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Measuring overall effectiveness of
processing equipment
This report by Dr.
Tanveer Hussain, Department of Textile Processing, National
Textile University, Faisalabad explains the majors aspects to
monitor, measure and improve the overall effectiveness of
processing equipment. The aim of any textile manufacturing
company is to deliver a consistent quality products to its
customers on time and every time. This is only possible if the
manufacturing equipment in operation is effective, efficient,
reliable and consistent in producing desired quality products
at the desired rate.
Overall Equipment Effectiveness (OEE) is a “Best Practice” way to monitor and
improve the effectiveness and efficiency of your processing equipment. It can
help you minimize downtime, speed and quality losses.
Downtime losses
(i) Machine break downs, e.g. equipment failure, unplanned maintenance, etc.
(ii) Machine set up and adjustments, e.g. batch changeover, adjustments, warm
up, etc.
Speed losses
(i) Small machine stops, e.g. jams, misfeeds, etc.
(ii) Reduced machine speed.
Quality Losses
(i) Machine start up rejects, e.g. scrap, rework, in-process fabric damage, etc.
(ii) Production rejects, e.g. scrap, rework, in-process fabric damage, etc.
Overall Equipment Effectiveness (OEE) can be calculated as
follows:
OEE (%) = Availability (%) x Efficiency (%) x Quality (%)
Where, Availability (%) describes the amount of equipment “uptime” and can be
calculated as follows:
Availability (%) = (Gross Equip. Operating Time / Planned Production
Time).
Where as,
Planned Production Time = Plant Operating Time – Planned Shutdown Time
Gross equipment operating time is that time for which the equipment is
working and producing output. It excludes all unplanned downtime i.e. time
elapsed during any event that stops planned production for an appreciable length
of time (e.g. equipment failure, unscheduled maintenance, and batch changeover
time, etc.).
Planned shutdown time is the time for which you have no intention of
running the equipment (e.g. lunch breaks, scheduled maintenance, or periods when
there is nothing to produce).
Plant operating time is the amount of time your plant is open and
available for equipment operation. See figure given as under.
Efficiency or Performance (%) describes the actual performance of
equipment relative to its ideal performance. It can be calculated as follows:
Efficiency (%)
= (Net Equip. Operating Time/Gross Equip. Operating Time)
= (Actual Production Rate / Max. Design Production Rate)
= [(Total Prod. output / Equipment Operating Time) / Max.
Design Prod. Rate]
Efficiency measurement takes into account speed losses due to any factors that
cause the equipment to operate at less than the maximum design speed (e.g. due
to material mis-feeds, and/or operator inefficiency, etc.). A 100 % performance
means that the equipment has been consistently running at its maximum design
speed.
Quality or Yield (%) describes the Right First Time production, i.e. the
amount of production output that meets the customer specifications without any
re-work. It can be calculated as follows:
Quality (%)
= (Fully Productive Time/Net Equip. Operating Time)
= (Right First Time Production/Total Production)
A 100% quality means that there have been no rejects or rework. An example data
for the calculation of OEE is given in the following table.
On the basis of this data, OEE can be calculated as follows:
Planned Production Time = (Shift Length – Breaks)
= (480 – 60) = 420 minutes
Operating Time = (Planned Production Time – Downtime)
= (420 – 47) = 373 minutes
Right 1st Time Production = (Total Production – Rejected)
= (19,271 – 423) = 18,848 meters
Availability (%) = operating Time / Planned Production Time
= 373/420 = 0.89 = 89%
Efficiency (%) (Total Production/Operating Time)/Max. Design Run Rate
= (19,271/373)/60 = 0.86 = 86%
Quality (%) = Right First Time Production/Total Production
= 18,848/19,271= 0.98 = 98%
OEE (%) = Availability x Efficiency x Quality
= 0.89 x 0.86 x 0.98 = 0.75= 75%
An average manufacturing plant works on an OEE of around 60% while a
world-class plant has an OEE of 85%, with minimum 90% availability, 95%
efficiency and 99.9% quality. The companies in Pakistan are advised to measure
OEE of their processing equipment and compare it with world-class OEE. If there
is a gap, implement Total Productive Maintenance (TPM) for making improvements.
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