Gather Data


Gather Data

The process of developing the current status of kanban candidates begins with gathering the necessary data to help characterize the potential process. To adequately define the process you will need the following information:

  • Number of parts produced by the process

  • Changeover times

  • Downtime

  • Scrap levels

When collecting this data, be honest with yourselves. The data is intended to help you develop a usable design. If the data is inaccurate, then you will potentially doom the project to failure before it even starts. When starting the data collection process, use the following guidance to make sure the team collects the proper data:

  • Be specific about the data required

  • Assess the data to confirm that it matches the team's experience and knowledge of the process

If you discover that the data does not make sense, then review the data again and sort out the truth. Don't be afraid to collect new data!

Number of Parts Produced by the Target Process

Start the data collection process by identifying the parts to be produced by the target process. Begin by breaking the production down into individual part numbers. Do not combine part numbers just because they are part of a common family, the same size , the same configuration, or the same color . We will use these similarities later in Chapter 5 during the design process to address preferred operating sequences. At this point we need to understand the magnitude of the project, which we can only do by knowing all the part numbers .

Conversely, if a part is common at this stage, but it is transformed into different part numbers later, then it should be considered one part number. For example, a 4"8" plate that is produced by a stamping die in one process, but is turned into five unique pieces downstream through future processing, would be considered only one part number in the original stamping process.

Be descriptive when gathering data ”look for both differentiation and commonality in the parts being produced. Take the time to sort through the data to determine these items; don't let a mound of data overwhelm you. During the data collection phase, keep asking questions until you arrive at a list that makes sense. Before beginning data collection by part number, you also need to determine what your production-scheduling interval will be. Essentially, do you produce to the monthly, weekly, or daily production requirements? The answer to this question will tell you the interval for the replenishment cycle. All your calculations must then be scaled to this interval, such as pieces per week, available time per week, etc.

Once you have selected a scheduling interval, then you need to determine the required parts for this interval. The required parts are the number of parts you use over the predetermined interval ”per day, per week, or even per month. These quantities represent the parts consumed by the "customer" at regular intervals, which you must regularly replenish to keep the customer supplied. (We use "customer" to refer to both internal and external customers.)

In conjunction with identifying the products that will be produced by the kanban system, you must also determine the rates of production. Review each product's production rate for realism . If you receive a blanket rate answer, use the team's experience to ask: Does everything really run at the same rate? Also, make sure you use consistent units and measurement systems for the production rate and description. Once again, the wrong rates will skew your numbers when creating the kanban design.

Changeover Times

Changeover time is the time from the last good production piece of the previous production run to the first good piece in the new production run. Many people cheat when they report changeover time by reporting the time from the last good production piece of the previous production run to the time the line starts up on the new production run. They conveniently decide to omit the time it takes to debug the start-up and begin running continuously. This subtly can be very important if you are trying to optimize the run quantities.

Don't fall into this trap. The kanban quantities and calculated replenishment cycle must be based on the time the process runs at the planned production rate.

Just like the part's description, consider the different products produced by the process and verify the changeover time for each changeover. Avoid broad-brushing the times and underestimating or overestimating the total changeover time.

Downtime

Downtime, or rather unplanned downtime, is the total time the process is scheduled to be producing parts, but it isn't. Basically, how many hours is the process not producing product but was scheduled to do so. Examples of unplanned downtime include shutting down for breakdowns or for lack of raw material. Unplanned downtime should not be confused with planned downtime, such as time allocated for breaks, lunches, maintenance, or cleanup. Scheduling the line down because of no production requirements is also considered planned downtime.

Realistically, look at the process's downtime. Determine an average for the downtime using experience as well as historical data. However, when looking at the historical downtime, don't let recent process improvements be overshadowed by the data. (Once again ”be honest and look at it as it is, not as you wish it were.)

Scrap Levels

Next, determine the system scrap rates for each product produced by the target process. System scrap is the process scrap rate plus the scrap rate of downstream processes. The system scrap rate will let you calculate the adjusted production requirements for each product. When calculating the adjusted production requirements you must account for the total amount needing to be produced. In Chapter 4 we will show you how to calculate the adjusted production requirements. If your plant tracks scrap by the process scrap and the downstream (or customer) scrap, then you will need to incorporate both numbers into the adjusted production requirement calculation.

To illustrate the impact of scrap on the adjusted production requirements let's look at the example in Figure 3-2. (Don't worry about the equations ”we'll discuss them in detail in Chapter 4.) In this example, to produce 100 parts with a process scrap level of 8 percent and a downstream scrap of 2 percent, we would need to produce 119 parts. This number is slightly larger than the 111 parts we would need to produce if we had calculated the required parts as a combined scrap rate of 10 percent.

A plant produces a part in a process with 8% scrap and the downstream scrap for processes that use the part are 2%. To meet a daily production demand of 100 for this part, how many parts would need to be run?

Adjusted process demand

=

100/(1 “8%)

=

100/0.92

=

108.7 or 109

Total adjusted demand

=

109/(1 “2%)

=

109/0.98

=

118.5 or 119

Total adjusted demand for 10%

=

100/(1 “10%)

=

111.1


Figure 3-2: Example of Calculating Adjusted Demand Scrap When Measuring Scrap by Process Scrap and Downstream Scrap.

When looking at the scrap levels, check to see if your current schedule quantities already account for system scrap rates. If they do, then no further calculations will be required.