SIX SIGMA HAS BEEN TOUTED AS a powerful quality improvement method that boosts employee job satisfaction and increases profits. Although many shops striving to improve operations and profits have adopted lean production and other qualityimprovement methods, relatively few smaller enterprises have implemented six sigma techniques. In the 2006 AMERICAN MACHINIST BENCHMARKING SURVEY, 88 percent of the topperforming benchmark shops reported using lean-manufacturing methods, but only 22 percent of these shops were using six sigma.
The heavyweights of six sigma have typically been large companies, such as Motorola, General Electric, Honeywell, Ford and Caterpillar. Implementing six sigma can require a considerable dollar investment, dedication of resources and employee training. Although the benefits of six sigma are alluring to companies of all sizes, small or mid-sized manufacturing companies face significant challenges because many do not have the time or the financial resources to invest in the long-term benefits of six sigma. The short-term costs for training and the length of time to complete projects can cause more of an impact to small companies than to large companies.
Whether they want to or not, many shops are being pushed to implement six sigma by their large-company customers that are beginning to mandate six sigma to their supplier base as a condition for future business.
WHAT IS SIX SIGMA
With techniques based on statistical process control, six sigma practices are used to identify and eliminate defects, waste and quality-control problems. Defects are defined as any type of product or service that does not conform to a standard inspection unit or satisfy customers. The result of reducing defects is improved customer satisfaction and increased profitability. The six sigma methodology encourages teamwork and helps management focus and refine its methods of achieving efficiency.
Six sigma defines the process, whether focused on products and services, measuring performance, improving efficiency and customer satisfaction or even running the business, as the key vehicle for success. If a company can measure the amount of defects in a process, it can systematically determine how to eliminate them and approach, as close as possible, zero process defects.
Sigma represents a standard deviation in mathematical statistics indicating how tightly all the various samples are clustered around a mean in a set of data points. Most companies operate at three sigma (67,000 defects or defective parts per million opportunities) or four sigma (6,200 defects per million opportunities). A process with a six sigma quality level produces 3.4 defects per million opportunities, or a success rate of 99.9997 percent.
In a traditional implementation, two processes are involved in achieving six sigma quality: DMADV (define, measure, analyze, design and verify) for new products or processes, and DMAIC (define, measure, analyze, improve and control) for existing processes. These processes are carried out by trained professionals called green belts or more highly trained black belts and overseen by master black belts (see sidebar).
When using DMAIC to improve a process, first the project and process are defined. Then, the performance of the process is measured and the data analyzed to identify bottlenecks and problems. Then, improvement programs are defined and defects removed.
The most important requirements for successful six sigma implementation are management support, financial support for the implementation, an understanding of what six sigma is, reasonable expectations and overcoming the fear of cultural change.
A PRACTICAL SHOP-LEVEL IMPLEMENTAION
The traditional top-down black-belt six sigma implementation, with its heavy investment requirements of dollars, resources and training, is a barrier for many small and mid-size shops. Making six sigma work for small businesses means balancing the benefits of implementation against the investment in training.
An alternative deployment model allows smaller organizations to implement the methodology at a more economical and manageable pace. This abbreviated method uses so-called "yellow belts," who are project team members trained in the use of basic six sigma tools, but with much less training than either green or black belts. This addresses many of the constraints of smaller and mid-size companies in implementing six sigma methods. Some observers say that yellow belts are capable of capitalizing on at least a portion of six sigma opportunities.
The basic steps of implementing this method include:
Prepare management. by being sure they understand the procedure and benefits of the six sigma process. Lack of management understanding, support and commitment is a common and decisive factor for disappointing results of an implementation. At this point, the strategy and implementation approach are aligned within the organization's business plan, focusing on customer requirements. Also, a steering committee is established to promote the process throughout the organization.
Complete implementation planning by establishing baseline performance factors, expected performance and financial improvements, communicating program goals, implementation strategies and developing training schedules for all employees.
Initiate training during which methodology and tools are explained and illustrate how employees can increase the extent to which their work meets the expectations of customers by reducing cycle times and raising quality. As training continues, employees learn specific methodologies for resolving differences in product and service expectations, so mistakes that lead to customer dissatisfaction can be minimized.
Establish natural work groups to apply the methodology to improve their major product or service. The team starts to apply the methodology to improve their product or service. They identify customers, suppliers and their critical requirements, define value versus non-value-added tasks and implement quality performance measures to ensure continuous improvement.
Identify possible green or black belt candidates for further training and transition to the next level of six sigma achievement, if needed.
SIX SIGMA PLAYERS
A TRADITIONAL SIX SIGMA CORPORATE STRUCTURE involves a series of persons with various titles, but all are instrumental to making an implementation work. Their martial-arts titles are not adopted by all companies, but their functions are necessary for success.
Champions are upper-level managers who lead the deployment of six sigma. They are responsible for selection, support and, ultimately, project success.
SMART MACHINE TOOLS
ROBERT B. JERARD, PROFESSOR OF MECHANICAL ENGINEERING AT THE University of New Hampshire ([email protected]), points out that achieving six sigma quality in machining processes requires matching manufacturing process capabilities to the part requirements. This can be accomplished either by better manufacturing or improved designs, which means part tolerances no tighter than required to maintain proper function. Unnecessarily tight tolerances needlessly raise manufacturing costs.
To upgrade machining process capability, Prof. Jerard is conducting research on the development of machine tools that are smart enough to know their own process capabilities.
Jerard points out that there is a huge gap between current machine tool technology and where they need to be. Currently, CNC manufacturers provide only two indicators of precision: positioning accuracy and repeatability. But it is not clear how these specifications relate to the standard deviation of a machine tool, which has a dramatic influence on produced part quality. For example, a machine tool with a standard deviation of 0.002 in. achieves a six sigma quality level when the tolerance band of a part is 0.022 in. If the standard deviation doubles to 0.004 in., then defects jump from 3.4 defects per million (six sigma) to 66,800 defects per million (three sigma).
If machine tools are to become smart enough to know their own process capabilities, they must deal with such error sources as machine axis squareness, encoder inaccuracy, tool and workpiece deflection, thermal expansion, tool runout and tool wear. Many of these factors change with time, environmental conditions and usage.