1.1 What Is Six Sigma?
The name Six Sigma comes from the fact that it is a managerial approach designed to create processes that result in no more than 3.4 defects per million. One of the aspects that distinguishes Six Sigma from other approaches is a clear focus on achieving bottom-line results in a relatively short three- to six-month period of time. After seeing the huge financial successes at Motorola, GE, and other early adopters of Six Sigma management, many companies worldwide have now instituted Six Sigma management programs [see References 1, 2, 3, and 5].
The DMAIC Model
To guide managers in their task of improving short- and long-term results, Six Sigma uses a five-step process known as the DMAIC model, named for the five steps in the process: Define, Measure, Analyze, Improve, and Control.
- Define. The problem is defined along with the costs, benefits, and impact on the customer.
- Measure. Operational definitions for each critical-to-quality (CTQ) characteristic are developed. In addition, the measurement procedure is verified so that it is consistent over repeated measurements.
- Analyze. The root causes of why defects occur are determined, and variables in the process causing the defects are identified. Data are collected to determine benchmark values for each process variable.
- Improve. The importance of each process variable on the CTQ characteristic are studied using designed experiments (see Chapter 8, "Design of Experiments"). The objective is to determine the best level for each variable.
- Control. The objective is to maintain the benefits for the long term by avoiding potential problems that can occur when a process is changed.