Developing a Simulation Model of Resource Starvations in Automotive Assembly Lines

Competition in the automotive industry is becoming more intense, the product life cycle is getting shorter and there is an increasing demand of customization. High product variety along with faster new product introduction may result in an inefficiency in production. In order to be responsive to the market requirements, maximising the production rate is essential.
At one of the vehicle manufacturers in the UK, the current sub-assembly process of tailgates, where tailgates are lifted by carriers, assembled then fed to the main assembly line to be fitted to their matched vehicles, is facing problem of occasional starvations of empty carriers when they return from the fitting point. This problem flags a concern of stopping the main line and as a consequence, slowing down the production.
In order to solve this problem, a flow diagram is developed to represent the logic of the process. Discrete-event simulation approach is used to mimic operations of the sub-assembly line. A simulation model is then developed to identify the bottleneck(s), determine whether or not additional carriers are required and design scenarios for improving the process, taking into consideration random failures in the main line.
The results show that starvations are caused due to the main line failures, which lead to high buffer levels of carriers lifting tailgates within the sub-assembly process. This leads to less empty carriers remaining for a new assembly cycle. A slight improvement of 1.2% in production speed could be achieved by reducing the bottleneck time by 15 seconds and less than 1% improvement if five more carriers are added.