One of the key principles of the lean enterprise is to eliminate waste, and very little is more wasteful than poor quality. Scrap and rework are costly and inefficient. Unhappy customers and returned goods are expensive and can result in loss of market share. A focus on quality is a key value of a lean company.

Lean and Six Sigma

Six sigma is a discipline focused on identifying and eliminating root causes of poor quality and ensuring that process changes and corrections occur quickly. Six sigma uses many statistical methods to identify and measure quality, and there is also a body of techniques that are very similar to techniques in lean.

For example, lean uses Kaizen, the “Five Whys” and various performance metrics to drive down to the source of a problem and ensure its correction. This is very similar to six sigma’s focus on identifying a root cause using a technique called DMAIC (Define, Measure, Analyze, Improve and Control).

Lean and Mistake Proofing

One of the most important lean principles is Poka-yoke, or mistake proofing. This means to design a process in a way that eliminates mistakes or reduces the likelihood of errors. Poka-yoke techniques may include creating tooling that prevents incorrect set up or assembly or creating behavior shaping constraints such as automatically engaging safety latches or levers.

There are three distinct methods for engaging poka-yoke. They include:

  • Contact (testing for a specific product characteristic such as shape, placement or color)
  • Constant number (enforcing a specific number of movements or repetitions)
  • Sequence (determining whether all required steps have been followed)

Poka-yoke devices prevent a mistake from occurring and are considered a form of control. Other poka-yokes may simply issue a warning so the operator knows a mistake has occurred and can correct it.

Lean, Quality and Worker Autonomy

In a true lean environment, anyone can halt production if they suspect there is a quality issue. Workers may shut down machines or even entire assembly lines if they notice a problem. While some people believe this is a costly process, the reality is that production workers are closest to the product and are often the first to notice when something goes awry. By respecting the worker’s insight and knowledge, the company saves time and money because they don’t produce poor quality or out of spec goods. The process can be corrected quickly, before the company wastes a large amount of material or is forced to scrap or rework products to meet spec. A short line stoppage to investigate a potential quality issue is actually much less wasteful than fixing quality problems later in the process.

Lean and Clean Workspace

Keeping workspaces clean and well organized is another key aspect of lean that contributes to quality. One way is by ensuring that tools and components are stored in a consistent and orderly manner. This increases efficiency and also prevents errors from mixing up parts that have a similar appearance but different characteristics. A clean workspace also reduces the likelihood of contamination or spoilage.

Following lean principles makes a company more efficient and helps to control costs, but lean also contributes to product quality. Coupled with a companion discipline such as six sigma, lean has catapulted many companies to higher profitability and increased market share.