There is nothing wrong with mass production, but
normally the process is configured as a straight-line
assembly line system. The decision to transform straight-
line assembly systems to U-shaped assembly line systems
constitutes a major layout design change and investment
for assembly operations. Proponents of the lean
manufacturing and just-in-time (JIT) philosophies assert
that U-shaped assembly systems offer several benefits
over traditional straight-line layouts [1], especially an
improvement in labor productivity. U-lines have become
popular in order to obtain the main benefits of smoothed
workload, a multi-skilled workforce and other principles
of the JIT philosophy. Many researchers agree that U-
lines are one of the most important components for a
successful implementation of JIT production systems [2].