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Relevant Training Course / In-house Workshop Highlights:

M01 Designing, Implementing and Operating Kanban Systems

(The A-Z guide to Kanban)

SSC04 Production Planning and Control Back to Basics (Provides a detailed task list to simplify your processes)

The following training course provides a comprehensive introduction to materials planning & control & the options available:

M24 Materials Management & Stock Control (includes SSC02 below)

SSC02 Materials Control Process Selection (provides an introduction to all 28 types of Planning & Control (Push / Pull) Systems & how to choose one)

Expert Systems / Tools:

Diagnosing Manufacturing Control Problems

Relevant Further Reading: The following further articles were mentioned in this paper:

a. Permanently Maintained Website Articles:

Kanban Systems

Kanban Accumulator system

2 bin system

b. Previously Featured Articles from our Archives (Up to 2 per organisation available on request):

Previous Best Practices:

B009: Visibility of problems through simple and clear processes

B029: Bin Discipline (Labelling, counting, stock rotation, decanting and consolidation)

B035: Out tray Management

Previous Techniques:

T010: 2 Bin Systems

Previous Questions:

Q001: Managing "C" class items in a deliver to point-of-use situation

Previous Malpractices:

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Question 28: How do I handle partial Kanban quantities in shortage situations? (Kanban System Design)

For example. An empty storage bin travels to the storeroom for a parts replenishment of 10 pieces. It is only possible to fill the bin with 5 pieces due to lack of inventory in the storeroom. Would one solution be:

Send the bin back with 5 pieces and apply the other 5 to a shortage list? Or.. Hold the bin and wait for a shipment to arrive, then fill the bin to the appropriate quantity and return to the point of use location?

This is based on a 2 week, two bin supply, at the point of use. If all is working correctly the second full bin that has been pulled forward, at the point of use can be relied upon until the first bin makes its way back to the point of use.

Any suggestions appreciated... (name and address supplied)

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Answer

Hello ...

The default position is to only replenish Kanbans fully and solve the supply problem, however there are four key Kanban system design criteria at work here:

Type of Kanban system?
The Kanban population size in total? (In your example 20.)
The transfer batch size (How many items per Kanban)? (In your example 10.)
The signal mechanism?

Taking each in turn:

The system you have described is in fact a 2 bin system which predates Kanban systems by millennia. (But I will come back to this later.)
1. If there is one storeroom & to one point-of-use for this item, in the short term, I would send the 5 available rather than risk stopping the downstream process due to a shortage. (In fact ultimately deliver direct to point-of-use bypassing the storeroom.) (See B035: Out Tray Management & Q001 Managing "C" class items in a deliver to point-of-use situation) (This means that the system will cycle more quickly than your designed average one week interval, which you can easily monitor in a low administration way.) (See B009 Visibility of problems through simple and clear processes)
2. However if this is one storeroom feeding several points-of-use for a common item, I would suggest sending only full Kanban quantities. (You will also need a priority signalling system to tell the storeroom which is most urgent, such as provided in the "Kanban Accumulator" system) (Also see transfer batch size in paragraph 3.)
Your last sentence suggests that the that 20 items in the Kanban population plus storeroom stock is inadequate! (We provide a Kanban population calculator in our Kanban training and we will cover this in a future article.) Meanwhile you may need to increase the storeroom stock temporarily to protect your consuming process (& Kanban system) from this. The root cause of your problem is lack of availability. This needs further investigation. In addition, any shortages (inability to honour pull signals) should always trigger expediting activity and a review of the system design parameters. Kanban systems are not "fit and forget", (a common fallacy). You could also add the storeroom stock to your Kanban system and send resupply signals from this enlarged system directly upstream to the storeroom supplier, which might help stabilise supply.
However the main thrust of your question is about how many items per Kanban. Conventional wisdom suggests that a container size = a Kanban quantity. However this is only one option! We would normally suggest that the transfer quantity should be the minimum that any logistics constraints will allow (if necessary reducing container sizes). (Ultimately "single piece flow".) (You could start by halving your current transfer batch size, making 4 bins containing 5 items, rather than 2 bins containing 10.) (Converting this 2 bin system into a Kanban system.) For example an average consumption of 20 per 2 weeks = 2 per day (assuming a 5 day week). By reducing transfer batch size from 10 to say 5 you are delivering to point-of-use (& identifying storeroom shortages) twice as often & 2½ days earlier & reducing the risk of storeroom failure to service Kanban requests in full by about half. Also by doing this and assuming the Kanban cycle time & Kanban population remain the same, the buffer available at the point-of-use increases from an average of 5 with a minimum buffer of zero to an average of 7½ with a minimum buffer of 5, significantly reducing the risk of process stoppages. (I used "hand simulation" to calculate this, which we cover in our Kanban & scheduling training and we will cover in a future article.) Another way of expressing this, is that the minimum buffer of 5 could be removed from the Kanban population and held in the storeroom, or if it makes strategic sense, removed from the system completely if the supply problem was solved.
I think you are assuming that the empty container is in fact the signal to replenish. Although a common method, which has some other potential benefits, it does not have to be and in one rescue situation we have been involved in, the empty bins were being misappropriated or delayed, causing the shortages! (See B029 Bin Discipline (Labelling, counting, stock rotation, decanting and consolidation)

Also I would suggest you read the additional articles following the links on the left.

I hope this helps?

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