High Speed Machining Precision Tooling - Indobiz.biz

Just how good is your
process?
Check your O.E.E. and find out
There is no better statistical tool to
use when evaluating the all-around
effi ciency of a production process
than Overall Equipment Effectiveness.
O.E.E. is a simple series of formulas that
be can used with any calculator and
some basic data that are most likely
currently at your disposal. There are 3
factors within the production process
that are evaluated using O.E.E.
• Availability: The actual uptime of
the process divided by the scheduled
available runtime. Example: The
scheduled runtime was 7.2 hours (432
minutes). A broken parts feeder stopped
production for 45 minutes. The uptime
for the shift was 387 minutes. 387/432
= 0.89583 or 89.6 percent.
Bottom line– Availability represents
machine breakdowns.
• Performance efficiency (P.E.): During
the actual uptime, how effi cient was the
process when compared the designed
optimum cycle time. Example: The
optimum cycle time for the process
is 15 seconds per part or 4 parts per
minute. For 387 minutes of uptime, the
process would produce 1548 parts if it
never stopped once. During our shift,
we produced 1357 parts. 1357/1548 =
0.87661 or 87.7 percent.
Bottom line- Performance effi ciency
represents short stoppages of the
process.
• Rate of quality product (R.O.Q.P):
Of the total number of parts produced
during the uptime, what percentage was
conforming. Example: During our 387
minutes in which we produced 1357
parts, 14 were defective and 12 need
re-worked. 1331 conforming parts were
made. 1331/1357 = 0.9808 or 98.1
percent.
Bottom line- Lower your in-process
scrap and rework.
The Overall Equipment Effectiveness is
computed by the formula – Availability x
P.E. x R.O.Q.P.
0.896 x 0.877 x 0.981 equals 77.1
percent, which is our O.E.E. for this
process.
A “World Class” process would produce
a consistent 85 percent O.E.E. (or
an average of 95 percent in each
category).
There are some simple items to look at
for an O.E.E. improvement. Availability
deals with scheduled uptime. Be
sure routine items such as machine
changeovers, preventive maintenance,
and department meetings are scheduled
through the production controller
(however titled) at your facility.
Improving P.E. means correcting a short
stoppage before the cycle time is lost.
Never lose sight of the parts counter at
the end of the process. Some processes
are made up of smaller stations with
their own unique cycle times. The
stations form a chain and the optimum
cycle time of the process will be the
cycle time of the slowest station. This is
benefi cial because it can be determined
which stations are capable of “catching
up” after a stoppage. If more than one
stoppage occurs at the same time, it may
be best to correct them from the closest
to the end of the process and then work
backwards towards the beginning.
This goes against conventional thinking.
If a stoppage occurs down toward the
end of the process and at the same time
a machine jams up right in front of you
(while you’re at the front of the process),
it may be better to walk down to clear
the other stoppage fi rst. The reason
behind this is if the stoppage down the
line is not fi xed fi rst, it is possible the
last process will run out of parts. Each
and every 15 seconds is lost forever. By
fi xing the stoppages toward the end of
the line fi rst, you have a better chance
of parts “catching up” and there will be
no cycle time lost at the last process.
In some situations any stoppage will
shut the entire process down. In that
case I would suggest placing re-settable
trip counters at various intervals. When
a stoppage occurs, the operator can trip
the counter. After a week of production,
the counters will tell you where the most
stoppages are occurring and further
evaluation can be planned.
R.O.Q.P. is too product-specifi c to be
discussed in the article. If your facility
doesn’t have an organized quality
system, I suggest developing one.
Remember that no system will be any
better than the operators who use
it. Machines make parts, but people
make products. Keep an open mind and
always, always, always be creative.
indometalworking news Vol. 2 / 2008 37