Investigations into the production of achromatic lenses by two-component injection compression molding of transparent plastics
Final Report Abstract
Transparent polymers are widely used in optical applications. Due to their high dependence of the refractive index on temperature, process-related varying refractive indices and high dispersion of the materials, focussing lenses have different focal positions for different wavelengths. The resulting image defect, known as chromatic aberration, represents a limitation in the use of imaging optics. In the project, the combination of two lenses fabricated by polymers with different dispersion in assembly compression moulding to form an achromatic lens was investigated in order to reduce the chromatic aberration. The basis for this was an in-depth understanding of the material with focus on the pvT behaviour and thermomechanical behaviour for various process sequences. By means of the acquired process understanding, in combination with model tests and a comprehensive component analysis, a general process recommendation was derived. For the best optical properties, a dynamically tempered compression moulding process should be used, in which the shrinkage of the components is compensated through the correct choice of the pressure in the compression moulding process. The process should be further isochoric, as this minimises internal stresses in the component. The contact temperature at the interface between the two components is crucial for the bond. A conflict of objectives between the best optical properties and the bond integrity was identified as part of the research project. A limitation in the derived process control is the need of an adjustment time, which serves to homogenise the melt temperature of the complete cavity volume to the temperature of the dynamically tempered mold, during the production of the first component. To significantly reduce this restriction, the use of blowing agents to reduce the melt temperature during mould filling was also investigated selectively, which proved to be advantageous in terms of economic cycle times.
Publications
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High-Precision Thin-Walled Parts by Injection-Compression Molding with Dynamic Mold Temperature Control Seventh International Symposium Frontiers in Polymer Science. 2023 (Sweden)
Roth, B. & Drummer, D.
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Improving the optical properties of achromatic lenses due to the process conditions Scholars 2nd Edition International Conference on Optics, Lasers and Photonics. 2023 (London)
Natale, R. & Drummer, D.
