QMT Features: November 2010
Philips sees the light
Philips Lighting pushes innovation using NDT X-ray and CT Radiography to drive research, quality and productivity  - plus reduce its ecological footprint

The Philips Lighting business division produces billions of bulbs a year. Philips Lighting kicked off X-ray inspection in 2003 to support the design-through-manufacturing process of high-intensity discharge (HID) lamps. The multinational’s division in Turnhout, Belgium, manufactures long-lasting HID lamps from 20 to 4000 Watt offering high light output and premium light quality.

These innovative illumination solutions raise comfort standards in offices, public buildings and factory halls; enhance traffic safety through street lights and passenger car headlights; and add entertainment value with splashing light shows toning up rock stars’ performances.

“There is no doubt that X-ray inspection presents the best strategy to study the feasibility of new technologies, assemblies and materials and maintain high production quality,” says Chris Dries from Philips Innovative Applications in Turnhout. “For this reason we decided to further increase and sharpen our non-destructive testing (NDT) capability. To select a new system, we performed a thorough evaluation involving systems from most major X-ray and CT system vendors. Ultimately, the benchmark resulted in the purchase of a Nikon Metrology XT V 160 machine. We use the new system for critical measurement tasks and automated inspection jobs whereas the older system is still suitable for visual checks.”

Performance-critical aspects
The ability to literally look inside HID lamps is a great asset for Philips Lighting. X-rays penetrate the lamp and subsequently hit a 13x13-inch Varian flat panel, which generates radiography images with different shades of gray depending on material and geometry. On these translucent images, all the lamp’s constituent components are displayed in their entirety. The proprietary X-ray source incorporated into the system is equipped with a 1 micron transmission target. The XT V 160 is a high-precision imaging system that recognizes hidden features as tiny as 500nm, ideal for engineers to deduce structural, dimensional and connectivity related facts.

HID lamp electrodes are performance-critical components that undergo detailed X-ray research. Chris Dries explains that electrode characteristics influence the light the lamp produces by passing an electric arc through a compact tube filled with a high-pressure mixture of gases. “We measure the size and shape of electrodes contained in lamp prototypes as well as the distance between both electrodes. Inspect-X software allows us to automatically measure the distance between the electrodes’ tip planes. X-ray helps us a great deal in studying the way electrodes’ shape and structural characteristics evolve after every so many lighting hours. This is why Philips Lighting is able to successfully respond to the tight electrode requirements imposed on HID lamp engineering.”

Chris Dries mentions that submicron image resolution provides great insight into other internal lamp phenomena, such as wall corrosion, glass frit, crazes and salt and mercury fillings. The XT V 160 system also supports the reconstruction of a CT volume, generated on the basis of hundreds of X-ray images. “By navigating CT volumes, we are able to locate and investigate crazes that may develop in ceramic discharge tubes. Similarly, we change position, angle and zoom as desired to take a close look at the otherwise invisible welds connecting electrodes with their supports. High image quality and magnification make it even possible to detect minuscule cavities in salt particles, something we were unable to do in the past.”

Automation and off-line inspection
To allow engineers to focus on their research and production work, most measuring tasks are delegated to system operators. They slide a tray with an array of lamps in the X-ray and CT system and start automatic data capture. The tray is indexed from one lamp to the next in order to subject all items to the same X-ray imaging routine. “Zoom level consistency and flux normalization maximize the repeatability of X-ray imaging, generating output that is truly operator independent,” says Dries. “This offers us the possibility to reliably set up macros for X-ray jobs that can run unattended at any time.”

All acquired imaging data can be sent to an offline station that runs Inspect-X software for inspection and macro preparation purposes. Engineers analyze X-ray graphics or navigate a CT volume to drill down on a particular detail, while having all relevant numerical information available at their fingertips. They value the fact that they can easily include X-ray shots and CT sections in their engineering reports.

“The Nikon Metrology system is part of a strategic decision of Philips Lighting to make X-ray and CT an integral part of internal processes,” says Dries. “Angled views in highest resolution prove technical facts that are indispensible in stretching the performance limits of HID lamps. Important in this regard is studying the use of environmentally friendly materials and their impact on light, yield and reliability.

With the insight gained, the number of prototyping rounds can be reduced and life test activity can be downscaled to some extent, saving both time and money. The resulting decrease in power consumption also contributes to greener economics. By extending NDT capabilities, Philips Lighting underlines its position of leading innovator and supplier of high-quality illumination solutions.”l
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