Innovations in magnetic particle inspection are driven by customer demands

First and second-tier suppliers are now required to meet higher quality standards. Photo: Magnaflux

Bruised by the economic slowdown of recent years, companies that rely on liquid and dye penetrants for magnetic particle inspection are looking for ways to cut costs. The technology does not come cheap as inspection units can run tens of thousands of dollars and users may view it as a place to trim their budgets.

Not so fast, say developers of magnetic particle inspections systems. True, they have a vested interest, but, they argue, that now is not the time to cut back in this crucial area of quality control. Moreover, technological innovations, which could lead to savings for the end user, are driven by demands from their clients.

Reacting to the marketplace

"Most companies are looking for cost savings. Unfortunately, to fill their needs they're looking at the lower-cost product that, in some cases, may be of lower quality," says Kevin Walker, materials product manager of Magnaflux (Glenview, IL), a division of Illinois Tool Works Inc. "They're getting pressures to bring down their costs, so now they're looking at online bidding; we're seeing more of that on the larger OEMs (original equipment manufacturer). In my opinion, it is a little frightening that they're lowballing an important product inspection, especially in aerospace." He adds that as aircrafts age, inspection will be even more critical.

It is not an easy attitude to overcome. Unfortunately, Walker says, those who cut back on quality to save money could find out the hard way that this approach may not be the best. "I hate to say it, but it takes an event to happen," he says. In fact, he adds, a Japanese airline recently had to ground a fleet of about 25 aircraft when inspectors found previously undetected engine cracks. "The consequences are so high," he says.

He is not alone in his views. "In general, production has been pretty suppressed over the past couple of years," says Pat Jenkins, president of Magwerks Corp. (Indianapolis). "And the quality department in most manufacturing facilities is viewed as a necessary evil. It's not a profit- producing portion of the business, and a lot of times it's the last to get funded." As a result, he says, quality is being pushed onto the first- and second-tier suppliers or being outsourced.

That in turn has led to another recent shift. The first- and second-tier suppliers are often held to much higher quality standards than the manufacturers hold themselves. "Liability's being pushed downhill," Jenkins says. Those suppliers need to consider their own efficiency as well as liability. Therefore, there has been tremendous interest in automated systems that will perform data acquisition and provide traceability. "That's been one of the biggest things we've seen in this field," Jenkins says.

Data acquisition

Magwerks has not ignored that interest. The company's Integrated System (IS) handles data acquisition and ties the equipment to a host of variables, including the operator, date, time and daily process control checks. The information is then linked to the part being inspected, with the data stored on the local server or a network server, "pretty much without human intervention," Jenkins says.

Three to five years ago, Jenkins reports, sales of the company's IS machines were in the single digits. "Now, in the last two years, it's probably 40%," he estimates. "More and more downstream suppliers are turning to data acquisition systems, which is a big change."

Computer-controlled equipment in this field is hardly new, of course; Magwerks has been building it for some 15 years. But as demands for inspection efficiency rise, the equipment must continue to evolve. Recent developments include remote data acquisition, remote machine management capability, and a wide range of reporting options, from time and efficiency studies to defect rates. A large facility that manufactures gears, for instance, with 10 machine types that are set up for a different product, can all be managed now from a central point, Jenkins says.

"If a customer calls and says that they found a cracked part," Jenkins says, "The supplier can go and access the data by part number, find out how many parts were run, who ran them, on which machine, on what dates, under what process control parameters, if he subcategorized the product by steel vendor, by die number, or whatever way he subcategorized it."

The information flows through TCP/IP, the standard networking language used by local area networks as well as the Internet. "The Internet is opening up tremendous capabilities for us," Jenkins says. "We're building on that to include capabilities like remote diagnostics, as well as remote maintenance and even remote feature changes. There are lots and lots of variables in the dye penetrant process that can be monitored and controlled using this type of system."

Finally, he says, the field is coming under the influence of new software tools that have emerged in the past year or two, which generate process control sheets for documenting results. "There are a lot of new things that are coming out for quality control managers and metallurgists."

Magnaflux's Walker sees change coming in another area-the development of environmentally friendly products. Nonylphenol chemicals, or NPs, are a penetrant ingredient now considered to be marine pollutants. "So we're reformulating most of our penetrants to be more environmentally friendly," he says. Such reconfigurations will not affect the penetrant inspection process. "We're looking at other raw materials that have the same characteristics," Walker explains. "And obviously we're trying to improve performance of the penetrants."

Likewise, Walker says, there's a movement afoot to improve treatment of wastewater. "This is big concern. This type of inspection creates wastewater when you wash the penetrant off the part, which can't be dumped down the drain because of the FOGs [fats, oils and greases] and fluorescence." Magnaflux is developing a ozone treatment system, called MagnaPure, in which ozone is injected into the rinse water, converting the fats, oils and greases into carbon dioxide and eliminating the fluorescence. The water can then be disposed down the drain and handled by local water treatment plants. This will allow companies to eliminate the expense of having wastewater hauled away, as well as the cost of cartridges and filters associated with traditional nanofiltration and ultrafiltration systems.

Another area of development: an automated laser technology. Magna-flux's product, called ZygloScan, is aimed at high-volume production, such as automotive manufacturing. The laser excites the penetrants (the dye inside the crack), which are captured on an infrared camera and, in turn, trigger a "good" or "bad" reading to automatically sort out defective parts.

The company initially intended this technology for use in the aerospace industry. "But aerospace wants a handheld type of device," Walker says. "And since this [the automated laser system] is computer-generated, the camera has to be absolutely still-definitely not a good fit with this."

The technology does address one of the biggest issues in penetrant inspection-the human factor. "With this inspection, you've got someone in the darkroom, under a black light, looking at parts, trying to figure out if there's a crack and if the part is bad or not," Walker says. "But with this system, everything is automatic."

Such automated systems are the wave of the future, Walker says. But like Jenkins, he sees progress coming gradually.

"This industry is slow to change," Walker says. Part of it is cost. Because quality control expenditures do not have an immediate payback, manufacturers can be reluctant to invest in it. And because advances in automation are inevitably followed by loss of certain jobs, portions of the industry may be reluctant to embrace change.

The inspection process itself offers up its own limitations. The most commonly used type of penetrant inspection is the wet fluorescent method, which is used for particles 3 to 5 microns in size. These magnetic particles are treated with a dye, usually fluorescence, that will make them glow under long-wave ultraviolet light. Humans are particularly sensitive to the yellow-green spectrum, but as they get older, they start losing the ability to discern different contrast levels-which is the basic premise of penetration inspection. "We're essentially looking for these indications, these contrasts," says Jenkins. The method also requires trained and certified inspectors, with 20-20 correctable vision. "And you can't be colorblind in the yellow-green pastel range," says Jenkins.

Another drawback involves the direction of the magnetic field in relation to the discontinuity. The magnetic field needs to be perpendicular to the crack, so that the crack bisects the field and sets up a north and south magnetic pole, thus attracting the magnetic particles. If the field is applied in the wrong direction, the crack cannot be seen during the inspection process-even if it is a gross defect visible to the naked eye. One field direction can affect another, which means manufacturers also need written accept/reject criteria as well as a verifiable way to set up the equipment properly, in addition to well-trained, knowledgeable and visually sharp operators.

But given the far-reaching consequences of poor quality control, penetrant inspection is becoming more, not less, important. And with that in mind, vendors still have their sights set on technological improvements, even if the rate of change has been hampered of late. NDT