Metrology
“If You Can’t Measure it, You Can’t Make it.”
At Hexagon Optics, precision begins with measurement. Our state-of-the-art Form Talysurf® PGI Optics PRO enables highly accurate assessment of surface form, ensuring the quality and performance of every optic we produce. Combined with our internally developed OPTIMUM® mold compensation software and advanced design automation tools, this capability allows us to consistently deliver world-class, high-precision components.
Many aspects of Molded Optics require unique metrology from material properties to performance metrics to mechanical features. We have developed many techniques relevant to mold optics and build much of our own equipment. Some examples from our team:
The properties of glass are dependent on its thermal history, for the fast cycle times of precision glass molding this means that the molding process changes the properties of the glass. Most importantly the index of refraction changes, colloquially termed the ‘index drop’. It is important to measure the as-molded index for new glass qualification as well as in-process data. Hexagon Optics measure the as-molded index of refraction of all our qualified glasses.
The process is destructive using an actual molded lens for testing. Measurements are conducted for at least 3 wavelengths, and the as-molded dispersion is calculated.
Hexagon Optics has developed custom metrology for the measurement of the edge radii of molded lenses. A precision glass molded aspheric lens manufactured using a volumetric or finished lens molding process will have corner or edge radii. These radii are not explicitly designed but rather are formed as part of the molding process. Edge radii are the primary volumetric relief for the molding process compensating for the slight variations in preform volume. While seemingly trivial, edge radii are an important parameter when it comes to process control and for mounting a lens within an assembly and should not be ignored.
For non-volumetrically or free molded lenses, the corners are normally chamfered after edging the part to diameter, as the round edges are removed, any reasonable chamfer size can be applied.
Not only do we measure our lenses but we properly qualify all the materials we work with including the glass. We measure the thermal expansion of all qualified glasses by dilatometry. Dilatometry measures dimensional change by placing a sample in a controlled furnace while a high-resolution sensor continuously records its change in length as the temperature is increased or decreased at a defined rate. The resulting expansion curve is used to calculate the material’s coefficient of thermal expansion and to identify key thermal properties such as the glass transition and softening temperatures.
Measurements are conducted for at least 3 wavelengths, and the as-molded dispersion is also calculated. The process is destructive using an actual molded lens for measuring visible wavelengths.
We ensure that every lens meets your exact specifications. Mechanical features including center thickness, diameter, and edge radii are precisely measured. Using our custom-developed equipment, we can economically inspect 100% of these features, guaranteeing consistency and quality across every lens we produce.
Maintaining exceptional surface quality is critical to ensuring the optical performance, reliability, and longevity of precision optical components.
Hexagon Optics has developed custom inspection reticles for evaluating the surface quality of molded optics using industry-standard scratch/dig criteria. These reticles enable fast, repeatable, and highly effective identification of surface imperfections, making them ideally suited for high-volume production environments while maintaining strict quality control.
For larger or conventionally manufactured optical components, surface quality is inspected in accordance with MIL-PRF-13830B and ISO 10110-7, ensuring compliance with internationally recognized optical performance and cosmetic standards.