A Guide to Non-Destructive Testing for Precision Machined Parts

When machining mission-critical parts for aerospace and American defense manufacturing applications, it’s essential to ensure the highest quality possible. 

One way we guarantee quality at Alard Engineering is by running non-destructive testing on each part we make to check for cracks in the material that could lead to problems down the line. 

What Is Non-Destructive Testing? 

Non-destructive testing is a technique used to assess the properties of a material, component, structure, or system for cracks or defects without causing damage.

There are several methods of non-destructive testing, but the three we most commonly use at our precision machine shop are:

• Fluorescent penetrant inspection. This method uses a fluorescent dye to highlight cracks and identify material defects. A dye is administered to the part’s surface, and a blacklight is shone on the part to reveal chips or cracks. 

• Magnetic particle inspection. Magnetic particle inspection highlights cracks or chips in the surface of a ferromagnetic material, like iron, nickel, cobalt, or their alloys. This process generates a magnetic field inside the part. Surface disruptions like chips or cracks, the magnetic flux will “leak,” and fine magnetic particles, drawn to the flux leakage, will become visible. 

• Hardness testing. During hardness testing, an indenter made of diamond, tungsten carbide, or steel is used to make an impression in a partl. Depending on the type of test, the indentation is measured by the depth of the penetration or size of the impression. For example, the Rockwell hardness test measures the former, and the Vickers hardness test measures the latter. 

Why Is Non-Destructive Testing Important? 

Non-destructive testing is incredibly useful in defense and aerospace machining. It allows us to: 

• Identify potential defects. There’s no room for error when manufacturing aerospace and defense parts, and even minuscule cracks can be detrimental to a part’s performance. Non-destructive testing allows us to identify potential defects in a safe, risk-free environment. 

• Preserve parts. As the name implies, non-destructive testing gives us the opportunity to check for cracks and defects while keeping parts intact. Other testing methods, like pull testing, result in broken or destroyed parts, meaning we have to account for extra parts to test. With non-destructive testing, we test the parts intended for the end-use application, and if they pass, they remain in perfect condition.

As a precision machine shop specializing in aerospace and American defense manufacturing, we recognize the importance of non-destructive testing and carry it out for every part we machine.

How Does the Non-Destructive Testing Process Work? 

The American Society for Testing and Materials (ASTM) and the Department of Defense (DOD) have guidelines and specifications for how to cut different materials to minimize cracking or chipping. These specifications influence the method of non-destructive testing that will need to be performed. 

For example, ASTM or DOD guidelines may dictate that a cylindrical part made with aluminum 6061 must be cut from a square block because of how the material is produced. The material selection, cutting process, and types of cracks or chips likely to occur determine the optimal non-destructive testing method.

Once the test is performed, DOD and ASTM guidelines determine the threshold for cracks and chips for each material. 

After the tests are completed and parts are ready for use, we provide customers with documentation that certifies that the part conforms to industry standards. 

If you need mission-critical components for the aerospace or defense industry, request a quote from our CNC machine shop today!