Composites/AM – Circle of Life

By on February 7, 2019 in DESIGN/MODELING/SIMULATION

Holistic optical metrology reduces costs, improves quality.

Optical methods optimize composites and additive manufacturing (AM) for next-gen vehicles, from materials through life extension. Industry uses optical measurement systems throughout the design and manufacturing of next-generation material, structures and products. Optical metrology, Digital Image Correlation (DIC) and photogrammetry are critical measurement methods because of their ability to measure the material or structure holistically, simply and rapidly.

Advanced manufacturers, like Ford and GM, and aerospace Boeing and NGC, use the technology day in and day out, but smaller companies without the complex design and testing infrastructure can benefit even more. 3-D Digital Image Correlation is a finite element measurement and allows you to intuitively understand the material response of complex structures, providing the CAE (computer-aided engineering) engineer with powerful tools to understand structures and designs.

Optical metrology is playing an important role in the Factory of the Future from engineering to manufacturing operations and structural health monitoring. As the technology has evolved from its research origins to its current real-time capacities, it provides leaner and smarter ways to achieve better quality and optimized measurements.

At each step of the manufacturing process, optical metrology is expanding our knowledge of materials and structures for improved quality and digital manufacturing, subsequently reducing costs by reducing the time and effort to maintain and document quality.

In its simplest form, 3-D optical metrology uses two cameras for stereo-imaging photogrammetry to locate points in 3-D space by triangulation. Similar to your eyes, ARAMIS, a non-contact and material-independent measuring system, can locate and track points in 3-D space. Your eyes tell you the part is about an inch long. A 3-D photogrammetry system can locate the points in 3-D space with the precision of a coordinate measurement machine (CMM) to the micron level accuracy by “not-so” simply using camera images.

The powerful software is able to interpolate the 3-D image down to 1/1000th of a pixel of the camera for incredible accuracy and resolution. And be able to provide this same accuracy across the full field of your components and products.

Optical metrology is transforming the way we measure things. 3-D digital image correlation (DIC) is the ideal tool for precision materials-properties measurements, core to higher precision finite element analysis (FEA) models. Structurally testing complex composites with DIC can be company critical because it provides the reality of structural response, with precision full-field measurements of all the components working together. In this way, you can have a comprehensive understanding of what really is happening to your complex, nonhomogeneous structures.

Using the same tool for in-situ measurements and digital manufacturing means every step can be captured as the digital thread of the assembly or assembly line, with realtime quality assurance (QA), and in the end assembled, as the digital-twin data set.

Space applications are ideal for lightweighting. On the NGC James Webb Space Telescope (the successor to the Hubble), the structural testing was monitored with 3-D DIC on all four sides of the satellite, saving having to mount and calibrate many hundreds of linear variable differential transformers (LVDTs) and saving one week/ month of schedule, which was more than $2 million in savings during the three-month program. So, the systems paid for themselves in the first month of use and are still working hard, every day.

Instantly measuring shapes for part validation, locating parts in real time for precision assembly, monitoring assembly deformation and strain, confirming assembly tolerances—the applications are endless for improving manufacturing quality and lean manufacturing. Transparent manufacturing is the next step in lean, precision manufacturing. Understanding everything about streamlining your processes and methods leads to higher product quality.

At each step of the manufacturing process, optical metrology is expanding our knowledge of materials and structures for improved quality and digital manufacturing.

Modern 3-D photogrammetry is not your father’s photogrammetry. It is real time and highly accurate. In aerospace composites, digital manufacturing means you can build right from computer-aided design (CAD), placing components with high accuracy and documented cured location as part of the digital thread, for real-time documented QA in half the time of hard tooling and at a fraction of the cost. In automotive, the same digital thread allows precision, documented setup of tooling and the line.

When it comes to structural testing for material properties, fracture mechanics, full-field deformation and strain, vibration and shock testing, 3-D photogrammetry tests structures holistically, a true finite element measurement. These measurements are made just like your computer model calculates it, from the design’s 3-D coordinates. An accelerometer is interpolating for modal response, while ARAMIS measures it directly. Optical metrology is a better tool for our new world of advanced, nonhomogeneous materials and structures, especially for additive manufacturing and composites.

STRUCTURAL TESTING HOLISTICALLY

Optical methods let you understand your structures holistically because it is a full-field method. Individual components can be modeled effectively, but when they are combined into larger structures, the modeling assumptions exceed desired accuracies. It’s been said, “If you are developing with composites and are not using ARAMIS, you do not know what your structures are really doing.”

Buckling requires a real-time, full-field method for which optical measurements are ideally suited. Ron Slaminko, Boeing BT&E, Retired, was asked, “You got the ARAMIS system for composite buckling studies, what are you using the system for now?” He responded, “Everything.” He went on to describe the test he had just run on a smaller wing structure to validate the computer model.

Boeing Engineering had spent two weeks putting 200 strain gauges across the structure. Slaminko and his technician patterned the structure in the morning and tested in the afternoon. He immediately observed that the model was wrong and the strain gauges were not in the right places. They then used ARAMIS data to validate the model.

This is a good example of where ARAMIS is a better choice than strain gauges and can save companies millions of dollars. Those 200 strain gauges at an installed net price of $1,000 each were more than the cost of the ARAMIS system, which is still in use today. ARAMIS is now equivalent to a strain gauge at many companies and organizations, including NASA, the U.S. Air Force and Boeing.

The ultimate structural field test was performed on the Space Shuttle Discovery, grounded for cracks in the external fuel tank (ET). Two custom ARAMIS sensors were mounted to the launch platform, measuring the ET while the tank was fully filled with cryogenic fuels, liquid hydrogen (LH2) and liquid oxygen (LO2).

Engineers from Trilion Engineering Services were in the Launch Control Center, two-and-a-half miles away, controlling the optical measurements through a fiber-optic network interface. ARAMIS data helped validate the FEA models and repairs. Launch was then rescheduled for the following month. Trilion was invited to Space Shuttle Discovery’s final launch as VIPs and given awards for their work as the ET photogrammetry team.

HIGH-TEMPERATURE MEASUREMENTS

As a fully optical method, 3-D DIC is completely noncontact. This gives ARAMIS unique abilities in extreme or hazardous environments, like engine dynos. Accurate high-temperature measurements are readily achieved, even through an oven window. As long as the cameras are not directly affected by the hazardous environment, they maintain their calibration and remain accurate.

Light is basically unaffected by the environment. 3-D deformation and strain measurements, up to 1,400 degrees Celsius, are typical. This equipment is being used daily for high-precision measurements of low coefficient of thermal expansion (CTE) ceramics to 1,000 degrees Celsius—a very demanding application.

Engine studies regularly use the 3-D DIC method. The CAD coordinates are imported, so all measurements are in vehicle coordinates. Engine thermal 3-D deformation and vibration studies easily measure hundreds of points, and all points are measured synchronously.

This synchronous measurement is extremely powerful, enabling you to measure how all components are moving relative to each other, holistically, as a complete system. No other technology is capable of letting you see the complete response of your system.


Structural health monitoring (SHM), using optical metrology, is a simple enhanced visual inspection, but with the power of millions of strain gauges.


ADDITIVE MANUFACTURING:

Holistic non-destructive evaluation (NDE) is critical for non-isotropic materials

Optical metrology provides a holistic measurement of nonisotropic materials like additive manufactured (AM) parts that are point-by-point welded together. Witness coupons are validated in a full-field manner, providing complete understanding of the build process. Critical full structures are then use loaded and tested to confirm operational strength for its design purpose. This is to address qualification of additive manufactured parts in the context of their extensive variability, to achieve inexpensive and yet useful description and quantification of AM part performance.

ELECTRIFICATION CONFIGURATIONS
Toolless manufacturing with optical metrology

Real-time Virtual Assembly Tooling (RVAT) was developed so that advanced composite structures could be built directly from CAD, documenting accuracy and quality, and capturing the as-built design for the digital twin. Every composite part is a little different. Hard tooling is locating a generic part. RVAT tracks the actual part to its critical design location to the extent that the bondline thickness is determined for each component. The entire build is captured as-built, each digital thread of the build for the complete digital twin of the actual vehicle build. This same methodology works for automotive line and tooling setup right from CAD.

Other manufacturing operations are also completed simply and easily with higher quality and full documentation. Sub-components, such as click bonds, can be tracked in, in real-time, at 10 to 100 times faster and more accurately than traditional methods. Drilling operations are 10 times faster and more accurate. 3-D locations of click bonds or drill holes are dropped into the RVAT software, and their locations are precisely located in CAD coordinates on the real structures. Operators or robots are then guided in for rapid, real-time assembly with integrated QA.

Once completed, every step is documented for quality and precision. The digital twin can then be published for internal use or for customer documentation of as-built quality.

OPTICAL STRUCTURAL HEALTH MONITORING

Structural health monitoring (SHM), using optical metrology, is a simple enhanced visual inspection, but with the power of millions of strain gauges. Typical SHM is basic visual inspection. Sensor-based SHM uses wired sensors with large, power-hungry, real-time computers monitoring for “events,” but even then tells the user little about the effect on the structure. Optical SHM allows for robotic measurement of every vehicle rapidly and effectively without any onboard sensors and their attendant cost, weight and power requirements. Optical SHM provides real structural damage, or weakness data, for predictive maintenance and life-extension knowledge. With SHM, one customer expects to reduce their design allowables, with a 20-percent weight reduction in the aircraft structure. This is powerful for automotive testing and structural validation, for long duration testing or crash testing.

CONCLUSIONS

Holistic optical metrology provides a complete knowledge-based solution for the speed of change of new industry and for the everyday issues that confront industry. It greatly reduces costs, improves development schedules and overall quality.

Implementing optical metrology to the quality areas reporting back to engineering digitally dramatically improves communication between departments and makes entire processes more efficient. Completely understanding your materials’ behavior improves entire processes from start to finish—a primary objective of Lean Engineering.

Gathering data more efficiently and completely, with less wasted time and fewer resources, provides more educated assessments, resulting in more complete solutions to the typical issues that occur in the manufacturing arena—a primary objective of Lean Manufacturing and lightweighting. The auto industry can learn from what the aerospace industry already knows.

Today, optical metrology optimizes time, costs and quality, thereby increasing a company’s competitiveness with Lean Engineering and Lean Manufacturing. These measuring technologies are more and more being used for automated inspection tasks as they are integrated in the processes and available to powerful data-processing systems. The data is linked and automatically uploaded to the quality-control system for lean precision operations globally.

Authored by John Tyson II

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