Integrating ergonomics and lean manufacturing principles in a hybrid assembly line

•Bi-objective mathematical model for the design of lean processes in assembly lines.•Lean principles and ergonomic requirements for workers safety are included.•The model is applied to a case study from a tool case manufacturing company.•Results show different alternatives for assembly lines meeting the two objectives.

Lean manufacturing is a production method that was established in the wake of the Japanese Toyota Production System and rapidly established in the worldwide manufacturing industry. Lean characteristics combine just-in-time practices, work-in-progress and waste reduction, improvement strategies, defect-free production, and standardization. The primary goal of lean thinking is to improve profits and create value by minimizing waste. This study introduces a novel mathematical model to design lean processes in hybrid assembly lines. The aim was to provide an effective, efficient assembly line design tool that meets the lean principles and ergonomic requirements of safe assembly work. Given the production requirements, product characteristics and assembly tasks, the model defines the assembly process for hybrid assembly lines with both manual workers and automated assembly machines. Each assembly line solution ensures an acceptable risk level of repetitive movements, as required by current law.This model helps managers and practitioners to design hybrid assembly lines with both manual workers and automated assembly machines. The model was tested in a case study of an assembly line for hard shell tool cases. Results show that worker ergonomics is a key parameter of the assembly process design, as other lean manufacturing parameters, e.g. takt time, cycle time and work in progress.