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Building and Verifying Tooling for F-35 Fighter Jet Canopy

By James Barns Managing Director, Metrology UK

A fitting example of practical precision tooling using advanced metrology

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Pilots never see the outside world through the canopy. They see an image of it.

Hockley Pattern & Tool, Halesowen, England, is an example of a company dedicated to the art and science of making perfect tooling.

This article is about how Hockley builds and verifies advanced tooling. Form tooling and fixturing as a manufacturing concept has spanned the ages and today remains the foundation for many advanced parts, including the cockpit canopy for the most advanced aviation platform ever created—the F-35 fighter jet.

The complexity and precision of today’s composite parts rely heavily on the layup tools that make advanced forming possible. These layup tools—and those who design, manufacture, and inspect them—are the unsung heroes behind the many parts and finished products that rely on high-strength, lightweight composites.

As with most manufacturing applications, there is constant improvement in materials and processes that make the manufacturing of high-tech parts faster and cheaper with ever-improving quality. Throughout this ongoing evolution, one thing remains constant: layup tooling is critical for both functionality and quality.

There are many hand-offs in the manufacturing and assembly of composite parts, which often include machining, coatings, finishing, and add-on components. If the layup tooling is not perfect, the foundation is flawed.

At the heart of the UK tooling manufacturing industry for more than 25 years, Hockley Pattern & Tool supplies high quality tools domestically and internationally to major aerospace and automotive manufacturers and their supply chains. “When it comes to designing and making tooling, it can be both a creative and highly technical process,” said Neil Williams, director of Hockley. “Typically, we receive prismatic 3D CAD models that we use to design, build, and inspect finished tooling. But we are often asked to create tooling from an artifact, which can be an organic shape or prismatic part for which there are no CAD models or drawings available. Regardless of how a job comes to our shop, every finished tool includes a quality inspection report tied to a 3D CAD model.”

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Hockley Pattern & Tool is an example of a company dedicated to the art and science of making perfect tooling.

For Hockley to fulfill its promise of delivering a CAD model-based quality verification report with every finished tool, it relies on Verisurf software and compatible measurement devices from Verisurf Software Inc., Anaheim, Calif. With the operative word being CAD-based, Verisurf was selected on four compelling points:

  • Verisurf software is model-based and built on a CAD platform, including 3D modeling.
  • The software provides flexible measurement, reverse engineering (including Class A surfacing), inspection, tool building, and assembly guidance.
  • Verisurf software imports and exports intelligent CAD files and models seamlessly, can edit existing intelligent GD&T data, and can add new GD&T annotations as necessary.
  • Verisurf supports and runs virtually all digital measuring devices from contact probing to non-contact scanning, regardless of age, controller type or proprietary software, including CNC CMMs, arms, trackers, and all types of scanners.

The flexible combination of an open software platform and a variety of measurement device options allows Hockley to develop and/or maintain digital continuity, or the digital thread, throughout every job.

“Verisurf software has truly raised our quality control levels with its unique set of application tools that speed up our tooling inspection,” said Robin Walton, quality manager for Hockley. “We also use Verisurf Reverse integrated CAD and solid modeler to produce surface models direct from our scanner. The color error mapping and labeling is outstanding and allows us to confirm the accuracy of our work in real time.”

F-35 Canopy: A Fitting Example

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Verisurf Build, also known as the Virtual Gage, displays real-time deviation following the movement of a CMM laser tracker or probe, inspecting the part in relation to the nominal CAD model.

Hockley was tasked with building, inspecting, and delivering tooling for the canopy of the F-35 joint strike force fighter jet. The job required high tolerances given the fact that the canopy, or transparency as the assembly is commonly referred to, comprises a framed windshield and canopy that is produced from a single piece of stretched acrylic, with no steps or gaps in the outside mold line.

The F-35 is the world’s second fifth-generation tactical fighter designed to satisfy four key objectives: lethality, survivability, supportability, and affordability. The concept behind the F-35 Lightning II cockpit is to “return the pilot to the role of tactician,” according to its designers. This is accomplished by using computers to do what computers do best and allowing pilots to do what pilots do best, with optimum pilot/vehicle interface (PVI), manageable single-seat workload, and superior situation awareness.

Pilots never see the outside world through the canopy; they see an image of it. Every manufactured canopy optically distorts the view of the outside world in a unique way. Aerial and ground targets viewed through head-up and helmet-mounted displays can be distorted by imperceptible deviations in canopy thickness, curves, and material. In other words, the canopy can have a direct effect on weapon accuracy. To mitigate this, every canopy is manufactured and verified to extremely tight tolerances. Each canopy is then optically mapped and matched to a specific aircraft as part of the assembly process, with optical deviation data stored in onboard systems to correct the pilot’s view of the outside world, in real-time.

Live, Intuitive Interface for Build Module

As part of the tool building process for the F-35 canopy, Hockley used several key features of the Verisurf software, combined with appropriate measurement hardware devices, to ensure accuracy and quality verification.

Verisurf Build, also known as the Virtual Gage, displays real-time deviation following the movement of a CMM laser tracker or probe, inspecting the part in relation to the nominal CAD model. Following quick alignment to the CAD model, Build’s live, intuitive interface shows part-to-model deviations.

“The software has been a game changer for us by providing not only clear and decisive tooling verification, but also live digital tooling setup and positioning for advance tooling applications in our aerospace department,” said Paul Squire, engineering manager for Hockley.

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In this example of a 36' (10.97-m) wind turbine blade (not involved in the F-35 project), Verisurf is used to identify areas of ‘local’ waviness on the surface profile that need to be corrected. This is done across the entire profile of the part providing both global and localized analysis and reporting. Hockley used this Verisurf feature in the F-35 project.

In addition to dimensional control, Hockley utilizes the Verisurf Build interface for several additional functions, including:

  • intermediate setup inspection for machining datum establishment to optimize the machining process;
  • in-process positioning of ancillary components on tooling assemblies with live guided adjustment;
  • tooling point clarification and positional controls;
    off-site verification and inspection on larger in process tooling build items; and
  • the ability to live build reverse engineered CAD, especially when carried out off-site, which instills customer confidence in raw tooling data prior to final machining.

Determining ‘Waviness’ of the Tool Surface

The F-35 canopy is both an aerodynamic component and a lens that transmits and refracts light. Add to this the aircraft’s performance capabilities and piloting objectives and there is little room for error surrounding the entire transparency system. Identifying and minimizing waviness of the canopy tool surface helps mitigate optical and aerodynamic deviations, maintaining surface performance and lessening the amount of optical correction needed from onboard systems.

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The canopy is built to withstand the impact of a 4-lb bird at 480 knots on the reinforced windscreen and 350 knots on the canopy crown without breaking. Specialty coatings are applied to the finished canopy to maintain low-observable or stealth characteristics.

A specific analysis feature of Verisurf software is used to determine waviness of the tool surface, both within a local profile and relative to deviations across the entire surface. This provides data to the user to help them correct the tool if necessary. The feature provides:

  • Global Deviation Analysis: The first analysis performed is the global profile, which provides a deviation map showing the rigid body full point set. This is the standard analysis performed to view the total deviation compared to the nominal CAD model.
  • Local Range Analysis: The range is the first local profile analysis performed. It determines the total range of the points within the point set analyzed. In the example, every point within a user defined radius of 10" (25.4 cm) is analyzed to get the greatest high/low range within that local profile.
  • Local Deviation Analysis: The deviation of the local profile analysis provides the total deviation from the CAD nominal of the points within the established local profile. This is used to identify and repair high and low spots.
  • Local Profile Average Analysis: Averaging the local profile analysis provides an understanding of average deviations inside of the local profile to bench the part for better results.

Modern Metrology, Traditional Manufacturing

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Form tooling and fixturing have a long history and remain the foundation for creating many advanced parts, including the cockpit canopy for the most advanced aviation platform ever created, the F-35 fighter jet.

Verisurf software is an example of integrating modern metrology with traditional manufacturing methods to raise the bar on what is possible. Built on a CAD platform, Verisurf supports the natural progression of model-based design, engineering, manufacturing, and quality verification. This maintains digital continuity throughout every step of the design/build process.

“The evolution of tooling in manufacturing has advanced more in the past 20 years than any other period in history,” said Ernie Husted, president and CEO of Verisurf Software. “High-tech materials have been a critical contributor, but without the experience of expert toolmakers and the integration of CAD, reverse engineering, and metrology solutions, finished platforms such as the F-35 would not be feasible today.”

F-35 General Characteristics

  • Crew: 1
  • Length: 51.4' (15.7 m)
  • Wingspan: 35' (11 m)
  • Height: 14.4' (4.4 m)
  • Wing area: 460 ft2 (43 m2)
  • Aspect ratio: 2.66
  • Empty weight: 29,300 lb (13,290 kg)
  • Gross weight: 49,540 lb (22,471 kg)
  • Maximum takeoff weight: 70,000 lb (31,751 kg)
  • Fuel capacity: 18,250 lb (8,278 kg) internal
  • Powerplant: 1× Pratt & Whitney F135-PW-100 afterburning turbofan, 28,000 lbf (120 kN) thrust dry, 43,000 lbf (190 kN) with afterburner
  • Maximum speed: Mach 1.6 at altitude; 700 knots (806 mph; 1,296 km/h) at sea level
  • Range: 1,500 nautical miles (1,700 miles, 2,800 km)
  • Combat range: 669 nautical miles (770 miles, 1,239 km) on internal fuel; 760 nautical miles (870 miles, 1,410 km) interdiction mission on internal fuel, for internal air to air configuration
  • Service ceiling: 50,000' (15,000 m)
    G limits: +9.0
  • Wing loading: 107.7 lb/ft2 (526 kg/m2) at gross weight
  • Thrust/weight: 0.87 at gross weight (1.07 at loaded weight
    with 50 percent internal fuel)
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