Nondestructive Testing Relies on X-ray, IR Imaging for Product Integrity
| By: Winn Hardin, Contributing Editor
When manufacturers need to verify the structural integrity of a component or measure a specific characteristic of an object, they turn to nondestructive testing (NDT). While more than a dozen NDT techniques exist, machine vision companies are adapting their offerings with two subsurface inspection and evaluation methods in particular — industrial radiography and thermography — to reflect the realities of the modern manufacturing floor.
Diagnosing Problems with X-ray
Industrial radiography, which utilizes X-ray imaging, has been employed in NDT applications for more than a century. Although the fundamentals of radiography have remained the same over the years, advances in image resolution, scan speed, and detection of smaller defects are making the technology increasingly attractive across a range of industries.
Five years ago, Teledyne DALSA (Waterloo, Ontario) revamped its Rad-icon product line of CMOS-based X-ray detectors to make them quieter, faster, and more sensitive while offering a larger measurement area of about 4 by 6 inches. Available in GigE or Camera Link interfaces, the detectors are capable of frame rates up to 30 fps.
Rad-icon features Teledyne DALSA’s sixth-generation CMOS technology. The CMOS sensors “are advanced devices running at real-time frame rates and very high data rates with integrated analog-to-digital conversion,” says Thorsten Achterkirchen, Vice President of X-ray Imaging for Teledyne DALSA. “We can control the sensitivity inside the pixel and switch back and forth between low-signal and high-signal applications.”
One of the biggest markets using Rad-icon is electronics inspection. The X-ray detector inspects for imperfections in components such as wire bonds inside an integrated circuit package and ball grid arrays, a type of surface-mount packaging that uses solder balls placed on the printed circuit board.
“In general X-ray is growing as a market because more and more manufacturers are using X-ray inspection as a means of process and quality control,” Achterkirchen says. “In some cases, the market is also shifting from traditional image intensifiers to digital flat-panel detectors.”
Teledyne DALSA also has identified a growing demand for portable X-ray systems, particularly for safety-based inspections. “If you look at the oil and gas market, for example, every weld in their pipeline has to be inspected to ensure it’s structurally sound, or they need to identify something that could cause a rupture down the line,” Achterkirchen says. Teledyne DALSA is collaborating with sister company Teledyne ICM in Belgium, which makes portable X-ray generators specifically for the NDT market.
X-ray plays prominently in the automotive industry for safety-critical applications. Inspection includes aluminum wheels, tires, engine blocks, and air bags. But the industry is expanding its definition of “safety-critical.” That means more opportunities for X-ray NDT, says Rahul Alreja, Director of Global Sales and Marketing for the industrial division of VJ Technologies (Bohemia, New York). The company’s VJ X-ray division manufactures integrated X-ray sources and high-voltage generators.
“You can’t assess certain things in the lab environment,” Alreja says. “It’s only when the car is out in the field do you understand what’s happening. As automotive manufacturers collect more data, they determine which components are more likely to fail and risk injury, and those are deemed as critical components.”
Automotive OEMs require their suppliers from all tiers to perform 100 percent inspection on the components they provide, Alreja adds.
Feeling the Heat of Failure
Infrared (IR) thermography offers another way for manufacturing and other industrial segments to detect voids, cracks, and delamination in a variety of materials. IR maps or measures surface temperatures as heat flows through, to, or from an object.
“We have been able to continually reduce the cost of advanced thermography, and miniaturization has allowed us to build smaller, portable, lightweight systems,” says Markus Tarin, President and CEO of MoviTHERM (Irvine, California).
In addition to portable systems, MoviTHERM develops laboratory systems for manufacturers who want to test out structural designs, as well as integrates its products into fully robotic automated work cells.
Thermography is emerging as an alternative to ultrasonic testing (UT), especially for NDT inspection of carbon composites commonly used in the automotive and aerospace industries. In solid carbon composite laminate, IR can penetrate about 7 to 8 mm below the material’s surface. UT, which uses high-frequency sound waves to detect flaws, has been the preferred technology for NDT inspection of these composites.
However, manufacturers are “feeling the pinch in realizing that ultrasound isn’t suitable for parts with very complex shapes due to their radius, making it difficult to pick up the signal from ultrasound,” Tarin says. “Or they may have very large structures where it becomes impractical to use ultrasound because the measurement time is too long.”
Ultrasonic NDT requires a coupling agent such as water or air to facilitate the transfer of sound energy into the test subject, whereas a high-resolution IR camera “takes one noncontact shot to get one measurement and therefore obtains much quicker results over a larger area,” Tarin says.
MoviTHERM has developed multiple IR NDT systems for the aerospace industry, including one for NASA that tests advanced composite structures and materials for defects such as voids, foreign material inclusions, impact damages, and delaminated areas. MoviTHERM also provides data management solutions with its systems to help aerospace companies maintain their stringent trace-and-track requirements.
Despite the technical advantages and dropping cost of IR imaging systems, thermography providers still face one major barrier to entry. Companies have invested in training and certifying their NDT personnel primarily in UT, but by introducing an alternative method of measurement such as IR technology, “they now have to bear the cost of retraining and recertifying their workforce,” Tarin says.
Casting a Wider Net
X-ray and IR imaging system developers see a few paths forward to put more of these NDT technologies on the factory floor and in the field. Teledyne DALSA’s Achterkirchen expects broader adoption of digital radiography for NDT as capabilities improve. “One thing I find exciting is the ability to build X-ray systems that can see smaller and smaller features, especially when you get in the area of computed tomography,” he says. “Combined with advances in X-ray sources that have tiny focal spots, you can see some amazing fine details at the submicron level that haven’t been imaged before.”
When it comes to thermography, the need for speed during the manufacturing process will ultimately drive implementation of the technology, “because other methods, like ultrasonic testing, can’t keep up with throughput requirements that are ever increasing,” says MoviTHERM’s Tarin.
Tarin also points out that IR imaging is not a one-size-fits-all solution. “Physics limits thermography to certain types of measurements and applications. Sometimes a combination of different NDT methods is required depending on the complexity of the part.”
Beyond traditional industry segments currently using NDT, consumer product manufacturers are beginning to look at instilling the process. VJ Technologies’ Alreja attributes this development to social media trends. “Before, it was hard for one or two bad products to make a dent in your reputation,” he says. “Now, if one person gets a bad part and they have a strong social media following, they can tweet about it, and then it goes onto the evening news, and all of a sudden the reputation damage done to a firm is massive. NDT can help protect the brand by preventing bad product from hitting the market.”
While OEM customers in electronics inspection typically understand their X-ray imaging systems, Teledyne DALSA’s Achterkirchen cites a lack of knowledge among system integrators in more general applications as a critical challenge in X-ray NDT. “We make the detector, another company makes the X-ray source, and somebody has to have the knowledge and experience to integrate these two together, pick out the right components for the application, put it into radiation safety cabinets, and then add the machine vision software that drives the whole system,” Achterkirchen says. “That skill is not easy to find in the market today.”
Achterkirchen advises system integrators to learn as much as they can about FDA regulations and other safety requirements, particularly related to the radiation aspect of X-ray imaging. The process of integrating an X-ray system for NDT and other inspection tasks “is more complicated than putting together a traditional machine vision system,” Achterkirchen says.
Meanwhile, as manufacturing facilities and processes become more connected and automated while generating and analyzing increasing volumes of data, companies expect NDT equipment and service providers to fit into that mold. To anticipate its customers’ needs, VJ Technologies partners with universities and labs and reaches out to thought leaders “to leverage what each of us brings to the table in order to offer next-generation solutions,” Alreja says.
In that spirit, VJ Technologies hosted the Future of NDT Symposium in mid-October, bringing together experts not only in NDT but also in automation and software development to discuss how NDT and product quality will evolve as factories integrate big data, Industry 4.0, and the Internet of Things.
X-ray and IR imaging for NDT may represent a sliver of the market share for machine vision, but makers of these components and systems continue to develop solutions to keep pace with evolving demands from manufacturing and industry for tighter quality control and greater throughput.