If managing heat, ensuring strong bed adhesion, and adjusting your slicer settings don't correct the warpage in your 3D printed parts, change your design.

Any manufacturing process that involves cooling plastics or metals will have material shrinkage and distortion issues, whether it's injection molding plastics, metal casting, or 3D printing.

When it comes to plastic injection molding distortion, engineers must consider cooling rate, cavity pressure, and filling rate. Deformation in metal fabrication is controlled by heat, angle geometry and welding techniques.

In 3D printing, warping occurs when the front layers of the print cool at a different rate than the later layers. Distortion of the material can lead to both dimensional problems and aesthetic defects. When large cross-sections of material cool and shrink, they can dislodge elements from their intended locations. You may see surface defects on parts where this occurs, and it can cause fit or flatness problems if the deformation is large enough.

The truth is that in 3D printing all parts deform, it's just a matter of degree. The goal in designing the part is to mitigate this deformation as much as possible and to such an extent that it does not negatively affect the accuracy or aesthetics of the part.

The tips below apply not only to FDM printing, but to almost all 3D printing processes. As such, designing a part to mitigate material distortion also makes it much easier to transition to different materials and different 3D printing processes and still get a good part without a redesign.

Design is not the only factor to consider in 3D printing when it comes to deformation. The importance of heat, bed adhesion and multiple slicer settings are essential.

Flipbook Thinking Exercise

Example of thermal expansion (warping) causing print edges to peel off the bed (Source: Airwolf3d.com)

A good exercise is to visualize the print as a flipbook animation. Flipbooks create rudimentary animations on a sheet of paper by changing the position of the drawn characters from sheet to sheet. If your character doesn't animate smoothly from one sheet to the next, it's immediately noticeable and annoying. Building 3D printed parts is the same thing.

If your design doesn't flow, or worse, jumps from layer to layer, your parts will be at risk of problems. So if there are sudden changes in cross-section, your goal should be to make that transition more gradual either by changing the design or changing the orientation of the structure. The print should flow cleanly from layer to layer and present an organic flow of cross-sections. A part that flows smoothly through the entire structure is an accurate and aesthetically pleasing part.

Fortunately, the preview in your slicing software can show you how your part will be built layer by layer. Pay close attention and note any jumps or gaps or rough cross sections.

Choose organic shapes

The organic shapes of 3D printed lattice structures on a carbon resin printer (Source: Carbon3D)

There's a reason you see so many 3D parts in production take an organic wood-type shape instead of having hard edges and corners.

For many parts, adding radii (curves) to solid edges is the easiest way to reduce material deformation. By adding a radius, the change in cross-section becomes smoother from layer to layer. Adding radii to inner edges is more efficient than outer edges, but if your design allows it, it wouldn't hurt to add radii to outer edges as well. The radius can be quite small but have an excessive impact. For example, a radius of 0.15 mm is sufficient to help relieve the stress that builds up at that edge. The larger the radius, the better, until it starts to significantly affect the wall thickness. In general, the more the part resembles a melted candle, the better, since melted candles organically form curves as they drip, rather than creating sharp breaks. This is a more natural geometry.

Fracture angles and uniform wall thickness

An example of warping and splitting layers (Source: All3DP)

Hard angles (of 90 degrees) on parts usually result in drastic changes in cross-section unless they are built at complex angles. Wherever your design allows, consider splitting those 90 degree angles into two 45 degree angles instead.

Another good practice for parts intended for 3D printing is to ensure uniform wall thickness as much as possible. If a part quickly changes from thin to thick or thick to thin, this creates a large change in cross-section during printing and can cause the material to shrink. Some designs need thick and thin sections. In these cases, add radii or otherwise make the transitions as smooth as possible.

So what wall thickness should you use? It varies by material, geometry and printing process, but a good starting point is for the wall thickness to be 1% of the longest dimension of the part. This means that the 4 inch (101.6 mm) part is 0.040 inch (1.016 mm) thick and the 9 inch (228.6 mm) part is 0.090 inch (2.286 mm) thick. When you get under 3 inches (76.2 mm) you want it to be a little thicker, and when you get over 10 inches (254 mm) you want the wall to be a little thinner. If the design is more stable, it can be thinner, and if the design is fragile or not so stable, make the side a little thicker.

If a thick part element is required, we recommend hollowing the element into a shell approximately 0.100 in. (2.54 mm) to 0.125 in. (3.175 mm). If possible, match the total thickness of your part to the thickness of the case of the large element.

Rethink the orientation of the build

Deformation Example (Source: Protolabs)

If a part cannot be reworked to mitigate the distortion, another factor to consider is orientation. Orientation thinking should "tie the book" of your design process. This should be done in two stages. You want to plan around a build orientation at the beginning of your part design and rethink it again at the end. Often the first attempt at orientation is orthogonal, but many parts can be built more accurately at a more complex angle. Think of a part that is roughly shaped like the letter H, and think about the flipbook animation thought exercise. When the part is built up to the center bridge, the material steps at once, pulling both legs underneath.

So how do you fix this? Adding a radius to the hard inner edges will make the transition smoother and alleviate, but probably not eliminate, the problem. So more needs to be done. How about tilting the H at a 45 degree angle? Now the bridge is not stepped on at once, and the transition will be much smoother and more organic.

For some parts, the 45 tilt may not be necessary. Even a 10 or 15 degree incline can help. However, this can have a negative effect on layer lines or maintenance requirements. The negative impact depends largely on the 3D printing technology used. For example, Selective Laser Sintering (SLS) or Multi Jet Fusion (MJF) do not have scaffold supports and do not have significant layer steps, so this is a very common practice for these printing technologies.


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