Both machines are equipped with plug-assist for deeper draw products
and may employ forming pressures up to 10 bar.
Research into thermoforming has examined the entire process cycle
from the production of the sheet feedstock by extrusion, through
of thermoforming, to the performance of the final products. Much
of the work is ongoing.
A substantial part of the research effort has been directed towards
the development of robust finite element simulations of thermoforming
processes. In this area
thermoforming lags well behind competing processes such as injection
moulding. However, poor understanding of key aspects of the process
operation, such as
material deformation behaviour and tool/sheet tribology, has hampered
Finite Element Process
Tool / Sheet Contact
The tribological aspects of various thermoforming tool and polymer
sheet materials have been extensively investigated. Of
most interest are the
thermal and frictional
properties of plug and mould materials. In these studies
a number of experimental approaches have been employed, including thermal
and high speed video.
Thermoforming tests have been used to study in detail the
relationships between the main thermoforming process
variables and the properties
of the final product.
Experiments have included separate evaluation of the
plugging and blowing stages in plug-assisted thermoforming. The work
important role that sheet extrusion variables play in
the subsequent behaviour of the material during the thermoforming
Investigation of Plugging and Blowing Process Steps
Methods have been investigated to provide on-line control
of the thermoforming process. Normally industrial machines
amount of instrumentation
and automatic control, and instead rely heavily on trial
and error methods. The most obvious process variable
to measure and
is the sheet
temperature, immediately prior to forming. However, work
on the plug-assisted process has
provided an alternative approach that measures the force
drawn by the plug during the process stages. A prototype
be used either for on-line process control or for as
an aid in understanding the main process variables.
Sheet Temperature & Plug
When thermoforming semi-crystalline materials, such as
PP and PET, the morphological changes that are
of the sheet
have profound effects
on the subsequent thermoforming behaviour. Studies
carried out on PP materials have shown dramatic changes in the
form and degree
by extrusion parameters, and ageing effects have
been shown to alter material properties many days after extrusion.
Morhological Changes in Polypropylene
Extrusion & Thermoforming
of Cellular Polymers
Foams or cellular materials are employed in a range of
applications. In this work cellular structures
were produced by the addition
of chemical blowing
agents during the sheet extrusion process.
A large number of commercial blowing agents were investigated, producing
sheet with widely
varying cell densities.
The composition of the agents was shown to
have the greatest
effect on the foam structure. Subsequent work
is now examining the effect
processes on the cellular structure in thermoformed parts.
Extruded and Thermoformed Cell Structures
The deformation behaviour of polymer materials under realistic processing conditions is an essential
element of the understanding of thermoforming processes. However, the high temperatures, high strain rates processing conditions very
difficult. At Queen's University these difficulties
have been overcome through the design and development of a
This can replicate
thermoforming temperatures (up to 250C),
deformation speeds (up to 1.5 m/s) and biaxial deformation modes
Biaxial Testing Machine
For further information, please contact Dr. Peter Martin or Professor Eileen Harkin-Jones.
© QUB - Materials Research Group 2003