3.3 Effect of ultrasonic vibration on reducing embossing load

During the embossing stage, the mold is controlled by force or by displacement to emboss the glass. In general, at a higher molding temperature, the force required to emboss the glass is lower. As ultrasonic vibration is applied, the forces dropped rapidly, while the displacement continues to increase (Figure 10). However, this force reduction could not remain to the end of the embossing stage. After reducing to a finite value, the force increases again (Figure 11). This interesting effect was not only verified experimentally with different initial molding temperatures but also with different embossing speeds (Figure 12). This phenomenon could be explained by the heating effect of ultrasonic vibration. The high energy of ultrasonic vibration was mainly converted to heat, causing the temperature of the glass specimen to rise.

The force reduction under the effect of ultrasonic vibration is not only a safe solution for the mold but also decreases the molding time of the whole process. The stage which wastes most of the time is the cooling stage. In this stage, the glass needs quite a lot of time for stress relaxation and structural relaxation. The larger

the value of embossing load at the end of the embossing stage, the longer the required cooling time (Figure 13). Therefore, with the significant reduction force as applying ultrasonic vibration, the productivity of hot glass embossing process could

As mentioned above, hot glass embossing is a novel process to produce microstructures on glass substrate. Although the fabrication of microstructure should be performed by conventional process, the accuracy of the final shape of products is hard to achieve due to the surface defect or the adhesion between the glass and the mold as glass is filling into the micro cavities. These disadvantages especially appear

Comparison of the final height of microstructure between conventional process and ultrasonic process [11].

3.4 Effect of ultrasonic vibration on improving glass formability

Ultrasonic Vibration-Assisted Hot Glass Embossing Process

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

be improved.

Figure 15.

25

Figure 14. Scanning electron microscope (SEM) of pyramid structures [10].

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

3.3 Effect of ultrasonic vibration on reducing embossing load

Noise and Vibration Control - From Theory to Practice

specimen to rise.

Figure 14.

24

Scanning electron microscope (SEM) of pyramid structures [10].

During the embossing stage, the mold is controlled by force or by displacement to emboss the glass. In general, at a higher molding temperature, the force required to emboss the glass is lower. As ultrasonic vibration is applied, the forces dropped rapidly, while the displacement continues to increase (Figure 10). However, this force reduction could not remain to the end of the embossing stage. After reducing to a finite value, the force increases again (Figure 11). This interesting effect was not only verified experimentally with different initial molding temperatures but also with different embossing speeds (Figure 12). This phenomenon could be explained by the heating effect of ultrasonic vibration. The high energy of ultrasonic vibration was mainly converted to heat, causing the temperature of the glass

The force reduction under the effect of ultrasonic vibration is not only a safe solution for the mold but also decreases the molding time of the whole process. The stage which wastes most of the time is the cooling stage. In this stage, the glass needs quite a lot of time for stress relaxation and structural relaxation. The larger

the value of embossing load at the end of the embossing stage, the longer the required cooling time (Figure 13). Therefore, with the significant reduction force as applying ultrasonic vibration, the productivity of hot glass embossing process could be improved.
