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With China Plastic Machinery
With China Plastic Machinery
Thermoforming, also known as hot press forming, is a special plastic processing method for processing thermoplastic (see thermoplastic resin) sheets into various products. There are many thermoforming methods, but basically they are based on the combination or improvement of three methods: vacuum, air pressure or mechanical pressure. Originated from the metal stamping process, thermoforming is different from plastic molding processes such as injection molding, blow molding, and rotational molding. Thin-gauge thermoforming is mainly used for disposable cups and containers, while thick-gauge ones are used in transportation, furniture and electrical appliances. Recently, thermoforming is not only limited to plastic processing, but also extended to the processing of thermoplastic composite materials and is used in the aviation industry.
A special plastic processing method for processing thermoplastic sheets into various products. The sheet is clamped on a frame and heated to a softened state. Under the action of external force, it is pressed against the mold surface to obtain a shape similar to the mold surface. After cooling and shaping, it is trimmed to form a product. This process is also used in rubber processing. In recent years, thermoforming has made new progress, such as continuous production technology from extruded sheets to thermoforming.
In the market, there are more and more thermoformed products, such as cups, plates, food trays, toys, helmets, as well as automotive parts, architectural decorations, chemical equipment, etc. Compared with injection molding, thermoforming has the advantages of high production efficiency, low equipment investment and the ability to manufacture products with larger surface areas. The plastic used for thermoforming are mainly polystyrene, polyvinyl chloride, polyolefins (such as polyethylene, polypropylene), polyacrylates (such as polymethyl methacrylate) and cellulose (such as cellulose nitrate, cellulose acetate, etc.) plastic, and are also used for engineering plastic (such as ABS resin, polycarbonate). There are many thermoforming methods, but basically they are combined or improved based on the three methods of vacuum, air pressure or mechanical pressure.
There are dozens of thermoforming methods, and vacuum forming is one of the representative ones.
Thermoforming is formed by using vacuum to make the heat-softened sheet close to the mold surface. This method is the simplest, but the pressure difference caused by vacuuming is not large, and it is only used for products with simple shapes.
Use compressed air or steam pressure to force the heat-softened sheet to adhere to the mold surface for molding. Because the pressure difference is larger than vacuum molding, products with more complex shapes can be manufactured.
Place the heat-softened sheet between the paired female and male molds and use mechanical pressure to mold. This method has a higher molding pressure and can be used to manufacture products with complex shapes, but the mold cost is higher.
Use a plunger or male mold to partially pre-stretch the heated sheet, and then use vacuum or air pressure to mold it, so that products with large depth and uniform wall thickness distribution can be obtained.
The sheet is heated to a temperature not exceeding the melting point of the resin, so that the material remains in a solid state for molding. It is used for ABS resin, polypropylene, and high molecular weight high density polyethylene. The rigidity and strength of the parts are higher than those of general thermoforming products.
Two sheets are stacked together and air is blown in the middle to produce large hollow parts.
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