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PLASTIC THERMOFORMING

Thermoforming is the process of shaping plastic sheets into desired three-
dimensional shape through application of heat and pressure. The process utilizes
the plastic sheets as starting material which can be separate or part of a
continuous roll. In general terms, thermoforming refers to all sheet forming
methods and suitable for large area, light weight products.
Thermoforming involves two main steps: Heating and Forming.
Plastic sheet is clamped securely between a set of frames and heated to render it
soft and flowable. Heating is usually accomplished by infrared heaters or gas-fired
ovens. Once the sheet is pliable, it is pushed, pulled or stretched into a female or onto
a male mould by application of vacuum, air pressure, mechanical forming or
combination thereof, so that it conforms to the shape of the mould on cooling.
METHODS OF THERMOFORMING:
VACUUM THERMOFORMING: This is one of the most common thermoforming
methods. As the name implies, vacuum is formed between the mould and the heated
thermoplastic sheet. This removes air between the sheet and mould, and draws the
sheet into a male or female tool. The vacuum is applied through miniature venting
holes in the mould that are joined to vacuum lines. The plastic cools and hardens on
contact with the water cooled mould surface. The air is blown back in the mould so
the part is removed and subsequently trimmed from the sheet. The final part will
have edges with nearly original thickness, thin sidewalls and a thinner bottom.
Straight vacuum forming generally allows good mould reproduction and quick cycle
times making it suitable for parts with low profiles that don't require deep draws.

Heater
Clamps

Mold cavity Plastic sheet
Mold Vacuum holes

Molded part
Vacuum drawn
(1) (2) (3)

Drape Thermoforming: Drape forming is another
simple forming method that is used for parts with
deep draws. Similar to straight vacuum forming
except that after the sheet is framed and heated, it
is mechanically stretched, and a pressure
differential is then applied to form the sheet over a
male mould, which will give more sharp detail to
the inside of the part. The formed part solidifies at
nearly the original thickness of sheet where the
sheet touches the highest part of the mould. The
last area to be formed will be the thinnest and
weakest area.

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