Scientific, Authoritative and Reliable Digital Twin Manufacturing

The figure below shows a digital twin model of an airframe part. The model contains four thousand holes waiting to be filled by fasteners, and ten thousand holes waiting to be drilled. In this test the unfilled holes must be found and filled. The undrilled holes must be found, drilled and filled. All of the holes must meet requirements for position, placement and diameter. All of the fasteners must have sufficient grip to hold the pin, but not too much or the airframe will be too heavy. And all of the fills must have sufficient sealant to make the structure safe for traveling conditions.

Digital Twin Manufacturing needsuses scientific principles to build digital twins that are authoritative and reliable . The scientific principles are necessaryused to construct representations that have accurate visualizations, and full fidelity simulations. Authority is achievedThe twins are made authoritative by includinggiving them links to all the nominal design data, selected planning options, and met manufacturing requirements. The twins are made Rreliability is acquiredle by keeping them current with the physical product using messaging systems directly connected to manufacturing machines, by verifying them using metrology systems that measure physical dimensions, and by checking them against the design, planning and manufacturing requirements

We are helping the International Standards Organization (ISO) develop standards for digital twin manufacturing so that the world can build twins that are scientific, authoritative and reliable. Two sets of standards are being developed: definitions for interoperable manufacturing in ISO 10303; and definitions for digital twins in ISO 23247. The ISO 10303 standards define the information content of the models so that they can be processed in CAD, CAM and CNC systems. There are billions of STEP models available in CAD systems, and millions of STEP-NC models are being machined annually for assembly into airframes.

The ISO 23247 standards define how the digital twins are connected to each other and manufacturing machines. A three-layer network is used for connectivity. The lowest and fastest layer feeds instructions into the machines, and reads the locations of the actuated devices (shown as the OME in the figure below). The middle layer buffers the inputs and outputs so that data is always ready for the machines without overloading the modeling layer (shown as the DCE). The top layer keeps the digital twin model synchronized with the physical twin using the messages sent by the machine layer and buffered by the middle layer (shown as the DTE). New parts of the standard are going to describe how to link the digital twins together into a digital thread, and how to compose sets of twins to make larger twins that represent bigger products such as the airframe that is assembled when all its components are fastened together.

STEP and STEP-NC have been under development for forty years. Slowly and methodically, all of the features and attributes of products and processes have been modeled into an extensible framework. Using scientific principles, a team of experts determines what is necessary to completely and unambiguously describe a new kind of product or process. For example, the principles are currently being applied to Powder Bed Fusion. For this process, the engineer needs to describe how the product is sliced into layers, that are divided into regions, that are filled with hatches, and surrounded by contours. The result is then defined as data and added to the framework so that any STEP product can be materialized by a powder bed fusion process.

To enable deployment, digital twin manufacturing has to be more reliable than traditional manufacturing. Reliability requires a framework that delivers data that cannot be denied or synthesized. In the ISO 23247 framework the source is always a machine that performs an action. Not a person with excessive anticipation, or worse with malintent. However, even with the best science some processes cannot be fully quantified so measurement must also be in the framework. For example, the inner mold line (IML) of a composite structure has an irregular surface that must be measured so that it can be adjusted using shims or by machining. Metrology systems measure parts using an increasingly sophisticated range of devices. Many of them can report their results using QIF. Updating the geometry of a STEP part using QIF is an active development project of the STEP community.

In the Spring we will be making four thousand holes in Blackburn, Lancashire (obscure reference). Actually, it will be in Seattle, Washington. Digital twins will be made for the four thousand, and like the song says then we will know .how many holes if takes to fill the Albert Hall.. We will also know more about how to make digital twins for Powder Bed Fusion components, Composite Tape structures, Machined parts and Assemblies of large airframes containing variable components. The lessons learnt will strengthen both the ISO 10303 and ISO 23247 standards, and allow the community to more easily deploy digital twins that are scientific, authoritative and reliable.