1 Department of Energy Conversion and Storage, Technical University of Denmark 2 Electrofunctional materials, Department of Energy Conversion and Storage, Technical University of Denmark 3 Department of Mechanical Engineering, Technical University of Denmark 4 Manufacturing Engineering, Department of Mechanical Engineering, Technical University of Denmark 5 Department of Wind Energy, Technical University of Denmark
Recent improvements in the manufacturing process of camera lenses have introduced the use of a newtechnology involving wafer based precision glass moulding. The utilization of this technology has someimportant advantages such as cost reduction, supply chain simplification and higher image quality. How-ever, the required accuracy for the final size and shape of the moulded lenses as well as the complexity ofthis technology call for a high level of process understanding and numerical simulation is a very importantpart of achieving this goal. The viscoelastic parameters of the optical glass as well as the glass/mould inter-face friction coefficient play a key role in deformation behaviour and stress distribution of the mouldedglass lens. Therefore, a proper evaluation of these parameters is the first important step in numericalmodelling of the precision glass moulding process.The current paper deals with characterization of the interfacial glass/mould friction coefficient andviscoelastic behaviour of the L-BAL42 glass material above the glass transition temperature. Several glassrings are pressed at three different temperatures to various thicknesses and the experimental force, dis-placements, internal diameter and thickness of the rings are measured during the tests. Viscoelastic andstructural relaxation behaviour of the glass are implemented into the ABAQUS FEM software through aFORTRAN material subroutine (UMAT) and the FE model is validated with a sandwich seal test. Then, byFE simulation of the ring compression test and comparison of the experimental creep with the simulatedone in an iterative procedure, viscoelastic parameters of the glass material are characterized. Finally,interfacial glass/mould friction coefficients at different temperatures are determined through FEM basedfriction curves combined with experimental data points. The obtained viscoelastic parameters and inter-facial friction coefficients can later be employed for prediction of the final shape/size as well as the stressdistribution in the glass wafer during a real wafer based precision glass moulding process. © 2014 Elsevier B.V. All rights reserved.
Journal of Materials Processing Technology, 2014, Vol 214, Issue 7
Wafer based precision moulding; Glass lens; Numerical simulation; Interface friction; Viscoelastic behaviour
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