OEE Calculation differs with Manufacturing Processes

By Ranjith kumar DSM July 16, 2019

WeweweweMeasurement is one of the most toughest jobs in the production line. It needs a lot of effort to measure and analyse a production process in order to check the efficiency of production. Fortunately, OEE is the key production metrics, and you can easily calculate and apply it  to any manufacturing processes. But the entire spectrum in fact deserves their own method of calculating OEE. In other words,  OEE calculation differs with different manufacturing processes. This is because the manufacturing processes have varied ideal cycle time, production yields etc. The manufacturing process includes

  • Repetitive manufacturing
  • Discrete manufacturing
  • Job shop manufacturing
  • Continuous process
  • Batch process

It is very important to understand the process in order to apply the right form of the OEE Calculation for the right results. This blog captures the manufacturing process and their OEE Methods.

Repetitive Manufacturing

Repetitive manufacturing refers to the ongoing production of same production of same product for an extended period of time. The Quantity produced does not have a terminal value. Instead, the process targets a certain quantity  for production in each successive period. This situation most commonly arises when an industry has a steady stream of orders that do not vary over time.

OEE Calculation

Availability – The percentage of time that a machine is actually able to produce parts out of the total time that it should be able to produce parts. This number includes breakdowns, setups, and adjustments. The calculation for availability is simply the actual production time, including set up, out of the planned production time. Then it is necessary to set, time lost due to downtime through machine failure, lack of input materials, lack of operators,  against the calculation.

Availability = Runtime / planned production time

Runtime = planned production time – stop time

Performance – It is the actual achieved run rate against the ideal run rate for the machine. Since the repetitive manufacturing produces same products without  expected variability, We should keep ideal run rate as constant.

Performance = (Total parts / operating time) / Ideal run rate

Quality – It is the measure of good products divided by bad products.

Quality = good parts / Total parts

Discrete Manufacturing

Discrete manufacturing is a order based production that is the production in individual production order. In other words, it is a production of distinct items.

Therefore, we should measure Ideal cycle time as count (parts/time).

OEE Calculation

Availability – It is the comparison of potential operating time and time in which the machine is actually making products.

Availability = Runtime / Planned production time

Performance – It is the comparison of actual output with what the machine should be producing in the same time frame.

Performance = (Ideal cycle time * Total count) / Runtime

Quality – It is the comparison of number of parts per product made and the number of parts per product produced that meet customer specification.

Quality = Quantity of good parts / Total quantity made

Job Shop Manufacturing

Job Shop is a type of manufacturing process in which a small batches of variety of custom products are made. In addition, this deals in customization and relatively small production runs.

OEE Calculation

Availability – The planned downtime factor refers to schedule lapses, alloted breaks. In Job shop, some causes of downtime negatively affect OEE, but others do not. For example, if a machine is down for a long time, the operator can’t find the right tools to set up the machine which negatively affects OEE. But if a machine is idle, simply because it has no more work on schedule, though it is still available if it need. Depending on the situation, this may not have a negative impact on OEE.

Performance – Generally to calculate performance, we require a standard “ideal” cycle time. But in the job shop nothing is standard. Instead of trying to apply a single ideal performance by machine we should apply only a unique ideal performance rating to each machine/part combination.

Quality – Quality can be determined as good parts produced among the total parts produced.

Batch Manufacturing

Batch is the method of manufacturing where the products are made as specified groups or amounts within a time frame. Hence, Batch can go through a series of steps in a large manufacturing process to make the final desired product. But, there will be a pause between each step as a batch moves through. Therefore we need to calculate OEE differently.

OEE Calculation

Availability – It is the operating time divided by planned production time. Operating time is the difference between planned production time and downtime. Downtime occurred may be stop time or setup time. Planned production time refers to the time between a batch being scheduled and time it goes to a running state.

Availability = operating time / planned production time

Operating time = Planned production time – Downtime

Planned production time = Batch duration – Scheduled time

Performance

performance = Total product quantity / (theoretical production rate * operating time)

In addition, the rate is essentially an ideal throughput for each process unit in terms of capacity over time.

Quality -We can determine quality by dividing the actual product yield from target product yield.

Quality = Actual product yield / Target product yield

Continuous process

Continuous Process is a flow production method used to manufacture, produce or process materials without interruption. Similarly, it is the production of undifferentiated products. we should measure Cycle time as flow (volume/time).

OEE calculation

Availability – we can calculate it by dividing actual running time from time available for running.

Availability = Actual running time / Time available for running

Performance – Generally we should calculate performance by relating actual performance of equipment. But we cannot apply this metric to continuous process due to the varying performance of multiple equipments forming process chains. Hence we can calculate performance as

Actual Hourly rate / Average of Hourly rate overtime

Quality – We can calculate Quality by dividing good parts from total parts.

Quality = good parts / Total parts

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