Establish Standardized Processes and Procedures 137

Chapter 6. Establish Standardized Processes and Procedures 137

So how do we determine the demand and takt time? Select a demand num- ber that will be sufficiently high enough to meet the need most of the time. For example, suppose the demand varies from 10,000 to 20,000 per month but the average is 16,000 per month. Which number should you choose? It depends on the situation, but generally we advise a higher number. Here’s why. Let’s suppose we use the maximum: 20,000. If we calculate a takt time, we will get a lower num- ber (less time allotted per piece). We compare the takt time to the cycle time to determine the discrepancy. Selecting a higher demand number will create a larger discrepancy. The relevance of the discrepancy is only related to the amount of improvement necessary to achieve the takt rate, and the improvement potential is based on the waste that exists in the operation.

When presented with this dilemma, a Toyota sensei would respond, “No problem,” meaning that the pool of waste is large and the needed improvement can assuredly be made. The only risk of setting a demand level too large is that the amount of effort needed to achieve the takt time will be greater. You do not want to waste effort by falsely inflating the demand number (driving takt down), but it is not a major problem. If a process is improved beyond the actual need, the resources can be reduced or additional sales can be pursued.

The takt time serves as a common “beat” for all operations in the value stream. An operation balance chart is a powerful visual tool for seeing how cycle times compare to takt. In some cases it can be used for answering “What if?” ques- tions about the capability of the process. Figure 6-8 shows an operation balance chart that was used to compare cycle times in a value stream to takt time. In this case the company wanted to increase production in order to meet possible increased demand that was only roughly estimated. They wanted to know how

Line 1 Cycle Times

Takt time = 90 seconds 100

AD LO FORM 1 FORM 2

GRIND

BUFF

SPOT WELDFOOT WELD NOTCH/PIERCE

SPOT WELDSTUD WELDSEAM WELD

ATTACH COVER

Figure 6-8. Operation balance chart to compare cycle times

T HE T OYOTA W AY F IELDBOOK

much of a change would be needed to meet a hypothetical takt of 90 seconds per part. We see that two operations are currently over that estimated takt time.

If these two operations were improved, how much improvement would

be necessary before the next balance “plateau” is reached? Figure 6-9 shows the next plateau. Several other jobs have a cycle time of approximately 60 seconds. Reducing the two jobs to 60 seconds would allow the entire value stream to flow at a rate of one part every 60 seconds. Does that mean we should immediately pursue this goal? In fact if we do this and the takt time based on actual demand is greater than 60 second we will be over producing—the fundamental waste.

After reducing the time it took for the two operations, it was determined that the actual takt rate necessary to meet the demand was 80 seconds. This allowed for “rebalancing” the operations and reducing their total number. In this case, after reducing the time it took to grind and buff, the total amount of work across all operations added to 645 seconds. If we divide 645 seconds of work by the takt of 80 seconds, we get a total of 8 operations at the takt time, compared to the original 12. Thus, we could reduce one-third of the operations by rebalancing to the 80-second takt. If this were manual processes, it would equate to 4 fewer operators (note: these “extra” operators could be used to develop a team leader structure as outlined in Chapter 10). It is interesting to note that if we balanced

Thus, going faster can cost more (provided it was not necessary to go faster). Use takt time to help make decisions about how the work will be designed and which improvements need to be made to meet the need. If you select a takt time that is too high, you will not meet the production need, which is worse than choosing a number that’s too low and exceeding the need (provided you did not add resources to meet the false need). It is always easier to stop production

Line 1 Cycle Times

Takt Time = 90 seconds 100

80 Next Plateau 60 40 20

BUFF

FORM 1 FORM 2

GRIND

LOAD