SAPTechno

Note 517898 - PP: Standard methods for safety stock planning

Header
Version / Date 6 / 2003-08-06
Priority Recommendations/additional info
Category Consulting
Primary Component SCM-APO-PPS Production Planning and Detailed Scheduling
Secondary Components SCM-APO-PPS-HEU-PP PP Heuristics

Summary
Symptom

This note explains the standard methods SB, SZ, SM, MB, MZ and MM for the safety stock planning and safety days' supply planning as part of production planning.

Other terms

Production planning run, MRP, planning with standard lot sizes, heuristic, lot-size calculation, safety stock, safety days' supply, documentation, product heuristic

Reason and Prerequisites

Planning with a safety days' supply or safety stock.

Solution

1. Introduction

Safety stocks protect the logistics chain on the stock side from unstable influencing factors such as customer demand and replenishment lead time. In production planning, you have the option to define a safety stock method ("lot size" tab) in the product master for each location product.

In the case of standard methods, the planner must directly specify the information required to determine the safety stock.However, in the case of the enhanced methods, the safety stock is automatically (and fully) determined on the basis of the service level, the current requirements forecast and historical data.

The following standard methods are available:

  • SB - Safety stock from the location product master
  • SZ - Safety days' supply from the location product master
  • SM - Maximum of SB and SZ from the location product master
  • MB - Safety stock (time-dependent maintenance)
  • MZ - Safety days' supply (time-dependent maintenance)
  • MM - Maximum of SB and SZ (time-dependent maintenance)


SB, SZ and SM are static methods whose parameters are defined as time-independent in the location product master ("lot size" tab). MB, MZ and MM are dynamic methods whose parameters are defined as time-dependent, that is, they are defined during the SNP safety stock planning.The parameters for the dynamic methods are not maintained in Production Planning as a result. For more information, see note 504253 'SNP:Standard methods of the safety stock planning'.

2. Executing the standard methods during planning

The standard methods of the safety stock planning are used when you plan with heuristics that create receipts.

The planning methods for immediate automatic planning (APO 3.0a), or covering dependent requirements (APO 3.1, SCM 4.0 and higher) do not take safety stock methods into account. For more information, see note 413822 'Safety stock with automatic planning immediately'.

3. Static methods
  • SB - Safety stock from the location product master:


This method is used in PP if the 'safety stock' and the 'SB method' fields are maintained in the location product master.In addition, you must determine that the safety stock in PP/DS planning is considered in the 'PP/DS:Consider safety stock' field in the model/planning version administrator in the planning version.

The safety stock is the quantity that should meet unforeseeable high requirements in a coverage period.The task of the safety stock is to reduce the risk of shortfall quantities being created.

Technical execution

The safety stock is interpreted as a requirement (category EISBE for "safety stock").To cover the requirements, planning creates a planned order to the value of the safety stock.The start time of the planned order is the current time if the strategy settings permit this.The system does not consider the offset from the strategy settings.

If required, resource capacities are considered for the corresponding strategy when orders are created.An overcoverage alert may be generated during the safety stock planning. For more information, see note 374624 'APO overcoverage alerts for safety stock'.

  • SZ - Safety days' supply from the location product master:


The maintenance of the 'Safety days' supply' and 'SB method' fields is a prerequisite for considering this standard method.You must select SZ as an SB method.

The safety days' supply is the number of workdays between the availability date of an receipt element that has to be created and the requirements date of a requirements element.

Unlike the SAP R/3 system where you can only define complete days as a safety days' supply, you can also specify parts of days in APO.Two decimal places are permitted.For example, you can specify 0.5 days for 12 hours or 0.33 days for approximately 8 hours (more specifically, 7 hrs 55 mins 12 secs).(One workday corresponds to 24 hours.)

Scheduling is based on the production calendar from the location.

Technical execution

During planning, the requirements elements are virtually postponed by the safety days' supply into the past.This new situation is a basis for order generation.

Periodic lot sizes are based on the original requirements dates, that is, the safety days' supply is not used for the delivery scheduling of requirements to the periods.However, the generated replenishment element is postponed by the safety days' supply.

On the other hand, the safety days' supply is already considered when requirements (or requirements polygonal receipt segments) are allocated periods for technical reasons when you plan with continuous requirements.

  • SM - Maximum of SB and SZ from the location product master:


The SB and SZ procedures are executed (a "maximum" is not created for either procedure) for this safety stock method during PP/DS planning.As a result, you also have to maintain the 'safety stock' and 'safety days' supply' fields, in addition to the SB method, as a prerequisite for executing the method.

Technical execution

Technically, the safety stock is determined first and then the safety days' supply is considered since the safety stock should also be postponed by the safety days' supply.

4. Dynamic methods


Period-related safety days' supply and safety stocks are analyzed for dynamic methods. This data is displayed in the SNP as key figures.In PP/DS, the dynamic methods can only access these key figures if you have specified the SNP planning area, which contains the key figures, in the Customizing of the Production Planning and Detailed Scheduling under "Maintain global parameters and default values".For information on how to maintain parameters which are a basis for the dynamic methods, see note 504253 'SNP:Standard methods of the safety stock planning'.

  • MB - Safety stock (time-dependent maintenance):


The safety stock is determined in the same way as the SB method, however, the difference is that the period-dependent value is used instead of the "safety stock" field from the location master data.

Technical execution

If the dynamic safety stock in a period is larger than the dynamic safety stock in the previous period, virtual requirements, which represent the difference quantity, are generated.These requirements are covered by a corresponding receipt element in the planning run.

If the dynamic safety stock is smaller from one period to the next, fewer receipt elements are created (which correspond to the difference quantity) for requirements elements that have a smaller safety stock in the period.In the product view, you can see that the affected requirements are partially covered from the excess safety stock.

  • MZ - Safety days' supply (time-dependent maintenance):


The safety stock is determined in the same way as the SZ method where the period-dependent safety days' supply is used rather than the safety days' supply from the location product master.

Technical execution

The execution is the same as that for the SZ method, the only difference is that the requirements of a period are moved with the period-dependent safety days' supply.

  • MM - Maximum of MB and MZ (time-dependent maintenance):


The MB and MZ procedures are performed in quick succession and in the same way as the SM safety stock method.

Technical execution

In PP/DS planning, the MB method is considered first and then the MZ method.

Affected Releases
Software Component Release From Release To Release And subsequent
SAP_APO3030A30A
SAP_APO310310310
SCM400400400X
SCM410410410

Related Notes
761872No transfer of SNP safety stock to PPDS
504253SNP: Standard Methods of Safety Stock Planning
441102Consulting notes in PP/DS
413822Safety stock in APO PP/DS (documentation)
374624APO overcoverage alerts for safety stock