Using kanban to help flow

Creating flow in your operation is the ideal state if you want to have a lean process. Anything that stops you flowing product (or services) from start to finish in your organisation is something you want to eliminate, if you can't eliminate it completely then you need to minimise it. It is fair to say that in general terms anything that stops your product flowing comes down to some form of waste in the process and those can and should be one of your key focuses in your improvement activities.  

Uneven Processes

The opening paragraph comes from one of our initial training sessions we do with organisations who want to start on their lean journey. Invariably when we start discussions like this with companies there is the instant push back that the various processes within their organisation aren't all balanced. Process A takes 20 minutes, Process B takes 40 minutes, Process C takes 30 minutes for example. You can't flow that they would say, and they are right, you can't flow that, but you can fix it.

You can certainly explore why Process B takes 40 minutes and what can you do to lower that, is it rearranging the work, is it set up time, is it processing, quality, waiting and so forth. In variably as we focus in on it, we reduce the cycle time of each operation, but it is still not even.

The other thing we keep hitting is that Process A keeps going for the whole day, it is running twice as fast as the next operation, yet it keeps going, creating noise and WIP. However, if you only ran it 50% of the time then you would meet the requirements f the next process and have the people from that process available to you to use 50% of the time somewhere else, so effectively creating free labour. That labour could of course be used in Process B for example. The concept of stopping an area, especially a machining shop is tricky for people to take. There is the whole accounting overhead recovery to think about and so on, but keeping it running is costing money, so just stop, for a while, as you fix your processes and your flow you will need to increase your machining hours to keep up with the new volumes, assuming of course you have sales for them.

Flow where you can, Pull where you must

Learning to See - Rother and Shook (1999)

Create Pull with your Kanban

The reality is you will have some processes in your organisation that you need to build a Kanban for that will help smooth out your uneven flow. There are many thoughts on the order of doing this, fix your process first then put in a Kanban or put in a Kanban to give you the room to fix your process. Both have merits but I am in the 2^nd camp. I believe that you can use the Kanban to help remove the noise of the uneven flow and buy you some time to let you improve the processes and as you improve them reduce the level of your Kanban down. It is important to note that you always want to start with your bottleneck area, that's the area you never want to stop. However, there is also the situation where if you inset a Kanban you can use that to free up people. In other words if we worked to fill a Kanban and cold do that in 4 hours, and that fed the next operation for 8 hours or 16 hours then I have free resources from the last operation I can use elsewhere in the process.

We should step back a bit, however. Firstly, what is a Kanban, is it just a buffer? No, it's not a buffer, well not exactly. Kanban itself is a signal used to tell the last process to supply more. It can be a card, a light, a trolley, and empty bin, anything you can use to tell the previous process ok it is ok to make more because I've used some. The key is that the Kanban signal should tell the previous operation what to make and how much. If the next operation used 50 units, there is no point making 200, just make the 50. Equally, it doesn't have to be a quantity of units, it maybe time, the next operation has pulled the next job with is 4hrs of work so the signal back to the previous operation is make me another 4hrs of work. In one factory we simply marked an area on the floor and said, if that is empty, make enough to fill that area (it was a little more tightly specified than that, but you get the idea).

Sizing the Kanban  

If we think about your Kanban as purely internal just now, since you really don't want to start it with suppliers until you fully understand it we can figure out the size of your Kanban pretty quickly.

• Process A can make 60 parts an hour, that is its lead time. (or 120 in 2hrs or 0.25days)
• Process B uses 120 parts every 8 hours, or 15 parts an hour (demand).
• We decide we always want to have 30 parts (or 25% of the day) of work in the buffer as a safety stock in case there is an issue with Process A

In this example then the kanban size would be calculated at 37.5 as we are assuming the quantity in each kanban is 1. In reality you would probably round up to 40 parts. So, 45 minutes of Process A.

That is where you want to get to, however when you are starting out, keep it simple, I would be tempted in this simplistic example to run either 1 hour of Process A at the start of the day and then perhaps then after lunch or 2 hours anytime in the day and have a single day of Work in my Kanban which then frees up my people from Process A to do other things.

Kanban where you must

In order to create pull, you need something to pull from, in many cases within an uneven production process that place is the kanban. The aim however should always be to only do this where it is 100% essential and focus over time to continually reduce the size of the Kanban. If you start out with 8hrs of work or 100 units, how quickly can you cut that to 6hrs or 75 units and so on. Your Kanban is still inventory and you still want to eliminate or minimise it, but you must earn that ability by improving the performance of the upstream process. Perhaps then it is time to tweak the quote from Rother and Shook from "Flow where you can, Pull where you must" to

Flow where you can, Kanban where you must, but always improve your processes

by John Watt

By doing that, you will dramatically improve your ability to flow things in your process and better utilise your people and your equipment.