Milk Run Guide

Outline

• Why are milk runs important?
• What is a milk run?
• Procedures for milk run design
• What's next?

Why are milk runs important?

Transportation is one of the 3 “essential” non-value-added activities (NVA). With essential NVA, the goal is not to eliminate the waste, it’s to continually reduce it through standardization.

 

We standardize motion with standard work and inventory with supermarkets.

 

What does standardized transportation look like? Milk runs! A milk run is to the conventional internal logistics as a bus is to taxis.

 

 

What is a milk run?

There are two types of milk runs: internal (linking supermarkets to work centers)  and external (linking your facility to external suppliers or customers).

 

Here we are focusing on internal milk runs, which require both flow and pull to be implemented in the value stream.

 

There are five elements in a milk run:

1. A means of transportation (usually a tugger + trailers) 
2. A driver
3. A supermarket
4. A picker (who might also be the driver)
5. A route + schedule

 

Procedures for milk run design

1. Define the route, stops (for both unloading and loading), and frequency of the milk run 

For example, the route below connects the RM supermarket, 4 work centers in the value stream, and the FG supermarket, every 60 minutes.

 

2. Collect standard times for each activity required to pick, drive, unload, load, and place materials

Activity	Time
Take picking list, pick at RM supermarket, and load train	13m20s
Drive to cell 20	1m10s
Unload bins, pick up empties, collect kanbans from collection box	2m
Drive to cell 33 (etc…)	50s

 

3. Determine if you need a coupled or decoupled milk run

• Coupled means that the tug driver also does the picking and placing at supermarkets. This option maximizes productivity but lengthens the overall cycle time of a route.
• Decoupled means that the tug driver concentrates on driving and delivery at the work centers, while another person does nothing but picking and placing at the supermarkets. This option minimizes the route cycle time, but requires more carts and may increase idle time.

 

4. Calculate the number of kanbans

5. Build a heijunka box

The pitch corresponds to the frequency at which tug trains start a route. Pitch is also a multiple of quantity per container x Takt time.

 

6. Operate the milk run

1. Lay out the tug train floor markings at the start of the milk run (normally this is the heijunka box), if possible with a large screen showing the countdown to the next cycle.
2. Place the heijunka box next to the supermarket (FG if the pacemaker is shipping, RM/components/subassemblies if the pacemaker is in production)
3. If the milk run is coupled, when the countdown reaches 0, the material handler will go through the standard work sequence, which typically starts with picking cards from the box and then picking containers.
4. If the milk run is decoupled, when the countdown reaches 0, the tug train should be fully loaded with containers and kanban cards for the pitch. This means that the picker/placer must work to an offset schedule, picking the cards from the heijunka box for the next pitch when the countdown restarts at [pitch] minutes and having the train fully prepared and in place by the time the countdown reaches 0.
5. The driver will go to each station on the route, delivering and picking up containers and kanbans, and returning to the start position by the time the countdown reaches zero.

 

7. Follow procedures for abnormal conditions

• Drivers normally have a short waiting time at the end of each cycle before the countdown reaches zero. They must not leave before the end of the countdown! If they do, the risk is that we will overproduce, overload a supplier, interfere with another milk run (causing “traffic jams”), or any combination of the above.
• If a driver leaves before (or after) the scheduled time, this should trigger an andon signal. The andon can be automated, with a photocell or pressure pad detecting the presence of the train at its start point, and any state change from present to absent outside of a 20-second window around the 0-mark of the countdown will trigger the andon. In response, the supervisor or area manager must document what led to the deviation and what countermeasure to implement.
• If a card taken from the heijunka box cannot be matched with a container, the card is placed in a red mailbox, which triggers an andon (by manual or automatic activation but preferably the latter). Same response as above.
• Production cards for pacemaker processes are placed in a “launcher” rack, in FIFO sequence. The launcher should have green-yellow-red zones reflecting the amount in WIP and any time a kanban reaches into the yellow zone, the Team Leader is alerted. If it reaches the red zone, an andon is triggered, with the same response as described above. 

 

What’s next?

A milk run is nothing more than a standardization of transport. Since transport is non-value-added, but essential, the goal is to constantly work to reduce the waste of transport.

 

The goal with a milk run is to reduce the pitch time.

 

A shorter pitch doesn’t just reduce lead time, inventory and production footprint; it also means that we’re able to deal with problems and get back to normal faster.

 

Problems will always occur. If the deviation isn’t dealt with, it will show up as an abnormality when the milk run can’t match a kanban to a container, or kanban cards places in the launcher reach the red zone, or the tug train is delayed.

 

If you have an hour-long pitch, there are many problems that don’t cause abnormalities, because the team is able to resorb the deviation before any of these “triggers” occur.

 

With shorter pitches, that’s not possible and the smaller problems will trigger andons.

 

In other words, reducing the pitch time is a way to increase the system’s “sensitivity."

Need help implementing Milk Run? Contact the Lean Center of Excellence! 

Fill out this quick form and we'll get back to you within a couple of days with more information on how you can implement Milk Run on the shop floor.