Traditionally, 2D data (e.g., drawings, static documents, static parts lists) are the authoritative source for technical data used within the government to acquire products from its supply chain. Going beyond 2D data and introducing 3D data demands sophistication when establishing systems for the exchange and collaboration of 3D data. Since the benefits of using and re-using 3D data are significant, it is important to acknowledge the differences in 2D and 3D data that comprise TDP.
2D TDPs are often defined as a bundle of files with a finite list of file format types prescribed in MIL-STD-31000B. Traditionally, 2D TDPs consist of PDF (Drawings) and Microsoft documents (e.g., Word, Excel). 3D TDPs include 3D file formats (e.g., native CAD, neutral CAD, and data types not yet invented) but may also include the 2D files mentioned previously. Therefore, a single file does not, and will not, define 3D TDPs.
Adding 3D TDPs to the DoD Acquisition Process does not preclude 2D TDPs from also being procured. Acquiring 2D TDPs may be the most effective artifact to document products defined using schematics or those having very simple geometry, such as a washer. 3D TDP acquisition should focus on products with complex geometry, complex first article inspection requirements, complex assembly operations, and those products that experience quality escapes due to drawing documentation errors. A rigid binary “all or nothing” 3D acquisition process is not pragmatic.
A 3D TDP should consist of digitally connected files that define the product and optimize consumption during fabrication, assembly, inspection, test, and sustainment. Model-Based Definition (MBD) authoring practices divide native source 3D data into five categories: Geometry, Annotations, Attributes, Presentation States, and CAD Structure.
Figure 2 represents the framework of a product definition data set and depicts the complex relationships of native CAD data elements and how they connect to the most common artifacts used in manufacturing, quality, and sustainment activities. The figure illustrates the opportunity of connected 3D TDPs but is not intended to define the final future state of a 3D TDP for use by the DLA to acquire hardware. The persistence of 3D data throughout the lifecycle establishes the digital thread and is the fundamental principle defined in Figure 2. Any derivations of acquired 3D TDPs should persist from Native CAD into Derivative data. Persistent connected data results in a digital thread.
TDP Data Elements
A 3D Native CAD part consists of Geometry, Annotations, Attributes, and Presentation States. A 3D Native CAD Assembly has the same four parts plus CAD structure that feeds the Parts List. The source Native CAD product definition data and other associated data may be published and bundled into a 3D TDP. Subsequent sections describe each TDP data element in the effort to differentiate PxM software tool capabilities described in sections 3, 4, and 5.
2D and 3D Data Differences
The importance of distinguishing between 2D and 3D data is rooted in the how the data is consumed.
- 2D data: Technical information presented as a 2D drawing or other static document types that require manual human interpretation.
- 3D data: Technical information presented as a dynamic 3D model that facilitates machine consumption opportunities while also displaying much of the 3D data for the human reviewer.
Figure 3 represents the connected opportunity of 3D TDP data and illustrates the opportunities available.
TDP Data Elements
Geometry is the digital shape of a component. The CAD system uses mathematical functions and coordinates to define the 3D shape and features of the part digitally. Displayed dimensions are not required for this type of machine consumption and should only be displayed to support manual data entry scenarios. The geometry is theoretically perfect and replaces what used to be presented as basic dimensions on the drawing.
Annotations, often referred to as Product and Manufacturing Information (PMI), are tolerances, notes, and symbols used to capture the requirements of the product. Because the geometry is 3D, the tolerances must also be geometric to constrain the model features mathematically and be digitally associated with the geometric features they represent. The Digital Product Definition Data Practices Standard ASME Y14.41 requires both digital associativity of the tolerance to the geometry it represents and for humans to see that digital relationship on the screen. This relationship is called a visual response. Although not needed as computable data, the visual response is a courtesy to the human reader to build trust in the annotated 3D model and remove the ambiguity inherent in interpreting traditional 2D drawings. To further reduce ambiguity, reduce visual noise, and provide a focus for the human reader, the best practice is to display only those annotations that apply a modification or refinement of the basic dimensions inherent in the 3D model.
Because the geometry is 3D, the tolerances must also be geometric to constrain the model features mathematically and be digitally associated with the geometric features they represent.
Attributes do not require associativity to 3D geometry. Per ASME Y14.41, attributes are the information that is not visible on the model but available upon interrogation of the model. Attributes are often captured in text format and may also be known as metadata. ASME Y14.47, Model Organization Practices, defines the nomenclature of the metadata to standardize attribute interoperability across native and neutral CAD formats and data management storage systems. The most common attributes are Part Number, Part Description, and Material. Such prescribed attributes provide common variable names so that the PxM data interoperability remains consistent and provides the desired digital thread.
Presentation States are display snapshots that organize information for humans to read as non-orthographic views. Presentation States are not machine-readable, but they help build human trust in the attributes and annotations that contain the information expected, which are machine-readable. A significant benefit of Presentation States is that humans “learn” the products faster because there is less spatial interpretation than with a 2D drawing.
CAD Structure / Parts Lists
This TDP data element exists only in an Assembly. The CAD Structure is a hierarchy of components (parts and subassemblies) that comprise the assembly. The number of component instances, the component title, and other specified attributes are captured digitally in Native CAD systems to automatically populate a parts list. A digital parts list may be published as a 3D Interactive Parts List, reducing the cognitive load.
Other Associated Data
Any digital document can be associated with a TDP. Other documents often published from the five original TDP data elements (Geometry, Annotations, Attributes, Presentation States, and CAD Structure) are:
- 3D Interactive Viewable with Interactive Parts Lists (e.g., 3D PDF or web-based HTML)
- 3D Derivative (e.g., STEP, QIF, JT)
- 3D Derivative Validation Reports (e.g., 3D PDF or web-based HTML)
- 2D and 3D Change Reports (e.g., 3D PDF or web-based HTML)
- Manufacturing Data (e.g., in-process 2D or 3D data, plans, 2D or 3D work instructions)
- Quality Data (e.g., Bill of Characteristics, FAI/PPAP Reports)
- Sustainment Data (e.g., 2D or 3D Technical Manuals)
- Technical Data Package Lists
- Quality Assurance Provisions (QAP)
- Software Documentation
- Packaging Details