Common Denominators and Effectivities
by Ken Black
Interface Control?
What are the interfaces between master schedules, MRP and engineering changes? How do they influence each other and how is that influence controlled? MRP Functionality
MRP systems read the master schedule of deliverable items and then proceed to identify the on-hand and on-order status of materials and resources (item-by-item and level-by-level) as required to achieve the master schedule. MRP systems are capable of defining required materials and resources on a just-in-time basis for each deliverable item in each time period. Such systems believe that any two items having the same ID number are fully interchangeable.
Engineering changes are the "straw that broke the back" of many MRP systems. They cause revision levels to change. They may cause one or more item ID numbers to change. Deciding which item number is the right number and which revision is the right revision, becomes an issue. That is the purpose of "effectivities."
The item ID number is a common denominator at the interfaces between master scheduling, MRP and engineering changes. Timing, as required to maintain synchronization, is also a common denominator. Effectivities are part of the timing equation.
Proper management of change effectivities is essential; yet, also one of the greatest challenges. It is the weak link in most MRP systems and in most PDM systems alike. It is an area in which it is easy to distinguish between the pro's and the pretender's.
Want to improve the control of your interfaces? Start by learning how to manage effectivities. Get a jump-start. Learn CMII. Framework For Interface Control
Let's start by identifying the framework within which master schedules, MRP and engineering changes play together as one cohesive unit.
Planning bills of material provide that framework. A planning bill represents a hierarchy of physical items. A planning bill includes definition of the required materials (if MRP) and other resources (if MRPII) to produce deliverable end-items in accordance with the master schedule.
MRP systems run on planning bills and order bills. Order bills are derived from planning bills and represent "firm" customer orders wherein the specific configuration to be built is known.
The master schedule defines planned build completion schedules for deliverable items. The master schedule is used to drive resource requirements through planning bills and order bills.
Each item at each level in each physical item hierarchy has an identification number. Each item also has its own unique set of supporting documentation. Each document has its own unique identity (by document type, number and rev level).
Master schedules are stated in terms of deliverable item ID numbers. Engineering changes are made against items and their supporting documents.
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