Kanban-driven parts feeding within a semi-automated O-shaped assembly line: a case study in the automotive industry
Authors: Savino Matteo M. , Mazza Antonio 
Published: January 2015

Purpose
– The aim of the present work is to provide a case study where lean production (LP) techniques are implemented in a semi-automated assembly line with O-shaped (closed-loop) layout configuration. The action research has been conducted within an assembly line for automotive components. The work aims to provide insights on the impact of loop layout features with respect to lean principles’ application; operative solutions related to some logistic limit of loop layout; and how kanban technique can be adapted to an O-shaped layout.

Design/methodology/approach
– The main research methodology is based on action research within an assembly line of oil pumps. The two research questions find answer through literature analysis and implementation of LP in the O-shaped layout. In the A3 step, we identify the main weak points of a loop layout also under the perspective of operators’ feeling. The analysis of the main constraints is conducted in this step, with respect to the most common layout used within LP adoption. Steps A4 and A5 answer to RQ2 by an on-field results’ analysis.

Findings
– The use of an O-shaped layout may allow to improve ergonomic conditions for workers; to better organize parts feeding through slides and chutes because of the presence of operators outside the line. The new approach to determine the number of withdrawal kanban potentially extends the findings of Tardif et al. (2012): the minimum of the objective function is reached with a higher number of withdrawal kanbans.

Research limitations/implications
– The approach is applied within a stand-alone line, while in several industrial contexts, we may find several of these lines in the same shop floor. In this case, LP implementation would cope with the several kanban cards circulating, the over-saturation of the logistic operator in supplying all the lines with smaller quantities of materials.

Practical implications
– The action research resulted in the introduction of a new concept of supermarket, conceived as a decoupling buffer that lies near the line and in the review feeding devices, with the adoption of bins and operators’ feeding chutes. Parts’ feeding systems is reorganized with a two levels of withdrawal kanban. The introduction of line supermarket and the change of supply policies from pallets to bins contributed to the strong reduction of average work-in-progress. Yet, the double-withdrawal kanban and the small quantities supplied may cause an increase of material handling times and meters covered by operators.

Social implications
– Better working condition of the line operators because of the presence of ergonomic chutes for parts’ feeding. In contrast, we observed a high saturation of logistic operator because of the small quantities of components supplied on the line, with an increased stress of this worker.

Originality/value
– A decoupled withdrawal kanban (DWK) is developed. In DWK, the first withdrawal is issued to the supermarket that serves the line. The second withdrawal kanban is issued from the supermarket to the central warehouse. Within DWK, we propose a modified dimensioning formula through minimization of the objective function Z(k). Parts’ feeding is now organized with sliding chutes on operators’ workstations to collect components in accordance to kanban dimensioning.