How Many Operators Do I Need to Balance a Line (with SMV and Line Target)?

I have the following data of a sewing section. How many operators do I need to balance the line and what will be the production target per hour at 60% efficiency? SAM of different processes is given: Make Collar- 0.50; Top Stitch Attach Collar- 0.47; Attach Collar Band - 0.49; Top Stitch at Collar Band- 0.44; Make Button Hole (7 Point) - 0.36; Attach Button- .39; Please provide an answer with a proper explanation. I do badly need a solution. ...asked by an OCS reader.

Let me summarize the questions first. I read two questions are asked in the above paragraph. First I will answer the question related to calculating hourly target. Then I will explain how to calculate manpower for balancing a sewing line.

Question#1. Hourly production target calculation method for each operation at 60% efficiency level. With the given details, we can calculate the hourly production target. 

To calculate the hourly production target, use the following steps.

Step#1: Calculate SMV @ 60% using the formula = SMV/60%. I have shown operation-wise SMV in the 4th column in the Table#1. When the standard time is 0.50 minutes, at 60% efficiency, SMV will be 0.50/60% = 0.83 minute.

Step#2: Calculate hourly production target using this formula – 60/SMV @ 60% efficiency level. Here we get an hourly production target per operator. To calculate total target production from each operation, multiple operators are assigned to each operation. In the 5th column, the hourly target per operator is shown. For the first operation (Make collar), the hourly target will be 60/0.83 pieces = 72 pieces. Based on the Hourly line target, 2 operators are assigned to the first operation. Therefore, the hourly production target from the first operation will be 72 x 2 = 144 pieces. In the same way, the production target per operation per employee is calculated. The operation-wise targets for all the given operations are shown in theTable#1.

Table -1: Hourly production target calculation


In the last QnA post, I have also explained how to calculate hourly production targets using the given SMV and target line efficiency. You can refer to that article for more explanation.

Question#2. Calculating Operation-wise operator requirement for balancing a production line. For the manpower requirement calculation, we need hourly or daily production requirements from the production line (or from the group of operators).

I asked for the missing information and received it. Their hourly production requirement from the line is 140 pieces. To get 140 pieces from the line, each operation must produce 140 pieces/hour. He also shared that they work for 10 hours a day. 

Balancing a production line means producing the same number of units from all operations of a style (line). SMV of each operation may be different, so if you assign one employee to each operation, you will get different productions from different operations. In such situation, the line would be imbalanced after working sometimes. Therefore, to get balanced production from all operations, you need to assign a number of operators as required to get the target production.

Operator requirement is calculated using the following formula

= (Total SMV needed to produce / 60 minutes)
= (Operation SMV x Hourly production target of the line)/60

Here, 60 minutes represent equivalent to one operator per one hour. For the calculation, we need to convert operation SMV @ 60%.

Example: Hourly line target is 140 pieces. Therefore the calculated manpower for the first operation would be

= (0.83 x 140 /60) = 1.94. The rounded off manpower is 2 no.

The same ways operator requirement is calculated for all 6 operations. To make hourly 140 t-shirts, you need a total of 11 sewing operators (considering the given t-shirt operations).

Table#2: Sewing operator requirement calculation

	Shift Time (Hours)	10
	Expected Target / Hour	140
	Line Efficiency%	60
Operation Sequence	Operation	SMV	SMV @ Target Efficiency%	Calculated Manpower	Manpower (Rounded off)
1	Make collar	0.5	0.83	1.94	2.00
2	Top Stitch @ collar	0.47	0.78	1.83	2.00
3	Attach collar band	0.49	0.82	1.91	2.00
4	Top Stitch @ Collar Band	0.44	0.73	1.71	2.00
5	Buttonhole	0.36	0.60	1.40	1.00
6	Buttoning	0.39	0.65	1.52	2.00
	Total	2.65	4.4166667	10.3055556	11

Both the calculations are part of Operation Bulletin (OB). Download the sample OB template and use that one. The formula is given in the Excel templates. For more explanation about making operation OB read this article.

I hope you will find this QNA post helpful. If you have more questions related to industrial engineering calculations, drop me an email using the Ask OCS page.

Also Read: Number of sewing machines needed for making t-shirts