Thermoforming or Vacuum Forming

Vacuum Forming refers to the method of relying on a vacuum pump to pump a vacuum between the mold and the heated thermoforming plate (sheet) material, resulting in a pressure difference between the upper and lower parts of the plate (sheet) material, so that the plate (sheet) material is tightly attached to the mold surface. Vacuum forming can be divided into several forms such as single positive die (punch die), single negative die (concave die), and no die.Thermo formingis also called hot press forming or compressed air forming. It relies on the air compressor to pressure and stretch the heat-softened Plastic Sheet, so that it is close to the surface of the mold, and becomes a product after cooling. Vacuum forming, because the vacuum pump can form less than 0.1MPa, but the vacuum degree can be achieved in the industry is only 0.069 ~0088MPa, so the vacuum forming plate is thick or the shape of the product is complex, the forming pressure is insufficient, will cause the poor forming of the part, the outline is not clear, and even can not be formed at all. If the pressure molding is used, it is easy to reach 0.3~06MPa because of the pressure of the air compressor, and the molding of thicker plates and complex shapes can also be achieved. And the pressure molding speed is fast, about three times more than the vacuum molding. Therefore, under the following circumstances, pressure molding should be selected: 1, the molding parts are higher (the mold depth is larger); 2, the surface of the parts with fine patterns or reinforcement; 3. The corners of the parts are divided into acute angles; 4, the tensile strength of the material is large; 5. Large batch production of parts. However, the clamping force of pressure molding equipment is usually on the order of mpa in order to withstand the total pressure of compressed air, so the requirements for machinery and molds are high and the price is expensive.
The comparison of the characteristics of pressure forming and vacuum forming is shown in the following table:

Differential pressure molding is the simplest method of thermoforming, and its parts have many characteristics, for example, the side of the parts and the mold wall can get a smooth and flat surface; High precision of shape and dimension; The surface gloss of the parts is good, and the transparent parts can be obtained after the transparent materials are formed. However, differential pressure molding also has the disadvantage of uneven wall thickness, so in order to improve the uniformity of products, in actual production, it is often used to first stretch the plate (sheet), and then use vacuum or pressure forming and other comprehensive thermoforming methods.