This research develops an integrated mathematical framework that jointly determines assembly, inventory and vehicle routing decisions while explicitly incorporating sustainability considerations. The joint treatment of inventory control and routing activities is commonly referred to as the inventory routing problem (IRP). The primary objective of this research is to assist assembly firms in formulating sourcing strategies that balance cost efficiency and environmental performance while simultaneously fostering social responsibility. This research proposes a multi-objective IRP formulation that jointly optimizes economic performance, environmental impact and social outcomes. The problem is modelled as a MILP and reflects several practical characteristics, including various realistic supply chain costs, probabilistic demand, several capacity constraints and delivery failure probabilities. Nonlinear terms associated with social and environmental objective functions are reformulated through linearization techniques. Owing to the NP-hard nature of the proposed formulation, a metaheuristic algorithm is designed and employed to obtain approximate Pareto-optimal solutions.The proposed solution approach consists of four phases, beginning with problem definition and parameter setting, followed by model development and reformulation, Pareto front generation using a multi-objective algorithm and selection of representative compromise solutions. Numerical experiments are conducted on problem instances of varying sizes, adapted from established benchmark datasets. For each instance, the final compromise solution is obtained by averaging results over a large number of independent algorithm runs. Performance is reported for both compromise solutions and extreme solutions that emphasize individual objectives. A sensitivity analysis is carried out to investigate the effects of key parameter variations on model outcomes and to derive managerial insights regarding the interaction among economic, environmental and social objectives.Vehicle fleet composition is found to play a critical role in system performance. A homogeneous fleet of light-duty vehicles reduces shortages but incurs higher network costs and vehicle emissions. In contrast, a heterogeneous fleet of vehicles provides superior economic and environmental outcomes. Sensitivity results further indicate that component price variability substantially affects cost efficiency. Increasing supplier incentives is also found to have no substantial effect on reducing shortages. Moreover, variations in component prices or vehicle operating costs have limited impact on sustainability performance of IRP network.

Keywords

Assembly Supply Chain, Sustainable Logistics, Vehicle Routing, Optimization.