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material. Cups are received at the washing machine and
then they are transported to the area where the machining Fig. 7 Milkrun
Fig. 8 VSM for the month of
August
Int J Adv Manuf Technol (2009) 43:949–958 955one is realized. They are stored in supermarket shelves
with kanban card and receptacle of methacrylate. The
machine operator will have to take the kanban cards that
indicate the quantity that must be restored. In the
machining phase, there are two kanban circuits established
(one of raw material for restoration of material and the
other of material going to the next phase). Two colors have
been established for cards; these colors also are different
from those of the washer, so at first sight, the circuits to
which every card belongs are identified. Figure 5 illustrates
this phase.
6.3 Kanban circuit 2: machining 1
Kanban circuit of machining #1 (see Fig. 6) is the following
one: as soon as the cups are machined, a kanban card is
enclosed with them and they move to the washing area.
They are placed in the shelves of the washing machine
supermarket, depositing the cups at the back part and
retrieving them from the front side. In these shelves (see
Fig. 5), two places have been enabled to store the cups, to
have a safety buffer, for the instability of the previous
machining process. If the machining process stops for
quality problems, it is a safety quantity to continue with the
production.
Once the machined cups go on to the following phase,
the card settles in the pigeonholes enabled for it. These
pigeonholes are different from that of the supply of material
for the provider, and although it is placed near, they are
perfectly identified with a cartel with the origin and
destination of the cards (see Fig. 5). Implantation of kanban
system achieves that manufacture orders are always the
same cards, avoiding neither papers nor notes to arrange the
work; the administrative tasks are simplified. Also, since
every worker can only make the pieces withdrawn by the
later process, manufactured parts will coincide with real
requirements for every moment. Conversely, on having
reduced the inventories, location of problems that could
arise in the productive process is easier. It is also a perfect
tool to be able to realize and to update material flows and to
be able to prepare VSM.
6.4 Second improvement: milkrun
To create a fluid flow of materials that prevents some idle
stations and others from having excess of stock, two decisions
must be taken. The first one is related to the conveyor. A kind
of conveyormust run through the line without interrupting the
workers. This conveyor must have the capacity to transport
the trays between the workstations. After several studies of
capacity, distances, speed, and easy handling, the best solution
would be a conveyor with wheels handled by a worker instead
of other possibilities, called milkrun (see Fig. 7). The second
one is to establish the route for the milkrun, so it was
necessary to consider: (1) the rate of material consumption
and calculate the speed of the assembly line and (2) the
amount of trays needed for each part. Thus, it is necessary to
establish milkrun routings and visit frequency to work-
stations. After realizing the perse stage of trips, needs, and
times, the routes were established [11].
7 Results and discussion
A case study results have been evaluated across VSM
diagram. The calculation of several critical magnitudes
indicates if the manufacturing process improves or deterio-
rates according to the criteria previously established. The
outcomes appear in the diagram of the VSM (see Fig. 8) and
in the justificatory and comparative stages of the results.