How are tinplate two-piece cans made?

Both forming methods for making tinplate two-piece cans use metal sheet forming. This method is based on the "fluidity" of metals exhibited by rearranging the crystal structure under the action of compound stress, and the material should not break during this process.

1. Stamping. That is, a flat plate is punched into a cylindrical die using a punch of a punching machine, so that the flat plate is deformed into a cylinder. The diameter of the cup formed after the initial punching can be reduced by applying a re-punching process. The re-punching process uses a punching sleeve instead of a die, which is installed between the punch and the inner diameter of the punching cup. The equal area rule determines that the height increases with the reduction of the diameter. The re-punching process can be repeated once, and the diameter gradually decreases within a certain limit range, and the metal is prevented from breaking.

2. Thinning and stretching of the cup wall. The stamped cylindrical cup is put on the punch, and the punch is squeezed into a die along the axial direction. The gap between the die and the punch is less than the thickness of the cup wall, so that the wall thickness is thinned while the diameter remains unchanged. The metal volume of the thinned barrel is equal to the metal volume of the cup during the thinning process, and is also equal to the metal volume of the original sheet. In the manufacture of cans, this process is repeated two or three times, and the punch with the cup passes through a series of dies in succession, one die per stroke. The most convenient way to install the punched forest on the punch is to perform a re-punching operation before the first thinning and stretching.

3. Manufacturing of punched cups. The manufacturing process of punched cups is generally as follows: unwinding ordinary strip coils; applying lubricants; unloading and punching cups; re-punching; thinning and stretching of the cup side walls; forming the bottom; trimming the cylinder to the correct height; cleaning and processing. For dry beverage cans, external surface coating, printing and decoration, internal surface coating, flange forming and closing of the open end are also required. For food cans, external surface coating, flange forming of the open end, barrel corrugation and internal surface coating are carried out during the cleaning process or the can end is made of pre-coated sheet on a multi-die press, and the can cover is pressed with corrugations (reinforcement ribs) to bear internal and external pressures. The final step here is crimping to create a double crimped seam. Filling is placed over the final seal to act as a sealing gasket.