Changeover time calculation in sewing line

Changeover time in sewing line is the time taken from producing the last good quality piece of the completing style to the time taken in producing the first good quality piece for the new style.

The above definition will give the changeover of the entire sewing line. This is because the completing style will transition smoothly in the line while for the new style in every operation we need to set the machine and other things. Therefore with every passing operation the time gap between both the pieces will start increasing and the changeover time will keep adding.

So if the difference at the end of the line is calculated the output will be sum of changeover time of every operation.

But to control the changeover time we should be able to measure the changeover time of every operation. This data will specifically pin point in which operation the changeover time is the maximum and changeover time reduction tools like SMED can be applied.

To measure the changeover time of every operation RFID, barcode or manual data record can be used.

Calculating Changeover time in a digital factory

Factories don’t measure their changeover on daily basis. The project is done once in a while and then the outcomes becomes the constant measure. But with every passing style we need to know what is the changeover only then we will be able to accurately achieve the target set on the day of changeover.

Therefore having an automated system for calculating Changeover in a digital factory becomes an important factor in operations management.

The foundation for getting changeover time in a digital factory is getting to know when quality is passing a piece out of a sewing line, so the first step is:

  1. Having quality recording system where every passed piece is entered. I am specifically saying quality and not sewing data because though the first piece of the upcoming style may be stitched after one minute we cannot be certain if it is of the right quality. Therefore we must take only quality data for changeover calculation
  2. When we will have quality pass data we can calculate the changeover

Formula for Changeover time

Time of first good quality piece for the new style  – Time of last good quality piece of the completing style

7 thoughts on “Changeover time calculation in sewing line”

  1. How to calculate garment changeover time ?
    How to calculate changeover efficiency %?
    How to set target of changeover time ?
    Could you pls give the theory ?

    1. Hi Ibrahim,as mentioned in the post changeover time can be calculated by this formula :
      Time of first good quality piece for the new style – Time of last good quality piece of the completing style .
      Target for changeover should be zero .
      There is no need to calculate efficiency of changeover because line efficiency will anyways account for changeover but if you have to, it could be done mathematically by this formula:
      (Total time a line has worked – Sum of changeover time) / Total time a line has worked

  2. Any thoughts on thread change over due to color changes? I am looking for info on SMED as it would apply to this type of change over. Has anyone seen a SMED project on this?

    1. Hi David, thread change is one of the major contributing factor in changeover time. Every SMED project has to address thread changeover. For machines like Overlock , flatlock ,welt stitching etc where thread change takes more time need to be an external change , if the layout and machine availability allows it. I do have seen some SMED projects will try to get my hands on it and will share it with you.

  3. According to you COT of a style = Sum of (Last good output of old style – First good output of new style ) time of each operations of that line? if it is, then COT never come less than 10 minutes ( what SMED defines).

    1. Hi Prabir,
      The formula is not the sum of time it is difference of time only. At the end of line this difference will automatically accomodate the COT for individual operations. Secondly, the only rule to understand in SMED is external and internal changes , 10 mins or less will depend on the type of the industry it is applied

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