Zero Quality Control refers to an ideal system that produces no defective products and therefore does not require frequent inspections that waste both money and time. Organizations that aspire to process optimization and commit to continuous process improvement make Zero Quality Control the goal.

It’s a term coined by Shigeo Shingo, the inventor of the Single-Minute Exchange of Die and Poka-Yoke (POH-kah YO-kay). Shingo also became a key contributor to ideas that formed the Toyota Production System. Shingo died in 1990, but his ideas continue to influence those who use Lean Six Sigma tools and techniques.

The Two Main Tools of Zero Quality Control

Achieving Zero Quality Control depends on implementation of two Lean Six Sigma-related techniques: Poka-Yoke and source inspection.

Poka-Yoke

Also known as mistake-proofing or error proofing, Poka-Yoke involves identifying steps in a process where mistakes are most likely to occur and making changes to prevent those mistakes from happening. It’s an important tool in Lean, to identify waste, and in Six Sigma, to prevent mistakes that lead to defects. Poka-Yoke also involves giving workers the ability to stop a production system when a problem is seen, giving everyone an opportunity to address it so it does not happen again.

Source Inspection

This involves looking for errors in materials, equipment and fabrications that are used to create the final product. Finding defects at the source level prevents errors from happening in manufacturing or creation of the final product. The term sometimes is applied to the practice of inspecting a product before it’s shipped to a manufacturer.

Combining these two allowed Toyota to “virtually eliminate the need for Statistical Quality Control (SQC), which has been the very heart of quality control in this country for years,” according to publisher Norman Bodek in his forward to Shingo’s book, “Zero Quality Control: Source Inspection and the Poka-Yoke System.”

The Importance of Zero Quality Control

The bottom line for any business is that the quality of the finished product or service is the single biggest determinant of success.

One of the reasons for Toyota’s success against (initially) larger companies in Europe and the United States is the consistent quality of the company’s products. Models such as the Corolla and Camry became the benchwork for automotive reliability.

Ideas such as Zero Quality Control, much like the other ideas from Shingo and the Toyota Production System, also lower costs and make processes more efficient while simultaneously improving quality. Shingo and Toyota proved this is possible, and Shingo himself thought that business leaders needed to drop the idea that zero defect is impossible to attain.

Moving Past SQC

In his book, Shingo wrote that he spent 20 years believing that Statistical Quality Control represented the apex of quality control. It had evolved from simply throwing out defective products to attempts to stop defects from happening. But eventually he realized that the many SQC inspections “cost considerable time and trouble.” He reasoned that a better approach would be to eliminate the errors that cause defects early in the process, before the defects occur.

“It occurred to me that we were giving feedback and taking action only after defects had been detected, and I wondered whether there were not some inspection system that could prevent defects from occurring in the first place,” he wrote.

He then combined elements of source inspection and Poka-Yoke. The results: In 1977, Shingo wrote that zero monthly defects occurred in a 30,000-units-per-month washing machine assembly process at the Shizuoka plant of Matsushita Electric’s washing machine division.

That result, Shingo wrote, “freed me completely from the spell of statistical quality control.” These ideas eventually lead to Total Quality Control that has gained popularity worldwide.

Putting Poka-Yoke Into Action

Shingo wrote that Poka-Yoke “has the very real capacity to reduce, and eventually to eliminate, defects.” Putting Poka-Yoke to work involves following a series of steps.

  • Create a process flowchart that includes details on every step in a process, no matter how small.
  • Review each step to determine where human errors are most likely to occur.
  • After identifying potential errors, work through the process to find the root cause of the error.
  • Design solutions to reduce or eliminate the risk of the error occurring in the first place These solutions can include eliminating the step or replacing it.
  • If teams cannot eliminate the step, they must develop ways to minimize impact of the error should it occur. This includes changing source inspection methods.