Development of a friction model characterizing the temperature-, relative velocity-, and contact normal stress-dependent behaviors at glass-mold interface in Precision Glass Molding (FriPGM)
Final Report Abstract
The overall goal of this project is to enhance the understanding of tribological behaviour at the glass-mould interface during the Precision Glass Moulding (PGM) process. Glass moulding is a key manufacturing technology for producing high-quality optical components used in applications ranging from consumer electronics to automotive systems and semiconductor components. A critical aspect of this process is the interaction between glass and mould surfaces, particularly under the extreme conditions of high temperature and mechanical loading. However, the fundamental understanding of how friction and heat transfer behave under these dynamic conditions has remained limited, largely due to the lack of suitable experimental tools. To address this gap, the project developed a novel experimental setup - a Pin-on-Cylinder (PoC) tribometer - specifically designed to enable the simultaneous measurement of friction and contact heat transfer under dynamic, nonisothermal conditions. Unlike traditional tribological testing methods, which are restricted to isothermal environments where the temperature of the contact pair is identical and remains constant, the new PoC tribometer allows for realistic simulation of the highly dynamic conditions encountered during glass moulding. This includes rapid changes in temperature, varying contact stresses, and high sliding velocities, which are essential factors influencing the quality and reliability of the final glass optical components. The experimental investigations carried out with the new tribometer revealed that the friction behaviour of glass strongly depends on the temperature. In particular, friction coefficients were found to vary significantly at temperatures below the glass transition temperature (Tg), while becoming more stable as the glass material approached Tg. Additionally, the ability to simultaneously capture both friction and heat transfer characteristics in a single test run significantly reduced experimental effort and increased the reliability of the measurements. The results obtained were integrated into advanced simulation models for glass moulding processes. By incorporating more accurate friction and heat transfer coefficients into simulations, the project improved the prediction accuracy for the final shape and optical performance. The outcomes of this project not only contribute valuable insights to the scientific understanding of high-temperature tribology in glass forming but also have direct implications for industrial applications. In the future, the findings and methods developed could help optimize mould designs, improve product quality, extend mould service life, and reduce manufacturing costs in precision glass optics production. Furthermore, the developed tribometer concept can be directly transferable to other material forming processes beyond glass, supporting broader advances in high-temperature manufacturing technologies.
Publications
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Modeling relaxation nature of nonequilibrium glass in nonisothermal glass molding, Dissertation, RWTH Aachen University
Vu, A.T.
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Precision Glass Molding of Fused Silica, Technical Presentation at International Academy for Production Engineering, CIRP Meetings, PARIS, France
Grunwald, T. & Bergs, T.
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A novel method to investigate tribological behaviors under transient temperatures using Pin-on-Cylinder tribometer and IR-thermography in glass forming, Materials Forming Conference - ESAFORM, Presentation to [8], Toulouse, France.
Vu, A.T., Grunwald, T. & Bergs, T.
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A novel method to investigate tribological behaviors under transient temperatures using Pin-on-Cylinder tribometer and IR-thermography in glass forming. Materials Research Proceedings. Materials Research Forum LLC.
VU, Anh Tuan
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Friction in glass forming: Tribological behaviors of optical glasses and uncoated steel near glass transition temperature. Journal of Non-Crystalline Solids, 642, 123160.
Vu, Anh Tuan; Grunwald, Tim & Bergs, Thomas
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Glass Forming at Extremes: Challenges and Perspectives in Molding Fused Silica Glass, 97. Glass-Technology Conference (DGG), Aachen
Vu, A.T., Karimova, A., Grunwald, T. & Bergs, T.
