Creating with glass is an art that dates back centuries. While most bottles and jars made today are mass manufactured, using a technique in which molten glass is filled with pressurized air inside of a form, the art of forming glass by hand is still alive today. Mass manufacturing excels at creating standard shapes, but it requires expensive tooling changes to make custom designs. Making glass by hand requires a skilled craftsman with age-old skills such as blowing and working the glass, and glass blowing is also time consuming. This means that many glass items are still expensive and hard to find.

3-D Printing with glass would allow for both customization and repeatability, while opening up the medium to many more individuals and applications. Being able to print in glass could make replacing specialty glass parts a simple endeavor and allow for the printing of custom decorative or functional parts like lenses.

It may surprise you to learn that we have been able to print with glass for a long time using a selective laser sintering (SLS) type printer, which has been around since the 80s. This type of printer utilizes a laser to
Source: CC BY Robbie SprouleSource: CC BY Robbie Sprouleheat a powdered material until it bonds together. With this method, it is possible to produce parts out of nearly any material that can be sintered with a laser.

Unfortunately, SLS printers are substantially more expensive and much less common than many other printer types; however, they make up for that with their versatility. The problem with glass printed via an SLS printer is that it prints white rather than transparent since it is made up bonded powered glass. Additionally, sintered glass does not have the same structural strength as glass made with other methods, therefore it has not been very popular.

Only more recently have we been able to print clear or mostly clear glass as a finished product. Since the first transparent glass was printed, the technology has advanced much more rapidly.

The first to print transparent glass was MIT in 2015, and the process used was very different that of an SLS-type printer. Instead of heating a glass powder, the design was similar in function to a fused deposition printer (FDM) fed with molten glass rather than a filament. The result was that a thin stream of molten glass was extruded from the nozzle and bonded to the previous layer of molten glass, just as it is done with a traditional FDM printer. The resolution was quite low, and the finished print had a step-like appearance as if it has been made from ropes of glass, because, essentially, it had been. After this initial success, the company Micron 3DP took on the challenge and was also able to print in glass. This time, they achieved a resolution similar to a normal FDM printer. The method they used was similar to what was done at MIT, just in higher resolution. The finished product still has a rough appearance, but the lines are much finer and the part retains its translucent properties and strength.

FDM Printing with transparent glass is much easier said than done because of the extreme heat required to keep the glass molten and prevent thermal stresses as the shape is printed. A common problem with glass is that it builds up internal stress as it cools, unless it is cooled evenly. This is not unlike the problem of plastic curling as it cools, except that instead of curling, the glass shatters. In order to print with extruded glass, the printing area must be heated to very high temperatures and the print head must be able to withstand the flowing of molten glass at about 1,900 degrees Fahrenheit. To achieve this, the inside of the printer is set up like a kiln with molten glass in a heated hopper. To start and stop the flow of glass is also a difficult task, it isn’t like feeding filament. The MIT team stopped glass flow by cooling the nozzle down with air to temporarily solidify the glass. After the parts have been printed, they must be annealed by slowly cooling them to prevent internal stress that would crack them.

The most recent development in printing with glass may point to a future that utilizes a completely different method that is being called Honeycomb structure printed in fused silica glass exposed to a flame of 800 C showing the high thermal shock resistance of the printed glass part. Source: NeptunLab/KITHoneycomb structure printed in fused silica glass exposed to a flame of 800 C showing the high thermal shock resistance of the printed glass part. Source: NeptunLab/KIT“liquid glass.” Printed with the Stereolithography (SGA) method, an ultraviolet cured fluid is used as the printing medium. In the case of liquid glass, the material has a high percentage nano glass particles in it. This method can be utilized with a standard resin-based printer, and without the high temperature required during the printing process. The catch is that the finished printed part is not glass, it must be baked in a high temperature oven to bond the glass particles together. Despite the last step involving specialized equipment, the process is still much easier than acquiring and maintaining a specially designed printer.

In the future, we should expect to see 3-D printed glass parts in more products and custom parts. The potential of this development would make replacing that broken camera lens or matching an antique door knob much easier. After a survey of glass printing methods, it becomes clear glass printing has utilized the majority of printing technologies available (SLS, FDM, and now SLA), proving printing with glass has a shining future.