How durable are MJF parts over the long term?
From a manufacturing and materials engineering perspective, the long-term durability of Multi Jet Fusion (MJF) parts is a function of the base material's inherent properties, the quality of the printing process, the operating environment, and the mechanical loads applied. For components made from the most common material, Nylon PA12, MJF parts offer excellent durability for a wide range of applications, though their performance has specific boundaries that must be respected for long-term success.
Inherent Strengths for Long-Term Use
MJF produces parts with properties that lend themselves well to durable applications:
Isotropic Mechanical Properties: Unlike FDM, MJF parts exhibit nearly uniform strength in all directions because they are fused from a powder bed. This eliminates weak planes between layers, making them more reliable under complex, long-term loading.
Excellent Toughness and Fatigue Resistance: Nylon PA12 possesses good impact strength and resistance to crack propagation. This makes MJF parts suitable for functional prototypes, jigs, fixtures, and end-use parts that undergo repeated stress cycles, such as living hinges, snap-fits, and enclosures in consumer products and industrial equipment.
Good Chemical Resistance: PA12 is resistant to oils, greases, aliphatic hydrocarbons, and alkaline solutions, making it suitable for automotive and machinery applications where exposure to lubricants and mild chemicals is common.
Key Factors Affecting Long-Term Durability
To ensure long-term performance, the following factors must be carefully considered:
UV and Environmental Degradation: Like most standard polymers, unfilled Nylon PA12 is susceptible to ultraviolet radiation and oxidation. Prolonged exposure to direct sunlight will cause embrittlement and a loss of mechanical properties over time. For outdoor applications, parts must be protected with UV-stable paints or coatings.
Moisture Absorption: Nylon is hygroscopic, meaning it absorbs moisture from the air. This causes dimensional swelling and a reduction in stiffness and strength. However, it also increases toughness (impact resistance). For precision components, this moisture effect must be accounted for in the design. In saturated environments, properties can stabilize once the part has reached equilibrium.
Creep (Cold Flow): Under a constant, sustained load, all thermoplastics will gradually deform over time—a phenomenon known as creep. While PA12 has better creep resistance than many plastics like ABS, it is not immune. MJF parts should not be used to support significant constant structural loads indefinitely without design allowances to mitigate creep, such as generous fillets and adequate cross-sections.
Temperature Limitations: The functional long-term service temperature for MJF PA12 is typically up to around 100-120°C. Continuous exposure to temperatures near or above this range will lead to a rapid loss of mechanical properties and accelerated aging.
Enhancing Durability for Specific Applications
The durability of MJF can be significantly extended through material selection and post-processing:
Advanced Materials: Using MJF-compatible materials like PA12 Glass Beads (improved stiffness and dimensional stability) or TPU (flexible and high-impact) can tailor the part for specific long-term demands.
Protective Post-Processing: Dyeing the part does not significantly affect durability, but applying a UV-resistant coating is critical for outdoor use. For wear surfaces, a smooth surface finish achieved through tumbling can reduce friction and material loss.
Engineering Guidelines for Long-Term Success
Match the Material to the Environment: Do not use standard PA12 in high-temperature, UV-exposed, or constantly wet environments without protection.
Design to Mitigate Creep: Avoid thin, highly stressed sections in load-bearing applications. Use ribs and gussets to distribute stress.
Consider the Application Lifecycle: For parts requiring a multi-year service life under significant load, technologies that use more dimensionally stable and creep-resistant materials, such as CNC Machining of PEEK or aluminum, may be a more suitable choice.
Validate with Testing: For critical applications, conduct real-world aging tests or accelerated life testing on MJF prototypes to validate their performance over the intended lifespan.
In summary, MJF parts made from PA12 are highly durable for a vast range of functional applications, from custom fixtures to end-use consumer products. Their longevity is excellent provided they are used within their thermal, environmental, and mechanical limits. Understanding these boundaries is key to leveraging MJF's strengths for producing robust, long-lasting components.
