Evaluation of demolding force for glass-imprint process

Abstract

Demolding behavior of oxide glasses from molds was experimentally analyzed using a specially developed molding set up equipped with highly sensitive load cell and servomotor. The demolding point and the demolding force were apt to increase with the tensile force applied to the pressing axis, and also to the cooling rate. Especially the demolding force was strongly affected by the cooling rate when the demolding point was located near the glass transition temperature region. These results offer a useful direction for highly accurate glass-molding and glass-imprint processes. (C) 2013 Elsevier B.V. All rights reserved

Temperature and rate dependent debonding behaviors of precision glass molding interface

“…In addition, based on the in-depth analysis of the dissipative process, it is formulated that at high separation rate, the fracture energy Γ(V) is a decreasing function proportional to the inverse of the crack velocity 26 : In our cases, the crack length L = 3.45 mm, λ~10 4 is the ratio between Eʺ and Eʹ for BK7 glass, 35 and the stress relaxation time τ(680°C) = 0.003 s, 34 so L/λτ~115 μm/s. From the linear fitting curve in Figure 10B, the results of W deb at intermediate and high levels of a T v c are in good agreement with the theoretical prediction in Equation (9).…”

“…Our work would help better understand the interfacial interactions for glass molding, thus explore feasible physical strategies to mitigate the negative influences of the glassto-mold adhesion during demolding. Besides, the fully characterized debonding behaviors would provide the basic conditions for establishing the traction-separation law in (9)…”

“…The observation that the demolding force increases as the temperature of glass at the separation moment is decreased, has been implicitly confirmed previously. 3,9 But the opposite conclusion was drawn with respect of the "interface" temperature. 2 The contradiction also noticed by other authors, 3,14 could be attributed to the differences in the experiment conditions and the used concept of temperature.…”

“…But even if the chemical reaction is suppressed by coating deposition, remarkable adhesion could still exist because of the physical interaction at least the Van der Waals force. 9,10 No matter the bonding developed in the pressing stage is chemical or physical, the adhesion mainly takes effect in the demolding process where the glass piece is separated from the molds in the cooling stage. During demolding, fatal damage of glass or/and mold could emerge because of the adhesion.…”

“…[1][2][3]9,10,[15][16][17] For PGM, the demolding stress was evaluated in the range of 0.3-0.6 MPa for different mold materials. 9 Generally, the demolding force in hot-forming processes could be affected by numerous factors, including the forming parameters (the interface temperature, 2 pressure and contact duration 3 ), the surface's wetting 10,18 and roughness 19 conditions, the mechanical properties of contact bodies (the elastic modulus of both molds 9 and the pressed piece, 15 and the substrate thickness 16 ), and the material types of mold. 20 The explanations for these factors were mainly attributed to the changes in the physical interface contact status and the extent of chemical reaction.…”