Model-Centric Makes Sense
by Jerry Fireman

The practice of using 2D drawings as the master deliverable in the design process is fading fast, as many leading companies are adopting a new approach called model-centric design, where the 3D model is the central source of all design information.

One key driver in this trend is the development of new standards for 3D model annotation which specify that 3D drawings now include all information to satisfy the needs of downstream users.

By giving design engineers the power to annotate the 3D model, model-centric design can save time during the design process by enabling a single 3D master model to replace many 2D drawings and other deliverables that define the product. A single, centralized model also reduces the potential for errors because everyone operates from a single source of information.

Model-centric design reduces the product lifecycle by making it possible to quickly produce ‘build-to’ packages, that is, sets of documents that contain all data required to manufacture components, and provide all the information contractors need to begin production.

Conventional drawing-centric design process. Even though most companies have adopted advanced 3D design tools, most of these tools do not provide complete information in the 3D model needed to fully define the design. For example, data regarding dimensions, notes, symbols, surface finishes, geometric design and tolerance data, signatures, revision numbers, material specifications, and other information — missing from the model — must be added to 2D drawings, which then become the primary source of design information.

Engineering and detailing departments typically create one drawing, but there may be different deliverables for each downstream consumer, such as procurement, manufacturing, inspection, and so forth. There is usually a considerable amount of duplication of data in these deliverables, which increases overall product development time. Each unique deliverable must be managed and maintained throughout the product lifecycle. When a change is made to a design, it generally takes too long to redo all the associated drawings, so “hanging paper” is attached to the drawings to denote the change. Continual changes to the design create the potential for errors, and drive the need for frequent discussions to ensure everyone is working with the latest information.

A key role for 3D models. A 3D solid model that provide the complete geometric definition, product definition, process characteristics, and key design characteristics can become the source of all product definition communications, thus eliminating the need to create most engineering drawings. These models can then flow seamlessly throughout the organization to satisfy the requirements of all product stakeholders. The 3D model displays all the annotations needed to fully design the product, and can be used to generate whatever deliverables are required, while maintaining full associativity.

Advanced users — having access to the CAD software used in creating the model — can query and extract any information they need. The requirements of the majority of downstream stakeholders, however, can be satisfied with technical data packages, which can be produced from the master model in a fraction of the time required to create a drawing set.

The technical data package typically consists of a ‘lightweight’ (small byte size) 3D model of the part, which can be zoomed, panned and rotated using free downloadable software, providing a much greater understanding of the design than could ever be obtained from 2D drawings.

This 3D model can be annotated with notes and critical dimensions that are tighter than any standard dimensions that can easily be held with a computerized numerical control (CNC) machine. The build-to package usually includes both a PDF file with information such as the revision history and signatures, and a STEP file that can be used as the basis for creating a CNC program for machining the part.

Downstream users, who traditionally rely on extracting or deriving data from a drawing-based data set, can now use model data instead. Also, other important product information can be easily accessed through the 3D model data, including requirements and their evolution, design decisions and their rationale, engineering change notifications and their justifications, and logistics information through disposal.

Annotating the 3D model. A critical additional requirement for model-centric design is the ability of the 3D model to support complete product geometric annotation. Pro/ENGINEER enables you to save parameter data with the model, plus it offers a wide range of annotation features. Notes, surface finish symbols, dimensions, geometric tolerances, set datums, and other annotations can be created and organized right within the Pro/ENGINEER 3D model. These features are interactive, intelligent and fully associative. Both conventional and user-defined 3D symbols can be placed on annotation planes and displayed in the model.

Annotations can be displayed in a variety of ways in the native CAD software, such as with and without leaders, and be attached to any geometry or features. Text styles, colors and fonts are also customizable.

Annotation features can reference specific model geometry and can be associated to features, so they will ‘fail’ if their reference is removed. For example, if an annotation called ‘remove burrs’ is associated to an edge; the annotation will be removed if the edge is removed. Annotation features can be classified and visually organized such that views can easily be established for specific users to see content related to their role.

Annotations can also include parameters. For example, a parameter called ‘color’ might take different values in design variants. Annotation features are also searchable via the search tool based on references or classification types.

Capturing process knowledge in the 3D model. Beyond 3D model annotations, model-centric design provides a host of additional benefits to downstream processes. Manufacturing process characteristics can also be captured in the design model and leveraged in downstream applications. Pro/ENGINEER provides capabilities for generating computerized CNC machining programs. Computer machining simulation capabilities make it possible to simulate the machine, tooling, and controls to optimize productivity and quality.

Model-centric design can take this approach one step further by enabling the manufacturing engineer to both create parametric design features and associate validated manufacturing processes with them. The design engineer uses these features to create the product. Then, in the manufacturing environment, all process information is automatically extracted from the design model to optimize the process. Once again, all information emanates from the single 3D master model. This integrated environment enables both ‘traditional’ manufacturing toolpath simulation, as well as more advanced simulation that takes into account machine dynamics, forces and tool loads.

Powerful simulation tool. The model-centric design approach streamlines the use of simulation when evaluating alternatives, early in the design process, to optimize performance and reduce or eliminate expensive late-stage design changes.

With a conventional simulation approach, design engineers throw the initial product design ‘over the wall’ to analysts who work independently to optimize it, often without much interaction with design engineers or any knowledge of changes that are being made concurrently while they are working.

With the model-centric approach to simulation, changes made to the 3D master design model can be used to update the analytical models at any time, at the discretion and timing convenient to the analyst. The analyst can perform trade studies and complete multi-disciplinary optimizations, and then send the optimized geometry or additional features back to the design engineer.

Generating associative deliverables from 3D models. All information captured in the 3D master model can easily be extracted for publication in drawings, manuals, and reports. The data can also be viewed or queried in a product viewer, and accessed by other applications.

Deliverables appropriate for other specific purposes can also be easily generated. Machine tool paths, rapid prototype formats, casting and mold designs can be automatically generated from the solid model. Harness layouts and sheet metal flat patterns, along with part nesting, can be automatically generated based on the 3D model. The associativity of Pro/ENGINEER, ensures that all of this information will update automatically whenever the design changes. Annotation features can also be accessed downstream in the product development cycle by non-CAD users via easy-to-use product visualization tools.

Compressing the product development cycle. Model-centric design has the potential to dramatically compress the product development cycle. The use of a single, unified, consistent, and complete digital product definition data source greatly reduces the time required to produce design deliverables. Further, product development lead-time is substantially reduced because the master model can be used to quickly produce a technical data package that contains complete and more current information than a traditional drawing package. And lastly, the potential for errors is substantially reduced since the master model always contains the latest engineering changes, and even the smallest supplier can now work from a full 3D model.