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How to Reduce Waste While Ensuring Inventory is at Your Workers' Stations When they Need It

To reduce waste we must first SEE IT.

The challenge we face in designing line-side or at-workstation replenishment systems is the wide assumption that VMI programs will take care of it.  Vendor managed inventory (VMI) has become so broad that it can fall anywhere from vendors assisting with assembly to vendors dropping off at the front door.  We can’t slap a VMI program in place and assume waste will go away.

First, we need to see the waste.  Then, we can build the process to eliminate it.

Here are a few tools to help you.

Spaghetti Diagram.

In this example the spaghetti diagram is a visual representation of the physical steps the team in this work cell take each shift to get the hardware they need.  Each line is one trip and the associated number is an average of the number of steps.


This is done by spending time on the manufacturing floor where the work is done.  You are watching, counting steps, tallying the trips team members take, and if possible getting some hands on work in.  It can absolutely be grueling and tedious.

Here’s why you do it.

VMI could mean stocking the “hardware shelf” once a week, or the “A inventory” location twice a week.  It could mean a skid is dropped off at the “shelf” or your supplier fills each workstation daily.

Here is our question…do you see the waste?

This diagram makes a clear case for what solutions can be put in place to eliminate real waste and get parts where we need them.  As the steps add up, the plate of spaghetti fills up, and a problem becomes visible which we most likely didn’t see before.

Material Flow Diagram.

At this point maybe you already have a system where your team has everything they need at the work cell.  How do the parts get there?  How many different processes are used to get them there?  How complex is your entire replenishment model?

The purpose of a material flow diagram is to show clearly how material enters your building, gets to where it is used, and which system gets it there.  Here is an example of what this would look like with just two replenishment methods over the course of one week.  Each line is the movement of either a delivery for a trip to check on and pick up Kanban cards.

Here are a few questions I have.  Why do we check so many Kanban card locations each day?  Why does this look like a mess?  To eliminate this, where do we put a VMI system?  Is this cost of low inventory?  Can a VMI supplier provide consignment and where should we put it?So here is our question…do you see the waste?


Data is a tool because it will tell us how much.  Data correlates to priorities the same way perfection correlates to quality.  The waste we are looking for in material movement is not about seeking perfection.  It is about finding which instances of movement are the priority to eliminate.  Frankly, this type of exercise will not get us to completely eliminate walking and movement.  But the data can tell us what parts to put where.

Here is a very simple example of the type of data you want to be looking for over a 4 week period of time.  What part is it?  Where is it in the building?  And how often are we touching it?  When designing or asking for a VMI system this very basic information can tell you a lot about wasted movement, space, inventory, and certainly usage.


So here is the data…what questions do you have?

Why so many trips in 4 weeks?  How big is the building and do we have parts in the right place?  How much does each transaction cost?  Let’s go see these areas and talk to the production floor.

To summarize… spaghetti diagrams will show us the movement of people to get the parts they need, material flow diagrams will show us the movement of materials, and data will show us the transactions.  Combine all of these with physically being on the production floor and you are on you way to SEEING IT (waste). Reduce waste and ensure inventory is at your workers’ stations when they need it.