Model and simulation of a gas cookers assembly line: performance analysis and suggestions to increase efficiency

The environment is an factory with 110 employees which produces high class cookers and ovens, destined to both Italian and foreign markets. In such a factory raw materials and components are bought from external suppliers, works-in-process are partly manufactured inside and partly outsourced, final products are assembled inside; the factory includes three production departments, where all final products are assembled and some works-in-process are manufactured, and a logistic department, where final products are temporary stored and then dispatched to customers. We consider one of the production departments, which includes: an office; two warehouses where final products, works-in-process and components are stored; three workrooms dedicated to work-in-progress manufacturing; an assembly shop, containing a serial assembly line with 23 on-line working stations and 9 off-line working stations, which perform either test operations or pre-assembly operations on components and works-in-process, and feed the assembly line. The assembly shop in its whole is the object of the present paper; at the beginning of the study, the line had been repeatedly adjusted, adapted and modified, in correspondence with new products design and new technological solutions; unfortunately, such changes concerning processed parts, performed operations and employed machines had not been supported by the necessary actions on line management, with special attention to operating speed and distribution of single operations among workers. Therefore the study had the scope of analysing performed operations and related interactions, of modelling and simulating the whole shop and finally of looking for possible improvements; two peremptory condition had been imposed: improvements had to be obtained with zero investment and minimal structural revolution. The study was limited to one of the products, by considering that the developed model may be easily adapted to other products by suitably changing operating parameters; moreover we think the adopted method may be extended to different serial assembly lines. The work performed included in the order: analysis of all information about assembly cycles at disposition; check on its correspondence with reality; after a negative result of the check, rebuild a new valid information, by taking all assembling times and generally all other operating times; building up and implementation of a simulation model on the computer; simulation experiment based on current times; model validation based on current behaviour; critical analysis of current performance parameters; new experiments based on different cycle times and related analysis of resulting performance parameters; new experiments based on both different cycle times and different operations scheduling, and related analysis of performance parameters.