In its simplest form ,thermoforming is the stretching of a heated rubbery sheet into a final shape. As the sheet is stretched against the mold surface, it stops
drawing. As a result , the final part has thick walls where the sheet touched the mold first and thin walls where it touched last. In many thin-gage forming
applications, the extent of sheet thatis stretching is small and so the areal draw ratio is small. The package integrity and durability are therefore uncompromised.
Typical applications are in packaging areas such as blister and bubble packs, form/fill/seal packages and fast foodcontainers and picnic plates. If a high degree
of stretching is needs, as with disposable drink cups or for heavy-gage sheet forming, simple stretching techniques are insufficient.. The methods of
forming are divided into the number of sequential steps needed to form the part once the forming temperature.   Thermoforming Machine

There are at least five types of one-step forming:

l         In drape forming，the clamped, heated rubbery sheet is either lowered onto the male mold or the mold is raised into the sheet. The sheet in contact with the
mold does not stretch. For modern drape forming, the air trapped between the sheet and the mold is evacuated as the mold penetrates and stretches the
sheet against the mold flange. Either vacuum or air pressure is used to produce the differential pressure needed to force the sheet against the male mold. In drape
forming , the formed part has a thick bottom and thin sidewalls. The part is thinnest at the rim. Drape forming is also called male molding.  Cup Making Machine

l         In vacuum forming,the clamped, heated rubbery sheet is sealed against the rim of the female mold. Vacuum is then applied. The differential pressure presses
the sheet against the surface. As noted before, the formed part has a thick rim and is thinnest in the bottom corners. The is also called cavity forming or female molding.     Printing Machine

l         Pressure forming,is similar to vacuum forming.A pressure box is fitted over the sheet as it is held against the mold rim and positive air pressure is used to
push the sheet into the mold corners. Since air pressure to 1.4 Mpa or 2001b_f/in² is used, the pressure box must seal against the free surface of the
sheet. Pressure forming is used for difficult-to-form roll-fed thin-gage polymers such as PP and for production of highly detailed heavy-gage parts [18].

l         In free blowing, the clamped heated rubbery sheet is stretched with air itto a free-form shape. The amount of air pressure is controlled with a photocell that
senses the height of the expanding bubble. Sunce the environmental air is slightly cooler than the sheet, the sheet cools in the free-from shape. This techinque was
pioneered for aircraft gun enclosures. Since the sheet does not touch a solid surface during forming, it remains mar-free. The bubble wall
thickness is quite uniform execept near the clamping area. Freely blown roll-fed thin-gage bubbles are used for blister packs.   Automatic cup stacker

l         Matched die molding, is a common way of forming shapes form relatively stiff polymers, such as PS foam or fill polymers. The clamped heated rubbery sheet is positioned between two mold halves. As the mold halves close,
vacuum is applied to the female half of the mold halves. As the mold halves close,vacuum is applied to the female half of the mold to assist with forming. Part wall thickness depends on the mating tolerance of the two mold halves.Appreciable material movement is possible if applied forces are relatively large.
Usually the applied pressures do not exceed about 1 Mpa or 150 1b/in and are usually about 0.34 Mpa or 50 1b_f/in².