When we talk of Process Control and plan to initiate it in our operational processes, it is important to understand the variables that most affect our processes. The process designers must identify the vital few controls that will receive priority, and for this designers and operational personnel must understand the concept of dominance.
Processes are influenced by various input variables like environment, skill, setup and many more; and often one variable is more important than all combined and such a variable is called dominant variable. In the book "Juran on Quality by Design", Juran classifies these dominant variables into five types, which we are listed below:
* Setup-dominant: Processes which once set-up will exhibit stability and reproducibility over repeated cycles of operations are know to be setup-dominant processes. These processes must be so designed that importance is given for precise setup and validation before operations proceed, because there is no real control during the repeated cycle of operation that will impact the quality of the output. For example in the printing process, once the setup is made and approved the operator has no influence on the spellings, font size or other parameters on the printed matter. Similarly in the manufacture of plastic molded parts, wherein the manufacture of the mould ( tool ) plays a vital role and is also called tool dominant process.
* Time-dominant: In this case the process is known to change progressively with time, this is typical of machining processes wherein there is wear out of tools over a period of time, similarly consumption of consumables, heating up. The process design must take into consideration the periodic evaluation and adjustment of the process. Process Control charts are most commonly used for time dominant processes.
* Component Dominant: The main variable in this case is the quality of the input materials and components. This is typical in assembly processes like assembly of mechanical and electronic equipments; like assembly of a television. Many organizations resort to incoming inspection to bring control, though this is probably required for a short time, in the long run it is important to develop suppliers to provide quality parts. Joint planning with suppliers to improve supplier's process will also be required.
* Worker Dominant: When the quality of the output depends mainly on the skill and knack possessed by the workers, it is called a worker dominant process. For these processes the candidates employed are almost always form qualified with the basic skill sets. The design for control of these processes must emphasize aptitude testing, training, certification and quality rating of workers. Well, training and certification is indeed important for all types of process, but in this case it is even more important.
* Information Dominant: In this case the processes are of "job shop" nature, wherein there is frequent changes in the products that need to be produced. Since the job information changes frequently, the design for process control should concentrate on providing an information system that can deliver accurate, up-to date information on just how each job differs from the others.
A common mistake I see people make while solving process problems and customer complaints is to attribute the problem to "operator error", no matter on what type of dominance the process is. Even in worker dominant process it is important for us to see how much of control we can bring by error proofing the processes, so that there is less and less of operator influence. Process control is very important to ensure quality of products, but to ensure better process control it is vital to understand the dominating variables in the process and plan control mechanism based on the same.
Pradeep Kumar E.T. A Master Black Belt in Six Sigma , is the Country Manager- Operational Excellence with Tyco Electronics Corporation India Pvt Ltd. Feedback can be e- mailed to pradeep@ businessgyan.com