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Shop Order Requisition Start Date Issue

  • 14 September 2020
  • 5 replies
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We have a problem with Shop Order requisition due dates relative to shop order start dates that result from a MRP run. If our order quantity is 1, the manufacturing lead-time is 5, and the due date is 09/25/2020 then the start date will be 09/24/2020; why is it not offset 5 days?  Should be offset by the fixed manufacturing lead-time. If we change the order quantity to 10, then the start date is offset by 10 days and is 9/15/2020; this is not good.  We want to use “standard practice” where the lead-time offset is not affected by the order quantity size.

 

Can anyone please help with this?

 

EDM

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Best answer by majose 15 September 2020, 19:43

Hi again,

I just double checked the server code in Apps10 right now, and I know it is the same logic in Apps9. 

In the heart of the MRP, when the engine is creating shop order requisitions, (yes it happens in “main MRP step” these days) system gets hold of the Routing for the part, and it uses the information that you have in Routing screen. Using the lead time information in the tab Routings,  in the mid-portion of the screen. To be more precise, MRP logic uses the Fixed By Day and the Variable by Day fields. The Variable by Day is multiplied with the Shop Order Req Qty. The start date of the Shop Order Req is basically calculated like this: Required Date - (Fixed Lead Time per Day + Variable Lead Time per Day * Shop Order Req Qty). Please note that we are talking manufacturing calendar days here, so I simplified the equation a bit, to make it more readable.

Only if the expression (Fixed Lead Time per Day + Variable Lead Time per Day * Shop Order Req Qty) is 0,  THEN it goes for the manufacturing lead time on the Inventory Part screen.

Then you can always customize this, but it is a bit scary.

 

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Userlevel 2
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I have a dataset with following details, made some tweaks and ran your flow.

  1. Manufactured part with one component
  2. Routing has 1 operation, MRF=40h, work center average capacity=8h  (site manuf calendar, all work center calendars are 24*7)
  3. Routing made buildable, lead time calculated and updated on routing alternate
  4. Also run cumulative lead time calculation with update setting on
    (if everything is fine upto this point, manufacturing tab in inventory part shows cumulative lead time and manufacturing lead time as 5)
  5. Material requisition for top part due on Next Friday +10 days (a Monday)
  6. Ran MRP

Created SOR has SO start date as Next Friday+5 days (a Wednesday) which is 5 days apart from due date

 

So the calculation is done correctly. I however, did not quite understand “problem with Shop Order requisition due dates relative to shop order start dates” but i assumed we’re talking about SOR due dates and start dates. My pointers are,

  • check calendars
  • check work center average capacity
  • check whether ‘Manufacturing Lead Time Calculation’ and ‘Cumulative Lead Time Calculation’ (good practice for all scenarios) are run with update setting

 

Userlevel 2
Badge +3

Hi!

In the beginning of year 2000 we introduced lot sized lead times in MRP calculation based on customer feedback. Customers with a significant run time in their part routing setup, with lot sizes that could vary quite a lot, asked for this.

Nevertheless we hear from time to time customer who are asking for a fixed lead time when setting the start dates in the MRP explosion! I guess it becomes more predictible.

Some other ERP vendors just use the fixed lead time. And there are DDMRP-gurus out there, who complains about “the old-fashioned MRP logic” that uses fixed lead times in the MRP explosion…not good... So there are different oppions. I am not saying anything is wrong. There are too many hard-core lean advocates and old-fashioned MRP scouts out there, that thinks they own the truth. Perhaps you should log a case with as much description as possible.

Userlevel 1
Badge +2

A point of note: When you calculate the lead time from a routing, the resulting lead time is stored in the “Manufacturing Lead Time” field on the Inventory Part screen, acquisition tab. MRP uses the lead time shown in that field. It’s possible to manually enter a lead time directly into that field, rather than doing the calculation from the routing if you prefer.

Userlevel 2
Badge +3

Hi again,

I just double checked the server code in Apps10 right now, and I know it is the same logic in Apps9. 

In the heart of the MRP, when the engine is creating shop order requisitions, (yes it happens in “main MRP step” these days) system gets hold of the Routing for the part, and it uses the information that you have in Routing screen. Using the lead time information in the tab Routings,  in the mid-portion of the screen. To be more precise, MRP logic uses the Fixed By Day and the Variable by Day fields. The Variable by Day is multiplied with the Shop Order Req Qty. The start date of the Shop Order Req is basically calculated like this: Required Date - (Fixed Lead Time per Day + Variable Lead Time per Day * Shop Order Req Qty). Please note that we are talking manufacturing calendar days here, so I simplified the equation a bit, to make it more readable.

Only if the expression (Fixed Lead Time per Day + Variable Lead Time per Day * Shop Order Req Qty) is 0,  THEN it goes for the manufacturing lead time on the Inventory Part screen.

Then you can always customize this, but it is a bit scary.

 

Badge +1

Thank you all for your responses! 

What I’m understanding is there is no fixed manufacturing lead time field that factors into MRP. For instance, the Supplier Manufacturing Lead Time field on the Supplier for Purchase Part screens provides MRP with a fixed lead time for that part. It appears that manufactured parts do not have this option, as everything is calculated from the routing. Is this accurate?

 

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