3D printing is fun, fast, and highly effective—but it is more art than science. Trial and error printing is a common experience among users, as prints almost never turn out as expected on their first try. Many things can go wrong in a print, but warping is by far the most common occurrence in 3D printing that delays many projects. This article will help those frustrated with their warped prints by explaining how warping happens and how to prevent it in consecutive projects. Pragmatic steps and avoidable mistakes will also be included to provide real world solutions to this pesky manufacturing defect.

As you can see, the filament is extruded through the heated nozzle, changing phase into a liquid (or melts). It then condenses back into a solid (or cools) to form a part layer once it is laid on the build platform. Thermoplastics retain their mechanical properties across multiple phase changes, making them ideal for 3D printing applications; however, they are not exempt from physical effects like expansion and shrinkage during these phase changes. For example, ABS plastic shrinks up to 1.5% when cooled from 446F to ambient temperatures. Uneven heating and cooling between layers are the primary sources of warping, where cooler layers pull on hotter layers and cause them to bend. 

Warping tends to show itself at the base of the print, as the bottom layers have a longer time to cool and are therefore subjected to the effects of all successive layers above it. Figure 2 shows the basic sequence of events that lead to warping:

As hotter layers cool on top of already cool layers, they tend to pull up on the bottom layer and cause warping. This effect is especially apparent at the interface between the first layer and the print bed, as the first layer is fixed to it and cannot contract, meaning it will experience the highest curling forces from the next layer. This problem also scales with size- the larger the layers, the stronger the forces warping your print. 

A second source of warping can be caused by the above effect, where the first layer of a print adheres well to the build platform but warps the actual print bed with it. This usually happens with large parts on spring steel plates and is mitigated with print beds made of glass or other non-ductile materials. Misalignment of the print bed is also a common cause of warping, where the nozzle is not close enough to the platform and creates a weak connection between the part and the plate. These are rare effects, but if the below tips do not reduce warping, then you should check your print bed for curvature and/or its level. 

A draft shield can also be a cheap and effective means of temperature control. Draft shields are essentially walls printed concurrently around a 3D print that will prevent drafts and air currents from cooling a part too much. Figure 3 shows an example of a draft shield in modeling:

The last means of temperature control is through the ambient temperature around the print. Close all doors and windows in the room when a 3D print is on, and if it is still too drafty/cold you can place the printer near a heat source (baseboard, radiator, heat ducts, computers, etc.). Just make sure there is not too much heat- otherwise, you can damage your printer and make a bad situation worse!

Adhesives

Applying adhesive glues to the build plate before printing is probably the easiest (and one of the best) methods of warping prevention. The type of adhesive largely depends on the material, but common adhesives include hairspray, a PVA glue stick, blue painter’s tape, polymer adhesives, or proprietary build plate tape.

Slicer/model settings

Settings in the model and the slicer software can also help reduce warping. Making the first layers thicker will not only adhere to the build plate easier, but the additional material will also make it warp-resistant. A slower print speed and lower nozzle temperature can also reduce warping simply by minimizing temperature differences; however, the print will naturally take longer. 

Adding specific features to the model can also prevent warping such as brims, rafts, skirts, and mouse ears. See Figure 4 and 5 below for visual examples of these features, along with their basic descriptions. 

Skirt: an outline surrounding the model (but not actually touching the model) meant to prime the nozzle and even out material flow (a in Figure 4).

Brim: A single/ few layers of material attached to the edge of the 3D print’s base meant to counteract pulling forces on the initial layers and increase bed adhesion (b in Figure 4).

Raft: A thick layer of material that serves as a base for the print, creating better grip on the build plate and removing initial layer warp effects from the part (c in Figure 4).

Mouse ears: Thin circular layers placed near the corners of a 3D print to reduce warping while conserving material (also sometimes referred to as brim ears). Mouse ears are less wasteful, easier to add, but are more targeted that the features in Figure 4:

Finally, altering the infill density of voids can help warping. Denser infills (such as a and d in Figure 6) will impart stronger pulling forces than less dense infills (c and b in Figure 6).

Printer Maintenance

The last way to avoid warping is to ensure your printer is clean and calibrated. Before every print, you should use a microfiber cloth on the build plate with either some ammonia-based cleaner or isopropyl alcohol. This will remove previous adhesive, grime, and grit that may make the print less sticky. 

Check the fan speed in the printer settings to ensure it remains off/slow during the first few initial layers, or for the whole print if using high temperature filaments. As previously mentioned, also make sure that the build plate is leveled and un-warped. Finally, calibrate the extruder head so that its Z-coordinates are adjusted to prevent unnecessary layer cooling—some newer 3D printers come with level sensors that self-adjust, making this step much simpler.