Introduction

Due to the nature of polymers, when returning from melted to a solid state the plastic will shrink and cause parts of the 3D-print to “lift” from the buildplate, it could be one side, several or all sides of the print. Many refer to this as “warping” and it´s one of the more notorious pitfalls one may encounter when 3D-printing thermoplastics.

Both internal and outer geometries of any part are subject to shrinkning. The level of warping/shrinking can vary alot between different plastics.


Background

Polymers (thermoplastics) consists of Monomer Molecules. Once extruded the temperature will decrease from extrusion temperature to ambient temperature and the plastic will reach a solid state. This process causes a chemical reaction and the monomers will “rearrange”, this is refered to as Polymerization. The visible effect of this is retraction/shrink and/or warping of the 3D-printed part.

Polymers are generally divided into “Amorph” and “Crystalline” groups and even though the Crystalline polymers are more prone to polymerize this is also common among Amorph polymers.


Symptoms

The symptoms of warping can be easy to identify as parts of the print will lift from the buildplate leaving a gap between the print and the buildplate. In some cases the entire part can detach from the buildplate. Horisontal cracks in the print can also be a a sign of shrinking in combination with unstable build chamber temperature.

Warping is particularly common on large prints, sharp corners and longer thin geometries with small areas touching the build plate.

While also being the reason for warping shrinking is especially noticable on horisontal dimensions and in particular smaller geometries such as holes.


Solution

While we cannot eliminate shrinking or the polymerization itself what we can do is reduce the effects caused by this.

Buildplate adhesion is important. As soon as the part starts to warp you cannot undo it. Heat is also an important factor because it slows down the process of polymerization itself.

Therefore there are a few things to check before initiate a print.


  • Is the print bed leveled and is the nozzle at the right distance from the build plate? If unsure how to check this, have a look in your printers documentation.
  • Use a raft
  • Make sure the buildplate is properly calibrated and in level. 
  • Clean the buildplate, replace it if needed or add an adhesive such as PVA glue or a commercial product engineered specifically for this purpose
  • If the printer have one, use the heated bed. If needed increase the bed temperature slightly. Check the filament manufacturers recommendations. 
  • Heated build chamber can help slow down cooling/polymerization. If the printer is "open" it can sometimes help by enclosing it, putting sheets of cardboard on the sides to keep the temperature around the print stable.
  • Avoid having the 3D printer in a place where drafts occur.
  • As mentioned above some plastics are more prone to shrink than others, consider using other type of plastic.