Transiting toward the factory of the future: Optimal buffer sizes and robot cell design in car body production

Recent improvement in robotics has sharply increased the adoption rate of robotic systems as robots are now more cost-effective when compared to human labor and a lot easier to use. Consequently, more people with little or no experience of line design are overseeing line automation. This paper proposes an easy-to-use tool with an application in a car-body shop - extension for application to other processes is feasible with minor modifications. In car-body shops, most of the operations are performed by robots that load and weld stamped steel parts. These robots are organized in cells separated by buffers. One of the main objectives of car-body shop designers is to keep cost as low as possible with no impact on the production rate and the quality of the parts produced. To do that, they have at their disposal two main levers: the size of buffers and the number of robots. Adding more buffers could reduce the impact of disruptions and, consequently, increase the production rate. On the other hand, adding robots will speed up the lines which would also increase the production rate. Both add significant but different costs. Also, additional robots means additional failures, and this may reduce or reverse the increase in production rate. Given a target production rate, the goal of the method submitted in this paper is to help production line designers answer the following questions: What robot and buffer space allocation will meet the target at least cost? This paper proposes a judicious analytic solution based on simplifying yet realistic assumptions.