MRP Calculations

I have item A, manufactured from C & D, Item C is Manufactured from E. I have stock of D and E. The routing for A is for work-centre1 setup to 24hrs run time, and for C work-centre2 for 8hr run time. Each work-centre is setup for an 8 hr day with 7 day working week. For a sales order item a qty 1, I was expecting capable to promise to suggest 4 days hence. but it suggests 3. My production order for C starts day1 8:00 finishes 16:00, but my production order for A also starts day1 8:00. I was expecting that A couldn’t start until C was complete. In effect the production orders for A & C are starting at the same time. This is standard 3.60 with HF29. MRP seems to be really fragile. Yes it works but sometimes the calculations seem impossible to comprehend. Any help appreciated.

Hi Navicons I will presume you are not using routing link codes. What is your flushing method? Backward? If this is the case you need Item C at the completion of A. If you used rouing link codes (probably - I would need to check this[:D]) or altered the flushing to forward you would get the scenario you are looking for!


MRP seems to be really fragile

It only does what you tell it too! [:D]

Hi Steven, No there are no routing link codes. I wouldn’t have expected the flushing methods to come into the calculation for ATP. I’ve always thought of flushing methods being important when a production order is released or completed, or with RLC at the appropriate stage in the routing. Do flushing methods really effect the calculation of CTP in S&R ?

Hi Navicons I have not tested this nor am I a developer so I would fail to understand the code, but for CTP to work correctly it must take flushing methods and RLC’s into account to correctly. I believe from earlier recollections the critical field has to be ticked on the item card to plan in this manner, but essentially if you have BOM’s within BOM’s and flushing is not taken into consideration then the planned fulfillment date will be wrong.

Hi Steven, I can understand the logic, If A takes 3 weeks to manufacture from C & D, if C & D take 3 weeks to purchase, and C is used in week 1 and D in week 3, then clearly I don’t need to puchase D until later. I’ll try forward flushing and let you know. You’re right about the critical field, on the component rather than the item.

Hi Navicons, The thing is you have to define the A Item as a Make To Order item to make Navision run properly but if you launch another PO for the A item, Navision will probably plan both at the same time. We have a finite capacity scheduling to avoid this problem and it will improve work planning and load distribution. Please visit our web at to see how it works, there is a downloadable demo version. Best regards, Susana

sorry, i forget to put the name !! the FCS

Hi Susana, Yes you are right Item A should have a manufacturing policy of make to Order, Item C being a sub-assembly I have as make to stock. Navision did plan both production orders to start at the same time, and equally you can end up with work centres overloaded. However CRP capacity constrained resources prevents this from happening. It’s all working fine now, but the data setup is not exactly obvious. And I think we’ll spend hours supporting it when it goes live, because our users won’t fully understand it. I think its just a little easier in 3.70. Thanks for the info on your product. Best Regards, Navicons.