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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 Sag Distance Thinning Strain hardening Forming Depth mm Thermoformability Index= slope
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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 Temperature 35 Mil Black HIPS, 130 C,40 mm/s - No control -
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Effect of controlling Plug Temperature HIPS, 40 mm/second with T control
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Effect of Plug Geometry
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Effect of plug material HIPS, 170 C, 40 mm/second, 35 mil
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Effect of forming Speed on HDPE @ 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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Force 100 = 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%)
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Effect of Thickness PC/ABS, 40 mm/sec, 200 C
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Lot to lot variation in TPO 170 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 TPO 20% 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-3500 170 C, 40 mm/s, 190 mil
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Technoform Features BasicStandardAdvanced Fixed heaters, 120 VManual AdjustmentAutomated Adjustment = F (thickness, material) Fixed WattFixed WattsClose loop Chamber at AmbientChamber T control Speeds 0-120 mm/s0-200 mm/second Plug T @ ambient Plug T Controlled Plug mode onlyPlug and Vacuum No Vacuum modeNo Vacuum vs. depthVacuum vs. Depth record Basic softwareBasic SoftwareAdvanced 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.
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