Fused Deposition Modeling (FDM) is a 3D printing technology that extrudes molten thermoplastics in a precise toolpath to form a three-dimensional structure. Despite being an accurate and repeatable technology, FDM printing has its limitations. FDM printing can take longer to produce each individual part compared to some traditional subtractive manufacturing methods. However, the customizable nature of FDM printing allows us to manipulate components of the print file to increase the print speed and ensure that the mechanical properties won’t be impacted. In this article we will discuss how the part infill patterns and shell properties influence print time and structural integrity.

Infill Patterns

First, we will discuss infill. It is rare that FDM parts are produced completely solid, like injection molded parts. This is simply due to the amount of time required for the toolpath to cover all aspects of the internal cross sections of the part. In order to avoid this and retain the structural integrity of the part, the slicing software will create internal structures known as infill.

Typically, infill can reduce the parts overall density by 80%. This greatly reduces the print time and the overall material and operational cost of the machine. However, the percentage of infill density has a direct negative impact on the strength of the part. Although, the savings in both time and production cost generally outweighs the loss in part strength.

In addition to infill density, infill patterns and orientation have a big impact on overall strength of the printed part. Despite having the same infill density, some of the strongest infill patterns are Triangular or Hexagonal, which have more desirable strength properties than others such as Sparse. If it is important for the parts to be isotropic, the designer can use custom groups in the insight slicing software and select the Gyroid infill pattern. This pattern is symmetrical in several planes, resulting in the ability to mimic structural uniformity regardless of the direction the load is applied.

Shell Thickness

Next, we will discuss how Shells impact the structural properties of a FDM print. In a FDM print, the shell is a consistent contour that maps out the physical surface of the part. The shell is also the separation barrier between the parts infill and the external surface of the part. In both GrabCad and Insight, you can manipulate the thickness of the shell wall, which in turn will affect the parts density, strength, and rigidity. Intuitively, as you increase the shell thickness you will also increase the parts strength. However, this again will increase the amount of material needed for the build, increasing the parts time and cost. Due to this, it is important for the designer to have a wall thickness that can sufficiently withstand the parts load and conditions but not over design the part to the point where the parts build time becomes inefficient.

Understanding the parts final application gives the designer the ability to manipulate both the infill pattern and shell properties. With proper planning, parts will meet the structural requirements of the application with the least amount of material and machine time. These techniques should be implemented and fine tuned to ensure a more efficient process with lower cost per part and optimal performance.