Improving sustainability in combined manual material handling through enhanced lot-sizing models

Abstract

Lot-sizing models play an important role in optimizing the performance of internal logistics systems that involve a large amount of manual material handling (MMH) tasks. The performance of MMH tasks should be assessed using multiple criteria rather than being merely cost-oriented, considering the fact that the lot size affects the workload and can result in work-related musculoskeletal disorders (WMSDs). This study aims to integrate biomechanical and physiological guidelines into a cost-based performance optimization model of MMH tasks. In this study, we consider the impact of lot size on lifting frequency, which is reflected in the Composite Lifting Index (CLI), an extension of the National Institute for Occupational Safety and Health (NIOSH). In addition, the energy expenditure rates of operators are estimated by applying an established physiological method. The energy expenditure results are used to calculate rest allowance during a handling process that help keep workload levels acceptable. To make the model more general, we consider different manual material shipping scenarios and intermodal replenishment cases. Finally, a sustainable lot-sizing model is applied in a two-stage intermodal replenishment case and several numerical experiments to determine the influence of item weight, speed, distance, and opportunity cost. The results indicate that the proposed model can ease the ergonomic strain of operators without compromising economic efficiency.