MRP Procedure Types, Lot-Sizing Procedures, and Planning Run Execution

Explanation

MRP is only as good as the master data logic that feeds it. Three material master fields drive the core planning behavior for every material: MRP type (in the MRP1 view), lot-sizing procedure (MRP1), and procurement type (MRP2). The MRP type determines whether the system runs deterministic MRP (based on actual requirements such as sales orders and dependent demand), reorder point planning (triggered when stock falls below a threshold), or forecast-based planning (using consumption-based forecast values). Deterministic MRP, configured typically as PD, is the most common in discrete and process manufacturing because it reacts directly to demand rather than statistical consumption patterns. Lot-sizing procedure controls how the system bundles net requirements into planned order or purchase requisition quantities. Static lot-sizing (for example, fixed lot size or replenishment up to maximum stock level) creates orders in fixed quantities or replenishes to a target level regardless of demand pattern. Periodic lot-sizing (daily, weekly, monthly lot size) groups all requirements within a time bucket into a single order — useful for reducing order frequency but risking overstock if demand is lumpy. Optimizing lot-sizing procedures (such as least unit cost or part period balancing) calculate an economically optimal order quantity by balancing setup/ordering costs against carrying costs; these require additional cost master data (storage costs percentage, order costs) maintained in the plant/material master or costing views and are less commonly used because they add planning complexity that many project teams avoid unless there is a clear TCO justification. Procurement type (MRP2 view) tells the system whether the material is produced in-house (E), externally procured (F), or both (X, allowing the planner to choose per requirement). This determines whether MRP creates planned orders (converted later to production/process orders) or purchase requisitions (converted to purchase orders). Special procurement keys (also MRP2) override or refine this — for example, indicating subcontracting, stock transfer between plants, or procurement from an alternative plant, which changes both the object created and the BOM/routing sourced. During the planning run itself (executed at plant, MRP area, or multi-plant scope depending on configuration), the system nets available stock and firmed receipts against gross requirements, then explodes the resulting net requirement through lot-sizing rules to generate a procurement proposal, and finally explodes the BOM (for in-house produced materials) to generate dependent requirements at the next BOM level down. This low-level code-driven explosion ensures materials are planned in the correct sequence — components are only planned after their parent assemblies. Planning horizon, planning time fence, and firming logic (via order and requirements type settings) protect near-term production from being disrupted by minor demand changes, which is critical in make-to-stock environments with short lead times. In S/4HANA, MRP Live (executed via a dedicated MRP Live cockpit or transaction) replaces the classical background job architecture with an in-memory, multi-threaded calculation that reads and writes directly against the database using optimized ABAP/HANA logic, dramatically reducing runtime for large material scopes. Functionally the lot-sizing and procurement logic described above is unchanged, but the operational behavior — such as how planning results are made visible on the stock/requirements list in near real time and how the run can be scoped — differs from classic MRP (MD01/MD02-equivalent processing), and project teams migrating from ECC must revalidate planning file entry maintenance and any custom exits tied to the classical run.

Code example

* Illustrative MRP master data check via material master fields* (conceptual, not a real transaction sequence) Material: 100-100Plant: 1000MRP1 view:  MRP Type = PD   (deterministic MRP)  Lot size  = EX  (lot-for-lot / exact requirements)MRP2 view:  Procurement type = E (in-house production)  Special procurement = blank  Planned delivery time = 0 (in-house, uses in-house production time)  In-house production time = 3 days * Expected planning behavior:* - Net requirement of 500 pieces on day X* - Lot size EX -> single planned order for exactly 500 pieces* - Planned order start date = day X minus 3 working days* - BOM explosion creates dependent requirements for components*   dated at the planned order start date (backward scheduling)

Real project scenario

A discrete manufacturer using lot-for-lot (EX) lot sizing for a high-runner subassembly found planned orders were being created almost daily in very small quantities, overwhelming the shop floor with excessive small production orders. The planning team analyzed demand patterns and switched the material to a weekly lot-sizing procedure (WB) after confirming with production control that batching demand into weekly buckets would not violate customer delivery commitments, cutting order volume by roughly 70 percent while keeping schedule adherence within acceptable limits.

Common mistakes

• Assuming lot-sizing procedure changes take effect retroactively on already-created planned orders instead of only future planning runs. • Using optimizing lot-sizing procedures without maintaining accurate storage and order cost master data, producing meaningless order quantities. • Setting procurement type X (both) without also maintaining a clear source list or quota arrangement, leading to inconsistent make-or-buy decisions per run. • Ignoring special procurement key implications when a material is subcontracted or stock-transferred, resulting in the wrong document type being proposed. • Not distinguishing MRP Live scope and parallelization settings from classic MRP job variants when troubleshooting differing results in S/4HANA.

Best practices

• Align lot-sizing procedure selection with actual demand volatility and shop floor capacity constraints, not just planner convenience. • Document special procurement key usage per material category so procurement and production teams understand deviations from standard in-house/external logic. • Validate in-house production time and planned delivery time against actual lead times using historical order data rather than static estimates. • When migrating to S/4HANA MRP Live, run parallel comparisons against classic MRP results for a representative material scope before cutover. • Periodically review MRP type assignments as product lifecycle stage changes (e.g., moving a mature product from PD to reorder point planning if demand stabilizes).

Interview angle

Interviewers commonly probe whether a candidate understands the practical trade-offs between static, periodic, and optimizing lot-sizing procedures, and can explain how MRP type and procurement type together determine whether a planned order or purchase requisition results. Be ready to describe a real scenario where you changed lot-sizing to solve an operational pain point, and to explain the functional (not just technical) difference between MRP Live and classic MRP.