Establishing Baseline Dimensional Metrology for Injection Molded Polymers
Establishing baseline polymer metrology requires controlling thermal soak kinetics, rigid GD&T fixturing, and accounting for post-mold crystallization drift.
X-Ray Computed Tomography
Meaning
Non-destructive inspection technologies that use penetrating radiation to create three-dimensional internal and external maps of a part reveal hidden defects and complex geometry. This process involves taking hundreds or thousands of two-dimensional x-ray images as a component rotates on a precision stage. Specialized software then reconstructs these images into a volumetric model.
Each pixel in the reconstructed volume is called a voxel and represents the density of the material at that location. This allows for the inspection of internal features that are invisible to optical or contact metrology. Manufacturers use x-ray computed tomography to check for voids in castings, the orientation of fibers in composites, and the assembly of complex electronics.
The ability to see inside a part without cutting it open saves time and material. Accuracy depends on the power of the x-ray source and the resolution of the detector. High-energy systems can penetrate thick metal parts while micro-ct units offer micron-level detail for small items.
Internal Inspection
Verification of hidden features is the primary application for this technology in a production environment. X-ray computed tomography allows for the measurement of wall thicknesses and internal diameters that cannot be reached by probes. This is especially important for parts produced by additive manufacturing, which often have complex internal lattices.
The software can automatically identify and measure voids or inclusions within the material. This data helps engineers understand the root causes of failure and optimize their manufacturing processes. For safety-critical components in aerospace or medicine, this level of detail is a requirement.
The inspection provides a complete record of the internal state of every part produced. This ensures that only perfect components reach the final assembly line.
Resolution Capacity
Detail that can be captured in a scan is determined by the size of the x-ray spot and the distance between the source and the detector. X-ray computed tomography systems are designed to balance the need for high resolution with the need for a large field of view. To see smaller details, the part must be placed closer to the source, which limits the size of the object that can be scanned.
Modern systems use multi-focus tubes to provide flexibility for different part sizes. The quality of the final image also depends on the number of projections taken during the rotation. More projections lead to a cleaner image but increase the scan time.
Quality managers must select the right settings for each part to ensure that the required tolerances can be met. Sub-voxel algorithms further improve the measurement precision beyond the base resolution.
Defect Detection
Identification of cracks, porosity, and foreign material is a major task for industrial tomography systems. X-ray computed tomography provides a non-subjective way to assess the quality of a component. The software can be programmed to flag parts that exceed a certain level of internal porosity.
This removes the variation that occurs with human inspectors. It also allows for the tracking of defect trends over time. If a certain area of a casting consistently shows voids, the mold design can be adjusted to improve the metal flow.
The high-contrast nature of the data makes it easy to distinguish between the base material and any contaminants. This capability is vital for ensuring the purity of high-performance materials. Final reports include 3D visualizations that make it easy for production teams to understand the location and severity of any issues.