Understand batches and lots for OEE and estimated times

It is important to understand the difference between batches and lots so that your OEE results are within expected ranges.

• A lot is generally used to uniquely identify a group of consumed or produced items for tracking purposes.

• A batch is an amount of product that is processed simultaneously. A batch is used to determine the standard production time for a given amount of product. Standard production times are expressed either in time per batch, or batches per time.

For example, assume that you want to track all of the cookies that are baked during a shift as a group, and that you want to determine the cookie production’s OEE. A unique lot number can be assigned to the group of cookies produced during the shift. But the lot size has nothing to do with the OEE calculation. That calculation would be based on the batch size and the batch production rate. If a batch size is 100 cookies and it takes 20 minutes to bake a batch of cookies, then up to 24 batches of cookies could be baked during an 8-hour shift, or a maximum of 2,400 cookies in a lot.

Also, note that the amount of production might not be an integral number of batches. This is because the standard production time for a batch will be constant, regardless of whether the batch actually includes the maximum number of items for the batch. For example, if the oven capacity, and thus a batch, is 100 cookies, it takes as long to bake 90 cookies as it does to bake 100. The performance component of OEE factors in this nonlinear behavior. So, for OEE to be reported accurately, it is important that the batch size be set according to the way production actually occurs.

The other usage of batch size is with estimated job start and end times. When creating a work order with a required finish time, the batch size and production rate is used to determine the start and end times for each operation in the process to determine the required start time of the initial job. Incorrect batch size and production rates can create unattainable start times and even overflow date/time calculations in the database.