A new take on non-destructive testing.

"Compensated quadratic resonance combinations?"

According to Bob Nath, co-founder of Quasar International, Inc. (Albuquerque, NM; www.quasarintl.com), which provides non-destructive testing (NDT) systems that use "compensated quadratic resonance combinations", compared with traditional approaches, they can:

* Reduce testing costs by a factor ranging between 3 and 10

* Reduce the possibility of shipping defective parts

* Eliminate scrapping good parts.

In addition, the process can help design engineers develop parts that aren't stronger and heavier than necessary--often the case in application-critical parts (e.g. suspension and steering components). "Some of these parts are designed to be 10 times stronger than needed," Nath claims. "With proper testing, this easily could be cut in half without affecting safety."

Also, says Nath, "Conventional NDT methods focus on indications of possible defects instead of structural integrity, and rely on operator judgment in place of statistical controls. In practice, this allows defective parts to make their way through the system, and scraps structurally sound but visually defective parts."

Quasar's method uses compensated resonance testing that is correlated to the material properties and structural performance. "We start with 100 good parts, one from every wax cavity, different pours from different days, different cooling temperatures, etc. in order to get an accurate picture," says Nath. "Then we do the same process with 100 bad parts in order to get our sort and a robust sample." Each batch takes about a day to test as the system runs the parts through 50 frequencies and determines the quadratic combination of anywhere from four to eight frequencies that provide the best discrimination. "The computer churns away using a 'genetic' algorithm that takes 1,000 combinations and determines which has the best discrimination results," says Nath. From there it distills the 100 best, crossbreeds these into 1,000 new combinations, and repeats the process. "It's very Darwinian," says Nath, "and this continues until it finds the best frequency combination for that application."

Once the set-up is completed, online testing takes about five seconds per part. At GM's Toluca, Mexico, engine plant, the Quasar systems--there are eight machines in parallel--inspect 5,000 lost wax investment-cast rocker arms per hour. Prior to Quasar's arrival, the failure rate, according to Nath, was 3 ppm, which means there were six field failures in the 21 million parts produced each year. This happened despite testing that included X-rays of 50% of the parts, and two magnetic particle and four visual inspections. "They were throwing out 6% to 7% of their product before we replaced the X-ray, magnetic particle, and three of the four visual inspections," claims Nath. "They are now down to a 1% reject rate and we have zero ppm on parts that break." Ford and GM use currently Quasar systems to inspect suspension components, while GM also uses the device to inspect its lost foam-cast inline six-cylinder engine blocks.--CAS