How to Calculate Operator Number in the Operation Bulletin

An operation bulletin is an essential tool for garment analysis, manpower and machine number estimation for producing planned quantity. The operator number requirement for each operation is calculated on the OB sheet.

Sewing Line

The operator number is calculated using the formula

Calculated manpower = (Operation SAM * Production target per shift) / (Total Work minutes in a shift * Target Efficiency)

Read the operation bulletin preparation method.

Let’s assume

  • Daily production target is 500 pieces, 
  • Operation SAM is 1.5 minutes, 
  • Factory works 8 hours a day (i.e. 480 minutes) and 
  • Target line efficiency is 70%. 

Therefore, calculated manpower

= (500 x 1.5)/(480x70%) = 2.2

For your understanding, I have shown four more operations of a T-shirt. No. of calculated operators and actually allocated operators are shown to produce 2400 pieces per day at 75% target efficiency in 8 hours shift.

Part of OB sheet
The calculated operator number often comes in decimals. But in practice, we can’t assign a fraction of an operator to any operation. So use the nearest round number for calculating operation wise manpower requirement.

Grouping of operations:

Remember, the calculated manpower is not the final manpower requirement for the given style. You have to look at each operation and check whether an operator is utilized fully. You might find that there are some operations which don’t need 8 hours of an operator to produce the target quantity. In such cases assign multiple operations to the operator. To do this you also need to check machine types required for doing the selected operation.

In a critical operation, you may need to add more than one machines (higher than the calculated machine numbers) and thus need an additional manpower.

All this decision is made by the engineer to achieve the target production. Simply following the calculated data for manpower and machine allocation may build up WIP in some operations in the line and form bottlenecks.

Grouping of machines:
In lean manufacturing, we target optimize manpower utilization. In a modular line, more than one machine are allocated to one operator. These are done considering operation SAM, operation sequence, and the takt time.

Note: When we calculate manpower requirement for the line or for a factory as a whole, we consider the operator absenteeism factor in calculating total manpower requirement for the line. The same can be used in calculating operation manpower in the OB sheet.
Read this article: How to calculate manpower requirement in an OB

Hope you find this helpful.

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