Understanding and Preventing 3D Print Warping

Ever wonder why your 3D prints curl up at the corners like a sad smile? Most people immediately point the finger at poor bed adhesion and start reaching for glue sticks, bed adhesive helpers or cranking up the brim settings.

While keeping your print stuck to the plate is important, it’s actually not the root cause of warping. If you want to stop the "warping" for good, you have to understand what’s happening at a microscopic level during the cooling process.

TABLE OF CONTENTS

• The Stages of Cooling
  • 1. From Printing Temp to Glass Transition (Tg)
  • 2. Below the Glass Transition Temperature
• Amorphous vs. Semi-Crystalline Materials
• 5 Practical Ways to Stop the Warp
• Pro-Tips for Better Success

The Stages of Cooling

To understand warping, you have to look at how plastic behaves as it cools down. This happens in two distinct stages:

1. From Printing Temp to Glass Transition (Tg)

• As the molten plastic leaves the nozzle, the polymer chains are moving fast. As they cool toward the Glass Transition Temperature (Tg), they slow down and eventually lose their ability to rearrange.
• If this happens too fast, because of a cold room or high fan speeds. The polymer chains get "trapped" in a high-stress state. This creates internal tension (residual stress) before the parts even solidified.

2. Below the Glass Transition Temperature

• Once the plastic is solid and drops below its Tg, it begins to shrink toward the temperature of the surrounding air. The bigger the gap between the material's Tg and your chamber temperature, the more it wants to shrink. Since the print doesn't cool all at once, new layers constantly pull on the older ones, eventually overpowering your bed adhesion.

Amorphous vs. Semi-Crystalline Materials

Not all filaments are created equal. How they warp depends heavily on their molecular structure:

• Amorphous (PLA, PETG, ASA, PC): These stay arranged like a "bowl of noodles" with no specific order. They lose almost all strength once they hit their Tg.

• Semi-Crystalline (Nylon, PET, PPA): These form tightly packed, strong regions between their melting point and Tg. These materials stay stiff even above their Tg and only fail when they hit their actual melting point.

The Paradox: For semi-crystalline materials, higher chamber temperatures actually help form these strong regions, making the part tougher. However, because these regions are more dense, they can actually cause more shrinkage and warping. So this why some nylon can be printed in open chamber but will require post processing like annealing to improve layer strength/stiffness. 

5 Practical Ways to Stop the Warp

If you're tired of seeing your prints lift, try these five strategies instead of just adding more glue:

1. Close the Temperature Gap: Keep your chamber temperature as close to the material's Tg as possible without causing the part to droop or your hotend to jam.

2. Kill the Cooling Fan: Use minimal or no part cooling, especially if you don’t have steep overhangs.

3. Choose Better Materials: Some filaments naturally shrink less than others.

4. Use Additives: Filaments reinforced with carbon fiber or glass fiber warp significantly less.

5. Smart Bed Adhesion: Yes, use glue or a clean PEI plate, but don't expect it to fix a temperature problem.

Pro-Tips for Better Success

• Design for Cooling: Avoid sharp 90-degree corners on the bed. Rounded corners allow for a more even cooldown.

• Pick the Right Infill: Patterns like Gyroid can stretch and flex with the internal stresses, whereas Grid or Triangle patterns pull hard on the outer walls.

• The Patience Rule: Never rip a print off the bed while it's hot. Let it cool to room temperature so the bottom layers solidify completely, or you might permanently deform the part while bending the plate.

Need help dialling in your chamber settings for a specific material? I can help you find the ideal temperature range to avoid both warping and hotend jams. [Contact us]