What Is Cold Forming?

Cold forming is the processing method of punching, bending, stretching and other materials without heating. Cold forming (or solid phase forming) is neither a primary forming nor a secondary forming, but a new and promising processing technology, which is a transplanted metal processing method (such as forging, rolling, stamping, etc.) , Make the plastic at normal temperature (also can be below the polymer) molding.

Cold forming raw materials do not need to be melted or softened to a viscous state, and can be molded in the glass state. Such a molding method has the following advantages:

(1) Avoid degradation of polymer or resin at high temperature and improve the performance of the product.

(2) Due to the rapid orientation of the polymer during cold forming, the properties of the product are significantly improved.

(3) Because the heating and cooling stages are eliminated in the molding process, the production cycle is greatly shortened, and the production process is greatly reduced.

(4) Cost reduction. Under the condition of mass production, the cost of equipment is 1-2 times lower than the cost of injection molding.

(5) Polymers with very high molecular weights can be processed without being limited by general processing methods.

(6) There are no weld seams and gate marks formed when the product flows. ^[1]

Cold forming also has some disadvantages.

(1) The size, shape, and precision of the product are poor. This is because the elastic recovery force of the plastic after the processing force is released is much greater than that of the metal material, and the elastic modulus is much smaller. The modulus of elasticity of mild steel is 21,000 kg / mm2, while the maximum modulus of thermoplastics does not exceed 400 kg / mm2, so even if the processing conditions are improved, the size, shape and precision of the product cannot be completely solved problem.

(2) In cold-formed products, there is a very obvious molecular orientation, which causes anisotropy of strength.

The cold forming process and equipment of plastic are generally similar to metal forming equipment. According to the direction of force application, there are roughly the following:

1. Forging. After the neck of the plastic blank is heated, it is placed between the upper and lower molds of the press. With the closing of the upper and lower molds, the product is formed by the mechanical force of the mold.

2. Rubber pad molding. The upper mold of the press is a rubber pad. The plastic blank is in direct contact with the rubber pad. The lower mold is a male mold. When the mold is closed, the rubber pad deforms and actually becomes a female mold. The plastic is between the metal male mold and the rubber female mold. Between molding.

3. Hydroforming. A rubber diaphragm is installed in the upper mold, and the pressure of the liquid can be transmitted to the plastic through the film. When the mold is closed, the pressure of the fluid forces the rubber diaphragm to deform and transmit the force to the plastic, so that it is formed between the upper and lower molds.

4 Stamping. The blanks are formed into plastic products by mechanical force. Usually, the stamping method can only form products with a depth of 6.2 mm (1/4 inch). Mainly used for processing modified polypropylene, ultra high molecular weight polyethylene, ABS, polyoxymethylene, polyamide 6 and polyamide-66.

5. Roll forming. By means of the mechanical action of the upper roll of the calender, plastic plates and films are formed. Mainly used for processing polyethylene, polystyrene, rigid polyvinyl chloride, polyamide-66, polyamide-6, polytetrafluoroethylene and polyformaldehyde. ^[1]

The basic conditions for solid-phase molding are: the molding material itself should be a complete blank, and its shape should preferably be similar to the molded product. For example, when the gear is used to produce a disk or a ring, the molding temperature range is from room temperature to higher than room temperature. 10-20 , even below the melting point or softening point. In addition, the molded product is pressurized at the yield point. When processing the polymer by solid phase molding, special attention should be paid to these conditions when determining the process parameters, and the structural defects of the processing material should be prevented.

There have been great developments in the production of plastic products by cold forming methods, such as cream cans, gears, automobile parts, etc. It is reported that solid-phase forming processing technology is also used to make so-called artificial islands; large plastic products such as floating bridges. Solid-phase molding has a short history in practical application, so the research on this molding method is not enough. With the deepening of research work, the theory and process technology of solid-phase molding will inevitably have greater development. ^[1]