Variation


Do you understand the sources of variation in your manufacturing processes?
As described the FDA Process Validation: General Principles and Practices, the manufacturer should use the product and process knowledge as a basis for establishing an approach to control that is appropriate for the manufacturing process. This includes:

• understanding the sources of variation
• detecting the presence and degree of variation
• understanding the impact of variation on the process and ultimately on product attributes
• control the variation in a manner commensurate with the risk it represents to the process and product

Juran (Juran’s Quality Handbook (Edition 5)) identifies that operating processes are influenced by many variables, but often one variable is more important than all of the rest combined. Such a variable is said to be the “dominant variable.” Knowledge of which Process variable is dominant helps planners during allocation of resources and priorities. The more usual dominant variables include:

Set-up dominant: Some processes exhibit high stability and reproducibility of results, over many cycles of operation. A common example is the printing process. The design for control should provide the operating forces with the means for precise setup and validation before operations proceed. Examples of such processes are drilling, labeling, heat sealing, printing, and presswork.

Time-dominant: Here the process is known to change progressively with time, for example, depletion of consumable supplies, heating up, and wear of tools. The design for control should provide means for periodic evaluation of the effect of progressive change to enable the worker to make compensatory changes. Screw machining, volume filling, wood carding, and papermaking are examples of time-dominant processes.

Component-dominant: Here the main variable is the quality of the input materials and components. An example is the assembly of electronic or mechanical equipments. The design for control should be directed at supplier relations, along with incoming inspection and sorting of inferior lots. Many assembly operations and formulation processes are component-dominant.

Worker-dominant: In these processes, quality depends mainly on the skill and knowledge possessed by the workers. The skilled trades are well-known examples. The design for control should emphasize aptitude testing of workers, training and certification, quality rating of workers, and error-proofing to reduce worker errors. Workers are dominant in most manual processes such as welding, painting, and order picking.

Information-dominant: Here the processes are of a “job-shop” nature, so that there is frequent change in what product is to be produced. As a result, the job information changes frequently. The design for control should concentrate on accuracy and up-to-dateness of the information provided to the worker (and everyone else). Examples include order editing and “travelers” used in job shops, ERP Systems and other computer aided information systems and networks.

Do you understand the sources of variation in your manufacturing processes? Have you identified what type of dominance is influencing your process? Have you designed and implemented control procedures to reduce the impact of this variation? As reported in the FY 2019 FDA Inspectional Observation Data Sets there were 81 citations by FDA to drug manufacturers where control procedures were not established which [monitored the output and validated the performance] of those manufacturing processes that may be responsible for causing variability in the characteristics of in-process material and the drug product.

Click here for more information on on the application of dominance to process validation (note registration is required).