Matt Hrivnak

Kaizen: There's always another future state


One of the toughest aspects of the Toyota Production System (TPS) for people to understand is why single piece flow is so important, and how it works.  I can’t count the number of times I’ve answered questions and statements like these: 

“What is single piece flow?”

“If we make one, move one, then our efficiencies will fall and we can’t have that…”

“Why use smaller batch sizes?”

“How will smaller batch sizes help?  We’ll just have more changeovers and our costs will go up.”

“We can’t achieve single piece flow and if we are able to, it will be too costly for us to operate that way.”

“Our customers will never get their orders if we do that because all we’ll ever be doing is changing over and setting up machines…” 

When it comes down to it, single piece flow is the best way that a manufacturing system can be set up.  Now, in most industries, systems are setup that will never allow for single piece flow in the traditional sense because of machining capacities and capabilities.  Examples of this are piece work items that are manufactured automatically by machines that have multiple machining heads that are performing the same task concurrently – something like the minting, pressing and stamping of coins – multiple dies punching hundreds of coin blanks out at one time, etc.  With time and revolutionary machine designs, single piece flow would ultimately be possible. 

In order to highlight the benefits of single piece flow, I’m going to use a list that is characterized by Liker in The Toyota Way (if you don’t own it, buy it – it is well worth the money), pages 95-97.  I’ve kept the list the same, but have added my own reasons as to why these benefits occur: 

  1. Builds in quality – this is the aspect that is most overlooked by opponents to single piece flow.  Since you are not dealing with batches, in particular, large batches, any defects can be correctly instantly or removed from the system at that time by the operator.  Defects are fixed or removed instead of being passed on.  Defects also become more noticeable and do not become hidden amongst a batch.  The most significant benefit is that any quality issues are more apt to begin and end with that one particular unit.  This happens because the defect is located, a cause is determined and a solution is remedied (PDCA in action).
  2. Creates real flexibility – because you are dealing with a lot size of 1 you can end production for that product at any point throughout the day within the number of minutes it takes for that 1 unit’s cycle time to elapse.  This is improved with the advent of SMED as changeovers are reduced and a larger mix of products can be produced within a shift, servicing more customers than a system processing larger batches of products.  If processing a lot size of 20 takes 5 hours of machine cycling time to complete, then processing a lot of 1 will take .25 hours.  In this way, you would be able to switch products and start producing something else after 15 minutes, instead of waiting 5 hours for the previous lot to complete its cycle.
  3. Creates higher productivity – operators focused on single piece flow are working on mostly value added activities leaving less time for non-value added time to interfere.  In addition to this, as each piece is processed, it can be moved onto the next workstation and processing can begin there – eventually you will get to the point where you are producing units at an output rate nearly equivalent to your slowest individual process (i.e. theory of constraints).  Also, any quality issues can be quickly removed or remedied within minutes on a single piece as opposed to reworking an entire lot, this saves larges amounts of rework time that would normally bog down a production line and utilize operators in a completely non-value added manner.
  4. Frees up floor space – because single piece flow naturally works within a cell there is less space for the accumulation of inventory between processes.  A cell is setup to maximize production floor space and improve communication between processes to improve quality and increase throughput.  There is no waste associated with defects, scrap, unneeded stacks of raw material, stacks of finished goods waiting for the next process – none of that because as soon as inventory is created (in the form of 1 unit) it is absorbed and processed by the next station and so on, down through the line.
  5. Improves safety – single piece flow means that there is no need for large batches to be shuttled back and forth, over thousands of feet within a production facility.  All of the processes are arranged in a cell with minimal space between them.  Again, inventory does not build up and will not require movement, batch sizes are 1 so bins and containers used to move products will be very small, allowing for operators to lift small, light packages instead of large, heavy packages that may contain multiple units.
  6. Improves morale – this is a natural phenomenom that occurs because each operator gets to see the outcome of their hard work instantly.  This instant gratification builds a passion for creating well-made, quality items.  Overtime, operators will pride themselves on high levels of quality and products that they produce because they can actually see the benefits that they add to the product – and each one they produce is, in and of itself, a unique special well crafted item.
  7. Reduces cost of inventory – simply due to the fact that you have less inventory of raw materials, inventory of WIP, and inventory of finished goods means that your company will be able to dedicate their capital and resources in other areas instead of overhead.  Additionally, any inventory that becomes obsolete because it is sitting around waiting to be processed will no longer occur.  This could mean expanding by purchasing new capital or technologies, improving existing work centers, giving more benefits, providing higher salaries to attract a better workforce.

Related posts

Related Posts


Comments (0) Posted by matt on Tuesday, June 17th, 2008


You can follow any responses to this entry through the magic of "RSS 2.0" and leave a trackback from your own site.

Post A Comment