These articles are portions of a lecture presented to APICS by our friend Gene Caiola.

In our last segment titled “Finite Scheduling – Not So Easy To Be Successful” we left off after realizing that Finite Scheduling was a bit more work than it was worth…

Protected Flow Manufacturing – a Revolutionary New Approach

The understanding of Protected Flow Manufacturing requires a new method of thinking about scheduling. It starts with combining the notion of ‘time buffers’ for protection with the measurement of work completed on a Work Order. These combine to create a “Threat Level” that allows each Work Order’s status to be judged relative to all other work orders. Also unlike finite scheduling that schedules every operation within a work order consecutively, Protected Flow Manufacturing looks at each operation from any work order discreetly, and will schedule just one operation and then move on to another Work Order.

Sometimes an analogy is the best way to describe something. The analogy below uses cars as a means to represent shop flow.

Driving a car at night - pretty, young woman driving her modern car at night in a city (shallow DOF; color toned image)

Explaining Protected Flow Manufacturing to a Friend

A few weeks ago I had the fun (and challenging) job of trying to explain Protected Flow Manufacturing to a good friend. We had grown up in the early days of MRP, seen Rough Cut (aka infinite scheduling) fail and done our time fighting the complexities of finite scheduling.

So describing something very new and sort of backwards to what we have known was what I was up against. Analogies are always a good way to explain things so I had to pick one that might work. I went with the analogy of a car trying to be on time to its destination. This would represent a work order trying to get to the back shipping dock on time.

Let me first preface this story with the fact that my friend and I have been successful with finite scheduling. For those of you who have tried it you know that it takes a good amount of care and feeding, lots of number crunching and sometimes more art than science to get a “good” schedule. And then the next day it all changes again. Going with the car analogy, finite scheduling creates a new “map” every day for every car and highlights roads that may get congested if everyone followed their directions to a “T”. Of course no driver ever does that so we need to recreate the maps every day (for every car) just to try to keep going.

So here’s how I tried to explain the difference with Protected Flow Manufacturing…

Protected Flow Manufacturing – true to its name – first creates PROTECTION. The real name is a “buffer” in its lingo. For us in the car, it’s our best guess of getting to our slow driver. It’s a bit like saying, “I’ll leave at 5 and should be there no later than nine” even though all of the turns and distances on the map add up to only 2 hours of driving. This adds a 2 hour “travel buffer” buffer to the actual driving time.

Finite scheduling systems do not provide this buffer; they expect things to move at the speed they have been assigned (run standards). Of course that never happens (run standards are only so accurate and mostly inaccurate) so we have to create the schedule again, every day, and it’s brand new every time.

So back to the car and Protected Flow Manufacturing. My friend now asks “so when does Protected Flow Manufacturing create my schedule to get there?” This is the part that hurts the head. It doesn’t.


It just tells you to get in the car and start driving. That is why we have to be honest with ourselves and say it’s NOT a scheduling system – it’s an Execution and Planning system. Even that sounds funny – how can you execute before you plan?

Well, in our analogy of the car (really a work order starting on the floor), you just start driving – and when you do – you just started executing, you are on the road. One quick but sensible rule here is that you start driving at the right time. In our example the 2 hour buffer time plus the 2 hour drive time should put you on the road 4 hours before you wanted to arrive. So don’t start the trip before this time or you’ll just be clogging up the road for others that are starting at the RIGHT time.

Now that you are on the road (executing) going to the first turn (possibly a congested work center) a few things are happening.

FIRST, your time on the road is always being measured against your “travel” buffer. This part of Protected Flow is very simple, and it’s meant to be. If I have used up 1/2 hour of my buffer (25% in this example) and I have not gone very far (say 10% of the trip in pure miles measured) Protected Flow Manufacturing has just assigned me a value – called a threat level. Sounds a bit scary but that’s really what it is. All cars (work orders) are assigned a threat level. It’s really just the relative chance that I will be on time. The threat level grows if your buffer time is being used up faster then the rate you are gaining distance.


Now the SECOND thing that is happening is that every future mile and turn that you have to take on your map is being simulated against every other car on the road. Like the popular “community based traffic app” called WAZE , Protected Flow Manufacturing knows the position of every other car on the road.

But beyond what WAZE does, Protected Flow Manufacturing now PREDICTS where every car will be in future increments of time. It’s called a Current Future State Moment in the Protected Flow manufacturing world (and also sounds like an oxymoron). This simulation of each moment into the future provides what we need to get every car where it’s going on time.

And think about it. I am not regenerating a map every day for every car like finite scheduling. I have the same map, the same directions and I am just driving (executing). But now I am getting information about what is up ahead and now I am PLANNING to be on time by taking the appropriate measure to avoid predictable problems. And by the way, remember the threat level? It’s being used to help me focus on the most threatened car routes (work orders).


Like a traffic cop that knows where all cars are going and exactly where they are now, Protected Flow Manufacturing is trying to get all cars to their destinations on time. If many cars need to get over the same narrow bridge at once (think work center), the threat level is used to determine which car should travel the bridge next and which ones can afford to wait a bit longer – but still arrive on time.

This is when my friend understood that Protected Flow Manufacturing is really an Execution and THEN Planning system.

If we take all of this and truly apply it to the shop floor then we see that Protected Flow Manufacturing will revolutionize how we get work orders out the door. First, buffers protect us by realizing that things go wrong AND they create a natural priority or “Pull” through the shop.

Next, we do not need any huge number crunching like typical scheduling system do to get a work order going – just start it at the time of its buffer start time.

Finally, by simulating the future progress of ALL jobs and creating PLANNING (assigning more capacity, expediting materials, etc.) I produce the highest possible protection against being late.

And it was easy to do and to understand. Typical implementations of Protected Flow Manufacturing occur in days and weeks rather then the months it takes to fine tune a finite system…

In our final blog post for this series we’ll wrap up by looking toward “The Future of the Manufacturing Industry“.