Mark Jonaitis and Scott Coles are evangelists—not for any particular religious perspective, but rather for “Six Sigma,” a rigorous approach to using statistical analysis for improving manufacturing processes. Jonaitis, Coles, and other Six Sigma team members have been working to bring this methodology to all corners of Varian Medical Systems’ Salt Lake City, Utah, X-Ray Products design and manufacturing facility.

“Six Sigma seeks to minimize process variations in order to eliminate manufacturing defects,” explains Jonaitis. “With Six Sigma standards, you want to see fewer than four defects per million. Most factories run somewhere around two or three sigma, which equates to anywhere from 65,000 to 300,000 defects per million. Moving toward Six Sigma pays for itself by saving labor, time, and money, and avoiding customer dissatisfaction.”

HISTORY OF SIX SIGMA
The main idea of Six Sigma is that sustainable process improvements can be achieved by taking a statistical approach to identifying and solving problems. The Six Sigma method was developed by Motorola engineers in the mid-1980s based on statistical concepts from Carl Frederick Gauss (1777–1855) and on work during the 1920s by Walter Shewhart, a Bell Telephone Laboratories engineer who created statistical tools for controlling industrial processes. Six Sigma spread from Motorola to AlliedSignal (later Honeywell) and, in 1995, to General Electric. Since its inception, hundreds of companies around the world have adopted Six Sigma quality programs.

SIX SIGMA AT VARIAN X-RAY PRODUCTS
“The steps for solving a problem using Six Sigma methods are: Define the problem, take measurements, analyze the data, design process improvements, and put controls in place so the process improvements are sustained,” explains Coles. “It means asking people not to rely on their ‘gut feelings,’ but to make observations, collect data, and base decisions on carefully documented statistical analysis.”

For example: “Gut feelings” turned out to be wrong when a group of engineers was trying to account for some electrical instability showing up in a line of industrial X-ray tubes. Nearly everyone assumed it was caused by a problem with the insulating material. “A Six Sigma study showed us we were wrong,” says Coles. Through factor identification, data collection, and experimentation—important components of a Six Sigma process—a team discovered the real causes of the problem and devised process improvements that virtually eliminated tube scrap or rework costs. A similar project fixed a brazing process that was resulting in misalignments of metal components about 40 percent of the time. The fix raised the yield to 98 percent.

BLACK, GREEN, AND YELLOW BELTS
At Varian, a group of Six Sigma “master black belts” is qualified to train and certify other “black belts.” These project leaders are particularly adept at using statistical analysis to improve manufacturing. They, in turn, have trained 16 “green belts” in how to use Six Sigma to solve specific problems. Finally, as projects result in process improvements, another group—the “yellow belts”—takes over. “Yellow belts ‘own’ the improved processes, and control them into the future,” says Jonaitis. “After the problem solvers walk away, the yellow belts are the ones who maintain the gain” in terms of improved yields, decreased failure rates, or a reduction in the number of units that do not meet quality standards.

“Varian has a reputation for making high-quality, long-lasting X-ray tubes,” says Bob Kluge, president of the X-Ray Products business. “Six Sigma helps us maintain the highest quality in everything we do.”

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