1. Experimentation for Heating Parameter Design and PMMA Characterization on a Hot Embossing Set-up

2. Heating Experiments Objective : Check uniformity of heating.
Record the time to heat a block to a certain temperature (200 deg C).
Compare experimental results (uniformity and time) with ANSYS analysis.
Extrapolate results for the original heating blocks.

3. Experimental Setup Heating mode: Heating cartridges (Power 1kW).
Specimen : Two-hole and four-hole blocks.
Temperature sensor : J type Thermocouple.
Data Acquisition and monitoring: LabVIEW.
Miscellaneous : Relays, power source, etc.

4. Experimental Setup (Cont..)

5. Thermal Analysis (Heating)
3.65”
10.00”
Water inlet
Water outlet 1 2 3 4 5 6 7 8 9 10 11 12 13
Temperature distribution for the experimental block with two heating cartridges
Thermocouple locations
on the block

6. Temperature Profile (Heating)
Comparison of temperature profile obtained
at location 7 from thermal analysis and experimental data

7. Temperature Difference (Heating)
Temperature difference plot between thermocouple
locations 8 and 3

8. Temperature Profile (Cooling)
Temperature profile at thermocouple location 7 during cooling
(volume flow rate of 0.52 gpm of water)

9. Temperature Difference (Cooling)
Temperature difference plot between thermocouple locations 1 and 4

10. PMMA Characterization
Objective :
Obtain stress-strain curves for Poly methyl methacrylate (PMMA) at different temperatures.
Calculate Young’s modulus from the available data.
Find glass transition temperature PMMA.

11. Important Embossing Parameters
Temperature of embossing
Viscosity of the polymer is directly proportional to the temperature.
Pressure
Embossing pressure depends on the depth of embossing.
Speed of embossing
Speed of embossing controls flow of the polymer.

12. PMMA Properties Stress strain curves are nonlinear.
Glass transition temperature has significant effect in properties of PMMA.
At elevated temperatures:
Modulus (Compressive) values drop.
Compressive strength drops.
Creep effects increase.

13. Stress-Strain Curve
Stress-Strain curve for PMMA obtained using a cylindrical tool of 1” diameter

14. E variation with Temperature
Variation of Young’s Modulus with temperature obtained
using two different tool sizes

15. Specimen Pictures

16. Conclusions
Experiments show good temperature uniformity on the experimental block.
Experimental temperature profile and simulation (ANSYS) profile are similar.
E values for PMMA drops with temperature.
E drops substantially after 105 deg C indicating the glass transition temperature.

17. Future Work Polymer behavior Williams-Landel-Ferry (WLF) equation
Time to fill a cavity
Polymer flow during Embossing

18. Hot Embossing Machine

19. Mini-Vacuum Chamber
Mini vacuum chamber used to provide a clean and moisture free environment during embossing.
Mini vacuum chamber can accommodate an 8” substrate.