The layer lines from the creation of a 3D part are often considered to be a bad feature of large scale additive manufacturing. But how bad are they and what are some solutions that make 3D Printed parts better than injection molded.
When part is made with high volume production 3D Printing, it is composed of individual layers. Much like the coil pots made from the playdough snakes that you created in kindergarten, only 1000 times smaller (5-30 microns).
Depending on the resolution a part is printed at (generally low resolution for functional pieces and high resolution for cosmetic pieces) the layers can be more or less pronounced. But unavoidably the virgin surface of even a very high resolution part will have a "linearity" to it that is unavoidable even if the layer lines are not individually visible. And the only way to eliminate the layer texture entirely is to post process the part somehow. Either through painting or sanding.
But is that surface finish really a bad thing. Photos below show some average cosmetic and engineering parts made with production FDM 3D Printing.
Why is the Linear Texture Bad?
Let us ask this question. Why are molded parts smooth? Because it is better looking? Actually no. Molds are smooth because they have to be. Did you know that an injection molded part can't really have a texture without incurring huge expenses and design changes. It is exceptionally difficult to apply a texture to molded or machined parts. Because it adds so much complexity to a part. Whereas smooth surfaces are very easy to create and produce. Smooth parts are a result of limited engineering. Not of actual design. We like smooth parts because we have always had smooth parts. Not because we chose to have parts with a smooth surface finish. But 3D Printed parts are not so limited. Textures can be applied for free.
3D Printing Creates Textures for Free
Since 3D Printing is designed to grow a part slowly it is able to give that part any sort of feature or surface finish that is desired by the client. This means that textures are not some secondary process that must be done later. A texture can be designed in CAD and then literally printed with the part. Below is an example of our Texture Cube and Sample Brick. With or without the complex textures on the surface, these parts cost the same to manufacture. That is not the case with traditional methods. And 3D printing can apply any texture you want. From fuzz to diamonds.
These textures have a huge number of applications. They make it possible to print grips onto handles. Create a toy with a truly unique look and feel. Or at the most basic level, hide the layer line of the 3D print so that it is more affordable to manufacture With production 3D Printing you have the equivalent of grain in wood. Only you control the direction and look of the grain.
Hiding the Layer Lines with Textures
The Textures perform a very simple function outside of the purely functional. They help on the asthetic side to hide the layer lines. A texture on a 3D Printed part can be applied to overwhelm the appearance of the the layer lines. This is very evident in the Red Texture cube above. It is impossible to tell the 3D Printed part from an injection molded part. Below are a few parts where the surface of the part was roughened so that the layer lines would be hidden and the surface of the solver part would sparkle.
Hiding the Layer Lines with Material
If a texture of any sort is out of the question. Then there is another option. Create the illusion that the linear texture is not present. The reason layer lines are so visible in 3D Printed parts is because the parts are often monochromatic. So each layer catches and reflects the light, highlighting the layer on the single color part. This problem can be addressed by using a material with particulates added that either roughen it or add specks through the color. This breaks up the appearance of the part and the layer lines are not visible. A good example is shown below with marble-colored filament. The finished part actually looks and feels like stone, even though it was made with 3D printing at a relatively low resolution (larger than normal layer lines)
Lean into the Layer Lines
All of this comes to the point where layer lines are just a part of the process. Just like smoothness is just a part of injection molding. Neither is bad or good. It is just a part of the process. And as part of the process you can use it as a strength rather than as something to hide. The Layer lines in 3D Printing are line the grain in wood. It is random and can look messy. Until someone with skill figures out how to turn that wood into a beautiful table. Designers can do the same with 3D Printed layer lines. And actually do so makes them more like wood than many people think.
Above is a part that was printed with wood-filled PLA filament, at a relatively low resolution. But the layer lines add to the model. They actually give the wooden piece a grain. So that is looks like it was carved from a solid piece of tree trunk. That is practically impossible to achieve with other processes. But the designer found a way to use the layer lines of 3D Printing as an advantage.
Conclusion
The Layer lines of 3D printed parts are often considered a problem. But they don't have to be. There are many ways of eliminating or hiding the layer lines of mass produced 3D printed parts. But good designers will recognize them as simple a feature of the process. A feature that can be exploited to create
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