Hi lean practictioners!
Today I want to discuss the use of the loading diagram and how it can help us improve productivity and help drive throughput. The loading diagram is also known as the cycle time/takt time bar chart. This chart shows us how each staff member (operator) is loaded against the takt time. To complete the loading diagram we need three pieces of data. First we need the takt time for the process and this is added to the chart at the appropriate time on the y axis. The takt time is drawn on the chart with a red, dashed line. Remember that takt time is a theoretical calculation where we get the ratio of hours available to do the work divided by the volume of work to be done. For example if we have 8 hours of time to to the work and we need to process 8 units, then our takt time is 8 hours/8 units or 1 hour. We would draw a red line at the one hour mark on our cycle time/takt time bar chart.
The next piece of data we need is the cycle time to complete one unit of work, for each staff member (operator) in the process. The manual cycle time is taken from the time observation sheet. To calculate the manual cycle time for an operation, we would prefer a minimum of 10 observations for any given task. 10 cycles will show enough repeatability and consistency to determine the lowest repeatable time element for each sub-step in the operation, and it is from the lowest repeatable time elements that we calculate the manual cycle time. Each different operator in the process will have their own manual cycle time. We would show a stacked bar chart with the elemental times for each operator. The sum of the elemental times will equal the manual cycle time.
An example of the loading diagram is detailed here.
The third piece of information captured on the loading diagram is the minimum staffing. The minimum staffing is calculated by dividing the total manual cycle time by the takt time. This figure is the minimum number of people necessary to operate the process. In most instances, I find the operation is overstaffed.
The loading diagram now shows us where the operational bottlenecks are by operator (makes on time delivery impossible), where the staff is underloaded against the takt time (wasted resources, and what the minimum staffing could be.
Before adjusting the minimum staffing, we want to eliminate the waste, and create standard operations. When these two things are done, we may consider balancing the work to ensure each staff member can perform their cycle time within the takt time.
The net result of all of this analysis should result in a process where fewer resources are needed, more throughput is generated, and higher on time service performance is achieved. A lot of benefit can be derived from this lean tool.
Understanding this tool is considered the key to productivity.