Experimental study and numerical analysis of compression molding process for manufacturing precision aspherical glass lenses

Aspherical glass lenses are increasingly being used in consumer products like high power laser generators, digital cameras, projectors and scientific instruments. However, conventional manufacturing processes are not suitable for medium to high volume production of aspherical glass optical elements. Recently, compression molding has emerged as a promising alternative in which a glass gob or blank is pressed in a single operation into the shape of a finished lens. Annealing of the formed lens is required to achieve optical quality. The process is net shape, environment friendly and suitable for high volume production. Further implementation of this innovative process is hindered by technical challenges associated with curve conformance, tooling cost and mold life.; This dissertation research seeks a fundamental understanding of the lens molding process by adopting a combined experimental, analytical and numerical Finite Element Method (FEM) approach. Preliminary experiments were performed involving molding of a test aspherical glass lens on a commercial lens molding machine to study process capability to manufacture an optic component within the desired specifications. Experiments were also performed to determine the effect of different molding parameters i.e. molding temperature, velocity and cooling rate on the final molded lens quality.; A compression molding machine was designed and built in the laboratory on which viscoelastic glass material characterization was performed under lens molding conditions. High frequency dynamic measurements using Brillouin light scattering technique were performed to measure the elastic modulus of glass at lens molding temperatures. The measured glass properties were used as input to the numerical simulation of cylinder compression experiments as well as lens molding experiments. A numerical FEM simulation model of lens molding was developed and predictions were compared with the experiments. Additionally, a 1D analytical heat transfer model during lens annealing has been presented that takes into account transient heat transfer at the glass-mold boundary. The possibility of implementing molding to make microlens array, freeform lens and diffractive lens has also been demonstrated.; Experimental results have showed that molding process is capable of producing precision glass lenses with shape and form accuracy comparable to lenses manufactured using conventional abrasive techniques. Within the range investigated, the experiments did not show a significant influence of the molding parameters on the final lens quality. The FEM simulation model incorporating stress and structural relaxation properties showed excellent agreement of predicted lens curve shape with experimental measurements. Additionally, numerical simulation was able to predict, residual stress in the glass lens as a function of process parameters which shows that FEM can possibly be used to predict, optimize and improve the performance of a lens molding process.