JEC COMPOSITES MAGAZINE - Issue #120 - April 2018 - 57

Simulating the effects of warpage in an additively-manufactured composite layup tool

Fig. 2: Comparison between measured warpage on a physically-printed part
(RMS signed distance, left) and Digimat-AM warpage prediction (X displacements, right)

Fig. 4: Warpage prediction after geometry compensation in Digimat-AM.
Left: superposition of the as-printed (red) and as-designed (green) parts;
right: RMS signed distance, maximum deviation is less than 0.1 mm

the impact of design decisions on the manufacturing process before the
part is printed.
The development of this process simulation is facing several challenges:

- Loading the toolpath issued from the manufacturing processing
software and extracting information about the deposition sequence;
- Modelling, via micromechanics, the heterogeneous material microstructure as a function of the toolpath (e.g., porosity volume fraction
and orientation);
- Predicting the resulting warpage induced by the printing process;
- Iterating the design and optimizing the manufacturing process parameters to minimize warpage.

- Complex thermomechanical loadings occur during the layer-by-layer deposition of the material and the successive cooling of the part;
- Additive manufacturing is a true multi-scale challenge: the position
of bead deposition creates specific microstructures based on the
printing toolpath pattern, which drives the macroscopic mechanical
behaviour - typically inducing anisotropy;
- The thermal history of the material deposition generates differential
shrinkage between adjacent beads or layers that affects the end tolerances of the part.
Overall, modelling the printing process requires taking into account the
material state evolution to model the stress build-up as well as the stress
relaxation over time. Numerical predictions of warpage need to account
for the process parameters, the material characteristics and the printing
strategy (part orientation, toolpath, supports, etc.).
A multi-scale approach
Stratasys is working with e-Xstream to create FDM process simulation
via a multi-scale approach as a function of the process setup and material
choice. This approach includes the following steps:
- Solving a fully-coupled thermomechanical problem of the deposition process to identify the warpage behaviour of the printed material accounting for thermal exchanges inside the printer build (conduction, convection and radiation);

Results and benefits
As a direct result of the collaboration between Stratasys and e-Xstream
Engineering, the main objective of the process simulation is to print
right the first time. Designs and process parameters can be investigated
through the numerical simulation while the printed part fidelity can be
controlled before the first physical printing. More importantly, the simulation workflow enables to minimize warpage in only two steps using a
predeformed geometry. Working with Digimat-AM, Stratasys engineers
are thus able to save time and material by anticipating printing issues
with simulation (e.g., evaluate the impact of the printing direction and
location on the results).
Virtual engineering is the solution to optimize the manufacturing process because it enables the user to explore the process sensitivity to
manufacturing parameters at virtually zero marginal cost. The process
simulation experience in Digimat-AM is accessible to non FEA experts
thanks to its easy, efficient and user-friendly GUI designed to follow the
physical printing workflow.
Results correlation to test data
The warpage prediction was compared to 3D-scan measurements of
a physically-printed composite tool. Given the different mod¬elling
assumptions, the comparison shows a good general correlation with a
similar deformation pattern and amplitude. The warpage compensation
procedure significantly decreases the maximum deviation between the
reference geometry and the as-printed part (from 0.5 mm to less than
0.1 mm).
More information:
www.e-xstream.com

Fig. 3: Digimat-AM simulation approach for optimal printing

N°120 April 2018

/ jec composites magazine

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http://www.e-xstream.com
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #120 - April 2018
