Marking aerospace components ensures that they can be traced throughout the supply chain. With some parts worth more than $100,000, marks must be reliable and repeatable.
Pryor Technology Inc. Vice President Alastair Morris explains that aerospace companies “stipulate that parts be marked permanently to give them a unique identity, which allows them to be tracked, assembled, replaced, and correctly maintained and positioned.”
The AS9132: Data Matrix (2D) Coding Quality Requirements for Parts Marking standards issued by the International Aerospace Quality Group (IAQG) defines process requirements for 2D:
- Dot size between 65% and 105% of the criteria
- Dot center offset within 0% to 20% of ideal grid
- Angle of distortion within 6° variation of L-shaped finder pattern
Individual manufacturers have their own marking specifications, which include details of how the mark should be applied, formatted, and positioned, as well as critical engineering details and specifications on how parts are put together. Operators are also introducing their own standards. Following the inflight failure of a CFM56 engine in April 2018 that lead to the death of a passenger, Southwest Airlines developed an internal system to track engine fan blades by serial number.
Codes produced to standards and specifications serve as components’ passports. By scanning it, a manufacturer can access production data, including material supplier and person(s) responsible for its manufacture. If the part fails, data can help determine the reason(s) why.
Many manufacturers, however, are not doing enough to verify the quality of the marks they make. Fortunately, effective marking and verification is simple: study the process to identify weak links, then strengthen them.
Inspect parts with microscopes and metrology equipment to verify that marks meet the full requirements of the specifications. Because this is time consuming and expensive, some companies only inspect a small sample of parts, a practice that can miss deviations. The company may then have to inspect or recheck hundreds of other marks from the same batch.
Failing to ensure compliant product markings can create two huge problems:
- A customer could reject non-compliant marks, a costly and disruptive problem, especially if parts have already been shipped by the time the deviation is identified
- Substandard marks could further degrade and become unreadable, causing problems for in-service use and difficulty in smart manufacturing environments where marks track components during production
Some parts can be marked adequately using hand-held devices, but large parts may require multiple markings in precise locations. A large, expensive part, such as a blisk, may require 15 or more marks at various points on its surface, with 0.1mm position tolerances. A typical aero engine may have hundreds of parts that need to be marked in this way.
Performing this task manually would be impossible. Further, with some engine components worth more than $100,000, incorrectly applying a mark can be expensive. Therefore, a precise marking technique, such as robotic control, is needed.
Rely on robots
Multi-axis robotic systems can move a large part into a marking cell, load it onto a rotary table, and clamp it in place. An operator scans the part’s unique identification code, which calls a program with marking instructions, carried out by a robot-mounted marking head. The whole software-controlled process links to the manufacturer’s plant production system to ensure correct data are applied.
Users often build a business case for multi-axis robotic systems by using them to mark a wide range of parts, including smaller ones that are usually marked manually. Manufacturers can mark parts more efficiently – ensure better traceability – by using idle time to mark smaller components.
Robotic marking can ensure the traceability of aerospace parts, allowing each component to be marked correctly and to specification on the first attempt, making the manufacturing process more efficient. The cost of marking components incorrectly can be much greater than investing in a reliable robotic system.