Experimentation for Heating Parameter Design and PMMA

Characterization on a Hot Embossing

Set-up

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.

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.

Experimental Setup (Cont..)

Thermal Analysis (Heating)

3.65”

10.00”

Water inletWater 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

Temperature Profile (Heating)

Comparison of temperature profile obtained at location 7 from thermal analysis and experimental data

Temperature Difference (Heating)

Temperature difference plot between thermocouple locations 8 and 3

Temperature Profile (Cooling)

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

Temperature Difference (Cooling)

Temperature difference plot between thermocouple locations 1 and 4

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.

Important Embossing Parameters

Temperature of embossingViscosity of the polymer is directly proportional to the temperature.

PressureEmbossing pressure depends on the depth of embossing.

Speed of embossingSpeed of embossing controls flow of the polymer.

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.

Stress-Strain Curve

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

E variation with Temperature

Variation of Young’s Modulus with temperature obtained using two different tool sizes

Specimen Pictures

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.

Williams-Landel-Ferry (WLF) equation

Time to fill a cavity

Polymer flow during Embossing

)(

)(log

)(

00

0

02

01

T

T

TTC

TTC

Future Work

20

2

20 11

2 hhp

St

ff

Polymer behavior

Hot Embossing Machine

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.