With the media focused lately on the airplanes, helicopters, and drones in the sky, we are revisiting how component manufacturers can play a safety role in the aerospace industry. One of the ways is to help ensure manufacturing quality assurance by utilizing Positive Material Identification (PMI) to help confirm their products are in compliance with specifications.
If aerospace parts are not manufactured with the precise alloy specified for the application, the parts may not be able to support the weight and stresses they are designed to bear. So how do manufacturers confirm that the parts they are selling meet the specifications of the alloy the engineers requested? By PMI.
Positive Material Identification in manufacturing is a method used to verify the composition of a material and confirm it’s the correct type and grade according to specifications. It’s particularly useful for metals and alloys, helping to ensure product quality, safety, and compliance with regulations.
Technologies Used in PMI
Two of the portable technologies used in PMI are XRF and LIBS, because operators of these types of analyzers can identify metals right on the shop floor. Without having to send samples to a lab, manufacturers can quickly make decisions about the raw materials being used, adjust the alloy during the process, or even scrap parts because of material errors.
X-ray fluorescence spectroscopy (XRF) is a non-destructive analytical technique used to determine the elemental composition of materials. Handheld XRF analyzers work by measuring the fluorescent (or secondary) X-rays emitted from a sample when excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays, or “unique fingerprints”. These “fingerprints” are distinct for each element, making handheld XRF analysis an excellent tool for quantitative and qualitative measurements.
Laser Induced Breakdown Spectroscopy (LIBS) is another analytical technique used to determine the elemental composition of materials. Handheld LIBS analyzers work by using a high-focused laser to ablate the surface of a sample. A plasma is formed consisting of electronically excited atoms and ions. As these atoms decay back into their ground states, they emit characteristic wavelengths of light, or “unique fingerprints”. These “fingerprints” are distinct for each element, making handheld LIBS analysis an excellent tool for quantitative and qualitative measurements.
How are XRF and LIBS Analyzers Used?
We previously wrote about how metal fabricators were using handheld XRF analyzers for performing Positive Material Identification (PMI) of incoming raw material to help ensure it matches the alloy grade and composition documented on the material test report prior to product manufacture to help prevent critical components from failing due to material defect. These analyzers are also used for final quality inspection before finished parts are sent to the customer. This “double-check” process helps ensure that the incoming raw materials and the outgoing finished parts meet the expected engineering requirements. (Read Quality Assurance of Critical Fasteners.)
Examples of how Handheld XRF and LIBS analyzers are used in aerospace parts manufacturing include:
- Verifying high-temp nickel, titanium, aluminum alloys, and superalloys
- Analyzing light elements in aluminum and titanium alloys
- Detecting high-purity tin and prevent tin whiskers before they start
- Measuring thickness of cadmium and zinc-nickel coatings
PMI Part of an Overall Safety Plan
The National Transportation Safety Board advocates for safety systems being used, and their website notes: “By establishing an effective safety management system (SMS) and creating a safety culture aimed at making safety a focus first and always, operators will improve aviation safety and reduce the risk of accidents. An SMS is a formal, top-down, organization-wide approach to managing safety risk and assuring the effectiveness of safety risk controls. An SMS should address four components: safety policy, safety risk management, safety assurance, and safety promotion.”
It make sense that a PMI program where components are being made, and where material integrity is critical, should be considered part of an airline’s safety system.
Additional Resources
- Application Note: Quality Assurance of Critical Fasteners
- eBook: XRF technology for non-scientists
- eBook: LIBS technology for non-scientists
- Online Handheld XRF Learning Center
- Periodic table of elements with X-ray energy references
- XRF and LIBS glossary
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