OEE is a production efficiency indicator that measures how efficiently a manufacturing operation is running in a factory and how far it is from reaching peak production. But the most important thing is that it shows where the points to improve are to get closer to a world-class production.
Since its introduction in 1960, OEE has become a Key Performance Indicator (KPI) adopted by leading manufacturing companies and its analysis is critical among companies that have earned the title of "World Class Factory" (WCM).
However, there are 3 relevant levels to calculate OEE: On each machineon a production line or on the entire plant.Although, in theory, the equation is the same, there is one consideration that will change the outcome of each.
OEE is the percentage ratio of Availability, Yieldand QualityWe will first explain how to find each value on each machine and then explain the variation to calculate it on the production line and the whole plant.
A common mistake that we have found in Colombian companies is to consolidate the OEE as a single value, since they use averages where it should not be, as we will see later.
Availability
Availability is the percentage of time that a machine was actually producing, out of the total time it could have produced.
First of all, the Total Working Time that a machine is capable of producing must be calculated, counting the programmed stoppages that it has as Preventive Maintenance, Implementation of Improvements or Inspections.
We propose as an example a machine that manufactures caps for packaging (injection) and that works 3 shifts of 8 hours a day. This gives a theoretical 24 hours. This variable is called Total Time Worked (TTL)..
TTL = 24
Then you must measure the time that the machine was actually producing, for this you can use the spreadsheets that the operators carry by hand or you can use a much more reliable and accurate automatic capture software(see how the automatic system works)The times that the machine was not operating are added and the Stoppage Time (TP) is taken out.
For example, the cap machine was stopped for 1.5 hours for set-up (30 minutes in each shift), 3 hours for lunch time for the operators, 1 hour for adjustment in production, it suffered a breakdown that stopped it for 1 hour and 0.5 hours due to lack of packaging material. (If automatic capture is used, you will find an additional 1 hour of unreported stoppages by users because they are considered short-lived, but when you add them up it makes a big difference). That gives us the variable Stoppage Time (TP) is taken out (1,5 + 3 + 1 + 1 + 0,5 + 1 = 8)
We then calculate the Effective Time (TE) by subtracting TP from TTL.
TE = TTL–TP = 24 – 8 = 16
Finally, Availability is the percentage of Effective Time over Total Time Worked.
Availability = (TE/TTL)
Availability = (16/24) = 66%
Yield
It is the comparison of the number of actual units produced, with the units that could be produced by the machine working at the standard speed, measured as a percentage.
First you must count the Units Produced (PU), then find the Theoretical Units (TU). The TUs are obtained by multiplying the hours the machine was producing (Effective Time) by the Standard Speed (SR, the number of units it can produce per hour) of the machine under optimal conditions. The Units Produced (PU) will be divided by the theoretical units (TU). An advantage of having an automatic capture system is to know if the operators are running the machines at the correct speed or if they are intentionally slowing them down, missing the opportunity to produce more units.
It is important that the Units Produced include those with defects or that are unfit for delivery.
Performance = UP / UT
Continuing with the example, the cap machine has the capacity to produce 1,000 caps per hourVE = 1000and worked 16 hoursTE= 16producing a total of 11,520 capsUP = 11.520).
UT = TE x VE = 16.000
Yield = 11,520 /16,000 = 72%
Note: It is important to note that the Standard Speed of the same machine may be different depending on the reference, volume or type of material. The standard speed for each of these cases should be known.
Quality
It is the percentage of parts that are produced without defects of the total parts that the machine produced. The total number of Good Units produced (BU) and the total number of units that do not meet the quality conditions and will be considered Waste (D) (so that they can be reprocessed) must be counted. When you have an automatic capture software, you can program a functionality that calculates the waste produced by starting the machine and, in this way, be more precise with the problems to be improved.
Quality = UB/(UB+D)
The cap machine produced a total of 11,250 units, of which there were 10,237 Good Units and 1,013 Waste.
Quality = 10.237 / (10.237+1.013) = 91%
Final calculation.
To calculate the OEE it is only necessary to obtain the percentage relationship of the 3 variables.
OEE = Availability x Performance x Quality
In our example, the OEE is (64% x 70% x 91%) = 40.7%
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How to Calculate OEE When There Is More Than One Machine.
Calculating the OEE of a production line (series machines).
When you have a process that involves multiple machines working in sequence to get a single product, you should look for the OEE of that entire production line. For this, it is only necessary to identify which of the machines involved is generating the bottleneck and obtain the Availability, Performance and Quality variables of that machine to then calculate its OEE. That result is the same OEE of the entire line (ignoring the other machines).
It is possible that if you analyze the reasons for the decrease in OEE and improve this bottleneck, another machine will become the new bottleneck. In that case, the OEE of that machine will be obtained and will be the new OEE value of the line.
Read the 6 problems that OEE will allow you to improve.
The production line of the caps involves 3 machines: An inkjet machine (we measured its OEE in the examples above), a printer that puts the product mark on the lid and a die-cutter that makes the safety tabs. The printing process depends on the units produced by the injection machine, in turn, the die-cutting process needs the product already printed. Repeatedly these last two machines are stopped waiting for the delivery of the caps, which would position the injection machine as the bottleneck. Thus we will find that the OEE of the production line is equal to the OEE of the injection machine = 40.7%.
Calculating the OEE of the entire plant.
To understand how OEE is calculated throughout the plant, you don't have to do it with the average OEE of machines, since some machines don't work all the time and manufacture products at different speeds. The correct thing to do is to obtain the values of each production line (and machines outside production lines), and add them in the calculations of Availability, Performance and Quality before making the respective divisions.
Performing these measurements with manual data capture is highly inaccurate and will provide data that will hardly reveal the real points to improve in the plant.
Nomenclature:
Availability Planta = (TEM1+TELP1+TELP2) / (TTLM1+TTLLP1+TTLLP2)
The sum of the effective time of all Production Lines (and machines outside production lines) divided by the sum of all Total Worked Time. In this case it is an M1 machine and two LP1 and LP2 Production Lines.
Plant Yield = (UPM1+UPLP1+UPLP2) / (UTM1+UTLP1+UTLP2)
The sum of the units produced by all Production Lines (and machines outside production lines) divided into the independently calculated Theoretical Units per machine and production line.
Plant Quality = (UBM1+UBLP1+UBLP2) / (UTM1+DM1+UBLP1+DLP1+UBLP2+DLP2)
The sum of the good units of all Production Lines (and machines outside production lines) divided by the sum of all Good and Waste Units.
Finally, multiply these three values and calculate the OEE normally:
Plant OEE = Plant Availability x Plant Yield x Plant Quality.
As mentioned before, OEE is one of the most important indicators measured by world class companies and its interpretation allows you to improve most of the elements that cause you to lose production. It is very important not to make mistakes when obtaining this value, as they may not reveal the true causes of losses and may not generate real value to your company. The chances of making mistakes are reduced to almost zero by using automatic capture systems that calculate it automatically .(read Common mistakes measuring OEE).
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