The Application of Other Quality Tools in Six Sigma
There is a wide range of tools necessary for the planning, maintenance, and troubleshooting of quality problems and defects. These tools include quality planning tools that are helpful in estimating and planning for contingencies when a new product is launched, or when a production process is being upgraded or improved. They include the tools described in the following subsections.
Process mapping is a structured approach focused on improving processes to deliver the highest quality and value of products and services to the customer. It is based on structured analysis (SA) and structured designs, which were tools that were developed for the software industry as a means toward hierarchical decomposition and description of software modules. Structured analysis and design were developed to replace the traditional tools of flowcharting as software projects and programming complexities increased.
The advantage of process mapping is the presentation of information flows between different systems and departments in a graphical manner. Using a hierarchical approach, process mapping allows for easy understanding of a complex system or process. Process mapping has been used successfully in management information systems to design the information and data flows for manufacturing operations. It could also be used to describe the complex marketing, sales, manufacturing, and quality systems that are used to develop and introduce new products to manufacturing and the marketplace.
Structured analysis uses few symbols and techniques to present a complex system or operation. The top-level boundary of the system being described is called the context diagram, and the decomposition of the system into smaller, more detailed units is called data flow diagraming. This process, known as “top-down partitioning,” occurs when data flow diagrams are decomposed from a very high level and general view of the system, to a very detailed view of specific operations.
A data flow diagram may be defined as a network of related functions showing all data interfaces between its elements. These elements are:
• The data source or destination, represented by a rectangular box. A source is defined as an originator of data and a destination is denned as the target for data receipt. Sources and destinations are used to determine the domain of the study of the system，such as departments, suppliers, and customers.
• The data store is represented by two parallel lines or an open box.
It represents a repository of information. Data can be stored in electronic files or in physical locations such as file drawers. The name of the file or the storage system should be written alongside the symbols. In complex diagrams, the same data stores might be drawn at different locations to minimize nesting of the lines. In these cases, another vertical line is added to the symbol to indicate that it is repeated elsewhere in the diagram.
The data flow, represented by an arrow, symbolizes the information being carried from different parts of the systems in order to be transformed or recorded. The name of the data flow should be written alongside the arrow.
Every data flow and data store should have an associated data dictionary which provides a single document to record information necessary to the understanding of the data flow diagrams. The information can take the form of what records are kept for each data item and the associated information for each record. The definition of each element of process mapping is as follows:
• Process—activities to satisfy customers’ requirements
• Inputs—the material or data that is changed by the process
• Outputs—the results of the operations of the process
The basic elements of structured analysis or process mapping are shown in Figure 1.6. The process mapping procedures consist of the following steps:
1. Establish process boundaries (“as is” flow), including discussions among the team members regarding the basic elements of the process to be examined, their inputs, and outputs. This would constitute the context diagram of the process and the data flows of current information originating from sources, transformed by processes and arriving at destinations and data stores. The current process operation is recorded, including the relationship of the various processes and the types of data stores and how the data is manipulated.
2. For each process, establish definitions of inputs, outputs, customers, and key requirements. Document process specifications and data dictionary for each process.
3. Analyze the current “as is” process map, then create a more efficient process map, called “should be.”
4. Reestablish the process definitions and data flows for the “should be” process map.
These elements of structured analysis, shown in Figure 1.6, are very useful in documenting and explaining to the enterprise how the methods, techniques, responsibilities, and operations of the different parts of the organization interact with one another. It serves as a powerful documenting tool for current processes. In addition, the inherent inefficiencies of the process can be visualized easily, and can be optimized by eliminating excess loops and data transcriptions.
Each department should record its procedures, responsibilities, and functions in its own data flow diagram. This serves as an excellent documentation tool for the total process and its interactions. The visual presentation of the diagrams is much easier to comprehend than written procedures and documentation. For example, design engineers can quickly grasp the interconnection of the different parts of the organization in such cases as design implementation and production of prototypes.