Glass 3D printing design rules

This documents describes the applicable design rules for the Glass 3D printing process on Shapeways.

  1. About the production process
  2. Maximum object size
  3. Minimum wall thickness
  4. Make large and irregular shapes hollow
  5. What is distortion?
  6. Avoid abrupt changes in thickness
  7. No moving parts
  8. Models must be self-supporting
  9. Watch out with very thin connections
  10. A combined example: bird in a cage

About the production process

Tiny spherical glass particles are bound together with an organic binder, and cured in an oven. This step is comparable to how Metal printing works – the object is built layer by layer. The glass particles are only held together by the binder. In this stage, which is referred to as the 'green' stage, the printed objects are still very brittle.

Next, the 'green' products are 'fired' in an oven. At a temperature of over 750 degrees Celsius, the glass particles fuse together into a solid object. During firing, the product density increases and the object slightly shrinks in size.

After firing, the product is ready to be shipped.

Fun fact: The glass powder is recycled glass, and the parts made with it are also 100% recyclable. Also, as with most 3D printing processes, there is no solid waste in our process.  All glass powder which is purchased for printing can be recycled continuously until it is literally used up in the making of glass models.

Maximum object size

The larger the design become, the higher the failure rate. We currently support sizes of up to 75mm x 75mm x 75mm.

Minimum wall thickness

The minimum wall thickness for glass is 3mm.

Make large and irregular shapes hollow

A complex design, such as that of anything organic, like a person or frog, will have varying cross-sectional thickness which can lead to distortion. Making the design hollow eliminates many of these inconsistencies.

Also, the glass itself has very little color to begin with, but it does have a greenish tint to it, and the thicker the cross-section the more apparent this green hue becomes. This is in the production of any soda-lime glass, and if you care, you only need to compare the apparent difference in color of a car window. These differences in color become more evident in solid parts with varying cross-sectional thicknesses, and hollowing these pieces out would make the piece appear more consistent in color. The High Gloss Black Glass and the High Gloss White Glass are made from sode-lime glass but with a black or white finish.

What is distortion?

Distortion is the result of inconsistent shrinkage during the sintering process. The printed parts are comprised of roughly 60% solid material after printing, and during densification while sintering can shrink to roughly 80% of their original gross volume.

A solid sphere would shrink rather uniformly, so distortion in that case would be limited to affects due to the force of gravity alone, but as the shape of the part becomes more complex, the shrinkage becomes less consistent, which usually leads to distortion to some degree or another.

Since shrinkage is a percent change in volume, the greater the part is in size, the greater the stresses induced by inconsistencies in shrinkage are and therefore, the greater potential for distortion.  Some distortion is very predictable, as in the case of a printed cube which will always come out of the firing process with the surfaces being slightly concave.  However, there are many causes of inconsistent shrinkage, such as changes in cross-sectional thickness, which would cause even more significant and troublesome deformation that is often hard to predict, especially with complex shapes.

Avoid abrupt changes in thickness

Like above, an abrupt change in thickness will cause quite a bit of stress and distortion during firing and cooling of your product. In the example below, the transition occurs where the 'flame' connects to the body.

If an area has a transition from thick to thin it would have to have a large radius to prevent cracking.

Turret 2” by Lsutehall

No moving parts

In glass, we cannot under any circumstance keep parts loose no matter what gap is provided. The following models cannot be printed in glass:

A 3D mesh & 2D chain”, by saint

Designs must be self-supporting

This technique cannot print 'floating' product parts. For example, the following material would probably crack:

Escheresque Face peeling”, by BAROBA

Watch out with very thin connections

The droplet below necks down to a very thin cross-section. The droplet on the end is too large then goes to a small cross-section. This will crack or tear.

Water Crown Chopsticks stand”, by wuct88

A combined example: bird in a cage

As an illustration, here's a product and the requirements that it needs to satisfy:
  • The bird inside the cage cannot be loose and should be attached to the cage. (No moving parts requirement).
  • The bird would have to be hollow. (Preventing distortion and cracking of irregular and large bodies).
  • Also the wire cage cross-section needs to be 3mm.

Happy bird micro” by Michiel Cornelissen