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Inspection/Measurement 20 MoldMaking Technology —— AUGUST 2016 By Sean Lennard A Practical Case for Model-Based Definition I n today's digital-everything world, it is amazing to see how many parts are newly manufactured, remanufactured or modified without the benefit of comprehensive CAD data. In some cases, this can- not be helped, such as with certain maintenance, repair and overhaul situations, in which the original part, once subjected to operational stresses, no longer meets design specifications. Regardless of the reasons, incomplete data is a challenge manufacturing and quality engineers face every day. As a way to compensate, many shops are adopting model-based definition (MBD) as a strategy, whereby the CAD model becomes more than the nominal against which all parts are measured and inspected (see Figure 1, page 22). MBD keeps the all-important digital thread intact, from design to manufacturing to inspec- tion and quality reporting. Everything that defines the part exists in a single digital archive, including specifi- cations for how to manufacture and inspect it. Deployment of MBD can be done ad hoc at an individual part or component level, or it can go far beyond this to com- plete product lifecycle management. For many shops working as sub-contractors, MBD will meet or exceed the requirements for file management, documentation, inspection, reporting and repeatability without the need for a good part to be used as a nominal or comparative for future production. With MBD, everything needed for future production and quality assurance is together, digital and virtual. Reverse Engineering If design or manufacturing data needs to be added to a model— for example, a complex surface profile requiring reverse engi- neering—it easily can, along with geometric dimensioning and tolerancing (GD&T;) annotations that will enable accurate This strategy ensures that all components in the inspection value chain work together, keeping the digital thread intact from design to quality reporting. In-process inspection can be completed on a CNC machine using a portable coordinate measuring machine. inspection of that feature against the model when complete. This is extremely useful to mold builders, in particular, as complex sur- face profiles can be very difficult, if not impossible, to dimension. A CAD platform must be at the root of any MBD strategy, including the quality inspection and reverse engineering func- tions. This will allow the user to import CAD from virtually any platform and increase value through added reverse engineering data, solid modeling, intelligent annotations, inspection and reporting. Modified MBD files must be exportable for manufac- turing or back to the native platform from which the CAD data originated. When combined with appropriate digital measuring devices or coordinate measuring machines (CMMs), these files will allow manufacturing and quality engineers to fill in manu- facturability data gaps and provide confirmation of design intent through integrated quality reporting.