November 9, 2018

Dan’s Second Rule of Process Mapping Continued

The second rule of process mapping is that the problems in the process should be easy to see. In my last post, I talked about using different colored post it notes and symbols to draw attention to process issues. I suggested using blue post it notes for worker frustrations, orange notes for quality issues, green post it notes for value-added activities, and red dots for delays and waiting.

The next way to make the problems visible is with data. Here is a list of items that can give us insight into process performance:

  • Process time (P/T)
  • Lead time (L/T)
  • Setup time
  • Batch sizes
  • Demand rate
  • Percent complete and accurate (%C%A)
  • Number of people
  • Inventory
  • Reliability
  • Available time

Process time is the amount of time spent working. One way you can get this data for a particular activity is to ask people “If you were not interrupted, how long would it take you to do _______?” Or you can use a stop watch to time someone when they are doing the activity. We represent process time as P/T.

Lead time is the amount of time from when the step or activity starts to when it ends. Lead time includes process time,  move time, set up time, wait time, review time, and rework time. There is lead time for a particular step. There is lead time for a complete process, called total lead time. Lead time is represented as L/T. If you find a small amount of process time for a step, yet a large amount of lead time, usually the difference is caused by waiting. A simple equation might make this easy to understand. Lead time = process time + wait time. 

Setup time is the amount of time consumed in preparation to do the work. For instance, suppose you have to do a report. Before you can start the report, you must go get files, load a software program, and finally scroll to the page you need. Now you can begin the report. Setup time is the work that precedes the work of the step. If setup time is large, it encourages people to do multiple activities of the step, which we call batching. In lean, we do not like batching. So in order to cut batch sizes down, setup time needs to be shrunk.

Batch sizes tell us how many items are processed at one time. Batching is only convenient for one person, the batcher. Everyone else has to wait for the batch to be done. Batching leads to waiting, overproduction, inventory, mistakes, extra processing, and movement. As we cut down on batch sizes and run them more frequently, the above issues diminish and we get closer to continuous flow (nirvana).

Demand rate comes from the customer. Demand rate is the time frame expected by the customer for something to be done.

The percent complete and accurate is our quality measure for office and service processes. Don’t we want everything we get to be complete and accurate? This measure is represented as %C%A.

The number of people refers to the number of people who perform a particular activity.

Inventory is measured by how long items are in inventory. This could be measured in seconds, minutes, hours, or days. Obviously if the amount of time something is in inventory is large, we want to find out why.

Reliability refers to the reliability of the systems and software you use. Here we are looking for uptime. If your system is “down” how long does that typically happen?

Lastly is available time. Available time is the amount of time allocated for this person to do this activity. In office and service work, people wear multiple hats. It could be that demands for other tasks impinge on the amount of time available for another task. By calculating available time and comparing that to demand rate, process time, and the number of people, we could see the cause of a bottleneck.

Below is a process map with some of these items. There is a time line across the bottom of the map that shows process time and lead time by step and also the sum totals for the process. Batch sizes, inventory and percent complete and accurate are also shown. If you compare this process map to the one from the prior post, you can see we converted the post it notes and symbols into data.

Process data helps us focus our resources. It tells us how large a problem might be. And when we institute countermeasures, it tells us if our countermeasures are working.