The simplicity of measuring and calculating OEE is compounded by the factors that ultimately influence the end result. Because the concept of OEE can be readily embraced by most employees, it is easy for many people to get involved in the process of making improvements.
Unfortunately the variables involved with OEE, like those of many other measurement systems, fall under scrutiny. The goal of achieving yet even higher OEE numbers is met with yet another review of the factors and how they are treated. Usually the scope of this often heated discussion is focused on Availability.
The greatest task of all occurs when attempting to classify what qualifies as planned versus unplanned downtime. Availability is the primary factor where significant improvements can be realized and is most certainly the focus of every TPM program in existence. However, another significant factor that can greatly impact Availability is setup time.
We still receive questions and comments from our readers regarding setup time and whether or not they should “take the hit” for it. We have met up with different rationale and reasoning to exclude setup time from the availability factor such as: “We have all kinds of capacity and do the setups in our free time.” Or, “We do the setups on the off shift so the equipment is always ready when the first shift comes in.”
Regardless of the rationale, our short answer to the question of inclusion for setup time remains a simple, “Yes, take the hit.” Before we get to much further let’s define what it is. Setup time is typically defined as the time required to change or setup the next process. The duration of time is measured from the last good part produced to the first good part produced from the new process.
Improving setup times provides for shorter runs, reduced inventories, increased available capacity, increased responsiveness, improved maintenance, and in turn, improved quality. Shorter runs also provide the opportunity to maintain tools more effectively between runs as they are not as subject to excessive wear caused by longer run times and higher production levels.
Setup and Quick Die Change / Quick Tool Change
An exhaustive amount of work has been completed in many manufacturing disciplines to reduce and improve setup times. Certainly, by simply ignoring the setup time, there is no real way to determine whether the new methods are having an impact unless another measurement system for setup is introduced. We already have a measurement system in place, so why invent another one?
Quick Die Change and other Quick Tool Change strategies are common place in industries such as automotive stamping plants. The objectives for Quick Die Change are attributed to LEAN principles such as single part flow and reduced inventories. The benefits of these efforts, of course, extend to OEE and availability.
Setup and Production Sequencing
To exemplify the effect of sequencing and setup, consider a single tool that makes 8 variations of a product. For the sake of discussion, let’s assume the only difference is the number of holes punched into the part. The time for each punch removed from, or added to, the tool is the same.
The objective for scheduling this tool is quite obvious. We need to minimize the number of punch changes to minimize the downtime. If the parts required range from 1 hole to 8 holes, and we need 100 parts of each variant, we would arrange the schedule in such a manner as to make sure we are only adding one punch to the tool as we move on to the next variant.
In this case, setup time and sequencing are clearly a cause for concern and consideration. Secondly, it is much easier to calculate the time required to run all the parts and how much capacity is required. Including setup in the OEE factor also simplifies the calculation of overall capacity utilization for the piece of equipment in general.
As we have stated in previous posts, the objective of measuring OEE is to identify opportunities for improvement. Achieving higher numbers through the process of debate and elimating elements for consideration is not making improvements. Don’t masquerade the problem or the opportunities.
Setup is certainly one area where improvements can be measured and quantified. Availability and OEE results provide an opportunity to demonstrate the effectiveness of these improvements accordingly.
If the leadership of the company is setting policy then the explanations for performance in this regard should be understood. The only numbers that really matter are on the bottom line and hopefully they are black.
We would also encourage you to visit two of our recent posts, Improving OEE – A hands on approach (posted 03-Jan-09) and OEE and Availability, (posted 31-Dec-2008).
Until next time, stay LEAN.