If you run a manufacturing operation, you probably hear a lot about lean manufacturing and Six Sigma. Often they are used in conjunction with each other but they are in fact different things.
Lean manufacturing can be difficult to define because it encompasses many layers and applies to all levels of the business of manufacturing, from the workers on the line all the way up to the CEO. Essentially, lean is a way of doing things in a business; it’s a culture, a way of life, an overall philosophy. Lean, at its core, dictates that the customer is the most important part of the business, and the customer determines what about a product has value. Any part of the manufacturing process that is not adding value to the product is wasteful and must be eliminated so it does not interfere with the value stream, the process of creating and delivering a product.
Six Sigma, on the other hand, is a specific set of process improvement strategies. Originally developed by Motorola, it focuses on the identification and removal of defects in business and manufacturing processes. A defect is considered to be anything that causes customer dissatisfaction.
Lean manufacturing and Six Sigma do have some similarities. Six Sigma is focused on eliminating variation in processes, and lean also considers variation to be waste and a target for elimination. Lean, however, is an all-encompassing philosophy for managing all aspects of a company, whereas Six Sigma only focuses on process improvement. Six Sigma is about creating quality for the customer; lean is about creating value for the customer. Six Sigma can be used in a lean manufacturing environment, that is, the two methodologies do not work at odds. The most important thing to remember is that Six Sigma is a strategy and lean manufacturing is a way of life.
Lean identifies three different kinds of wastes, using Japanese terminology from the Toyota Production System where lean originated: muda (waste of time and materials), mura (unevenness/variation), and muri (the overburdening of workers or systems). Every employee in a lean manufacturing environment is expected to think critically about his or her job and make suggestions to eliminate waste and to participate in kaizen, a process of continuous improvement involving brainstorming sessions to fix problems. Simultaneously, lean manufacturers are obliged to have great respect for their employees and seek to enrich them.
One of the most interesting features of lean is called JIT, for “just in time.” This process eliminates waste by attempting to provide what is needed exactly when it is needed on the assembly line. It involves the lean principle of takt, which links customer demand directly to the flow of manufacturing. Instead of management “pushing” products down the line, each product is “pulled” through the system by demand, as a supermarket shelf is replenished when it is empty. The empty shelf is a signal that it needs replenishing; in lean, this signal is called a kanban.
Another important principle of lean manufacturing is called jidoka. This is the idea that quality cannot be “inspected into” products at the end of the assembly line, that defects must not pass each station on the assembly line until fixed. Lean employees use a technique that traces problems to their source and resolves them.
The name Six Sigma is derived from the calculation of the standard deviation, the mathematical idea that all manufactured parts must fall within a certain range, or standard deviation, from the center of a bell curve. (Standard deviation is represented by the Greek letter sigma.) All processes have variation; Six Sigma dictates the gathering of information about variation to improve a product or process. The fundamental goal of Six Sigma is to increase process quality such that there are 3.4 defective parts per million opportunities, or DPMO.
To achieve this goal, practitioners of Six Sigma use two critical methodologies: DMAIC, used for correcting existing products or processes, and DMADV, used for creating new products or processes. DMAIC stands for define, measure, analyze, improve, control:
- Define: This step involves identifying goals for process improvement.
- Measure: This step uses one of the many statistical tools in Six Sigma to gather data.
- Analyze: This step involves using the data from the measure step to infer relationships between the data and the goals.
- Improve: This step optimizes the process based on the collected data.
- Control: This step implements measures to regulate performance.
DMADV stands for define, measure, analyze, design, verify. This methodology is used for developing new products. As such, it varies slightly from its counterpart:
- Define: This step identifies what is being designed and why.
- Measure: This step identifies product capabilities and production process capabilities.
- Analyze: This step creates a high-level design.
- Design: This step fleshes out the details of the product or process.
- Verify: This step verifies the design and production begins.
Six Sigma endeavors are called “projects” and involve job roles created specifically for Six Sigma. Projects are initiated by Executive Leadership, which includes the CEO and other top managers. They empower the Champions, who oversee all of the Six Sigma projects. The Champions identify Master Black Belts, who act as guides to the Black Belts. Black Belts oversee implementation of Six Sigma methodology in a specific project. Both levels of Black Belt devote 100 percent of their time to Six Sigma projects. The Green Belts assist the Black Belts in Six Sigma projects but also have other job responsibilities.