Introduction
The two main 3D printing processes for creating commercial-grade nylon parts are HP Multi Jet Fusion (MJF) and Stereolithography (SLS). Each process produces parts with a high level of detail and structural integrity, but how do they compare?
HP completed an experiment to examine the impact of accelerated weathering on HP Nylon PA12 W to two main SLS competitor materials. The experiment tracked changes in colour, mechanical properties, and dimensional properties. This article summarizes the main findings of the study.
Test Description
For this study, HP simulated long-term weathering conditions on 3D printed parts using a combination of fluorescent UV light, temperature, and condensation. The purpose was to compare Nylon PA 12 W produced with HP Multi Jet Fusion, and two comparable Nylon PA 12 materials produced with SLS 3D printing technology.
Results
Overall, HP Nylon PA 12 W performed better than the Nylon PA12 materials produced with SLS technology. The HP Nylon PA 12 W retained 80 – 90% of its initial mechanical properties, and it didn't show any visible aesthetic changes after extensive exposure to the test conditions. The results are summarized in the table below.
Colour
The colour of the HP Nylon PA12 compared to the SLS materials was compared at 200 hours, and again at 1,000 hours. After only 200 hours (approx. 8 days) of accelerated weathering, the SLS materials show a clearly visible colour change compared to the HP Nylon PA 12 W material.
After 1,000 hours of accelerated testing (around 41 days), the SLS materials have an ∆Ecmc that’s at least 3 times higher than HP Nylon PA 12 W material.
Mechanical Properties
The graphs below show how the accelerated weathering testing affected the mechanical properties of HP Nylon PA 12 W and the SLS materials. The testing parameters can be defined as follows:
Elongation at break (%) shows ductility and how much the material can stretch before breaking.
Young’s modulus (MPa), also known as modulus of elasticity, measures the stiffness of the material.
Tensile strength at break (MPa) measures the maximum stress a material can withstand before breaking.
Charpy impact strength measures the amount of energy absorbed by a material during fracture.
During the testing process, all of the materials exhibited relatively stable stiffness over time. However, the HP material exhibited stable ductility and strength properties over time, while SLS materials showed significant degradation after the testing was complete.
Dimensional Changes
The dimensional change of each of the materials was measured through the weathering study, using the charpy impact bars as a reference. All materials show very little change in their dimensions over time. The variations ranged mostly between +0.5% and -0.5%.
Conclusion
The results of the accelerated weathering study showed that the HP Nylon PA12 material showed superior colour retention and ductility when compared to the Nylon PA12 3D printed with SLS technology. The HP Nylon 12 showed great colour stability and retained 80-90% of ductility at the end of the test period.
The results of the study combined with customer feedback suggests that HP Nylon PA12 W material will be suitable for applications such as medical devices or cosmetic parts where white colour consistency is important, and also suitable for parts which require an extended use or shelf life.
.Data and images courtesy of HP.
Click on the link below to read the full accelerated weathering study.