Build orientation and strength
In 3D printing, parts are built layer by layer. Depending on the process, this can result in a part whose material properties are anisotropic.
Processes that use light to cure liquid resins (for example, SLA, DLP and Polyjet) produce parts whose properties are effectively isotropic. In contrast, processes that melt and solidify plastics (SLS and FDM) typically result in parts whose strength in the X and Y axes is several times greater than that in the Z axis. This is due to the inter-layer bond strength being lower. If strength is critical for a part’s performance, then the part might need to be orientated to ensure the load paths are not in the Z axis. This information must be provided by the customer.
Build orientation and surface finish
If 3D printing processes had infinitesimally small resolutions in the X, Y and Z axes, then build orientation would not influence surface finish. However, 3D printers do have a resolution in the X and Y axes, and the layer depth gives the Z axis resolution. Any resultant micro stepping can be sanded smooth, but the amount of finishing required can be minimised by selecting the build orientation to suit the part’s surface geometry. Usually, the resolution in the X and Y axes is better. As a result, a radius in the XY plane will have a smoother surface than a radius in the XZ or YZ plane.
Build orientation and distortion
3D printing is an additive manufacturing process. Each time new material is added, whether by curing a liquid resin, melting a powder, or extruding molten plastic, it will affect the material to which it is bonding. This can give rise to residual stresses and result in distortion or, sometimes, delamination. Careful consideration of build orientation can help to minimise or prevent distortion, depending on the 3D printing technology and the part’s geometry.
Support structures for 3D printing (SLA, DLP & Polyjet)
In some cases, the choice of orientation can be influenced by the desire to minimise support structures. If a part has an overhang or bridging feature, a skeletal support structure may be required to prevent the part drooping under the influence of gravity while it is being built. Support structures add cost due to the material and build time required. In addition, post-processing time is required for removing the structure and, when necessary, cleaning up any witness marks left by the supports. It is worth noting also that the DLP process will need to have substantially more support than SLA due to the inverted print direction.
We never select a build orientation with a view to saving costs by minimising support structures.
SLS parts do not need supporting as they are suspended within un-sintered powder during the whole build process.
Build orientation and build time
The more layers a part needs, the longer the build time. If time is of the essence, you might choose to orientate the part to minimise the Z axis dimension. However, as we have seen already, build orientation also influences other key parameters such as strength and surface finish.
We never orientate parts to minimise build time (unless speed is more important). Instead, we select an orientation that produces parts with the requisite strength and surface finish.
The world is not ideal, but this is where experience counts
Customers may require parts with a high-quality finish on more than one face. Or parts capable of withstanding loads in more than one direction. Because we have been 3D Printing for over 20 years, we have printed many hundreds of thousands of parts using our five different 3D printing technologies and in multiple materials, we can overcome these challenges.
First of all, our 3D printing operatives are highly experienced, so they can often resolve issues such as delamination and distortion by fine-tuning the parameters on the 3D printer. But this approach cannot overcome every problem encountered.
Sometimes, it is sufficient to simply orientate the part at 45 degrees. Alternatively, a small offset can orientate an overhang at an angle of less than 45 degrees from vertical, which avoids the need for a support structure.
Depending on the purpose for which the part is required, it might be that 3D printing it with SLA instead of a lower-cost process provides isotropic material properties and, therefore, the necessary strength in all three axes. Indeed, switching to an alternative 3D printing process or material can be a simple way to solve issues relating to build orientation.
For larger parts in particular, we sometimes split the part into two, three or more elements. Building these separately and then assembling them can result in a final part that meets the necessary criteria, without having to compromise on other aspects, this would generally be done for a visual model where strength is less important.
Support structures are created automatically, using specialist software, when we prepare CAD models for downloading to the 3D printer. However, we use our expertise and experience to adjust support structure designs manually if, for example, we want to keep witness marks away from critical areas on the finished part’s surface, especially if there are internal features that cannot have support as there is no access to remove them.
Complementary technologies
If a part has features with critical dimensions, one option is to CNC machine those features into the 3D printed part. Or a secondary component can be CNC machined and bonded to the 3D printed part. This is straightforward for us, as we have CNC machining facilities in-house.
Because we have both 3D printing and CNC machining facilities, we can also give unbiased advice on whether a part is best produced by 3D printing or CNC machining. The latter is sometimes the better option, particularly if material isotropy and precision are both critical.
Conclusion
By now, you might have decided that build orientation is a complex subject and, indeed, there is much to consider. Nevertheless, we usually find that a quick conversation with the designer allows us to select a build orientation and supply the part with the required characteristics.
Our extensive experience with multiple 3D printing technologies and materials gives us a deep understanding of build orientation. This enables us to manufacture high-quality prototype parts so designers can focus on product development.
Find out more
If you need 3D printed prototype parts or have any questions about build orientation, please talk to us on 01763 249760.
