Design for Additive Manufacturing | Chapter 6: Optimizing Accuracy

In the previous chapters, we discussed the basic requirements for additive manufacturing design and presented strategies for optimizing functionalities and surfaces of additively manufactured components. In Chapter 6, we focus on how the accuracy of components can be improved within the context of Design for Multi Jet Fusion (DfMJF).

Chapter 6: Accuracy Optimization

6.1 Tolerances

Tolerances in 3D printing refer to the potential deviations between the dimensions of the printed component and the specifications of the 3D model. In general, tolerances for the Multi Jet Fusion process are ± 0.3%, with a minimum limit of 0.3 mm. These inaccuracies can be attributed to various factors:

  1. Thermoplastic Deformation: Due to the use of heat and thermoplastic materials (such as PA 12 and TPU) in the Multi Jet Fusion process, distortions and shrinkages can occur during the cooling process.
  2. Build Orientation: Accuracy on the X/Y axes is generally higher than on the Z-axis. Thoughtful orientation of the component in the build space can contribute to overall accuracy improvement.
  3. Post-Processing: After the printing process, components need post-processing. During this phase, which includes part blasting, dimensional inaccuracies can arise.
  4. Manufacturing-Related Inaccuracies: Despite the increasing precision of additive manufacturing processes, certain process-related inaccuracies persist.
  5. File Format Conversion: The conversion process of 3D models into the required connected triangles (tessellation) can also introduce minor inaccuracies. Inadequate resolution, meaning a low number of triangles, can lead to inaccuracies, although this effect is generally minimal.

6.2 Minimum Dimensions for Components and Individual Elements

Multi Jet Fusion is an additive manufacturing process based on thermoplastic processes. The conditions mentioned in Section 6.1 Tolerances influence the accuracy of produced components. By adhering to the following minimum sizes for elements of components, the risk of dimensional deviations in the components is reduced. Going below these minimum sizes increases the risk of elements breaking or not being correctly represented.

  • Minimum Hole Diameter with 1 mm Wall Thickness: 0.5 mm
  • Minimum Shaft Diameter at 10 mm Height: 0.5 mm
  • Smallest Printable Size of an Engraving or Embossing: 6 pt
  • Minimum Gap between 2 Walls: 0.5 mm
  • Minimum Height or Depth (Z-Axis) of an Engraving/Embossing: 0,5 mm

6.3 Component Orientation

The accuracy in the Multi Jet Fusion process can be significantly influenced by the position and orientation of the component in the build space.

  1. Orientation: Due to layer-by-layer construction, the Z-axis is the least accurate as the layer thickness can vary. The Y-axis is the most accurate, as elements on this axis are not dependent on the linear axis (in the X-direction). The X-axis is slightly less accurate, and differences are generally only marginally noticeable in very large components.
  2. Position in Build Space: The position of a component in the build space can also affect the end result. This is particularly relevant for components prone to warping. Such components can only be produced in high quality in specific areas of the 3D printer. In our quality-optimized manufacturing approach, we position such components exclusively in these areas. However, this can lead to longer production times as fewer components can be produced per print job.

6.4 General Notes

  • Elements with critical dimensions should be oriented in a plane.
  • Critical distances or dimensions (e.g., hole spacing) should ideally be oriented in the X or, even better, Y direction.
  • Avoid transitioning between delicate and massive elements, as uneven cooling can lead to unwanted shrinkage effects.
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