By Claire Swedberg
Feb. 14, 2012—As the aerospace industry transitions from the use of metal to composite materials for its aircraft—in order to make planes lighter—component manufacturers must accommodate this change by working with composite materials that sometimes have short shelf lives and require both very hot and very cold conditions. The raw materials must be stored at freezing temperatures to prevent degradation, and must then be heated for curing after being molded into an aircraft wing or other component. Monitoring that process via radio frequency identification
can be challenging, since RFID
tags are not typically rugged enough to withstand temperatures of 300 degrees Fahrenheit (149 degrees Celsius) during curing, or freezing temperatures during storage.
, in partnership with Xerafy
, has developed a solution known as Extreme RFID, that employs Xerafy tags designed to withstand those temperatures, and thus can track these composite materials and the products made from them within the manufacturing facility. OATSystems' software enables a user to track the amount of time materials have been kept out of cold storage—and, in that way, to ascertain their remaining shelf life. One U.S. company that manufactures aircraft wings and some fuselage parts (which has asked to remain unnamed) has been utilizing the new system since autumn 2011, to track its components and the tooling used to mold them. Other aerospace firms are also now beginning to use the system, says Su Doyle, OATSystems' head of industry programs.
The OATSystems-Xerafy solution consists of several Xerafy tag
models, including the MicroX II tags for items that must be tracking through high temperatures, as well as Oat Foundation Suite software for identifying a tag's location (along with a timestamp) from the moment that a material arrives at the site until a finished part leaves en route to a customer.
In the case of the manufacturer already using the solution, the RFID tags are being employed to track composite materials from when they are received until when they are placed in autoclaves for curing purposes. In the future, the company indicates it intends to use tags to track the materials through the curing process and throughout the remaining work-in-progress, until each finished component leaves the facility. In addition, the firm has begun applying Xerafy MicroX II tags to its tooling (the molds on which the composite materials are shaped prior to being cured) since the tooling—also composed of composite materials—is also exposed to high temperatures as parts are cured, and thus has its own limited shelf life.
The company has installed an Impinj reader
and two antennas at each of two freezers at which composite prepreg material (pre-impregnated composite fibers) is stored prior to cutting, layout and curing. When cartons containing rolls of prepreg arrive at the facility, a Xerafy tag
is attached to each carton, thereby creating a record of that material's movements, along with its time of arrival. That information is stored in the OAT Foundation Suite software. A second tag is applied to the roll of prepreg itself, in order to provide redundancy, since the roll does not always stay with the carton.
The carton containing the roll is then brought to the freezer, where the Impinj reader captures the ID numbers encoded to the carton and roll tags and forwards that information to the OAT Foundation Suite software via a cabled connection. Because there are two antennas, the software is able to determine whether each item is entering or leaving the freezer.
When a carton is removed from the freezer and moved to the clean room, another interrogator
captures the tag IDs on that carton and roll, updating the software to indicate the roll's location. A worker within the clean room cuts the required pieces from the roll, places them into a polyurethane bag and attaches an RFID tag
to that bag. The bag's tag ID number is then married to the IDs of the tags attached to the roll and its carton, thereby providing a continual record of the length of time that piece of composite material has remained out of cold storage. Raw materials generally must be stored at 0 degrees Fahrenheit (-18 degrees Celsius), and can be kept at room temperature for only up to 400 hours, at which point they will become unusable.
Once the bagged piece of material is brought to the layout room for molding—prior to being transported to the autoclave for curing—the tag is read
once more, thus indicating that the material is about to be cured.
Although tags are not currently being placed into the autoclave, Doyle says, the plan is for this to be the process in the future, as a tag will be attached directly to each composite part. The curing process can reach 400 degrees Fahrenheit (204 degrees Celsius) or more, says Eric Heineman, Xerafy's marketing manager, noting that the MicroX II tag can survive temperatures of up to 482 degrees Fahrenheit (250 degrees Celsius).
The tooling is also made of composite materials, Doyle says, and has a recommended duty cycle
in the autoclave for a specific number of hours, after which it must be discarded. "The tooling is now being tracked by an accompanying work order tagged by an encoded RFID tag
," he explains.
The OAT Foundation Suite resides on the manufacturer's enterprise resource planning (ERP) system at another facility. The OAT software issues alerts to authorized personnel, Dole says, when a composite roll's "out time" approaches the 300-hour mark. What's more, the software tracks tooling duty cycles and updates the customer's Solumina
manufacturing management system for weekly inventory reports indicating where tooling is located, and how long it has remained at that site.
"These material management and assembly processes are used for building mission-critical aircraft and aircraft engine components," Doyle states, "and the customer has stated that they would never be able to achieve such a detailed level of tracking without RFID
. This level of precision enables them to ensure a higher level of quality and efficiency in their manufacturing operations, and reduces excess inventory and material waste."