Yamazumi Charts and Boards
What is a Yamazumi Chart or Board
A Yamazumi chart or Yamazumi board is a visual tool used within lean manufacturing to aid in cell design and continuous improvement; it allows you to visualize the various work elements within a process and compare them to the required customer output or Takt time.
Yamazumi literally means to "stack up" and the yamazumi chart is a simple stacked bar chart of your activity times within your process.
By using this process you can highlight areas where operators are facing stressful levels of work (Muri – overburden) whilst other operators may be spending time waiting or idle “marking time” to allow previous operations to catch up. You process can only flow at the speed of the slowest link in the chain; using the yamazumi board can help you to identify the weak links in your processes.
The yamazumi board also distinguishes between value adding and non-value adding operations allowing you to visualize the savings that could be made by eliminating these non-value adding operations to make your processes more efficient.
Yamazumi Chart in use
What is Takt time?
Your Takt time is the demand rate required by your customers in number of minutes per part. It is calculated by dividing you total available work time by the average number of parts required by the customer.
The Takt time is the speed at which your factory should run, slower would mean that you would fail to meet customer demand and faster would cause you to build inventory. The Takt time of your factory is one of the most important factors to consider when designing your processes and work cells.
When you create your yamazumi chart you will draw a line across it at the height of your takt time, each operation should then be just below the Takt time when you have balanced the work between each operation.
How many people do I need?
If you know the Takt time and you know how long a product takes to produce you can calculate the number of people you need to produce your product. For example;
If your takt time is one minute, and your product cycle time is 4 minutes and 45 seconds then you need to have 4.75/1 or 4.75 people (obviously you can’t have 0.75 of a person so we round up to 5 people.) If you are left with a fraction of less than say 0.25 you should round down the number of people required to allow for process improvement when doing your yamazumi board analysis.
Timing Work Elements for Yamazumi
To balance a work cell you need to know both the takt time (demand) and how long each individual element of work takes; this requires the work to be measured.
In the past an industrial engineer would stand over the operators (who would often slow their work pace) with a stopwatch and time the various elements of work to arrive at standard times and other measures which would then be used to either reward or beat the operators with when they either achieved or failed to achieve output.
To use a yamazumi chart, as in other lean manufacturing tools, we wish to involve the team in the analysis and improvement, a far better way to make these measurements in today's technological age is to take a video of the operations involved and have the whole team analyse and time the process.
Video Work Elements for Your Yamazumi Board
By using a simple video you can have the whole team involved in making the timing of each element of the work involved.
Each process should be broken down into small manageable steps that can be both timed and identified as being either value adding or non-value adding. So you would time;
- walk to container (non-value),
- select component (non-value),
- return to work place (non-value),
- place component into fixture (non-value, unavoidable),
- operate drill (value adding)
By videoing the different shifts involved and the different people that do the work you can also see how different processes are being used and how they affect the output from the process. This allows you to not just time the process but to better standardize and choose the best methods for your production.
Look at this article on work study for more detailed information on conducting your timings.
Creating a Yamazumi Chart
Magnetic yamazumi charts
Magnetic Paper to print your work elements onto; cut to size and add to your magnetic yamazumi board
Using a Yamazumi Chart
Your yamazumi board is a simple stacked bar chart; the left hand (Vertical) scale is time marked off in seconds, the lower horizontal axis is used to display the number of operators. A line is drawn across to indicate the Takt time for the process, your aim is to ensure that all operators’ workloads fall below the takt time (but not by too much as they would be idle.)
The individual work elements are then recorded onto pieces of coloured paper (green; value adding, Red; non-value adding, Orange; non-value adding but unavoidable), these papers are cut to length to represent the number of seconds taken. The best to use here is either magnetic card to stick to a metal board or simple post-it notes.
You then stack the work elements on the yamazumi chart for each operator, the ideal is that they have around 95% of the takt time taken up by their work in the cell.
If the operation takes more than the takt time you need to take some elements of their work and pass it to the operators either before or after them. Alternatively and more effectively you can review the non-value adding elements and remove them or try to reduce the time taken for other elements of their work.
Using magnetic printable paper (above) allows you to easily create a yamazumi chart using just a standard magnetic white board.
Yamazumi Line Balancing
If an operators workload exceeds the takt time on the Yamazumi board you have two options;
Eliminate the non-value adding elements of his work to bring below the Takt time.
Reallocate some of their work elements to an earlier or later operator in the process.
Using the yamazumi board you can balance the line for varying Takt times and numbers of operators as your heart desires. Whilst your Takt time should remain constant, in practice you may wish to have the ability to flex your work-cell to operate with fewer operators or more to cope with demand fluctuations caused by unforeseen events (such as an outbreak of flu causing absenteeism) or even seasonal demand patterns. It is good practice to create a work flow diagram based on the ideal number of operators, then additional diagrams for fewer or more operators such as in the examples below.
Line BalancingClick thumbnail to view full-size
One of the most important aspects to consider when using yamazumi is that you need to have a standardized way of performing the work. There should not be differences between operator A and operator B, nor should there be differences between shifts. The work needs to be carefully documented to clearly show exactly how the work is conducted.
Standard Operating Procedures (SOPs) or Work Instructions should be used to detail out the best way to do the work and should contain timings for help in changing your Yamazumi chart at a later date should you need to add or remove operators.
These are very easy to create with today's word processing packages and the use of a digital camera or even your phone.
If you have any questions regarding the use of yamazumi boards or Yamazumi Charts for line balancing or about lean manufacturing principles in general please leave a comment below.
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