Process of forming a thermoplastic sheet into a three-dimensional shape by clamping the sheet in a frame, heating it to render it soft and flowable. Then applying differential pressure to make the sheet conform to the shape of a mold or die positioned below the frame.
Types of Thermoforming
- Vacuum Forming
Vacuum forming is a plastic thermoforming process that involves forming thermoplastic sheets into three-dimensional shapes through the application of heat and pressure. In general terms, vacuum forming refers to all sheet forming methods, including drape forming, which is one of the most popular. Basically during vacuum forming processes, plastic material is heated until it becomes pliable, and then it is placed over a mold and drawn in by a vacuum until it takes on the desired shape.
- Plug assist forming
Plug assist forming is a widely used forming technique and requires the use of a female (cavity) mold. The limited depth of draw of female molds is improved by the use of plug assist.
- Vacuum snapback
Vacuum-snap back is an excellent and often used process for forming deep draw products with uniform wall thickness. Vacuum is used to pre-stretch the hot plastic before the mold makes contact with the sheet. Vacuum snap-back, while more complex than plug assist, can produce deeper drawn products with better wall uniformity and less mark-off. A vacuum pre-stretch box is required.
- Billow Forming
A method of thermoforming sheet plastic in which the heated sheet is clamped over a billow chamber. Air pressure in the chamber is increased causing the sheet to billow upward against a descending male mold.
- Free Forming
This method of thermoforming does not use a mold. Instead, an acrylic sheet is clamped in a frame and either a vacuum or compressed air draws the material to a desired depth. An electric eye determines when the proper depth has been reached and cuts off the pressure. Since only air touches the sheet of material, there is no markoff.
- Pressure Forming
This process is similar to vacuum forming, except with the addition of pressure, which pushes the sheet into the shape of the mold. This process is mainly used for parts that require styling and aesthetic qualities because pressure forming creates greater detail, allowing for textured surfaces, undercuts and sharp corners, which are not as easily created with vacuum forming.
- Drape Forming
In drape forming, a sheet of plastic is heated and stretched down, generally over a male mold. Next, depending on the shape of the mold, gravity alone will pull the material to the mold or commonly, a vacuum is applied to draw the sheet to the mold which will more detail to the inside of the part.
- Stretch Forming
A plastic sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and subsequently cooled. It is quick, efficient, and has a high degree of repeatability.
- Matched Die Forming
In this process, both halves of the part are formed by molds with no vacuum or air pressure. The sheet is heated until it is soft, and then both mold halves clamp together to form the part. Used with parts that do not have large draws.
- Inline thermoforming
In this process the plastic film moves from a roll onto the inline equipment and through the heating section. The heated material advances into the forming section where pressure and/or vacuum force the plastic onto a mold. It then proceeds to another station where formed parts are die-cut.
- Twin sheet forming
Twin-sheet thermoforming is a process of vacuum or pressure forming two sheets of plastic essentially simultaneously, with a separate mold on the top and bottom platens. Once the plastic has been molded, it remains in the molds, and while still at its forming temperature the two molds are brought together under high pressures, and the two sheets are welded wherever the molds dictate a weld.