thermoforming 2.810 fall 2002 professor tim gutowski
Post on 22-Dec-2015
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Thermoforming Process Plan
Hardware Requirements Tool Trim Fixture
Set-up Mount Tool in Thermoformer Mount Trim Fixture
Run Fixture Sheet; Heat; Form; Cool; Trim
ThermoformingHeater
Plastics sheetClamping
Vacuum
*
**
* Source: R. Ogorkiewicz, “Engineering Properties of Thermoplastics.”; ** http://www.arrem.com/designguide/dgprocesscap.htm
Thin corner
Variations on the process
Drape Forming
Vacuum Forming
Vacuum Snap-Back Forming
Billow Vacuum Forming
Variations on the process
Plug-assist Vacuum Forming Plug-assist Pressure Forming
Pressure Reverse Draw with Plug-assisted
Heat Transfer in Thermoforming
Heating convectionqradiationqradiationq
conductionq
Coolingconvectionradiation qq &
conductionq
Temperature regimes for polymers
Log E(t)
TemperatureTg Tm
Semi-crystalline Polymer
Log E(t)
TemperatureTg Tg+60C
Amorphous Polymer
Viscoelastic Effects During processing
Unloaded sample
Coiled polymer chain
Extended polymer chain
Loaded sample
Polymer chains tend to exist in coiled configurations. Loading the sample can extend the chain and alter the mechanical behavior. Generally, abrupt, high rates of loading will extend the chain and lead to elastic effects. On the other hand, gradual slow rates of loading allow the chain to more or less retain its coiled configuration, with a resulting primarily viscous response
Simple Viscoelastic System
ddss
ds
ds
E
; :behavior veConstituti
2 :itycompatibil Kinematic
:mEquilibriu Force
2 gives This E
Modulus Elastic
Viscosity Newtonian""
:isconstant Time tic viscoelasThe
E
)1(2
0at 0 I.C. with 2 : oSolution t
te
t
behavior ous visc2
i.e. / of valuesLarge
tt
behavior elastic 2
behavior thens,let
2 ))/1(1(2
i.e. / of valuesSmall
E
t
tt
tt
“FAST” t << Elastic“SLOW” t >> Viscous“INBETWEN” t ~ Viscoelastic