![How to Standardize? Thermoforming Index (TFI) Force required to draw a sheet of thickness X at speed Y mm/second using a Plug of specified geometry G at Temperature T f to area ratio A (or volume ratio V), with plug temperature Tp. TFI = [Force (M, Tm)/ Force (GPPS, Ts)]](https://image.slidesharecdn.com/spe-aug15-100827191708-phpapp02/85/Technoform-A-test-tool-to-determine-Thermoformability-43-320.jpg)
Technoform- A test tool to determine Thermoformability
- 1. Applications of Thermoformability Analyzer Amit Dharia Transmit Technology Group, LLC Irving, Texas
- 2. Objectives To demonstrate the need for an industry wide standard Quantitative test method for “Measuring” and “Reporting” Thermoformability of plastic materials (2005) To illustrate applications of test equipment and test method in understanding and resolving issues related to Thermoformability.
- 3. Outline Structure-Property- Process relationship Current test methods Description of Technoform Application and data interpretation Products – Basic, Standard, Advanced Conclusion
- 4. Thermoforming Process Extruding sheet stock Heating sheet above Tg Stretching heated sheet in rubbery state Cooling Trimming Finishing Regrinding and recycling scrape
- 5. 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, Rheology
- 6. 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)
- 7. Test Methods Inconsistent results, grip extrusion, annealing Hot tensile test Repeatable, effect of temperature DMTA Repeatable, correlates with Sag test, expensive equipment Stress Relaxation No external force, geometry dependent, measure of only melt strength Sag test > Tm, cooling effect, uni-directional, not applicable to all materials Melt Tension Easy, measure of only MW MFR Major Short coming Test Method
- 8. Major disadvantages of current methods Most tests are conducted in melt or near melt phase Test Specimens do not reflect actual test geometry (shape, size, clamping mode) Tests do 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.
- 9. 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 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?
- 10. 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?
- 11. 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 least amount of material. Easy to use “Thermoformability Index” standard for comparing, contrasting effects of selected process/ material variables
- 12. Variables Shrinkage Extrusion, storage Additive package impurity % of fillers Forming speed % regrind Type of fillers Plug temperature Volatiles Rho, k, Cp Plug material Color η o , η el Plug geometry Layers % LCB, % Xl Part geometry Residual stresses Tg, Tm, % Xc Forming Method Thickness Molecular Structure Process Feed Stock Material
- 13. Desired Test Method MEANINGFUL Rapid Easy to use Quantitative Repeatable A good problem solving tool
- 14. Output Range Input Temp. vs. Time Plug assist, Vacuum Method Force vs. Time Any type Resin Type Test Input – Output Variable Plug Dwell time 10- 180 mm/second Forming Speed Variable Cooling Time 100 lb Maximum Force 23 C to 120 C Plug temperature Force vs. Depth Epoxy, Polished Aluminum Plug Material Force at Max Draw Depth Variable Heat Soak time Draw vs. time 60 C to 280 C Forming Temperature Force vs. Draw Depth 10 mil to 375 mil Sheet Thickness
- 15. Typical GUI Screen Sag Elastic Plastic Strain hardening Thinning
- 16. Results V,T
- 17. Technoform
- 19. Melt Strength = Resistance to Deformation @ T Melt Elasticity =Capability to deform @ T Stress (Force) % Draw or A/Ao Strain Hardening
- 20. Heating rates for various plastic materials (Heater at 600 C, 3” from upper, 2” from lower)
- 22. Comparison of various PE
- 23. Effect of Forming Temperature
- 24. 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%)
- 25. Effect of Melt Strength (% HMSCOPP in COPP)
- 26. HMSCOPP
- 27. COPP vs. HMSCOPP
- 28. Isothermal vs. Non-Isothermal 20 mm/s, 130 C, HIPS
- 29. Effect of Plug Temperature HIPS 35 mil, 130 C, 40 mm/s, No control
- 30. Effect of Plug Temperature-II 35 mil HIPS, 130 C, 40 mm/s, Plug at 23 C
- 31. Effect of Plug induced cooling -III HIPS (with and without hole)
- 32. Effect of Plug Material 35 mm HIPS, 40 mm/s, 130 C
- 33. Effect of Sheet Thickness on heating rates
- 34. Effect of Sheet Thickness
- 35. Effect of Color on heating Rate
- 36. Effect of Color CoPP, 35 mil, 40 mm/s, 160 C
- 37. Effect of Lot to Lot Variation 170 C, 40 mm/s, 190 mil TPO
- 38. Effect of Regrind (FR-ABS) 125 mil, 160 C, 40 mm/sec
- 39. Effect of Regrind (GPPS) 125 mil, 190 C, 40 mm/sec
- 40. Processing Window of Commercial TPOs
- 41. COPP- Nano clay Composites
- 43. How to Standardize? Thermoforming Index (TFI) Force required to draw a sheet of thickness X at speed Y mm/second using a Plug of specified geometry G at Temperature T f to area ratio A (or volume ratio V), with plug temperature Tp. TFI = [Force (M, Tm)/ Force (GPPS, Ts)]
- 44. Thermoforming Index (example) 125 mil, GPPS, 40 mm/s force to draw to 45 mm depth @ 160 C is 7 lbs. 125 mil, PP, 40 mm/s Force required to draw to 45 mm depth @ 170 C is 3.5 lbs. TFI of PP = F 45,PP * thickness (GPPS) F 45, GPPS * thickness (PP) = 3.5*0.125/ 7* 0.325 = 0.5
- 45. Conclusions Easy and rapid test method with overall operation similar to actual Thermoforming process Economical vs. Field trials Test equipment and method can be applied to wide range of Industrial applications TFI offers one simple number (like MFI) representing material’s Thermoformability Test equipment and method can be applied to wide range of Industrial applications