Consideration of model based definition, sometimes called digital product definition, is important. This is the methodology where 3D solid models and associated forms of data provide specifications for product. The collection of such data is sometimes collectively referred to has the 3D digital data set. Specifications that may be included within the 3D digital data set include general dimensions, geometric dimensioning and tolerancing, component material, features and geometry external links, configurations, design intent, function, bills of materials and other details. Most advanced 3D CAD software allows users to include many types of specifications within the 3D solid model. PDM and PLM systems may also be employed to contain some types of data.
Model based definition is often seen as a way to replace the use of engineering drawings. Drawings commonly contain most of specifications under traditional systems. Some view drawings as time consuming to produce, and too far removed from the original 3D digital data set. Paul Hamilton commented on this last year,
Much time goes into creating fully detailed drawings. They can be expensive to create and manage. They can be easily misinterpreted. If developed from a 3D model, there is much duplication of effort. With duplication of effort comes a higher potential for error. Drawings can quickly become detached or unrelated to the 3D model. Once printed, they can become even more detached from the 3D model, and the opportunity for error increases.
Even still, Mr. Hamilton notes that he has not seen a notable example of a successful implementation of MBD to the extent of completely elimenating drawings.
In my view, 3D CAD software is not yet up to the task to completely use MBD to the exclusion of drawings for many cases. One reason is because any information traditionally included on an engineering drawing has to now be stored in the 3D solid model. 3D CAD applications may not have the ability to contain certain types of specifications within their file format. Additionally, the amount of work to document specifications within the 3D solid model may increase workload because the detail no longer relies on drawing shorthand avaiable in ASME Y14.5 or ISO. Another factor is low adoption rate of the software necessary to communicate this information from customer to vendor (and sometimes back). 3D CAD software that is sophicated enough to contain this type of information within their file format is very expensive and requires expensive yearly maintenance. Most MBD information is not carried over in neutral formats such as STL, STEP, or IGES. It’s not uncommon to find a scenario where the MBD is used in conjunction with partially dimensioned drawings.
ASME Y14.41-2003 was created to standardize practices within certain aspects of MBD. In my view, this standard is not developed well enough to be useful as such. It’s up to companies to work with their downstream and upstream partners to development a system where MBD may be used, at least partially.
I am interested to hear from everyone about attempts they’ve experienced (successful or failed) in the implementation of model based definition. Let me know.