I‑MR Control Chart: A Tool for Judging the Health of the Current Manufacturing Process of an API and for Setting the Trial Control Limits in Phase I of the Process Improvement

It
has been observed that the main focus during the process development
and manufacturing of an API is to meet the customer’s specifications
(LSL and USL) rather than estimating and improving the natural control
limits (LCL and UCL) of the process. It results in the overlap of
the natural control limit and customer’s specification, which
in turn increases the chance of failure with respect to the customer’s
specifications. A better approach is to work on decreasing the variability
of the process so that natural control limits become much tighter
than customer’s specification. The statistical control charts
not only help in estimating these internal/natural control limits
but also raises an alert when the process goes out of control. These
alerts trigger the investigation through root cause analysis leading
to the process improvements which in turn lead to the decrease in
variability of the process. This process continues till inherent variability
of the process is due to common causes only and cannot be attributed
to assignable causes. At this point, the natural control limits of
the process can be taken as internal specification for an output quality
parameter.