1. Novel Method for Rapid
Determination of Thermoformability
Dr. Amit Dharia
Transmit Technology Group, LLC, TX
Dr. Don Hylton
McConnell Co. Inc., GA

2. Outline
® Properties –Thermoforming Process
relationship
® Current test methods
® Description of new test apparatus
/operation/ data acquisition
® Application and data interpretation
® Future plans
® Conclusion

3. Thermoforming Process
® Extruding sheet stock
® Heating sheet above Tg
® Stretching heated sheet in rubbery state
® Forming stretched sheet
® Cooling
® Trimming
® Finishing –painting, printing

4. Structure - Properties -
Thermoformability
® Rate of change of strength with the
change in strain rate at forming
temperature
® % Crystallinity – Breadth of rubbery
Plateau
® Molecular weight, Molecular weight
distribution, molecular architecture
(branching, crosslinking) – MFR, Melt
Elasticity

5. Other parameters
® Density - % filler, type of fillers, degassing
® Geometry – Thickness, area, multi-layered
structures, adhesion between layers
® Residual stresses between and within in
extruded layer sheet stock
® Thermal diffusivity (Cp, K. Rho)
® Extrusion quality ( gels, unmelts,
thickness variation, grain patterns)
® Color (IR absorption)

6. Current tests
® Low shear melt viscosity (MFR, RMS)
® Hot tensile test (2 in gauge length, 0.2 to 20
ipm, or 0.002 to 0.33 1/s vs. 10/1s for TF
process)
® Melt Tension (Draw Force –Melt strength,
Break Velocity –Draw down)
® Sag Test (sag distance, sag time)
® Hot Creep Test
® DMA (Relaxation time)

7. Major disadvantages of current
methods
® Most tests are conducted in melt or near melt
phase – TF at Tg + 30-40 F
® Specimen do not reflect actual test geometry
(shape, size, thickness clamping mode)
® Do not account for orientation, thermal stresses,
thickness variations
® Isothermal environment, does not account for
transient nature during heating/ cooling steps
® Effects of secondary process parameters can not
be evaluated
® Results cannot be directly used.

8. What we want to know?
® Will this material thermoform?
® Will this new material process the same?
® Will this lot process the same as the last one?
® Why this lot does not process the same?
® How much time is needed to heat the sheet?
® How fast material will heat?
® What is the right forming temperature range?
® Will melt adhesion between layers survive
heating and stretching step?
® Will material discolor, fed or degrade during
heating?

9. What processors want to
know?
® What is the maximum draw down ratio?
® How fast part can be made?
® What is the MD and TD shrinkage?
® Will material tear?
® How much regrind can I use?
® Will grains retain shape and depth?
® Does extruded sheet have gels or
unmelts?

10. What Industry Needs?
® A standard test method which reflects all unit
steps – heating, 3D stretching, forming, and
cooling
® A test equipment which can be precisely
controlled, is rapid, easy to use, provides
repeatable and quantitative information, using the
lease amount of material.
® Easy to use “Thermoformability Index” standard
for comparing, contrasting effects of selected
process/ material variables

11. TECHNOFORM TM
Patent PendingTTG
TECHNOFORM

12. Typical Data input
® Mode of operation – Plug, vacuum, vacuum +plug
® The heating element distance from the sheet
surface
® The heating element temperature
® The sheet temperature
® Heat Soak time at given temperature
® Plug velocity (2 to 400 mm/second)
® Plug Delay Time
® Plug Temperature
® Cooling time

13. Typical user Input Screen
Sag Distance
Thinning
Strain
hardening
Forming Depth mm
Thermoformability Index=
slope

14. Typical Data Output
® Heating rate (Delta C/ time)
® Sag distance
® Forming force (Stress) vs. forming
distance (strain)
® Forming Force vs. time
® Yield force
® Forming force vs. actual temperature
® Shrinkage

15. Heating rates for various plastic materials
(Heater at 600 C, 3” from upper, 2” from lower)
30
80
130
180
230
0 20 40 60 80
t (seconds)
T(c)
PP
HDPE
HIPS
PVC
ABS
Acetal
PMMA
Nylon

16. Effect of Crystallinity
0
5
10
15
20
25
30
50 70 90 110 130
Forming distance, mm
Force(N)HDPE PP HIPS PETG ABS PMMA PVC

17. Effect of Forming Temperature
0
2
4
6
8
10
12
14
125 145 165 185
Temperature (C)
Force(N)
ABS
PP
HDPE
HIPS
PETG
PMMA
ACETAL

18. Force100 = f (T, V, material)
® F(ABS) =9.2348 -0.0547 T (R2 =99%)
® F(PMMA)=7.1587 -0.0341 T(R2=98%)
® F(PETG)=10.096 -0.0601 T (R2=92%)
® F(HIPS)=9.6782 - 0.0503T(R2=93%)
® F(HDPE)=5.2771 -0.0266 T (R2=86%)

19. Comparison of Acetal, Nylon, TPO
0
1
2
3
4
5
6
0 50 100 150
Time (seconds)
Formingdistance(mm)
Delrin (206)
PA (241 C)
TPO (161 C)

20. Effect of forming Speed on HDPE @ 150 C
Effect of Forming Speed on HDPE
0
2
4
6
8
10
0 50 100 150
Distance (mm)
Fromingforce(N)
20 mm/sec
30 mm.sec
50 mm/sec

21. Comparison of filled vs. HMS-TPO
0
10
20
30
40
50
0 20 40 60 80 100
Distance (mm)
Force(N)
40HMSTPO 20HMSTPO
40 FTPO 20FTPO

22. Effect of adding HMSPP in PP
0
1
2
3
4
5
6
7
40 60 80 100 120 140
Form ing Dist ance, mm
FormingForce,Lbf
10%H MSPP 20%HMS PP 30% HMSPP
0
1
2
3
4
5
6
7
40 60 80 100 120 140
Form ing Dist ance, mm
FormingForce,Lbf
10%H MSPP 20%HMS PP 30% HMSPP
0
1
2
3
4
5
6
7
40 60 80 100 120 140
Forming Distance, mm
FormingForce,Lbf 10%HMSPP 20%HMSPP 30%HMSPP

23. Formability of HMSPP/PP Blends
0
2
4
6
8
10
12
10 20 30
%HMSPP
thickness(High/Low)

24. Effect of % Regrind on formability TPO
20% regrind / Five Successive Extrusions
0
1
2
3
4
5
6
40 60 80 100 120
Forming Distance, mm
FormingForce,Lbf
1st
2nd
3rd
4th
5th

25. Comparison of Test Methods
Relaxation Time (s) Vs. Force @ 75 mm depth
R2
= 0.9968
0
2
4
6
8
10
12
0 2 4 6 8
Relaxation Time (sec)
FormignFroce(75mm)
PP, 165 C
HDPE,140C
HIPS,160 C

26. Future Plans
® Develop a standard “Thermoformability
Index” similar to Melt Flow Index; which
can be used by industry as specification
to describe thermoformability of material.
® Refine force-vs. displacement data into
stress vs. strain data for each plug
geometry
® Develop an integrated predictive modeling
system like “Moldflow”.

27. Conclusions
® A novel and simple test equipment is
developed which closely reflects all four
unit steps of the typical thermoforming
process and generates quantitative and
repeatable information.
® The test data can be used in raw form to
compare or contrast various materials and
process parameters input or can be
further modeled as a design or predictive
tool.