How Accurate Are SLA Parts, and What Testing Methods Ensure Their Precision?

Inherent Accuracy and Influencing Factors

Stereolithography (SLA) is renowned for producing parts with high dimensional accuracy and excellent surface finish. Typical SLA systems can achieve an accuracy of **±0.1% to ±0.25%** of the part dimension, with a lower limit of around **±0.05 mm to ±0.15 mm**, depending on the specific printer, resin, and part geometry. This high precision stems from the fine laser spot size and the precise, layer-by-layer photopolymerization process. However, accuracy can be influenced by factors including resin shrinkage during curing, support strategy, part orientation, and post-processing. For critical applications in industries like medical and healthcare or aerospace and aviation, these variables are meticulously controlled through validated process parameters.

Primary Dimensional Verification Methods

To ensure precision, SLA parts undergo rigorous dimensional inspection. **Coordinate Measuring Machines (CMM)** are the gold standard for validating critical features against CAD data with micron-level resolution. For full-field surface analysis, **3D Optical Scanners** or **Laser Scanners** create a high-resolution point cloud of the entire part, which is compared to the original design to generate a color deviation map. Basic checks are performed using **Precision Calipers, Micrometers, and Height Gauges**. This stage is crucial before any further CNC machining of functional interfaces.

Advanced Non-Destructive Internal Inspection

Beyond external dimensions, the internal integrity of SLA parts is vital for functional prototypes. **Micro-Computed Tomography (Micro-CT) Scanning** is a powerful non-destructive method used to detect internal voids, porosity, and layer fusion defects without cutting the part. It provides a complete 3D volumetric analysis, ensuring that internal channels or structures—common in fluidic or complex assembly prototypes—are printed to specification. This level of inspection is often part of a comprehensive material testing and analysis protocol.

Post-Processing Impact and Functional Validation

Testing must account for the effects of post-processing. Washing and UV curing can induce slight dimensional changes. Therefore, final inspection is performed *after* post-curing. **Functional Validation Testing** is the ultimate check, where the part is tested in its intended application. This may include pressure testing for fluidic parts, wear testing for moving components, or assembly fit-checks with other system parts. This holistic approach from print to application ensures that SLA parts meet not just geometric tolerances, but also functional performance requirements for demanding sectors like automotive and consumer electronics.