Sorry. I’m a bit of a master planning grove with posts this week, but I’ve just been working on an issue with a nice little ‘gotcha’ in it, and as it’s the second time I’ve come across this particular master planning wrinkle I’m putting in out there in the hope that it’ll save you some time and frustration.
On the Item coverage record you can see the Freeze time fence:
It’s inherited from the item’s coverage group:
The help text says: “Specify the period during which planned orders cannot be created. You also use this field to specify where planned orders from previous requirement calculations cannot be changed. All requirements that are not covered in this period are covered by a purchase order or a production order that is created at the end of the period, together with an action message that suggests advancing the date of the planned order. During the period, if an earlier requirement calculation created a planned purchase order, that order remains in the period and is not moved. The time fence is expressed in days, and it is calculated from the requirement calculation date.”
Now there’s nothing wrong with that help text, it’s an accurate definition of the freeze time fence, but I feel that it has a lot a traps for the unwary hidden in it.
Let’s un-pick it bit by bit. First: “Specify the period during which planned orders cannot be created.” Great. That’s exactly what we want. A frozen period inside which master planning not going to be messing up my production plan by creating planned orders – or creating planned purchase orders that my vendors don’t have a hope of supplying.
We meet production plants where the production schedule for the next two weeks is ‘Frozen’. (Know the old joke about frozen plans? They melt when you increase the pressure). Obviously you use set the Freeze time fence and then you won’t get planned orders in your Frozen period. Right?
Carry on reading the help text: “You also use this field to specify where planned orders from previous requirement calculations cannot be changed.” Oh well that doesn’t sound so bad – who changes planned orders anyway? Carry on: “…if an earlier requirement calculation created a planned purchase order, that order remains in the period and is not moved“. So we read the words ‘can’t be changed’ and ‘is not moved’ but never see outright “is not deleted“.
Everyone knows (well everyone reading this sort of blog anyway) that when you run master planning you can use ‘Regeneration’ or ‘Net change’:
Although if you’re updating the Static master plan you always use ‘Regeneration’. ‘Regeneration’ is a full calculation from first principles, and the first thing that master planning does is to delete all existing planned orders. Except that there are two important exceptions to that rule which are easy to overlook: master planning deletes all existing planned orders except ‘Approved’ planned orders; and planned orders within the freeze time fence”.
Here’s how this goes. It’s the 1st March. I have a Freeze time fence of 14 days and a sales forecast. Run master planning:
Just like is says on the tin. My forecast demand is within the Freeze time fence. My planned order is created at the edge of my Freeze time fence with an Action advance message, and just for good measure my forecast gets a futures message (because the supply it’s pegged to is going to deliver late).
Now move forward one day to the 2nd March, and re-run master planning:
That’s a nasty surprise. The demand has changed. In this case it’s disappeared because master planning ignores past due demand forecasts. But the planned order is still there, because now it’s inside the Freeze time fence and isn’t deleted. These planned orders within the Freeze time fence aren’t even deleted if you run ‘Delete plan’.
The best clue to what’s going on is that the planned order number hasn’t changed when you re-planned. That’s subtle, but quite noticeable when you’re tuned into this.
In an ideal world of course you wouldn’t get yourselves into this situation – you would have firmed all of your planned orders or re-set the demand forecast/safety stock/sales orders or other demands. But a couple of times now I’ve seen busy planners caught out by this. They just never got around to firming all the planned orders on all their items, and some planned orders ‘crept’ into the Freeze time fence, and then confused the heck out everyone when they did finally notice them.
My advice is not to use the Freeze time fence, but if you do, be very wary of this feature. Be aware of your planned order numbers (so that you can spot the ‘old’ ones) – or as we did for another customer, create a customisation that deletes them.