Lens manufacturing technique avoids expensive molds

Researchers developed a liquid mold from droplets that they can manipulate with magnets to create lenses in a variety of shapes and sizes.

Researchers from Washington State University and The Ohio State University have developed a low-cost, easy way to make custom lenses that could help manufacturers avoid the expensive molds required for optical manufacturing.

Led by Lei Li, assistant professor in the School of Mechanical and Materials Engineering, and graduate student, Mojtaba Falahati, the researchers developed a liquid mold from droplets that they can manipulate with magnets to create lenses in a variety of shapes and sizes.

Their work is featured in the journal Applied Physics Letters.

Traditional molding and casting processes for manufacturing high-quality lenses require expensive metal molds, which can limit manufacturers to mass production of one type of lens.

“The molds are precisely finished and are difficult to make,” Li says. “It isn’t worthwhile to make a mold for low-volume production.”

The researchers ran into the problem as they searched for lenses for their work to develop a portable laboratory reader on a phone, so at first tried to 3D print their own lenses but found it difficult to control the lens’ shape.

Then they came up with the idea of using magnets and surface tension of liquids to create free-flowing molds.

They placed tiny, magnetic iron particles into liquid droplets and built a device to surround the droplets with magnets. They then poured the plastic material used in lenses over the droplet. As they applied a magnetic field, the droplet took on a conical lens shape – creating a mold for the plastic lens material. Once they cured the plastic, it hardened and had the same optical properties and imaging quality as a commercially purchased lens. The liquid droplet remains separate and can be re-used.

The magnets can be moved to change the magnetic field, the shape of the mold, and the resulting lens. The researchers also used bigger or smaller droplets to create lenses of varying sizes.

The work was funded by the National Science Foundation.