Article 39 - How MRP Runs

Article 39 - How MRP Runs


Article 39: How does the MRP run process work step-by-step?

What happens during an MRP run?

The MRP run is a systematic calculation process that evaluates each material individually to determine if procurement action is needed. It follows a logical sequence to analyze supply, demand, and generate proposals.

What are the key MRP calculation steps?

Step 1: Collect Scheduled Receipts

What are scheduled receipts?

  • Existing purchase orders not yet delivered
  • Production orders currently in process
  • Firmed planned orders confirmed by planners
  • Stock transfers already initiated

Step 2: Identify Requirements

What are requirements?

  • Sales orders with delivery dates
  • Planned independent requirements (forecasts)
  • Dependent requirements from higher-level BOMs
  • Safety stock maintained as buffer
  • Pipeline requirements for distribution

Step 3: Calculate Available Stock

Formula: Current Stock + Scheduled Receipts - Requirements = Available Stock

If Available Stock is:

  • Positive: No action needed (sufficient stock)
  • Negative: Shortage exists, procurement proposal needed

Step 4: Generate Procurement Proposals

Based on procurement type:

  • "F" (External): Creates purchase requisition
  • "E" (In-house): Creates planned production order
  • "X" (Both): System chooses based on lot size and lead times

How does lot sizing affect proposals?

Lot Size Type

Code

How It Works

Example

Fixed Lot Size

FX

Always orders fixed quantity

Need 50, lot size 100 → Order 100

Lot-for-Lot

EX

Orders exact requirement

Need 50 → Order 50

Replenish to Max

HB

Orders up to maximum level

Max 1000, current 200, need 50 → Order 850


What timing does MRP use?

  • Requirements date - when material is needed
  • Procurement lead time - how long to get material
  • Proposal date - when to start procurement action
  • Safety lead time - additional buffer time

How often should MRP run?

Frequency options:

  • Daily - for high-volume, fast-moving items
  • Weekly - for standard materials with stable demand
  • Monthly - for slow-moving or seasonal items
  • Event-driven - triggered by significant demand changes



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