CAT scans for castings.

Radiography has been used to inside parts or structures, looking for internal discontinuities. Cracks, voids, and other internal flaws could be captured on Xray film in a manner similar to chest X-rays. You simply cranked up the X-ray beam from the 120 keV needed to penetrate bone and tissue (or composites) by a factor of five or ten to be able to penetrate metals and get 2D snapshots of their internal geometries and flaws.

Today, just as the medical world has adopted advanced CAT scanners to map body parts in 3D, materials radiography has adopted digital-detector arrays to capture Xray images in real time and feed these slices of information to computers for complete 3D reconstructions of cast parts. With the latest technology, the part is rotated by multiaxis manipulators before a stationary X-ray beam to zero in on key areas of interest. The image is enlarged, reduced, or otherwise enhanced, and the operation totally automated, if desired.

According to Fred Schlieper, IRT Corp, San Diego, CA, the range of available radioscopy systems is broad. "Cabinet-based systems range from benchtop models for 8" parts to room-size systems for parts up to 48". Special systems with robots can provide extensive part mobility for inspecting several points on a part from various angles.'

Simple operation

Automated radioscopy is relatively simple. An X-ray beam is projected from a fixed point at an array of sensors in an image-detection plane, a fixed distance away. This produces a 2D slice of in through the part being manipulated in between. The X-ray shadow is then converted to visible light (either by a fluorescent screen or image intensifier), viewed by a video camera, and digitized by an image processor for quantitative analysis and display.

The entire process can be computer-controlled, including part manipulation, X-ray parameters, image collection, and data analysis. Software can deal with artifacts to prevent them from interfering with the imaging process. The result can be untended inspections and high-throughput rates (minutes and hours, instead of days), based on inspection programs tailored to the specific part areas of interest.

For detecting small defects in thick, dense materials, IRT offers the High-Output Microfocus X-ray (HOMX) with a focal-spot size adjustable from 5 to 200 microns and geometric magnifications of defects to 100X with fine image definition.

Casting inspection

Finding flaws early in the manufacturing process is the key, before expensive machining or value-added processing. Le Sueur Foundry Co Inc, Le Sueur, MN, a manufacturer of aluminum castings, is using an IRT HOMX-161 microfocus system to inspect die castings, sand castings, and permanent-mold castings. It features an advanced water-cooled anode for detecting very small features, such as 0.010"-dia porosity. Parts up to 150 lb are programmably manipulated in a room-size enclosure 10 ft x 10 ft x 10 ft.

"We're very quality-conscious and looking for new methods to monitor processes," says Dennis Janke, Le Sueur quality manager. "Using real-time X-ray technology to inspect castings gives us tighter foundry control." The real-time system's speed means more parts can be X-rayed. It also cuts X-ray film costs (20% the first year), and reduces scrap and the number of defective parts returned by customers. -The cost of a defective part is 20 to 50 times greater when you send it to a customer," Mr Janke says.

Assembly inspection

Another application area is assembly verification. The X-ray system can look inside otherwise uninspectable assemblies to verify that they have been properly manufactured. This not only eliminates destructive testing, but can be done on a 100% basis and eliminate the need for statistical sampling.

Although most on-line systems today digitally compare a given part against a good or "golden part", says IRT's Schlieper, advanced systems can now do. better than that. "Although this procedure works in simple cases, it does not provide for extensive analysis desired in many applications for process control. More advanced systems in use today can employ automated gathering and analysis software.

"These systems do not rely on a golden part, but rather use analytical processing routines that provide a wealth of data to the process engineer or QA manager. Process data can be fed directly into the factory computer network for monitoring and adjusting the manufacturing process itself."

At a US Army munitions plant, he reports, an automated system inspects fuse assemblies for rocket-propelled grenades. The system automatically loads a number of fuse assemblies into positioning fixtures, and each is imaged, analyzed, and reported as go/no go, in accordance with predetermined threshold values. As conditions warrant, management can tighten or relax criteria, modify reporting issues, or modify up-stream fuse processing.

IRT Corp, San Diego, CA, circle 276.

By Eugene Sprow Special Projects Editor

The need for NDT 

The growing expense of product recalls and product liability, combined with the need to improve product quality and productivity, is providing commercial incentives to invest in nondestructive testing. A study by Frost & Sullivan, New York, NY, predicts the market for NDT test equipment will reach $529 million by 1994, from $430 million last year.

In 1990, X-ray radiography, at $214 million, accounted for half the market; followed by ultrasonic testing at $115 million, eddy current at $53 million, liquid penetrant at $21 million, magnetic particle at $11 million, acoustic emission also $11 minion, and gamma-ray radiography at $5 million. By 1994, Frost & Sullivan predicts X-ray will reach $252 million and ultrasonic $151 million.