Page 127 - C:\Users\Adik\Documents\Flip PDF Professional\Marketer PPT LR\

PRESSURE THERMOFORMING: In the pressure forming process, heated sheet is
forced into the tool using compressed air. The sheet makes contact with the edge of
the mould, forming a seal. Air pressure is then introduced which pressurized from above
pushing the sheet against the mould to form the part. Often, a vacuum is also applied
underneath the sheet to help bring the sheet into contact with the mould. The process
offers forming at lower temperatures and thus faster cycles than vacuum forming.
C
A B
Air Pressure
Blow Air
Plate
Mold 0-Ring
Seal
Vent or Vacuum
The pressure forming process.
Also provide improved distribution of material creating a more even wall thickness,
allows the forming of thicker sheets and enhances reproducing creating finer details,
textures which are not as easily created with vacuum forming. The formed part has
less residual stress. Disadvantage over vacuum forming is that moulds are more
expensive since they feature more intricate detail
FREE FORMING: This method does not use a mould; instead heated sheet is blown
into a bubble with air pressure or drawn into a cavity by means of a vacuum. An
electric eye determines when the proper depth has been reached and cuts off the
pressure. The bubble formed is then held in place by the pressure or vacuum until the
Light Source Toggle Thinnest Thinnest
for Photo Cell Clamp Photo Cell Unit Toggle Clamp
Clampink Ring
Photo Cell Unit
Clamping Ring
Light Source
for Photo Cell
Solenoid Valve
Vacuum Box
Solenoid Valve Controlled by
Pressure Box
Controlled by Photo Cell
Photo Cell
Pressure free draw forming Vacuum free draw
forming.
part cools. Being untouched, sheet will have optics as good as the optics of the
original, unprocessed sheet. Applications in skylights and windows requiring good
optical properties
Mechanical Thermoforming (Matched Moulds): It's a pure mechanical forming
method in which the softened plastic sheet is captured between matching positive
and negative moulds (male-female) forcing it to conform to their shapes. No pressure
(vacuum or air) is applied. Offers better dimensional control and the opportunity for

Male Ram
Mold B
A
B
Female Formed Part
Mold
Thermoforming using
matched molds.
Trapped-Air
Vents
DAVE TECHNICAL SERVICES 127