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Thursday, December 8, 2011

Blocker Door Inspection

Level 3 Inspection Serves AAR PMA Group
Through the Complete Product Modernization Cycle
Advanced technologies and new process capabilities in expert services support market demands for improved replacement parts in the jet engine industry.
Companies who are engaged in commercial aviation replacement parts production under FAA Parts Manufacturer Approval (PMA) often need to capture and reproduce complex part geometry with higher accuracy and even tighter tolerances than the original manufactured part.
For some suppliers, these strict requirements can be insurmountable. For PMA companies such as AAR, the ability to meet these requirements with technical services support from Level 3 Inspection, has become a comparative advantage that leads to expanded business. This Article illustrates an unusual "full circle" approach from reverse engineering through first article inspection and into production with production sampling inspection.
AAR, founded in 1951, is a worldwide aviation support company offering services that include MRO, supply chain, structures and systems, and sales and leasing. Their product development center is in greater Atlanta and they employ many design engineers who use traditional measurement technologies and current CAD programs to produce the parts their airline customer's demand.
Level 3 Inspection combines a depth of aerospace expertise with state-of-the-art 3D White Light Scanning (WLS) and advanced geometric processing technologies to reverse engineer, quality inspect, design optimize and then validate turbine engine components and assemblies.
AAR originally worked with the technical professionals who founded Level 3 Inspection ("L3I") to reverse engineer a complex jet engine thrust reverser part without any existing CAD data.  After the new CAD models were created from OEM part scans, and the investment casting process optimized to produce the first parts, AAR also requested the First Article Inspection of the new produced parts to be performed by L3I. Production inspection is anticipated to happen as soon as the first lot of new PMA parts is available.

Beyond CMM and CAD

AAR provided L3I with five sample OEM-produced parts that needed to be accurately 3D digitized then averaged into a nominal CAD model.  In the past, AAR would have used their own touch-point CMM to gather the data and then build the model in CAD software from averaged data.  This particular part, however, was a blocker door for a turbine engine made up of complex, organic shapes.  The part would have been difficult or impossible to capture and recreate using a CMM point-data and CAD software.
The geometry for the part was very challenging,” said Paul Ilenda, Manager of Outside Engineering Services for AAR’s PMA Group.  “There were no flat surfaces and seemingly many irregularities from part to part.”
Level 3 Inspection was uniquely qualified to do the work because of its expertise in aerospace parts digitizing using a White Light Scanner for data capture and then comprehensive post-processing of the scan files with software for aligning, averaging and modeling the large data sets generated by the scanner.  3D WLS is particularly suited to MRO projects because it enables engineers to quickly capture and process the average or optimal shape with tremendous accuracy, within 0.0005 inches (13 microns).
Using automated features in post processing software, Level 3 Inspection created a new average dataset From multiple 3D scans of the five AAR sample parts.
“The ability to create an average data set automatically saved a large amount of time and eliminates the guess work of manual averaging,” says Scott McAfee, Level 3 Inspection’s Vice President of Engineering.  “It provides a complete visualized data set rather than just specific dimensions.  This aids tremendously in the highly iterative CAD model-development process.”
McAfee took the sections taken from the average model and imported them into CAD/CAM software to create the nominal model.  From the nominal model, a detailed dimensional report, including GD&T, was created in their software.  The software then was used to batch-process report results from the original five data sets.

New capabilities and credibility

The final steps for Level 3 Inspection were converting the optimized CAD model to CATIA, and delivering the supporting dimensional package to AAR.  The entire process of digitally reconstructing the complex part, averaging the data for the samples and providing trend reports, took about two weeks.  McAfee estimates that Level 3 inspection's ability to automate saved about a week of time or 33%.
Level 3 Inspection used software to compare the CAD model  to each of the scanned sample parts provided by AAR.
Perhaps even more important than time savings for AAR were the new capabilities that L3I brought to the table and the fact that the outsourcing freed AAR to concentrate on other projects.
“It was difficult for us to understand the intended surface geometry given the limited data from our touch-point CMM,” says AAR’s Ilenda.  “Level 3 Inspection was able to use the combination of the White Light Scanner and post processing software to provide much more comprehensive detail.  A big additional benefit was that we freed up resources internally to work on other projects while L3I was performing the reverse engineering.”
Ilenda says that the ability to tap into part digitization capabilities through Level 3 Inspection will help AAR create a greater competitive advantage in the MRO market.
“Because this was a difficult part to reverse engineer, it adds credibility to our PMA team and sets us apart from companies unwilling to take on such challenges,” says Ilenda.  “We are also able to provide a quality part to our customers at substantial savings over OEMs.”

Automation saves time and tedium

Once data was collected for the five samples, it was aligned in the post processing software.
Level 3 Inspection used software to align data sets from five AAR sample parts digitized with a 3D White Light Scanner.
Level 3 positioned the multiple scans into alignment, as the color plots graphically show any alignment problems for each scan, making it simple to identify alignment and/or part geometry deviations.
Sections from the average model were used to develop the nominal CAD model
Level 3 Inspection used software to compare the CAD model to the average data set created from each of the scanned sample parts provided by AAR.
“The ability to batch-process the reports on the five individual parts using the average report as a template was tremendously efficient,” says McAfee.  “It enabled us to compare trends from the five individual OEM parts to the average data set, which added credibility and supported AAR with plenty of information to use directly for PMA approval.”
Computer Aided Inspection Closes the Loop
Several months after their Blocker Door part was produced in the investment casting manufacturing process, AAR again called on Level 3 Inspection to perform the First Article Inspection. This critical step in part production and PMA approval was necessary to confirm that the multiple manufacturing steps were optimized to consistently produce quality parts for use in aircraft.
Level 3 Inspection used software to compare the CAD model  to the first article sample in order to report dimensional information based on the part drawing requirements (CAD model is RED - WLS data is BLACK).
All of these detailed inspections and the positive results that were the inspection outcome from this FAI process gave AAR even greater confidence in the CAD model and the production process. Based on all of the top quality outcomes and consistent geometric conformance, production runs are now being ordered from the investment casting foundries.
Most recently, AAR asked L3I to provide a proposal for production inspection on some to be agreed statistical sampling basis of the hundreds of parts contracted to be produced over the coming months. Based on the observed degree of part consistency identified in the first lot, the part sampling rate for inspection may be reduced over subsequent lots of production parts.
Updates to this unusually complete, 'full development cycle' of reverse engineering through first article inspection through production inspection in the PMA marketplace will be made available through this publication and on L3I's web site,
By performing another comprehensive 3D digitization, using the same White Light Scanning of the new produced part, and within the separate post processing software suite, comparing it to the previously produced CAD model, L3I was able to identify the casting process results accuracy and quality conformance.
Level 3 Inspection used software to compare the CAD model  to the first article sample in order to report surface deviations.
The ability to completely and accurately scan the part and make the digital comparison between scan file and CAD model, with the level of detail and dimensional tolerances built into the Computer Aided Inspection process makes this the ideal method for proving out the manufacturing process. Additionally, L3I was asked to make a comparison of the new produced part to the OEM parts for further proof and support in the PMA process. This PMA part to OEM part comparison was critical in the acceptance and approval process.
For further information about this particular application of modern manufacturing and quality engineering technologies or any other interest applying these services and tools to solve industrial and business problems, contact Level 3 Inspection at 888-4AS-9102 or

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