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One Piece Flow

Definition of One Piece Flow:

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Would you like to improve safety, flexibility, productivity, floor space usage, inventory, and build in quality? If so, then using a one-piece flow in your organization might be the answer.

Overview: What is one-piece flow? 

One of the basic approaches in Lean Manufacturing is one-piece flow. The concept is to process one piece at a time as it flows between different processes. 

This is the opposite of batch processing, where pieces are accumulated before the entire group of pieces moves to the next operation. As a result, the WIP (work in process) is greatly reduced. 

One-piece flow requires:

  • Kanban or pull system
  • Consistent processing times able to meet takt time requirements
  • Reliability and high uptime for equipment 
  • Efficient and low changeover times consistent with SMED (single minute exchange of dies)
  • Product quality must be high

Below is a graphic illustrating some of the differences between the traditional manufacturing process and one-piece flow.

Traditional manufacturing vs one piece flow

An industry example of one piece flow 

A tour bus pulled up in front of a sub shop for a lunch break. The ten passengers got out and went in to order. Five ordered a hot meatball sub while the other five ordered Philly cheese steak.

The owner, being used to producing subs using a batch approach proceeded this way. He: 

  • Laid out the five sub rolls on the work counter 
  • Split the roll into a top and bottom part 
  • Laid both parts on the work counter
  • Put the meatballs on all five bottom parts of the roll 
  • Added the toppings on all five
  • Put on the top of the roll on all five
  • Wrapped them all
  • Took them to the cash register

By the time the five customers started eating their meatball subs they were no longer hot because of the batching time to produce all five at once. The same thing happened with the five Philly cheese steak subs.

One of his employees, who had previously worked at Subway, suggested they switch to a one-piece flow. Once a customer ordered a sub, an employee would walk down the counter and build the sub one at a time. This reduced the need for a large countertop, sped up the process, reduced the WIP, and allowed the shop to deliver a hot meatball sub to a customer while it was still hot.

Frequently Asked Questions (FAQ) about one piece flow

1. How does one-piece flow improve safety in my operations? 

One-piece flow can improve safety because the workplace layout is more efficient, has less clutter, and is more ergonomic in design. 

2. Does using one-piece flow improve the quality of my process? 

Yes. One-piece flow can improve quality and reduce defects. Since you are working on only one piece at a time, you can easily detect a problem, and it will only affect that one piece. In batch processing, you can affect an entire batch before something is noticed.  

3. What is the core concept underlying one-piece flow? 

The core principle of batch production involves building up in-process inventory, or WIP, between the steps in the process. Once the batch is produced the whole batch moves to the next step in the proces. The core concept of one-piece flow is to build at the pace or rate of customer demand. This rate of customer demand is measured by takt time.

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