How to implement a replenishment pull system using kanban

Darren Dolcemascolo
Tags: inventory management

Pull is one of the key principles of lean thinking. There are essentially two different types of pull systems: sequential pull and replenishment (or supermarket) pull. In sequential pull, the downstream customer pulls parts from the upstream supplying process in the sequence in which the supplying process produces; that is, the supplying process dictates the sequence of work. Sequential pull limits the amount of inventory between the two processes. In replenishment pull, the downstream customer pulls from a supermarket according to what it needs (based on a schedule dictated by its customer). The supermarket is replenished by the supplying process. In this article, I will describe a case study in which a California manufacturer implemented replenishment pull between an injection-molding operation and two assembly cells.

The company in question had 12 plastic injection-molding machines. Each produced a number of components that were assembled into a finished product by the assembly cells. Before the implementation, the company had approximately 10 days of injection-molded inventory (work in process, or WIP). There were also a significant number of material shortages affecting the productivity of the assembly cells.

A kaizen team was formed, consisting of a materials person, assembly and injection-molding operators, an industrial engineer, an area supervisor, and a few employees from outside the area. After spending day one in training and mapping out the current state process, the team discovered significant waste in the process:

  • Daily material shortages resulting in significant overtime costs/reprioritization
  • Inefficient planning for changeovers in the injection-molding department due to shifting schedule/priorities
  • Out-of-cycle work: Operators were doing their own material handling and preparation
  • Excessive WIP (10 days)

After analyzing material usage and variability in usage, the team created and properly sized a supermarket of plastic materials. The system would work as follows:

  • Material handlers would pull from the supermarket into the assembly cells, replenishing point-of-use inventory using a two-bin system. That is, as bins of plastic parts are emptied, the empty bin was used as a signal to replenish material to the cells.
  • As materials in the supermarket were consumed (moved into assembly), a trigger point (visually indicated by the number of bins remaining) was reached. When the trigger point was reached, a kanban card would be pulled and delivered to the injection-molding lead.
  • The injection-molding lead would place the kanban on a scheduling board in sequence.
  • The injection-molding machines would run product according to the kanban on the scheduling board and replenish the supermarket.

The new system resulted in a 90 percent reduction in shortages and 70 percent reduction in WIP (from 10 days to three days).
Click here to subscribe to our free e-newsletter Learning to Lean and receive three articles like this one each month.

About the author:
Darren Dolcemascolo is an internationally recognized lecturer, author and consultant. As senior partner and co-founder of EMS Consulting Group, he specializes in productivity and quality improvement through lean manufacturing. Dolcemascolo has written the book Improving the Extended Value Stream: Lean for the Entire Supply Chain, published by Productivity Press in 2006. He has also been published in several manufacturing publications and has spoken at such venues as the Lean Management Solutions Conference, Outsourcing World Summit, Biophex, APICS and ASQ. He has a bachelor of science degree in industrial engineering from Columbia University and an MBA with graduate honors from San Diego State University. To learn more, visit or call 866-559-5598.

Begin a Free Subscription to Machinery Lubrication

About the Author