How to Calculate Machine Requirement for Sewing Operations in an Assembly Line?

You may often to need estimate machine requirement calculation. In this post I have discussed the steps to estimate how many machines and what types of machines you need to make your garment in an assembly line. The primary information you need for calculating number of machines -

A. Daily production target – it means how many pieces you want to stitch per day.

B. Number of hours in a shift – How many hours you plan to work each day

C. SMV of each operation – Standard minutes for each operation

D. Present efficiency of the factory (in case you don’t aware about present factory efficiency, use 50% efficiency). Efficiency is required because production will depends on how efficiently workers may do their job.

Step 1: Operation breakdown 
Select a garment for which you want to calculate machine requirement. Analysis the operations required to sew the garment and list down operations in a spread sheet in a sequence. For example, see operation break down of a Crew neck Tee in following table.

Step 2: Identify machine type 
Observe what stitch class has been used in the operations and according to those select machines against each operation.

Step 3: SMV of each operation
Write down SMV or standard minutes at right column of machine type. SMV is the most important part for calculating machine requirement. You can use SAM of each operation from your database. If you don’t have database for standard minutes then calculate it. Read the article how to calculate SAM of a garment.

Step 4: Calculate Theoretical machine requirement 
Set your production target for the day (8 hours shift). Example- 400 pieces per line. Use present efficiency level of the factory. And now,  calculate machine requirement using the following formula. It is called as calculated machine number. Because formula gives you fraction of machine but in real you can’t able to use fraction of machine.

               = (Target quantity in pieces* individual operation SMV)/(8 hrs*60 minutes*desired efficiency)
               = (A*C)/(B*60*D)
             
Step 5: Physical machine requirement 
Now simply round off the machine number. Or you can club operations those use similar machine class. To do operation "Serge margin" half machine is required and the operation "sew side seam with label" required 1.4 machines. So can use first 4TOL machine to do the second job. Hence you can reduce the machine number and increase machine utilization.

Example: Operation bulletin for Tee Shirt (Crew Neck)

 Production target/day
 (8 hours) =400 pieces
Shift hours = 8 hours
or 480 minutes
Plan on  Efficiency
=50%
Opr.
No.
Description
Machine
Type
SMV
No. of Calculated M/c
Round-off
Machine No.
1
Make Neck Rib & Runstitch
SNLS
0.55
0.9
1
2
Join shoulders
4TOL
0.45
0.8
1
3
Insert Neck Rib
SNLS
0.45
0.8
1
4
Serge Margin
4TOL
0.31
0.5
1
5
Top stitch on Neck rib
3TFL
0.34
0.6
1
6
Attach Sleeve
4TOL
0.78
1.3
1
7
sew side seam with labels
4TOL
0.84
1.4
1
8
Hem sleeves
3TFL
0.68
1.1
1
9
Bottom Hem
3TFL
0.56
0.9
1

TOTAL

4.96
8.27
9

Machine requirement Summary:
Single Needle Lock Stitch (SNLS): 2 No.
Four thread Overlock machine (4TOL): 4 No.
Three thread Flatlock machine (3TFL): 3 No.

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