Completing the digital twin with a digital triplet

In recent years the concept of keeping a “digital twin” of a manufactured part has moved from being a concept in military aviation to a reality across many industries. The idea is that for every part made and sold, a digital CAD copy of the part is kept to record the design of that part. For many though it isn’t enough to just record the design of what the part should have been, but also they require a final inspection report of what the part was when it shipped.

A full final inspection report needs to include every surface on a part, and this can only be achieved by using a combination of measurement tools capable of the task along with software able to combine the measured data together in one place.

Manufactured parts have become increasingly complex due to more capable design and optimisation software tools allied to improved capabilities of injection molding, additive manufacturing and 5-axis machining, resulting in the combination of many different types of features in a single part. This is the measurement challenge of today.

Where a part interfaces with another part in an assembly, such as through a pattern of holes, there is a need to measure the holes for position, diameter, cylindricity and maybe perpendicularity to a flange that might only be possible to measure to the required accuracy using a Coordinate Measuring Machine (CMM). It is entirely possible that the same part could also have complex aerodynamic features such as on a turbine wheel where the complexity of the surface of a blade might require millions of measurement points to fully define it, which sometimes might be more practical to measure with additional inspection systems.

It is a similar story with styled components such as electrical consumer goods or automotive interiors, usually moldings that combine complex styled surfaces on their visible “A” side with patterns of holes, ribs, slots and snaps on their “B” sides.

With parts being made by multiple suppliers in far and wide locations, the importance of the mating surfaces between parts is paramount. To ensure that there are never any assembly issues, designers make certain that the known specific critical mating features are correctly toleranced for inspection. These are usually the features that are best measured on a CMM.

Aerodynamic parts, the surfaces of which are crucial to the performance of a machine (be it the outside surface of a vehicle or an internal surface in a gas turbine), also need to be measured and sometimes non-contact inspection methods are best. Similarly, with styled surfaces on consumer electronics, appliances and automotive interiors, how these parts’ surfaces fit together, reflect light, or feel to the touch are crucially important to their success and require an optical 3D scanner to be measured.

Another factor that puts pressure on the inspection process is that increasingly designers put a note on their prints such as: “The CAD is the master and any feature not explicitly dimensioned must be within 0.2mm of CAD”. In one sentence this tells the inspector of the part they will not get away with a CMM inspection alone, unless the part has a very simple geometry

Finally, the concept of keeping a digital twin of a part has moved from being a fantasy to a reality across many industries. Some might call this “actual” model the “Digital Triplet”. This would include the key features of the part denoted on the print, but in order to be a true record it needs also to include all the dimensions not specified; a full 360-degree scan of the whole part, achievable with a 3D optical scanner.

Is it possible then to have only an optical 3D scanner such as a structured light or laser scanner alone and just use that to meet the requirement that all surfaces of the part are within a certain distance of the CAD? The answer is yes provided the part has no holes much deeper than their diameter or any features with tolerances that only a CMM could meet. The answer in most cases must be to look for the best way of combining data derived from a CMM with that collected by a 3D Scanner.

Inspection data, however it is collected, is made up of three dimensional coordinates based on a reference frame with XYZ axes and an origin. This is the case whether the source of the data is a CMM in which the number of data points is likely in the hundreds or from an optical 3D scanner where the point cloud would be in the millions.

The challenge is to have software that can easily combine both sets of data in a common user interface where the task of aligning data sets with CAD nominals is automated. It needs to be easy to use and employ the same programming skills to create inspection reports that include data sets from multiple measurement tools. Hexagon has a wide range of measurement tools available including all sizes of CMM and both structured light and laser scanners. Hexagon also offers the world’s most widely used metrology software PC-DMIS into which its CMMs and Scanners are integrated and in which the data from these tools can be combined.

Don’t miss our upcoming webinar for strategies and tips on how complex 3D part data can be gathered and input into software common to multiple devices and output in multiple different forms. Register for Presenting complex 3D scanned data using PC-DMIS.

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