What is Sheet Metal Stamping

Stamping is a forming processing method that relies on presses and dies to apply external force to plates , strips , pipes and profiles to cause plastic deformation or separation, so as to obtain workpieces (stamping parts) of the required shape and size . 

Stamping and forging are both plastic processing (or pressure processing ), collectively called forging . The stamped blanks are mainly hot-rolled and cold-rolled steel plates and strips. Of the world’s steel, 60 to 70% are plates, most of which are stamped into finished products. The car body, chassis, fuel tank, radiator fins, boiler drums, container shells, motors and electrical appliances are all stamped and processed. There are also a large number of stamping parts in products such as instruments, household appliances, bicycles, office machinery, and living utensils. 

Stamping is the production technology of using the power of conventional or special stamping equipment to directly subject the sheet metal to deforming force and deform in the mold, so as to obtain product parts with a certain shape, size and performance. Sheet material, mold and equipment are the three elements of stamping processing. According to the stamping processing temperature, it is divided into hot stamping and cold stamping . The former is suitable for sheet metal processing with high deformation resistance and poor plasticity; the latter is carried out at room temperature and is a commonly used stamping method for thin plates. It is one of the main methods of metal plastic processing (or pressure processing ), and it also belongs to material forming engineering technology. 

The die used in stamping is called stamping die , or die for short. The die is a special tool for batch processing of materials (metal or non-metal) into the required stamping parts. Punching dies are very important in stamping. Without a die that meets the requirements, mass stamping production will be difficult; without advanced dies, advanced stamping processes cannot be realized. Stamping process and die, stamping provided equipment and materials stamping press working of the three elements, are combined with each other in order to obtain only the stampings . 

Processing characteristics 

Compared with castings and forgings , stamping parts are thin, uniform, light and strong. Stamping can produce workpieces with ribs, ribs, undulations or flanges that are difficult to manufacture by other methods to improve their rigidity. Due to the use of precision molds, the precision of the workpiece can reach the micron level, and the repeatability is high, the specifications are consistent, and holes, bosses, etc. can be punched out. Cold stamping parts are generally no longer processed by cutting , or only a small amount of cutting processing is required. The precision and surface condition of hot stamping parts are lower than cold stamping parts, but still better than castings and forgings, and the cutting amount is less. 

Stamping is an efficient production method. Using compound molds, especially multi-station progressive dies, multiple stamping processes can be completed on a single press (single-station or multi-station) to realize uncoiling, Fully automatic production from leveling, blanking to forming and finishing. High production efficiency, good working conditions, low production cost, generally hundreds of pieces per minute can be produced. Compared with other methods of mechanical processing and plastic processing, stamping processing has many unique advantages in both technical and economic aspects. The main performance is as follows.

  • The production efficiency of stamping processing is high, and the operation is convenient, and it is easy to realize mechanization and automation. This is because stamping relies on punching dies 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. May get a punch. 
  • When the stamping die guarantees since the size and shape of precision stamping, and generally does not damage the surface quality of stamping, and generally longer life of the die, the stamping of stable quality, good interchangeability with ” identical ” Features.
  • Stamping can process parts with a large size range and more complex shapes, such as the seconds hand of a clock and watch, as large as automobile longitudinal beams, covering parts, etc., plus the cold deformation and hardening effect of the material during stamping, and the strength of the stamping And the stiffness is high.
  • Stamping generally does not generate chips and scraps, consumes less material, and does not require other heating equipment, so it is a material-saving and energy-saving processing method, and the cost of stamping parts is lower.

Due to the superiority of stamping, stamping processing is widely used in various fields of the national economy. For example, in aerospace, aviation, military industry, machinery, agricultural machinery, electronics, information, railways, post and telecommunications, transportation, chemicals, medical appliances, household appliances and light industry, there are stamping processes. Not only is it used in the entire industry, but everyone has direct contact with stamping products. There are many large, medium and small stamping parts on airplanes, trains, cars, and tractors. Parts such as the car body, frame and rim are all stamped out. According to relevant survey statistics, 80% of bicycles, sewing machines , and watches are stamped parts; 90% of TV sets, tape recorders, and cameras are stamped parts ; there are also food metal tank shells, steel boilers, enamel bowls and stainless steel tableware . They are all stamped products that use molds; even computer hardware cannot lack stamping parts. 

Process classification

Stamping is mainly classified by process, which can be divided into two categories: separation process and forming process. The separation process is also called punching, and its purpose is to separate the stamping part from the sheet along a certain contour line while ensuring the quality requirements of the separated section. The purpose of the forming process is to make the sheet metal plastically deform without breaking the billet to make a workpiece of the required shape and size. In actual production, multiple processes are often applied to one workpiece. Blanking , bending , shearing, stretching, bulging , spinning , and correction are the main stamping processes. 

Separation process 

It is a basic stamping process that uses molds to separate materials. It can be directly made into flat parts or prepare blanks for other stamping processes such as bending, deep drawing, forming, etc. It can also be cut and trimmed on the formed stamping parts Wait. Blanking is widely used in industries such as automobiles, household appliances, electronics, instrumentation, machinery, railways, communications, chemicals, light industry, textiles, and aerospace. The blanking process accounts for about 50% to 60% of the entire stamping process .

Forming process 

  • Bending : a plastic forming method of bending metal sheets, pipe fittings and profiles into a certain angle, curvature and shape. Bending is one of the main processes widely used in the production of stamping parts. The bending of metal materials is essentially an elasto-plastic deformation process. After unloading, the workpiece will produce directional elastic recovery deformation, which is called springback. Springback affects the accuracy of the workpiece and is the key technology that must be considered in the bending process.   
  • Drawing: Deep drawing is also called drawing or calendering . It is a punching method that uses a die to make a flat blank after punching into an open hollow part. The drawing process can be used to make cylindrical, stepped, tapered, spherical, box-shaped and other irregularly shaped thin-walled parts. If matched with other stamping forming processes, parts with extremely complex shapes can also be manufactured. In stamping production, there are many types of deep-drawn parts. Due to the different geometric characteristics, the location of the deformation zone, the nature of the deformation, the distribution of the deformation, and the stress state and distribution law of each part of the blank have considerable, even essential differences. Therefore, the method of determining the process parameters, the number of processes and the sequence, and the principles and methods of mold design are different. According to the characteristics of deformation mechanics, various deep-drawn parts can be divided into four types: straight wall revolving body (cylindrical part), straight wall non-revolving body (box-shaped body), curved revolving body (curved part) and curved non-revolving body. Types of. 
  • Stretch forming is by drawing-die sheet pulling force on the sheet an uneven tensile strain and tensile stress, and pulled along the sheet forming die bonding surface gradually expanded, and pulling up the mold surface shape completely fit . The applicable object of stretch is to manufacture hyperbolic skins with a certain degree of plasticity, large surface area, gentle and smooth curvature changes, and high quality requirements (accurate appearance, smooth streamline, stable quality). Because of the relatively simple process equipment and equipment used in the stretch forming, the cost is low and the flexibility is large; but the material utilization rate and productivity are low.
  • Spinning is a metal turning process. In the process of processing, the blank is actively rotated with the spinning die or the spinning head actively rotates around the blank and the spinning die. The spinning head makes a feed motion relative to the core mold and the blank to cause continuous local deformation of the blank to obtain the required hollow rotation Body parts. 
  • Shaping is the second trimming of the shape of the product by using the predetermined shape of the abrasive tool. Mainly reflected in the pressure plane, spring foot, etc. Re-processing is used when some materials have elasticity and cannot guarantee the quality of one-time molding.
  • Bulging is a processing method that uses a mold to stretch and thin the sheet and increase the local surface area to obtain parts. Commonly used are undulating forming, bulging of cylindrical (or tube) blanks and stretch forming of flat blanks. Bulging can be achieved by different methods, such as rigid die bulging, rubber bulging and hydraulic bulging.
  • Flanging is a plastic processing method that bends the material in the narrow band area of ​​the edge of the sheet blank or the edge of the prefabricated hole on the blank into a vertical edge along a curve or a straight line. Flanging is mainly used to strengthen the edges of parts, remove trimming and make parts assembled and connected with other parts or three-dimensional parts with complex and specific shapes and reasonable spaces on the part, while improving the rigidity of the parts. When forming large sheet metal, it can also be used as a means to control cracks or wrinkles. Therefore, it is widely used in industrial sectors such as automobiles, aviation, aerospace, electronics and household appliances.
  • Necking is a punching method that reduces the diameter of the stretched flangeless hollow part or the open end of the tube blank. The diameter of the end of the workpiece should not change too much before and after the necking, otherwise the end material will wrinkle due to severe compression and deformation. Therefore, it is often necessary to shrink the neck from a larger diameter to a smaller diameter.

Materials 

 The surface and internal properties of stamping sheet material have a great influence on the quality of stamping products. The requirements for stamping materials are:

  1. The thickness is accurate and uniform. The stamping die is precise and has a small gap. If the thickness of the sheet is too large, the deformation force will be increased, and the material will be jammed, and even the die will be swelled. If the sheet is too thin, it will affect the quality of the finished product and even crack during deep drawing. 
  2. The surface is smooth, without spots, scars, scratches, and surface cracks. All surface defects will remain on the surface of the finished workpiece , and the crack defects may extend deep and wide during the process of bending, deep drawing, and forming, resulting in waste products. 
  3. The yield strength is uniform without obvious directionality. Anisotropy (see plastic deformation in the drawing, flanging, bulging and other stamping processes, due to the occurrence of all-directional yielding, the inconsistent amount of plastic deformation will cause uneven deformation and inaccurate forming. Defective or scrap. 
  4. High uniform elongation. In the tensile test, the elongation of the sample before the neck phenomenon begins to appear is called the uniform elongation. During deep drawing, the deformation of any area of ​​the sheet material cannot exceed the uniform extension range of the material, otherwise uneven deformation will occur.
  5. The yield ratio is low. The ratio of the yield limit to the strength limit of a material is called the yield ratio. The low yield ratio can not only reduce the deformation resistance, but also reduce the tendency of wrinkling during drawing, reduce the amount of springback after bending, and improve the accuracy of the bending part. 
  6. Low work hardening. The work hardening that occurs after cold deformation will increase the deformation resistance of the material and make it difficult to continue to deform. Therefore, plates with a low hardening index are generally used . However, materials with a high hardening index have good plastic deformation stability (that is, more uniform plastic deformation) and are not prone to localized cracks. 

In actual production, process tests similar to the stamping process are commonly used, such as drawing performance test, bulging performance test, etc. to check the stamping performance of the material to ensure the quality of the finished product and a high pass rate. 

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