“Whenever there is a product for a customer, there is a value stream. The challenge lies in seeing it.” -Learning to See, Lean Enterprise Institute
Since starting our series on value stream mapping we have discussed what a value stream is and how to identify the product or products to initially focus our VSM efforts on. To read about these topics in more detail please follow the links below.
In this third installment we will discuss how to go about creating a current state value stream map.
It is what it is
The key to creating an excellent current state VSM is to document what you actually see with your own eyes. We are not interested in how the process is supposed to work, or was designed to work.
Instead, we are interested in how the process is performing today. Will the process change a bit tomorrow? Sure. But that’s OK.
Fun with Icons
I remember the first time I saw a value stream map. I wondered how anyone could benefit from it. It was a bit messy, and I didn’t know what any of the little shapes and icons meant. In short, I was a bit intimidated by the whole experience.
Luckily, I had some great instructors and I did quite a bit of self study to get past my initial fears.
So, the only way you will not be a bit intimidated (assuming you have never seen a VSM before that is) is to study a bit and practice, practice, practice. There are really only a hand-full of icons you will always use. And for the rest, you can use a cheat sheet like I do!
It’s time to create the map!
OK, let’s learn how to create a current state value stream map. To help you visualize things I have created a fictitious example of a peanut butter and jelly sandwich factory.
Our PB&J manufacturing company goes by the name of KB&R Inc. For those interested, that’s the first letter of each of my three kid’s names!
Step 1: Calculate takt time. Don’t proceed until this step is done. If you don’t remember how to calculate takt time this free resource should help you along.
In our example, we have a daily demand of 700 pieces with the following arrangement.
- Hours per shift: 8
- Break minutes per shift: 30
- Shifts per day: 1
- Days per week: 5
I recommend you practice punching this out. But in case you don’t, I’ll tell you the takt time is 39 seconds per piece. In other words, we need to produce a completed PB&J sandwich every 39 seconds in order to satisfy customer demand.
Step 2: Get a pencil and BIG eraser. The best value stream maps have eraser marks all over them. Please, I beg you; don’t use a pen when drawing these.
Step 3: Have a big piece of paper ready. Your standard 8.5”x11” piece of paper won’t cut it. Personally, I prefer the 11”x17” paper size. It’s big, but not too big to carry around.
Finally, while I will be drawing the value stream map using software in this article, I recommend you always draw the map on paper first. Then, when you are ready to share your masterpiece with senior management you may choose to go for the software.
Step 4: Walk the process front to back. Quickly walk the process with your team in order to understand the general flow. It’s important to also define the start and stop point of the process. Don’t attempt to take on too much. Remember, we eat an elephant one bite at a time.
We also note their monthly and/or daily demand along with the takt time as calculated in step 1. Click to enlarge the picture to see what this looks like.
Step 6: Go to the end! Next, we start at the END of the process and begin drawing the map back to front. And don’t forget about that eraser. You will need it. I recommend you nominate a scribe and have them draw the map for the team.
Another trick is to ask each person on the team to map it out so you can compare and consolidate when you get back to the room. Yet another trick is to have the team divide and conquer as you send some off to map the beginning section, some to the middle, and some to the end.
There are many ways to do this. Experiment and do what works best for your situation.
Regarding the data boxes, if you don’t have all the data perfectly collected on the day of the mapping exercise just do the best you can. You can always assign homework to go back and validate the figures later.
In fact, even if you think you have solid data, the six sigma side of me urges you to validate your measurement systems to make sure we can trust the data. If you want to get really tricky state both a measure of central tendency and dispersion. You won’t see this advice in most lean VSM books… I guarantee it!
After studying the KB&R manufacturing process for an afternoon we learned that each process step is staffed with 1 operator. We also collected cycle time information at each step. Additional “homework” will be to collect information such as defect rates and changeover times.
Step 8: Add the Inventory/Wait Times. Once you have all the process and data boxes in, it’s time to add in inventory and/or waiting times. These are the little yellow triangles with an “I” in the middle.
For inventory, we simply count the number of pieces in between the processes and note them under the triangle.
We also want to convert these pieces into days’ supply. To do this, we divide the number of pieces by the average daily demand (which we used to calculate takt time).
So, if your average daily demand is 10 pieces and you count 20 pieces of inventory in between process step A and process step B you have 2 days’ supply (20/10) in between the two processes. We will note this number on our timeline (to be added in a future step).
Lastly, don’t attempt to map every part number! Choose one or two key components to start with. You can always add more to the map later.
In our example, we chose to simply count two pieces of bread as one subassembly since they move together down the production line.
Also, we are not accounting for the peanut butter and jelly “raw material” at this point since KB&R’s expert supply chain team negotiated a killer consignment stock deal with Sam’s Club so this inventory is quite low on the line.
During the study, we learned that, as one example, there were 486 sub-assemblies (972 pieces of bread) in between the jelly application and packaging stations. This equates to 0.69 days’ supply (486 units / 700 daily demand).
Lastly, during the walk through of the process we noticed that each process step seemed to be working in isolation. In other words, the lady working at the peanut butter application seemed to produce as many units as she could and then pushed them along to the jelly application process.
This “push” process is found in just about every mass production process known to man kind. When we see this pushing action we note it on a VSM with a dashed line through the yellow inventory symbol.
Step 9: Draw in the information flow. This step is what really separates a VSM from traditional process maps in my opinion. You see, in addition to learning about how material flows we also want to understand how information flows.
For example, we want to know it is moves about electronically? If so, we use a lighting bolt looking arrowed line. Is it communicated manually? If so, we use a straight arrowed line.
During this step we also draw in our production control box. For many, this box will include the letters “MRP” in it. In most mass production systems we typically see several manual information (straight) lines coming out of the MRP box aimed straight at each process step box.
In our example, we learned that production schedules each process step in isolation. In other words, each work station gets its unique production schedule. We draw this using straight “manual” information lines.
We also add in the information flow from our customers as well as to our suppliers. In our example, we learned that PB&J’s customer sends 30 days electronic forecasts as well as electronic daily orders. Conversely, PB&J sends its bread supplier an electronic weekly forecast.
Step 10: Add in the timeline. We can now add the timeline to the bottom of the value stream map. This saw tooth looking line helps us separate the value added cycle time (taken from data boxes) from the non value added time (days’ or hours’ supply info).
The last step in the process is to sum up all the “value-add” cycle times and note them at the end of the timeline. Likewise, we also sum up the “inventory” times and note that on the timeline.
In our example, the total value add cycle time sums to 97 seconds and the total non value add “inventory” time sums to 2.39 days! We call the total inventory time the production lead time (PLT).
To calculate the process cycle efficiency (PCE) we divide the value-add time by the PLT. When we do this we get a PCE of 0.15%. To see exactly how this was done please read this article.
And that’s it my friends. You just created a current state value stream map. This may seem a bit daunting initially, but with just a little practice you will be a current state VSM drawing machine!
Up next, we will see what improvements we envision for this process as we draw up a future state value stream map. If you have a thought to share or question to ask please don’t hesitate to leave a comment below or contact me.
Continue at: http://blog.gembaacademy.com/2008/02/24/lets-create-a-current-state-value-stream-map/
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