Some people may think of 3D printing as this magical technology that can turn anything in a computer screen into a real-world three-dimensional object. This is far from the truth, as any 3D printing professional would know. Translating a digital design into a 3D printed object is a process that requires a lot of tweaking, trial and error, and knowledge of many scientific principles.
Dimensional accuracy is something that many 3D printing projects struggle with, particularly in FDM printing . After all, any plastic material will naturally expand or contract when exposed to extreme temperatures. How can one improve the dimensional accuracy of a 3D printed project?
What is dimensional accuracy?
In a nutshell, dimensional accuracy refers to how accurate the dimensions of the 3D printed project is compared to those of the digital model. In a lot of cases, dimensional accuracy isn’t even that important. If you’re 3D printing a project meant just for display, then an error of a fraction of a millimeter hardly matters.
Dimensional accuracy becomes more critical when designing functional parts that have very tight tolerances. These can include replacement components for industrial equipment or functional prototypes of a product being developed.
One thing to note about accuracy is that it is a relative variable. A 3D printed project that is off by 1 millimeter (a large deviation as far as 3D printing goes) still may not look as bad if it measures a few feet across. This means that dimensional accuracy becomes more important when working with small models, such as miniatures and figurines.
What factors affect dimensional accuracy?
Before jumping into ways to improve dimensional accuracy, we must first look at the factors that affect it in the first place. The unfortunate characteristic of 3D printing is that these factors are virtually unavoidable. However, they can be controlled to minimize their effects.
Filament is in a molten state when it exits the nozzle. As soon as it is exposed to the environment, it rapidly starts cooling. This is the physics from which the concept of FDM is based on. However, it is also one of the major causes of dimensional accuracy.
As the material cools down, it starts to contract. However, the hardening of the material and its adhesion to the previous layer counteracts this thermal stress. The goal is to keep this thermal stress from overcoming any of the forces that oppose it, thus helping the material keep its original appearance.
When molten material is first laid down on the print bed, it is in a form that cannot support its own weight. For this reason, it relies on the strength of the previous layer to supports its weight while it cools down and develops strength. This tendency of the material to collapse under its own weight also contributes to dimensional inaccuracy, particularly in the z-axis.