Using SPC Chart Techniques in Production Planning and Scheduling:

Theoretical scheduling has reached a mature state but there are difficulties in using the theory in practice. One of the issues is the occurrence of disturbances. Studies have been done to investigate the possibility of using control chart techniques to detect disturbances in production planning and scheduling. Appropriate control chart techniques have been developed that avoid statistical problems, assuming that the whole system may be viewed as a dynamic process. To validate the new techniques, data have been collected in two different business sectors. The control charts show their ability to detect changes and their potential for practical implementation. Key words; production planning and scheduling, dynamic process, control chart Introduction Statistical Process control (SPC) is a tool which has been successfully used in both manufacturing and non-manufacturing sectors. SPC charts were first developed to distinguish between common causes and special causes of variation. The ability to distinguish between the two causes results in improvements in a process by reducing the variation. If no points fall outside the control limits and non-random trends are not evident, the process is said to be stable or in statistical control. Reduction in process variation can be achieved even when the process achieves stability, but radical change may be required. Therefore, SPC charts are tools that can be used to achieve process stability, to provide a guideline to reduce process variation, to assess a process’s performance and to provide information for management (Dale ,1994). Classical production planning and scheduling have been viewed as being in a mature state (MacCarthy and Liu, 1993), but there are difficulties in using the theory in practice and many organisations continue to have problems in planning, scheduling and control. Stoop and Wiers (1996) give a number of causes which affect the applicability of scheduling techniques in practice. Disturbances from machine breakdowns, unavailability of raw material, rush orders and human factors may occur frequently. To achieve the stability of production planning and scheduling, Wasusri and MacCarthy (2000) have proposed that production planning, scheduling and control be looked at as a dynamic control process. SPC techniques could be applied in order to detect all changes in the process. However, many caveats have been raised in implement SPC charts in non-manufacturing applications (Humble, 1998), (Lewis, 1999), (Finison, et al., 1993), (Wood, 1994). MacCarthy