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pass a visual control by lots, stocking the rest of production
on the shelf. Later, cups are pushed up to shelves along
with the preassembly. From washing machine #1 up to the
above-mentioned shelves, there are 20 m. From these
shelves, the components are taken to obtain finished
preassembly final cup. These cups will be stored in other
shelves waiting for a new visual control to eliminate
defective cups, and finally, finished cups have to be washed
again in washing machine #2. From this point, the cups
arrive to the assembly area to meet the other components of
the valve. In the achievement of the VSM, it is taken into
account whether it is added value or not. The results can be
perceived in Fig. 2. There are some points that accumulate
a major time without added value. These points, marked
with circles in Fig. 2, are those where more stock is
accumulated and there are already long waiting times. These
are the points where we focused our actions of improvement.
The first one appears in the external store until
machining #1. This total time is the sum of three partial
times: The one that spends the cup in the external store, the
time which remains in the supermarket, and finally, the time
at the feeder of this machining. The second one appears just
before washing machine #2 and the third one is focused on
the storage of the finished cups before passing to assembly.
The assembly area does not cause problems, except
workstation #5 where there is an accumulation in time of
1.34 day and in the final store where the assembled EV6
wait until they are shipped to Germany. The mean lead-time
at this store is 22 days (annual turnover of about 10 days).
The final calculations of DtD and LR provide the following
results: DtD=19.82 days and LR=0.383%. These metrics
have been calculated without the external stores, so they
only depend on what happens inside the factory. The
amount of parts stored at the different critical points is also
very important. One of the improvement objectives is to
reduce these intermediate stocks.
6 Improvements
A first analysis of the line reveals that it is convenient to
convert the push system into a pull production system by
means of kanban and supermarkets. The intention is to
reduce stocks and times of step, and thus to increase LR. In
order to solve the problem that an external store uncon-
trolled represents, the following change is introduced:
shelves in which the cups are stored before spending to
the machining #1 raisin, working as a supermarket. They
are regulated by kanban cards against the external store.
Fig. 2 VSM for the month of
March
952 Int J Adv Manuf Technol (2009) 43:949–958This action limits the stock in the mentioned supermarket
and it allows a self-controlled system. Another kanban
circuit is needed to control stocks between machining of
cups and washing processes. This kanban circuit will be
referred to later. Another objective was the reduction of
stock of cups. A lower lot size is adequate in order to
reduce stock of the finished cups, ready to be assembled in
one of the critical workstations of stock accumulation. The
lot came down to 682 opposite to the previous setup of
1,232. The shelves are not completely filled up, but they are
left empty to the middle of its capacity. With this lot size,
reduced flow of cups speed up across the process.
A critical point is workstation #5, the assembly starting
point. Assembly problems appear in some workstations due
to a reduced space available to accumulate parts-in-process
and finished parts. Parts cover the different workstations in
dissimilar amount because the trays have different capac-