Technoform For Rapid, Repeatable Thermoformability Analyses

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Technoform For Rapid, Repeatable
Thermoformability Analyses

• Dr. Amit Dharia
• Transmit Technology Group, LLC, TX
• www.transmit-technology.com

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Outline

• Properties Thermoforming Process relationship
• Current test methods
• Description of Technoform
• Application and data interpretation
• Products Basic, Standard, Advanced
• Conclusion

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Thermoforming Process

• Extruding sheet stock
• Heating sheet above Tg
• Stretching heated sheet in rubbery state
• Cooling
• Trimming
• Finishing

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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

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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)

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Current tests

• Low shear melt viscosity (MFR, RMS)
• Melt Tension (Draw Force Melt tension, Break
  Velocity -extension)
• Sag Test (sag distance, sag time)
• Hot Creep Test
• DMA (Relaxation time)

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Major disadvantages of current methods

• Most tests are conducted in melt or near melt
  phase
• Test Specimens does not reflect actual test
  geometry (shape, size, clamping mode)
• Tests does not account for orientation, thermal
  stresses, thickness variations
• Isothermal environment, does not account for
  transient nature of heating/ cooling
• Effects of secondary process parameters can not
  be evaluated
• Results cannot be directly used.

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What processors 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?

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What processors want to know? -II

• What is the maximum draw down?
• How fast part can be made?
• What is the MD and TD shrinkage?
• Will material tear at the corners and ribs?
• How much regrind can I use?
• Will grains retain shape and depth?
• Does extruded sheet have gels or unmelts?

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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

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TECHNOFORM TM
Patent Pending
TTG
TECHNOFORM
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Schematics of Technoform
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Typical Data input

• Mode of operation Plug Assisted, Vacuum
• 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 200 mm/second)
• Plug Delay Time
• Plug Temperature
• Part Cooling time

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Typical user Input Screen
Strain hardening
Thinning
Thermoformability Index slope
Sag Distance
Forming Depth mm
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Typical Data Output

• Heating rate (Delta C/ time) f (thickness)
• Sag distance
• Forming force (Stress) vs. forming distance
  (strain)
• Forming Force vs. time
• Yield force
• Forming force vs. actual temperature
• Shrinkage (manual measurements)

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Effect of Heating time
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Plug Material and Shapes

• Truncated cone with flat end (2.5 Top D, 0.75
  Bottom D, 4 Height)
• Truncated cone with Rounded End (2.5 Top D, 1 D
  bottom, 4 Height)
• Hemisphere of 3.5 Diameter
• All tools made of Foam Epoxy

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Effect of Plug Temperature35 Mil Black HIPS, 130
C,40 mm/s- No control -
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Effect of controlling Plug TemperatureHIPS, 40
mm/second with T control
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Effect of Plug Geometry
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Effect of plug materialHIPS, 170 C, 40
mm/second, 35 mil
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Effect of forming Speed on HDPE _at_ 150 C
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Heating rates for various plastic
materials(Heater at 600 C, 3 from upper, 2
from lower)
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Effect of Crystallinity
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Comparison of various PE
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Effect of Forming Temperature
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Force100 f (T, V, material)

• F(ABS) 9.2348 -0.0547 T (R2 99)
• F(PMMA)7.1587 -0.0341 T(R298)
• F(PETG)10.096 -0.0601 T (R292)
• F(HIPS)9.6782 - 0.0503T(R293)
• F(HDPE)5.2771 -0.0266 T (R286)

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Effect of ThicknessPC/ABS, 40 mm/sec, 200 C
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Lot to lot variation in TPO170 C, 40 mm/second,
190 mil
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Effect of Color Co PP, 160 C, 40 mm/second, 35
mil
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Effect of thickness on the Heating Rate
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Effect of Regrind on formability TPO20
regrind / Five Successive Extrusions
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Effect of Regrind in FR-ABS
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Comparison of filled vs. HMS-TPO
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Effect of adding HMSPP in PP
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Formability of HMSPP/PP Blends
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Comparison of Test Methods
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Processing window for E-3500170 C, 40 mm/s, 190
mil
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Technoform Features
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Conclusions

• Technoform is a simple to operate test equipment
  is which closely reflects all unit steps of the
  typical thermoforming process and generates
  quantitative and repeatable information in short
  time.
• The test data can be used in raw form to compare
  or contrast various materials, process
  parameters or can be further modeled as a design
  or predictive tool.