Polypropylene (PP) is a widely used material in battery enclosures due to its excellent chemical resistance, durability, and lightweight nature. Traditionally, injection-molded PP has been the material of choice for battery housings, but advances in additive manufacturing, specifically Selective Absorption Fusion Polypropylene, are opening up new possibilities for rapid prototyping and even low-volume end-use applications.
To validate the performance of polypropylene for battery housing applications, testing was conducted on the materials' dimensional, weight, and mechanical properties when exposed to battery acid (concentrated sulfuric). For each test, controls were placed at room temperature during the experiment, while the experiment group specimens were submerged in the battery acid for 168 hours (1 week). Each sample was tested in the XY & Z orientation to capture the slight anisotropy that is present in 3D printed parts. For weight, there was an immediate value taken when removed from the bath, then after they had been dried for 168 hours.
|
Value |
XY % Change |
Z % Change |
|
Diameter |
-0.1% |
0.0% |
|
Thickness |
-0.1% |
-0.2% |
|
Weight |
0.3% |
0.5% |
|
Weight (168 hours dried) |
0.0% |
0.0% |
Each tensile specimen was conditioned and exposed to chemicals the same as the dimensional and weight coupons. The parts were manufactured and testing according to ASTM D638, and the tensile tests were conducted within 30 minutes of removal from the battery acid. The noise within a data set for tensile testing is inherently more than dimensional testing.
|
Value |
XY % Change |
Z % Change |
|
Ultimate Tensile Strength |
+6% |
+5% |
|
Young’s Modulus |
+4% |
+4% |
|
Elongation at Break |
-25% |
-7% |
While SAF PP retains good chemical resistance, it differs from injection molded PP in two key ways:
All 3D printing technologies are built layer by layer, rather than all at once like injection molding. SAF relies on bonding between layers rather than a continuous molten flow. This means that the properties in the XY plane are going to be slightly different than the Z. This is mostly seen in the modulus and elongation values in the XY & Z planes. It is best practice to orient load-bearing elements in the XY plane.
SAF PP has had several tests conducted to characterize it’s performance at temperature. Below is a table summarizing the results.
|
Value |
Value |
Unit |
|
Heat Deflection Temp (0.46 MPa) |
107 |
°C |
|
Heat Deflection Temp (1.82 MPa) |
56 |
°C |
|
Coefficient of Thermal Expansion |
169 |
μm/°C.m |
|
Specific Heat Capacity (20°C) |
1.76 |
J/g.°C |
|
Thermal Conductivity (23°C) |
0.196 |
W/m K |
Injection molding rapidly cools polypropylene within a metal mold, creating a relatively uniform and fine-grained crystalline structure. In contrast, SAF has an extended cooling time due to the powder bed fusion process. The entire build remains heated for hours before cooling, allowing for more extensive crystallization. This prolonged cooling results in a coarser structure, which can lead to a higher stiffness and reduced ductility in comparison.
SAF polypropylene offers unique advantages for particular applications, particularly where speed, cost, and design flexibility are critical.
Many components require multiple iterations before finalizing a production-ready version. SAF enables rapid prototyping without the need for expensive tooling. This allows engineers to test different design variations quickly, while still providing the performance that would be expected from a molded polypropylene. By eliminating the lead times associated with mold fabrication, SAF helps teams move from concept to functional prototype in days rather than months.
Traditional injection molding requires high upfront tooling costs, making it cost-prohibitive for low to mid volume production runs. SAF is a cost effective alternative for pilot production runs before transitioning to mass manufacturing. This allows for more time to ensure the final design validation and produce parts while your final mold is being machined. Also, this is a great option for extending the life of current products with spare parts or legacy parts without having to retool for a small batch of parts. For production runs in the hundreds to few thousand units, SAF can bridge the gap between prototyping and full-scale injection molding, offering flexibility and cost savings.
Unlike injection molding, SAF enables the creation of intricate and fully optimized geometries without additional tooling costs. This can help designers reduce their overall bill of materials (BOM) by building in the mounting features such as clips, channels, or additional reinforcements, like ribs, on a single part. This reduces the overall BOM of a project while eliminating the need for secondary assembly. It is also a great solution as battery manufacturing becomes more unique and custom with non-traditional form factors. This can be parts like curved or modular enclosures that may be challenging to mold. SAF allows engineers to push the boundaries of battery housing design, creating enclosures that are stronger, lighter, and more customized to the specific application than previously thought.
SAF polypropylene presents a compelling option for battery housings, offering chemical resistance, design flexibility, and fast turnaround times that traditional injection molding cannot match. While it may not completely replace molded polypropylene for high-volume production, it fills a crucial gap in prototyping, bridge production, and specialized applications where speed and customization are key.
As additive manufacturing continues to evolve, the role of SAF in functional, end-use applications will only grow—offering companies a powerful tool to bring battery innovations to market faster and more efficiently.
With over a decade of experience in additive manufacturing, Kevin drives the success of Stratasys Direct’s 3D printing services portfolio, shaping material strategies, optimizing product sales, and enhancing customer experience through e-commerce platforms. He has expertise in powder bed fusion technologies like SLS, SAF, and MJF, contributing to material development and process innovations in industries such as aerospace, automotive, and consumer goods. Kevin holds both a BS and an MSE in Mechanical Engineering from the University of Texas at Austin and is an active speaker at industry conferences like AMUG and RAPID + TCT.
