What is Style Changeover Time?
Style Changeover Time is the time between the last piece output of the previous style from the last machine of a line and the first piece output of the next style from the last machine of the line. It means if style-A was running on a line and its last piece was out from line at 12:30:35 PM. Simultaneously, a new Style-B was fed in line, and its first piece reached (passed) output at 14:30:35 PM. This time duration for which there was no output will be called COT (changeover time) or Style Changeover Time.
In this article, I will discuss the reasons for style changeover time, its implications, and methods to reduce style changeover time.
The main causes are-
Apart from these general causes, there are some other factors also which we see in our day to day life. I am trying to list a few of them.
All these factors are quite reasonable (part of the production process). At first sight, you will not find them troublesome, but after in-depth process study, they will show their true nature. With proper break-up one can find hidden wastes in these activities.
External elements are those elements that are independent of your sewing line. For example, you need a special machine for next style. You can arrange that machine before the line change over starts.
Internal elements are those elements for which you need to stop the line, or you have to wait till the last piece is out. For example, you want to set that new special machine in your line for next style. This activity can’t be performed till the old style is out of line.
Now our approach will be converting internal activity into external activity and reducing time duration of both activities.
Here is another example, mechanic is setting that special machine after placing that machine in line. Now you say that this setting can be done before start of changeover outside the line. Here you have converted internal activity into external activity. Now there can be another condition where mechanic does not have a proper toolbox and for each tool, he is going back to the tool room. In this case, time consumption will be higher.
This is an example sheet and more detailed study should be done. The best way to do that is to record all the activity done by changeover team (IE, Mechanic & Supervisor) and also making video simultaneously.
Once all activities are reordered in study sheet, we will get a changeover time data of a particular line. After this, we need to analyze that data for internal and external activities.
What internal activities can be converted into external activities, and also how to minimize time duration of those activities?
For this, we need to do a detailed study of each activity. We have to segregate them into value added, non-value added and essential non-value added activities. Once we remove non-value adding activity from our process/line change over time will further reduce.
The above discussion can be summarized as
Major reasons for higher style changeover time
The approach in which we work to minimize COT is called QCOT Approach. Before we discuss how to reduce COT, I would like to discuss the causes of COT. To be frank cause of Changeover Time is Changeovers but what I meant earlier was, causes of High Duration Change Over Time.The main causes are-
- Variety of products with different specs and requirements
- Diversity in the raw materials and their handling mechanism
- Labour-intensive with different level of skill sets
- Lack of pre-planning and preparation
- The attitude of middle management
- Prolonged machine setting time
- Non availability of tools for initial machine setting
- Sudden plan change
- Supervisor sample not ready
- Initial quality setting takes a longer time
- Old style creates a blockage
- Operator training is given at the time of Batch Setting
- No measure of operator COT performance
- Parallel Batch Settings making it difficult to control
- Non availability of specialized machines
- Cut part feeding not available
All these factors are quite reasonable (part of the production process). At first sight, you will not find them troublesome, but after in-depth process study, they will show their true nature. With proper break-up one can find hidden wastes in these activities.
SMED – The Lean Method of Reducing Style Changeover Time
SMED stands for Single Minute Exchange of Dies. In simple terms any change over time should be in single digit (minutes). Now we will discuss, how to apply SMED approach in a sewing line. For this, we need to list down all the elements of a line change over along with time.Internal elements are those elements for which you need to stop the line, or you have to wait till the last piece is out. For example, you want to set that new special machine in your line for next style. This activity can’t be performed till the old style is out of line.
Now our approach will be converting internal activity into external activity and reducing time duration of both activities.
Here is another example, mechanic is setting that special machine after placing that machine in line. Now you say that this setting can be done before start of changeover outside the line. Here you have converted internal activity into external activity. Now there can be another condition where mechanic does not have a proper toolbox and for each tool, he is going back to the tool room. In this case, time consumption will be higher.
A glimpse of the SMED Study
For the sake of easy understanding, start the study after your last piece is out of the sewing line and stop the study till first piece of next style is out of line. In idle scenario, change over activity will start before the last piece is out but that should be left as it is due to diligence of team.
This is an example sheet and more detailed study should be done. The best way to do that is to record all the activity done by changeover team (IE, Mechanic & Supervisor) and also making video simultaneously.
Once all activities are reordered in study sheet, we will get a changeover time data of a particular line. After this, we need to analyze that data for internal and external activities.
What internal activities can be converted into external activities, and also how to minimize time duration of those activities?
For this, we need to do a detailed study of each activity. We have to segregate them into value added, non-value added and essential non-value added activities. Once we remove non-value adding activity from our process/line change over time will further reduce.
The above discussion can be summarized as
- Observe the current style changeover process; identify all the activities as internal or external set-ups.
- Separate the external and internal set-up and note them down.
- Convert internal set-up actions into external ones.
- Further, optimize internal and external set-ups to improve overall effectiveness of style changeover process.
Conclusion
Some key points in consideration before style changeover:
Low COT has numerous benefits, the most eminent and visible one is that it increases Available Time thus increasing floor OEE.
- The new style needs to be allocated to that line only where there is a minimum style variation.
- The batch Supervisor and QC along with the COT team should be there at pre-production meetings to judge critical operations and operator availability.
- New Style Requirement (NSR) to be made and discussed. It will ensure the availability of trims, machines, skilled operators, cutting before the line setting.
- Supervisors/IE need to analyze the skill-matrix prior to the style changeover; the concerned Floor Manager must ensure the availability of operators along with the skill.
- The spare machines should be allotted before the start of the process to stimulate the offline batch setting.
- The mechanic needs to ensure the availability of templates, guides, attachments with settings.
Low COT has numerous benefits, the most eminent and visible one is that it increases Available Time thus increasing floor OEE.
Post updated on: 10/05/2023
Original post date: 27th Sept 2020