3.2 Viscoelastic dissipation during the embossing stage of ultrasonic hot glass embossing process

embossing stage with the assistance of ultrasound, it must determine the amount of

<sup>q</sup>\_ <sup>¼</sup> <sup>f</sup> � <sup>π</sup> � <sup>G</sup>″ � <sup>ε</sup><sup>2</sup>

<sup>0</sup> (9)

In the previous section, we introduced the loss modulus G" which represents the

heat which is the conversion of energy of ultrasound absorbed by the glass.

finite element simulations is [6]

Ultrasonic Vibration-Assisted Hot Glass Embossing Process

DOI: http://dx.doi.org/10.5772/intechopen.86546

Figure 12.

Figure 13.

23

Embossing load at initial temperature of 425°C and at different speeds [8].

Experimental result of stress relaxation at 556°C (Tg + 50°C) and the fitted curve [9].

energy dissipated by the material. The significance of G" is made apparent by calculating the energy absorbed by the specimen. If dissipated energy is converted to heat completely, then the heat generation rate which would be inputted into the

During the embossing stage of the ultrasonic hot glass embossing process, besides embossing load (force or displacement input), high-frequency longitudinal waves are applied to the mold; thus, using this kind of load is similar to applying an oscillating load to the glass material. As propagating through the glass material, the energy of ultrasonic vibration is absorbed and converted into other kinds of energy. Since glass is an amorphous material, energy of ultrasonic vibration should be mostly converted into heat. The amount of heat will cause the temperature rise of both glass and molds, which should be the explanation for experimental observations, including the reduction of embossing force and the improvement of the micro-replication of the glass. In order to model the glass behavior during the

Figure 10. Force-displacement results for the flat hot embossing experiments [7].

Figure 11. Reduction of embossing load with different embossing temperatures [8].

Ultrasonic Vibration-Assisted Hot Glass Embossing Process DOI: http://dx.doi.org/10.5772/intechopen.86546

3.2 Viscoelastic dissipation during the embossing stage of ultrasonic hot glass

During the embossing stage of the ultrasonic hot glass embossing process, besides embossing load (force or displacement input), high-frequency longitudinal waves are applied to the mold; thus, using this kind of load is similar to applying an oscillating load to the glass material. As propagating through the glass material, the energy of ultrasonic vibration is absorbed and converted into other kinds of energy. Since glass is an amorphous material, energy of ultrasonic vibration should be mostly converted into heat. The amount of heat will cause the temperature rise of both glass and molds, which should be the explanation for experimental observations, including the reduction of embossing force and the improvement of the micro-replication of the glass. In order to model the glass behavior during the

embossing process

Noise and Vibration Control - From Theory to Practice

Figure 10.

Figure 11.

22

Force-displacement results for the flat hot embossing experiments [7].

Reduction of embossing load with different embossing temperatures [8].

embossing stage with the assistance of ultrasound, it must determine the amount of heat which is the conversion of energy of ultrasound absorbed by the glass.

In the previous section, we introduced the loss modulus G" which represents the energy dissipated by the material. The significance of G" is made apparent by calculating the energy absorbed by the specimen. If dissipated energy is converted to heat completely, then the heat generation rate which would be inputted into the finite element simulations is [6]

$$
\dot{q} = \mathbf{f} \cdot \boldsymbol{\pi} \cdot \mathbf{G}'' \cdot \mathbf{e}\_0^2 \tag{9}
$$

Figure 12. Embossing load at initial temperature of 425°C and at different speeds [8].

Figure 13. Experimental result of stress relaxation at 556°C (Tg + 50°C) and the fitted curve [9].
