BM1708
OPTIMIZING AND CONTROLLING PROCESSES THROUGH STATISTICAL PROCESS CONTROL
Definition and Rationale for Statistical Process Control (SPC)
Statistical Process Control (SPC) is an industry–standard methodology for measuring and controlling
quality during the manufacturing process to enable continual improvement. The degree of process
conformity or non–conformity is determined by the following factors:
• Quality of conformance. It refers to a manufacturing state where the product fully conforms with
its intended design and characteristics.
• Chance variation/Random variation. It refers to a manufacturing state where the product differs
in design and characteristics due to the combined natural influences in the production process.
For instance, the use of older machines may generally exhibit a higher degree of variability to the
output, in comparison to the use of newer machines that may have incorporated design
improvements that lessen the variability of the output.
• Assignable variation/Nonrandom variation. It refers to a manufacturing state where the product
differs in design and characteristics due to an identifiable cause which can be easily eliminated.
The typical sources of assignable variation include an equipment that needs adjustment, defective
materials, or human sources such as carelessness, fatigue, and incapacity to perform assigned
task.
The rationale of Statistical Process Control are the following:
