Balance table. Or the Yamazumi chart. This tool is intended to see the balance of work according to the takt time.
My coach introduced a modified version of this tool. He called this a “Color-coded balance table.”
This tool intends to facilitate balancing based on the quantity and characteristics of work.
After all, line balancing is a very strategic activity.
Here is how it works.
My coach suggested using a “color-coded” balance table when balancing an assembly line. His observation was that the typical line balancing of balancing the work elements to the takt time is not making the work easy and efficient. We need a different approach.
“Color-coding” is the name he gave, but this does not mean using only color to highlight different work characteristics. Sometimes, we can use patterns or symbols. The idea is to highlight those differences on the balance table so that we can consider them when using them. But don’t try to highlight everything. Decide two to three characteristics to highlight. Otherwise, it becomes too chaotic. Line balancing is strategic.
Here are some ideas for work characteristics to think about;
Location
When I rebalanced, one of the cycle times got longer. Why? The two work elements were in entirely different locations of the product. Now, the operator has to move more. To avoid such errors, we can highlight the location on the balance table. The location can be the position of the fixtures or many other things.
Skill type
Another aspect of work to look at is the skill type. When you mix different skill types, you might create additional time. For example, some skills require different types of gloves. If I start changing the gloves, I will waste lots of time. By consolidating skill types, we can also make the training more efficient.
Tool
Similar to the above skill type but in more detail. Even in the same skill types, you might have a situation that uses different tools—for example, bolting. Bolting might be one skill, but different sizes of bolts require other tools. If so, allowing the consolidation of the same tool usage will bring the benefit of not exchanging tools.
Skill level
Another topic is the skill level. In operations, we will always have some rookies. If so, why not create a rookie process? Having such a process will ease the introduction of a worker to get familiar with the environment. Mixing skill levels and blaming a rookie for not keeping up with the rate is rude. Design some process to allow one to learn is respect for humans.
Lead time
The final example is lead time. Inside assembly work, some work elements require a customer order. Instead of mixing these elements, separating them and consolidating them helps reduce the lead time. An example is a sushi restaurant. Fishes are processed up to some cuts before opening the store. But then, each fish is processed for each order. Such separation reduces the lead time and improves flexibility.
The benefit of this thinking is explainable.
Suppose there are two skills in a three-person work cell. If we don’t think about the skills and all three processes require both skills, we need to train all three personnel to have both skill sets. On the other hand, two stations would become a single-skill process if the line were balanced based on skills. Such a condition is much easier to train.
Every time I mention this thinking, there’s always a cynic. “Didn’t TPS say we need multi-skill operators?” This thinking does not deny multi-skilled operators. Instead, it is a practical approach. Anybody who tried to become a multi-skilled operator or implement such a workforce will understand its complexity. Also, turnover is inevitable in operations. If so, designing a line based on work characteristics helps to create something simple.
Also, there is no such thing as perfect categorizations of work characteristics. Therefore, there are multiple ways of balancing the line. What to prioritize becomes a management decision. Good management will be able to link strategy and line balance. It could change based on product mix, labor market, etc. Line balance is a reflection of strategy.
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