Formulas
Estimated Production Time
The planned production duration is calculated as the difference between the estimated finish time and the estimated start time of the production item (PI) at the moment of production start to ensure that the calculation takes into account the right number of operators during production.
Formulas:
Estimated Production Time = Estimated Finish Time - Estimated Start Time
Estimated Start Time = Estimated Finish Time (of previous item in queue) + Changeover Duration
Estimated Finish Time (per produced unit) = Estimated Start Time + (Quantity x tact time* ) + Production breaks duration + time between shifts**
Estimated Finish Time (any quantity) = Estimated Start Time + Tact Time + Production breaks duration + time between shifts**
*from parametrization for current number of operators on shift
**if the item is produced over more than one shift
Actual Production Time
The actual production duration time for production is calculated as the time when the item was in status “In Production”. This means, that when the item is sent to Redbox or paused, this time is noc included into the Actual Production Time.
Formulas:
Actual Production Time = sum of times when item in status “In Production”
Production Efficiency
Production efficiency is calculated as a percentage based on the estimated production time versus the actual duration.
Formulas:
Efficiency = (Estimated Production Time / Actual Production Time) x 100
Scrap Ratio
The scrap ratio is calculated dynamically when the production item (PI) changes.
Formulas:
Scrap Ratio = (Scrap Quantity) / (Quantity + Scrap Quantity + Bad Quantity)
OEE (Overall Equipment Efficiency)
The OEE (Overall Equipment Effectiveness) formula is composed of three key metrics: Availability, Performance, and Quality, calculated as follows:
Availability = Available Production Time / Planned Production Time = B / A
Performance = Actual Number of Units Produced / Theoretical Number of Units Produced = D / C
Quality = Good Units / Actual Number of Units Produced = F / E
A: Planned Production Time
This is the planned shift time for production on the line over the selected period.
B: Available Production Time
This is the sum of Actual Duration Time produced on the line over the selected period.
C: Theoretical Number of Units Produced
Since production depends on the number of operators and their skills, we first abstract a list of all materials produced on the line during the selected period. For these materials, we determine their fastest tact times and average them. This gives us the average fastest tact time per unit for all materials produced on this line. By dividing the available production time (B) by this average, we obtain the theoretical number of units that could be produced on this line during the period.
D: Actual Number of Units Produced
This is the sum of the quantity declared on the line during the selected period.
E: Actual Number of Units Produced
This is the same as above, the sum of the quantity declared on the line during the selected period.
F: Good Units
This is the same as above, but we subtract the defective units. Here we encounter the question of what to consider as defective units – whether just scrap or also bad quantity. Therefore, in the Settings - Main section, there is a select-type switch called "OEE Production line scrap / discard" with options:
scrap
bad quantity
scrap + bad quantity
Depending on what is selected here, the corresponding quantities of scrap, bad quantity, or both are included in the calculation of defective units.
Overall OEE Calculation
Finally, the OEE is calculated as follows:
OEE = Availability × Performance × Quality = B/A x D/C x F/E