Potential performance of dock versus line assembly

Abstract

The potential performance of two different ways of designing truck assembly systems, namely line and dock assembly, are analysed. The line system denotes assembly at a mechanically paced moving belt with fixed items, divided in several one-worker stations with a common station time around 20 minutes and located in parallel with up to three other stations. The dock system denotes assembly at stations with typical station times around 4 hours; the items are moved between stations by the workers, who are divided in groups of around ten persons assembling complete trucks. Theoretical models for these specific systems are presented, which together with the results are applicable to more general situations.

The net and gross work times are derived for line and dock assembly, where net work time denotes time when work is done and gross work time is net plus lost work time. The potential efficiencies are expressed as the quotient between the net and gross time. The models are analytic and based partly upon published and partly on new models and hypotheses of human behaviour.

A difference between the gross work times of around 30% is obtained in favour of dock assembly, when data from the literature and an existing line are used. Experiments support this result. A maximum work speed consistent with personal comfort and safety for each individual and a rational cooperation between the group members are assumed