Reliable 3D measurement guarantees high quality injection molded components – Metrology and Quality News


Reflective and shiny surfaces often allow the creation of high-quality individual designs. As such, the demand for products with reflective surfaces is continuously increasing. These include housing parts for electronic devices, displays, mirrors or deflection
mirrors in head-up displays, as well as exterior car components such as B-pillars, panels, decorative trim, fuel caps or headlights. Today, piano black as a glossy variant of plastic surfaces in vehicle interiors has become almost the norm in high-quality automotive construction.

These products are typically made using injection molding processes, where hot liquid plastics are injected into a shape or mold and then allowed to cool and harden. Once the plastic has cooled completely and the mold is opened, the cured plastic is ideally shaped to fit perfectly into the cavity of the vehicle. However, processing errors can lead to many faults and defects on the component. Manufacturers must differentiate between two challenges when it comes to quality control.

Reliably detect cosmetic defects

Cosmetic defects, such as burrs on gaskets, dirt or inclusions, are often caused by incorrect injection pressure. It depends on the component whether these faults can be corrected in downstream processes or whether they are insignificant. For non-transparent components, or if they are polished, painted or coated after the injection molding step, surface defects are often not relevant at this point in the process.

However, this is not the case for defects that occur after coating or painting, including scratches or orange peel effects. These cosmetic flaws on the shiny components are easily apparent to the human eye. Yet common inspection procedures such as strip projection or photogrammetry, based on diffuse reflection, barely manage to detect them and turn them into actionable measurement data. Measurement methods such as white light interferometry are rarely viable here due to their often insufficient measurement field size. At the same time, manual inspection of the surface of these parts is a laborious, expensive and error-prone procedure.

Reliably detect deformities

Smear on the B-pillar

Unwanted deformation remains one of the typical defects of injection molded components. Among other causes, these can occur when the temperature of the mold or in the injected plastic is not adjusted correctly. Distortions and indentations can also appear if the surface collapses. For example, if the mass of plastic injected into the deeper areas of the component shrinks or if not enough plastic has been injected.

When it comes to optical components such as heads-up displays, distortions in the millidiopter range can drastically affect the performance of the components. Unlike cosmetic defects, these deformations are not visible to the naked eye, thus preventing manual inspection.

Deflectometry detects both: Shape and defects in a single measuring step

Phase measurement deflectometry is a particularly reliable method for measuring reflective or partially reflective surfaces. With its SpecGAGE3D line of sensors, ISRA VISION has set new standards and perfected the process. The system projects stripe patterns onto the reflective surfaces to be inspected. The reflective stripe pattern is then recorded by multiple cameras from different perspectives and evaluated. Based on the distortion of the recorded tape pattern, the topology of the component can be calculated.

CAD comparison color card: The measurement data (right) is compared with the CAD model (left).

The topology determined by this process is then compared to the CAD model – a digital twin of the component – in just a few seconds. An elevation map, accurate to the nearest micrometer, illustrates the deviations from the expected model. At the same time, the sensor detects local roughness and cosmetic defects on the surface.

In one time-saving measuring step, SpecGAGE3D reliably detects shape and defects on high-gloss injection-molded components and other reflective or transparent components. By comparing the images to the CAD model, the system detects height deviations up to the millidioptric range, with local defects being detected down to the nanometric range. Paint defects, inclusions, injection defects and other defects are detected, classified and documented quickly and reliably. The conclusions drawn from these inspections allow rapid adjustment of processes, thereby optimizing productivity – saving resources and reducing machine uptime.
In addition, shorter measurement times allow higher cycle rates to be achieved. This comprehensive measuring process puts zero-defect quality at your fingertips, both technically and economically.

For more information:



About the author