Batching or Single-Piece Flow?

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One critical aspect of lean thinking that many people have trouble grasping is the importance of moving from batching to single-piece flow.  After all, if improving productivity is one of the things we're ultimately trying to achieve, isn't batching the most logical choice?

WHY WE THINK BATCHING MAKES SENSE

If we're striving for higher efficiencies within an individual step of an operation without regard for the effect on the overall process, then batching tends to make sense.  In fact, batching is a common practice in so many organizations today because of a fragmented approach to setting goals that forces people to maintain an inward focus to improvement.

When following a systems thinking mindset, on the other hand, it becomes clear that local ideas for improvement need to be evaluated - before they are implemented - as to whether or not they result in improvement to the organization.  And in the end, isn't organizational improvement what we're ultimately after?

Although batching often appears more efficient than single-piece flow for an individual task, the practice tends to create waste for other parts of the organization that more than offset the perceived benefits.  Some of the wastes that result from batching include:

• increasing the time between spending money in a process and receiving money from customers due to an increased overall cycle time and inventory that is not yet sold;
• waiting and downtime in one or more steps of the process while previous steps complete work on multiple units;
• larger amounts of inventory between process steps to reduce the likelihood that one step will shut down while waiting for a previous step to complete a batch;
• increased rework and delays when a defect is discovered that affects an entire batch of work rather than a single unit;
• increasing the time required to implement a design improvement because of the need to use up a larger  amount of inventory.

A dilemma commonly associated with a batching mindset is determining the the optimum batch sizes.  It is very likely that the "best" quantity to run for each step in the process will differ, resulting in further increases in inventory throughout the system.

IS SINGLE-PIECE FLOW ALWAYS POSSIBLE?

There are situations where batching is more cost effective because of limitations resulting from tooling, equipment, technology, or process design.  Although producing work in batches under these circumstances may be the most logical and cost-effective choice today, it should never be considered acceptable into the future. Batching must be considered a countermeasure until the process can be improved to the point where single-piece flow (or smaller batches) can occur.

Whether applying lean to a manufacturing process, administrative operation, or drilling gas wells, it is important to understand the effect that batching has on process flow, operating costs, and overall competitiveness of the organization.  To do this requires a systems thinking mindset, as well as a deep understanding of the process and the needs of the customer.

As long as people are evaluated on objectives that are not carefully aligned throughout the organization or do not clearly support high-level objectives, batching will appear to be preferable to single-piece flow.  Like many other aspects of lean thinking, trying to move to single-piece flow before transformation of leadership has occurred will most likely result in frustration among team members and disappointing results for the organization.