides convenient conditions for surface painting, electroplating, phosphating and other surface treatment.
Design principles
⑴ The designed stamping parts must meet the product use and technical performance, and be easy to assemble and repair.
⑵ The designed stamping parts must be conducive to improving the utilization rate of metal materials, reducing the varieties and specifications of materials, and reducing the consumption of materials as much as possible. If allowed, materials with low price shall be used to make the parts blanking without waste and with less waste as far as possible.
(3) The designed stamping parts must be simple in shape and reasonable in structure, which is conducive to simplifying the mold structure and the number of processes. That is, the minimum and simplest stamping process is used to complete the processing of the whole part, and the use of other methods is reduced. It is also conducive to stamping operations, so as to facilitate the organization of mechanized and automated production and improve labor productivity.
(4) Under the condition that the designed stamping parts can be used normally, the requirements for dimension accuracy grade and surface roughness grade should be as low as possible, which is conducive to product interchange, reducing waste products and ensuring stable product quality.
⑸ The designed stamping parts shall be conducive to the use of existing equipment, process equipment and process flow to process them as much as possible, and to the extension of the service life of the stamping die.
Stamping parts Common problem handling
1. Adhesion and scratch: defects on the surface of parts or molds due to friction between materials and punch or die;
2. Burr: mainly occurs in the shearing die and blanking die, and the gap between the cutting edges may produce burrs when it is large or small;
3. Line offset: When forming a part, the part that first contacts the die is extruded and forms a line;
4. Concave and convex: foreign matters (scrap iron, rubber, dust) are mixed in the uncoiling line to cause concave and convex;
5. Zigzag: the r corner or embossing part of the workpiece is zigzagged and strained due to uneven stress, poor matching of the drawbead or poor control of the press slider;
6. Wrinkles: Wrinkles at the edge or r part are caused by poor adjustment of the press slider, low accuracy of the press, improper adjustment of the air cushion pressure, and large punch or r part.
7. Other specific problems: In daily production, the punching size is too large or too small (may exceed the specification requirements) and has a large difference from the punch size. In addition to the design size, processing accuracy, blanking clearance and other factors of the forming punch and die, the following aspects should also be considered to solve.
⑴ When the cutting edge is worn, the tensile stress of the material increases, and the tendency of the stamping parts to turn over and twist increases. When the material is turned over, the punching size will become smaller.
⑵. The strong pressure on the material will cause plastic deformation of the material, which will lead to larger punching size. When reducing the strong pressure, the punching size will become smaller.
(3) Shape of punch edge end. If an inclined plane or arc is trimmed at the end, the blanking part is not easy to turn over and twist due to the slowing down of blanking force, so the punching size will become larger. When the punch end is flat (no inclined plane or arc), the punching size will be relatively small.
8. Methods to restrain the stamping parts from turning over and twisting
(1) Reasonable mold design. In progressive die, the arrangement of blanking sequence may affect the forming accuracy of stamping parts. For blanking of small parts of stamping parts, generally, large area blanking is arranged first, and then small area blanking is arranged to reduce the impact of blanking force on the forming of stamping parts.
(2) Press the material. To overcome the traditional mold design structure, open a material holding gap on the discharge plate (that is, when the mold is closed, the material can be compressed. For key forming parts, the discharge plate must be made into a block type structure to facilitate the grinding (pressing) loss of the pressing part of the discharge plate caused by a long time of stamping, which can not compress the material.
⑶. Add strong pressure function. Namely, the pressing part of the discharge insert is thickened (the normal discharge insert thickness is H+0.03mm) to increase the pressure on the material at the side of the die, so as to prevent the stamping parts from turning over and twisting during blanking.
(4) The end of the punch edge shall be trimmed with a bevel or arc. This is an effective way to reduce the blanking force. By reducing the buffering cutting force, the tensile force on the material at the side of the die can be reduced, so as to achieve the effect of restraining the stamping parts from turning over and twisting.
(5) During daily die production, attention should be paid to maintaining the sharpness of the cutting edges of the punch convex and concave dies. When the cutting edge is worn, the tensile stress of the material will increase, and the tendency of the stamping parts to turn over and twist will increase.
(6) Unreasonable or uneven blanking clearance is also the cause of stamping parts turnover and distortion, which should be overcome.
Stamping Parts Dimensional tolerance
GB/T13914-2002 Dimensional Tolerance of Stamping Parts specifies the dimensional tolerance of stamping parts. The dimensional tolerances are specified for flat stampings and formed stampings respectively. The dimensional tolerance value of stamping parts is related to the dimensions of stamping parts and plate thickness, on the other hand, it is related to the accuracy level.
Dimensional tolerance of flat stampings: it is divided into 11 grades, which are represented by ST1 to ST11, where ST represents the dimensional tolerance of flat stampings, and the tolerance grade code is represented by Arabic numerals. The accuracy level decreases from ST1 to ST11.
Dimensional tolerance of formed stampings: the formed stampings are divided into 10 accuracy grades, which are expressed by FT1 to FT10, where FT represents the dimensional tolerance of formed stampings, and Arabic numerals represent the tolerance grade. The accuracy level decreases from FT1 to FT10.
Limit deviation of stamping parts: the hole size shall have a press deviation of 0, and the upper deviation shall be the lower deviation plus dimensional tolerance; The upper deviation of shaft size is the basic deviation, the value is 0, and the lower deviation is the upper deviation minus the dimension tolerance. The upper and lower deviations of hole center distance, hole edge distance, length and height of bending and drawing are specified as half of the dimensional tolerance.
Stamping parts Feature Application
Stamping parts are the production technology of product parts with certain shape, size and performance by means of the power of conventional or special stamping equipment to directly subject the sheet metal to deformation force in the die and deform it. Sheet metal, die and equipment are the three elements of stamping processing. Stamping is a metal cold deformation processing method. Therefore, it is called cold stamping or sheet metal stamping. It is one of the main methods of metal plastic processing (or pressure processing), and also belongs to material forming engineering technology.
50-60% of Universal’s steel products are made of plates, most of which are finished products after stamping. The car body, radiator sheet, steam drum of the steam boiler, shell of the container, iron core silicon steel sheet of the motor and electrical appliances are all stamped and processed. There are also a large number of stamping parts in instruments, household appliances, office machines, storage containers and other products. Stamping is an efficient production measure. The compound die is adopted, and the exception is the multi station progressive die. Multiple stamping operations can be completed on a press to complete the automatic generation of materials. With fast production speed, long rest time and low production cost, the group can produce hundreds of pieces per minute, which is popular with many processing plants.
The bucket strength between stamping parts and castings and forgings is thin, uniform, light and strong. Stamping can produce workpieces with reinforcing ribs, ribs, curling or flanging that are difficult to manufacture with this skilled hand diameter, so as to improve their rigidity. As the rough die is rejected, the precision of the workpiece can reach the micron level, and the precision is high, the specification is consistent, and the holes and sockets, bosses, etc. can be punched. In actual production, process tests similar to the stamping process, such as deep drawing performance test and bulging performance test, are often used to inspect the stamping performance of materials to ensure the quality of finished products and high qualification rate.
In addition to thick plate forming with hydraulic press, the pressing equipment usually adopts the stagnation press. Focusing on today’s high-speed multi station stagnation press, the passive stamping production line with high production rate can be formed by setting up equipment configuration, uncoiling, product collection, escort and other stagnation, as well as mold library and quick mold change placement, and using computer style tube bundles. Under the condition of producing tens or hundreds of stamping parts per minute, the stamping and output processes can be completed in a short time, and personal, equipment and quality incidents often occur. Therefore, the safety production in stamping is a rather critical issue
Stamping parts Inspection method
Touch testWipe the surface of the outer covering with clean gauze. The inspector needs to wear touch gloves and touch along the longitudinal direction of the stamping parts close to the surface of the stamping parts. This inspection method depends on the experience of the inspector. If necessary, the suspected area detected can be polished with an oilstone and verified, but this method is an effective and fast inspection method.
Oil stone grinding
1. First, clean the surface of the outer cover with clean gauze, and then polish with an oilstone (20 × twenty × 100mm or more), and relatively small oilstone shall be used to polish the places with arc and hard to reach (for example: 8 × 100mm semi-circular stone)
2. The selection of stone size depends on the surface condition (such as roughness, galvanization, etc.). Fine grained oilstone is recommended. The grinding direction of the oilstone is basically along the longitudinal direction, and it fits the surface of the stamping parts well. In some special places, the horizontal grinding can also be supplemented.
Flexible screen grinding
Wipe the surface of the outer covering with clean gauze. Use flexible sand mesh to grind the surface of stamping parts to the whole surface along the longitudinal direction, and any pitting and indentation will be easily found.
Oiling inspection
Wipe the surface of the outer covering with clean gauze. Then use a clean brush to evenly apply oil to the entire outer surface of the stamping along the same direction. Put the oiled stamping parts under strong light for inspection, and it is recommended to erect the stamping parts on the vehicle body. With this method, it is easy to find tiny pits, pits and ripples on the stamping parts.
Visual inspection
Visual inspection is mainly used to find the appearance abnormalities and macro defects of stamping parts.
Inspection with inspection tools
Put the stamping parts into the inspection tool, and inspect the stamping parts according to the operation requirements of the inspection tool manual.
Production problems Safe production
In actual production, process tests similar to the stamping process, such as deep drawing performance test and bulging performance test, are often used to inspect the stamping performance of materials to ensure the quality of finished products and high qualification rate.
Stamping equipment
Stamping equipment
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. Mold design and manufacturing require more time, which extends the production preparation time of new stamping parts.
The standardization of die bases, die bases and guide parts and the development of simple dies (for small batch production), compound dies, multi station progressive dies (for mass production), as well as the development of rapid die changing devices can reduce the preparation workload and shorten the preparation time for stamping production, and can be used to reduce the preparation workload and shorten the preparation time for stamping production, The advanced stamping technology suitable for mass production can be reasonably applied to small batch and multi variety production.
In addition to forming thick plates with hydraulic presses, mechanical presses are generally used for stamping equipment. Conveying and other machinery, as well as die library and rapid die changing device, can form an automatic stamping production line with high productivity by using computer program control.
When tens or hundreds of stamping parts are produced every minute, the processes such as feeding, stamping, outgoing and waste disposal are completed in a short time, and personal, equipment and quality accidents often occur. Therefore, safety production in stamping is a very important issue.
Generally, during the stamping process of workpieces, because the temperature will rise rapidly during the stamping process, especially during the cold forging and stamping process, lubricating products must be added for lubrication. If the workpieces are directly stamped without lubrication, welding assembly. Parts without oil on the surface are easy to weld and assemble. The research and practice show that AMC metal inert gas arc welding, tungsten gas shielded arc welding and resistance welding have good results.
Overturning and twisting
1. Reasons for turnover and distortion during stamping
In the progressive die, the shape of the stamping part is formed by cutting the residual materials around the stamping part. The influence of blanking force is the main reason for blanking parts to turn over and twist. During blanking, due to the existence of blanking clearance, the material is stretched on one side of the female die (the material is warped upwards) and compressed on the side near the punch. When the unloading plate is used, the unloading plate is used to compress the material to prevent the material at the die side from warping upward. At this time, the stress condition of the material changes accordingly. The material near the punch side is stretched (the compression force tends to decrease) and the material on the die face is compressed (the tension force tends to decrease) with the increase of the pressing force on the discharge plate. The turnover of stamping parts is caused by the material on the die face being stretched. Therefore, during blanking, pressing and compacting the material is the key point to prevent the stamping from overturning and twisting.
2. Methods for suppressing the overturning and twisting of stamping parts
(1). Reasonable mold design. In progressive die, the arrangement of blanking sequence may affect the forming accuracy of stamping parts. For blanking of small parts of stamping parts, generally, large area blanking is arranged first, and then small area blanking is arranged to reduce the impact of blanking force on the forming of stamping parts.
(2). Press on the material. The traditional die design structure is overcome, and a material holding gap is opened on the discharge plate (that is, when the die is closed, the discharge plate and the female die fit together, while the gap between the discharge plate and the female die at the material holding position is t-0.03-0.05 mm thick). In this way, the movement of the discharge plate in the stamping is stable, and the material can be compressed. For the key forming parts, the unloading plate must be made into an inlaid structure, so as to solve the grinding (pressing) loss of the pressing part of the unloading plate caused by long-time stamping, and the material cannot be compressed.
(3) Add strong pressure function. Namely, the pressing part of the discharge insert is thickened (the normal discharge insert thickness is H+0.03mm) to increase the pressure on the material at the side of the die, so as to prevent this from turning over and twisting during blanking.
(4). The end of the punch edge shall be chamfered or curved. This is an effective way to reduce the blanking force. By reducing the buffering cutting force, the tensile force on the material at the side of the die can be reduced, so as to achieve the effect of restraining the stamping parts from turning over and twisting.
(5). In daily die production, attention should be paid to maintaining the sharpness of the cutting edges of the punch and die. When the cutting edge is worn, the tensile stress of the material will increase, and the tendency of the stamping parts to turn over and twist will increase.
(6). Unreasonable or uneven blanking clearance is also the cause of stamping parts turnover and distortion, which should be overcome.
3. Handling of common specific problems in production
In daily production, the punching size is too large or too small (may exceed the specification requirements) and has a large difference from the punch size. In addition to the design size, processing accuracy and blanking clearance of the forming punch and die, the following aspects should also be considered to solve the problem.
(1). When the cutting edge is worn, the tensile stress of the material increases, and the tendency of the stamping parts to turn over and twist increases. When the material is turned over, the punching size will become smaller.
(2). The strong pressure on the material will cause plastic deformation of the material, which will lead to larger punching size. When reducing the strong pressure, the punching size will become smaller.
(3). The shape of the end of the punch edge. If an inclined plane or arc is trimmed at the end, the blanking part is not easy to turn over and twist due to the slowing down of blanking force, so the punching size will become larger. When the punch end is flat (no inclined plane or arc), the punching size will be relatively small.
In specific production practice, specific analysis should be made for specific problems, so as to find solutions to the problems.
The above mainly introduces the causes and solutions of blanking parts’ overturning and distortion during blanking.
