MD04 and rescheduling date

Question

Hi,
This is my scenario:
Material A is composed by material B. When the stock of material B is 0, MD04 does not take in account the time to provisioning Material B when a Material A has to be produced.
Example:
Time to create Material A: 3 days. Created using a Purchase Requisition (subcontracting).
Time to provisioning Material B: 6 days.
MD04 (for Material A) always shows 3 days (today3days), never mind if the quantity of material B in our warehouse is 0 (in this case should be: today6days3days, but always is today3). Maybe the problem is the rescheduling date at MD04 (always is today, not today+6days)? 
What do I have to modify? (Maybe master material?)
Thanks in advance,
Ricard.

Answer 1

Ricard,
Means that MD41 creates a Purchase Requisition of Material A independently of the availability of Material B
Ah, we are talking about MD41, not MD04.  MD41 is a version of MRP (well, technically it is an MPS, but in this case it makes no difference).  SAP MRP in ERP does NOT perform availability checking.  The behavior your are describing is normal.
MRP/MPS in SAP runs level by level, from the top level of the BOM down.  When MRP runs for 'A', it has no information about the availability of 'B'.   When you are making a mulitlevel run (such as during MD41),  MRP runs for A, finishes, creates and saves the PlndOrdr/PurReq for A, and then runs for B. During the run for 'B', MRP performs a net requirements calculation (NOT an ATP).  This is when MRP discovers that there is a shortage of B.  It creates its proposals for B, and also creates any required exception message(s). 
You can configure SAP to perform an ATP check for the components of Planned orders and Purchase Reqs.  You can then execute the availability check individually (when you create/change the order manually) or you can set up a collective check.  None of these ATP checks are triggered by MRP.  The typical output of an ATP check is a Missing Parts List, and whether the quantity/date can be confirmed as it stands.  Neither will these checks automatically re-schedule an existing Purchase req.
Some companies choose to include the procurement time for B in their procurement time for A.  In your example, you would use 40 days procurement time for 'A'.  In this way you are never caught short.  However, this drives up stock levels of B (B will be procured earlier than required).  Some other companies place safety stock in B, and then assume that B will always be available.  Still other companies will manually juggle 'A' PurReq according to the availability of B.  Take your pick.
SCM has the ability to perform Multilevel availability checks, and thereby automatically produce schedules which reflect true availability of all components in the entire BOM.  SCM also offers a heuristic (similar to MRP) that performs bottom-up scheduling, in which the procurement proposals are run from the lowest level of the BOM upward, automatically resulting in a plan that has no material shortages.  ERP lacks both of these features.  If this is a requirement, consider changing your planning engine to SCM.
Rgds,
DB49