Using Spc To Ensure Haccp Control

SPC emphasizes building product safety and quality into the manufacturing process by focusing on the process rather than the product. SPC tools are used to measure and interpret different kinds of variation that affect the behavior of a process. An important part of dealing with variation in a process control system is to have knowledge of the extent of variability. The critical point in process control is not to eliminate all variation, but to have any variation that is present in the process to be stable and predictable.

The key to controlling safety and quality in manufacturing is to understand how to recognize the different types of variation present in a process. Common cause variation is the inherent, random chance events expected in every process which fluctuate in a normal, predictable manner. Variation is small in magnitude and therefore difficult to locate and eliminate from a process. Special cause variation is sporadically induced variation that impacts a process, causing large fluctuations that are easily discernable and therefore can be effectively eliminated from a process [34] (see Figure 15.1). The basic objective of SPC is to use valid statistical methods to identify the existence of special causes of variation and to eliminate them from a process. This will produce a stable, constant-cause system which can be measured and controlled [35].

Although SPC is the most effective tool to achieve process control in an operation, most processes do not naturally operate in a state of control. They tend to deteriorate over time. Process control is defined as the functioning of an operation within predetermined statistical limits, such that only common cause (controlled) variation is occurring among its manufactured products [36]. While a process may be in control initially, it will not remain there. The only way to determine whether a process is in or out of control is

Special cause variation

• Incorrect setting

• Faulty materials

• Machine breakdown

• Operator error

• Incorrect specification

• Change in temperature

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