Most 3D printing processes result in warpage and residual stress in parts due to the way the incremental layers cool from their fusion/deposition temperatures and the orthropic nature of a layered material. Choosing the right orientation and build parameters can reduce this effect, but doing so through trial and error by printing physical parts can be costly. In addition, measuring residual stress is not straightforward and since it can have an effect on part durability it is important to understand.
Simulation using Finite Element Analysis can help us decide on the best additive manufacturing strategy, as well as developing compensated initial shapes to offset for warpage and shrink resulting in higher tolerance, better quality parts.
Digimat AM, from MSC Software, is a dedicated AM simulation tool for plastics. It uses the powerful Marc non-linear FEA solver to simulate SLS, FFF and FDM processes but through a manufacturing-centric interface that does not require an in-depth knowledge of the FEA process or the Marc solver.
The best way to illustrate the benefits of this software is through example. We'll use a component created with Apex Generative Design as an example.
We can use Digimat AM to simulate printing the part in Nylon 12 using the SLS process in three different orientations (on the two planar surfaces and on end) to compare the overall distortion and residual stress levels. Setting up these simulations is a simple as importing an STL file and choosing the orientation, material and machine settings.
The meshing of the part is automatic using a voxel based method to achieve layers of elements through the part in the build direction so requires nothing more than a single size setting. The solver uses the Inherent Strain method to reduce the complex thermo-mechanical problem to a solely mechanical one while retaining good predictive capabilities that have been validated through correlation.
Comparing the results, we can see that the maximum distortion value doesn’t vary much (+/- 0.08mm) but the part formed on end has a residual stress of just 5MPa compared with 28MPa for the other two orientations.
Orientation 1
Displacement - Orientation 1 Stresses - Orientation 1 Orientation 2
Displacement - Orientation 2 Stresses - Orientation 2 Orientation 3
Displacement - Orientation 3 Stresses - Orientation 3 After selecting the best orientation we can use Digimat AM to automatically compensate for the shrinkage/warpage predicted and produce a new STL file that accounts for the potential distortion/shrinkage and, if used to print from, will result in a part much closer to the design intent.
Digimat AM is available standalone or as part of the MSC.One token system. This flexible licensing system gives access not just to Digimat, but also to Simufact for simulating metal powder based printing process and both Apex Generative and Nastran Optimisation to support a process for developing this type of component as part of a lightweighting strategy. A wide range of other FEA tools are also included in MSC.One.
If this is of interest, or you wish to understand more about Digimat or any other aspect of MSC.One please don't hesitate to get in touch.