Batch production is not easy
We’ve all heard the age-old debate initiated by Taiichi Ohno: batch production vs. one-piece flow production.
There is one problem with this discussion.
Many people have this belief that batch production is easy.
It’s not. The only reason why people believe that batch is easy is that they are allowed to break the batch.
I like batch production.
I love one-piece flow.
I hate chaos and liars who claim that they are doing batch production.
What is “Batch production”?
The batch is calculated based on optimizing cost per piece. Typically, there are two types of cost, a cost that goes up as batch size goes up and a cost that goes down as batch size goes up. There are many calculation methods, but that doesn’t matter. We should produce according to that batch size once it is calculated.
But keeping this batch quantity is not as easy as most people think. The truth is that it is broken most of the time.
Here is a list of problems causing batches to break;
1️⃣ Quality, quality, and quality
Ohno has stated that one of the Kanban rules is 100% quality. When we produce a defect, we break a batch. The defects permanently destroy the batch without a fantastic quality assurance process and management. It doesn’t matter if that defect was a few pieces or X%. As soon as a defect had been produced, we broke the batch.
I have seen some factories that add some allowances for defects. Let’s say 5%. But the factory is not producing to the batch size when they added that allowance. And, the defect hardly ever hit that allowance. Sometimes more, sometimes less. This is a problem of fractions. This problem becomes other problems, such as the 5S issue. The only solution is to get to 100% quality. Ohno is correct, as always.
I typically ask the production people what the batch quantity is. A typical operator will look back at me and ask, “what do you mean by batch production?” Then two of us look at each other strangely.
Many people work without knowing the batch quantity. There’s no information. There’s no control. And somehow, the operator is supposed to produce the batch. It is mission impossible.
3️⃣ Machine breakdown
The machine breaks in the middle of the batch. It might be a brilliant fire-fighting decision to end the batch immediately so they can use the downtime to change to the next batch. But doing this all the time is wrong. Unfortunately, this is happening a lot.
4️⃣ A machine that is not used for the whole batch
Once in a while, I ran into machines whose operators don’t use the total capacity. When I ask them this question, they will say, “the batch size is too big!” These operators know from experience that they overproduce by keeping the machines at total capacity. They know the batch quantity won’t allow them to be flexible to meet the demand. So they don’t fully produce the batch.
Sporadic, but such cases exist. In such cases, I need to change the batch size officially and connect the entire system so that the smaller batch does not increase the cost. I need to reduce other costs using the small batch size, like warehouse costs. Otherwise, we end up killing this momentum towards a smaller batch.
5️⃣ Material availability
In the middle of batch production, materials run out. Or you have more materials, so keep the production running until the materials run out.
It sounds simple to prevent. Only start the batch when you have the materials. Stop when the batch is reached. Unfortunately, many don’t check, or the system says materials are available, but they can’t find them. Or additional materials seduce to continue producing. The truth is that many production schedules are according to material availability.
6️⃣ Production batch vs. transportation batch
Just like production has a batch, there is an optimum quantity for transportation. Typical, load as much as possible. I have seen cases where they load too much and damage the quality. But who cares? The more, the more efficient transportation. Although such thinking should be corrected, there is still a problem.
The production batch size and transportation batch size are not the same. The gap between the two becomes a fraction. And when this fraction happens, the batch tends to end or overproduce.
7️⃣ Lead time
Sometimes, the only location to count whether they have reached the batch is at the end of the line. In such cases, the timing to stop the input becomes tricky. Sometimes too much, sometimes too low. Yet, the operator has to make the decision based on observation. The actual problem is that the quantity inside the line is unclear. Plus, there are too many dropouts that they don’t know how many will come out.
8️⃣ Sales rush order
A day in the plant suddenly gets noisy when the sales make a phone call. They want a product to be shipped immediately. So in the middle of a batch, the production changeover to a new product. It’s everyday scenery inside a factory.
This should not be. There should be some order freeze period in which no one can change the order. Rush orders should be made according to rules, not creating chaos.
So when someone claims they have “batch” production, have they overcome these problems and constantly produce in “batch”? Never. And that is the reason why people think that batch production is easy. If you don’t have to keep the batch, it is easy. By the time when you are doing proper batch production, one-piece flow is around the corner.