[原创]Can A Part be Pulled and Pushed Simultaneously

A well managed electronic kanban system with suppliers may greatly facilitate the procurement processes of a company. For more details, readers may refer to my previous blog of Introduction to Electronic Kanban Systems. However, this simple system may create confusions in the company, especially when its main business activities are deeply shaped by traditional push systems like most mainstream ERP systems (This doesn’t imply that push systems can’t coexist with pull systems). In most cases, the confusions are related to this question: Can parts be pulled and pushed simultaneously?

 

Well, the question seems to be a silly one. And everyone will answer “NO” without any hesitation. Nevertheless, let’s have a look at the following story.

 

In Superb Company Materials Manager Johnson noticed that Buyer Apple complained a lot about the lousy Electronic Kanban System introduced recently: in order to avoid the coming material shortages she always had to pull in deliveries for those kanban parts purchased from Supplier Metal International instead of simply following the messages generated by the electronic kanban system. Were those parts purchased from Supplier Metal International not suitable for kanban? All of them were small, common metal parts with short lead times used in most of the products manufactured by Superb, and their requirements were relatively stable. In short, all of them should be perfect kanban parts. A further investigation showed that the kanban formulas for those metal parts were set up properly. What’s going wrong here?

 

Johnson had a look at the on hand stocks of those metal parts. To his surprise, most of them were actually much more than what was required, for those on hand stocks were sufficient enough to cover the expected consumption until the next scheduled ship dates considering the average daily consumption rate. some of those on hand stock even covered too many buffers. MBW (management by walking) was Johnson’s style. He went to the shop floor and asked the production supervisor and the planner. All of them confirmed that the supply of metal parts from Metal International was generally in a good shape. Nothing went wrong so far, though they frequently urged Apple to prepare those materials in advance to avoid possible material shortages.

 

A detailed talk with Buyer Apple revealed such a fact: Apple had in fact asked Supplier Metal International to stop reacting to messages generated by the electronic kanban system. Instead, she frequently called and emailed Supplier Metal International to ship those parts in quantities and dates that were suggested by the material shortage reports generated by the ERP system. This was because the ERP generated material shortage reports combined the weekly requirements of a specific part and urged her that a specific quantity of that metal part must be available on a specific date (Here come two assumptions: in the ERP system there exists a planning parameter called something like “number of days of supply” that controls how long a delivery of a part may cover; and the upfront kitting method is adopted in Superb Company). Besides, kitting transactions were not always performed in time in the ERP system, which made the consumption information uploaded into the kanban system a bit twisted and thus unreliable.

 

After this talk with Apple, Johnson realized that he had overlooked this important issue: a part can’t be pulled and pushed at the same time. To be more specific, once the electronic kanban system (a pull system) is introduced in an ERP dominated environment (a pull system), some modifications to the ERP system are necessary. Otherwise, the ERP system will definitely generate some misleading messages. However, the most important lesson is “general kanban training is not enough”, concrete examples must be provided to clearly demonstrate to his team what “consumption driven” really means. He should have made clear the following points:

l         Once a part is driven by the kanban system, ERP generated messages are longer appropriate

l         Some mechanism must be established to guide his team to go through the transition period with the aim to build confidence when old (potential) material shortage reports are not used and the new replenishment by consumption is introduced.

l         All transactions in the whole process (the replenishment cycle in this case) must be closely linked together and are timely and faithfully reflected by the ERP system

l         Daily consumption average should be used to judge how long the current how long the current on hand stock may last.

l         The bigger the delivery frequency, the less on hand stock qty is needed

l         The faster the consumption rate, the faster the delivery speed

l         In any cases, it’s abnormal if nearly all kanban numbers are in either Superb’s premises or in either the supplier’s premises, something must be wrong.

 

At last but not least, when some non value added activities are eliminated, the whole process becomes lean meaning each part links closely with one another just like numerous rings made upon a chain. If one ring becomes loose, say, consumption transactions are not entered into the ERP system in a timely manner; this might halt the whole chain. Ironically, in some cases wastes seems to have created a safer (though more costly) operations environment for us and most of us are too comfortable with it to notice this. It’s the other side of the coin.

 

In short, the small case helps us understand why people claim that pull systems are simpler but more demanding; it also supports the statement that lean is an operations philosophy , it’s not just a set of tools.

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