One Piece Flow Vs. Batch Work

One-Piece flow is one of the most important principles of lean manufacturing. One-piece flow means that parts are moved through operations from step-to-step with no work in process in between; either one piece at a time or a small batch at a time. Once work on a product begins it never stops moving until it is a finished product.

As opposed to one-piece flow, batch-and-queue processing is the action of producing more than one piece of an item and then moving those items forward to the next operation before they are all actually needed there. Batching and queuing tends to drive up inventory and lead time, and creates inefficiency in an operation. It also increases the space needed for production. Using One Piece Flow is important if you want to achieve Just in Time Manufacturing or Inventory policies.

The ideal state for a production process is continuous one-piece flow. If you can’t manage to get down to one-piece flow, always the question … can you get two-piece or three-piece? The most important thing to remember is the idea of continually moving closer to the ideal state.

Examples

Using One Piece Flow in an Assembly Line - Notice one piece flow is 50% faster!

Single Person Stuffing Envelopes - Total time using mass production is 3:42 Vs. 2:56 for one piece flow.

Reasoning

One piece flow works so much better than mass production because there is less time with material handling. In the example of the letter stuff above, he picked up a piece of paper folded it, stuffed it in the envelope, then sealed the envelope and stamped it. In the mass production version of that he picked up each paper, folded it, then set it down, then picked up each paper again and stuffed it into the envelope. One piece flow is faster because when he is already holding the paper he stuffs it into the envelope. Easy to see how that can reduce material handling time.

The issue is that many processes are setup as batch work, but the more you can see the difference between batch work vs. one piece flow, the more you can try and change it to work better for one piece flow. Once you do that you can really start to speed up your processes.