The quality and precision of parts produced by Fused Deposition Modeling (FDM) are influenced by several factors during the 3D printing process. Understanding these factors is crucial for optimizing the manufacturing process and ensuring high-quality output. In this article, we will analyze the key factors that affect the FDM process, including material properties, temperature control, extrusion speed, layer thickness, and more.

1. The Impact of Material Properties

The material used in FDM has a direct effect on both the molding process and the final precision of the printed part. The material undergoes two phase transitions—solid to liquid and back to solid—during the process. Stress-induced deformations due to material shrinkage during the solidification process can affect the part’s accuracy.

For example, with ABS filament, two primary factors contribute to shrinkage:

• Thermal Shrinkage: Thermal expansion causes the material to undergo a volume change as it cools. This is the most significant factor contributing to material shrinkage.
• Molecular Orientation Shrinkage: During the printing process, the molten polymer material is stretched in the filling direction. Upon cooling, this stretching leads to shrinkage. The shrinkage rate in the filling direction is greater than in the perpendicular direction.

To improve dimensional accuracy, reducing the material’s shrinkage rate is key. This can be achieved by improving the material’s formulation. Furthermore, compensating for shrinkage during the design stage is essential. Most software allows for applying a “shrinkage compensation factor” in the XYZ axes, where the final dimensions of the part are adjusted slightly larger to account for expected shrinkage during cooling.

2. Influence of Nozzle and Chamber Temperature

Both nozzle temperature and build chamber temperature are critical for ensuring good material flow and adhesion in FDM printing.

• Nozzle Temperature: The nozzle temperature determines the material’s viscosity, extrusion rate, and layer adhesion. If the nozzle temperature is too low, the material becomes more viscous, slowing down extrusion, which can lead to clogs and weaker interlayer bonding. Conversely, if the temperature is too high, the material becomes too liquid, leading to excessive flow, inaccurate filament deposition, and potential collapse of the printed layers.It is crucial to select the appropriate nozzle temperature based on the filament’s properties to ensure smooth and accurate extrusion.
• Build Chamber Temperature: The temperature of the build chamber influences thermal stress in the printed part. A chamber that is too hot can lead to surface wrinkling, while one that is too cold can cause the printed material to cool too quickly, resulting in warping and poor layer adhesion. Generally, setting the chamber temperature about 1-2°C lower than the material’s melting point can help maintain part stability.

3. The Impact of Extrusion Speed

Extrusion speed refers to the rate at which molten filament is pushed through the nozzle. As extrusion speed increases, the width of the extruded filament increases. However, if the extrusion speed exceeds a certain point, the material begins to adhere to the cone-shaped outer surface of the nozzle, leading to printing problems.

Extrusion speed must be carefully balanced with the filling speed to ensure a consistent and smooth deposition of the material.

4. The Interaction Between Filling and Extrusion Speed

The filling speed (the rate at which material is deposited to fill the area between layers) must be well-matched with the extrusion speed for proper material deposition.

• If the filling speed is faster than the extrusion speed, the printed part will have insufficient material in certain areas, leading to gaps or broken strands of filament.
• On the other hand, if the filling speed is slower than the extrusion speed, excess material will accumulate on the nozzle, causing an uneven surface with bumps or blobs, thereby affecting the surface finish and overall part quality.

Achieving an optimal balance between these two speeds is essential for ensuring smooth and accurate layer formation.

5. The Effect of Layer Thickness

Layer thickness refers to the thickness of each slice of the 3D model during the printing process. Thicker layers may reduce processing time but tend to result in a rougher surface with visible “steps” along the printed object’s surface. This can negatively impact the part’s dimensional accuracy and surface finish.

For FDM, it is not possible to entirely eliminate the step-like pattern on the surface of the printed object. However, thinner layers can reduce the visibility of these steps, leading to higher surface quality, although they also increase processing time.

Conversely, thicker layers can speed up the printing process but sacrifice surface finish. Striking the right balance between layer thickness and processing time is key to improving the part’s overall quality.

6. The Impact of Printing Time

The total time required to print a part depends on several factors, including the area to be filled, the complexity of the part’s shape, and the printing speed. For smaller or simpler parts, the printing time may be short, while larger or more complex shapes require more time to print.

The printing time also affects the cooling and solidification of layers. If each layer’s formation time is too short, the material may not have enough time to solidify before the next layer is deposited, leading to issues like collapse or stringing. On the other hand, if the layer time is too long, excess heat could cause warping or unwanted deformations.

For parts with small cross-sections, additional cooling methods, such as applying forced air, may be used to accelerate the cooling process and ensure stability during the printing of subsequent layers.

7. The Influence of Scanning Path

The scanning pattern during FDM printing plays an important role in determining the precision and internal stress distribution of the printed part. There are several common scanning strategies:

• Spiral Scanning: The path starts from the center of the part and spirals outward. This method ensures smooth surface transitions but may not be the most efficient for certain geometries.
• Offset Scanning: This method scans in a zigzag pattern, moving in and out of the part’s contour layer by layer. This method often offers better dimensional accuracy on the outer contours.
• Rotational Scanning: This method involves scanning along the X and Y axes, followed by a rotation step. While this method is less efficient than others, it simplifies the path and is often used for parts with rotational symmetry.

Using a combination of these scanning techniques can help balance surface finish and scanning efficiency. For example, offset scanning is used for outer contours, while rotational scanning is used for internal filling, optimizing both the surface quality and the overall process speed.

Conclusion

The FDM process is influenced by a variety of factors, including material properties, temperature settings, extrusion speeds, layer thickness, and scanning techniques. By carefully managing these variables, manufacturers can improve the precision, strength, and surface quality of the printed parts. Understanding and optimizing these factors is key to achieving high-quality results in FDM 3D printing.