Metal Stamping (I)

After the metal substrate is printed, it is generally subjected to two processes of polishing and forming. The purpose of the polish oil is to protect the ink film, increase the gloss of the printed material, make the product more beautiful, and can enhance the ability to withstand bending and mechanism impact during the can manufacturing process. For the principle of glazing and its processing methods, please refer to Chapter 12 of this book. This section focuses on the molding process and major equipment of metal packaging products.

It should be pointed out that since the manufacture of metal packaging products is carried out in an automated assembly line, printing is a key process among them, and the substrates are often molded products. In the molding process of products, a considerable number of processes are in fact It was completed before printing. In order to ensure the integrity of the system, this section does not strictly distinguish its prepress or postpress process.

First, the molding process

1. Stamping process. Metal packaging containers, whether they are boxes or cans, are mostly formed from two major processes of separation and plastic deformation from the point of view of the molding process.

The separation process is a stamping process that separates the stamping and sheet material from each other along the required contour and obtains a certain section quality. The separation process often includes operations such as cutting, blanking, punching, cutting, trimming, and cutting.

The plastic deformation process is a stamping process in which the punched blank is shaped and deformed without breaking to obtain the required shape and dimensional accuracy. There are three types of bending, stretching and forming. Bending includes bending, curling, twisting, bending, rolling, bending, bending and stretching; stretching is mainly drawing and thinning and deep drawing; there are many forming methods, including turning holes, flanging, and flaring. Shrinking, forming, crimping, bulging, spinning, shaping, school equal operations.

2. Can making process. The traditional production method of metal packaging cans is: first, the metal blanks are cut into squares, then the blanks are rolled into cylinders (ie, cylinders), and then the formed longitudinal bonding wires are soldered to form a side seal, one of the cylinders. The ends (ie, the bottom of the tank) and the round end caps are mechanically flanged and rolled (ie double crimped seams) to form the can body; the other end is closed after the product has been filled. As the container is composed of three parts: the bottom of the tank, the body of the tank, and the lid of the tank, it is called a three-piece tank. This type of can making method has been basically unchanged for more than 150 years. It has only been greatly improved in terms of automation and processing accuracy. In recent years, the welding of side sealing has been changed to welding.

In the early 1970s, a new canning principle emerged. According to this principle, the can body and the bottom of the can is a single body, which is stamped and formed by a round blank. After the product is sealed, it is a two-piece can. There are two types of molding methods for such cans: stamping - thinning stretching (ie drawing and drawing) and stamping - re-stamping (ie deep drawing). These technologies are not new in themselves. Drawbacks were used to make shells as early as World War I. The difference between canning is the use of ultra-thin metals and the high production speed (the annual output can reach hundreds of millions).

(1) Manufacture of three-piece cans. The production process is: cutting the coil into rectangular plates with a shearing machine; painting and mounting printing; cutting a length of billet; rolling into a cylinder and welding side seams; repairing the joints and coating; cutting the barrel; forming a recess Slots or corrugations; flanges are pushed out at both ends; rolled back; check and code on pallets.

1 cylinder processing. The key process is coil forming and welding side seams. Side sealing methods are soldering, welding and bonding three.

Solder tin solders typically consist of 98% lead and 2% tin. The cylinder forming machine for rolling the plate blank into a cylinder is used in pairs with a side seam sealing machine for soldering. In the cylinder maker, the edge of the slab is cleaned and bent into a hook shape, which facilitates fixing when the cylinder is formed. The barrel is then passed through a side sealer, plus solvent and solder, preheated in the sealing area with a gas torch, heated by a longitudinal soldering roller, and the solder is then filled with seams, after which the excess of the solder, mainly in the form of drops, is used with a rotating scraper. The solder is clean.

Welding is the use of self-contained wire electrode principle, the use of resistance welding process. The earlier welding systems used large laps to increase the temperature of the steel to the melting point and weld it at a lower roller pressure. The latest welding machine uses a small overlap (0.3 to 0.5 mm), the metal temperature is just below the melting point, but to increase the pressure of the welding roller, the two overlapping surfaces are forged together.

The weld breaks the original or painted smooth surface of the inner surface so that exposed iron, iron oxide, and tin are present on both sides of the weld. In order to prevent the product from being contaminated and the weld seam from being eroded by the product, in most cases the side seals need to be coated.

Side seals for tanks containing only dry products can be glued. That is, the longitudinal seam is pasted with a nylon belt, and the nylon belt melts and condenses after the cylinder is formed. The advantage is that the original edge can be completely protected but can only be used for TFS because the melting point of tin is close to the melting temperature of the plastic.

2 simplified post processing. Flanges must also be machined at both ends of the Simplified to install the end caps. For processed food cans, the cans may be subjected to external pressure during processing or may be internally vacuumed during storage. In order to increase the strength of the tank, the simplified surface may also need to make ribs. This process is called crimping. In order to increase the production efficiency, the length of the shallow container made of shallow containers is usually two to three cans. At this time, the first procedure is to cut the cylinder. The traditional method is to form the front blank on the cutting machine (notch machine). Make an unbreakable cut. However, recently, due to the appearance of a tank trimmer shearer developed for the production of two-piece cans, it has been possible to use this shearing machine for the cutting of cylinders that are not pre-scored.

(2) Production of two-piece cans. Both methods of forming two-piece cans are formed using sheet metal forming methods. This method is based on the "fluidity" of the metal exhibited by the rearrangement of the crystal structure under the action of the composite stress, and the material should not break during this process.

1 stamping molding. That is, a punch is used to punch a flat plate into a cylindrical die to deform the flat plate into a cylinder. The diameter of the cup formed after the initial stamping can be reduced by applying a re-punching process. The re-punching process replaces the die with a stamped sleeve and is mounted between the punch and the inner diameter of the cup. The equal area rule determines that the increase in height is accompanied by a decrease in diameter. The re-pressing process can be repeated once more. The book diameter is gradually reduced within a certain limit, and the metal is prevented from breaking.

2 cups of thinning stretch. The stamped cylindrical cup is placed on the punch, and the punch is axially squeezed into a mold. The clearance between the mold and the punch is smaller than the thickness of the cup wall, so that the wall thickness is maintained when the diameter remains unchanged. Thinned. After thinning, the metal volume of the barrel is equal to the metal volume of the cup during thinning and is also equal to the metal volume of the original slab. In the manufacture of the tank, this process is repeated two or three times, and the punch with cup passes through a series of molds one after another through one mold. The most convenient method of installing the stamped forest on the punch is to perform a re-pressing operation before the first thinning.

3 punch cupping manufacturing. The manufacturing process of cupping and cupping is generally as follows: unfolding a common strip coil; Xu lubricant; blanking and cupping; re-punching; thinning and stretching of the sidewall of the cup; bottom forming; simplified trimming at the correct height; cleaning and handling . For dry beverage cans, exterior coating, printing, inner surface coating, flange formation and closing of open ends are also required. For food cans, exterior coating, open-end flange formation, barrel crimping, and inner surface coating are performed during the cleaning process.
1-End cap crimped and folded over the flange of the cylinder 2- Seal packing 3 - Sealing overlap amount 4 - Tube 5 - End cap

The lid or can end is manufactured on a multi-die press with pre-coated sheet material, and the lid is crimped with corrugations (ribs) to take the internal and external pressures. The final process here is the crimping to form a double crimp seam (see Figure 17-1). Place filler on the final seal to act as a sealing gasket.

4 deep-impregnated tank manufacturing. The steps for manufacturing a deep-flush can are as follows: the thin strip coil is cut into a vortex-like sheet; the sheet is coated and finished (also can be coated with a coil); the blank blank is blanked and the cup is washed; Or two times, depending on the size of the tank); Forming of the bottom of the tank; Edge trimming to the correct width; Inspection and sterilization.

Like the punching process, a multi-die punching machine is used to load and unload a wide roll of sheet material or plate and punch it into shallow cups.

Shallow cups are gradually reduced in diameter and height by once and twice re-pressing. When the final punching is stopped to a certain extent, a flange is left on the can, like all other sheet metal forming processes. Irregular edges are cut off and the bottom of the tank is machined to the desired shape.