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Production Scheduling – Level the Mix

Level the Mix

This post is part of our series discussing the 7 lean manufacturing guidelines. In this post we’ll discuss supermarkets as a way to design a lean future state.

Post 1: The 7 Lean Manufacturing Guidelines
Post 2: Building to Takt Time
Post 3: Developing Flow
Post 4: Supermarkets & Pull
Post 5: The Pacemaker Process

This post will discuss the fifth of the seven guidelines for designing a lean future state, which is to level the production mix by distributing production of different products evenly over time at the pacemaker process.

Unconventional Thoughts on Batching

While it’s easier to schedule long runs of one product type to avoid changeovers, larger batches creates serious problems for the rest of the lean manufacturing value stream. Larger batches increases the lead time to fulfill any order and makes your operation less flexible.

Rather, we recommend you level out the product mix by spreading out the work as evenly as possible over time and running with as small a batch as you have capacity. While this is contrary at every level of conventional thinking, you should use all of your capacity to run as many changeovers as possible in order to keep your batch size as small as possible.

Why Smaller Batches Can Be Better

Let’s say that production is scheduled weekly and the pacemaker is producing 3 different products. We could accomplish our work by running each product once a week and incur only 3 changeovers. That would mean that we are producing in batches of 1.67 days with a lead time of over 3 days. If we can absorb the changeover time to run each product each day, then we have moved from 3 day lead time to just 1 day lead time. Do the math! That strategy can free up a lot cash tied up in inventory. If we can move that from 8 hours to 2 hours, now we are have a 4 hour lead time and may be able to move our entire operation to make to order.

Look at it graphically.

Without leveling the mix:  AAAAAABBBBBBCCCCCC
First improvement to level the mix: AABBCCAABBCCAABBCC
Ideal state of leveling the mix: ABCABCABCABCABCABC

The same number of units is produced but the frequency that each unit is produced is reduced.

Leveling Production in a High Mix Manufacturing Environment

For high mix manufacturing, the pacemaker process may have many products that can be produced. However, not all of these products may be ordered in any schedule period. Some manufacturers plan for a rotating cycle of their highest running products and then reserve certain amount of time on each schedule to accommodate the infrequently ordered items. Of course, some products take more time to build than others and there higher volumes of some than others. Leveling might result in the following:

High mix leveling: AAABBCAAABBCAAABBC

There’s a repeating cycle of all products being produced subject to capacity constraints at the pacemaker.

The more you can level out the product mix at the pacemaker, the more your manufacturing operation will be able to reduce lead time and reduce inventory. This guideline helps us come ever closer to being able to produce to our ideal state of one piece flow with a batch size of one.

Stay tuned for the next segment on this series about leveling the production volume.

 

Want to learn more about our Areteium Lean Manufacturing Software? Read our whitepaper Achieving Lean Transformation in High Variation Environments.

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Written By:  Phil Coy

Phil 300