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control intermediate stores (kanban system), and in addi-
tion, it allows improving the material flow between work-
stations to obtain a more flexible process, optimising the
job of each workstation (milkrun). Every 2 months, a new
VSM is checked and metrics are recalculated and analyzed
to control improvements.
4 Manufacture and product description
The product is a combustible injection valve called EV6.
This paper deals with the assembly process of three main
components of the valve: the stem, the cup, and the needle
with a major pursuit of the cup due to its machining
processes.
The major process steps in manufacturing are sketched
in Fig. 1. To emphasize that washing machine #2 is the
same as washing machine #1, they are named with different
numbers to avoid difficulty in understanding the order of
activities. All the parts of EV6 are received in production
area #1 where they are stored. It is necessary that it undergo
full decontamination, demagnetization, and washing before
the assembly. Area #2 includes three main subassemblies at
different workstations. Subassembly processes have several
stages which are carried out in automatic and independent
workstations that do not permit a continuous materials flow.
Finally, after subassembly tasks, 20 stations with a
continuous materials flow compose the assembly line.
5 Initial value stream mapping
Initial conditions for the analysis of the VSM of March
appear in Fig. 2. This state is based on the cup because it is
the component that requires the longest trip inside the
factory: before the subassembly, there are two machining
processes and two washes. The production of the cups is a
push system due to the two machining process that they are
always producing and storing parts. The flow of informa-
tion and WIP are described as follows (see Figs. 1 and 2).
The central factory in Germany is at the same time the
main supplier and final customer of the valves plant. Every
4 weeks, the factory introduces, in a computerized system,
the material requirements for the manufacture. In parallel,
Fig. 1 Manufacturing line
flowchart
Int J Adv Manuf Technol (2009) 43:949–958 951an external store is sent an electronic order about the
mailing that is going to realize the factory in German. The
German factory is about 2,500 km from external store,
located near Madrid, and mailing is realized once a week.
The external store is 6 km from Madrid and there is mailing
by truck every 2 h. Cups are stored as raw material at
machining #1 workstation in shelves very close to it. This
machining has a feeder in which the cups settle to be
machined. Cups in the feeder are considered stock and two
parts is the lot size. Machined cups settle in containers to
lead the washer. After that, the cups are washed in the
preassembly washer following first in first out (FIFO), and
still following FIFO, go to machining #2. This installation
is close to the first machining (approximately 50 m) and
near the preassembly washer. The lot size is two parts
again. Machined cups settle in containers to lead the
washing machine #2 (see Fig. 1) and they remain in the
supermarket of the washing machine #2 until they are
processed. The machining processes require 14 and 9 s per
piece, respectively. There is a continuous work of 24 h/day,
which implies that everyday about 2,500–3,000 cups are
ready, when the daily demand is about 1,800 valves. So,
there is an overstock of machined cups caused by the push
production system.
In the washing process, the lot size is 2,464 and the time
of step is always the same because the process time is
unique regardless of the lot size. Under a FIFO order, parts