Abbreviated as OEE, Overall Equipment Efficiency is the most important indicator in a company using Field Data Collection System. At a glance, OEE of a production line or a machine informs us on how well the production is going. OEE is the result of multiplication of 3 factors. These are: Availability Rate X Performance Rate X Quality Rate. Availability Rate is the division of a machine’s actual active work duration by its planned active work duration. Active work duration is calculated by subtracting planned maintenance duration from shift duration. Actual active work duration is the duration in which the machine was in effect without unplanned halts. For instance, let’s say an 8-hour shift is comprised of 30 minutes of lunch and 15 minutes of tea breaks. Planned work duration for this shift is 480-45 = 435 minutes. Let’s say the machine broke down and waited for new parts for 15 minutes during the shift. Actual active work duration in this situation is 435-15 = 420 minutes. Availability rate is 420/435 = 0,9655.
Performance Rate is the ratio of the number of products a machine produced versus its capacity for the same duration. For instance, if a packaging machine has the capacity to produce 400 units in an 8 hour shift and it only produced 350, its performance rate is 0,875. Quality Rate is the ratio of fine products versus all products. In a 1000 unit batch produced by a machine, if 50 of these products are faulty we can say that this machine has a quality rate of 0,95. When we multiply these 3 values we arrive at the conclusion that this machine’s OEE value is 0,8026. Minimum OEE value for a machine to be regarded as efficient is 0,80. OEE values below 0,40 are considered alarming and should be treated immediately. Sometimes, although rarely, OEE value could be more than 1. Having a high performance value makes the parameters jump above 100%. This result notifies us that machine capacities need reviewing. If a machine with a capacity of 500 units usually produces 800 in a shift makes it obvious that that 500 capacity is undervalued. In my opinion, maximum calculated OEE should be no higher than 1,10.
In our previous articles on OEE, we talked about OEE and its components, we gave examples and talked about when improvements should be made. Our main talking point when all this is being discussed was machines. But does OEE values only work on machines? No… Along with machines, operators also have availability, performance, quality and naturally OEE values. In fact, operators’ OEE values are more significant than machines’ OEE values. Because methods of improving a machine is limited meanwhile improving personnel has unlimited methods. The most you can improve a machine’s OEE is by 25-30% while personnel OEE could be increased by 1,5 – 2 folds. Before deciding on the OEE level of operators you must carefully consider the differences between machines and operators. Meaning if your operators are merely standing near the machines while they work and interact with it minimally, you could dismiss this line’s operator OEE. Because in this line operator is almost a part of the machine and rarely takes the initiative. But for instance, when you consider works such as manual labor, assembling manual packaging, these lines all but replace machines with operators.
Before talking about calculating and maximizing operator OEE values, let’s look at how many different combinations of operator/machine there are in the field.
3 conditions apply:
1) Single machine – single operator (Effectively machine): This is the category with which minimal OEE improvements could be made. Because machine is non-stop working during the shift and operator interference is very much limited. Operator’s role in this combination is merely control and observing. In such process, Operator OEE analysis is applied only if the operator is causing the machine to take long halts.
2) Single machine – single operator (Effectively operator): Almost all of the productional participation is made by the operator. In operations such as assembly, packaging and manual labor Operator OEE takes precedence. The way to effectively calculate improvements in these processes is to either comparing multiple operators doing the same job or comparing the same operator in different days.
3) Single machine – n operators: This is the category to focus when it comes to maximizing OEE values. It’s available to comparisons and improvements because the machine is shared between different operators .
Comparing performance in a production field is only possible when the conditions are similar. Meaning you could only compare a personnel working in 8AM-16PM shift with other personnel working in that same shift. Factors like hunger, sleepiness and tiredness will come up as different values for you. Correct way of doing comparisons is to do it between operators that work the same day, same timeframe, same job on the same machine. You could do the comparison yourself manually while you could get help from Production Data Collection panels. Summary information such as end product, materials being used and halt-work durations begin being collected on an operator as soon as he/she starts his/her shift. Comparisons work in two ways: 1) Comparing work durations: OEE value is comprised of worker’s job duration, number of fine (non-faulty) products and if the worker has gone up above the production capacity.
Let’s say a machine with two operators working on has an OEE value of 70. And take operator based OEE values to be 90 and 50, respectively. 70 is a good score for the machine but the operators have a huge gap between their contributions to this score. If you take a look at the second operator’s availability, performance and quality values which make up its OEE value, you will see that at least one of them is considerably low. This difference in this shift will cause great fluctuations in whole production area over the month. Operators’ product result could be the same but one operator could achieve that in 4 hours while it takes only 3 hours and 20 minutes for the other operator to produce the same number of products. Achieving the same production amount can be convincing but one must consider where the 40 minutes of difference was spent on. 2) Comparing halt durations: Calculating how much of their shift duration was wasted with an idle machine is possible with comparing halt (stoppage) durations. Comparing how much time two operators spent on tea breaks, lunch or waiting for material and analysing them allows us to increase OEE values company-wide.