Inspection in a FLASH

November 1, 2003
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NDT technology can apply the benefits of mass production to lots of one.

It sounds like an oxymoron-mass customization. In reality, this technology represents a leading edge in manufacturing.

It comes courtesy of technology that, until recently, was more common in the world of medicine than in manufacturing: computed tomography, or CT. HYTEC Inc. (Los Alamos, NM) has developed a high-speed, 3-D X-ray CT scanning system, known as FlashCT. Rather than scanning the human body, FlashCT can be used to obtain 3-D images of components' external and internal contours.

Though FlashCT boasts several applications, its use in mass customization is particularly exciting, says Naomi Engelman, director of operations at HYTEC's Sensors & Imaging Group, a wholly owned subsidiary of HYTEC Inc.

"Mass customization is the mass production of a custom lot of one," says Engelman. "The oldest example of that is in the tailoring business, where men get their suits customized to fit them." This same concept has entered into mass manufacturing with items such as bicycles, cars, furniture, cabinets and jeans. "People go in, they get measured and they get the bicycle manufactured to fit their specific anatomical dimensions," Engelman says. "Or you get a pair of jeans that fit a person perfectly."



Goodbye wires and brackets

HYTEC has been working with Align Technology Inc. (Santa Clara, CA) in another application: mass customization of orthodontic products. With this technology, teenagers around the world can say goodbye to braces made of wires and brackets. Align Technology makes Invisalign aligners to straighten teeth. These teeth adjusters, which the company calls appliances, are nearly invisible and are removable. Users wear each customized aligner, which is made from medical-grade plastic, for a set period of time to produce extensive tooth movements in both the upper and lower arches.

"The product looks just like a retainer," says Engelman. "And the concept is you can gradually shift your teeth by using a series of these Invisalign aligners. You wear one for two weeks, and your teeth shift slightly. You replace that with the next one, and so on. They manufacture up to 29 customized appliances for a patient."

The process begins with the traditional trip to the orthodontist, where an impression of the patient's teeth is made.

Previously, after the negative impression was made, a positive was created using plaster. The manufacturer would then destructively scan the positive impression to create a 3-D digital model of the patient's teeth. "They would literally shave off a fraction of an inch of the plaster material, take a picture, shave off another fraction, take another picture, and so on," Engelman explains. "In the end you would have a pile of dust."

The pictures would then be assembled to create the image. From there, the data would be exported, using Align Technology's proprietary software, into a program that creates the 29 "steps" for correcting the patient's teeth. That data, in turn, would be exported into a rapid prototyping machine that created the 29 sets of customized appliances.



Improved efficiency

With the FlashCT technology, the process is considerably more efficient. After the initial dental impression is taken, the impression is scanned directly, producing the 3-D digital data in the form of 1,300 X-ray images. "You skip pouring the plaster and its destruction," Engelman says. "In other words, you skip the time-consuming, expensive part of the process." By avoiding the pouring and destruction steps, Align Technology reduces its use of consumable products as well as the need for intensive labor. The images are then combined to form a 3-D image of the position and outside contouring of teeth; Align uses its software producing the sets of aligners to realign the teeth into proper position.

The newer process has also reduced the processing time. "Previously the process took about four hours. When we perfected the process with Align Technology, we brought it down to 12 minutes," Engelman says. "And we're doing it even faster now, because we continue to spend a lot of money on internal R&D (research and development) to speed up the process."

Kamesh Tata, data acquisition laboratory supervisor at Align Technolo-gy, says that the technology has improved the company's production efficiency. "One of the most complex, most challenging issues we have is scanning the impressions. With earlier scanning technologies we could not scan directly-we had to pour plasters and scan the plasters, which is time-consuming, expensive and also pretty cumbersome."

With the FlashCT machines, however, Tata says that the impressions can be scanned directly. "And FlashCT machines provide us with an elegant and inexpensive solution to an enormously challenging problem we have. We've cut our costs, and we've already built thousands of aligners using the digital data we get from the CT machines. Our customers are satisfied with the product we have been building."

The FlashCT system incorporates an amorphous silicon flat-panel detector, a coupled-motion control system and off-the-shelf X-ray equipment. It also uses three software components, which are controlled by a single Windows-based (2000/XP) workstation: data acquisition, or DAQ; data processing, or DAP; and visualization, or VIZ. Output formats include STL and PLY files. "Those are two of the most common file formats for digital manufacturing," Engelman says. "So it's easy for people to work with."

Depending on the product, it's not uncommon for clients, especially those on a high-throughput manufacturing setting-to use their own custom software as part of the manufacturing process. "So we'll do the first two steps-the acquisition and processing-and then we create an STL or PLY file, and then export the data into their software."

Operating the machine is simple, Engelman says-literally a matter of loading the part into the system and pushing a button. "It's completely automated. We made it so that you do not need to be a skilled technician in order to operate these machines. We want them to be accessible to anybody."

At the same time, HYTEC is also establishing a scanning services bureau. "Given the current economic situation, we've recognized that it's difficult for people to spend a lot of money on capital equipment. And we're also the experts in scanning," Engelman says. "So we're setting up a new business unit where we will receive the impressions and do the scanning for them, and just ship them the digital data over the Internet."



Cooperative agreement

FlashCT grew out of a Cooperative Research and Development Agreement (CRADA), a government-sponsored technology transfer mechanism, that HYTEC participated in with the Los Alamos National Laboratory. CRADAs allow for the further development of technologies that were originally designed for research settings. "The CRADA assists with getting technology ready for the commercial marketplace, which is exactly what we did," says Engelman.

FlashCT was originally developed for nondestructive testing and evaluation purposes, Engelman says, for use in the quality control and quality assurance arenas. "A lot of this work was done in 2-D, previously, using what's called film radiography. So you would basically take an X-ray of a part and try to decipher if there are any cracks or flaws inside the part."

A 2-D image, however, does not provide manufacturers with the necessary information to ensure that complex components, such as rocket motors, are made correctly-that there aren't flaws deep inside these components, she says. With FlashCT, says Engelman, "You can actually see them without having to take apart that complex component. So you're literally seeing through the part-with our software you can strip off the different layers and see inside. And this is all based on density differentials, so a lighter material will appear a different shade of gray than a heavier material. And then we add color enhancements so you can really see what you're looking at, instead of just using a gray scale."

A second role for FlashCT emerged in the area of models-based engineering, or reverse engineering. "You scan your part. You create this 3-D digital file of that part, and you can export that data into a CAD/CAM system," Engelman explains. "You can lay over that information with your original design information, and check your manufacturing tolerances to make sure your machines are in specification. You can also change the design after it's in your CAD/CAM format. And it's all done digitally, so you don't need to do anything physically."

Citing a current application, Engelman notes, "We're scanning molded plastic parts. We can measure the exact wall thickness so manufacturers can see how their process is working and where their weak points are."

Though FlashCT received an award for the technology in October, HYTEC is investigating other uses for FlashCT, especially in the realm of mass customization. Hearing aids represent a strong possibility. So do orthotic and prosthetic devices.

Says Engelman, "Mass customization is a huge leap for companies-it's a tremendous leap to go from doing everything by hand to digital manufacturing." NDT

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