In Nigeria, license vehicle number plate production is characterized by high variability in process times and inter-arrival times resulting in long job waiting time on queues. The objectives of this paper are to investigate the process variability and evaluate the impact on output as well as to identify assignable variables, estimate variability indices and develop matching solutions for improved performance. The paper adopted method of variability pooling for a job shop operating in a non competitive environment with zero buffered inventory policy. Structured questionnaires were administered on the plant workers. Data collected from the plant production records for 2012, 2013, 2014 and in seven production lines were analyzed. Prior to this study, the coefficient of variation (CV) for Awka, Gwagwalada, Lagos and Lagos State Plants showed that measured variability level of the plant were 0.62, 0.67, 0.60 and 0.78, respectively. Comparatively, results obtained after the study showed a significant reduction in process time, cycle time, machine utilization, queue length and waiting time on queue, leading to increased production rate in all the plants. The main contribution of this work from a process efficiency perspective is the low CV achieved that enables 40% increase in net annual income for each plant.

Keywords: assignable variable, variability pooling, process efficiency, vehicle number plate, machine utilization.