Flow When You Can – Pull When You Can’t

The goal of perfect flow is to produce a product or service one at a time, defect free, immediately at the request of the next process. Successful operations accomplish this by flowing the value added activity of their products or services in sequence from order entry to shipment. Any time waiting or resequencing is a barrier to flow and waste. A good example is the Subway sandwich line. An order is placed for a foot-long Italian sub. The sandwich maker takes out the bread, builds the meats and flows the product down the line until completed without interruption. This of course is the goal, but even at Subway there are barriers to flow that cause us to choose another strategy: pull.

The three most common barriers to perfect flow are long changeovers, large imbalances in operation time between processes, and processes that vary by practice or procedure.

Long Changeovers  

Successful organizations understand that short changeover time is a competitive advantage. Businesses able to respond to their customer’s needs by quickly changing from one product to the next offer the shortest lead-time and do it with the lowest inventory levels. The opposite is true as well. Organizations with long changeovers are not able to respond to customer’s needs quickly and usually build up large quantities of inventory to try and take advantage of all of the time it takes to set-up for the new product. The conversations usually sounds something like, “I spent all of this time set-up to do this job, I am not going to make less than 100.” Others talk about the benefits of economic order quantities that attempt to balance the ordering costs and holding costs. The problem is the increase in lead-time to the customer is not considered.

Large Imbalances in Time Between Processes

Subway does a great job of flowing the value added elements of its product from order entry to shipment. But even it is faced with barriers to flow that cause waste, arguably necessary waste, but nonetheless waste.  The challenge comes when the request is to heat the sandwich up. It is necessary to place the cheese steak in an oven for 2 minutes to melt the cheese and toast the bread. The imbalance is caused by the previous processes (adding meats) and the subsequent processes (adding toppings), which takes far less time. Inventory builds up in the form of sandwiches in the process of being made. Additional sandwiches are added to the inventory to work on while the cheese steak heats up. And the sequence is changed as the finished cheese steak enters the line behind those completed while it was cooking.

Processes That Vary Their Practice or Procedure

A third barrier to flow is a process with practices or procedures that vary from product to product. The easiest example may be baking something in an oven.  While a cheese steak may only take 3 minutes to melt cheese and toast, frozen soup can take as much as 30 minutes to defrost and cook. A more practical example may be furnace practices for annealing glass or metal to strength it.  Different metals may have different temperature ramp up, soaking time, and specific cool down periods. This requirement causes inventory to build up, either to collect all of the metals with the same practice or varying delay between the different metals as they are annealed.

Pull When You Can’t

When it is not possible to maintain the sequence of products at the specified pace (takt time), it is important not to allow the lead time to grow unmanaged.  Simply adding more and more lead time based on historical performance just makes the problem worse. The strategy successful organizations use is to implement a Pull System. (Warning: this system requires stable processes to attempt.) In this type of system, components used in the process are only replaced once they have been consumed so companies only make enough products to meet customer demand. There are several ways to accomplish this, but the key is to have a strategy and create a managed inventory level.

Help your organization see the value in flowing product from order entry to shipment. Work hard to flow whenever you can and pull when you can’t.

Learn more in Patrick’s book, “Facilitating Effective Change,” available online through Amazon and Barnes & Noble.


Patrick Putorti

Patrick Putorti

Patrick Putorti

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