Numbers are critical to the smooth functioning of the international aerospace industry. Regulatory authorities such as the Federal Aviation Authority (FAA) and the US Department of Defense (DoD) mandate that aero components be permanently marked to ensure authenticity and traceability throughout the supply chain and into service.
Although, marking adds no intrinsic value to a component and forms no technical functional purpose, it is central to the smooth operation of the industry. It allows components to be correctly tracked, identified, assembled, maintained and positioned. Marking also helps address issues such as the use of counterfeit parts in the supply chain which have been implicated in a number of air accidents.
Typically, the requirements for marking aircraft components are set out in international standards such as the Unique Identification Marking (UID) standards established by the DoD. However, these markings also fall under general civil aviation certification requirements.
Under FAA rules, for example, the requirements for the identification and registration markings on engines, engine components, and items such as propellers are set out in 14 CFR, Part 45. Under these rules, manufacturers that produce, for example, propellers, propeller blades, or hubs under a type certificate or production certificate must mark each product or part. These regulations also cover the identification of certain replacement and modified parts produced for installation on type-certificated products.
These markings must be placed on a non-critical surface, where they cannot be defaced or removed during normal service, or be lost or destroyed in the event of an accident. In addition, there are a series of requirements establishing the information that must be contained in the markings. For instance, under FAA rules the data included in the identification must contain the manufacturer's name, the model designation, serial number, type certificate number and production certificate number, if there is one, and for aircraft engines, the established rating.
In addition, the FAA approves components produced by some manufacturers under its Parts Manufacturer Approval (PMA) scheme, which is a combined design and production approval for modification and replacement parts. Again, under FAA rules, all manufacturers of PMA parts must permanently and legibly mark each item with the PMA holder's name, trademark, symbol, or other FAA approved identification and the unique part number, as well as the letters “FAA-PMA”.
Alongside mandated markings, individual manufacturers have their own marking specifications that detail how the mark should be applied, formatted, and positioned, as well as adding various critical engineering details such as how parts are assembled in the engine.
Alongside FAA rules for marking, there are also specific standards that detail requirements for the qualities of the physical marks. For instance, SAE International's AS9132 marking standard defines the uniform quality and technical requirements for marking of metallic parts using 2D Data Matrix symbol coding, as used within the aerospace industry. The unique data matrix code may also provide a link to additional information concerning its manufacture that allows precise traceability, such as in the case of part failure. This data may include details such as the source of the materials used in the manufacture, as well as which operator and even which specific machine was used in the manufacture of the part.
Similarly, DoD UID markings must meet standards set by the International Organization for Standardization (ISO). The ISO 16022 standard specifies general requirements for component marking covering items such as data character encoding, error correction rules and decoding algorithms, as well as requirements to ensure electronic reading of the Data Matrix is possible. The marking processes covered by this standard include common techniques such as dot peen and laser etching and measures characteristics such as the size of the dots, the angle of distortion and any center offset.
Making a Mark in Aerospace
Although the requirements for component marking are clearly set out under FAA and similar regulatory authority rules as well as international standards organizations, execution of the marking process can nonetheless represent a significant challenge for manufacturers. For example, aircraft components such as those found in jet engines can feature complex geometry and may also be extremely costly, in excess of $100,000 in some cases. Badly placed or poorly executed marking can result in a very expensive failure if components are effectively deemed worthless.
Historically parts have been marked using manual processes and even today, some low-cost, short run components may still be marked using manual handheld tools. However, for larger and more costly components, which need multiple marks to be applied in specific locations, a more precise, robotically-controlled marking process may be required. For example, large aero engine components such as disks, rings, blades and bladed disks (also known as blisks) may require 15 or more marks to be made at different locations and within positional tolerances of 0.1 mm or less. With a typical aero engine containing hundreds of parts that need to be marked this way, manual marking would effectively be impossible. In addition, many of these components are round or cylindrical, making precise marking all the more challenging.
Instead, robotic multi-axis marking tools are used to apply component identification marks. As components have grown in both size and complexity, robotic marking tools have also evolved. For example, initially dealing with relatively small parts, marking heads were fixed and the component was grasped by the machine and manipulated to the appropriate orientation for marking. This improves accuracy and allows multiple marks to be made across the surface of the part to very tight tolerances.
Today, the robotic control typically takes place on the marking head itself and Pryor's system, for example, works with parts up to 1.2-meters in diameter. Even larger components could be handled if required. For the aero industry, the robots are usually fitted with dot peen marking heads, but lasers or scribes may also be used for component marking if appropriate.
The dot peen process, in which a hard stylus is repeatedly projected forward using electricity or compressed air as the head moves, induces far less stress in the component being marked than alternatives such as scribing. In addition, dot peen can produce marks through any coatings or films that may have been applied to the component. For aircraft component manufacturers, these are key considerations.
In a typical scenario, an aero component is moved into a ‘marking cell’ where it is loaded onto a rotary table and clamped in place. An operator scans a unique ID associated with the component that is linked to the plant manufacturing system and ensures the correct data is applied. Software can automatically create the correct unique identifiers, such as serial numbers or the necessary 2D Data Matrix codes. Having produced an appropriate marking schedule, it is then executed by the robotic dot peen head.
Robotic marking systems can ensure aircraft components are marked efficiently and accurately while still meeting all relevant regulatory and OEM standards. Using such a system allows a cumulative history of a component to be built up over time as it moves through the various stages of the production process and throughout its in-service lifespan. Ultimately this supports better traceability and root cause analysis in the event of a failure. In addition, as aero engines become larger and more complex in the drive for efficiency, component marking is set to become still more challenging for manufacturers.
With large components such as blisks set to become even more sophisticated and, therefore, more expensive, the impact of poor quality marking will continue to grow in importance. Robotic systems allow individual components to be marked correctly and to specification on the first attempt. This means the manufacturing process for aircraft components can be much more efficient.
This article was written by Alastair Morris, Vice President of Pryor Technology Inc. (Ashland, VA). For more information, visit here .