SPC techniques using M/M/1 queueing model

In a manufacturing process, no two products can be exact, which might be due to many factors. These variations need to be monitored and controlled through the use of statistical process control (SPC). When they are small, and their effects are barely noticeable, we say the process is 'in control'. Otherwise, they lead the process to 'out of control'. Items enter the system and wait in a line for measurements; by following a queue discipline. Such a queue is then characterised according to service time, number of quality inspectors and waiting space. A good process control will also protect the product in the sense that the lots produced at permissible levels of quality will have a good chance to be in control. The objective of this paper is to introduce a control chart using M/M/1 queueing discipline to study and maintain a process control in a regular interval.