Originally Published MPMN April 2009
New Testers Provide Better Results without the Destruction
Nondestructive analysis can save time and increase accuracy, regardless of the application
TomoScope x-ray measuring technology enables nondestructive inspection of complex components.
Medical device manufacturers invest a substantial portion of their time and money in developing their products. So it makes sense that they wouldn’t want to see it all go down the drain during the testing or inspection phases of production. If a faulty product is found on the production line, it may not only cost the company, but it could also cost someone his or her life. By employing nondestructive testing and inspection methods, OEMs can increase their throughput and achieve more-accurate results.
X-ray technology has been available in various forms for a long time; however, recent improvements have made it much more accurate for part-measurement applications. Werth Inc. (Old Saybrook, CT; www.werthinc.com), a manufacturer of optical and multisensor coordinate-measuring machines (CMMs) for high-precision dimensional measurement, has combined x-ray with a multisensor CMM to create its TomoScope units.
The TomoScope can measure internal and external features of plastic, rubber, and ceramic parts with micron-level accuracy, which is achieved by using the point cloud from a precise sensor to recalibrate the x-ray point cloud. “Due to the speed, accuracy, and ability to best fit the entire point cloud to the 3-D CAD model—which displays in color where and how far the deviations are from the model—this is probably the way of the future,” says Jeff Bibee, Werth vice president of sales and marketing.
In the past, the only way to take internal measurements with some degree of accuracy was to cut the part open, thereby destroying the product. For most plastic products, the cost of the sacrificial part is insignificant. “However, often when a plastic part is sliced in half, stresses are released and the part can ‘spring,’ ” Bibee says. “The measurements taken from a cut part are often not the real measurements of the internal features of the part when it was whole.”
Because molding intricate plastic parts can be a lengthy process, first-article inspection of 100% of the features can take days or even weeks to accomplish, according to Bibee. But the TomoScope can x-ray a part and capture all the dimensions in 20 minutes, he says. Such time savings can result in higher throughput for manufacturers.
The TomoScope is available in versions with emitter voltages of 130, 225, and 450 kV. The low-voltage model is capable of penetrating plastic, rubber, ceramic, and some thin metals. Metals that have higher densities, including aluminum and titanium, can be measured using the mid- and high-voltage machines.
Fischerscope x-ray fluorescence instruments provide nondestructive analysis of hazardous substances in electrical and electronic equipment.
In the process of complying with WEEE and RoHS directives, some electrical and electronic component suppliers have continued to use the same part number for a component after revising its composition to eliminate hazardous substances, such as lead. This practice has caused some medical device OEMs—that are exempt from complying with the directives—to unknowingly order parts with compositions that can negatively affect the performance of their medical devices.
Unfortunately, due to the large number of components available, it is up to OEMs to screen their parts to make sure they know what they’re getting, says Paul Lomax, marketing director for Fischer Technology Inc. (Windsor, CT; www.fischer-technology.com). If they get a part with the wrong tin-lead composition, for example, product defects such as tin whiskers could form on the finish of a component and cause the electronic system to fail. In medical device applications, system failure can have dire consequences for a patient, and, in turn, the manufacturer.
But because electronic components are so expensive, destructive part analysis is not an option. “Previously, you could test one component against a sample from the supplier,” explains Lomax. But now there are too many parts and variables to make that a viable option. “OEMs need to quickly determine the composition of the components they’re purchasing by using a nondestructive method of screening,” he says.
To help OEMs do this, the company created its Fischerscope XDAL for nondestructive analysis of small electronic components used in medical devices. The benchtop unit is capable of positioning and analyzing component surfaces with targeted accuracy using an integrated video camera with high-resolution optics. It also allows users to factor in coating thickness and the layered structure of most components. Because the unit does not require any sample preparation, it can perform analysis even more quickly.
“Short measurement times allow for greater throughput and more-extensive screening,” Lomax says. “The trend in the industry is to rely on benchtop XRF instruments that measure from the top down and provide the user with a programmable stage to measure multiple components.”
It also is possible that OEMs may receive a mixed lot of RoHS- and WEEE-compliant and noncompliant parts, Lomax adds. “With the possibility of mixed lots and other variables on the supplier end, testing one component from a specific lot is not enough,” he says. “OEMs need to nondestructively screen 100% of their components to prevent the wrong type of component from getting into their critical medical device.”
Medical device materials need to be inspected for a range of performance capabilities, often requiring multiple costly and time-consuming tests. Nondestructive methods of analysis enable manufactures to perform more tests with fewer samples in less time—and in ways that are just not possible with destructive, static methods.
Buzzmac International LLC (Glendale, WI; www.buzzmac.com) offers PC-based nondestructive testing systems and services for measuring the elastic and damping properties of materials used in medical device applications. Its Buzz-o-sonic tester measures the elastic and acoustic properties of materials using a technique called impulse excitation. The technique involves lightly tapping a test product with a small hammer that generates a standing wave. The resulting sound is analyzed using a fast Fourier transform algorithm, and the waveform and power frequency spectrum are displayed so that the resonant frequencies can be determined. The Young’s modulus, shear modulus, and Poisson’s ratio can then be calculated from the known mass and dimensions of the solid, according to the company. The nondestructive dynamic methods employed by the system also can be used to measure internal friction, which is not possible using static methods.
“Compared with static, destructive methods, such as four-point bend tests and nanoindentation, Buzz-o-sonic has been shown to be more precise and repeatable in measuring the elastic properties of materials,” says Paul Bosomworth, president and CEO of Buzzmac. “Because the sample is not destroyed or damaged during testing, the same sample can be used repeatedly in a series of tests,” he adds. For example, the same sample material can be subjected to thermal shock, hydration damage, and cryogenic or high-temperature testing.
The testing unit also performs analysis quickly and stores data digitally. A range of shapes and sizes can be tested for material properties and defect or crack detection. “Static tests usually require a test piece of a specific shape and size or of limited size range,” Bosomworth explains.
So far, the tester has been used for measuring the speed of sound in titanium alloys used in transplants and specialized equipment, such as an apparatus for removing plaque from blood vessels. Other uses include measuring biomaterials such as hydroxyapatite, synthetic and real bone, and coated materials.
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