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(milkrun), lean tools applied in an assembly line. The study
is focused on a specific products family, an injection valve.
2 Brief literature review
Lean manufacturing has received ample attention in
academic literature and practical performance, from how
the lean production concept was formulated and dissemi-
nated [19] until recent comprehensive literature review [3,
15, 16]. In them, a common topic appears, that is, the need
to explore the implementation and performance relation-
ship with a practical focus and with a definition of the
context because the results depend on the manufacturing
environment.
However, it has been defined from a macroscopic or
organizational viewpoint [3]. We affirm that it is not
possible to define the context without including the product
and the manufacturing process, at least from an operational
and technological perspective. In this sense, a real and
detailed case study provides the sufficient items to valuate
the implementation and under what conditions, allowing the
benchmarking between practical of companies. It is
possible to find analysis of case studies about steel
production [7], forging processes [9], aircraft manufactur-
ing [15], or assembly lines of vehicles [1]; although the last
one has been studied deeply, some criticisms can be found
in the literature due to lack of resulting data [19]. Their
methodology is similar, using lean tools, and they are
adapted to the study variables, but the improvement point
and the results achieved are different. Furthermore, in line
with Milterburg [20], how an implementation can be done
is a subject that benefits from research. In addition, “a line
of interesting researches is one that follows real one-piece
flow production systems over time to learn what problems
are most difficult at different points in time, how these
problems are solved” [20].
Currently, assembly lines are still fundamental to get the
smoothing of production system [20], and they are studied
under several operative perspectives seeking its flexibility
[21, 22]. Both concepts are subjects of pull systems. In
assembly lines, pull and lean systems are concepts
frequently connected, although they pursue different objec-
tives; pull system toward the reduction of work-in-process
(WIP) and lean system toward minimizing the buffer
variability [23]. Moreover, with respect to the election of
production control system in a pull system, the alternatives
considered are focused on kanban [24] and constant work-
in-process (CONWIP) [25], both of them focused toward
the reduction of WIP. Although some authors have
observed the advantages of the CONWIP with respect to
the kanban [25, 26], others argue that when the total
number of cards in both systems is equivalent, the average
WIP will can be less in the kanban system, being the
appropriate distribution of kanbans a relevant element to
get the minimum WIP [27]. Besides, kanban allows
maintaining the flexibility of the system [28] and also, in
favor of kanban, Yang [26] found that kanban is a system
more flexible and that “CONWIP may require a larger
storage space between alternate stations because all full
containers may gather between any pair of alternate
stations.” On the other hand, kanban and pull are still
considered synonymous by practitioners [16]. So, in a small
space, we suggest that the better option is a kanban system.
Once more, we can appreciate that similar systems can give
different solutions, hence the importance to detail how the
line assembly runs and what processes and operations are
carried out.
Although many tools exist, from its origin, VSM has