This paper elaborates and compares how the thickness of the 3D printing layer affects the printing accuracy from different perspectives, and also gives optimization methods to help everyone improve the accuracy of 3D printing
The influence of layer thickness on accuracy in 3D printing
(1) Layer thickness directly affects printing resolution
The layer thickness determines the printing resolution in a way similar to how the number of pixels determines the resolution of a TV or computer display. Smaller layer thicknesses usually make the surface of the part smoother, better presenting the details of the model and improving printing accuracy. Assuming a fine-grained artwork is printed, a smaller layer thickness (such as 0.1mm compared to 0.3mm) can more clearly reproduce those texture details, thereby improving the overall printing accuracy. However, when the layer thickness is larger, due to the relatively more obvious boundaries between layers, the phenomenon of stepped surfaces on the printed product surface will be more severe, which is very unfavorable for some models that require high-precision performance (such as the microstructure of precision mechanical parts), and will directly reduce the overall accuracy of the part.
(2) There are differences in the impact on the accuracy of different printing processes
- FDM process
In the FDM (Fused Deposition Modeling) process, a larger layer thickness will lead to more obvious principle errors (step effect). Because FDM constructs objects by stacking wires layer by layer, when the layer thickness is large, the height difference of each layer will form traces similar to stairs on the surface of the model, which is a serious accuracy defect for complex shapes or parts that require high-precision coordination. Although a smaller layer thickness helps to improve accuracy, it also increases printing time. During the printing process, due to the increase in the number of layers, it is more susceptible to external factors (such as temperature changes, vibration, etc.) interference, and may even cause printing failure. For example, when printing a complex small-sized model using FDM technology, the smoothness and clarity of details at the corners of the model will be improved when the layer thickness is reduced from 0.3mm to 0.1mm, but the printing time may increase from 3 hours to 6 hours.
- SLA process
In the SLA (Stereoscopic Light Solidification Molding) process, layer thickness also affects accuracy. SLA constructs objects by laser curing each layer shape on the surface of liquid resin. Larger layer thickness may lead to incomplete curing or decreased accuracy, especially for models with thin-walled or complex internal structures. Smaller layer thickness can improve printing accuracy and surface quality, but it also requires more frequent adjustment of resin level and printing platform, and increases printing time. Taking printing a transparent resin model with fine internal structure as an example, smaller layer thickness can accurately restore the internal structure, but it also requires longer time and more precise equipment operation.
(3) Impact on dimensional accuracy
The change in layer thickness will affect the dimensional accuracy of the printed product. This is because when the layer thickness is large, the deviation of the overall size in the Z-axis direction (vertical direction) will be more obvious after accumulating a certain number of layers. For example, if the thickness of each layer is 0.05mm more than expected, there will be an additional 5mm error in the Z-axis direction after printing 100 layers. This dimensional error is not allowed for some components with strict dimensional requirements (such as some high-precision parts in the aerospace field). In addition, the unevenness of layer thickness (such as the fluctuation of layer thickness due to nozzle blockage or uneven feeding) will also cause irregular deviations in the shape of the printed object in different parts, thereby affecting the overall accuracy.
Comparative case of 3D printing accuracy under different layer thicknesses
(1) Taking Fused Deposition Modeling (FDM) 3D printer testing as an example
In traditional FDM 3D printer testing, experiments have been conducted to print standard 3D printing test models (such as 20x20x20mm cubes) at different layer thicknesses of 0.1mm, 0.2mm, and 0.3mm.
- 0.1Mm layer thickness
When printing at a layer thickness of 0.1mm, the surface details perform well. When observed closely with the naked eye, the interlayer lines are relatively inconspicuous, and the clarity of the edges and corners of the model is high. From the perspective of printing accuracy, it can restore some small-sized structures (such as small through holes or thin-walled structures) in the printed model well. However, the printing time is relatively long. For example, printing the above 20x20x20mm cube takes about 1.5-2 hours (depending on the printer model and specific parameter settings). Moreover, this layer thickness is easily affected by small external interference factors, such as slight vibration of the printer placed on the desktop or large changes in ambient temperature, which may cause printing failure or surface defects.
- 0.2Mm layer thickness
When the layer thickness is 0.2mm, the printing speed will increase by 30% -50% relative to the 0.1mm layer thickness (roughly estimated, different printers have differences). A printer with a 0.2mm layer thickness may only take 1-1.3 hours to print the above cube. However, the surface fineness has decreased, and some interlayer patterns can be seen with the naked eye. The restoration of small-sized structures is not as accurate as the 0.1mm layer thickness, and the accuracy is slightly reduced. However, at normal viewing distances, for some functional models that do not require extremely high accuracy, this loss of accuracy is acceptable.
- 0.3Mm layer thickness
The printing speed is further improved under a layer thickness of 0.3mm, which may be about 20% -30% faster than a layer thickness of 0.2mm. For a 20x20x20mm cube, it may only take 0.8-1 hour to print. However, the accuracy drops significantly, and the surface step phenomenon is more prominent. The surface of the model looks rough, and both small-sized structures and overall shape accuracy are greatly affected. Moreover, when printing models with special matching requirements (such as structures where multiple components need to be nested accurately), due to the large size deviation caused by a layer thickness of 0.3mm, precise nested assembly may not be achieved.
(2) Comparison cases between different 3D printing technologies
- FDM vs. SLA comparison
Assuming FDM and SLA are used to print a small-sized model with complex internal structures (such as internal honeycomb structures with thin walls). FDM printers use a layer thickness of 0.1mm, while SLA printers use a layer thickness of 0.05mm (SLA can support smaller layer thicknesses to reflect its high-precision characteristics). Due to the limitations of the FDM printing process, although the 0.1mm layer thickness is a relatively fine setting in FDM, there will still be a significant layer thickness accumulation effect. The internal thin-walled structure will have a certain layer thickness deviation in the Z-axis direction, and there will be slight step-like marks on the surface. The model printed by SLA has high accuracy in the internal thin-walled structure, almost no layer thickness deviation, very smooth surface, and significantly higher accuracy than the model printed by FDM. However, SLA printing takes much longer than FDM (for example, FDM takes 2 hours, while SLA may take 3-4 hours).
- Comparison of DLP and FDM
The test object for DLP (Digital Light Projection) and FDM printing is a disc model with fine scales and textures. FDM uses a layer thickness of 0.15mm, while DLP uses its adapted layer thickness setting (the layer thickness setting of DLP varies depending on the equipment and resin material, assuming 0.08mm here). The disc printed by FDM is not as clear as that printed by DLP in the scale and texture parts due to the layer thickness, and the edge of the disc printed by FDM has a certain layer thickness causing unsmoothness. The disc printed by DLP has sharp and clear scales and textures, and the edges are very smooth along the circumference. Its accuracy is significantly better than that of FDM printers. However, DLP devices have stricter design requirements for the support structure of the model. Improper early design can easily lead to printing failure, while FDM is more inclusive in this regard.
Method for optimizing the relationship between layer thickness and accuracy in 3D printing
(1) Select the layer thickness according to the characteristics of the printing material
- Special engineering plastics
For special engineering plastics, such as certain high-strength and high-toughness engineering plastics, they require a smaller layer thickness during printing to ensure good interlayer bonding and strength performance. This is because these materials may have unstable interlayer bonding or uneven internal stress under larger layer thicknesses, which affects printing accuracy. Taking polyether ether ketone (PEEK) material as an example, it is commonly used for printing parts in the aerospace and high-end medical equipment fields. It is generally recommended to use a layer thickness of less than 0.1mm to ensure printing accuracy, so that the printed parts can meet the high-precision and high-strength requirements of these fields.
- General consumables material
Like commonly used PLA (polylactic acid) materials, they have relatively good adaptability to layer thickness, but there is still an optimal layer thickness range. Generally speaking, a layer thickness of 0.2-0.3mm is more suitable for both accuracy and printing speed. Within this layer thickness range, PLA materials can quickly complete printing tasks while ensuring certain accuracy. For example, for some ordinary DIY enthusiasts to print some home decorations or creative decorations, a layer thickness of 0.2-0.3mm can not only quickly form, but also meet basic accuracy requirements in appearance.
(2) Starting from the perspective of model design
- Complex model design
When designing complex models, especially those with fine details, thin-walled structures, or combinations of multiple structures of different sizes, the impact of layer thickness on accuracy should be considered in advance. For example, for models with many small protrusions or grooves, a smaller layer thickness should be selected to ensure that these details can be accurately printed. If the model is of higher height, a variable speed layer thickness strategy can be selected, and a smaller layer thickness can be used at the bottom and top of the model to ensure appearance and accuracy. The layer thickness can be appropriately increased in the middle body of the model to improve printing speed and reduce the time impact on the entire printing process.
- Special treatment for overhanging and bridging parts
In addition to considering adding necessary support structures, the selection of layer thickness is also important for the overhanging and bridging parts in the model. Generally speaking, a smaller layer thickness helps to reduce the sagging deformation caused by the overhanging part due to its own weight and improve accuracy. When encountering long-distance bridging structures, if the layer thickness is too large, it is easy to collapse or deform without sufficient support. At this time, the layer thickness should be appropriately reduced, and special bridging strategies (such as increasing the number of bridging starting points) should be combined to ensure printing accuracy.
(3) Make adjustments to the comprehensive printing environment and equipment capabilities
- Printing environment stability
If the stability of the printing environment is poor, for example, there is a lot of vibration (such as near some large machine tools, compressors and other equipment) or the temperature fluctuates greatly (such as non-constant temperature workshops without air conditioning regulation), it is not suitable to use a too small layer thickness for printing. Because the possibility of external interference is greater when printing with a small layer thickness. You can first improve the printing environment (such as adding shock absorbers to the printer and placing it in a relatively constant temperature space) and then consider reducing the layer thickness to improve accuracy, or directly increase the layer thickness appropriately in the current environment to ensure the success rate of printing, but this will sacrifice some accuracy.
- Equipment’s own capabilities
Choose the layer thickness according to the hardware capabilities such as resolution and positioning accuracy of the printer itself. If the nozzle diameter of the printer is large, the corresponding layer thickness can be appropriately increased. For example, some industrial-grade FDM printers have a nozzle diameter of 0.8mm. In this case, you can try to adjust the layer thickness from 0.4mm to find a layer thickness value that can ensure certain accuracy and take advantage of the device’s printing speed. For printers with high resolution and motion system accuracy, you can try smaller layer thicknesses to tap into their potential for high-precision printing.