The challenge of using a physical model or prototype as the inspection nominal is you need to digitize the model. Reverse engineering software is designed for just that purpose. Using a portable CMM with a laser line scan head attachment, instead of a touch probe, the physical part is painted into the software (‘paint’ is a term used to scan a part because the process is similar to spreading paint onto the part with a wide brush). Where a touch probe might capture up to 100 data points per second and is excellent for high precision inspection, a scanner will capture 50,000 points per second, accurately capturing the most subtle design features. From the scanned data points, reverse engineering software creates meshes, surfaces, solids and prismatic features to create precise CAD models. Once the completed 3D CAD model is in place, it can be used for manufacturing, tool building or inspection—using the MBD inspection process outlined previously.
Model Based Inspection of Plastic Mold Tooling
Using the 3D CAD model as the inspection nominal is great for inspecting plastic mold tooling as well as plastic molded parts. Most molds are machined with CNC machine toolpaths generated directly from a 3D CAD model, so inspecting the tool surface profile with the same 3D CAD model from which the toolpaths were created is an easy Align-Inspect-Report process (see Figure 1).
Using metrology software and a portable CMM, moldmakers can efficiently handle exceedingly complex surface profile requirements. Dimensioning, inspecting and reporting that used to be difficult, if not impossible can now be provided quickly and easily on molds or finished molded parts.