Developing 3D-Printed Glass Optics and Microfluidics

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3D printing can be used to make intricate 3D objects, and has proved to be very useful in the formation of complex components, such as those used in aerospace and even artificial limbs. However, the variety of materials that can be used in the process has, until lately, been limited. Currently, new advances in the technology mean materials such as glasses and metals can be used in 3D printing.

3D printing uses computer-aided design processes to construct objects layer by layer. Items can be of any shape. This contrasts with material detached from a blank in conventional machining or molding of products in injection molding processes. The age of desktop manufacturing is well and truly in progress.

Although materials such as metal, clays, plastic, and even biological cells have been used in 3D printing, the 3D printing of glass has stayed elusive. However, new research has broken this convention and 3D-printed glass to a high quality. It is anticipated that this is going to have a huge impact on the production of lenses, laser optics, and other complex glass components.

Why is it Difficult to 3D Print Glass?

Glass is a crucial high-performance material largely because of its unrivaled optical transparency, chemical, mechanical, and thermal resistance and its electrical insulating properties. The problem is that glass, particularly high-purity glass such as fused silica glass, is extremely tough to shape into preferred forms.

The traditional process requires high-temperature melting and casting processes for large objects or the use of caustic chemicals to etch microscopic attributes. These weaknesses have rendered glasses inaccessible to 3D printing. Most groups which 3D print glass melt the glass first and cool it down later, which has the possibility of residual stress and cracking.

Researchers have proven some 3D printing techniques for glass objects but these have considerable disadvantages. Binder jetting has been applied to glass to overcome the high viscosity and high melting temperatures, and sintered glass objects from this technique are on the market. However, they are very fragile and can seem opaque because of light scattering from the glass powders used.

There can also be filaments formed in the glass, which could be the focus of thermal or mechanical stress. A manual wire feeding method is slightly better; however, it restricts control and automation. All-in-all the glass structures created by early 3D printing techniques have been porous, opaque, and with non-uniform internal structures, making them of a lesser quality than glass structures produced using conventional techniques.

3D Printing with Glass Liquid Ink

A team at Karlsruhe Institute of Technology in Germany described in ‘Nature’ on a way to print 3D objects made of pure glass using conventional 3D printing equipment.

The new system is based upon the development of a ‘liquid glass’ ink. This glass ink has a glass nanocomposite, with glass nanoparticles suspended in a photocurable prepolymer. Once 3D printed, the glass is moved to an oven for heat treatment, which cures the glass and burns off the extraneous materials in the composite. The result is an object composed of pure, transparent fused silica glass, and can be printed with features on the micrometer scale.

The printed fused silica glass is non-porous, having an optical transparency comparable to commercial fused silica glass, and a smooth surface, with an irregularity of just a few nanometers. The process has been improved further by doping the glass ink with metal salts which allow colored glass objects to be printed.

Using Molten Glass as the Medium

The Mediated Matter research groups at MIT have also been examining the 3D printing of glass. The team has used a different method to create the first molten glass material 3D extrusion system, which they can use to create optically transparent items.

Their novel process uses glass from the molten state which is then printed, using a ceramic nozzle to endure the high temperatures, and then annealed. The printing parameters and process are under full digital control, allowing a high repeatability and good dimensional stability. Developing the process was hard – the viscosity of the glass had to be modeled and new systems with variable temperatures in glass kilns had to be created.

The process has been completely modeled, examined, and optimized and this has involved a ceramic nozzle of controlled geometry, modeling glass viscosity, regulating glass levels, modifying the temperature distribution in different kilns, as well as varying layer height and feed rate. Integration of colors was attained as well as the production of coiling patterns to create objects of varying length scales.

Characterization of the produced 3D glass objects displayed strong adhesion between layers and a considerable strength increase when the process was done in a heated build chamber, with approximately 60% of material strength across layers. With regards to optical properties, high transparency was noticed and multifaceted caustic patterns were created with LED light sources based on sample geometry.

3D Printing Glass Objects at Room Temperature

In April 2017, for the first time ever, a team at the Lawrence Livermore National Laboratory (LLNL) 3D-printed transparent glass at room temperature. This technique uses silica inks, which are 3D-printed and thermally processed to create optically transparent glass structures with sub-millimeter resolution features.

The inks have silica powder suspended in a liquid and are printed using direct ink writing. The custom inks that are created from concentrated suspensions of glass particles with extremely controlled flow properties so they can be printed at room temperature. Printed structures are then dried and sintered at temperatures well below the silica melting point to form solid, amorphous, transparent glass structures, which would have formerly required conventional glass fabrication.

Following printing, the object is opaque, but once the printed object goes through a thermal treatment, the material densifies and all indication of printing vanishes. The heat treatment ensures transparency and optically uniformity. The final step is an optical quality polish which allows the glass to acquire optical uniformity.

This technique is mainly beneficial for optical manufacturers as it allows the refractive index of the glass to be controlled. This means glass with varying refractive indices can be created into a single flat optic instead of a complex-shaped optic. Flat optics is a lot easier to polish and refine than traditional curved optics, and it is hoped that this method will make optical components more economical.

Expected Trends in 3D Printing with Glass

The 3D printing of glass is positively going to increase the capabilities of optical engineers, and it is also anticipated to impact the world of microfluidic devices. Glass is a superior material for microfluidics because of its chemical resistance, optical transparency, and it’s facility towards chemical surface modifications. Mo-Sci Corporation in partnership with Northwestern University is presently developing a 3D printing technique for complex-shaped soda-lime, sealing, borosilicate, and other glass components for high-temperature applications.

Technical Glass from Mo-Sci

Mo-Sci Corporation provides expertise and quality in precision glass technology. It can offer a variety of specialty glasses to custom requirements or even work together with other companies in the development of glass materials for revolutionary applications.

References

  1. Kate Cummins, The rise of additive manufacturing, The Engineer, May 2010, Retrieved December 2017
  2. Frederik Kotz et al., Three-dimensional printing of transparent fused silica glass, Nature (2017). DOI: 10.1038/nature22061
  3. John Klein et al., Additive Manufacturing of Optically Transparent Glass, 3D Printing and Additive Manufacturing, Volume 2, Number 3, 2015
  4. D. T. Nguyen, et al., 3D-Printed Transparent Glass, Adv. Mater. 2017, 29, 1701181.

Mo-Sci

This information has been sourced, reviewed and adapted from materials provided by Mo-Sci Corp.

For more information on this source, please visit Mo-Sci Corp.

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