MRP Mechanics–The Basics


· 3 functions

1. Plans and controls inventories

2. Plans and controls order releases

3. Provides accurate planned order loading for CRP

Design Characteristics

· Planning Horizon

o At least as long as the longest cumulative lead time item

· Time Buckets

· Replanning Frequency

o MRP Nervousness: rapid, small requirements changes that cause material plan to change back and forth…disrupts planners, vendors, and floor.

· Firm Planned Orders

o Reduces/suppresses MRP nervousness

o Firm means the planner can’t alter due date, release date, and planned order quantity

· Pegging

Mechanics of MRP


· Material balance needs

o What

o When

o How much

· Material and Capacity Plan

· Maintaining Plan

· Manual MRP

Gross Requirements: quantities that must be issued to support a parent order or orders

Filling in an MRP Grid

1. Gross requirements from Master Schedule (independent demand)

2. Gross requirements from service-part demand (independent demand)

3. Inventory Data

a. Factors: lot size, lead time, safety stock

b. Stataus data: On-hand, allocated, scheduled receipts

c. Where does inventory data come from? The item (part) master record

4. Net Requirements and Planned Orders for low-level code 0

a. Gross Requirements + Allocations – Scheduled Receipts – Projected Available + Net Requirements

Net requirements for first period with inventory on hand:

· Gross Requirements + Allocations – Scheduled Receipts – On-Hand Inventory = Net Requirements (if net requirements is a negative number, set net requirements to “0” and the projected available to that number but positive)

2 Comments (+add yours?)

  1. Vikki
    Jan 24, 2013 @ 07:17:04

    Thanks very much ! I passed 2 and on my way to the third one. :)


  2. Tom Mogyorossy
    Aug 17, 2014 @ 10:48:03

    Your statement:
    o Firm means the PLANNER can’t alter due date, release date, and planned order quantity

    I think it is the planner who actually initiates the firm order and it is the MRP system that can’t change it when regenerated.


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