Six Sigma Concept

The objective of robust design is to achieve product designs with few defects during manufacture and very few latent defects after a product is delivered to a customer. It focuses on identifying the characteristics of the product that are critical to meeting the product requirements and then seeking the DFSS process capability.

The DFSS is an integrated approach to design with the key issue of reducing the scope for mistakes and inefficiencies – that is, make a product right the first time to prevent the waste of company resources [2]. DFSS is a collection of product tools

Table 17.1. Sigma distribution of defects

Sigma distribution process capability

Defects per million











and topics used to assist the design of products for manufacture by processes oper­ating at the Six Sigma capability. It is a management-driven task to facilitate the improvement of labor efficiencies from employees and find new ways to improve on any routine approach so that the product can be manufactured at the highest quality and lowest cost, thereby satisfying all of a customer’s requirements. Six Sigma helps expose the “hidden factory” of waste that robs organizations of profits by using a routine approach to issues with the product and manufacturing process. The vision of Six Sigma is as follows:

• reduce costs and improve margins in a context of declining prices

• surpass customer expectations by a margin few competitors can match

• improve at a faster rate than the competition

• grow a new generation of leaders

Six Sigma is a systematic methodology for eliminating defects in products, services, and processes while also yielding cost and cycle-time reductions. By significantly improving process capability, it can achieve operational excellence in delivering almost defect-free products and services, at the lowest possible cost, and on time.

For manufactured products, the Six Sigma methodology makes use of a variety of managerial, technological, and statistical techniques to change the manufacturing processes, the product, or both in order to achieve the Six Sigma process capability. DFSS is the collection of tools and topics used during the design phase to achieve a Six Sigma product.

One measure of process capability is in the sigma, a, a statistical measure. For example, when a process is operating at Six Sigma capability, the long-term yield is 99.99966%, corresponding to 3.4 defects per million opportunities. The demand for Six Sigma is high, thereby guaranteeing a robust design. Table 17.1 lists the sigma distribution in a statistical histogram of defect levels relative to process capability.

To gain a competitive advantage through customers’ satisfaction, their needs must be understood. One way to capture customer requirements is by using selected quality function deployment (QFD), which consists of a series of interlocking matrixes that are used to translate customer requirements into product functional requirements and process characteristics.

However, development and implementation of DFSS is difficult. It requires employee behavior characteristics such as leadership, commitment, professional­ism, and perseverance to overcome the attitudes heard in phrases such as “no time,” “not invented here,” “doesn’t apply to us,” “we’ve been doing it for years,” “I prefer

design rules,” and “I refuse to use the tools.” DFSS demands a culture change – not easy to achieve but possible.