We recently received an e-mail regarding OEE calculations for batch processes and more specifically the effect on down stream equipment that is directly dependent (perhaps integrated) on the batch process. While the inquiry was specifically related to the printing industry, batch processing is found throughout manufacturing. Our more recent experiences pertain to heat treating operations where parts are loaded into a stationary fixed-load oven as opposed to a continuous belt process.
Batch processing will inherently cause directly integrated downstream equipment (such as cooling, quenching, or coating processes) to be idle. In many cases it doesn’t make sense to measure the OEE of each co-dependent piece of equipment that are part of the same line or process. Unless there is a strong case otherwise, it may be better to de-integrate or de-couple subsequent downstream processes.
Batch processing presents a myriad of challenges for line balancing, batch sizes, and capacity management in general. We presented two articles in April 2009 that addressed the topic of where OEE should be measured. Click here for Part I or Click here for Part II.
Scheduling Concerns – Theory of Constraints
Ideally, we want to measure OEE at the bottleneck operation. When we apply the Theory of Constraints to our production process, we can assure that the flow of material is optimized through the whole system. The key of course is to make sure that we have correctly identified the bottleneck operation. In many cases this is the batch process.
While we are often challenged to balance our production operations, the real goal is to create a schedule that can be driven by demand. Rather than build excess inventories of parts that aren’t required, we want to be able to synchronize our operations to produce on demand and as required to keep the bottleneck operation running. Build only what is necessary: the right part, the right quantity, at the right time.
Through my own experience, I have realized the greatest successes using the Theory of Constraints to establish our material flows and production scheduling strategy for batch processes. Although an in-depth discussion is beyond the scope of this article, I highly recommend reading the following books that convey the concepts and application through a well written and uniquely entertaining style:
- In his book “The Goal“, Dr. Eliyahu A. Goldratt presents a unique story of a troubled plant and the steps they took to turn the operation around.
- Another book titled “Velocity“, from the AGI-Goldratt Institute and Jeff Cox also demonstrates how the Theory of Constraints and Lean Six Sigma can work together to bring operations to all new level of performance, efficiency, and effectiveness.
I am fond of the “fable” based story line presented by these books as it is allows you to create an image of the operation in your own mind while maintaining an objective view. The analogies and references used in these books also serve as excellent instruction aids that can be used when teaching your own teams how the Theory of Constraints work. We can quickly realize that the companies presented in either of the above books are not much different from our own. As such, we are quickly pulled into the story to see what happens and how the journey unfolds as the story unfolds.
Please leave your comments regarding this or other topics. We appreciate your feedback. Also, remember to get your free OEE spreadsheets. See our free downloads page or click on the file you want from the “Orange” box file on the sidebar.
Until Next Time – STAY lean!